期刊文献+
共找到28篇文章
< 1 2 >
每页显示 20 50 100
Evaluation of PS-DInSAR technology for subsidence monitoring caused by repeated mining in mountainous area 被引量:4
1
作者 刘振国 卞正富 +2 位作者 雷少刚 刘东烈 Andrew SOWTER 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 2014年第10期3309-3315,共7页
The high resolution Terra SAR-X dataset was employed with DIn SAR and persistent scatterer interferometry(PSI) technique for subsidence monitoring in a mountainous area. For DInS AR technique, the generally used SRT... The high resolution Terra SAR-X dataset was employed with DIn SAR and persistent scatterer interferometry(PSI) technique for subsidence monitoring in a mountainous area. For DInS AR technique, the generally used SRTM and relief-DEM, which was derived from aerial topographic map, were used to evaluate the influence of external DEM. The results show that SRTM could not fully compensate the complex topography of the research area. The corner reflectors installed during the acquisition of SAR dataset were used to estimate the accuracy of geocoding. The terrain corrected geocoding results based on relief-DEM were much better than using SRTM, with the root mean square error(RMSE) being 6.35 m in X direction and 11.65 m in Y direction(both in UTM projection), around one pixel of the multilooked intensity image to be geocoded. For PSI technique, the results from time-series analysis of multi-baseline differential interferograms were integrated to restrict only persistent scatterer candidates near the boundary of subsiding area for regression analysis. The results demonstrate that PSI can refine the boundary of subsidence, which could then be used to derive some angular parameters to help people to learn the law of subsidence caused by repeated excavation in this area. 展开更多
关键词 DIn SAR GEOCODING persistent scatterer interferometry(PSI) repeated excavation corner reflector subsidence monitoring
下载PDF
Mathematical demonstration of correlation of optical prime code 被引量:1
2
作者 李传起 张明德 孙小菡 《Journal of Southeast University(English Edition)》 EI CAS 2006年第2期153-158,共6页
Starting from the configuration of the optical prime code, a kind of key signature code for the optical code-division multiple access (OCDMA) system, based on the linear congruence theory in the finite Galois field,... Starting from the configuration of the optical prime code, a kind of key signature code for the optical code-division multiple access (OCDMA) system, based on the linear congruence theory in the finite Galois field, the correlation properties of the basic prime code, the extended prime code and the modified prime code are mathematically analyzed, the distribution of cross-correlation values is given and the overlap area of "1"s in the case of periodically circularly shifting is indicated. It is mathematically demonstrated that the maximum cross-correlation of the basic prime code is 2, and that of the extended prime code and the modified prime code is 1. The integrated correlation analysis process is proposed. The signal-interfere ratio (SIR) and the BER performance of the systems employing different signature codes are calculated, respectively, and the performances of OCDMA systems employing different signature codes mode are compared. 展开更多
关键词 fiber-optic communication optical code-division multiple access optical prime code CORRELATION
下载PDF
龟皇别墅
3
作者 张天羽 周荷英(指导) 《作文新天地(小学版)》 2017年第3期14-14,共1页
我家的乌龟近期搬进了一栋豪华'别墅'. 整栋别墅的墙体都采用健康环保的亚克力塑料,还是翠绿色的, 从颜色心理学上讲,它能给予'房主'一种温馨的情调. 别墅内部设计精美, 而且在使用上考虑得面面俱到:北边有宽敞的'... 我家的乌龟近期搬进了一栋豪华'别墅'. 整栋别墅的墙体都采用健康环保的亚克力塑料,还是翠绿色的, 从颜色心理学上讲,它能给予'房主'一种温馨的情调. 别墅内部设计精美, 而且在使用上考虑得面面俱到:北边有宽敞的'泳池',里面有四季温暖的'温泉',可以让我的乌龟在里面畅游. 因为别墅的地板设计得与我家的地板隔开, 从而使别墅中'游泳池'的水温不会因地面温度低而下降. 游泳池旁有楼梯, 通往食槽和'阳台'. 每天它游完泳,都会不紧不慢地爬去食槽享受美食. 那整整齐齐地码在长方形食槽里的一粒粒饱满、喷香的龟粮使它垂涎三尺. 展开更多
关键词 地码 地板 水温 食槽 游泳池 设计 别墅
下载PDF
A Memory Efficient Belief Propagation Decoder for Polar Codes 被引量:3
4
作者 SHA Jin LIU Xing +1 位作者 WANG Zhongfeng ZENG Xiaoyang 《China Communications》 SCIE CSCD 2015年第5期34-41,共8页
Polar codes have become increasingly popular recently because of their capacity achieving property.In this paper,a memory efficient stage-combined belief propagation(BP) decoder design for polar codes is presented.Fir... Polar codes have become increasingly popular recently because of their capacity achieving property.In this paper,a memory efficient stage-combined belief propagation(BP) decoder design for polar codes is presented.Firstly,we briefly reviewed the conventional BP decoding algorithm.Then a stage-combined BP decoding algorithm which combines two adjacent stages into one stage and the corresponding belief message updating rules are introduced.Based on this stage-combined decoding algorithm,a memory-efficient polar BP decoder is designed.The demonstrated decoder design achieves 50%memory and decoding latency reduction in the cost of some combinational logic complexity overhead.The proposed decoder is synthesized under TSMC 45 nm Low Power CMOS technology.It achieves 0.96 Gb/s throughput with 14.2mm^2 area when code length N=2^(16)which reduces 51.5%decoder area compared with the conventional decoder design. 展开更多
