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   339764篇
  免费   18224篇
  国内免费   715篇
林业   25038篇
农学   14310篇
基础科学   3032篇
  48794篇
综合类   49043篇
农作物   17768篇
水产渔业   18796篇
畜牧兽医   148573篇
园艺   6638篇
植物保护   26711篇
  2019年   3828篇
  2018年   4633篇
  2017年   5133篇
  2016年   5221篇
  2015年   4584篇
  2014年   5964篇
  2013年   16655篇
  2012年   8778篇
  2011年   11395篇
  2010年   8499篇
  2009年   8855篇
  2008年   10671篇
  2007年   9903篇
  2006年   10090篇
  2005年   9352篇
  2004年   9132篇
  2003年   8911篇
  2002年   8237篇
  2001年   9294篇
  2000年   8930篇
  1999年   7684篇
  1998年   4479篇
  1997年   4515篇
  1996年   4236篇
  1995年   4963篇
  1994年   4395篇
  1993年   4071篇
  1992年   6292篇
  1991年   6548篇
  1990年   6348篇
  1989年   6313篇
  1988年   5732篇
  1987年   5782篇
  1986年   5883篇
  1985年   5944篇
  1984年   5210篇
  1983年   4749篇
  1982年   3655篇
  1981年   3452篇
  1980年   3394篇
  1979年   4767篇
  1978年   4079篇
  1977年   3643篇
  1976年   3398篇
  1975年   3446篇
  1974年   4024篇
  1973年   4042篇
  1972年   3724篇
  1971年   3512篇
  1970年   3364篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
Ohne Zusammenfassung  相似文献   
993.
994.
995.
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   
996.
997.
998.
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   
999.
1000.
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