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   402279篇
  免费   1773篇
  国内免费   729篇
化学   159645篇
晶体学   5407篇
力学   23465篇
综合类   3篇
数学   73309篇
物理学   113740篇
无线电   29212篇
  2021年   3377篇
  2020年   3801篇
  2019年   4667篇
  2018年   18260篇
  2017年   17991篇
  2016年   15272篇
  2015年   4516篇
  2014年   7688篇
  2013年   13096篇
  2012年   14603篇
  2011年   23652篇
  2010年   17211篇
  2009年   17546篇
  2008年   19197篇
  2007年   21503篇
  2006年   11059篇
  2005年   10890篇
  2004年   10791篇
  2003年   10659篇
  2002年   9781篇
  2001年   8578篇
  2000年   7038篇
  1999年   5263篇
  1998年   5039篇
  1997年   4847篇
  1996年   4268篇
  1995年   3750篇
  1994年   3775篇
  1993年   3770篇
  1992年   3679篇
  1991年   4082篇
  1990年   4131篇
  1989年   4134篇
  1988年   3830篇
  1987年   3851篇
  1986年   3532篇
  1985年   4043篇
  1984年   4265篇
  1983年   3613篇
  1982年   3800篇
  1981年   3480篇
  1980年   3254篇
  1979年   3715篇
  1978年   3785篇
  1977年   3922篇
  1976年   3989篇
  1975年   3732篇
  1974年   3574篇
  1973年   3751篇
  1972年   3223篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
We study the variety of divisors of a polynomial operator bundle and the action of the natural symmetry group on it—the group of invertible operators that commute with the linearizer of the bundle. It is established that the orbits can be parametrized by standard Young tableaux whose form and weight depend on the spectral parameters of the bundle and its divisors. We consider the question of existence of factorizations with prescribed spectral characteristics. The correspondence is given in terms of the Littlewood-Richardson combinatorial rule.Translated fromMatematicheskie Metody i Fiziko-Mekhanicheskie Polya, Issue 34, 1991, pp. 8–12.  相似文献   
972.
973.
974.
Light transmission of nematic liquid crystals dispersed in a polymeric matrix is investigated. The paper gives a theoretical analysis of light transmission by the liquid crystal-polymer and liquid crystaldye-polymer systems based on determination of the total cross section of extinction. The mathematical model is considered in the anomalous diffraction approximation. The theoretical calculations are in good agreement with experimental data obtained for films based on cyanodiphenyl dispersed into a polyvinyl acetate matrix.Institute of Theoretical and Applied Mechanics, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 6, pp. 118–122, November–December, 1993.Translated by L. Chernomorskaya  相似文献   
975.
A method is proposed for determining the technological residual stresses in glass shells of revolution based on the solution of inverse problems of shell theory with proper stresses and the use of experimental data obtained by the photoelastic method. Translated fromMatematicheskie Metody i Fiziko-Mekhanicheskie Polya, Issue 35, 1992, pp. 100–105.  相似文献   
976.
A gas-discharge gold-vapor laser on self-terminating transitions with operating wavelength λ=312.2 nm has been used to develop a highly efficient system for image transfer. An optical scheme and all its parameters have been chosen optimal for image quality. It has been found both theoretically and experimentally that the best results on micron-structure image transfer are obtained with 2–5-times image reduction. Various types of masks have been used. A 1-µm structure has been resolved due to the choice of optimal exposure time of 10 ms under a period of pulse repetition (0.6 – 0.8) ms; in this case, the minimal fringe dimension was ≈2 µm with an image dimension of 2 mm for a laser tube 1.8 cm in diameter.  相似文献   
977.
Energy dispersive X-ray fluorescence spectrometry with radionuclide excitation has been applied to determine As, Cu, Fe, Pb, Rb, Sr, Ti, Zn and Zr in inorganic pollutants of gravitation dust sediments. Application of this technique required a complete optimization including sampling and their preparation for analysis and evaluation. This method has been finally used to analyze series of samples of dust sediments.  相似文献   
978.
Nucleon polarizations are examined in the hypernucleus decays5He, 4He + p + ,4H, 3H + p + , and4H, 3He + n + . The effect of the strong interaction in the final state is taken into account. A significant role is predicted for the resonance interaction in the p-4He system in the formation of the proton polarization in the5He decay. It is also shown that in the4H, 3H + p + decay the proton-polarization components should attain significant magnitudes, while in the charge-exchange decay4H, 3He + n + , the neutron polarization is expected to be not too large.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 100–103, October, 1988.  相似文献   
979.
On the basis of numerical calculations and experimental studies we analyze the possibilities of measuring the electrophysical parameters of indium phosphide by means of infrared reflection spectra at wavelengths ranging from 5 to 200 m. We demonstrate that contactless nondestructive measurements of the electron density in the range 1016–1020 cm–3 can be made with a relative error not exceeding 15%, and of mobility with a relative error not exceeding 25%. A nomogram method is presented for rapid conversion of data from infrared reflection spectra into the parameters being measured.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 22–27, January, 1988.  相似文献   
980.
The results of a calculation of the characteristics of fluctuations in the absorption of energy of electrons and gamma rays in small sensitive volumes of a material in electronic equilibrium are presented. The calculations were performed by the method developed in [1]. The efficiency and accuracy of the method are demonstrated by comparisons with the experimental results and direct numerical simulation. The experience gained in using the method is analyzed. The main numerical result of this work is a table of coefficients enabling the calculation of the probability of the absorption of energy and the first two moments of the energy absorbed in spherical regions with radii of 1, 2, 4, and 8 m, starting only from the electronic spectrum in these regions, for water absorbers with arbitrary shape and arbitrary electronic or photonic sources with energies up to 1 MeV.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 77–82, February, 1988.  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