关键词 polar codes belief propagation stage-combined memory-efficient IMPLEMENTATION
下载PDF
A Cryptographic Scheme Based on Spatiotemporal Chaos of Coupled Map Lattices 被引量:1
5
作者 MA Hui CHEN Tian-Lun 《Communications in Theoretical Physics》 SCIE CAS CSCD 2006年第3期477-482,共6页
We propose a cryptographic scheme based on spatiotemporal chaos of coupled map lattices (CIVIL) ,which is based on one-time pad. The structure of the cryptosystem determines that the progress in decryption implies t... We propose a cryptographic scheme based on spatiotemporal chaos of coupled map lattices (CIVIL) ,which is based on one-time pad. The structure of the cryptosystem determines that the progress in decryption implies the progress in exploring the dynamical behavior of spatiotemporal chaos in CML. A part of the initial condition of CML is used as a secret key, and the recovery of the secret key by exhaustive search is impossible due to the sensitivity to the initial condition in spatiotemporal chaos system. Specially the software implementation of the scheme is easy. 展开更多
关键词 spatiotemporal chaos coupled map lattices CRYPTOGRAPHY
下载PDF
More efficient ground truth ROI image coding technique: implementation and wavelet based application analysis 被引量:5
6
作者 KUMARAYAPA Ajith 《Journal of Zhejiang University-Science A(Applied Physics & Engineering)》 SCIE EI CAS CSCD 2007年第6期835-840,共6页
In this paper, more efficient, low-complexity and reliable region of interest (ROI) image codec for compressing smooth low texture remote sensing images is proposed. We explore the efficiency of the modified RO! cod... In this paper, more efficient, low-complexity and reliable region of interest (ROI) image codec for compressing smooth low texture remote sensing images is proposed. We explore the efficiency of the modified RO! codec with respect to the selected set of convenient wavelet filters, which is a novel method. Such ROI coding experiment analysis representing low bit rate lossy to high quality lossless reconstruction with timing analysis is useful for improving remote sensing ground truth surveillance efficiency in terms of time and quality. The subjective [i.e. fair, five observer (HVS) evaluations using enhanced 3D picture view Hyper memory display technology] and the objective results revealed that for faster ground truth ROI coding applications, the Symlet-4 adaptation performs better than Biorthogonal 4.4 and Biorthogonal 6.8. However, the discrete Meyer wavelet adaptation is the best solution for delayed ROI image reconstructions. 展开更多
关键词 Smooth low texture remote sensing (SLTRS) image Modified region of interest (ROI) image codec Wavelet filters Low bit rate (LBR). High bit rate (HBR). ROI coding
下载PDF
Biosecurity Practices and Geospatial Map of Ontario Backyard Poultry Flocks
7
作者 Jean Marie Buregeya Scott McEwen +2 位作者 John Neil Tom Baker Gwen Kerry Zellen 《Journal of Environmental Science and Engineering(B)》 2013年第12期694-701,共8页
The CFO (Chicken Farmers of Ontario) has taken important steps to increase biosecurity practices within backyard poultry flocks in order to thwart infectious diseases. The present study originally intended to descri... The CFO (Chicken Farmers of Ontario) has taken important steps to increase biosecurity practices within backyard poultry flocks in order to thwart infectious diseases. The present study originally intended to describe biosecurity practices within this milieu, so as to determine their nearest neighbor and density, as well as the average distance between backyard and commercial broiler flocks. To that effect, paper questionnaire and survey interviews were used (May-July, 2011), while backyard and commercial broiler chicken flocks were geocoded. The response rates collected from the study produced these findings regarding: growers' health practices toward flocks, hygienic precautions relative to the production area, regularity of bird inspection and cleaning after each folk, protocol used to dispose of dead birds, mixing (or lack thereof) of flocks with other livestock, as well as the average distance between small flocks and commercial farms. The study concludes that education material should focus on improving the growers' understanding of issues examined in the study, focusing on areas of weakness in respect to biosecurity practices. 展开更多
关键词 Backyard flocks BIOSECURITY infectious diseases Ontario poultry.
