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   199206篇
  免费   10624篇
  国内免费   132篇
林业   8426篇
农学   6080篇
基础科学   1342篇
  22851篇
综合类   36800篇
农作物   7629篇
水产渔业   9678篇
畜牧兽医   101158篇
园艺   2505篇
植物保护   13493篇
  2018年   2392篇
  2017年   2605篇
  2016年   2437篇
  2015年   2153篇
  2014年   2636篇
  2013年   7179篇
  2012年   4945篇
  2011年   6186篇
  2010年   3963篇
  2009年   3931篇
  2008年   6089篇
  2007年   5915篇
  2006年   5643篇
  2005年   5313篇
  2004年   5149篇
  2003年   5157篇
  2002年   4991篇
  2001年   6065篇
  2000年   5912篇
  1999年   4871篇
  1998年   1957篇
  1997年   1970篇
  1995年   2276篇
  1994年   1994篇
  1993年   1984篇
  1992年   4086篇
  1991年   4276篇
  1990年   4407篇
  1989年   4374篇
  1988年   4044篇
  1987年   4098篇
  1986年   4219篇
  1985年   4095篇
  1984年   3452篇
  1983年   3073篇
  1982年   2141篇
  1981年   1967篇
  1980年   1886篇
  1979年   3152篇
  1978年   2596篇
  1977年   2227篇
  1976年   2049篇
  1975年   2204篇
  1974年   2891篇
  1973年   2965篇
  1972年   2930篇
  1971年   2665篇
  1970年   2512篇
  1969年   2294篇
  1967年   1996篇
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
91.
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   
92.
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   
93.
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   
94.
Washed and unwashed red blood cells (RBC) from young calves, adult cattle, hamsters and humans were incubated with Leptospira interrogans serovars pomona and ballum. Washed cells suspended in saline were always haemolysed while unwashed cells and those which were washed and resuspended in plasma were never haemolysed, despite the presence of large numbers of organisms within the culture supernatant. Pomona produced greater haemolysis of cattle and human RBC than did ballum, but with hamster RBC ballum produced greater haemolysis than did pomona. A group of 6- to 9-month-old cattle infected with pomona showed no signs of clinical disease and RBC taken from them before infection and during the development of antibodies to pomona were haemolysed by pomona only after the cells were washed. Plasma therefore appears to have a protective function. This in vitro protective function of plasma even extended to plasma from young seronegative calves.  相似文献   
95.
96.
97.
Ohne Zusammenfassung  相似文献   
98.
99.
100.
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