期刊文献+
共找到35篇文章
< 1 2 >
每页显示 20 50 100
辽河地域文化与民族精神交织的日常图谱——与作家杨春风的对话 被引量:2
1
作者 林喦 杨春风 《渤海大学学报(哲学社会科学版)》 2021年第2期6-10,共5页
辽宁作家杨春风的长篇小说《辽河渡1931—1945》描写了抗战时期东北小镇底层百姓的苦难与挣扎的生活。作家以饱满的情愫书写了当异族侵略国土的时候,曾经静默的生民在日常生活形态被无端打破后的觉醒,进而表现出潜在意识里“民族意识”... 辽宁作家杨春风的长篇小说《辽河渡1931—1945》描写了抗战时期东北小镇底层百姓的苦难与挣扎的生活。作家以饱满的情愫书写了当异族侵略国土的时候,曾经静默的生民在日常生活形态被无端打破后的觉醒,进而表现出潜在意识里“民族意识”的提升和抗争意识的行动自觉。小说行文细腻隽永、结构铺陈严谨、人物清晰丰富,具有史传性的底层叙事风格。 展开更多
关键词 辽宁作家 杨春风 《辽河渡1931—1945》
下载PDF
《辽河》杂志2019年作者名录
2
《辽河》 2019年第12期116-120,共5页
关键词 宋晓杰 李秀文 《辽河》
原文传递
欢迎订阅2019年《辽河》
3
《辽河》 2018年第11期14-14,共1页
菜里一点盐生活一点甜A.2019全新亮相第一期,将有辽宁省作协主席和鲁迅文学奖评委的小说、散文作品,柳沄刘川、宋晓杰、张二棍、聂权等诗坛名家的力作领衔登场;将有'河风海韵·醉美辽河'全国诗歌大赛获奖作品集中亮相;将举... 菜里一点盐生活一点甜A.2019全新亮相第一期,将有辽宁省作协主席和鲁迅文学奖评委的小说、散文作品,柳沄刘川、宋晓杰、张二棍、聂权等诗坛名家的力作领衔登场;将有'河风海韵·醉美辽河'全国诗歌大赛获奖作品集中亮相;将举办国际征文大赛。 展开更多
关键词 欢迎订阅 2019年 《辽河》
原文传递
《辽河》多篇作品入选获奖
4
《辽河》 2019年第7期121-121,共1页
4月5日,学习强国平台发布一篇题为《辽河口湿地的鸟类朋友》的散文,引发读者热议和大量转发。该文是曾刊登于《辽河》杂志第四期'散文'栏目头题文章,并在《辽河》杂志封面做了导读。该文作者就是著名作家宋晓杰。据统计,2018~2... 4月5日,学习强国平台发布一篇题为《辽河口湿地的鸟类朋友》的散文,引发读者热议和大量转发。该文是曾刊登于《辽河》杂志第四期'散文'栏目头题文章,并在《辽河》杂志封面做了导读。该文作者就是著名作家宋晓杰。据统计,2018~2019年上半年,《辽河》杂志已有多篇小说、诗歌等作品被各类选刊选用或获奖。基本篇目如下: 展开更多
关键词 微型小说选刊 《小小说选刊》 《辽河》
原文传递
2019年《辽河》作品入选、获奖篇目
5
《辽河》 2020年第1期F0003-F0003,共1页
邵燕云:散文《童年记忆》,原发《辽河》2017年第5期,2019年8月荣获第11届河北散文名作奖二等奖岳晓东:组诗《村口的路》,原发《辽河》2019年2期,《诗选刊》2019年4期转载远航:散文《干塘捉鱼》原发《辽河》2015年4期,《南方农村报》2019... 邵燕云:散文《童年记忆》,原发《辽河》2017年第5期,2019年8月荣获第11届河北散文名作奖二等奖岳晓东:组诗《村口的路》,原发《辽河》2019年2期,《诗选刊》2019年4期转载远航:散文《干塘捉鱼》原发《辽河》2015年4期,《南方农村报》2019年2月16日转载薛培政:《隐痛》原发《辽河》2019年4期,《小小说选刊》2019年第8期转载余清平:《大哥》原发《辽河》2019年5期,《微型小说选刊》 展开更多
关键词 微型小说选刊 《小小说选刊》 《辽河》
原文传递
大辽河波浪飘香——2020年《辽河》寄语
6
作者 张国鹏 《辽河》 2020年第1期3-3,共1页
关键词 辽河 《辽河》
原文传递
《辽河》杂志2019年总目录
7
《辽河》 2019年第12期104-115,共12页
关键词 《辽河》 小小说
原文传递
学者王向峰新作《辽河水润千章秀》出版
8
《艺术广角》 2020年第1期91-91,共1页
辽宁大学教授王向峰新作《辽河水润千章秀——辽沈地区文艺作品序评集》近期由万卷出版公司出版。本书收入王向峰先生为辽沈地区作者的文艺作品撰写的序评文章300余篇,时间跨度40余年。这些序评,皆为王向峰先生在紧张的学术研究之余助... 辽宁大学教授王向峰新作《辽河水润千章秀——辽沈地区文艺作品序评集》近期由万卷出版公司出版。本书收入王向峰先生为辽沈地区作者的文艺作品撰写的序评文章300余篇,时间跨度40余年。这些序评,皆为王向峰先生在紧张的学术研究之余助益同行、奖掖后学之作,同时也是从一个独特的角度对改革开放40多年来辽宁文学艺术创作的一次总结。王向峰先生多年来始终心系辽宁文艺发展,作为"在场者",他以为数众多的书评勾勒出一个辽宁文艺简史。作者认为:"序言和评论的价值需要评论者在评论对象当中看出什么。如果是非常有成就的书,你要把它的成就揭示出来;如果书里面有某种可以深入研究的迹象,你要能把它升华;如果说这些都没有,你也能就这个‘没有’提出些什么。这时候,序言者、评论者的水平和价值就完全显示出来。"这部序评集,正是王向峰先生揭示、升华、发现的思想成果。 展开更多
关键词 王向峰 《辽河水润千章秀》 文艺作品
下载PDF
Research on Drainage Network Extraction in Liaohe Basin Based on SRTM DEM and ASTER GDEM 被引量:2
9
作者 马兰艳 周春平 +2 位作者 胡卓玮 王志恒 马国斌 《Agricultural Science & Technology》 CAS 2010年第9期157-160,197,共5页
In this study,SRTM DEM data and ASTER GDEM data were used as the basic topographic data,and Arc Hydro Tools was utilized for extension module so as to study on extracting digital drainage network of watershed based on... In this study,SRTM DEM data and ASTER GDEM data were used as the basic topographic data,and Arc Hydro Tools was utilized for extension module so as to study on extracting digital drainage network of watershed based on surface runoff model,as well as to compare the two extracted results.The result showed that through the introduction of drainage density parameter to determine the river drainage area threshold,the both extracted drainages showed the goodness-of-fit with the factual drainage network on 1∶250 000 scale topographic map,and the extracted digital river could be used in practical operation of the risk assessment model of mountain torrents disaster in Liaohe basin. 展开更多
关键词 Drainage density River drainage area threshold Liaohe basin
下载PDF
Study of the water quality in Liaohe Park based on the model of GAM 被引量:1
10
作者 宋文平 戴媛媛 董玉波 《Marine Science Bulletin》 2012年第1期90-96,共7页
