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   124648篇
  免费   6489篇
  国内免费   85篇
林业   6315篇
农学   4204篇
基础科学   695篇
  14349篇
综合类   20749篇
农作物   4993篇
水产渔业   6144篇
畜牧兽医   64830篇
园艺   1552篇
植物保护   7391篇
  2018年   1661篇
  2017年   1792篇
  2016年   1718篇
  2015年   1529篇
  2014年   1860篇
  2013年   4679篇
  2012年   3267篇
  2011年   3975篇
  2010年   2639篇
  2009年   2502篇
  2008年   3809篇
  2007年   3794篇
  2006年   3557篇
  2005年   3298篇
  2004年   3153篇
  2003年   3151篇
  2002年   2971篇
  2001年   3973篇
  2000年   3883篇
  1999年   3154篇
  1998年   1284篇
  1997年   1224篇
  1995年   1353篇
  1994年   1129篇
  1993年   1156篇
  1992年   2468篇
  1991年   2660篇
  1990年   2832篇
  1989年   2687篇
  1988年   2504篇
  1987年   2455篇
  1986年   2426篇
  1985年   2409篇
  1984年   2004篇
  1983年   1731篇
  1982年   1203篇
  1979年   1885篇
  1978年   1490篇
  1977年   1220篇
  1976年   1242篇
  1975年   1318篇
  1974年   1696篇
  1973年   1731篇
  1972年   1736篇
  1971年   1663篇
  1970年   1576篇
  1969年   1436篇
  1968年   1224篇
  1967年   1307篇
  1966年   1215篇
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
61.
62.
Star catalogues     
  相似文献   
63.
64.
Ohne Zusammenfassung  相似文献   
65.
66.
67.
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   
68.
Various combinations of reoviruses and coccidia were studied to see if interactions would occur. Two reoviruses were used: virus 2035, a moderate to low pathogen, and virus 2177, a nonpathogen. Coccidia used were Eimeria acervulina, E. mitis, and E. maxima at dosages of 10(3) or 10(4) sporulated oocysts/chick and E. brunetti at 10(4) sporulated oocysts/chick. In Hubbard-Hubbard cockerels, a combination of virus 2035 and E. acervulina (10(4) oocysts/chick) or E. maxima (10(3) oocysts/chick) significantly (P less than or equal to 0.05) increased the frequency of stunting (% of chicks with body weight less than 80% of controls) and further depressed weight gain over that seen with either virus or coccidia alone. Conversely, virus 2177 ameliorated the same effects in Shaver-Arbor Acre cockerels given 10(4) oocysts/chick of E. mitis or E. maxima. The interaction could not be attributed to changes in the degree of coccidial infection based on oocyst production. Reovirus did not generally change the effect of coccidia on levels of plasma pigment and plasma protein. In Hubbard-Hubbard cockerels, coccidia-induced effects were not ameliorated by virus 2177, suggesting that breed difference in interaction can be expected.  相似文献   
69.
Vanilla is a large genus of about 110 species in the orchid family (Orchidaceae), including the species Vanilla planifolia from which commercial vanilla flavoring is derived. Since most species of vanilla are considered rare and endangered there is an urgent need to conserve them through genetic analysis and propagation/conservation studies on this crop.The present study investigated the genetic diversity among nine leafy- and leaf-less Vanilla species employing 30 decamer RAPD primers and 10 ISSR primers. The species under study were diverse and displayed a range of variability (0–66% and 0–81% for RAPD and ISSR, respectively). A total of 154 RAPD polymorphic markers (83.24%, h = 0.378) and 93 ISSR polymorphic markers (86.11%, h = 0.363) were used to generate a genetic similarity matrix followed by the cluster analysis. Specific groupings were revealed by each cluster analysis with slight variation between two different markers. Among the nine species studied, V. planifolia, Vanilla aphylla and Vanilla tahitensis revealed very low level of variation within their collections, thus indicating a narrow genetic base. The large genetic distance of Vanilla andamanica from other species suggests its different origin. A close genetic affinity was observed between the pairs V. planifolia, V. tahitensis and Vanilla albida, V. aphylla. These are the first comparative results for RAPD and ISSR reporting inter-relationship among nine cultivated, wild and hybrid Vanilla species.  相似文献   
70.
Ohne Zusammenfassung  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