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   97519篇
  免费   3439篇
  国内免费   1622篇
  2022年   505篇
  2021年   877篇
  2020年   677篇
  2019年   817篇
  2018年   1665篇
  2017年   1623篇
  2016年   3530篇
  2015年   7075篇
  2014年   6870篇
  2013年   6599篇
  2012年   5976篇
  2011年   3116篇
  2010年   2727篇
  2009年   2674篇
  2008年   1241篇
  2007年   1084篇
  2006年   1016篇
  2005年   7036篇
  2004年   5737篇
  2003年   3969篇
  2002年   1488篇
  2001年   1450篇
  2000年   590篇
  1999年   1699篇
  1998年   476篇
  1992年   1977篇
  1991年   2073篇
  1990年   2124篇
  1989年   2030篇
  1988年   1980篇
  1987年   1838篇
  1986年   1640篇
  1985年   1675篇
  1984年   1091篇
  1983年   838篇
  1982年   462篇
  1979年   1074篇
  1978年   759篇
  1977年   606篇
  1976年   629篇
  1975年   872篇
  1974年   994篇
  1973年   1005篇
  1972年   953篇
  1971年   928篇
  1970年   820篇
  1969年   830篇
  1968年   734篇
  1967年   751篇
  1966年   584篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The present study has shown that on the level of the parasitic system the epidemic process is a biological system, wherein the host population serves as the internal regulator, the mechanism of transmission serves as the external regulator and the parasite population, as the regulated object. The biological regulating mechanisms of the epidemic process have fundamental differences in the groups of infectious with various mechanisms of transmission, and the specific nature of the mechanism of transmission determines the peculiar features of the biological mechanism which governs the self-regulation of the epidemic process. In contrast, on a higher level of the organization of the epidemic process, i. e. on the level of the socio-ecological system, the epidemic process is a biosocial system, wherein the human society serves as the regulator, the parasitic system serves as the regulated object and the mechanism of transmission plays the role of the filter which determines the scope of social factors, most important in the regulation of the epidemic process in a given infection. The spontaneous regulation of the epidemic process is the freed forward channel from the regulator to the regulated object, and the controlled regulation is the feedback channel.  相似文献   
82.
Series of nanoporous carbons are prepared from sunflower seed shell (SSS) by two different strategies and used as electrode material for electrochemical double-layer capacitor (EDLC). The surface area and pore-structure of the nanoporous carbons are characterized intensively using N2 adsorption technique. The results show that the pore-structure of the carbons is closely related to activation temperature and dosage of KOH. Electrochemical measurements show that the carbons made by impregnation-activation process have better capacitive behavior and higher capacitance retention ratio at high drain current than the carbons made by carbonization-activation process, which is due to that there are abundant macroscopic pores and less interior micropore surface in the texture of the former. More importantly, the capacitive performances of these carbons are much better than ordered mesoporous carbons and commercial wood-based active carbon, thus highlighting the success of preparing high performance electrode material for EDLC from SSS.  相似文献   
83.
84.
Protoplasts of Schizosaccharomyces pombe, grown on a rich nutrient medium, were treated with a peptide factor isolated from cultures of the protozoan Tetrahymena pyriformis. The peptide factor is known to inhibit RNA synthesis in Tetrahymena. It has now been shown that the peptide factor also inhibits RNA synthesis in yeast protoplasts without affecting protein synthesis.  相似文献   
85.
86.
87.
88.
89.
The cytotoxic and radiosensitizing effects of hyperthermia was shown on Ehrlich ascites tumor cells heated in vitro. The effect of hyperthermia resulted in the formation of local lesions in membranes of dying cells.  相似文献   
90.
By using the yeast two-hybrid system we identified a novel protein from the human brain interacting with the C terminus of somatostatin receptor subtype 2. This protein termed somatostatin receptor interacting protein is characterized by a novel domain structure, consisting of six N-terminal ankyrin repeats followed by SH3 and PDZ domains, several proline-rich regions, and a C-terminal sterile alpha motif. It consists of 2185 amino acid residues encoded by a 9-kilobase pair mRNA; several splice variants have been detected in human and rat cDNA libraries. Sequence comparison suggests that the novel multidomain protein, together with cortactin-binding protein, forms a family of cytoskeletal anchoring proteins. Fractionation of rat brain membranes indicated that somatostatin receptor interacting protein is enriched in the postsynaptic density fraction. The interaction of somatostatin receptor subtype 2 with its interacting protein was verified by overlay assays and coimmunoprecipitation experiments from transfected human embryonic kidney cells. Somatostatin receptor subtype 2 and the interacting protein display a striking overlap of their expression patterns in the rat brain. Interestingly, in the hippocampus the mRNA for somatostatin receptor interacting protein was not confined to the cell bodies but was also observed in the molecular layer, suggesting a dendritic localization of this mRNA.  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