This paper assesses the quality of Daliao river through Liaohe Park based on the model of GAM for water quality analysis and the monitoring data from 2006 to 2011.The results showed that the value of pH per year tende... This paper assesses the quality of Daliao river through Liaohe Park based on the model of GAM for water quality analysis and the monitoring data from 2006 to 2011.The results showed that the value of pH per year tended to the average; the DO in 2011 was much higher than that in other years, and the DO in 2006 .was lower than the standard value; the quality risk in six sections was still higher than the standard value in 2007, which was caused by the high concentrations of COD. However, the value of ammonia nitrogen changes was only 40% related to DO and COD. 展开更多
关键词 Liaohe Park water quality monitoring EVALUATION
下载PDF
Nitrate Nitrogen Content Characteristics in Groundwater of Typical Planting Areas in Liao River Basin
11
作者 牛世伟 宫亮 +4 位作者 蔡广兴 何志刚 陈玥 刘子琪 隋世江 《Agricultural Science & Technology》 CAS 2016年第1期204-208,共5页
The contents of nitrate nitrogen(NO-3-N) in underground water from typical planting areas in Liao river basin were analyzed, so as to provide theoretical basis for rational fertilization and effectively prevent the ... The contents of nitrate nitrogen(NO-3-N) in underground water from typical planting areas in Liao river basin were analyzed, so as to provide theoretical basis for rational fertilization and effectively prevent the NO-3-N content from exceeding standard. The results showed that difference of the contents of NO-3-N in groundwater from different typical planting areas was significant. The highest content of NO-3-N in underground water was 37.4 mg/L from flower-growing region, then 22. 3 mg/L from maize-growing region, 21.9 mg/L from vegetable-growing region, and the lowest content of NO-3-N in underground water was 19.2 mg/L from rice-growing region. Except rice-growing region, the contents of NO-3-N in underground water of the samples in all planting areas were exceeding standard limit; potential health risk still existed in rice-growing region. Accordingly 12.5%-87.5%, 9.4%-75.5%, 17.9%-58.9% and 21.4%-96.0% of the samples were exceeding standard limit in maize growing region, rice-growing region, vegetable-growing region and flower-growing region. The contents of NO-3-N in under-groundwater before the rainy season was higher than that of NO-3-N in under-groundwater after the rainy season at the same depth of the well. 展开更多
关键词 Liao river basin Planting area Underground water Nitrate nitrogen
下载PDF
Moving Dynamics of Nitrate Nitrogen in Soil of Maize Field on Meadow Soil of Daling River Valley in Liaoning and Its Fertilization Controlling
12
作者 刘慧颖 董环 +1 位作者 张鑫 韩晓日 《Agricultural Science & Technology》 CAS 2010年第9期121-125,共5页
The moving dynamics of nitrate nitrogen(NO3-N)in soil of maize field on meadow soil of Daling river valley in Liaoning and its rational fertilization controlling were discussed in this study by the designing of diff... The moving dynamics of nitrate nitrogen(NO3-N)in soil of maize field on meadow soil of Daling river valley in Liaoning and its rational fertilization controlling were discussed in this study by the designing of different kinds of N application methods.The results showed that the content of NO3-N in soil was increased with the amount of nitrogen fertilizer;At the same amount of nitrogen fertilizer,the content of NO3-N in soil showed a trend of chemical fertilizerstraw treatmentslow controlled release fertilizer.Based on the requirement of roots in different growth stages to nutrition,the migration directions of NO3-N could be regulated by each layer of soil.In the early growth stage,the NO3-N would move upward,while it moved downward in the late growth stage.Straw returning treatment could improve the keeping ability of soil to NO3-N and avoid the downward migration of NO3-N,as well as reduce the damage of groundwater pollution.The use of slow controlled release fertilizer had achieved the continuing releasing of nutrition.Moreover,the peak of nutrition releasing had been delayed for 30 d,which had met the requirement of nutrient supply in maturing stage.The yield of slow controlled release fertilizer treatment was the highest with the least accumulation of NO3-N and less negative influence on environment.The yield of straw returning treatment and chemical fertilizer treatment was closed to each other. 展开更多
