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   182篇
  免费   16篇
林业   2篇
基础科学   2篇
  26篇
综合类   17篇
农作物   2篇
水产渔业   6篇
畜牧兽医   130篇
植物保护   13篇
  2023年   3篇
  2019年   4篇
  2015年   3篇
  2014年   3篇
  2013年   3篇
  2012年   4篇
  2011年   9篇
  2010年   6篇
  2009年   6篇
  2008年   6篇
  2007年   15篇
  2006年   6篇
  2005年   7篇
  2004年   5篇
  2003年   9篇
  2002年   9篇
  2001年   5篇
  2000年   6篇
  1999年   6篇
  1998年   2篇
  1997年   2篇
  1995年   2篇
  1991年   5篇
  1989年   3篇
  1987年   2篇
  1985年   2篇
  1983年   2篇
  1982年   4篇
  1980年   2篇
  1979年   3篇
  1978年   3篇
  1977年   2篇
  1976年   2篇
  1975年   2篇
  1974年   4篇
  1973年   1篇
  1972年   4篇
  1971年   5篇
  1970年   6篇
  1969年   1篇
  1968年   3篇
  1967年   1篇
  1966年   2篇
  1965年   2篇
  1962年   2篇
  1961年   1篇
  1960年   3篇
  1957年   1篇
  1942年   1篇
  1940年   1篇
排序方式: 共有198条查询结果,搜索用时 234 毫秒
1.
The cleistogamous species Collomia grandiflora produces dimorphic cross-incompatible flowers on a single plant. The open or chasmogamous flower has smaller, flask-shaped stigmatic papillae, larger pollen grains, longer styles, and faster pollen tube growth rates down the style than the closed or cleistogamous flower. In intermorph crosses, pollen tube growth rates are greatly decreased and fertilization does not occur.  相似文献   
2.
Communities invest considerable resources to address the animal welfare and public health concerns resulting from unwanted pet animals. Traditionally, research in this area has enumerated the pet-owning population, described pet population dynamics in individual communities, and estimated national euthanasia figures. Recent research has investigated the human–animal bond and explored the community implications of managed feral cat colonies. These reports have utilized traditional epidemiologic study designs to generate observational data to describe populations and measure associations. However, rigorous scientific evaluations of potential interventions at the group level have been lacking. Group-randomized trials have been used extensively in public health research to evaluate interventions that change a population's behavior, not just the behavior of selected individuals. We briefly describe the strengths and limitations of group-randomized trials as they are used to evaluate interventions that promote social and behavioral changes in the human public health field. We extend these examples to suggest the appropriate application of group-randomized trials for pet population dynamics research.  相似文献   
3.
4.
5.
There is a clear need to monitor the health of wildlife in the UK, to help to understand the population dynamics of endangered species and to detect any harm to the welfare of wild animals caused by human beings. Despite previous proposals, there has been little progress in the development of a national programme of monitoring. With notable exceptions, the current schemes for investigating the morbidity and mortality of wild animals cover only limited groups of animals and are fragmented and uncoordinated. They consist of statutory schemes of restricted scope, and studies in universities, institutes and wildlife rehabilitation centres with limited funding. As a result, significant disease incidents may remain undetected and others may not be investigated fully, posing risks to the welfare and conservation of wildlife, the welfare of domestic animals, and in some cases to human health. Coordinated national schemes for the surveillance of the health of wildlife are already established in France, the USA and Canada and their best characteristics could be used to develop a scheme for the UK.  相似文献   
6.
7.
8.
9.
10.
Membrane extraction with sorbent interface (MESI) has been applied to monitor plant fragrance volatiles emitted into indoor air. The main components of the MESI system are a membrane module and a trap, which can be connected directly to a GC or GC-MS for simultaneous multicomponent extraction and monitoring. A polydimethylsiloxane (PDMS) membrane and two different traps, PDMS and Tenax, as well as a DC current supply for trap desorption have been applied in this research. After the membrane module is placed in contact with the plant, the MESI/GC-MS provides semicontinuous characterization of volatile compounds emitted. The MESI device has been applied to monitor the biogenic volatile organic compounds released during the first 8 h after a branch was cut from a Eucalyptus dunnii tree. The study demonstrates that the MESI system is a simple and useful tool for monitoring changes in emission processes as a function of time.  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