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   465260篇
  免费   2293篇
  国内免费   928篇
化学   204915篇
晶体学   6592篇
力学   28911篇
综合类   9篇
数学   87086篇
物理学   140968篇
  2020年   4162篇
  2019年   5056篇
  2018年   17510篇
  2017年   17398篇
  2016年   15331篇
  2015年   5225篇
  2014年   8701篇
  2013年   16118篇
  2012年   16454篇
  2011年   25101篇
  2010年   17983篇
  2009年   18605篇
  2008年   20897篇
  2007年   22705篇
  2006年   13063篇
  2005年   12407篇
  2004年   12264篇
  2003年   11919篇
  2002年   11283篇
  2001年   10693篇
  2000年   8385篇
  1999年   6321篇
  1998年   5849篇
  1997年   5610篇
  1996年   5194篇
  1995年   4577篇
  1994年   4578篇
  1993年   4597篇
  1992年   4638篇
  1991年   5133篇
  1990年   5047篇
  1989年   5106篇
  1988年   4750篇
  1987年   4828篇
  1986年   4518篇
  1985年   5398篇
  1984年   5589篇
  1983年   4759篇
  1982年   5013篇
  1981年   4669篇
  1980年   4331篇
  1979年   4967篇
  1978年   5137篇
  1977年   5314篇
  1976年   5466篇
  1975年   5072篇
  1974年   4896篇
  1973年   5156篇
  1972年   4320篇
  1971年   3952篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
Curcumin, a naturally occurring, intensely yellow dye extracted from the spice turmeric, is an efficient photosensitizer for diaryliodonium salt photoinitiators at wavelengths ranging from 340 to 535 nm. With curcumin as a photosensitizer, it is possible to carry out the cationic photopolymerization of a wide variety of epoxide, oxetane, and vinyl monomers with long‐wavelength UV and visible light. An example of the photopolymerization of an epoxide monomer with ambient solar irradiation is provided. Several other curcumin analogues were synthesized, and their use as photosensitizers is examined. With such photosensitizers, the range of spectral sensitivity can be extended well into the visible region of the electromagnetic spectrum. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5217–5231, 2005  相似文献   
93.
94.
Analysis of stochastic processes governed by the Langevin equation is discussed. The analysis is based on a general method for non-parametric estimation of deterministic and random terms of the Langevin equation directly from given data. Separate estimation of the terms corresponds to the decomposition of process dynamics into deterministic and random components. Part I of the paper presented several possibilities for qualitative and quantitative analysis of process dynamics based on such decomposition. In Part II, some of these analysis possibilities are applied to experimental datasets from metal cutting and laser-beam welding.  相似文献   
95.
Aeroacoustic resonant oscillations (aeolian tones) are studied for flow past two plates forming a cross in a square cross section channel. Possible oscillation modes are classified on the basis of admissible symmetry groups and the existence of the modes is proved. The infinite linear system of equations for these modes obtained by the sewing method was simplified and studied numerically. Curves of eigenfrequency versus plate length are constructed. The form of the eigenfunctions is studied.  相似文献   
96.
Biographical information on the eminent Soviet geometer Boris Lukich Laptev (4/23/05–1/15-89) is given as well as a survey of his research in the areas of differential geometry and history of mathematics.Translated from Itogi Nauki i Tekhniki, Seriya Problemy Geometrii, Vol. 21, pp.27–42, 1989.  相似文献   
97.
98.
The contribution of electrons moving at large angles to the barrier junction plane to the tunnel current is calculated. This contribution turns out to be small only if the Fermi energy of the electrons equals several electron volts. Otherwise, specifically, when the Fermi energy is no higher than 1–2 eV, this contribution dominates in high and thin potential barriers. It is found that the tunnel magnetic resistance in ferromagnet-insulator-ferromagnet contacts correlates with this contribution. It is this correlation that is responsible for a decrease in this contribution as the potential barriers get lower and thicker.  相似文献   
99.
Rostov-on-Don. Translated from Sibirskii Matematicheskii Zhurnal, Vol. 30, No. 4, pp. 69–75, July–August, 1989.  相似文献   
100.
An infinite row of periodically spaced, identical rigid circularcylinders is excited by an acoustic line source which is parallelto the generators of the cylinders. A method for calculatingthe scattered field accurately and efficiently is presented.When the cylinders are sufficiently close together, Rayleigh–Blochsurface waves that propagate energy to infinity along the arrayare excited. An expression is derived which enables the amplitudesof these surface waves to be computed without requiring thesolution to the full scattering problem.  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