关键词 Meadow soil Soil nitrate nitrogen Rational fertilization Daling River valley
下载PDF
Water Quality Evaluation in Tidal River Reaches of Liaohe River Estuary, China Using a Revised QUAL2K Model 被引量:7
13
作者 YE Hanfeng GUO Shuhai +1 位作者 LI Fengmei LI Gang 《Chinese Geographical Science》 SCIE CSCD 2013年第3期301-311,共11页
Rivers in the Liaohe River Estuary area have been seriously polluted by discharges of wastewater containing petroleum pol- lutants and nutrients. In this paper, The Enhanced Stream Water Quality Model (QUAL2K) and i... Rivers in the Liaohe River Estuary area have been seriously polluted by discharges of wastewater containing petroleum pol- lutants and nutrients. In this paper, The Enhanced Stream Water Quality Model (QUAL2K) and its revised model as well as One-dimensional Tide Mean Model (1D model) were applied to predict and assess the water quality of the tidal fiver reach of the Liaohe River Estuary. Dissolved oxygen (DO), biochemical oxygen demand (BODs), ammonia nitrogen (NH3-N) and total phosphorus (TP) were chosen as water quality indices in the two model simulations. The modelled results show that the major reasons for degraded rivers remain petroleum and non-point source pollution. Tidal water also has a critical effect on the variation of water quality. The sensitivity analysis identifies that flow rate, point load and diffuse load are the most sensitive parameters for the four water quality indices in the revised QUAL2K simulation. Uncertainty analysis based on a Monte Carlo simulation gives the probability distribution of the four wa- ter quality indices at two locations (6.50 km and 44.84 km from the river mouth). The statistical outcomes indicate that the observed data fall within the 90% confidence intervals at all sites measured, and show that the revised QUAL2K gives better results in simulating the water quality of a tidal fiver. 展开更多
关键词 tidal river reach water quality evaluation revised QUAL2K model uncertainty analysis Liaohe River Estuary
下载PDF
Effects of Vegetation Type on Surface Elevation Change in Liaohe River Delta Wetlands Facing Accelerated Sea Level Rise 被引量:5
14
作者 WANG Guodong WANG Ming +3 位作者 JIANG Ming LYU Xianguo HE Xingyuan WU Haitao 《Chinese Geographical Science》 SCIE CSCD 2017年第5期810-817,共8页
Rising sea levels threaten the sustainability of coastal wetlands around the globe. The ability of coastal marshes to maintain their position in the intertidal zone depends on the accumulation of both organic and inor... Rising sea levels threaten the sustainability of coastal wetlands around the globe. The ability of coastal marshes to maintain their position in the intertidal zone depends on the accumulation of both organic and inorganic materials, and vegetation is important in these processes. To study the effects of vegetation type on surface elevation change, we measured surface accretion and elevation change from 2011 to 2016 using rod surface elevation table and feldspar marker horizon method (RSET-MH) in two Phragmites and two Suaeda marshes in the Liaohe River Delta. The Phragmites marshes exhibited higher rates of surface accretion and elevation change than the Suaeda marshes. The two Phragmites marsh sites had average surface elevation change rates at 8.78 mm/yr and 9.26 mm/yr and surface accretion rates at 