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   30411篇
  免费   1833篇
  国内免费   2133篇
  34377篇
  2024年   78篇
  2023年   355篇
  2022年   639篇
  2021年   853篇
  2020年   711篇
  2019年   1066篇
  2018年   988篇
  2017年   662篇
  2016年   739篇
  2015年   950篇
  2014年   1744篇
  2013年   2019篇
  2012年   1402篇
  2011年   1834篇
  2010年   1322篇
  2009年   1466篇
  2008年   1574篇
  2007年   1704篇
  2006年   1492篇
  2005年   1308篇
  2004年   1162篇
  2003年   1001篇
  2002年   884篇
  2001年   605篇
  2000年   601篇
  1999年   573篇
  1998年   581篇
  1997年   470篇
  1996年   493篇
  1995年   507篇
  1994年   426篇
  1993年   419篇
  1992年   405篇
  1991年   358篇
  1990年   317篇
  1989年   286篇
  1988年   261篇
  1987年   218篇
  1986年   201篇
  1985年   267篇
  1984年   281篇
  1983年   199篇
  1982年   242篇
  1981年   158篇
  1980年   135篇
  1979年   116篇
  1978年   86篇
  1977年   56篇
  1976年   55篇
  1975年   25篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
The present study explains the intraspecific variation in Indian Hill trout (Barilius bendelisis) on the basis of image based truss network system and D‐loop region of mtDNA. A total of 210 samples were collected from three different rivers (Teesta, Kameng and Myntudu River) of North East India in Indo‐Burma Biodiversity Hotspot. By using the software applications (tpsDig version 2.1 and PAST), a total of 25 morphometric measurements were generated from 10 landmarks. The Analysis of Variance (ANOVA), Factor Analysis (FA) and Discriminate Function Analysis (DFA) showed, out of the total variations, factor 1 explained 46.74% while factor 2 and factor 3 explained 27.14% and 11.92%, respectively. Using these variables 83.33% of the cross‐validated specimens were classified into distinct groups. Analysis of Molecular Variance (AMOVA) and pairwise Fst value for D‐loop region of mtDNA also showed high to medium level of genetic variation among the stocks and within the stocks. We conclude that the observed discrete stocks might be the result of changing environmental conditions in different rivers of the hotspot as the rivers are present at different altitudinal labels. It is also believed that the variation might be due to the construction of barrages across the river which hinder the mixing among the stocks.  相似文献   
202.
Inhibitory effect of bFGF on endochondral heterotopic ossification   总被引:4,自引:0,他引:4  
Basic fibroblast growth factor (bFGF) is reported to stimulate repair of fracture and bony defects in in vivo animal studies. However, most studies performed in vitro demonstrate inhibitory effect of bFGF on cartilage and bone differentiation. To understand the discrepancy observed in in vivo and in vitro studies, we evaluated the effect of bFGF on chondro-osteogenesis initiated by bone matrix powder (MP). MP was implanted in the murine hamstring muscles with or without administration of bFGF. Injection of 1 microg of bFGF markedly reduced the size of heterotopic bone induced by MP, as detected by X-ray. Injection of 10 microg of bFGF completely inhibited ossification and only fibrous tissues were observed at the site of MP implantation. The expressions of alkaline phosphatase and osteocalcin mRNAs, markers for bone differentiation, were completely suppressed by 10 microg of bFGF. These results demonstrate the inhibitory effect of bFGF on endochondral ossification in vivo, implicating a precaution for its use in musculo-skeletal disorders.  相似文献   
203.
204.
205.
206.
苔藓植物对环境变化的响应及适应性研究进展   总被引:4,自引:0,他引:4  
苔藓植物由于其结构相对简单,对环境变化的反应较为敏感,是一类良好的生物指示植物.本文综述了水分、光照、温度等方面的环境因子变化对苔藓植物的影响以及苔藓植物对环境污染的响应及适应的最近研究进展,以期促进国内深入开展苔藓植物对环境污染和全球变化的响应、适应及其生态指示作用等研究.  相似文献   
207.
208.
The signal systems of the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe, coupled to heterotrimeric G-proteins and sensitive to pheromones and alimentary molecules, are prototypes of hormonal signal systems of the higher vertebrate animals and are widely used in studies on molecular mechanisms of their functioning. This review summarizes and analyzes data on structural-functional organization of the first two components of these systems—receptors of the serpentine type and heterotrimeric G-proteins; mechanisms of functional coupling of receptors and G-proteins both between each other and to other signal proteins are discussed. It has been shown that at the early stages of evolution of signaling systems, at the yeast level, various models of transduction of signals into the cell were tested; many of them differ essentially from the classic model of the three-component, G-protein-coupled signal system of the higher vertebrates.  相似文献   
209.
Incorporation of proteins in biomimetic giant unilamellar vesicles (GUVs) is one of the hallmarks towards cell models in which we strive to obtain a better mechanistic understanding of the manifold cellular processes. The reconstruction of transmembrane proteins, like receptors or channels, into GUVs is a special challenge. This procedure is essential to make these proteins accessible to further functional investigation. Here we describe a strategy combining two approaches: cell-free eukaryotic protein expression for protein integration and GUV formation to prepare biomimetic cell models. The cell-free protein expression system in this study is based on insect lysates, which provide endoplasmic reticulum derived vesicles named microsomes. It enables signal-induced translocation and posttranslational modification of de novo synthesized membrane proteins. Combining these microsomes with synthetic lipids within the electroswelling process allowed for the rapid generation of giant proteo-liposomes of up to 50 μm in diameter. We incorporated various fluorescent protein-labeled membrane proteins into GUVs (the prenylated membrane anchor CAAX, the heparin-binding epithelial growth factor like factor Hb-EGF, the endothelin receptor ETB, the chemokine receptor CXCR4) and thus presented insect microsomes as functional modules for proteo-GUV formation. Single-molecule fluorescence microscopy was applied to detect and further characterize the proteins in the GUV membrane. To extend the options in the tailoring cell models toolbox, we synthesized two different membrane proteins sequentially in the same microsome. Additionally, we introduced biotinylated lipids to specifically immobilize proteo-GUVs on streptavidin-coated surfaces. We envision this achievement as an important first step toward systematic protein studies on technical surfaces.  相似文献   
210.
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