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   14095篇
  免费   285篇
  国内免费   152篇
  14532篇
  2024年   31篇
  2023年   104篇
  2022年   131篇
  2021年   171篇
  2020年   157篇
  2019年   219篇
  2018年   275篇
  2017年   240篇
  2016年   293篇
  2015年   555篇
  2014年   638篇
  2013年   964篇
  2012年   406篇
  2011年   833篇
  2010年   669篇
  2009年   979篇
  2008年   1102篇
  2007年   871篇
  2006年   746篇
  2005年   760篇
  2004年   553篇
  2003年   415篇
  2002年   400篇
  2001年   181篇
  2000年   171篇
  1999年   194篇
  1998年   179篇
  1997年   174篇
  1996年   137篇
  1995年   154篇
  1994年   189篇
  1993年   150篇
  1992年   129篇
  1991年   164篇
  1990年   177篇
  1989年   147篇
  1988年   112篇
  1987年   56篇
  1986年   52篇
  1985年   40篇
  1984年   154篇
  1983年   89篇
  1982年   81篇
  1981年   71篇
  1980年   60篇
  1979年   60篇
  1978年   25篇
  1977年   22篇
  1976年   12篇
  1975年   11篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
The experimental and theoretical studies on the molecular structure and vibrational spectra of bis(thiourea)zinc(II) chloride (BTZC) crystals were investigated. The Fourier transform infrared, Fourier transform Raman and UV–vis spectra of BTZC were recorded. The molecular geometry and vibrational frequencies of BTZC in the ground state were calculated by using B3LYP with LANL2DZ as basis set. Comparison of the observed structural parameters of BTZC with single-crystal X-ray studies yields a good agreement. Vibrational analysis of the simultaneous IR and Raman activation of the Zn–Cl stretching mode in the molecule provides the evidence for the charge transfer interaction taking place within the molecule. The energy and oscillator strength are calculated by time-dependent density functional theory. The simulated spectra satisfactorily coincide with the experimental spectra.  相似文献   
22.
23.
Effects of materials extracted from potatoes with hot 80% ethanol on the course of phosphorylase reactions were examined. These materials had no effect on phosphorylase activities as determined by the rate of liberation of inorganic phosphate from glucose-1-phosphate in the presence of a large amount of primer; however, in the presence of a small amount of primer or in its absence, these materials had significant effects on the liberation of inorganic phosphate and starch formation. These results suggested the presence of a small amount of primers in these materials. Evidence was presented against the participation of d-enzyme on the formation of starch when partially purified preparations of potato phosphorylase or crude extracts from potatoes were used as the enzyme.  相似文献   
24.
《MABS-AUSTIN》2013,5(4):1069-1083
Modification of antibody class and binding properties typically requires cloning of antibody genes, antibody library construction, phage or yeast display and recombinant antibody expression. Here, we describe an alternative “cloning-free” approach to generate antibodies with altered antigen-binding and heavy chain isotype by mimicking the germinal center reaction in antibody-secreting hybridoma cells. This was accomplished by lentiviral transduction and controllable expression of activation-induced cytidine deaminase (AID) to generate somatic hypermutation and class switch recombination in antibody genes coupled with high-throughput fluorescence-activated cell sorting (FACS) of hybridoma cells to detect altered antibody binding properties. Starting from a single established hybridoma clone, we isolated mutated antibodies that bind to a low-temperature structure of polyethylene glycol (PEG), a polymer widely used in nanotechnology, biotechnology and pharmaceuticals. FACS of AID-infected hybridoma cells also facilitated rapid identification of class switched variants of monoclonal IgM to monoclonal IgG. Mimicking the germinal center reaction in hybridoma cells may offer a general method to identify and isolate antibodies with altered binding properties and class-switched heavy chains without the need to carry out DNA library construction, antibody engineering and recombinant protein expression.  相似文献   
25.
Abstract

Insulin plays an important role in various metabolic as well as anabolic actions in cells, including osteoblast cells. In the present study, we explored to determine if insulin receptor could associate with syndecan-1 in response to insulin and such association could lead to the activation of subsequent ERK I/II and alkaline phosphatase (ALP) in osteoblast cells. Insulin rapidly induces the association of insulin receptor with syndecan-1. Synstatin is a specific peptide inhibitor that blocks the binding of syndecan-1 to integrate. In the presence of synstatin, insulin-stimulated ERK I/II activation was dramatically inhibited, suggesting that syndecan-1/integrin interaction is essential in the activation of ERK I/II by insulin. Pretreatment of synstatin also inhibited the insulin-stimulated ALP activity. Taken together, these results suggest that insulin stimulates the association of insulin receptor with syndecan-1 and the complex formation of syndecan-1 and integrin could play an important role in ERK I/II–ALP signaling pathway in osteoblast cells.  相似文献   
26.
Abstract

Urotensin‐II (U‐II) was identified as the natural ligand of the G protein‐coupled receptor GPR14, which has been correspondingly renamed Urotensin‐II receptor (U2R). The tissue distribution of U2R and the pharmacological effects of U‐II suggest a novel neurohormonal system with potent cardiovascular effects. We here report the human rhabdomyosarcoma cell line TE‐671 as the first natural and endogenous source of functional U2R in an immortalized cell line. In TE‐671 cells, U‐II stimulated extracellular signal regulated kinase phosphorylation and increased c‐fos mRNA expression. Furthermore, we demonstrate that the expression of U2R mRNA and functional U‐II high affinity binding sites are serum‐responsive and that they are specifically up‐regulated by interferon γ (IFNγ). We propose that IFNγ contributes to the previously observed increase of U2R density in the heart tissue of congestive heart failure (CHF) patients and we suggest that U2R up‐regulation, as a consequence of an inflammatory response, could lead to a clinical worsening of this disease.  相似文献   
27.
Abstract

A new species of Stipa, endemic to Sicily, named Stipa valdemonensis is described here. The new taxon is related to Stipa crassiculmis. Owing to the small number of individuals observed, in few restricted localities only, it is assigned the IUCN threat status “vulnerable”.  相似文献   
28.
A new series of 6, 7-dihydroxy-3-(methylphenyl) chromenones, including three new derivatives, i.e. 6,7-dihydroxy-3-(2-methylphenyl)-2H-chromen-2-one (OPC); 6,7-dihydroxy-3-(3-methylphenyl)-2H-chromen-2-one (MPC); 6,7-dihydroxy-3-(4-methylphenyl)-2H-chromen-2-one (PPC) and one previously described, namely 6,7-dihydroxy-3-phenyl-2H-chromen-2-one (DPC), were synthesized. These compounds were investigated as inhibitors of human carbonic anhydrase I (hCA-I) and human carbonic anhydrase II (hCA-II) which had been purified from human erythrocytes on an affinity gel comprised of L-tyrosine-sulfonamide-Sepharose 4B.  相似文献   
29.
30.
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