17.56 mm/yr and 17.88 mm/yr, respectively. At the same time, the two Suaeda marsh sites had average surface elevation change rates at 5.77 mmJyr and 5.91 mm/yr and surface accretion rates at 13.42 mm/yr and 14.38 mm/yr, respectively. The elevation change rates in both the Phragmites marshes and the Suaeda marshes in the Liaohe River Delta could keep pace and even continue to gain elevation relative to averaged sea level rise in the Bohai Sea reported by the 2016 State Oceanic Administration, Peo- ple's Republic of China projection (2.4-5.5 mm/yr) in current situations. Our data suggest that vegetation is important in the accretionary processes and vegetation type could regulate the wetland surface elevation. However, the vulnerability of coastal wetlands in the Liaohe River Delta need further assessment considering the accelerated sea level rise, the high rate of subsidence, and the declining sediment delivery, especially for the Suaeda marshes. 展开更多
关键词 sea level rise wetland elevation surface accretion Phragmites marsh Suaeda marsh Liaohe River Delta
下载PDF
ANALYSIS OF HABITAT PATTERN CHANGE OF RED-CROWNED CRANES IN THE LIAO HE DELTA USING SPATIAL DIVERSITY INDEX 被引量:3
15
作者 WANGLing LIXiu-zhen +1 位作者 HUYuan-man GUODu-fa 《Chinese Geographical Science》 SCIE CSCD 2003年第2期164-170,共7页
Habitat pattern change of red-crowned cranes (Grus japonensis) in t he Liaohe Delta between 1988 and 1998 was analyzed with the help of Spatial Dive rsity Index based on remote sensing data and field investigation. Th... Habitat pattern change of red-crowned cranes (Grus japonensis) in t he Liaohe Delta between 1988 and 1998 was analyzed with the help of Spatial Dive rsity Index based on remote sensing data and field investigation. The result sho wed that the influence from human activities on the wetland habitat of red-crow ned cranes was prominent with the development of oil and agricultural exploitati on, and the habitat pattern of red-crowned cranes had been obviously changed by the human disturbance during the ten years. The areas with high Spatial Diversi ty values (SD≥0.65) and that with mid-high values (0.5≤SD< 0.65), which const ituted the main part of suitable habitat of red-crowned cranes,had reduced to 9142ha and 5576ha respectively, with the shrinking of natural land cover, such a s reed and Suaeda community. The habitat pattern became more fragmented, which w as caused by roads and wells during oil exploration. It was indicated that the s uitability and quality of habitat for red-crowned cranes in the Liaohe Delta we re degraded in the last decade. The results also showed that diversity index cou ld reflect the habitat suitability of red-crowned cranes quantitatively and des cribe the spatial pattern of the habitat explicitly. This study will provide a s cientific basis for habitat protection of red-crowned cranes and other rare spe cies in wetlands. 展开更多
关键词 spatial diversity Index red-crowned crane ( GrUS japonensis) habitatpattern the liaohe delta
下载PDF
Hydrological Impacts of Climate Change on Streamflow of Dongliao River Watershed in Jilin Province,China 被引量:3
16
作者 ZHANG Lei LU Wenxi +3 位作者 YANG Qingchun AN Yongkai LI Di GONG Lei 《Chinese Geographical Science》 SCIE CSCD 2012年第5期522-530,共9页
