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   664218篇
  免费   5661篇
  国内免费   1674篇
化学   344338篇
晶体学   10052篇
力学   31748篇
综合类   26篇
数学   83190篇
物理学   202199篇
  2021年   5852篇
  2020年   6485篇
  2019年   7306篇
  2018年   9550篇
  2017年   9746篇
  2016年   13633篇
  2015年   7592篇
  2014年   12651篇
  2013年   29759篇
  2012年   22563篇
  2011年   26961篇
  2010年   20003篇
  2009年   19872篇
  2008年   25246篇
  2007年   24977篇
  2006年   22873篇
  2005年   20524篇
  2004年   18976篇
  2003年   17213篇
  2002年   16946篇
  2001年   18598篇
  2000年   14388篇
  1999年   11134篇
  1998年   9446篇
  1997年   9300篇
  1996年   8711篇
  1995年   7967篇
  1994年   7876篇
  1993年   7509篇
  1992年   8409篇
  1991年   8734篇
  1990年   8437篇
  1989年   8342篇
  1988年   8210篇
  1987年   8057篇
  1986年   7688篇
  1985年   9800篇
  1984年   10137篇
  1983年   8367篇
  1982年   8709篇
  1981年   8298篇
  1980年   7840篇
  1979年   8566篇
  1978年   8817篇
  1977年   8784篇
  1976年   8591篇
  1975年   8144篇
  1974年   7955篇
  1973年   8117篇
  1972年   5849篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
Possibilities of utilization of by-products formed in manufacture of epichlorohydrin are considered. A promising way to utilize wastes from production of epichlorohydrin by synthesis of 2,3-dichloropropene from 1,2,3-trichloropropane is suggested.  相似文献   
63.
64.
65.
66.
Polymer films with a dispersed liquid crystal were prepared by photopolymerization of (meth)acrylic monomers. The electrooptical properties of these films were studied. The influence exerted by the composition of the monomer mixture, cross-linking agents, and chain-transfer agent on the liquid crystal drop size and on the transmission of the polymer-liquid crystal films was examined.  相似文献   
67.
ABSTRACT. We consider autonomous population models under periodic harvesting and population models in periodic environments and seek conditions under which there is an asymptotically stable periodic solution.  相似文献   
68.
Electrohydrodynamic instability in homeotropically oriented nematic samples of 4'-n-octyl-4-cyano-biphenyl and 4'n-alkyloxy-4-cyanobiphenyl, (n = 8.9) have been studied in an a.c. electric field. The domain patterns during the instability in these compounds in a very low frequency a.c. field are very similar to those in a d.c. field. The domain patterns observed at higher frequencies have been identified as 'maltese crosses' or 'crossed isogyres'. The electro-convective 'isotropic' flows near the electrode play an important role in the observed instability.  相似文献   
69.
On-line sample pretreatment by means of the phase-system switching approach is an interesting technique for the analysis of aqueous samples, e.g., plasma, by means of supercritical-fluid chromatography. In order to analyse plasma samples the following analytical procedure is used. The plasma sample is injected on to a short precolumn, which is washed with water and subsequently dried with nitrogen. Next, the solutes are desorbed with the supercritical mobile phase, analysed with packed-column supercritical-fluid chromatography and detected with either a UV detector or a mass spectrometer, equipped with a moving-belt interface. The herbicide diuron is selected as a test compound to study the feasibility of this approach. Using a selective detector the procedure is sufficiently sensitive to detect diuron in plasma, but not appropriate to detect the diuron metabolites in a post-mortem plasma sample. These have been identified with liquid chromatography/mass spectrometry. The detection limit of diuron in plasma using the procedure described is about 30 ng/mL.  相似文献   
70.
Settling of a large solid particle in bioconvection flow caused by gyrotactic microorganisms is investigated. The particle is released from the top of the bioconvection chamber; its settling pattern depends on whether it is released in the centre of the bioconvection plume or at its periphery. The Chimera method is utilized; a subgrid is generated around a moving particle. The method suggested by Liu and Wang (Comput. Fluid 2004; 33 :223–255) is further developed to account for the presence of a moving boundary in the streamfunction‐vorticity formulation using the finite‐difference method. A number of cases for different release positions of the particle are computed. It is demonstrated that bioconvection can either accelerate or decelerate settling of the particle depending on the initial position of the particle relative to the plume centre. It is also shown that the particle impacts bioconvection plume by changing its shape and location in the chamber. Copyright © 2005 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