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   1029篇
  免费   70篇
林业   82篇
农学   21篇
基础科学   2篇
  170篇
综合类   86篇
农作物   36篇
水产渔业   44篇
畜牧兽医   518篇
园艺   14篇
植物保护   126篇
  2023年   9篇
  2022年   8篇
  2021年   29篇
  2020年   23篇
  2019年   28篇
  2018年   24篇
  2017年   27篇
  2016年   34篇
  2015年   25篇
  2014年   41篇
  2013年   42篇
  2012年   80篇
  2011年   90篇
  2010年   37篇
  2009年   46篇
  2008年   67篇
  2007年   70篇
  2006年   71篇
  2005年   64篇
  2004年   52篇
  2003年   39篇
  2002年   45篇
  2001年   12篇
  2000年   13篇
  1999年   15篇
  1998年   10篇
  1997年   9篇
  1996年   8篇
  1995年   9篇
  1994年   8篇
  1993年   3篇
  1992年   7篇
  1991年   8篇
  1990年   3篇
  1987年   5篇
  1986年   3篇
  1985年   4篇
  1983年   3篇
  1982年   2篇
  1978年   3篇
  1976年   1篇
  1975年   1篇
  1974年   3篇
  1973年   3篇
  1972年   2篇
  1971年   4篇
  1970年   1篇
  1969年   1篇
  1958年   1篇
  1955年   1篇
排序方式: 共有1099条查询结果,搜索用时 328 毫秒
51.
In its 40‐year history, the science of conservation has faced unprecedented challenges in terms of environmental damage and rapid global change, and environmental problems are only increasing as greater demands are placed on limited natural resources. Conservation science has been adapting to keep pace with these changes. Here, we highlight contemporary and emerging trends and innovations in conservation science that we believe represent the most effective responses to biodiversity threats. We focus on specific areas where conservation science has had to adjust its approach to address emerging threats to biodiversity, including habitat destruction and degradation, climate change, declining populations and invasive species. We also document changes in attitudes, norms and practices among conservation scientists. A key component to success is engaging and maintaining public support for conservation, which can be facilitated through the use of technology. These recent trends in conservation and management are innovative and will assist in optimizing conservation strategies, increasing our leverage with the general public and tackling our current environmental challenges.  相似文献   
52.
A 2-year-old neutered male golden retriever dog presented for lameness secondary to ulcerations of multiple digital paw pads was diagnosed with vasculitis and hypercholesterolemia. Despite treatment, ischemic necrosis progressed to include all distal extremities and the dog eventually expired due to myocardial infarction secondary to severe atherosclerosis. The rapid demise and the dermatologic lesions may have been secondary to cholesterol embolism syndrome which has never before been reported in a dog.  相似文献   
53.
54.
55.
56.
57.
58.
59.
The yellow-legged hornet (Vespa velutina) is the first invasive Vespidae predator of honeybees to be accidentally introduced into Europe from Asia. In the current pollinator decline, V. velutina is an additional stressor for honeybees and other pollinators. Although V. velutina contributes to the loss of honeybee colonies, little is known about its biology and behaviour both in the native and in the invaded area. Here, we review the current knowledge of this species and describe its life cycle and life history traits (reproduction, overwintering, foraging and dispersal) in the light of the biology of other Vespidae. We also review the impact of this species on ecosystems, on the economics of beekeeping, and on human health (this species being potentially deadly for allergic people). Based on this information and on previous worldwide experiences with Vespidae invasions, we propose key research topics for the development of effective management plans. We identify methods to limit the impact and proliferation of V. velutina in Europe that are based on nest destruction, trapping, population genetics, and biological control. In our opinion, research effort on the means to detect and destroy V. velutina nests at an early stage is required in order to short-circuit the colony cycle and thus limit both its impact on honeybees and its expansion through Europe. Finally, we discuss the impact of this biological invasion on the development of methods that should be used to manage alien species in the future.  相似文献   
60.
Thermal acclimation may directly modify muscle metabolic capacities, or may modify them indirectly via effects upon physiological processes such as growth, reproduction or senescence. To evaluate these interacting effects, we examined the influence of thermal acclimation and acclimatization upon muscle metabolic capacities and tissue masses in 1 + stickleback, Gasterosteus aculeatus, in which confounding interactions between temperature and senescense should be absent. Furthermore, we examined the influence of thermal acclimation upon individual growth rate, muscle enzyme levels and tissue masses in 2 + stickleback sampled at the beginning of their final reproductive season. For 1 + stickleback, cold acclimation more than doubles mitochondrial enzyme levels in the axial muscle. Thermal acclimation did not change the condition of 1 + stickleback at feeding levels which could not maintain the condition of 2+ stickleback. Compensatory metabolic responses to temperature were not apparent in field acclimatized 1 + stickleback. The growth rate of 2 + stickleback was markedly affected by temperature: warm-acclimated fish generally lost mass even at very high levels of feeding (up to 78 enchytraid worms per day) while cold-acclimated fish gained mass. This suggests that warm temperatures accelerate the senescence of 2 + stickleback. Generally, muscle enzyme activities increased with growth rate. In axial muscle, the relationships between CS activity and growth rate differed with acclimation temperature. Independent of the influence of growth rate, CS activities were consistently higher in cold- than warm-acclimated 2 + stickleback, suggesting compensatory increases of CS activity with cold acclimation. Corresponding author; This paper is dedicated to the memory of Gerry J. FitzGerald who passed away on March 14, 1994.  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