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   62909篇
  免费   2899篇
  国内免费   42篇
林业   2553篇
农学   1663篇
基础科学   430篇
  6299篇
综合类   14794篇
农作物   2473篇
水产渔业   2389篇
畜牧兽医   31154篇
园艺   647篇
植物保护   3448篇
  2017年   559篇
  2016年   551篇
  2014年   546篇
  2013年   1901篇
  2012年   1214篇
  2011年   1471篇
  2010年   926篇
  2009年   891篇
  2008年   1449篇
  2007年   1421篇
  2006年   1389篇
  2005年   1412篇
  2004年   1340篇
  2003年   1409篇
  2002年   1377篇
  2001年   1495篇
  2000年   1480篇
  1999年   1211篇
  1998年   535篇
  1997年   540篇
  1995年   600篇
  1994年   575篇
  1993年   567篇
  1992年   1315篇
  1991年   1395篇
  1990年   1451篇
  1989年   1490篇
  1988年   1401篇
  1987年   1359篇
  1986年   1401篇
  1985年   1373篇
  1984年   1151篇
  1983年   1005篇
  1982年   718篇
  1981年   692篇
  1980年   645篇
  1979年   1129篇
  1978年   918篇
  1977年   823篇
  1976年   768篇
  1975年   863篇
  1974年   1130篇
  1973年   1065篇
  1972年   1131篇
  1971年   1080篇
  1970年   1026篇
  1969年   874篇
  1968年   710篇
  1967年   848篇
  1966年   695篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
61.
Analysis of ligand binding specificity of receptor chimeras   总被引:1,自引:0,他引:1  
  相似文献   
62.
The article considers the attractions and dangers of homeopathic therapy from the view of a pharmacologist. Homeopathic drugs may exert pharmacodynamic (but also toxic) effects at low dilutions (D0-D6), but there is no scientific proof for specific effects of higher dilutions except for substances with a high toxic potential. Most homeopathic drugs have no reasonable basis for clinical use but, in case of toxic compounds, especially those with carcinogenic or allergic potential, homeopathy may bear risks for the animal and, because of residues in food animals, also for humans. Thus, homeopathic treatment should not be used when effective conventional treatments are available, and the use of homeopathic drugs with toxic potential should be avoided.  相似文献   
63.
64.
Restriction endonuclease analysis and DNA hybridization revealed five ovine strains of Mycobacterium paratuberculosis from South Africa had identical DNA patterns to an ovine strain from Canada. Genetically this strain type has features in common with the two major groups of M. paratuberculosis.  相似文献   
65.
Serologic recognition of common lipopolysaccharide core antigens has been related to enhanced resistance to gram-negative bacterial disease in several species. Class-specific titers (IgG, IgM) were determined by direct ELISA, using intact Escherichia coli (J5) as a plate antigen. Serum samples were obtained from 224 neonatal swine between the ages of 36 and 60 hours. The mean (+/- SEM) log10 IgG titer against gram-negative core antigens was 1:1,713 +/- 0.4718 and the mean log10 IgM titer was 1:202 +/- 0.5644. The IgG titer was directly related with litter size, birth weight, and serum total IgG concentration; IgM titer was directly related with dam parity and serum total IgG concentration.  相似文献   
66.
瘤胃阳离子和可溶性蛋白与牛易感受苜蓿膨胀病的关系   总被引:1,自引:0,他引:1  
Hall  JW 《牧草与饲料》1989,(1):53-56
  相似文献   
67.
68.
Recombinant strains of herpesvirus of turkeys (HVT) were constructed that contain either the fusion protein gene or the hemagglutinin-neuraminidase gene of Newcastle disease virus (NDV) inserted into a nonessential gene of HVT. Expression of the NDV antigens was regulated from a strong promoter element derived from the Rous sarcoma virus long terminal repeat. Recombinant HVT strains were stable and fully infectious in cell culture and in chickens. Chickens receiving a single intra-abdominal inoculation at 1 day of age with recombinant HVT expressing the NDV fusion protein had an immunological response and were protected (> 90%) against lethal intramuscular challenge at 28 days of age with the neurotropic velogenic NDV strain Texas GB. Recombinant HVT expressing the NDV hemagglutinin-neuraminidase provided partial protection (47%) against the same challenge. Chickens vaccinated with recombinant HVT vaccines had low levels of protection against NDV replication in the trachea when challenged ocularly. Recombinant HVT vaccines and the parent HVT strain provided similar levels of protection to chickens challenged with the very virulent RB1B strain of Marek's disease virus, indicating that insertion of foreign sequences into the HVT genome did not compromise the ability of HVT to protect against Marek's disease.  相似文献   
69.
A Pyrenophora teleomorph was recently found on barley stubble in South Africa. Single-ascospore isolates, mated on water agar containing sterile pieces of barley stubble, produced the teleomorph within 12 months of incubation at 15°C in the dark. Based on morphological characteristics and symptom expression on barley plants, the teleomorph is ascribed to P. japonica (anamorph Drechslera tuberosa ). This is the first report describing the occurrence of the teleomorph of D. tuberosa in South Africa.  相似文献   
70.
Neurological Manifestations of Niemann-Pick Disease Type C in Cats   总被引:3,自引:1,他引:2  
Seven Domestic shorthair cats with a lysosomal storage disorder analogous to human Niemann-Pick disease type C, from a breeding colony were studied to characterize the neurological manifestations of this disorder. Affected cats were identified by means of liver biopsies at 4 to 6 weeks of age. Neurological examinations were performed at 2 week intervals from the onset of clinical signs. All cats displayed signs referrable to the cerebellum, with a subtle intention tremor noticed initially at 8 to 12 weeks of age; the disease was rapidly progressive. The tremor became more pronounced, menace response was lost, and severe dysmetria and ataxia developed. Three cats also had signs referrable to other areas of the central nervous system. Cats died or were euthanized between 12 and 43 weeks of age. Pathological findings included accumulation of substrate within neurons throughout the central nervous system, and axonal spheroid formation. The clinical and pathological findings in these cats are comparable to those in the human form of the disease.  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