首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   272篇
  免费   13篇
  国内免费   14篇
林业   36篇
农学   9篇
基础科学   7篇
  32篇
综合类   64篇
农作物   8篇
水产渔业   13篇
畜牧兽医   54篇
园艺   37篇
植物保护   39篇
  2023年   3篇
  2022年   7篇
  2021年   4篇
  2020年   10篇
  2019年   7篇
  2018年   7篇
  2017年   5篇
  2016年   9篇
  2015年   6篇
  2014年   13篇
  2013年   20篇
  2012年   22篇
  2011年   13篇
  2010年   11篇
  2009年   20篇
  2008年   11篇
  2007年   28篇
  2006年   13篇
  2005年   9篇
  2004年   14篇
  2003年   17篇
  2002年   5篇
  2001年   8篇
  2000年   10篇
  1999年   6篇
  1998年   2篇
  1997年   3篇
  1996年   1篇
  1995年   2篇
  1994年   3篇
  1993年   2篇
  1992年   3篇
  1991年   1篇
  1990年   1篇
  1988年   2篇
  1987年   1篇
排序方式: 共有299条查询结果,搜索用时 15 毫秒
21.
高羊茅褐斑病的初步研究   总被引:4,自引:0,他引:4  
对高羊茅褐斑病菌的鉴定、致病性测定、发生规律的调查及室内外药效测定等进行了研究。结果表明:引起高羊茅褐斑病的病原菌为Rhizoctoniasolani。在PDA培养皿上25~30℃为菌丝生长最适温度。室外调查表明此病害发病高峰期为6月中下旬至9月。经室内外药效试验筛选,结果表明较好的防治药剂为宝草津、力克菌、敌力脱、甲基托布津,室外防治效果分别达到91.54%、90.64%、72.94%、72.83%。  相似文献   
22.
膜片钳技术及其应用   总被引:3,自引:0,他引:3  
膜片钳技术是在电压钳基础上发展的,将尖端为1μm的玻璃微电极吸附到细胞表面,使微电极与细胞膜形成高阻封接,从而可记录到膜上pA级的离子通道电流,目前已发展了多种记录模式,对细胞进行电压和电流钳制,以观察各种离子通道及其调控。此外膜片钳技术与胞内纤维荧光测钙技术、膜电容监测技术、碳纤维电极局部电化学微量检测技术、逆转录多聚酶链式反应技术(PCR)结合,在药理学、病理学、神经科学、脑科学、细胞生物学和分子生物学等生物科学方面,得到越来越广泛的应用。  相似文献   
23.
建立了2个斑块上种群扩散的食饵-捕食系统,主要研究了当其中一个斑块受到输入量存在极限值的外来毒素污染时,扩散对2个斑块上3个种群生存的影响。结果表明,当扩散存在且扩散率满足一定条件时,食饵种群和捕食者种群在未来时刻将全部灭绝;而当扩散率满足另一条件时,食饵种群和捕食者种群将持续生存,进而会影响斑块上的生物多样性。  相似文献   
24.
比较大鼠心肌膜、肺、肠黏膜微血管内皮细胞静息膜电位,为内皮细胞电生理特性研究提供数据。用植块法培养大鼠心肌膜、肺、肠黏膜微血管内皮细胞,采用膜片钳放大器全细胞记录模式,分别测定3种细胞的静息膜电位。结果表明:心肌膜微血管内皮细胞的静息膜电位为(-24±4)mV;肺微血管内皮细胞的静息膜电位为(-27±6)mV;肠黏膜微血管内皮细胞静息膜电位为(-18±4)mV。3种不同组织来源的微血管内皮细胞在静息膜电位上存在异质性。  相似文献   
25.
在利用现时高分辨率航片获取大比例尺、翔实的土地利用现状图的基础上,结合研究区的特点进行了景观分类,选择和计算了景观多样性指数和景观优势度、分离度、破碎度指数及斑块分形维数等景观格局指数,对浙江省桐乡市大麻镇进行了小尺度、大比例尺(1∶2000)景观格局分析。结果表明,景观多样性指数与最大多样性指数有很大的差异;研究区内的各景观类型所占比例差异较大,优势度数值高,耕地成为起支配作用的优势景观,如果将耕地、园地、林地和其他农用地当成一种景观类型,则研究区内整体景观生态特征明显由农业景观所支配;其他农用地景观类型的景观破碎度最高,受人为干扰和破坏最为严重,因近年来土地整理的实施,耕地景观以面积大而且形状较规则的斑块广泛分布于研究区中;居民点及独立工矿景观的斑块几何形状趋近于简单且规则,但受人为干扰程度大。  相似文献   
26.