The impacts of future climate change on streamflow of the Dongliao River Watershed located in Jilin Prov-ince, China have been evaluated quantitatively by using a general circulation model (HadCM3) coupled with the ... The impacts of future climate change on streamflow of the Dongliao River Watershed located in Jilin Prov-ince, China have been evaluated quantitatively by using a general circulation model (HadCM3) coupled with the Soil and Water Assessment Tool (SWAT) hydrological model. The model was calibrated and validated against the historical monitored data from 2005 to 2009. The streamflow was estimated by downscaling HadCM3 outputs to the daily mean temperature and precipitation series, derived for three 30-year time slices, 2020s, 2050s and 2080s. Results suggest that daily mean temperature increases with a changing rate of 0.435~C per decade, and precipitation decreases with a changing rate of 0.761 mm per decade. Compared with other seasons, the precipitation in summer shows significant downward trend, while a significant upward trend in autumn. The annual streamflow demonstrates a general down-ward trend with a decreasing rate of 0.405 m^3/s per decade. The streamflow shows significant downward and upward trends in summer and in autumn, respectively. The decreasing rate of streamflow in summer reaches 1.97 m^3/s per decade, which contributes primarily to the decrease of streamflow. The results of this work would be of great benifit to the design of economic and social development planning in the study area. 展开更多
关键词 streamflow climate change Soil and Water Assessment Tool (SWAT) statistical downscaling DongliaoRiver
下载PDF
Vertical Distribution of Soil Nematode Communities under Different Tillage Systems in Lower Reaches of Liaohe River 被引量:2
17
作者 HOU Xuekun HU Ning +2 位作者 ZHANG Xiaoke LIANG Lei ZHAI Ruichang 《Chinese Geographical Science》 SCIE CSCD 2010年第2期106-111,共6页
Vertical distribution of soil nematode communities under conventional tillage (CT),no-tillage (NT) and fallow field (FF) treatments in the Lower Reaches of the Liaohe River was investigated at six soil depths (0-5 cm,... Vertical distribution of soil nematode communities under conventional tillage (CT),no-tillage (NT) and fallow field (FF) treatments in the Lower Reaches of the Liaohe River was investigated at six soil depths (0-5 cm,5-15 cm,15-30 cm,30-50 cm,50-75 cm and 75-100 cm). The results show that total nematode abundance gradually decreases with depth,and the highest number of total nematodes is observed at 0-5 cm depth under NT and FF treatments. The number of fungivores and plant parasites is significantly higher under FF and NT treatments than under CT treatment at the 0-5 cm depth. There is significant soil depth effect on the abundances of bacterivores and omnivores-predators,which exhibits a similar trend to that of total nematodes; whereas,no significant tillage effect is found. Tillage effect on soil nematode communities can be reflected by values of relative tillage response of index V. Results of index V indicate that total nematodes,bacterivores,fungivores and plant parasites are mildly inhibited,and omnivores-predators is moderately inhibited under CT treatment; while,under FF treatment total nematodes is mildly,and fungivores and plant parasites are moderately stimulated,respectively. 展开更多
关键词 soil nematode tillage system vertical distribution tillage response
下载PDF
An rescaled range analysis on the characteristics of coal seam development in the Eastern depression of the Liaohe Basin 被引量:2
18
作者 Zhao Zhongying Wang Yulin +1 位作者 Liu Guangdi Sun Xiang 《Mining Science and Technology》 EI CAS 2011年第2期223-227,共5页
The characteristics of coal seam development,and the prospects of a favorable coal-forming area,were evaluated for the Liaohe Basin located in China.The Number 3 and Number 9 coal seam thickness series from 60 nearly ... The characteristics of coal seam development,and the prospects of a favorable coal-forming area,were evaluated for the Liaohe Basin located in China.The Number 3 and Number 9 coal seam thickness series from 60 nearly equally spaced bores in the Eastern depression of the Liaohe Basin were examined by a rescaled range analysis.The results indicate that the Hurst exponents of the Number 3 and Number 9 coal seam thickness series are 