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   150817篇
  免费   7498篇
  国内免费   91篇
林业   6397篇
农学   4327篇
基础科学   1027篇
  16229篇
综合类   31986篇
农作物   6037篇
水产渔业   6403篇
畜牧兽医   75593篇
园艺   1711篇
植物保护   8696篇
  2018年   1605篇
  2017年   1738篇
  2016年   1687篇
  2014年   1660篇
  2013年   5266篇
  2012年   3426篇
  2011年   4200篇
  2010年   2771篇
  2009年   2707篇
  2008年   4210篇
  2007年   3908篇
  2006年   3820篇
  2005年   3627篇
  2004年   3678篇
  2003年   3693篇
  2002年   3570篇
  2001年   4269篇
  2000年   4228篇
  1999年   3268篇
  1997年   1456篇
  1995年   1662篇
  1994年   1565篇
  1993年   1502篇
  1992年   3175篇
  1991年   3440篇
  1990年   3425篇
  1989年   3483篇
  1988年   3210篇
  1987年   3289篇
  1986年   3408篇
  1985年   3315篇
  1984年   2688篇
  1983年   2468篇
  1982年   1681篇
  1981年   1602篇
  1980年   1491篇
  1979年   2536篇
  1978年   2064篇
  1977年   1756篇
  1976年   1674篇
  1975年   1824篇
  1974年   2326篇
  1973年   2353篇
  1972年   2385篇
  1971年   2295篇
  1970年   2148篇
  1969年   1904篇
  1968年   1531篇
  1967年   1710篇
  1966年   1498篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Ocular diseases in birds are very rarely investigated. Increased keeping of often very expensive caged birds makes it necessary for veterinarians in practice to deal with the problems of ornithoophthalmology. Fundamental physiological and anatomic differences between the mammalian and the avian eye, interspecies variables and general problems in handling do not allow a simple transfer of knowledge of mammal ophthalmology to birds. Therefore, it is necessary to find differentiated, species-orientated solutions in investigation as well as suitable treatments of ocular diseases in birds. An update on ornithoophthalmology is given.  相似文献   
112.
A field experiment was conducted during the winter seasons of 1992–93 and 1993–94 at Anand to study the effect of FYM, nitrogen and source of fertilizer on growth and yield of mustard [ Brassica juncea (L.) Czernj & Cosson]. The results showed significant variation in leaf area index (LAI), crop growth rate (CGR), dry matter production and seed yield. The direct effect of farmyard manure (FYM) was conspicuous in improving the growth of mustard. FYM application at 10 tonnes ha−1 significantly increased the LAI, CGR and dry matter accumulation per plant at almost all the stages during first year study (1992–93) and in pooled analysis. Similarly, nitrogen application registered maximum LAI, CGR at 75 kg level and RGR and NAR at 50 kg level at almost all the during both years. Sulphur carrying source (Ammonium sulphate plus single super phosphate) increased all stages growth characters. Maximum dry matter accumulation per plant and seed yield were recorded with highest levels of FYM (20 tonnes ha−1), N (75 kg ha−1) and source having S. Seed yield was strongly associated with LAI and dry matter accumulation per plant at all the stages.  相似文献   
113.
114.
The determination of differentiation and transplantation antigens will be of growing importance in immune diagnosis for individual animals as well as for breeding purposes in populations. Differentiation antigens characterize subsets of cell populations and indicate their functional capacity while transplantation antigens represent markers of individuals of a species. Occurrence and significance of these antigenic systems are briefly reviewed.  相似文献   
115.
There is only limited information on sheep interferon available. Recent publications have reported on: 1. an interferon (IFN) alpha subtype, which is secreted by the fetal trophectoderm into the lumen of the uterus between the 10th and 21st day of gestation. It was therefore named ovine trophoblast protein (oTP-1), and is responsible for signalling pregnancy to the ewe via high affinity receptors in the endometrium. It is thought that oTP-1 acts by directly influencing prostaglandin metabolism. 2. the role of lentivirus-induced interferon (LV-IFN) in the pathogenesis of Maedi/Visna. The results indicate that LV-IFN limits viral replication and therefore contributes to virus persistence and is also responsible for a chronic inflammatory process. 3. the mitogen- or antigen-dependent induction of ovine interferon gamma (IFN gamma) and its characterization.  相似文献   
116.
Eine Methode zur langfristigen Lymphsammlung aus der jejunalen Lymphbahn bei Schweinen und Schafen Es wird eine Methode zur langfristigen Lymphsammlung im Dünndarmbereich von Schweinen und Schafen vorgestellt. Mit Hilfe eines chirurgischen Eingriffs wurde ein Silikon-Katheder im truncus lymphaticus jejunalis implantiert. Zusätzlich wurde ein zweiter Katheter in die hintere vena cava in Richtung Herz eingesetzt. Beide Katheter wurden sofort miteinander verbunden, um die Wiedereinführung der jejunalen Lymphe in den Blutkreislauf zu gewährleisten. Der negative Druck in der hinteren vena cava im Thoraxteil förderte den Lymphfluß durch das Katheter im truncus lymphaticus jejunalis. Der preprandiale Lymphfluß des Jéjunums betrug bei Schweinen 0,3 ml/h/kg Körpergewicht und stieg postprandial auf 0,78 ml/h/kg an. Beim Schaf betrug der Basiswert 0,75 ml/h/kg. Er stieg nach intraduodenaler Infusion von Rapsöl auf 4,75 ml/h/kg. Eine mechanische Stimulation der intestinalen Receptoren durch 0,9% NaCl-Lösung stimulierte ebenfalls den Lymphfluß.  相似文献   
117.
118.
119.
The accumulation of soluble carbohydrates in vegetative parts of sweet sorghum ( Sorghum bicolor (L.) Moench.) represents an intermediate reserve pool for grain filling as well as an irreversible storage up to maturity. In order to study the effect of Sterility on soluble sugar accumulation in vegetative parts, two cytoplasmic male sterile (CMS) lines of sweet sorghum were compared with their corresponding fertile mamtainers for non-structural carbohydrate concentrations in shoots. Plants were harvested at four different physiological stages. The lines showed significant differences in the yield of non-structural carbohydrates. At maturity, the yields of soluble carbohydrates from vegetative parts of the two sterile lines were 93 % and 43 % higher than the yield of the two corresponding fertile lines. At that stage, sucrose represented about 80 % of total soluble carbohydrates and the higher yield of soluble carbohydrates of sterile lines was mainly due to the higher yield of sucrose. This indicates that the yield of extractable carbohydrates, especially sucrose, in vegetative parts of sweet sorghum could be considerably improved by using sterile lines which are utilized in hybrid production.  相似文献   
120.
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