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   340052篇
  免费   18388篇
  国内免费   672篇
林业   25346篇
农学   14411篇
基础科学   3017篇
  49328篇
综合类   47560篇
农作物   17916篇
水产渔业   19093篇
畜牧兽医   149171篇
园艺   6648篇
植物保护   26622篇
  2019年   3821篇
  2018年   4739篇
  2017年   5188篇
  2016年   5357篇
  2015年   4658篇
  2014年   6048篇
  2013年   16763篇
  2012年   8887篇
  2011年   11417篇
  2010年   8582篇
  2009年   8914篇
  2008年   10647篇
  2007年   9982篇
  2006年   10022篇
  2005年   9314篇
  2004年   9102篇
  2003年   8949篇
  2002年   8123篇
  2001年   9466篇
  2000年   9100篇
  1999年   7834篇
  1998年   4495篇
  1997年   4547篇
  1996年   4236篇
  1995年   4882篇
  1994年   4292篇
  1993年   4031篇
  1992年   6276篇
  1991年   6534篇
  1990年   6395篇
  1989年   6495篇
  1988年   5788篇
  1987年   5870篇
  1986年   5876篇
  1985年   5881篇
  1984年   5117篇
  1983年   4713篇
  1982年   3584篇
  1981年   3381篇
  1980年   3257篇
  1979年   4512篇
  1978年   3836篇
  1977年   3501篇
  1976年   3302篇
  1975年   3309篇
  1974年   3765篇
  1973年   3878篇
  1972年   3590篇
  1971年   3430篇
  1970年   3341篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
993.
Regarding the estimation of the energy concentration or digestibility of herb-dominated forage and plant samples from winter pastures, it could be expected that the estimation is only reliable when in vitro methods with rumen fluid as inoculum (= gas production techniques) are used. For the verification of this thesis based on logical reflections, an in vitro-method with rumen fluid added as inoculum, as well as chemical, and enzymatic methods were applied under consideration of existing estimating functions. As a possible reason for the observed divergence of the methods, effects of fungal infections or, respectively, secondary compounds in herbs are discussed. At the present state of knowledge, it is adequate to estimate the energy concentration in vitro by gas tests, as far as fattening types like suckler cows and beef cattle are concerned, maybe in contrast to the forage evaluation for dairy cows.  相似文献   
994.
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   
995.
996.
997.
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   
998.
999.
Diagnosis of mastitis for therapy decisions.   总被引:2,自引:0,他引:2  
Identifying specific groups of mastitis pathogens by their growth on selective agars can help identify the pathogens that are present in mastitic milk samples. This article addresses issues that are essential in making good use of diagnostic procedures to improve udder health on dairies.  相似文献   
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