In order to evaluate economic and ecological benefits, site-specific weed control was realised in a 4-year experiment on five fields with a GPS-guided sprayer. An average of 54% of the herbicides could be saved. Savings were strongly dependent on crop and year. For grass weed herbicides, the savings were 90% in winter cereals, 78% in maize, and 36% in sugar beet. For herbicides against broadleaf weeds, 60% were saved in winter cereals, 11% in maize, and 41% in sugar beet. The monetary savings resulting from the reduction in herbicide use varied between the crops, depending on the amount of herbicides saved and the price of the herbicides. In maize, savings of 42euro/ha were realised, in winter wheat of 32euro/ha, in winter barley of 27euro/ha and in sugar beet of 20euro/ha. Large sections of the fields needed herbicide treatment significantly less frequently. In those areas where weed density remained below the weed control threshold, flora and fauna were allowed to establish largely without disturbance.  相似文献   
27.
A pepper esterase (PepEST) gene was introduced into creeping bentgrass (Agrostis stolonifera) by Agrobacterium‐mediated transformation. Purified recombinant PepEST proteins were sufficient to inhibit the growth of the fungal pathogens Rhizoctonia solani AG2‐2 (IIIB) (causing brown patch) and Sclerotinia homoeocarpa (dollar spot), but not the oomycete responsible for pythium blight, Pythium aphanidermatum. PepEST proteins were most effective against R. solani. After genetic transformation of creeping bentgrass with PepEST, the genomic integration of transgenes bar and PepEST was confirmed by Southern blot analysis, and their expression was also validated by northern blot and western blot analyses. Disease severity on R. solani‐inoculated leaves of transgenic plants was <10% compared to ca. 50% in non‐transgenic plants. Microscopic observation of infected leaves indicated that PepEST inhibited the growth of hyphae upon fungal infection.  相似文献   
28.
库布齐沙漠东缘沙地植被近自然恢复研究   总被引:1,自引:0,他引:1  
本文调查研究了沙地植被自然恢复过程,并结合地植物的自然分布规律及其生长的特点,提出了沙地植被恢复中自然斑的重要作用。  相似文献   
29.
Metapopulations are conceived as spatially structured populations consisting of distinct units (subpopulations), separated by space or barriers, and connected by dispersal movements. Metapopulations characteristically demonstrate a turnover of local populations going extinct and becoming re-established, resulting in a distribution pattern that shifts over time. Metapopulation theory is used to analyse the effects of habitat fragmentation on birds in the temperate zone, integrating various explanations for the paucity of species in isolated ecotopes.There is some evidence that turnover of local populations occurs in fragmented systems. A few studies based on time series demonstrate the local extinction rate to be related to the size of the habitat fragment, whereas the recolonization rate depends on the degree of isolation. Most evidence comes from short-term pattern studies in which the probability of occurrence was found to depend on the size of habitat fragments, on their relative position in the landscape and on the density of corridors lowering the landscape resistance. These data are consistent with predictions from metapopulation theory. However, almost all investigations consider wood fragmentation in agricultural landscapes, and there is a great need for studies in naturally fragmented landscapes as well as for studies focussing on other, less predictable, habitat types.  相似文献   
30.
Jonsen  Ian D.  Fahrig  Lenore 《Landscape Ecology》1997,12(3):185-197
The purpose of this study was to investigate the effect ofchanges in landscape pattern on generalist and specialistinsects. We did this by comparing the species richness andabundance of generalist and specialist herbivorous insects inalfalfa (Medicago sativa, L.) fields on 26 agriculturallandscapes that differed in spatial structure. The insects werefrom the families Curculionidae (Coleoptera), weevils, andCicadellidae (Auchennorhyncha), leafhoppers.We hypothesized that: (1) generalist richness and abundancewould be highest in landscapes with high diversity(Shannon-Wiener); (2) specialist richness and abundance would behighest in landscapes with (i) high percent cover alfalfa and(ii) low mean inter-patch distance. We tested for these effectsafter controlling for the patch-level effects of field size,field age, frequency of disturbance and vegetation texture.The important findings of the study are: (1) generalist richness andabundance increased with increasing landscape diversity and (2)isolation (percent cover alfalfa in the landscape and/or meaninter-patch distance) does not affect specialist insects. Theseresults are significant because they indicate that bothgeneralist and specialist insects may move over much largerdistances than previously thought. This is one of the firststudies to demonstrate a large scale effect of spatial structureon insects across a broad range of landscapes.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号