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   339843篇
  免费   18224篇
  国内免费   715篇
林业   25036篇
农学   14308篇
基础科学   3031篇
  48796篇
综合类   49159篇
农作物   17767篇
水产渔业   18800篇
畜牧兽医   148524篇
园艺   6635篇
植物保护   26726篇
  2019年   3829篇
  2018年   4632篇
  2017年   5134篇
  2016年   5222篇
  2015年   4585篇
  2014年   5965篇
  2013年   16650篇
  2012年   8772篇
  2011年   11395篇
  2010年   8501篇
  2009年   8848篇
  2008年   10675篇
  2007年   9921篇
  2006年   10115篇
  2005年   9373篇
  2004年   9150篇
  2003年   8940篇
  2002年   8251篇
  2001年   9316篇
  2000年   8936篇
  1999年   7683篇
  1998年   4476篇
  1997年   4515篇
  1996年   4235篇
  1995年   4964篇
  1994年   4391篇
  1993年   4068篇
  1992年   6294篇
  1991年   6541篇
  1990年   6347篇
  1989年   6310篇
  1988年   5729篇
  1987年   5778篇
  1986年   5881篇
  1985年   5946篇
  1984年   5206篇
  1983年   4746篇
  1982年   3653篇
  1981年   3450篇
  1980年   3395篇
  1979年   4764篇
  1978年   4078篇
  1977年   3641篇
  1976年   3399篇
  1975年   3449篇
  1974年   4024篇
  1973年   4041篇
  1972年   3725篇
  1971年   3515篇
  1970年   3363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