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   1380篇
  免费   85篇
林业   51篇
农学   15篇
基础科学   6篇
  137篇
综合类   514篇
农作物   21篇
水产渔业   75篇
畜牧兽医   575篇
园艺   15篇
植物保护   56篇
  2023年   14篇
  2021年   21篇
  2020年   49篇
  2019年   34篇
  2018年   33篇
  2017年   28篇
  2016年   29篇
  2015年   18篇
  2014年   29篇
  2013年   46篇
  2012年   62篇
  2011年   86篇
  2010年   42篇
  2009年   25篇
  2008年   91篇
  2007年   85篇
  2006年   88篇
  2005年   59篇
  2004年   60篇
  2003年   65篇
  2002年   84篇
  2001年   30篇
  2000年   24篇
  1999年   18篇
  1998年   9篇
  1996年   5篇
  1995年   18篇
  1994年   21篇
  1993年   16篇
  1992年   20篇
  1991年   17篇
  1990年   7篇
  1989年   9篇
  1988年   9篇
  1986年   5篇
  1985年   8篇
  1984年   5篇
  1983年   7篇
  1982年   9篇
  1981年   5篇
  1979年   13篇
  1978年   5篇
  1975年   5篇
  1974年   9篇
  1973年   5篇
  1972年   9篇
  1970年   9篇
  1969年   9篇
  1968年   8篇
  1966年   6篇
排序方式: 共有1465条查询结果,搜索用时 250 毫秒
1.
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   
2.
Lupus-Type "Anticoagulant" in a Dog With Hemolysis and Thrombosis   总被引:1,自引:1,他引:0  
A circulating anticoagulant was detected in a 2-year-old Chesapeake Bay Retriever with hemolytic anemia, nephrotic syndrome, thrombocytopenia, polyarthropathy, and pulmonary thromboembolism. A persistent prolongation of the activated partial thromboplastin time (aPTT) was detected, and it did not correct with repeated administration of fresh frozen plasma. The aPTT was still prolonged, with a 1:1 mixture of patient's plasma and normal dog plasma in vitro, suggesting the presence of a circulating inhibitor. Results of assays to characterize the inhibitor were compatible with those described for the lupus anticoagulant in human patients with systemic lupus erythematosus. Paradoxically, patients having the lupus anticoagulant are at increased risk for thrombosis. Pulmonary thromboembolism has been described as a frequent complication of immune-mediated hemolytic anemia in the dog, and the presence of a circulating anticoagulant should be considered as a potential mechanism.  相似文献   
3.
4.
Six shipments totaling 3452 mummies of the blackmargined aphid,Monellia caryella (Fitch), parasitized withAphelinus perpallidus Gahan, were obtained by air freight during the years 1982-1985 from Texas A&M Research Center, El Paso, Texas. About two-thirds of the mummies did not yield parasites. A colony ofA. perpallidus was established in the laboratory. Under laboratory conditions the percentage of emerged parasites was higher than that in the imported mummies, and the parasite had very limited impact on the aphid population. Field releases of the parasite were made but no establishment ofA. perpallidus was observed through the years.  相似文献   
5.
6.
7.
8.
9.
Serums from infected cattle, cattle with persistent postvaccinal antibody, and serologically "positive" noninfected cattle were fractionated into major immunoglobulin classes by diethylaminoethyl (DEAE)-cellulose chromatography and by sucrose density gradient centrifugation. Each fraction was assayed for anti-Brucella activity by standard tube-agglutination test (STT), buffered tube-agglutination test (BTT), and complement-fixation test (CF). In the serums from experimentally infected cattle, anti-Brucella antibody could be found by all tests in 6 DEAE fractions and in slow, fast, and sediment regions of the density gradient. Serums from cattle with persistent postvaccinal titers had STT activity in all 6 DEAE fractions, BTT activity in 5 fractions, and CF activity in only 1 fraction. The STT and BTT activities were found in the slow and the sediment regions of the gradient, whereas the CF activity was found only in the slow region. Serums from a chronically infected animal had STT and BTT activities in 2 DEAE fractions and CF activity in only 1. The STT, BTT, and CF activities were found in the slow and the sediment regions of the gradient. The principal antibody in serums from noninfected cattle was immunoglobulin M, which had all of the CF activity and most of the STT and BTT activities. Low levels of STT and BTT activities were found in 3 other DEAE fractions. Only STT and BTT activities were found in the fast and the sediment regions of the gradient.  相似文献   
10.
Birds are becoming more popular as pets, and the need for veterinary professionals to learn more about these pets is crucial. This article introduces the veterinary staff to basic information required to provide high-quality care to avian patients. High-quality nutrition for a variety of species and ages is included in this article. The importance of proper husbandry and intellectual stimulation with toys is also discussed. Special emphasis is placed on instructions for clients when making appointments, as well as recognizing signs of illness for both clients and veterinary staff. Capture, restraint, and sample collection are an important part of this article, as well as medication administration, anesthesia, supportive care, preventive care and grooming. A variety of aspects concerning the care of the avian patient are covered for the benefit of the client and veterinary technician.  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