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   132875篇
  免费   7287篇
  国内免费   93篇
林业   5436篇
农学   4294篇
基础科学   835篇
  17155篇
综合类   21511篇
农作物   5415篇
水产渔业   6740篇
畜牧兽医   68042篇
园艺   1813篇
植物保护   9014篇
  2020年   1197篇
  2019年   1395篇
  2018年   2046篇
  2017年   2343篇
  2016年   2112篇
  2015年   1757篇
  2014年   2249篇
  2013年   5316篇
  2012年   4143篇
  2011年   5122篇
  2010年   3259篇
  2009年   3410篇
  2008年   4992篇
  2007年   4686篇
  2006年   4375篇
  2005年   4104篇
  2004年   3868篇
  2003年   3988篇
  2002年   3556篇
  2001年   4156篇
  2000年   4256篇
  1999年   3374篇
  1998年   1479篇
  1997年   1389篇
  1996年   1288篇
  1995年   1531篇
  1994年   1360篇
  1993年   1234篇
  1992年   2585篇
  1991年   2701篇
  1990年   2591篇
  1989年   2611篇
  1988年   2368篇
  1987年   2348篇
  1986年   2427篇
  1985年   2340篇
  1984年   1882篇
  1983年   1678篇
  1982年   1149篇
  1979年   1748篇
  1978年   1397篇
  1977年   1151篇
  1976年   1213篇
  1975年   1292篇
  1974年   1500篇
  1973年   1516篇
  1972年   1405篇
  1971年   1304篇
  1970年   1251篇
  1969年   1283篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
The effects of collection regimen and time of year on rabbit semen production were determined in this study. A total of 14 crossbreed Hyla bucks were used in winter and summer. In each season, rabbits were assigned to two groups. In group 1, (n = 7) rabbits were subjected to an extensive collection regimen (two ejaculates per male, once daily/week) and in group 2, (n = 7) a semi‐intensive semen collection regimen was performed (two ejaculates per male, twice weekly). The traits recorded for each sample were libido, volume, pH, motility, sperm concentration, percentage of alive spermatozoa and sperm abnormalities. The results obtained in this study indicate that when increasing collection frequency, the rate of useful collections decreased (from 0.81 ± 0.017 to 0.69 ± 0.016; p < 0.01). The rate of useful collection also decreased in the transition from winter to summer (from 0.79 ± 0.018 to 0.70 ± 0.017; p < 0.01). Among the ejaculate characteristics studied, only volume/ejaculate (from 0.64 ± 0.015 to 0.53 ± 0.017; p < 0.01) and spermatozoa/ml (from 406 ± 15 to 359 ± 13 million; p < 0.01) appeared negatively affected by collection. In winter fewer volume/ejaculates were produced (0.55 ± 0.015 vs 0.60 ± 0.016 ml; p < 0.01) and fewer spermatozoa/ml (360 ± 14 vs 394 ± 16 million; p < 0.01) than in summer. The doses produced per ejaculate decreased as collection frequency increased, but the number of doses produced per week was higher in the semi‐intensive than the extensive rhythm (26.5 ± 2.1 vs 20.9 ± 1.5; p < 0.01). The results suggest that a semi‐intensive rhythm may be viewed favourably.  相似文献   
142.
143.
144.
145.
146.
Colitis cystica profunda in dogs has been diagnosed in one case only. The two own cases were characterized by repeated, partly bloody diarrhea, vomitus, and painful defecation. The disease was diagnosed by clinical examination and colonoscopy with the ensuing histological examination of biopsy specimens. The disease could be managed by administration of a diet, sulfasalazine and corticosteroids.  相似文献   
147.
Thyroidal 99mTcO4(pertechnetate) uptake percentages were determined in unanesthetized euthyroid (n = 13) and hyperthyroid (n = 18) cats. Maximal uptakes were observed 60 minutes after IV injection of the radionuclide and ranged from 0.3 to 3.9% of the dose in euthyroid cats (median 2.23%) and from 5.2% to 23.9% of the dose in hyperthyroid cats (median 14.8%) ( P < .05). There were no overlaps in pertechnetate uptake percentages during any of the intervals evaluated. It is concluded that the optimal time for visualization of the thyroid by 99mTcO4-scanning is 60 minutes after IV injection of the radionuclide. Calculation of the percentage uptake is of additional diagnostic value.  相似文献   
148.
Western blot analysis of Theileria annulata antigens was carried out using sera collected from cattle which had been immunised and challenged with either T. annulata sporozoites or schizont-infected cells. Three antigens between 71 and 73 kDa proved to be common to the three stages of parasite studied: sporozoites, schizonts and piroplasms. An antigen was found at 32 kDa which was specific to T. annulata piroplasms. Results were reproducible using sera from Morocco and the UK. At least one of the proteins at 71-73 kDa, but not that at 32 kDa were also recognised by sera from animals infected with Babesia species.  相似文献   
149.
150.
Calicivirus was isolated from the joint of a kitten that had pyrexia, upper respiratory tract disease, and severe shifting-limb lameness. Marked mononuclear inflammation was found in the synovial fluid. Calicivirus infection or live-virus vaccination previously had been associated with arthropathy, but virus had not been recovered from affected joints. Calicivirus infection should be considered as a diagnosis in kittens with fever and arthralgia, especially if there is a history of recent vaccination or upper respiratory tract disease. Lameness associated with calicivirus infection may be severe, but appears to be self-limiting and is associated with an excellent prognosis for recovery.  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