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   220412篇
  免费   12070篇
  国内免费   144篇
林业   9274篇
农学   7292篇
基础科学   1388篇
  28521篇
综合类   34997篇
农作物   8631篇
水产渔业   11282篇
畜牧兽医   113496篇
园艺   3047篇
植物保护   14698篇
  2020年   1876篇
  2019年   2240篇
  2018年   3262篇
  2017年   3709篇
  2016年   3402篇
  2015年   2938篇
  2014年   3684篇
  2013年   8961篇
  2012年   6617篇
  2011年   8138篇
  2010年   5404篇
  2009年   5456篇
  2008年   8007篇
  2007年   7675篇
  2006年   7177篇
  2005年   6622篇
  2004年   6349篇
  2003年   6495篇
  2002年   5960篇
  2001年   7003篇
  2000年   6977篇
  1999年   5647篇
  1998年   2391篇
  1997年   2323篇
  1996年   2163篇
  1995年   2588篇
  1994年   2241篇
  1993年   2168篇
  1992年   4364篇
  1991年   4606篇
  1990年   4555篇
  1989年   4562篇
  1988年   4169篇
  1987年   4148篇
  1986年   4195篇
  1985年   3995篇
  1984年   3249篇
  1983年   2905篇
  1982年   1989篇
  1979年   2927篇
  1978年   2340篇
  1977年   1974篇
  1976年   1984篇
  1975年   2096篇
  1974年   2489篇
  1973年   2561篇
  1972年   2442篇
  1971年   2192篇
  1970年   2224篇
  1969年   2135篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
133 samples of food were investigated for comparison of a recent commercially available 1-2 test (Biocontrol) with a cultural standard method (non-selective pre-enrichment in buffered peptone water, selective enrichment in Rappaport-Vassiliadis-medium and selenite brilliant-green mannitol enrichment broth, inoculation on two selective agars) for presence of Salmonella. The 1-2 test showed in positive results an accuracy ("sensitivity") of 94.7% and in negative results an assurance ("specificity") of 97.9% and is therefore considered suitable for detection of Salmonella contaminated food.  相似文献   
942.
1. Muscle fibre composition, capillary-fibre ratio and mitochondrial density of the Iliotibialis lateralis muscle were monitored during growth from the age of 8 weeks to sexual maturity (24 weeks) in sedentary birds and in birds subjected to regular treadmill exercise. 2. The Iliotibialis lateralis muscle consists almost exclusively of type IIA and IIB fibres with a small percentage of "unclassified" fibres. Over the 16-week period of growth there was no change in fibre composition but a marked fibre hypertrophy linked with a fall in the capillary-fibre ratio. Mitochondrial volume density increased with age but this was not significant. 3. Exercise significantly increased the IIA:IIB fibres ratio from 0.77 to 1.1 but had no significant effect on any other measured characteristics. 4. It is concluded that exercise at the intensity and duration employed (10-15 min daily, ca. 70-80% maximum oxygen consumption) has little effect on the growth and development of avian skeletal muscle although there was evidence of an increased oxidative capacity of the muscle.  相似文献   
943.
944.
945.
The clinical, radiographic, arthrographic, arthroscopic, and pathological findings of three horses with femorotibial joint injuries are presented. Overall diagnostic accuracy is improved when clinical signs, arthrography, and arthroscopy are combined. Treatment of these injuries remains limited. One horse was euthanized, and two were treated by stall rest after diagnosis. Of the two surviving horses, one became a successful breeding animal, and the other was unable to perform as a pleasure horse.  相似文献   
946.
947.
The methods used in a large field study which investigated the health and productivity of Ontario beef breeding herds are described. Beginning in the calving season of 1986, 180 breeding herds on 170 randomly sampled farms were followed for a two year period, using producer records and annual farm visits.

The response (cooperation) rate among the eligible producers initially contacted was 70%. Approximately two-thirds of producers maintained individual animal records, primarily calving season records. Approximately 40% recorded disease occurrences.

The advantages, disadvantages, and interpretation of “on-farm” observational studies are discussed.

  相似文献   
948.
949.
950.
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