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   262089篇
  免费   15176篇
  国内免费   668篇
林业   23928篇
农学   14092篇
基础科学   2982篇
  43871篇
综合类   24409篇
农作物   17479篇
水产渔业   17214篇
畜牧兽医   103538篇
园艺   6318篇
植物保护   24102篇
  2021年   2518篇
  2020年   2906篇
  2019年   3688篇
  2018年   4200篇
  2017年   4626篇
  2016年   4946篇
  2015年   4419篇
  2014年   5759篇
  2013年   16301篇
  2012年   6682篇
  2011年   8774篇
  2010年   7634篇
  2009年   8128篇
  2008年   8140篇
  2007年   7167篇
  2006年   7631篇
  2005年   6742篇
  2004年   6616篇
  2003年   6370篇
  2002年   5674篇
  2001年   6704篇
  2000年   6357篇
  1999年   5808篇
  1998年   4182篇
  1997年   4265篇
  1996年   3980篇
  1995年   4538篇
  1994年   3937篇
  1993年   3616篇
  1992年   4543篇
  1991年   4680篇
  1990年   4406篇
  1989年   4392篇
  1988年   3791篇
  1987年   3834篇
  1986年   3761篇
  1985年   4055篇
  1984年   3694篇
  1983年   3473篇
  1982年   2891篇
  1981年   2796篇
  1980年   2754篇
  1979年   3215篇
  1978年   2892篇
  1977年   2630篇
  1976年   2494篇
  1975年   2427篇
  1974年   2592篇
  1973年   2499篇
  1972年   2244篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
191.
Monoclonal antibodies against hog cholera and bovine viral diarrhoea viruses were assayed on organ tissue sections of experimentally infected animals. The animals had been infected simultaneously with both viruses. The antibodies were tested using an indirect immunofluorescence test and an indirect enzyme immunoassay with a biotin/streptavidin/peroxidase detection system. A polyclonal hyperimmune serum was used as a control in direct immunofluorescence tests. Both techniques based on monoclonal antibodies were more sensitive and more specific than the conventional test, the enzyme immunoassay being more sensitive than the immunofluorescence test. Small amounts of BVD viral antigen were demonstrable with monoclonal antibodies in most organ tissues.  相似文献   
192.
Duration of maternal immunity to peste des petits ruminants   总被引:1,自引:0,他引:1  
  相似文献   
193.
Efficacy of ivermectin treatment (0.2 mg/kg) against 28-day experimental infections of Parascaris equorum was determined in 18 pony foals6–17.5 weeks old. There were 6 foals in each group: nontreated control, ivermectin injectable or oral paste. In comparison with larvae found in the nontreated controls, ivermectin injectable or paste was 96.0% and 99.9% efficacious. There was a distinct difference in drug effect against the larger (ca 26mm.) vs the smaller (13–19mm) larvae by the 2 formulations of ivermectin. There were no adverse signs related to treatment of the young foals.  相似文献   
194.
A survey of the potential use of synthetic oligopeptides in the field of virology is given. The potential value of synthetic peptides as vaccines and diagnostic antigens is discussed. The advantages compared to conventional vaccines as well as the limitations, e.g. the poor efficiency of immune response, are described.  相似文献   
195.
Clinical manifestations of anasarca, left displacement of the abomasum, abortion, and incoordination appeared in a group of heifers fed a vitamin A-deficient diet. Older heifers and heifers late in pregnancy were more affected. All clinical signs of disease disappeared within 14 days after vitamin A treatment was begun, and the diet was changed. Although vitamin A deficiency in dairy cows has been documented, this report differs from others in the main clinical manifestations of disease.  相似文献   
196.
197.
198.
The structure and ultrastructure of the adenohypophyseal pars distalis in kids of the Murciano-granadiana breed (18 males and 12 females), aged 2-3 months and with an average carcass weight of 8 kg has been studied. Techniques of staining (Tetrachrome Herlant's, and Cleveland-Wolfe) and histochemistry (PAS, PAS-OG and BA-PAS-OG) contrasted with immunolabelling (PAP) have been used. In addition an ultrastructural study has been made and nucleus and cytoplasm, secretory granules, mitochondria and lysosomes have been measured with a semiautomatic image analyzer (IBAS-1). TSH cells are found in sagittal section in the anterior area and in an antero-caudodorsal band, and transversally in the ventral and medial region; they are 6% and their average size is 14.15 microns. Ultrastructurally they are a single cellular type with spherical granules whose size is 195 nm in males and 149 in females; these granules are characterized by a clear halo and a variable electronic density. The rough endoplasmic reticulum is found as slightly enlarged vesicles with a homogeneous and moderately electro-dense content or in concentric stratifications.  相似文献   
199.
A total of 739 cattle from nine breeds maintained at the Roman L. Hruska U.S. Meat Animal Research Center, Clay Center, Nebraska were tested for 42 class I antigens of the bovine major histocompatibility system (BoLA). Each antigen appears to be the product of a distinct co-dominant allele of the BoLA-A locus. The number of antigens present in each breed ranged from a minimum of 10 in Hereford to a maximum of 21 in Charolais cattle. There were large differences among breeds in the frequencies of antigens. The effect of each antigen on birth weight, preweaning weight gain and postweaning weight gain was estimated in a gene substitution model. Each breed was analyzed separately. There were significant effects of some BoLA antigens on birth weight, preweaning weight gain and postweaning weight gain, which is consistent with previous reports showing associations between the major histocompatibility system and growth parameters in mice, rats and pigs. However, further research is necessary to confirm these findings and to determine the biological mechanisms underlying these associations.  相似文献   
200.
Two 7 day feeding trials were conducted with channel catfish swim-up fry to evaluate growth, feed conversion ratio, and body composition of fish fed one of the following feeds: salmon starter, catfish starter, or trout starter. Fish fed the salmon or trout starter feeds gained 50–75% more weight, converted feed more efficiently, and had higher body fat stores than fish fed the catfish starter feed. This may be related to the higher protein and energy content of these two feeds. It may be advantageous to feed salmonid starter feeds to hatchery reared catfish fry; however, it is not known whether or not the improved performance observed in the hatchery continues once the fish are stocked into nursery and grow out ponds.  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