下载PDF
Temporally Consistent Depth Map Estimation for 3D Video Generation and Coding 被引量:2
8
作者 Sang-Beom Lee Yo-Sung Ho 《China Communications》 SCIE CSCD 2013年第5期39-49,共11页
In this paper, we propose a new algorithm for temporally consistent depth map estimation to generate three-dimensional video. The proposed algorithm adaptively computes the matching cost using a temporal weighting fun... In this paper, we propose a new algorithm for temporally consistent depth map estimation to generate three-dimensional video. The proposed algorithm adaptively computes the matching cost using a temporal weighting function, which is obtained by block-based moving object detection and motion estimation with variable block sizes. Experimental results show that the proposed algorithm improves the temporal consistency of the depth video and reduces by about 38% both the flickering artefact in the synthesized view and the number of coding bits for depth video coding. 展开更多
关键词 three-dimensional television multiview video depth estimation temporal consistency temporal weighting function
下载PDF
Statistical Analysis on the Corner Period of Site-Related Design Spectra
9
作者 WuJian GaoMengtan 《Earthquake Research in China》 2005年第1期29-34,共6页
According to the results of site seismic hazard analysis accomplished in the past decades, 96 site-related design spectra are selected as samples in this study. The result shows that the value of the corner period (T ... According to the results of site seismic hazard analysis accomplished in the past decades, 96 site-related design spectra are selected as samples in this study. The result shows that the value of the corner period (T g) of the design spectrum in GBJ11-89 (China Seismic Building Code, issued in 1989) is lower than the value obtained by site seismic hazard analysis. The same situation exists when we compare the design spectra of the Codes to the spectra according to the earthquake records. The value in current seismic design code, GBJ50011-2001 issued in 2001, is greater than that in GBJ11-89, but still less than the value obtained by site seismic hazard analysis. If we accept the value got by site seismic hazard analysis, we have a suspicion that 2/3 of buildings built according to GBJ11-89 will not be safe when an earthquake with 2% probability of exceedance in 50 years occurs. 展开更多
关键词 Site-related design spectrum Corner period of design spectrum Seismic code
下载PDF
Levels of Probability of Exceedance for Current Code Spectra in China
10
作者 Shen Jianwen Liu Zheng Shi Shuzhong 《Earthquake Research in China》 2008年第2期131-136,共6页
Long-period acceleration spectra determined by seismic safety evaluation for project sites are generally lower than that given by relative code spectra.In this paper,we discuss the recurrence periods corresponding to ... Long-period acceleration spectra determined by seismic safety evaluation for project sites are generally lower than that given by relative code spectra.In this paper,we discuss the recurrence periods corresponding to the code spectra of different periods,by using ground motion attenuation laws for sites of types Ⅰ and Ⅲ.We show the results that the longer the periods of code spectra are commonly the more conservative the seismic level is.As for the project examples in this paper,when the periods are longer than 3.7 or 5.2 seconds for sites of types Ⅰ or Ⅲ,the recurrence periods corresponding to the code spectra are longer than 5000 years.We suggest that some problems need to be further discussed,including the reliability of the present attenuation laws,the performance of those project structures that suffer long period seismic waves and have been designed according to the conservative codes,and the effects of ground motion parameters such as velocity and displacement on seismic design. 展开更多
关键词 Seismic design Code spectra Probability level of exceedance
下载PDF
Access to Healthy Food Stores for Residents of Aboriginal Reserves in Rural British Columbia
11
《Journal of Food Science and Engineering》 2017年第7期342-350,共9页
The rate of food insecurity has increased tremendously over the past decade in Canada. This increase has been more pronounced in rural and remote areas especially among Aboriginal peoples. Substantial studies indicate... The rate of food insecurity has increased tremendously over the past decade in Canada. This increase has been more pronounced in rural and remote areas especially among Aboriginal peoples. Substantial studies indicated that nearly half of the on-reserve Aboriginal households in British Columbia (BC) suffer from some degree of food insecurity. Despite the valuable research about obtaining traditional food, the issue of access to market food has been less discussed in the literature. The aim of this study was to