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   406578篇
  免费   2071篇
  国内免费   446篇
化学   178970篇
晶体学   5975篇
力学   24559篇
综合类   3篇
数学   66532篇
物理学   133056篇
  2021年   3466篇
  2020年   3790篇
  2019年   4625篇
  2018年   12128篇
  2017年   12587篇
  2016年   11420篇
  2015年   4474篇
  2014年   7724篇
  2013年   14130篇
  2012年   14624篇
  2011年   21808篇
  2010年   15747篇
  2009年   16070篇
  2008年   20011篇
  2007年   22242篇
  2006年   11714篇
  2005年   13512篇
  2004年   11412篇
  2003年   11266篇
  2002年   10264篇
  2001年   9137篇
  2000年   7345篇
  1999年   5329篇
  1998年   5040篇
  1997年   4810篇
  1996年   4473篇
  1995年   3928篇
  1994年   3973篇
  1993年   3966篇
  1992年   4022篇
  1991年   4472篇
  1990年   4387篇
  1989年   4438篇
  1988年   4152篇
  1987年   4163篇
  1986年   3885篇
  1985年   4529篇
  1984年   4862篇
  1983年   4151篇
  1982年   4369篇
  1981年   3997篇
  1980年   3720篇
  1979年   4238篇
  1978年   4433篇
  1977年   4536篇
  1976年   4539篇
  1975年   4265篇
  1974年   4127篇
  1973年   4331篇
  1972年   3586篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
54.
55.
56.
We summarize the results of our recent work on Bäcklund transformations (BTs), particularly focusing on the relation between BTs and infinitesimal symmetries. We present a BT for an associated Degasperis–Procesi (aDP) equation and its superposition principle and investigate the solutions generated by applying this BT. Following our general methodology, we use the superposition principle of the BT to generate the infinitesimal symmetries of the aDP equation.  相似文献   
57.
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   
58.
59.
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   
60.
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