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   791篇
  免费   30篇
  国内免费   2篇
林业   104篇
农学   19篇
基础科学   1篇
  239篇
综合类   116篇
农作物   23篇
水产渔业   32篇
畜牧兽医   190篇
园艺   20篇
植物保护   79篇
  2023年   4篇
  2022年   10篇
  2021年   18篇
  2020年   30篇
  2019年   18篇
  2018年   16篇
  2017年   24篇
  2016年   21篇
  2015年   24篇
  2014年   28篇
  2013年   34篇
  2012年   50篇
  2011年   63篇
  2010年   46篇
  2009年   17篇
  2008年   47篇
  2007年   47篇
  2006年   48篇
  2005年   28篇
  2004年   28篇
  2003年   34篇
  2002年   27篇
  2001年   16篇
  2000年   8篇
  1999年   9篇
  1998年   6篇
  1997年   6篇
  1996年   3篇
  1994年   4篇
  1993年   3篇
  1991年   6篇
  1988年   5篇
  1987年   3篇
  1986年   7篇
  1984年   4篇
  1983年   5篇
  1982年   3篇
  1981年   6篇
  1980年   7篇
  1979年   5篇
  1978年   8篇
  1977年   6篇
  1975年   3篇
  1974年   2篇
  1973年   2篇
  1970年   2篇
  1969年   3篇
  1968年   2篇
  1967年   3篇
  1966年   7篇
排序方式: 共有823条查询结果,搜索用时 0 毫秒
821.
Fisheries provide nutrition and livelihoods for coastal populations, but many fisheries are fully or over‐exploited and we lack an approach for analysing which factors affect management tool performance. We conducted a literature review of 390 studies to assess how fisheries characteristics affected management tool performance across both small‐scale and large‐scale fisheries. We defined success as increased or maintained abundance or biomass, reductions in fishing mortality or improvements in population status. Because the literature only covered a narrow set of biological factors, we also conducted an expert elicitation to create a typology of broader fishery characteristics, enabling conditions and design considerations that affect performance. The literature suggested that the most commonly used management tool in a region was often the most successful, although the scale of success varied. Management tools were more often deemed successful when used in combination, particularly pairings of tools that controlled fishing mortality or effort with spatial management. Examples of successful combinations were the use of catch limits with quotas and limited entry, and marine protected areas with effort restrictions. The most common factors associated with inadequate biological performance were ‘structural’ issues, including poor design or implementation. The expert‐derived typologies revealed strong local leadership, high community involvement and governance capacity as common factors of success across management tool categories (i.e. input, output and technical measures), but the degree of importance varied. Our results are designed to inform selection of appropriate management tools based on empirical data and experience to increase the likelihood of successful fisheries management.  相似文献   
822.
Heavy metal content in Aporrectodea caliginosa (Oligochaeta, Lumbricidae) in the city of Kiel (Germany, Schleswig-Holstein) In November 1995 the content of lead, cadmium, copper and zinc in earthworms of the Aporrectodea caliginosa species was investigated at 28 sites of the Kiel area, as well as at one reference site (Belauer See, ca. 20 kilometres south of Kiel), and compared with the heavy metal content in the soil taken from all those sites. As for the lead and copper content, a positive correlation could be established between the earthworms and the soil. However, the lead content in the earthworms did not depend only on its amount in the soil, but also on soil pH and calcium content. Their copper content decreased exponentially as weight increased. The content of lead, cadmium and copper in A. caliginosa suggested an influence of urban soil pollution on the heavy metal content in earthworms. According to the grouping of heavy metal content in the earthworms, which was done in the course of the research work, the city of Kiel ranges among a minor to a medium degree of pollution caused by the investigated heavy metals.  相似文献   
823.
The application of enantioselective catalytic methods for the technical preparation of chiral agrochemicals is illustrated for three active ingredients of the acylanilide type. The key step for the technical synthesis of the herbicide (S)-metolachlor is the enantioselective hydrogenation of an imine intermediate using a novel iridium ferrocenyldiphosphine catalyst with an unprecedented high activity and 80% ee. (R)-metalaxyl and (αS,3R)-clozylacon were synthesized via the enantioselective hydrogenation of corre-sponding enamide precursors with Rh and Ru/binap catalysts with >95% and 99% enantiomeric purity, respectively. © 1998 Society of Chemical Industry  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