assess the local food environment of on-reserve Aboriginal peoples by using a proximity-based approach tool in terms of access to healthy food stores such as supermarket and grocery stores. In the first stage, the addresses of all healthy food stores were geocoded into a map layer. Then the locations of Aboriginal reserves were geocoded to a separate map layer. In the second stage, using "Closest Facility Analysis" tool in ArcGIS Version 10.3, the distance based on a 15-minute driving time was measured from each reserve to the closest healthy food destination on CanMapRouteLogistics network. The results indicated that 25% of Aboriginal reserves did not have reasonable access to healthy food stores. We concluded that Aboriginal peoples in low access rural reserves with lower socioeconomic status are at potential risk of perpetuate food insecurity. 展开更多
关键词 Food security rural aboriginal reserves network analysis ArcGIS.
下载PDF
Causes and prevention measures of foundation settlement of gravity type wharf
12
作者 YANG Yue 《International English Education Research》 2016年第4期30-32,共3页
foundation settlement is one of the common problems in the construction and use of gravity wharf. Causes gravity type wharf foundation settlement reason is very complex. Based on the full understanding of the concept ... foundation settlement is one of the common problems in the construction and use of gravity wharf. Causes gravity type wharf foundation settlement reason is very complex. Based on the full understanding of the concept of gravity quay wall, this paper analyzes the reasons of the foundation settlement of gravity wharf. And Put forward the corresponding prevention and countermeasures. 展开更多
关键词 Gravity wharf Foundation settlement REASON Control countermeasure
下载PDF
A non-synonymous coding SNP Lys45Glu of mmp3 associated with ESCC genetic susceptibility in population of Henan, China 被引量:1
13
作者 Gang Ouyang Pinfang Yao +4 位作者 Wenjuan Hu Qjngbo Chen Hong Wang Lidong Wang Jin Li 《The Chinese-German Journal of Clinical Oncology》 CAS 2009年第9期510-515,共6页
Objective: The aim of the study was to investigate the association of esophageal squamous cell carcinoma (ESCC) genetic susceptibility with the single nucleotide polymorphism (SNP) rs679620 (-Lys45Glu-) in exon... Objective: The aim of the study was to investigate the association of esophageal squamous cell carcinoma (ESCC) genetic susceptibility with the single nucleotide polymorphism (SNP) rs679620 (-Lys45Glu-) in exon 2 of the romp3 gene, and the population in high incidence region of Henan (China) was selected for exploring the mechanism by case-control study, Methods: The romp3 SNP was genotyped by PCR-RFLP analysis in total 605 cases of Henan population, in which there were 227 ESCC cases and 197 controls of An-yang in Henan plus 181 controls of emigrants in Hubei from Xi-chuan of Henan, China. Results: The statistic data showed that GIG and G/A genotype frequencies of SNP rs679620 were significantly different between the controls of emigrants of Xi-chuan in Hubei and controls of An-yang in Henan (P 〈 0.01) also the ESCC cases of An-yang in Henan (P 〈 0.01), respectively. Conclusion: This study suggests that the SNP rs679620 (-Lys45Glu-) in exon 2 of the mmp3 gene might be associated with ESCC genetic susceptibility. 展开更多
关键词 PCR-RFLP single nudeotide polymorphism (SNP) genotyping esophageal squamous cell carcinoma (ESCC) genetic susceptibility Henan population
下载PDF
RADAR HRR PROFILING FOR GROUND MOVING TARGET USING PHASE-CODED AND HOPPED-FREQUENCY WAVEFORMS
14
作者 Li Yan Wang Changming 《Journal of Electronics(China)》 2007年第2期187-190,共4页
To obtain the radar High Range Resolution (HRR) profile of the slowly moving ground target in strong clutter background, the Phase-Coded Hopped-Frequency (PCHF) waveform is proposed. By multiple-bursts coherent proces... To obtain the radar High Range Resolution (HRR) profile of the slowly moving ground target in strong clutter background, the Phase-Coded Hopped-Frequency (PCHF) waveform is proposed. By multiple-bursts coherent processing, the HRR profile synthesis, target velocity compensation and clutter compression can be accomplished simultaneously. The new waveform is shown to have good ability to suppress ground clutter and good Electronic Counter-CounterMeasures (ECCM) ability as well. The clutter compression performance of the proposed method is verified by the numerical results. 展开更多
关键词 Radar High Range Resolution (HRR) profile Phase-Coded Hopped-Frequency (PCHF) waveform Clutter compression Ground moving target detection
下载PDF
Language Policy in Nigeria and Nigerian Language Policy: Implications for Effective Communication in Non-Monolingual Nations
15
作者 Dare Owolabi Samuel Ayodele Dada 《Sino-US English Teaching》 2012年第11期1676-1685,共10页
