全文获取类型
收费全文 | 215703篇 |
免费 | 1575篇 |
国内免费 | 627篇 |
专业分类
化学 | 118143篇 |
晶体学 | 3272篇 |
力学 | 8359篇 |
综合类 | 6篇 |
数学 | 23330篇 |
物理学 | 64795篇 |
出版年
2020年 | 1974篇 |
2019年 | 2266篇 |
2018年 | 3206篇 |
2017年 | 3118篇 |
2016年 | 4275篇 |
2015年 | 2384篇 |
2014年 | 3826篇 |
2013年 | 9273篇 |
2012年 | 6906篇 |
2011年 | 8460篇 |
2010年 | 6091篇 |
2009年 | 5932篇 |
2008年 | 8151篇 |
2007年 | 8225篇 |
2006年 | 7648篇 |
2005年 | 6955篇 |
2004年 | 6185篇 |
2003年 | 5647篇 |
2002年 | 5503篇 |
2001年 | 5942篇 |
2000年 | 4684篇 |
1999年 | 3473篇 |
1998年 | 3009篇 |
1997年 | 3035篇 |
1996年 | 2825篇 |
1995年 | 2322篇 |
1994年 | 2422篇 |
1993年 | 2451篇 |
1992年 | 2596篇 |
1991年 | 2659篇 |
1990年 | 2561篇 |
1989年 | 2533篇 |
1988年 | 2465篇 |
1987年 | 2437篇 |
1986年 | 2357篇 |
1985年 | 3039篇 |
1984年 | 3197篇 |
1983年 | 2559篇 |
1982年 | 2829篇 |
1981年 | 2704篇 |
1980年 | 2504篇 |
1979年 | 2719篇 |
1978年 | 2833篇 |
1977年 | 2856篇 |
1976年 | 2832篇 |
1975年 | 2687篇 |
1974年 | 2665篇 |
1973年 | 2810篇 |
1972年 | 1875篇 |
1967年 | 1830篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
E. Lodi Rizzini 《La Rivista del Nuovo Cimento (1969-1970)》1992,15(8):1-29
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.
E. G. Ryabova 《Computational Mathematics and Modeling》1992,3(1):30-35
Translated from Vychislitel'nye Kompleksy i Modelirovanie Slozhnykh Sistem, pp. 98–106, Moscow State University, 1989. 相似文献
123.
I.L. Lyubchanskii N.N. Dadoenkova M.I. Lyubchanskii E.A. Shapovalov A.E. Zabolotin K.Y. Guslienko T. Rasing 《Applied physics. B, Lasers and optics》2002,74(7-8):711-714
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