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   216203篇
  免费   1584篇
  国内免费   639篇
化学   118321篇
晶体学   3276篇
力学   8383篇
综合类   6篇
数学   23428篇
物理学   65012篇
  2020年   1982篇
  2019年   2272篇
  2018年   3210篇
  2017年   3117篇
  2016年   4283篇
  2015年   2383篇
  2014年   3838篇
  2013年   9290篇
  2012年   6927篇
  2011年   8487篇
  2010年   6108篇
  2009年   5966篇
  2008年   8180篇
  2007年   8246篇
  2006年   7669篇
  2005年   6965篇
  2004年   6194篇
  2003年   5662篇
  2002年   5525篇
  2001年   5959篇
  2000年   4709篇
  1999年   3480篇
  1998年   3013篇
  1997年   3043篇
  1996年   2841篇
  1995年   2332篇
  1994年   2435篇
  1993年   2468篇
  1992年   2611篇
  1991年   2665篇
  1990年   2563篇
  1989年   2545篇
  1988年   2471篇
  1987年   2442篇
  1986年   2360篇
  1985年   3047篇
  1984年   3199篇
  1983年   2563篇
  1982年   2833篇
  1981年   2707篇
  1980年   2510篇
  1979年   2727篇
  1978年   2835篇
  1977年   2859篇
  1976年   2839篇
  1975年   2693篇
  1974年   2667篇
  1973年   2811篇
  1972年   1878篇
  1967年   1830篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Approximate properties of variable measures compose a base of the two-scale convergence method with respect to a variable measure, which is used in averaging on periodic thin and composite structures. The paper gives a survey of methods for verifying approximate properties. The main focus is on studying composite measures, which have been little studied. __________ Translated from Sovremennaya Matematika i Ee Prilozheniya (Contemporary Mathematics and Its Applications), Vol. 16, Partial Differential Equations, 2004.  相似文献   
132.
133.
134.
The paper considers the performance of multi-frequency, multi-channel, free field sound cancelling systems for the reduction of discrete frequency and periodic noise. The approach uses a method of directional active noise control. Large sound reductions from these systems have been made possible through: (a) synthetically generating the cancelling sound and synchronizing with the primary source; (b) automatic alignment of all stability regions of the control system and; (c) avoiding instability produced by these multi-channel systems.  相似文献   
135.
The nucleon-antinucleon (NN) annihilation process provides a fertile testing ground for microscopic hadron exchange and/or quark models. TheNN system offers a rich ensemble of annihilation channels, whose relative BRs provide strong constraints on dynamical models. Recent experiments show that values of BRs display a significant dependence onL, S andI. These dynamical selection rules,i.e. the suppression of transitions alloweda priori by conservation of quantum numbers, provide key signatures of the annihilation mechanism, and suggest dynamical content beyond simple statistical or flavour symmetry models.  相似文献   
136.
Translated from Vychislitel'nye Kompleksy i Modelirovanie Slozhnykh Sistem, pp. 98–106, Moscow State University, 1989.  相似文献   
137.
Nonlinear (at the second-harmonic frequency of the incident light) optical reflection by two-dimensional magnetic superstructures is theoretically studied. A square lattice of magnetic dots and a hexagonal lattice of magnetic bubbles (cylindrical magnetic domains) are considered. Because the periods of these structures are comparable with the wavelengths of the fundamental and the second-harmonic radiation, it would be possible to observe diffraction at the second-harmonic frequency. A polarization analysis of nonlinearly diffracted radiation is performed and the numbers of observable diffraction orders for the above structures are estimated. Received: 10 January 2002 / Published online: 11 June 2002  相似文献   
138.
We investigate some issues of minimax estimation of spectral intensity of acoustic sources in cases when the noise and the spectral amplitudes satisfy quadratic constraints. Recursive minimax filters are obtained.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 58, pp. 116–119, 1986.  相似文献   
139.
140.
A simple and precise high performance liquid chromatographic method for the determination of mexiletine in human serum or plasma is described. Following addition of N-propionylprocainamide as internal standard the specimens are extracted, under basic conditions, into methylene chloride. After removal of the aqueous layer the drug is back-extracted into dilute acid, which is then injected directly for analysis. The extraction efficiency is 79% for both mexiletine and internal standard, and the assay is linear to 4 mg/L (twice upper therapeutic concentration). Inter-run coefficients of variation are 3.0% or less. The relative retention time of mexiletine to internal standard averages 1.3. An adaptation of this method is described for an alternate application to the analysis of tocainide, procainamide and N-acetylprocainamide.  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