In Nigeria, almost 500 indigenous languages continue to compete with the English language that has assumed the status of a global linguistic code. The contact, in different domains between English and indigenous langu... In Nigeria, almost 500 indigenous languages continue to compete with the English language that has assumed the status of a global linguistic code. The contact, in different domains between English and indigenous languages in the country continues to affect performance in English and contact languages, making effective communication in either English or any of the indigenous languages unattainable. The purpose of this study is to show that although no particular document, so named, exists expressing the nation's policy on language, nonetheless, the country has a policy on language that accommodates the indigenous languages as substrates, while the English language holds sway in various linguistic domains. Using a simple descriptive survey with data from previous studies, this paper examines the linguistic implications of the contact between English and indigenous languages on the younger generations who are losing contact with the mother tongue, and also not demonstrating enough proficiency in the English language. It is recommended that the opportunities that competence and maturation afforded a second language learner should be latched onto to gain the needed proficiency in English thus making them effective bilinguals and communicators in a world that is fast becoming a global village, and the inhabitants global citizens. 展开更多
关键词 language policy MULTILINGUALISM BILINGUALISM language contact effective communication
下载PDF
Supervision Matters: Teenagers' Perception of Parents' Involvement in Their Internet Use
16
作者 Shujun Jiang 《Journalism and Mass Communication》 2015年第1期34-43,共10页
With the growing popularity of digital devices, lntemet has become an integral part of teenagers' daily life. As teenagers are in a complicated period of development, parents struggle in supervising their use of the ... With the growing popularity of digital devices, lntemet has become an integral part of teenagers' daily life. As teenagers are in a complicated period of development, parents struggle in supervising their use of the intemet. This study takes the teenagers' standpoint and explores how the teenagers perceive their parents' involvement in their Internet use. Survey was conducted towards teenagers in the UAE, which has the highest penetration of digital devices in the Gulf region as well as one of the highest in the world. The results showed that girls usually receive more supervision fi'om parents than boys. The older the teenagers are and the more they depend on the Internet, the more they perceive parents' supervision to be beneficial. However, not enough supervision has been given to those who access the Internet more frequently. The findings indicate more parents' supervision is needed from the teenagers' point of view. Discussions are made from psychological and socio-cultural perspectives and suggestions for future research are presented. 展开更多
关键词 Internet use TEENAGER PARENTS SUPERVISION
下载PDF
The Determination of Geographical Origin of Foodstuffs by Using Innovative Biological Bar-Code
17
作者 Aly E1 Sheikha Didier Montet 《Journal of Life Sciences》 2012年第12期1334-1342,共9页
Abstract: One of the great concerns of the customers is the traceability of the products. The authors proposed to link microbial ecology to geographical origin of foodstuffs by a molecular technique joined to an imag... Abstract: One of the great concerns of the customers is the traceability of the products. The authors proposed to link microbial ecology to geographical origin of foodstuffs by a molecular technique joined to an image analysis. Molecular techniques employing 16S and 28S rDNA profiles generated by PCR-DGGE were used to detect the variation in microbial community (bacteria, fungi) of Pangasius fish from Viet Nam harvested in different aquaculture farms and during different seasons and Shea tree fruits from five different districts in Mali. The bacterial DNA profiles from Pangasius fish and the fungal DNA profile from Shea tree fruits were specific to each place of production and could be used as a biological bar code certifying the origin of fish and fruit. To follow the product during processing, the authors proposed to identify and validate some pertinent biological markers which come from the environment of the food to assure their traceability during international trade. It is new analytical method which permits to determine the origin of food or to follow them during international trade. 展开更多
关键词 Geographical origin FOODSTUFF PCR-DGGE microbial community DNA profile biological bar-code.
