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   821篇
  免费   45篇
  国内免费   1篇
林业   79篇
农学   20篇
  145篇
综合类   138篇
农作物   48篇
水产渔业   100篇
畜牧兽医   255篇
园艺   10篇
植物保护   72篇
  2023年   4篇
  2021年   15篇
  2020年   15篇
  2019年   8篇
  2018年   17篇
  2017年   12篇
  2016年   19篇
  2015年   13篇
  2014年   19篇
  2013年   38篇
  2012年   47篇
  2011年   39篇
  2010年   29篇
  2009年   24篇
  2008年   49篇
  2007年   52篇
  2006年   36篇
  2005年   39篇
  2004年   33篇
  2003年   57篇
  2002年   30篇
  2001年   13篇
  2000年   16篇
  1999年   14篇
  1998年   5篇
  1996年   6篇
  1995年   8篇
  1994年   10篇
  1993年   8篇
  1992年   11篇
  1991年   13篇
  1990年   6篇
  1989年   8篇
  1988年   4篇
  1987年   5篇
  1986年   7篇
  1984年   5篇
  1983年   10篇
  1982年   5篇
  1980年   5篇
  1978年   5篇
  1977年   6篇
  1975年   4篇
  1974年   4篇
  1973年   7篇
  1972年   8篇
  1971年   5篇
  1959年   3篇
  1945年   3篇
  1925年   3篇
排序方式: 共有867条查询结果,搜索用时 125 毫秒
51.
We compared the amounts of learning achieved using two different instructional approaches under controlled conditions. We measured the learning of a specific set of topics and objectives when taught by 3 hours of traditional lecture given by an experienced highly rated instructor and 3 hours of instruction given by a trained but inexperienced instructor using instruction based on research in cognitive psychology and physics education. The comparison was made between two large sections (N = 267 and N = 271) of an introductory undergraduate physics course. We found increased student attendance, higher engagement, and more than twice the learning in the section taught using research-based instruction.  相似文献   
52.
53.
54.
The production of nitric oxide and other reactive nitrogen intermediates (RNI) by macrophages helps to control infection by Mycobacterium tuberculosis (Mtb). However, the protection is imperfect and infection persists. To identify genes that Mtb requires to resist RNI, we screened 10,100 Mtb transposon mutants for hypersusceptibility to acidified nitrite. We found 12 mutants with insertions in seven genes representing six pathways, including the repair of DNA (uvrB) and the synthesis of a flavin cofactor (fbiC). Five mutants had insertions in proteasome-associated genes. An Mtb mutant deficient in a presumptive proteasomal adenosine triphosphatase was attenuated in mice, and exposure to proteasomal protease inhibitors markedly sensitized wild-type Mtb to RNI. Thus, the mycobacterial proteasome serves as a defense against oxidative or nitrosative stress.  相似文献   
55.
56.
57.
Uncertainty and adaptive management for biodiversity conservation   总被引:2,自引:0,他引:2  
Adaptive management of natural resources is widely supported, but in biodiversity conservation there have been few practical applications of the approach in its entirety. Some of the contributions to this special publication examine progress in the implementation of adaptive approaches into conservation policy, while others explore novel theoretical and modeling approaches that seek to accommodate the complexities of real-world applications. Several of the papers address the treatment of uncertainty in adaptive management through innovative approaches to experimentation and monitoring, use and characterisation of expert knowledge and reconciliation of differences of opinion about parameters or systems. Drawing on these contributions, we discuss the major impediments to implementing adaptive management, why adaptive management has been slow to be implemented and how this can be redressed.  相似文献   
58.
The objective of this prospective study was to determine the prevalence of echocardiographic evidence of heart disease in apparently healthy cats with heart murmurs. Thirty-two privately owned domestic cats were examined. All cats were considered healthy on the basis of history and physical examination, except for the finding of a heart murmur on auscultation. Cats on any medications (besides regular flea, tick and heartworm preventative) or that were pregnant or lactating were excluded from this study. The prevalence of echocardiographic evidence of heart disease in this population of cats was 53%. Therefore, identification of a heart murmur on routine physical examination in apparently healthy cats warrants further investigation.  相似文献   
59.
BACKGROUND: Tricyclazole is a commercial fungicide used to control rice blast. As part of re‐registration activities, samples of metabolites and process impurities are required. In addition, isotopically labeled tricyclazole samples are also required. RESULTS: Four new compounds related to tricyclazole are reported. An isotopically labeled sample of tricyclazole was prepared that contained two 15N atoms and one 13C atom. Radiolabeled tricyclazole with 14C at the triazole C3 position was also synthesized. A new process impurity in technical tricyclazole was identified and synthesized. A new metabolite of tricyclazole was identified, independently synthesized and characterized by X‐ray crystallography. CONCLUSION: A previously unreported metabolite of tricyclazole has been identified and structurally characterized. In addition, a new process impurity has been identified by independent synthesis. Identification of these new compounds has facilitated the continued registration of this important fungicide. Copyright © 2011 Society of Chemical Industry  相似文献   
60.
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