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栽培甜菜助细胞退化进程的超微结构观察
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作者 李伟 申家恒 郭德栋 《作物学报》 CAS CSCD 北大核心 2013年第12期2220-2227,共8页
应用透射电镜技术研究栽培甜菜(Beta vulgaris)助细胞退化进程的超微结构特征,以丰富被子植物生殖生物学资料。结果表明:花蕾时期,2个助细胞相似,珠孔端具发达的丝状器,合点端无壁,极性明显,细胞器种类多,数量大,呈现较强代谢活性;随后... 应用透射电镜技术研究栽培甜菜(Beta vulgaris)助细胞退化进程的超微结构特征,以丰富被子植物生殖生物学资料。结果表明:花蕾时期,2个助细胞相似,珠孔端具发达的丝状器,合点端无壁,极性明显,细胞器种类多,数量大,呈现较强代谢活性;随后,一个助细胞的核质和胞质的电子密度显著高于另一个助细胞,液泡膜消失,线粒体、质体膜与核膜不清晰,细胞出现退化迹象,但内质网和高尔基体丰富,分泌活动旺盛;待花蕾刚开放(授粉前),此助细胞完全退化。另一个助细胞(宿存助细胞)内的细胞器逐渐增多,且功能状态趋于活跃,表现为核糖体、线粒体、质体等数量增加;线粒体内嵴丰富,可见DNA纤丝;质体形态多样,片层明显,内含淀粉粒。至卵细胞受精前(授粉后约13 h),宿存助细胞代谢达到最活跃状态;至合子合点端建成蜂窝状细胞壁且胚乳游离核形成后,宿存助细胞开始退化;至合子后期,此细胞退化完全,丝状器消失。上述结果表明,栽培甜菜助细胞的退化与授粉和花粉管生长无关;宿存助细胞做为传递细胞,为胚囊的发育吸收并转输营养。 展开更多
关键词 栽培甜菜 助细胞 退化进程 超微结构
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青藏高原高寒草甸退化演替进程中植被斑块特征 被引量:1
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作者 霍佳娟 朱珏妃 +3 位作者 宋明华 李以康 徐兴良 周华坤 《草地学报》 CAS CSCD 北大核心 2022年第11期3113-3118,共6页
为揭示斑块属性及各属性之间的关系、优势植物组成对高寒草甸退化进程的指示作用,本研究在青海省果洛州玛沁县选取轻度、中度、重度、侵蚀4个退化阶段的高寒草甸,以斑块为单元开展样带尺度调查。结果表明:沿退化进程极大斑块和大斑块的... 为揭示斑块属性及各属性之间的关系、优势植物组成对高寒草甸退化进程的指示作用,本研究在青海省果洛州玛沁县选取轻度、中度、重度、侵蚀4个退化阶段的高寒草甸,以斑块为单元开展样带尺度调查。结果表明:沿退化进程极大斑块和大斑块的相对面积、数量在侵蚀阶段显著下降,中等面积斑块和小斑块相对面积和数量在重度退化和侵蚀阶段显著增加。斑块组成中中等面积斑块变化最显著。嵩草和杂类草混合生长斑块面积随退化进程显著下降,杂类草优势斑块面积增加,并且只有杂类草优势斑块的周长和数量随退化进程显著增加。总斑块周长-面积比沿退化进程显著增加。其中,杂类草占优势的斑块周长-面积比呈先下降后增加趋势。综上,中等面积植被斑块的空间分布、莎草向杂类草占优势的斑块类型的转变,以及斑块周长-面积比可作为高寒草甸向黑土滩转变的指示指标。 展开更多
关键词 退化进程 斑块大小 斑块类型 周长-面积比 高寒草甸
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伴有衰减型随机冲击的竞争失效可靠性综合评估模型 被引量:2
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作者 郭一帆 唐家银 《湖北大学学报(自然科学版)》 CAS 2021年第1期6-15,共10页
对于承受随机衰减型冲击,产品性能退化进程会产生对应性激励的工况,建立伴有衰减型随机冲击的竞争失效可靠性综合评估模型.以Wiener过程拟合产品性能退化进程,再利用指数函数对冲击衰减过程进行刻画,考虑冲击响应量与冲击损伤量之间的... 对于承受随机衰减型冲击,产品性能退化进程会产生对应性激励的工况,建立伴有衰减型随机冲击的竞争失效可靠性综合评估模型.以Wiener过程拟合产品性能退化进程,再利用指数函数对冲击衰减过程进行刻画,考虑冲击响应量与冲击损伤量之间的函数关系,并用极大似然估计法对性能退化过程的漂移和扩散参数以及冲击过程的冲击到达率和幅值参数进行估计,采用均值估计对冲击衰减系数与损伤因子进行估计,最后通过仿真算例证明该模型的合理性与有效性. 展开更多
关键词 衰减型冲击 退化进程 竞争失效 可靠性
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Ecological Optimization Design Methods for the Green Space System in Densely Built-up Areas
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作者 BI Linglan ZHANG Fuwen ZHANG Fangming 《Journal of Landscape Research》 2018年第4期35-40,44,共7页
This paper is aimed at studying the environmental degradation of densely built-up areas in the process of urbanization in Qiina. In consideration of the severe environmental conditions of die densely built-up afeas, s... This paper is aimed at studying the environmental degradation of densely built-up areas in the process of urbanization in Qiina. In consideration of the severe environmental conditions of die densely built-up afeas, such as the lack of green space and. open space, ecological disturbance in some areas, poor landscape quality, this paper focused on the ecological space optimization in the process of urban renewal Firstly, theories related to this field were analyzed, and a comprehensive ecological efficiency evaluation sjrstem was established based on disciplines such as urban ecology, landscape ecology, urban sociology, behavioral psychology, biology, urban planning and design. Secondly, this system was used to judge the ecological efficiency of typical blocks on GIS platform and to find out the key spatial nodes that need to be updated. Thirdly, in different cases, space optimization projects witii different theories were designed, and the spatial model of influence was used to comprehensively evaluate their ecological efficiency. Finally, the parameters under different conditions were corrected to get a systematic system for evaluating the green space system in densely built-up areas* Due to the lack of undetstanding of the ecological fonction of green space in the past, die environmental condition of densely built-up areas is not good. Therefore, the most important task of urban oigauic renewal is ecological restoiation. In this paper, die exploiation is based on the reservation for built-up afeas to avoid repeated reconstruction and interference. Authors of this paper tried to find out a way to rebuild green space system that performed more complex functions with limited spatial resources. The application of “micfo-ttansfotmation” of green space system in densely built-up areas turns out to improve the quality of landscape while reducing the construction costrds 展开更多
关键词 Densely built-up area Gteen space system Ecological restoration Complex function Micto- cmation
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Doha Round: The Environment and Agricultural and Biofuels Markets
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《Sociology Study》 2012年第2期107-119,共13页
The agricultural liberalization market process remains stalled Doha Round. The terms in protection levels reductions are negotiated, but the emergence of the global crisis constrains public resources to sustain them. ... The agricultural liberalization market process remains stalled Doha Round. The terms in protection levels reductions are negotiated, but the emergence of the global crisis constrains public resources to sustain them. In addition, the use of some grains as inputs in the production of biofuels, has contributed to the price increase in foods, although this production is an alternative to fossil fuels use and can help to reduce further environmental degradation. In this paper we analyze the main variables to be taken into account when negotiating the liberalization of agricultural trade, but also ofbiofuels in the context of Doha Round. 展开更多
关键词 Doha Round agricultural world market LIBERALIZATION biofuels environment
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