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   133010篇
  免费   7318篇
  国内免费   93篇
林业   5402篇
农学   4276篇
基础科学   832篇
  17116篇
综合类   21540篇
农作物   5414篇
水产渔业   6722篇
畜牧兽医   68298篇
园艺   1816篇
植物保护   9005篇
  2020年   1199篇
  2019年   1405篇
  2018年   2044篇
  2017年   2345篇
  2016年   2110篇
  2015年   1763篇
  2014年   2250篇
  2013年   5317篇
  2012年   4150篇
  2011年   5137篇
  2010年   3274篇
  2009年   3407篇
  2008年   5013篇
  2007年   4706篇
  2006年   4390篇
  2005年   4113篇
  2004年   3879篇
  2003年   4003篇
  2002年   3568篇
  2001年   4152篇
  2000年   4254篇
  1999年   3378篇
  1998年   1476篇
  1997年   1388篇
  1996年   1288篇
  1995年   1532篇
  1994年   1358篇
  1993年   1232篇
  1992年   2585篇
  1991年   2700篇
  1990年   2593篇
  1989年   2611篇
  1988年   2369篇
  1987年   2348篇
  1986年   2428篇
  1985年   2341篇
  1984年   1883篇
  1983年   1679篇
  1982年   1149篇
  1979年   1749篇
  1978年   1397篇
  1977年   1151篇
  1976年   1212篇
  1975年   1293篇
  1974年   1500篇
  1973年   1516篇
  1972年   1405篇
  1971年   1305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
131.
132.
In this study, the effects of nitrogen (N) rate (60, 120, 180 and 240 kg N ha?1 applied in three equal dressings at seeding and after the first and second cuttings) and stubble height (7, 14 and 21 cm) on the dry matter (DM) yield, crude protein (CP) content, and CP yield of a sorghum–sudangrass hybrid [Sorghum bicolor (L.) Moench × Sorghum sudanense (Piper) Stapf., cv. Pioneer 988] in the three‐cut system was investigated. The N rate had no significant effect in the first and third cuttings, but in the second cutting DM yields increased significantly with increase in N rate. The highest yield of 9.1 t ha?1 was obtained with 80 kg N ha?1 for the average of 2 years at the second cutting, but no significant difference was found among the 40, 60 and 80 kg N ha?1 rates. CP content and yield were not significantly affected by N rate at the first and third cuttings, but CP content and yield were significantly affected by application of N at the second cutting. Stubble height had a significant effect on CP content at the third cutting. However, it had no significant effect on CP content at the first and second cuttings. Stubble height had a significant effect on the CP yield at the first cutting, but no significant effect on CP yield at the second and third cuttings.  相似文献   
133.
134.
135.
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   
136.
137.
138.
139.
140.
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   
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