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   116925篇
  免费   6260篇
  国内免费   122篇
林业   4854篇
农学   3681篇
基础科学   831篇
  13338篇
综合类   21917篇
农作物   4675篇
水产渔业   5495篇
畜牧兽医   60085篇
园艺   1402篇
植物保护   7029篇
  2018年   1497篇
  2017年   1613篇
  2016年   1562篇
  2015年   1346篇
  2014年   1515篇
  2013年   4404篇
  2012年   2929篇
  2011年   3626篇
  2010年   2445篇
  2009年   2392篇
  2008年   3647篇
  2007年   3419篇
  2006年   3187篇
  2005年   3052篇
  2004年   3047篇
  2003年   3042篇
  2002年   2910篇
  2001年   3879篇
  2000年   3879篇
  1999年   2929篇
  1998年   1208篇
  1997年   1208篇
  1995年   1369篇
  1994年   1294篇
  1993年   1220篇
  1992年   2626篇
  1991年   2823篇
  1990年   2676篇
  1989年   2710篇
  1988年   2490篇
  1987年   2602篇
  1986年   2672篇
  1985年   2550篇
  1984年   2055篇
  1983年   1892篇
  1982年   1237篇
  1981年   1186篇
  1980年   1090篇
  1979年   1877篇
  1978年   1508篇
  1977年   1208篇
  1976年   1173篇
  1975年   1219篇
  1974年   1576篇
  1973年   1653篇
  1972年   1631篇
  1971年   1567篇
  1970年   1451篇
  1969年   1319篇
  1967年   1136篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
As anaerobic sampling and culture techniques improved, the documented prevalence of anaerobic bacteria in periodontal disease has increased. The anaerobic bacteria have become more well-known in humans and consequently in dogs, since this species is a major model in periodontal studies. A review of the literature related to anaerobic flora is described.  相似文献   
83.
RNA was extracted from single or small groups of ovine ovarian follicles after treatment of ewes with FSH and/or LH. The content of mRNA for the alpha-inhibin and beta A-inhibin subunits was analyzed by hybridization with specific cDNA probes. All ewes were treated with progestin vaginal pessaries to suppress spontaneous preovulatory follicle maturation and ewes were given three intramuscular injections of gonadotropins at 8-hr intervals starting 24 hr prior to collection of ovaries. In experiment I, both Schering-FSH and NIDDK-oFSH-17 (oFSH) significantly increased alpha- and beta A-inhibin mRNA per ewe in 2-5 mm follicles and tended to increase alpha- and beta A-inhibin mRNA in large (greater than 5 mm) follicles. In experiment II, oFSH and NIDDK-oLH-25 (oLH) were administered in a 2X2 factorial arrangement. Separate administration of oFSH or oLH increased (P less than .05) the alpha-inhibin mRNA concentration in large follicles. alpha-inhibin mRNA concentration in 4-5 mm follicles was also increased by oFSH but was decreased by oLH. Concomitant treatment with oFSH and oLH did not change alpha-inhibin mRNA concentrations from those measured in oFSH treated ewes. In experiment II, beta A mRNA concentrations followed a pattern similar to that of alpha A mRNA, but the differences were not statistically significant. We conclude that, in the ewe, exogenous FSH increases the concentration of inhibin mRNA in the whole follicle. The ability of exogenous oLH to alter expression of the inhibin subunit genes may depend upon the stage of follicle maturation.  相似文献   
84.
Cellular alterations in level of expression of mRNA encoding for prostaglandin endoperoxide synthase were quantified within ovarian tissues of sheep obtained before, during and after induction of the preovulatory surge of LH and ovulation with LHRH. This was accomplished by isotopic in situ hybridization using a selective cRNA probe to ovine prostaglandin endoperoxide synthase mRNA. A significant elevation in mRNA was detected within the theca interna of the preovulatory follicle at 8, 16 and 24 hr following administration of LHRH. Very close to the time of ovulation (ie., at 24 hr post-LHRH) a marked rise in mRNA was observed in association with epithelial cells covering the apical surface of the follicle. Ovarian cyclooxygenase metabolites of arachidonic acid produced during the ovulatory process in the ewe originate within the thecal layer and germinal epithelium of the follicle destined to ovulate.  相似文献   
85.
Chuzan virus agglutinated erythrocytes of several species of animals including bovine. The hemagglutinating (HA) activity against bovine erythrocytes was dependent on NaCl molarity and was expressed best at 0.6 M, but it was independent of pH and temperature. Three strains of Chuzan virus isolated from 2 cows and a pool of culicoides midges had indistinguishable HA antigenicity. All cattle infected with the virus developed high titers of hemagglutination inhibiting (HI) antibody which changed in parallel with neutralizing (NT) antibody titers. Correlation between HI and NT antibodies was very high and the antibodies persisted for one year or more. Therefore it was concluded that the HI test is applicable for survey of Chuzan virus infection among cattle in place of the NT test.  相似文献   
86.
One-month-old Syrian hamsters of the APA and Std: golden strains were inoculated intraperitoneally with 10(5) PFU/head of the D variant of encephalomyocarditis (EMC) virus and examined virologically and pathologically up to 7 days after inoculation. APA hamsters developed apparent hyperglycemia due to pancreatic islet cell damage while Std:golden hamsters did not. Hamsters of both strains showed clear histopathologic changes in the testis with prominent viral replication as well as in the brain, heart and exocrine pancreas. The susceptibility to EMC virus-infection was higher in males than in females and in APA than in Std: golden hamsters.  相似文献   
87.
Samples of rapeseed from three Italian growing environments (Bologna, Perugia and Palermo) were analysed for glucose content and dry weight of 1000 seeds every three or four days starting from the end of flowering until complete ripening. In addition, the content of oil, soluble and total proteins, glucosinolates and myrosinase activity was determined in samples of mature seeds. The cultivars used were jet Neuf and Lingot (type 0) and Tandem, Jade and Santana (type 00). From the results it emerged that the point of intersection of the two branches of the linear regression plots for different glucose-consumption kinetics found during seed filling, in addition to being strongly affected by the climate of the test environment, is correlated with quantitative and qualitative production, independently of the genotype.  相似文献   
88.
89.
90.
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