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   103177篇
  免费   6501篇
  国内免费   48篇
林业   4981篇
农学   4011篇
基础科学   715篇
  14477篇
综合类   13956篇
农作物   3937篇
水产渔业   6126篇
畜牧兽医   53192篇
园艺   1386篇
植物保护   6945篇
  2021年   916篇
  2020年   1013篇
  2019年   1159篇
  2018年   2150篇
  2017年   2452篇
  2016年   2271篇
  2015年   1870篇
  2014年   2245篇
  2013年   4516篇
  2012年   3854篇
  2011年   4432篇
  2010年   2836篇
  2009年   2756篇
  2008年   4158篇
  2007年   3907篇
  2006年   3726篇
  2005年   3204篇
  2004年   3057篇
  2003年   3037篇
  2002年   2753篇
  2001年   3663篇
  2000年   3584篇
  1999年   2782篇
  1998年   1039篇
  1997年   1097篇
  1996年   940篇
  1995年   1053篇
  1994年   925篇
  1993年   924篇
  1992年   1980篇
  1991年   2029篇
  1990年   1963篇
  1989年   1984篇
  1988年   1736篇
  1987年   1710篇
  1986年   1742篇
  1985年   1632篇
  1984年   1306篇
  1983年   1118篇
  1982年   760篇
  1979年   1166篇
  1978年   904篇
  1975年   859篇
  1974年   993篇
  1973年   959篇
  1972年   912篇
  1971年   891篇
  1970年   823篇
  1969年   816篇
  1967年   763篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Summary Acute febrile diseases are characterized by specific and non-specific symptoms. The non-specific responses are presented under the headings: fever, inflammation and pain, experimental models for investigating febrile reactions, haematologic changes, blood biochemical changes, cardiovascular effects, changes in gastric function, and the effects of fever upon pharmacokinetics of drugs. It was the purpose of this review to describe present concepts of thermoregulation and fever, the associated reactions produced by bacterial pyrogens and the mechanisms of these reactions. The available data illustrate, that many questions have not yet been clearly answered. However, the entire field of research involving endogenous substances, such as interleukin-1, is now moving ahead with great speed. Furthermore, there is some evidence which suggests that fever and the associated lower plasma zinc and iron levels act together as a co-ordinated non-specific host defence mechanism. Since experimental fever has a distinct effect upon the pharmacokinetics of drugs, more attention should be given to this aspect.  相似文献   
42.
Prevention of renal carriage of leptospirosis in dogs by vaccination   总被引:1,自引:0,他引:1  
Dogs vaccinated with a Leptospira interrogans vaccine containing serogroups Canicola and Icterohaemorrhagiae and prepared from cultures grown in a protein-free medium resisted challenge with heterologous representatives of these serogroups. In contrast, control dogs were pyrexic and leptospires were isolated from the blood for nine days following Canicola challenge and six days after Icterohaemorrhagiae challenge. Leptospires were isolated from the urine of controls throughout the post challenge period and from kidneys at post mortem examination of six out of six and four out of six Canicola and Icterohaemorrhagiae challenged controls, respectively. There have been no reports of hypersensitivity reactions to this vaccine since its introduction in 1980.  相似文献   
43.
GRAY  S. J.; PRICE  COLIN 《Forestry》1990,63(2):161-175
Traditional forest economics deals with regularly-ordered activities.For many reasons, however, choices must often be made amongconflicting operational priorities. In these circumstances,maximizing net discounted revenue per hectare does not maximizeglobal profit. Priorities for action should be chosen in orderof urgency index ratio, defined as the cost of delaying an operationdivided by the units of limited resource needed to undertakethe operation. Forest managers tend to use informal and sometimesconflicting rules to assign priorities among uses of limitedresources. These priorities often differ from those indicatedby urgency index ratio. Urgency index ratio can be determinedby simple calculations based on readily-available data. Theconcept can be extended to include multiple constraints.  相似文献   
44.
45.
46.
47.
48.
49.
50.
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