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   220173篇
  免费   12061篇
  国内免费   144篇
林业   9268篇
农学   7287篇
基础科学   1387篇
  28500篇
综合类   34953篇
农作物   8608篇
水产渔业   11271篇
畜牧兽医   113379篇
园艺   3043篇
植物保护   14682篇
  2020年   1871篇
  2019年   2235篇
  2018年   3257篇
  2017年   3703篇
  2016年   3398篇
  2015年   2936篇
  2014年   3683篇
  2013年   8938篇
  2012年   6611篇
  2011年   8131篇
  2010年   5399篇
  2009年   5455篇
  2008年   8000篇
  2007年   7663篇
  2006年   7171篇
  2005年   6615篇
  2004年   6340篇
  2003年   6492篇
  2002年   5957篇
  2001年   7002篇
  2000年   6973篇
  1999年   5646篇
  1998年   2388篇
  1997年   2324篇
  1996年   2163篇
  1995年   2586篇
  1994年   2242篇
  1993年   2167篇
  1992年   4362篇
  1991年   4601篇
  1990年   4550篇
  1989年   4556篇
  1988年   4166篇
  1987年   4144篇
  1986年   4195篇
  1985年   3995篇
  1984年   3249篇
  1983年   2904篇
  1982年   1986篇
  1979年   2926篇
  1978年   2339篇
  1977年   1974篇
  1976年   1983篇
  1975年   2096篇
  1974年   2487篇
  1973年   2559篇
  1972年   2441篇
  1971年   2191篇
  1970年   2222篇
  1969年   2135篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
Vitamin E, selenium and polyunsaturated fatty acids (PUFAs) were determined in feed used at three piggeries over.a four week period and compared with corresponding concentrations in clinically normal grower pigs at slaughter. Mean values were vitamin E: 59 IU/kg (feed), 6 micromol/kg (liver), 1.7 micromol/l (serum); and selenium: 310 microg/kg (feed), 5200 nmol/kg (liver), 1700 nmol/l (blood). Alpha-tocopherol accounted for 80% of the mean vitamin E activity in the feed and over 95% that in the liver and serum. The mean ratio of PUFA to total fatty acid (FA) in the feed (38%) was similar to that in the serum (36%) and liver (39%), but the ratio of peroxidisable PUFA (PPUFA) to FA increased from 1.7% in the feed to 4.2% in the serum and 10.8% in the liver. The ratio of alpha-tocopherol (mmol) to PPUFA (mol) in the liver varied from 0.16 to 0.48. The relationship of these data to the VESD syndrome is discussed in the light of other published data.  相似文献   
992.
A one-year-old domestic long-haired cat was referred to the New York State College of Veterinary Medicine because of acute onset of paraparesis and hyperesthesia associated with trauma. Myelography and cerebrospinal fluid analysis revealed severe hydromyelia and myelitis, respectively. The definitive diagnosis of feline infectious peritonitis was made by histological examination at necropsy. Lesions were confined exclusively to the brain and spinal cord. Partial occlusion of the third and fourth ventricles with pyogranulomatous debris caused hydrocephalus and subsequent hydromyelia. The hydromyelia may have been the primary means of compensation for the hydrocephalus, thus masking subclinical disease.  相似文献   
993.
994.
995.
Sheep affected by broken mouth periodontal disease (P.D.) were examined over a twelve month period for different clinical parameters. It is suggested that P.D. in sheep is an episodic phenomenon similar to human P.D., and that only a few animals with signs of P.D. may undergo clinically significant destruction over a yearly period. No single parameter could reliably predict future deterioration in other parameters.  相似文献   
996.
997.
998.
999.
Thirteen (54%) of 24 Père David's deer (Eluphurus duvidianus) imported from England died of malignant catarrhal fever (MCF) within a year of arrival at Invermay Agricultural Centre. The duration of clinical illness was from one to approximately 33 days, and the most common clinical signs were depression, a hunched stance and diarrhoea. On post-mortem examination, most deer showed recent localised haemorrhages, often into the large intestine. In all deer there was histological vasculitis especially in the brain.  相似文献   
1000.
1. Observations were made on the use of food pans and food trays by commercially grown broiler chickens.

2. Birds fed by going inside the feeders on top of the food or from standing around the outside of the feeders. The feeding times of birds inside feeders were significantly longer than those of birds outside. Different reasons to account for this are proposed for the 2 types of feeder.

3. The total number of birds able to feed together from a tray or pan changed as the birds grew. With trays this change in the number of birds was a steady decline. With pans the change was non‐linear and reflected a changing ratio of birds eating in to birds eating out. This ratio was influenced by pan design features and by competition for feeding space.

4. The data suggest that a linear measure of feeding space, as used in research trials and Codes of Practice for Welfare, does not adequately describe birds’ access to and use of feeding space. Implications for both research and the commercial industry are discussed.  相似文献   

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