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   468237篇
  免费   7708篇
  国内免费   3700篇
化学   240835篇
晶体学   6495篇
力学   23176篇
综合类   195篇
数学   75033篇
物理学   133911篇
  2021年   3037篇
  2020年   3501篇
  2019年   3608篇
  2018年   13801篇
  2017年   13689篇
  2016年   12300篇
  2015年   5708篇
  2014年   7152篇
  2013年   18303篇
  2012年   18115篇
  2011年   27199篇
  2010年   16845篇
  2009年   16995篇
  2008年   21930篇
  2007年   23908篇
  2006年   15545篇
  2005年   15134篇
  2004年   13964篇
  2003年   13028篇
  2002年   12051篇
  2001年   12526篇
  2000年   9652篇
  1999年   7589篇
  1998年   6222篇
  1997年   5931篇
  1996年   5934篇
  1995年   5392篇
  1994年   5028篇
  1993年   4892篇
  1992年   5341篇
  1991年   5251篇
  1990年   4931篇
  1989年   4728篇
  1988年   4940篇
  1987年   4565篇
  1986年   4421篇
  1985年   6145篇
  1984年   6261篇
  1983年   5133篇
  1982年   5518篇
  1981年   5445篇
  1980年   5197篇
  1979年   5375篇
  1978年   5451篇
  1977年   5430篇
  1976年   5298篇
  1975年   5175篇
  1974年   5044篇
  1973年   5179篇
  1972年   3083篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Russian Journal of Organic Chemistry - Methyl (Z)-3-[(2R,3R,4S,5S)-5-(2-methoxy-2-oxoethyl)-3,4-(isopropylidenedioxy)tetrahydrofuran-2-yl]-prop-2-enoate was synthesized, and its intramolecular...  相似文献   
92.
Methodology and Computing in Applied Probability - The problem of optimally controlling one-dimensional diffusion processes until they enter a given stopping set is extended to include Markov...  相似文献   
93.
94.
Ding  Q.  Yao  M.  Wu  Sh.  Zeng  M.  Xue  N.  Wu  D.  Xu  J. 《Journal of Applied Spectroscopy》2022,89(4):712-718
Journal of Applied Spectroscopy - Based on partial least squares (PLS) analysis, the effects of different smoothing points and different preprocessing methods on the accuracy and precision of the...  相似文献   
95.
Xu  H. J.  Zhang  Q. G.  Debenest  G. 《Transport in Porous Media》2021,140(3):625-627
Transport in Porous Media - The theme of coupling problems for adsorption, absorption and thermochemical transport in porous media is very important for engineering applications. Based on the...  相似文献   
96.
97.
The biomimetic sol—gel synthesis of silicon—chitosan-containing glycerohydrogels was carried out using silicon tetraglycerolate as a precursor. It was found that chitosan accelerates gel formation in weakly acidic media. In more acidic media, the kinetics of the process changes according to the curve with a maximum, which can be attributed to different mechanisms of silanol condensation before and after the isoelectric point. The investigated silicon—chitosan-containing glycerohydrogels exhibit antibacterial, anti-inflammatory, and wound healing activity. The synthesized hybrid glycerohydrogels are promising materials for biomedical applications.  相似文献   
98.
99.
Monodisperse aqueous upconverting nanoparticles (UCNPs) were covalently immobilized on aldehyde modified cellulose paper via reduction amination to develop a luminescence resonance energy transfer (LRET)-based nucleic acid hybridization assay. This first account of covalent immobilization of UCNPs on paper for a bioassay reports an optically responsive method that is sensitive, reproducible and robust. The immobilized UCNPs were decorated with oligonucleotide probes to capture HPRT1 housekeeping gene fragments, which in turn brought reporter conjugated quantum dots (QDs) in close proximity to the UCNPs for LRET. This sandwich assay could detect unlabeled oligonucleotide target, and had a limit of detection of 13 fmol and a dynamic range spanning nearly 3 orders of magnitude. The use of QDs, which are excellent LRET acceptors, demonstrated improved sensitivity, limit of detection, dynamic range and selectivity compared to similar assays that have used molecular fluorophores as acceptors. The selectivity of the assay was attributed to the decoration of the QDs with polyethylene glycol to eliminate non-specific adsorption. The kinetics of hybridization were determined to be diffusion limited and full signal development occurred within 3 min.  相似文献   
100.
The density functional theory calculation of 1H and 13C NMR chemical shifts in a series of ten 10 classically known Strychnos alkaloids with a strychnine skeleton was performed at the PBE0/pcSseg-2//pcseg-2 level. It was found that calculated 1H and 13C NMR chemical shifts provided a markedly good correlation with experiment characterized by a mean absolute error of 0.08 ppm in the range of 7 ppm for protons and 1.67 ppm in the range of 150 ppm for carbons, so that a mean absolute percentage error was as small as ~1% in both cases.  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