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   443605篇
  免费   5133篇
  国内免费   1220篇
化学   228435篇
晶体学   6820篇
力学   21684篇
综合类   11篇
数学   53944篇
物理学   139064篇
  2021年   3567篇
  2020年   3996篇
  2019年   4634篇
  2018年   7174篇
  2017年   7054篇
  2016年   9333篇
  2015年   5663篇
  2014年   8706篇
  2013年   19687篇
  2012年   16468篇
  2011年   19056篇
  2010年   13706篇
  2009年   13528篇
  2008年   17242篇
  2007年   17178篇
  2006年   15631篇
  2005年   16441篇
  2004年   15491篇
  2003年   12861篇
  2002年   11376篇
  2001年   12062篇
  2000年   9196篇
  1999年   7085篇
  1998年   5969篇
  1997年   5935篇
  1996年   5700篇
  1995年   5036篇
  1994年   5108篇
  1993年   5075篇
  1992年   5499篇
  1991年   5654篇
  1990年   5365篇
  1989年   5381篇
  1988年   5283篇
  1987年   5153篇
  1986年   4916篇
  1985年   6559篇
  1984年   6799篇
  1983年   5473篇
  1982年   5755篇
  1981年   5616篇
  1980年   5356篇
  1979年   5742篇
  1978年   5775篇
  1977年   5816篇
  1976年   5953篇
  1975年   5435篇
  1974年   5432篇
  1973年   5551篇
  1972年   4007篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
74.
75.
76.
Mesoscopic modeling at the pore scale offers great promise in exploring the underlying structure transport performance of flow through porous media. The present work studies the fluid flow subjected to capillarity-induced resonance in porous media characterized by different porous structure and wettability. The effects of porosity and wettability on the displacement behavior of the fluid flow through porous media are discussed. The results are presented in the form of temporal evolution of percentage saturation and displacement of the fluid front through porous media. The present study reveals that the vibration in the form of acoustic excitation could be significant in the mobilization of fluid through the porous media. The dependence of displacement of the fluid on physicochemical parameters like wettability of the surface, frequency along with the porosity is analyzed. It was observed that the mean displacement of the fluid is more in the case of invading fluid with wetting phase where the driving force strength is not so dominant.  相似文献   
77.
78.
Seven new copper(II) complexes of type [Cu(A)(L)]?H2O (A = sparfloxacin, ciprofloxacin, levofloxacin, gatifloxacin, pefloxacin, ofloxacin, norfloxacin; L = 5‐[(3‐chlorophenyl)diazenyl]‐4‐hydroxy‐1,3‐thiazole‐2(3H)‐thione) were synthesized and characterized using elemental and thermogravimetric analyses, and electronic, electron paramagnetic resonance (EPR), Fourier transform infrared and liquid chromatography–mass spectroscopies. Tetrahedral geometry around copper is assigned in all complexes using EPR and electronic spectral analyses. All complexes were investigated for their interaction with herring sperm DNA utilizing absorption titration (Kb = 1.27–3.13 × 105 M?1) and hydrodynamic volume measurement studies. The studies suggest the classical intercalative mode of DNA binding. The cleavage reaction on pUC19 DNA was monitored by agarose gel electrophoresis. The results indicate that the Cu(II) complexes can more effectively promote the cleavage of plasmid DNA. The superoxide dismutase mimic activity of the complexes was evaluated by nitroblue tetrazolium assay, and the complexes catalysed the dismutation of superoxide at pH = 7.8 with IC50 values in the range 0.597–0.900 μM. The complexes were screened for their in vitro antibacterial activity against five pathogenic bacteria. All the complexes are good cytotoxic agents and show LC50 values ranging from 5.559 to 11.912 µg ml?1. All newly synthesized Cu(II) complexes were also evaluated for their in vitro antimalarial activity against Plasmodium falciparum strain (IC50 = 0.62–2.0 µg ml?1). Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
79.
A new strategy for the synthesis of tetrahydroisoquinolines based on the Pd0‐catalyzed intramolecular α‐arylation of sulfones is reported. The combination of this Pd‐catalyzed reaction with intermolecular Michael and aza‐Michael reactions allows the development of two‐ and three‐step domino processes to synthesize diversely functionalized scaffolds from readily available starting materials.  相似文献   
80.
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