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   280814篇
  免费   16058篇
  国内免费   688篇
林业   24122篇
农学   14132篇
基础科学   2990篇
  45163篇
综合类   30720篇
农作物   17543篇
水产渔业   17582篇
畜牧兽医   113977篇
园艺   6443篇
植物保护   24888篇
  2021年   2533篇
  2020年   2948篇
  2019年   3761篇
  2018年   4340篇
  2017年   4778篇
  2016年   4985篇
  2015年   4408篇
  2014年   5772篇
  2013年   16352篇
  2012年   7409篇
  2011年   9704篇
  2010年   7910篇
  2009年   8423篇
  2008年   9074篇
  2007年   8137篇
  2006年   8486篇
  2005年   7820篇
  2004年   7580篇
  2003年   7367篇
  2002年   6569篇
  2001年   7053篇
  2000年   6844篇
  1999年   6144篇
  1998年   4236篇
  1997年   4294篇
  1996年   4003篇
  1995年   4666篇
  1994年   4019篇
  1993年   3718篇
  1992年   4834篇
  1991年   5009篇
  1990年   4715篇
  1989年   4698篇
  1988年   4152篇
  1987年   4181篇
  1986年   4181篇
  1985年   4425篇
  1984年   4002篇
  1983年   3719篇
  1982年   3030篇
  1981年   2880篇
  1980年   2876篇
  1979年   3566篇
  1978年   3128篇
  1977年   2870篇
  1976年   2739篇
  1975年   2665篇
  1974年   2851篇
  1973年   2830篇
  1972年   2470篇
排序方式: 共有10000条查询结果,搜索用时 734 毫秒
801.
Ohne Zusammenfassung  相似文献   
802.
803.
804.
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   
805.
806.
A total of 595 faecal samples from raptorial birds, either captive or free‐living, residing in GREFA Wildlife Hospital were bacteriologically examined using various selective media and an Automated Diagnostic Assay System for Salmonella detection. Serotype and phage type of the strains identified as Salmonella was determined. In the captive group, of the 285 samples examined, 21 (7.36%) were positive for Salmonella. Serotyping revealed that most of the individuals were infected by Salmonella serotype Havana. This result suggested that there could be a source of contamination in the Hospital although it could not be established. In the wild free‐living group, over 310 samples examined (4.19%) were positive for Salmonella. The Salmonella isolates showed a major variety of serotypes: Enteritidis, Adelaide, Brandenburg, Newport, Typhimurium, Hadar, Saintpaul and Virchow. Most of them are similar to those commonly described in isolates from human and domestic animals. These results indicate that wild birds could be involved in the dissemination of Salmonella in humans or domestic animals or vice versa.  相似文献   
807.
808.
809.
810.
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