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   2405篇
  免费   79篇
  国内免费   8篇
化学   1475篇
晶体学   8篇
力学   112篇
数学   450篇
物理学   447篇
  2023年   25篇
  2022年   33篇
  2021年   78篇
  2020年   44篇
  2019年   59篇
  2018年   42篇
  2017年   40篇
  2016年   80篇
  2015年   65篇
  2014年   68篇
  2013年   127篇
  2012年   161篇
  2011年   152篇
  2010年   106篇
  2009年   111篇
  2008年   131篇
  2007年   142篇
  2006年   147篇
  2005年   130篇
  2004年   108篇
  2003年   69篇
  2002年   64篇
  2001年   32篇
  2000年   26篇
  1999年   22篇
  1998年   26篇
  1997年   25篇
  1996年   26篇
  1995年   22篇
  1994年   16篇
  1993年   18篇
  1992年   15篇
  1991年   10篇
  1990年   15篇
  1989年   13篇
  1987年   10篇
  1986年   12篇
  1985年   21篇
  1984年   25篇
  1983年   11篇
  1982年   21篇
  1981年   19篇
  1980年   19篇
  1979年   9篇
  1978年   10篇
  1977年   13篇
  1976年   10篇
  1975年   11篇
  1973年   11篇
  1972年   8篇
排序方式: 共有2492条查询结果,搜索用时 78 毫秒
171.
The diffusive behavior for a system of directed polymers in a random environment was first rigorously discussed by Imbrie and Spencer, and then by Bolthausen. By means of some basic properties of martingales we extend some results due to Imbrie and Spencer concerning the asymptotic behaviour of the mean square displacement. We also obtain a Wiener process behaviour with probability one for this system. Bolthausen already used some martingale limit theorems to prove a central limit theorem for this system.Partly supported by AvH Foundation.  相似文献   
172.
A digraphD is randomlyn-cyclic (n≥3) if for each vertexv ofD, every (directed) path with initial vertexv and having length at mostn−1 can be extended to av−v (directed) cycle of lengthn. Several results related to and examples of randomlyn-cyclic digraphs are presented. Also, all randomlyn-cyclic digraphs forn=3, 4, and 5 are determined. Research supported by a Western Michigan University faculty research fellowship. Research supported in part by a College of Arts and Sciences and Graduate College research assistantship from Western Michigan University.  相似文献   
173.
174.
Chemical evidence is given that the title photo-reactions proceed via hydrogen abstraction by the photo-excited base from the alcohol in neutral medium and via electron-transfer process between the photo-excited base and the alcohol in hydrochloric acid acidified medium.  相似文献   
175.
A new metabolite, 3,6-dimethyl-4,10-dihydroxy-2-oxaspiro[4.5]dec-7-en-1,9-dione (1a), was isolated from a strain of Mycosphaerella rosigena grown on potato-agar medium. The structure was determined on the basis of chemical and spectroscopic evidence and confirmed by X-ray analysis.  相似文献   
176.
Sets of electrooptical parameters (eop's), suitable for longer n-paraffins and less constrained than those already used to fit the IR intensities of CH4 and C2H6 and their deuterated derivatives, are presented and discussed. The technique adopted in the least-squares refinement of eop's from experimental data is discussed in detail.  相似文献   
177.
The anodic chlorination of aromatic compounds in anhydrous acetic acid has been further investigated. Evidence has been found for two different methods of electrochemical chlorination, in the systems Cl2/aromatic compounds and Cl?/aromatic compounds. These methods were also compared with the uncatalyzed chemical chlorination reaction. The yields of monochlorinated products and the related isometric distributions were taken into account. Since the isomeric distributions are equal with chemical and electrochemical chlorination methods, the formation of the same intermediate was proposed for both.  相似文献   
178.
In this article the adsorption of 3-methylthiophene on planar and nanoparticle Au surfaces is investigated. The resulting systems are compared with a benchmark system based on 1-decanethiol. The characterization data collected evidence the formation of a packed 3-methylthiophene SAM on the planar surface. In particular, spectroscopic investigations suggest that 3-methylthiophene aromatic system is not adsorbed on the surface through the pi-electron system but rather through the S atom alone. On the other hand, the behavior of 3-methylthiophene on nanoparticle surfaces is notably different from that of the alkanethiol. Only a limited fraction of the surface of Au nanoparticles results to be actually coated after purification; this notwithstanding, the nanoparticle growth seems to be strongly influenced by the presence of such a labile encapsulating agent.  相似文献   
179.
This paper describes ArQiologist, a Web-based tool that integrates chemical, analytical, biological, and computational data to facilitate decision support for lead optimization at ArQule. It features an easy-to-use graphical query builder that allows queries to be saved, reused, and shared by researchers. Query results can be viewed with built-in data browsers or exported with structures to external applications such as Microsoft Excel or Spotfire for further analysis.  相似文献   
180.
We prove the existence of positive symmetric solutions to the semilinear elliptic problem
in both the radial case N = k ≥ 3 and the cylindrical case N ≥ k + 3 ≥ 6. The potential V is measurable, positive and it is only required to satisfy a mild integrability condition. The nonlinearity is continuous and has a doublepower behavior, super-critical near the origin and sub-critical at infinity. If f is odd, we show that the radial problem has infinitely many solutions. In proving these results we exploit the compactness of suitable restrictions of the embedding Supported by MIUR, project “Variational Methods and Nonlinear Differential Equations”.  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