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   152762篇
  免费   8805篇
  国内免费   100篇
林业   6042篇
农学   5121篇
基础科学   1052篇
  18302篇
综合类   25063篇
农作物   5803篇
水产渔业   7796篇
畜牧兽医   81113篇
园艺   1884篇
植物保护   9491篇
  2019年   1396篇
  2018年   2268篇
  2017年   2591篇
  2016年   2371篇
  2015年   2035篇
  2014年   2481篇
  2013年   6005篇
  2012年   4373篇
  2011年   5420篇
  2010年   3501篇
  2009年   3563篇
  2008年   5250篇
  2007年   4872篇
  2006年   4810篇
  2005年   4184篇
  2004年   4055篇
  2003年   4096篇
  2002年   3768篇
  2001年   5208篇
  2000年   5157篇
  1999年   4005篇
  1998年   1593篇
  1997年   1677篇
  1996年   1507篇
  1995年   1772篇
  1994年   1590篇
  1993年   1533篇
  1992年   3304篇
  1991年   3457篇
  1990年   3288篇
  1989年   3326篇
  1988年   3041篇
  1987年   3106篇
  1986年   3160篇
  1985年   2999篇
  1984年   2435篇
  1983年   2102篇
  1982年   1422篇
  1979年   2174篇
  1978年   1756篇
  1977年   1472篇
  1976年   1482篇
  1975年   1610篇
  1974年   1945篇
  1973年   1925篇
  1972年   1831篇
  1971年   1768篇
  1970年   1686篇
  1969年   1578篇
  1967年   1434篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
1. There was a marked strain difference in the incidence of hepatic haemorrhage in White Leghorn hens receiving dietary rapeseed meal (RSM). 2. Tolerance to high dietary contents of RSM also varied between individual birds within a strain. 3. Glucosinolates were implicated in the development of hepatic haemorrhage among hens receiving dietary RMS but the exact relationship was not clear.  相似文献   
992.
The irritancy of chlorhexidine gluconate in the genital tract of the mare   总被引:2,自引:0,他引:2  
Uterine irrigation was carried out in eight Welsh pony mares using 50 ml of chlorhexidine gluconate solution diluted to give active ingredient concentrations of 0.25 per cent to 2 per cent. Treatment was repeated up to twice in mares showing no adverse effects and irritancy of treatment judged on clinical symptoms and uterine biopsy. Results indicated the inadvisability of using a higher concentration than 0.25 per cent. Three daily applications of a diluted surgical scub solution containing 2 per cent chlorhexidine gluconate to the penis of an arab stallion failed to produce symptoms or irritation. An in vitro minimum inhibitory concentration test performed with the contagious equine metritis organism confirmed its high sensitivity to both chlorhexidine gluconate preparations.  相似文献   
993.
994.
1. Indirect calorimetry was used to study the effects on the energy metabolism of cockerels and hens after peak lay of a hybrid layer strain of regulating food or energy intake to 80% of ad libitum for an extended period of time. 2. Regulation of food intake decreased fasting and fed heat productions per bird and per unit metabolic body weight (kg0.75). 3. Maintenance energy requirements (per kg0.75) of both sexes were reduced about 20% by regulation; maintenance requirements of cockerels were about 30% lower per kg0.75 than hens on the same treatments. 4. Reducing the intake of all nutrients by 20% had the same effect on the energy metabolism of cockerels as restricting energy alone by the same amount. 5. Gross efficiency of egg production, in terms of both mass and energy, was higher when intake was regulated. During weeks 21 to 52 of restriction, daily egg mass output was significantly higher in hens fed ad libitum. 6. After 52 weeks of food regulation, restricted hens weighed 20% less and their total carcass energy was 36% less than hens fed ad libitum; similar effects were found in the cockerels.  相似文献   
995.
996.
997.
Records of the Toxicology Laboratory, Veterinary Services Branch, Ontario Ministry of Agriculture and Food, indicate that 277 of 2,022 specimens of feedstuffs submitted between October 1, 1972 and September 30, 1978 contained one or more mycotoxins. The data indicate that zearalenone is an important mycotoxin in the provincial corn crops and that its incidence fluctuates from year to year. The percentages of specimens containing zearalenone were 16.3 (1972), 4.1 (1973), 5.5 (1974), 22.4 (1975), 9.5 (1976) and 13.0 (1977). Aflatoxins, ochratoxins and T-2 toxin were found in some specimens but their incidence was low.  相似文献   
998.
The effect of parturition on the blood picture of sheep   总被引:1,自引:0,他引:1  
Parturition in sheep was associated with significant increases in the packed cell volume, haemoglobin concentration and red cell counts. Subsequently these values gradually declined, attaining prepartum levels by the seventh day post partum. Blood leucocyte counts were also elevated at parturition and this was associated with marked neutrophilia, lymphocytopenia and mild eosinopenia. These changes were gradually reversed thereafter, with normal values being attained by the fourteenth day post partum.  相似文献   
999.
SURGICAL repair of the patent ductus arteriosus (PDA) is one of the most common cardiovascular procedures performed in veterinary and human medicine.1–3 The techniques have been well documented and used successfully.2–5  相似文献   
1000.
Ten dairy cows were infused intramammarily near drying off with concanavalin A (conA) or phytohemagglutinin (PHA). Mammary secretions were collected during physiologic transitions of the udder and were used in an in vitro microbiological assay to determine growth inhibition of mastitis pathogens. As mammary involution progressed, in vitro growth inhibition of Klebsiella pneumoniae, Escherichia coli, and Streptococcus uberis increased. Mammary secretions from conA- and PHA-treated glands had significantly increased bacterial growth inhibition. Secretions contained significantly increased concentrations of lactoferrin and a decreased citrate:lactoferrin molar ratio earlier in the dry period than did control mammary secretions. Greatest bacterial growth inhibition was observed in mammary secretions obtained 7 days before parturition. However, differences in secretion composition or bacterial growth inhibition were not found between conA- or PHA-treated and control udder halves during the prepartum period. Bacterial growth inhibition by mammary secretion decreased markedly during early lactation. A highly significant positive correlation was found between bacterial growth inhibition and concentrations of lactoferrin, serum albumin, and immunoglobulin G. A highly significant negative correlation was found in the citrate:lactoferrin molar ratio during early involution and the peripartum period.  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