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   495515篇
  免费   3353篇
  国内免费   1065篇
化学   226560篇
晶体学   6993篇
力学   29040篇
综合类   9篇
数学   86341篇
物理学   150990篇
  2020年   4260篇
  2019年   5067篇
  2018年   17243篇
  2017年   17133篇
  2016年   15556篇
  2015年   5548篇
  2014年   8952篇
  2013年   17705篇
  2012年   17629篇
  2011年   26741篇
  2010年   18671篇
  2009年   19288篇
  2008年   22249篇
  2007年   24091篇
  2006年   14544篇
  2005年   13846篇
  2004年   13326篇
  2003年   12779篇
  2002年   12030篇
  2001年   11394篇
  2000年   9063篇
  1999年   6762篇
  1998年   6258篇
  1997年   6032篇
  1996年   5552篇
  1995年   5024篇
  1994年   5029篇
  1993年   4932篇
  1992年   5107篇
  1991年   5623篇
  1990年   5380篇
  1989年   5389篇
  1988年   5127篇
  1987年   5120篇
  1986年   4751篇
  1985年   5753篇
  1984年   6076篇
  1983年   5144篇
  1982年   5484篇
  1981年   5071篇
  1980年   4787篇
  1979年   5344篇
  1978年   5567篇
  1977年   5558篇
  1976年   5666篇
  1975年   5312篇
  1974年   5227篇
  1973年   5391篇
  1972年   4261篇
  1971年   3844篇
排序方式: 共有10000条查询结果,搜索用时 93 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.
We prove that the group of diffeomorphisms of the interval [0, 1] contains surface groups whose action on (0, 1) has no global fix point and such that only countably many points of the interval (0, 1) have non-trivial stabiliser.  相似文献   
79.
80.
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   
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