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   374895篇
  免费   2831篇
  国内免费   990篇
化学   190992篇
晶体学   6100篇
力学   18555篇
综合类   15篇
数学   42668篇
物理学   120386篇
  2021年   3229篇
  2020年   3410篇
  2019年   4095篇
  2018年   5588篇
  2017年   5549篇
  2016年   7658篇
  2015年   4225篇
  2014年   7186篇
  2013年   16350篇
  2012年   12873篇
  2011年   15345篇
  2010年   11390篇
  2009年   11436篇
  2008年   14230篇
  2007年   14270篇
  2006年   13171篇
  2005年   11774篇
  2004年   11084篇
  2003年   9920篇
  2002年   9810篇
  2001年   10995篇
  2000年   8378篇
  1999年   6375篇
  1998年   5312篇
  1997年   5364篇
  1996年   4958篇
  1995年   4516篇
  1994年   4464篇
  1993年   4272篇
  1992年   4846篇
  1991年   4963篇
  1990年   4801篇
  1989年   4671篇
  1988年   4641篇
  1987年   4625篇
  1986年   4368篇
  1985年   5581篇
  1984年   5926篇
  1983年   4899篇
  1982年   5019篇
  1981年   4969篇
  1980年   4665篇
  1979年   5059篇
  1978年   5140篇
  1977年   5301篇
  1976年   5371篇
  1975年   4990篇
  1974年   4874篇
  1973年   5105篇
  1972年   3595篇
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
91.
An interconnection strategy with built-in adaptive controllersis presented which achieves synchronization of scalar linearsystems: the closed-loop network forces all outputs to followthe same signal asymptotically while maintaining the open-loopcharacteristics. In the design of the output feedback controllers,no knowledge of system parameters is assumed, but each systemmust have the same poles and be high-gain-stable. The proofof the main theorem relies critically on derived systems-theoreticresults and the special system topology as a network of interconnectedsystems. The topology is explained by first solving the simplerproblem of signal synchronization.  相似文献   
92.
Studies in the field of radical copolymerization of N-vinylsuccinimide were summarized, theeffect of the reaction medium on the process kinetics was examined. Factors governing the relative activity ofthe monomers were revealed, and ways to control the reactivity of N-vinylsuccinimide in binary copolymerizations were suggested.  相似文献   
93.
94.
The kinetics of hydrogen peroxide decomposition in a guaiacol solution, catalyzed by potassium hexacyanoferrate(II), were studied. The reaction mainly follows the pathway of guaiacol hydroxylation. The reaction order is 1 with respect to H2O2, 0.5 with respect to hexacyanoferrate, and from 0.4 to 0 with respect to guaiacol (the latter parameter decreases with increasing guaiacol concentration). The apparent activation energy is 105 kJ mol- 1. A kinetic scheme of the process was proposed. An expression consistent with the experiment was obtained for the rate of hydrogen peroxide decomposition in the presence of guaiacol, catalyzed by hexacyanoferrate(II).  相似文献   
95.
The influence of the charge of a metal cation and the nature of a coagulant on the recovery of butadiene-styrene rubber and properties of rubber stocks and vulcanizates was examined.  相似文献   
96.
A formulation of an implicit characteristic-flux-averaging method for the unsteady Euler equations with real gas effects is presented. Incorporation of a real gas into a general equation of state is achieved by considering the pressure as a function of density and specific internal energy. The Ricmann solver as well as the flux-split algorithm are modified by introducing the pressure derivatives with respect to density and internal energy. Expressions for calculating the values of the flow variables for a real gas at the cell faces are derived. The Jacobian matrices and the eigenvectors are defined for a general equation of state. The solution of the system of equations is obtained by using a mesh-sequencing method for acceleration of the convergence. Finally, a test case for a simple form of equation of state displays the differences from the corresponding solution for an ideal gas.  相似文献   
97.
If a given finite protoset, together with a given finite matching rule, gives rise to at most countably many different tilings ofd-dimensional space, then at least one of them is periodic. This research was supported in part by the SFB 343 “Diskrete Strukturen in der Mathematik” at Bielefeld University and the Russian Foundation for Fundamental Research.  相似文献   
98.
Methods and schemes to inspect the EUV mirror shape are developed on the basis of a point diffraction interferometer with computer processing of interferograms. A measurement accuracy to within 0.001 of a wavelength in the visual range is achieved.  相似文献   
99.
The kinetics of the formation of poly(carbosiloxane), as well as of alkyl-substituted poly(siloxane), by Karstedt's catalyst catalyzed hydrosilylation were investigated. Linear poly(carbosiloxane), poly[(1,1,3,3-tetramethyldisiloxanyl)ethylene], (PTMDSE), was obtained by hydrosilylation of 1,3-divinyltetramethyldisiloxane (DVTMDS) and 1,1,3,3-tetramethyldisiloxane (TMDS), while alkyl-substituted poly(siloxane), poly(methyldecylsiloxane), (PMDS), was synthesized by hydrosilylation of poly(methylhydrosiloxane) (PMHS) and 1-decene. To investigate the kinetics of PTMDSE formation, two series of experiments were performed at reaction temperatures ranging from 25 to 56 °C and with catalyst concentrations ranging from 7.0 × 10−6 to 3.1 × 10−5 mol Pt/mol CHCH2. A series of experiments was performed at reaction temperatures ranging from 28 to 48 °C, with catalyst concentrations of 7.0 ×10−6 mol of Pt per mol of CHCH2, when kinetics of PMDS formation was investigated. All reactions were carried out in bulk, with equimolar amounts of the reacting Si H and CHCH2 groups. The course of the reactions was monitored by following the disappearance of the Si H bands using quantitative infrared spectroscopy. The results obtained showed typical first order kinetics for the PTMDSE formation, consistent with the proposed reaction mechanism. In the case of PMDS an induction period occurred at lower reaction temperatures, but disappeared at 44 °C and the rate of Si H conversion also started to follow the first-order kinetics. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2246–2258, 2007  相似文献   
100.
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