0.69 and 0.68,respectively.This suggests the presence of persistence.As the bore spacing increases the Hurst exponent of the Number 3 series gradually decreases(H changes from 0.69 to 0.52) and shifts from persistence to randomness.The Hurst exponent of the Number 9 thickness data gradually increases(H changes from 0.68 to 0.91) and always shows the characteristic of persistence.A combination of geological characteristics and the series data allow the conclusion that it is more suitable for the Number 9 coal seam to form in the Northeastern part of the Eastern depression than the Number 3 coal seam. 展开更多
关键词 Rescaled range analysis Hurst exponent Coal seam thickness Eastern depression Liaohe Basin
下载PDF
Spatial Distribution and Seasonal Variations of Heavy Metal Contamination in Surface Waters of Liaohe River, Northeast China 被引量:6
19
作者 WANG Hui SUN Lina +1 位作者 LIU Zhe LUO Qing 《Chinese Geographical Science》 SCIE CSCD 2017年第1期52-62,共11页
Heavy metal pollutants are a worldwide concern due to slow decomposition, biocondensation, and negative effects on human health. We investigated seasonal and spatial variations of the five heavy metals and evaluated t... Heavy metal pollutants are a worldwide concern due to slow decomposition, biocondensation, and negative effects on human health. We investigated seasonal and spatial variations of the five heavy metals and evaluated their health risk in the Liaohe River, Northeast China. A total of 324 surface water samples collected from 2009 to 2010 were analyzed. Levels(high to low) of heavy metals in the Liaohe River were: zinc(Zn) > chromium(Cr) > copper(Cu) > cadmium(Cd) > mercury(Hg). Spatial and seasonal changes impacting concentrations of Cu and Zn were significant, but not significant for Cr, Cd and Hg. The highest concentrations of heavy metals were: Hg at Liuheqiao, Cu at Fudedian, Zn at Tongjiangkou, Cr at Mahushan, and Cd at Shenglitang. The highest concentrations of Hg and Cr were found in the wet period, Cu and Cd in the level period, and Zn in the dry period. The surface water of a tributary was an important accumulation site for heavy metals. Health risks from carcinogens and non-carcinogens increased from upstream to downstream in the mainstream of the Liaohe River. The total health risk for one person in the Liaohe River exceeded acceptable levels. The total health risk was the greatest during the wet period and least in the dry period. Among the five heavy metals in the Liaohe River, Cr posed the greatest single health risk. 展开更多
关键词 heavy metal metal contamination health risk Liaohe River
下载PDF
A Case History of Secondary 3D Seismic Exploration in the Liaohe Basin: An Example from the Rongshengpu–Qianjin Area
20
作者 田清波 《Applied Geophysics》 SCIE CSCD 2005年第3期175-181,F0003,共8页
The working area is located in the industrially developed region of Rongshengpu-Qianjin, where a surface water system is developed, surface-layer lithology is complicated, and various kinds of hydrocarbon traps are bu... The working area is located in the industrially developed region of Rongshengpu-Qianjin, where a surface water system is developed, surface-layer lithology is complicated, and various kinds of hydrocarbon traps are buried at depth. The seismic data acquired previously couldn't be interpreted due to the complex surface and geological conditions. Taking secondary 3D seismic from the Rongshengpu-Qianjin area as an example, this paper describes a set of techniques designed to overcome these difficulties and improve the quality of seismic data. The applied techniques included flexible acquisition geometry, low-noise receiver conditions, quantitative quality control, and so on. 展开更多
关键词 Damintun Sag 3D SEISMIC secondary exploration and complex area
下载PDF
上一页 1 2 下一页 到第
使用帮助 返回顶部