下载PDF
Extension of the Code COCOSYS to a Dispersion Code for Smoke and Carbon Monoxide
18
作者 G. Sdouz R. Mayrhofer 《Journal of Energy and Power Engineering》 2011年第3期215-221,共7页
The code COCOSYS (Containment Code System) was developed by GRS (Gesellschaft fur Anlagen-und Reaktorsicherheit) in Germany to simulate processes and nuclear plant states during severe accidents in the containment... The code COCOSYS (Containment Code System) was developed by GRS (Gesellschaft fur Anlagen-und Reaktorsicherheit) in Germany to simulate processes and nuclear plant states during severe accidents in the containments of light water reactors. It contains several physical models, especially a module for aerosol behaviour. The goal of this work was to extend COCOSYS for applications in more general geometries mainly for complex public buildings. For the application in public buildings, models for air condition systems and different boundary conditions according to different environments were developed. The principal application of the extended code COCOSYS is in the area of emergency situations especially in the simulation for carbon monoxide and smoke dispersion. As first achievement realistic fire emergency scenarios in the Vienna General Hospital (AKH) could be simulated. The results of the simulation can be used for the development of fire emergency training. 展开更多
关键词 Dispersion calculation emergency situation SMOKE carbon monoxide.
下载PDF
Seismic Fragility of Approach Bridge for the Large Port Terminals
19
作者 LIU Xinyue 《International English Education Research》 2016年第4期48-50,共3页
In order to study the seismic performance of typical approach bridge for port project, the seismic vulnerability model was created. 100 of the earthquake motion records are selected from the database of Pacific Earthq... In order to study the seismic performance of typical approach bridge for port project, the seismic vulnerability model was created. 100 of the earthquake motion records are selected from the database of Pacific Earthquake Research Centre, In order to obtain the maximum responses of structure dynamic response, the model was calculated by using non-linear time history analysis. Then reliability analysis method was used to generate the fragility curves of bridge components. And compared two kinds of bearing made differences to structure' s vulnerability. Researches show that bearing is easy to breakdown with earthquake action. Isolation bearing has good effect, and significantly reduces failure probability, fmaUy the fragility curves obtained can be used to evaluate the seismic performance of continuous beam bridge for port project, and provide the basis for seismic design of bridges for port project. 展开更多
关键词 Port project Approach bridge Seismic vulnerability Isolation bearing
下载PDF
The Study of Village Architecture and the Development of Ancient Villages:Taking Pazhou Ancient Village in Guangzhou as Research Object
20
作者 ZHONG Hai-yan LI Qiu-yu 《Journal of Literature and Art Studies》 2017年第9期1223-1228,共6页
Pazhou village, which is a small village located in the southeast edge of Guangzhou, naming is because of the village resembles shape of Pipa. In periods of Song and Yuan Dynasty, it had become important geographical ... Pazhou village, which is a small village located in the southeast edge of Guangzhou, naming is because of the village resembles shape of Pipa. In periods of Song and Yuan Dynasty, it had become important geographical indication and port wharf of Guangzhou, because it is located in the main waterway. In Ming Dynasty, Pazhou Tower had become the symbol of the country in local area which was built by Guangzhou gentry. After Qing dynasty, with the raise of Ancient Huangpu Harbor, Pazhou village had a greater influence. Pazhou Tower and Temple had become well-known scenic local attractions, which was one of the "Eight Top Scenic Spots in Guangzhou". 展开更多
关键词 ancient villages ARCHITECTURE Pazhou Village
下载PDF
上一页 1 2 下一页 到第
使用帮助 返回顶部