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   220009篇
  免费   11899篇
  国内免费   172篇
林业   9584篇
农学   7104篇
基础科学   1437篇
  27634篇
综合类   36036篇
农作物   8469篇
水产渔业   11021篇
畜牧兽医   113696篇
园艺   2894篇
植物保护   14205篇
  2019年   2021篇
  2018年   3065篇
  2017年   3508篇
  2016年   3235篇
  2015年   2733篇
  2014年   3403篇
  2013年   8617篇
  2012年   6198篇
  2011年   7793篇
  2010年   5030篇
  2009年   5146篇
  2008年   7531篇
  2007年   7149篇
  2006年   6816篇
  2005年   6273篇
  2004年   5948篇
  2003年   6100篇
  2002年   5535篇
  2001年   6934篇
  2000年   6950篇
  1999年   5545篇
  1998年   2344篇
  1997年   2283篇
  1996年   2182篇
  1995年   2570篇
  1994年   2305篇
  1993年   2174篇
  1992年   4520篇
  1991年   4764篇
  1990年   4706篇
  1989年   4618篇
  1988年   4320篇
  1987年   4329篇
  1986年   4418篇
  1985年   4267篇
  1984年   3498篇
  1983年   3020篇
  1982年   2093篇
  1979年   3219篇
  1978年   2622篇
  1977年   2148篇
  1976年   2219篇
  1975年   2298篇
  1974年   2859篇
  1973年   2863篇
  1972年   2698篇
  1971年   2571篇
  1970年   2426篇
  1969年   2361篇
  1967年   2151篇
排序方式: 共有10000条查询结果,搜索用时 87 毫秒
991.
The impairment of fluid, electrolyte and acid-base status which is observed in calves and juvenile cattle as a result of ileus and subileus is not only dependent on form and site of the obstruction, but is also influenced considerably by the duration of the condition and any coexisting disease. This publication reviews the most important blood, urine and ruminal fluid parameters in such patients. The diagnostic significance of the laboratory values under discussion is not so great with obstructions to the caudal part of the digestive tract. However, markedly raised ruminal fluid chloride levels, combined with hypochloraemia and a metabolic acidosis, are indicative of an "abomasoruminal reflux syndrome" resulting from an obstruction in the region of the abomasum or cranial small intestine.  相似文献   
992.
49 of 102 sheep of one production herd, which had returned to oestrus once or twice within the 1985 breeding season, were treated twice in a nine-day interval with the PGF2 alpha analogue Cloprostenol "Jenapharm". 53 animals received an additional dose of 10 micrograms of Gonavet "Berlin-Chemie". A lambing rate of merely 15% was achieved by subsequent term-oriented artificial insemination. 31 sheep still in oestrus one day after term-oriented artificial insemination were served, bringing the lambing rate from synchronisation of oestrus and ovulation to 26% and the lambing result to 154%. Serving of the remaining sheep in 2 subsequent oestric cycles, on balance, yielded lambing rates and results of the remaining sheep in 2 subsequent oestric cycles, on balance, yielded lambing rates and results which were higher with significance than those recorded from untreated sheep in the same herd.  相似文献   
993.
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   
994.
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   
995.
996.
997.
Rabies diagnosis in western Canada, 1985-1989   总被引:1,自引:0,他引:1       下载免费PDF全文
The results of laboratory examination of 20460 specimens for the diagnosis of rabies by the standard fluorescent antibody and mouse inoculation tests over a five year period are presented. Specimens were received from British Columbia, Alberta, Saskatchewan, Manitoba, and the Yukon and Northwest Territories. Of those examined, 9.96% were positive. The main reservoirs of rabies were skunks, bats, and foxes. During this observation period a rabies epizootic occurred in skunks in Saskatchewan. When both tests were performed, the fluorescent antibody test was found to agree with the mouse inoculation test in over 99% of cases.  相似文献   
998.
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