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   247820篇
  免费   26411篇
  国内免费   28279篇
林业   14379篇
农学   11928篇
基础科学   9327篇
  54829篇
综合类   60722篇
农作物   12639篇
水产渔业   14835篇
畜牧兽医   100707篇
园艺   4613篇
植物保护   18531篇
  2021年   2081篇
  2020年   3839篇
  2019年   7607篇
  2018年   8310篇
  2017年   9237篇
  2016年   9913篇
  2015年   9643篇
  2014年   9080篇
  2013年   13952篇
  2012年   11423篇
  2011年   11500篇
  2010年   8232篇
  2009年   7660篇
  2008年   8716篇
  2007年   8610篇
  2006年   8135篇
  2005年   7413篇
  2004年   7358篇
  2003年   7128篇
  2002年   6636篇
  2001年   7200篇
  2000年   6733篇
  1999年   5743篇
  1998年   2980篇
  1997年   3011篇
  1996年   2744篇
  1995年   3176篇
  1994年   2968篇
  1993年   2729篇
  1992年   4670篇
  1991年   4785篇
  1990年   4590篇
  1989年   4488篇
  1988年   4218篇
  1987年   4110篇
  1986年   4237篇
  1985年   3968篇
  1984年   3317篇
  1983年   2991篇
  1982年   2126篇
  1979年   3003篇
  1978年   2467篇
  1977年   2137篇
  1975年   2045篇
  1974年   2669篇
  1973年   2666篇
  1972年   2575篇
  1971年   2381篇
  1970年   2306篇
  1969年   2135篇
排序方式: 共有10000条查询结果,搜索用时 625 毫秒
991.
992.
993.
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   
994.
Analysis of whole blood samples from 174 cattle and, 174 sheep from 3 geographical regions of New Zealand over a 10 month period showed a mean (range) thiamine level of 122 nmol/l (71-237 nmol/l) for cattle and 118 nmol/l (67-227 nmol/l) for sheep. Regional and seasonal differences were noted with levels tending to rise over the summer period. A reference range of 75-185 nmol/l is proposed for both cattle and sheep to cover these variations. Levels below 50 nmol/l are considered indicative of deficiency.  相似文献   
995.
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   

996.
This paper examines the views of members of the veterinary profession towards the change in orientation of professional practice that is occurring. It contrasts the values of veterinarians with those of doctors, dentists, lawyers and accountants. Particular attention is given to the areas of business efficiency, competition and advertising. Data was derived from self-completion questionnaires containing 40 Likert scales which were mailed to 300 members of each of the five professions.  相似文献   
997.
998.
The detection of Mycobacterium paratuberculosis organisms in bovine faeces by isolation was compared with that by the microscopical examination of Ziehl-Neelsen stained faecal smears for the presence of clumps of acid-fast M. paratuberculosis organisms. Faeces were obtained from cattle naturally or experimentally infected with M. paratuberculosis as well as from uninfected cattle. Microscopical examination was an unreliable method for the detection of M. paratuberculosis organisms, since the organisms were only detected in 99 (=55.9%) of 177 culturally positive faecal samples. 1111 addition, clumps of acid-fast organisms indistinguishable from M. paratuberculosis were also observed iin three of 18 samples from cattle free from Johne's disease and in 18 of 37 culturally negative samples from paratuberculous cattle. When M. paratuberculosis organisms were added to faeces from an uninfected cow, results showed that isolation attempts should be positive when 15 or more M. paratuberculosis organisms per gram of faeces are present.  相似文献   
999.
1000.
Equine polymorphonuclear (PMN) and mononuclear (MN) leucocytes were separated on Percoll gradients and used to study the chemoattractant properties of the polar ether-linked phospholipid, platelet activating factor (PAF). Six concentrations of PAF ranging from 1 ng/ml to 100 g/ml were studied in each of two in vitro assay systems, the agarose microdroplet and a microfilter technique. Very significant (p<0.01) increases in the movement of both PMN and MN cells were obtained with most concentrations of PAF. In two instances there was no apparent concentration-response relationship, although the action of PAF was approximately bell-shaped in two others. The possible significance of these findings for equine inflammatory conditions is 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