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   78635篇
  免费   381篇
  国内免费   397篇
化学   24783篇
晶体学   793篇
力学   6761篇
数学   31986篇
物理学   15090篇
  2021年   48篇
  2020年   80篇
  2019年   67篇
  2018年   10481篇
  2017年   10279篇
  2016年   6114篇
  2015年   896篇
  2014年   364篇
  2013年   447篇
  2012年   3829篇
  2011年   10544篇
  2010年   5666篇
  2009年   6065篇
  2008年   6616篇
  2007年   8760篇
  2006年   209篇
  2005年   1297篇
  2004年   1522篇
  2003年   1962篇
  2002年   1007篇
  2001年   242篇
  2000年   286篇
  1999年   153篇
  1998年   188篇
  1997年   142篇
  1996年   194篇
  1995年   115篇
  1994年   76篇
  1993年   92篇
  1992年   54篇
  1991年   63篇
  1990年   50篇
  1989年   59篇
  1988年   58篇
  1987年   58篇
  1986年   57篇
  1985年   49篇
  1984年   42篇
  1983年   36篇
  1982年   42篇
  1981年   40篇
  1980年   48篇
  1979年   46篇
  1978年   35篇
  1914年   45篇
  1913年   40篇
  1912年   40篇
  1909年   41篇
  1908年   40篇
  1907年   32篇
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
1.
2.
In the paper, the authors establish several integral representations for the generating functions of the large and little Schröder numbers and for the large and little Schröder numbers.  相似文献   
3.
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   
4.
5.
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   
6.
7.
Journal of Solid State Electrochemistry - A stable suspension of nanopolyaniline (nPANI) particles can be used in various applications instead of a polyaniline film. The electrochemical behavior of...  相似文献   
8.
9.
10.
A simple to use nuclear magnetic resonance analysis method has been tested on complex 1H, 19F, and 13C multiplets. This open-source line-shape analysis method analysis of total lineshape (ANATOLIA)1 provides some significant advantages over traditional assign-iterate methods of NMR spectral analysis by avoiding false minima and progressing optimisation to the global minimum. The target molecules are 1-perfluorotol-4-yl-2-perfluorotol-4-yl-oxymethyl-1H-benzimidazole (molecule-I) and 1-tetrafluoropyrid-4-yl-2-tetrafluoropyrid-4-yl-thio-1H-benzimidazole (molecule-II) which were produced as part of a family of fluorinated drug scaffolds prepared for anticancer and antiparasitic screening. Spectra display significant second-order effects with 1H Δδ = 3.68 and 4.67 Hz for the aromatic hydrogen “triplets”, with 19F 4JAA', 4JBB', 4JXX', and 4JYY' coupling constants range from +4.8 to −14.0 Hz and for 13C-isotopomers 19F Δδ of up to 111.56 Hz. A spin-system of six coupling nuclei (HaHbHcHd FYFY') was analysed in 12 s, a spin-system of nine coupling fluorine nuclei (AA'BB'CCC-YY') was analysed within 2 min, and 10 coupling nuclei (XX'YY'ZZZ-BB'-Hd) was optimised in 6 min using a laptop computer. ANATOLIA was also robust enough to be able to yield accurate spectral values from inaccurate input values. In both compounds, a fluorine–fluorine coupling constant was identified between the two fluoro-aromatic rings (FBB' and FYY') of +4.05 and +4.67 Hz and attributed to a through-space interaction. Ab initio structure optimisations and coupling constant calculations provided useful input data for spectral analysis. A modern 19F nuclear magnetic resonance spectrum of perfluorotoluene (octafluorotoluene) and analysis from 1975 was used as a test data set to assess ANATOLIA.  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