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   217423篇
  免费   1604篇
  国内免费   638篇
化学   119062篇
晶体学   3276篇
力学   8438篇
综合类   6篇
数学   23553篇
物理学   65330篇
  2020年   1989篇
  2019年   2280篇
  2018年   3219篇
  2017年   3134篇
  2016年   4298篇
  2015年   2397篇
  2014年   3846篇
  2013年   9358篇
  2012年   6994篇
  2011年   8562篇
  2010年   6139篇
  2009年   5956篇
  2008年   8203篇
  2007年   8296篇
  2006年   7711篇
  2005年   7034篇
  2004年   6245篇
  2003年   5711篇
  2002年   5560篇
  2001年   5967篇
  2000年   4731篇
  1999年   3503篇
  1998年   3031篇
  1997年   3055篇
  1996年   2862篇
  1995年   2351篇
  1994年   2452篇
  1993年   2487篇
  1992年   2626篇
  1991年   2690篇
  1990年   2587篇
  1989年   2550篇
  1988年   2485篇
  1987年   2448篇
  1986年   2377篇
  1985年   3059篇
  1984年   3217篇
  1983年   2574篇
  1982年   2844篇
  1981年   2726篇
  1980年   2527篇
  1979年   2758篇
  1978年   2851篇
  1977年   2874篇
  1976年   2853篇
  1975年   2703篇
  1974年   2694篇
  1973年   2839篇
  1972年   1886篇
  1967年   1835篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
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   
122.
Translated from Vychislitel'nye Kompleksy i Modelirovanie Slozhnykh Sistem, pp. 98–106, Moscow State University, 1989.  相似文献   
123.
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   
124.
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   
125.
126.
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   
127.
A new metastable liquid-crystalline phase BPS was observed in pure chiral compounds. The BPS is transformed reversibly from the supercooled BPI and is thermodynamically stable with respect to the BPI and metastable to the cholesteric phase. Rhombic single crystals of the BPS probably indicate a cubic lattice structure as in other BPs, but the lattice constant exhibits an anomalous temperature dependence.  相似文献   
128.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 47–55, March, 1991.  相似文献   
129.
A new formalism is presented for the theory of scanning LLL x-ray interferometry, which takes account also of the amount of x-ray absorption and of crystal yawing. It is based on the Takagi approach to the dynamical theory of x-ray diffraction and uses, to a great extent, the formalism of quantum mechanics, in order to reduce the algebraic complexity of the Ewald-von Laue approach. The formalism presented here is an easy-to-handle tool for the study of x-ray propagation in multicrystal systems and for the investigation into deviations of the travelling-fringe period from the spacing of diffracting planes, as it explains how interference features change when moving in paramater space.  相似文献   
130.
A system for display of magnetic resonance (MR) spectroscopic imaging (SI) data is described which provides for efficient review and analysis of the multidimensional spectroscopic and spatial data format of this technique. Features include the rapid display of spectra from selected image voxels, formation of spectroscopic images, spectral and image data processing operations, methods for correlating spectroscopic image data with high resolution 1H MR images, and hardcopy facilities. Examples are shown for 31P and 1H spectroscopic imaging studies obtained in human and rat brain.  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