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   155836篇
  免费   10596篇
  国内免费   94篇
林业   6973篇
农学   5573篇
基础科学   936篇
  18845篇
综合类   26524篇
农作物   6151篇
水产渔业   9373篇
畜牧兽医   80017篇
园艺   1922篇
植物保护   10212篇
  2020年   1446篇
  2019年   2164篇
  2018年   2764篇
  2017年   3050篇
  2016年   2905篇
  2015年   2499篇
  2014年   2930篇
  2013年   6389篇
  2012年   4500篇
  2011年   5438篇
  2010年   3792篇
  2009年   3489篇
  2008年   5138篇
  2007年   4852篇
  2006年   4680篇
  2005年   4116篇
  2004年   3973篇
  2003年   4027篇
  2002年   3764篇
  2001年   4937篇
  2000年   4892篇
  1999年   3845篇
  1998年   1531篇
  1997年   1586篇
  1995年   1662篇
  1994年   1403篇
  1993年   1441篇
  1992年   2979篇
  1991年   3093篇
  1990年   3145篇
  1989年   3104篇
  1988年   2831篇
  1987年   2773篇
  1986年   2847篇
  1985年   2748篇
  1984年   2249篇
  1983年   1986篇
  1979年   2135篇
  1978年   1677篇
  1977年   1398篇
  1976年   1400篇
  1975年   1590篇
  1974年   1936篇
  1973年   1959篇
  1972年   1905篇
  1971年   1834篇
  1970年   1755篇
  1969年   1666篇
  1968年   1478篇
  1967年   1542篇
排序方式: 共有10000条查询结果,搜索用时 202 毫秒
61.
Two serological tests (indirect immunofluorescence and enzyme-linked immunosorbent assay) were developed for the detection of fetal antibody to Chlamydia psittaci. Fetal blood and thoracic fluid from 126 field cases of suspected ovine chlamydial abortion were examined using both tests. Placenta and fetal tissues (lung, liver, and kidney) from the same animals were also examined by the following conventional diagnostic methods: isolation in McCoy cells, detection of chlamydial lipopolysaccharide (LPS), modified Ziehl-Nielsen staining, and direct fluorescent antibody staining of chlamydia in frozen cryostat sections. Seventy cases were positive by fetal serology, and of these, 68 were also positive by isolation and/or LPS detection. The remaining 56 cases had negative fetal serology, and of these, 39 were positive by isolation and/or LPS detection. Results indicate that fetal serology, although less sensitive than either isolation in McCoy cells or detection of chlamydial LPS antigen, may be of particular use when placenta is not available.  相似文献   
62.
Subgroup-specific peptide-based enzyme-linked immunosorbent assays from the G-protein of the ovine and bovine respiratory syncytial virus (RSV), respectively, were used to determine the prevalence of the ovine and bovine subgroup strains of RSV infections in cattle. A total of 1,102 bovine serum samples were obtained from 6 diagnostic laboratories located in the northwestern and the southeastern USA and were tested for antibody to either the bovine or ovine subgroups of RSV. Antibody to viruses from each subgroup was present in samples from each region and all states tested. The Southeast had a higher prevalence of the bovine subgroup strains (69.5%). Then did the Northwest (40.9%). The prevalence of the ovine strain was similar for the two regions (16.7% in the southeast, 14.9% in the northwest). The overall prevalence was 56.6% for the bovine strain and 15.9% for the ovine strain. These results suggest members of the ovine subgroup of RSV circulate in the cattle population but with less frequency than those viruses of the bovine subgroup.  相似文献   
63.
64.
Star catalogues     
  相似文献   
65.
66.
67.
68.
The feet of three two-humped camels (Camelus bactrianus), one lama (Lama glama) and four alpacas (Lama pacos) from zoos and a circus in the Netherlands were examined for the mange-mite Choroptes bovis. Mites were found on two of the camels, the lama, and three of the alpacas. On one camel and one alpaca small mange lesions on the feet were present. This is the first report of Chorioptes bovis and chorioptic mange in the two-humped camel.  相似文献   
69.
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   
70.
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   
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