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   1187篇
  免费   23篇
  国内免费   7篇
化学   791篇
晶体学   45篇
力学   24篇
数学   198篇
物理学   159篇
  2023年   4篇
  2022年   6篇
  2021年   15篇
  2020年   14篇
  2019年   21篇
  2018年   15篇
  2017年   25篇
  2016年   28篇
  2015年   20篇
  2014年   27篇
  2013年   66篇
  2012年   51篇
  2011年   74篇
  2010年   52篇
  2009年   47篇
  2008年   66篇
  2007年   62篇
  2006年   63篇
  2005年   59篇
  2004年   56篇
  2003年   43篇
  2002年   42篇
  2001年   16篇
  2000年   17篇
  1999年   11篇
  1998年   19篇
  1997年   12篇
  1996年   26篇
  1995年   15篇
  1994年   16篇
  1993年   13篇
  1992年   17篇
  1991年   16篇
  1990年   13篇
  1989年   18篇
  1988年   14篇
  1987年   15篇
  1986年   13篇
  1985年   18篇
  1984年   11篇
  1983年   13篇
  1982年   9篇
  1981年   10篇
  1980年   5篇
  1979年   4篇
  1977年   8篇
  1976年   6篇
  1975年   3篇
  1913年   2篇
  1907年   2篇
排序方式: 共有1217条查询结果,搜索用时 34 毫秒
1.
In this article, a way to employ the diffusion approximation to model interplay between TCP and UDP flows is presented. In order to control traffic congestion, an environment of IP routers applying AQM (Active Queue Management) algorithms has been introduced. Furthermore, the impact of the fractional controller PIγ and its parameters on the transport protocols is investigated. The controller has been elaborated in accordance with the control theory. The TCP and UDP flows are transmitted simultaneously and are mutually independent. Only the TCP is controlled by the AQM algorithm. Our diffusion model allows a single TCP or UDP flow to start or end at any time, which distinguishes it from those previously described in the literature.  相似文献   
2.
Computational Management Science - In this paper, a new approximation method for a characterization of (weak) Pareto solutions in some class of nonconvex differentiable multiobjective programming...  相似文献   
3.
4OR - In this paper, the class of differentiable semi-infinite multiobjective programming problems with vanishing constraints is considered. Both Karush–Kuhn–Tucker necessary optimality...  相似文献   
4.
5.
In the present research, the synthesis, spectroscopic characterization, and structural investigations of a unique ZnII complex of imine-functionalized polyhedral oligomeric silsesquioxane (POSS) is designed, and hereby described, as a catalyst for the synthesis of cyclic carbonates from epoxides and CO2. The uncommon features of the designed catalytic system is the elimination of the need for a high pressure of CO2 and the significant shortening of reaction times commonly associated with such difficult transformations like that of styrene oxide to styrene carbonate. Our studies have shown that imine-POSS is able to chelate metal ions like ZnII to form a unique coordination complex. The silsesquioxane core and the hindrance of the side arms (their steric effect) influence the construction process of the homoleptic Zn4@POSS-1 complex. The compound was characterized in solution by NMR (1H, 13C, 29Si), ESI-MS, UV/Vis spectroscopy and in the solid state by thermogravimetric/differential thermal analysis (TG-DTA), elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), cross-polarization magic angle spinning (CP MAS) NMR (13C, 29Si) spectroscopy, and X-ray crystallography.  相似文献   
6.
Nonlinear Dynamics - The work is primarily devoted to the peridynamic model elaborated for a solid body made of shape memory alloys (SMAs). The superelasticity effect is taken into consideration as...  相似文献   
7.
8.
Ammonium ionic liquids with the 4-chloro-2-methylphenoxyacetate anion were synthesized and characterized. Physicochemical properties, such as thermal stability, phase transition temperatures, viscosity, density, refractive index, as well as surface activity and herbicidal activity were determined. Improved physicochemical properties suggest a reduced environmental impact of newly formed group of herbicidal ionic liquids (HILs). HILs with a longer substituent can be characterized with better herbicidal activity in comparison with commercial products.  相似文献   
9.
10.
The asymmetric unit of the title salt, C12H24N+·C2H2BrO2, contains a dicyclohexylammonium cation connected to a bromoacetate anion by means of an N—H...O hydrogen bond. In the crystal, the ion pairs assemble via N—H...O interactions, forming zigzag infinite chains parallel to the c axis with the (...H—N—H...O—C—O...)n motif that is considered to be a prerequisite for ensuring gelation properties of secondary ammonium monocarboxylate salts. The title salt was characterized by FT–IR, X‐ray powder diffraction (XRPD), TG–DTA and 1H NMR spectroscopy in solution. Gelation experiments revealed that dicyclohexylammonium bromoacetate forms molecular gels with dimethylformamide and dimethyl sulfoxide. Scanning electron microscopy (SEM) was used to reveal morphological features of dried gels.  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