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   4334篇
  免费   501篇
  国内免费   1篇
  2021年   56篇
  2019年   40篇
  2018年   54篇
  2017年   37篇
  2016年   81篇
  2015年   113篇
  2014年   139篇
  2013年   158篇
  2012年   202篇
  2011年   190篇
  2010年   145篇
  2009年   122篇
  2008年   175篇
  2007年   176篇
  2006年   140篇
  2005年   155篇
  2004年   150篇
  2003年   153篇
  2002年   145篇
  2001年   95篇
  2000年   98篇
  1999年   87篇
  1998年   54篇
  1997年   56篇
  1996年   48篇
  1995年   48篇
  1994年   46篇
  1993年   52篇
  1992年   82篇
  1991年   69篇
  1990年   81篇
  1989年   78篇
  1988年   80篇
  1987年   72篇
  1986年   61篇
  1985年   64篇
  1984年   63篇
  1983年   52篇
  1982年   59篇
  1981年   57篇
  1980年   39篇
  1979年   59篇
  1978年   45篇
  1977年   37篇
  1976年   52篇
  1975年   55篇
  1974年   67篇
  1973年   80篇
  1972年   57篇
  1971年   35篇
排序方式: 共有4836条查询结果,搜索用时 765 毫秒
11.
12.
Phytofluene     
The extraction and purification of phytofluene from tomatoes is described. The purity of the best preparations obtained is approximately 25% higher than previously reported (2). The present light-absorption value for the longer wavelength maximum is that expected by extrapolation of the values obtained for ζ- and δ-carotenes, tetrahydrolycopene, and lycopene.  相似文献   
13.
The plastic response of phenotypic traits to environmental change is a common research focus in several disciplines - from ecology and evolutionary biology to physiology and molecular genetics. The use of model systems such as the flowering plant Arabidopsis thaliana has facilitated a dialogue between developmental biologists asking how plasticity is controlled (proximate causes) and organismal biologists asking why plasticity exists (ultimate causes). Researchers studying ultimate causes and consequences are increasingly compelled to reject simplistic, ‘black box’ models, while those studying proximate causes and mechanisms are increasingly obliged to subject their interpretations to ecological ‘reality checks.’ We review the successful multidisciplinary efforts to understand the phytochrome-mediated shade-avoidance and light-seeking responses of flowering plants as a pertinent example of convergence between evolutionary and molecular biology. In this example, the two-way exchange between reductionist and holist camps has been essential to rapid and sustained progress. This should serve as a model for future collaborative efforts towards understanding the responses of organisms to their constantly changing environments.  相似文献   
14.
World Journal of Microbiology and Biotechnology - The current study is the first one to demonstrate the wine fermentation potential of members of several species of the genus Kazachstania including...  相似文献   
15.
16.
The complete nucleotide sequence of the mitochondrial (mt) genome was determined for specimens of the coral species Montipora cactus (Bernard 1897) and Anacropora matthai (Pillai 1973), representing two morphologically distinct genera of the family Acroporidae. These sequences were compared with the published mt genome sequence for the confamilial species, Acropora tenuis (Dana 1846). The size of the mt genome was 17,887 bp and 17,888 bp for M. cactus and A. matthai. Gene content and organization was found to be very similar among the three Acroporidae mt genomes with a group I intron occurring in the NADH dehyrogenase 5 (nad5) gene. The intergenic regions were also similar in length among the three corals. The control region located between the small ribosomal RNA (ms) and the cytochrome oxidase 3 (cox3) gene was significantly smaller in M. cactus and A. matthai (both 627 bp) than in A. tenuis (1086 bp). Only one set of repeated sequences was identified at the 3′-end of the control regions in M. cactus and A. matthai. A lack of the abundant repetitive elements which have been reported for A. tenuis, accounts for the relatively short control regions in M. cactus and A. matthai. Pairwise distances and relative rate analyses of 13 protein coding genes, the group I intron and the largest intergenic region, igr3, revealed significant differences in the rate of molecular evolution of the mt genome among the three species, with an extremely slow rate being seen between Montipora and Anacropora. It is concluded that rapid mt genome evolution is taking place in genus Acropora relative to the confamilial genera Montipora and Anacropora although all are within the relatively slow range thought to be typical of Anthozoa.  相似文献   
17.
18.
19.
20.
Serotonergic projections from the raphe nuclei are thought to modulate locomotor activity in the rat, and serotonin injection into the nucleus accumbens attenuates the hypermotility elicited by amphetamine. The purpose of the present study was to characterize the effects of various classes of serotonergic agonists administered into the nucleus accumbens on d-amphetamine-stimulated locomotor activity in order to determine which serotonin receptor subtypes are involved. Administration of the nonselective 5-HT agonist quipazine, the 5-HT-1 agonist mCPP, the 5-HT-1a agonist 8-OH-DPAT, the 5-HT-1b agonist CGS-12066B, and the 5HT-1c/2 agonist DOI did not inhibit d-amphetamine-stimulated locomotor activity. Pronounced lateral head weaving was noted after 8-OH-DPAT administration. The combination of the 5-HT-1a agonist 8-OH-DPAT and the 5-HT-1b agonist CGS-12066B, however, did inhibit d-amphetamine-stimulated locomotor activity. In contrast, the 5-HT-3 agonist 1-phenylbiguanide enhanced the locomotor effect of d-amphetamine. This effect was partially reversed by the 5-HT-3 antagonist MDL-7222. These studies suggest that serotonin has complex and multiple effects on the regulation of locomotor activity within the nucleus accumbens.  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