全文获取类型
收费全文 | 409810篇 |
免费 | 3906篇 |
国内免费 | 1301篇 |
专业分类
化学 | 220269篇 |
晶体学 | 6148篇 |
力学 | 18529篇 |
综合类 | 16篇 |
数学 | 46107篇 |
物理学 | 123948篇 |
出版年
2020年 | 3098篇 |
2019年 | 3367篇 |
2018年 | 4153篇 |
2017年 | 4148篇 |
2016年 | 6561篇 |
2015年 | 4376篇 |
2014年 | 6492篇 |
2013年 | 17324篇 |
2012年 | 13417篇 |
2011年 | 16554篇 |
2010年 | 11240篇 |
2009年 | 11138篇 |
2008年 | 15366篇 |
2007年 | 15619篇 |
2006年 | 14762篇 |
2005年 | 13532篇 |
2004年 | 12282篇 |
2003年 | 10994篇 |
2002年 | 10848篇 |
2001年 | 12094篇 |
2000年 | 9349篇 |
1999年 | 7157篇 |
1998年 | 5990篇 |
1997年 | 5960篇 |
1996年 | 5696篇 |
1995年 | 5196篇 |
1994年 | 5263篇 |
1993年 | 4843篇 |
1992年 | 5545篇 |
1991年 | 5562篇 |
1990年 | 5233篇 |
1989年 | 5113篇 |
1988年 | 5199篇 |
1987年 | 5059篇 |
1986年 | 4781篇 |
1985年 | 6585篇 |
1984年 | 6848篇 |
1983年 | 5674篇 |
1982年 | 5919篇 |
1981年 | 5775篇 |
1980年 | 5677篇 |
1979年 | 5652篇 |
1978年 | 5990篇 |
1977年 | 5911篇 |
1976年 | 5929篇 |
1975年 | 5589篇 |
1974年 | 5517篇 |
1973年 | 5750篇 |
1972年 | 3877篇 |
1971年 | 3065篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
A successful application of ultrasound Doppler velocimetry in liquid sodium flows is described. To obtain sufficient Doppler
signals, different problems had to be solved: the transmission of the ultrasonic beam through the channel wall made of stainless
steel, the acoustic coupling between the transducer and the channel wall, and the wetting of the inner surface of the wall
by the liquid metal, respectively. A sodium flow in a square duct exposed to a transverse magnetic field is investigated.
In accordance with the existing knowledge about MHD channel flows, we found that the velocity profiles modified to a M-shape
owing to the effect of an inhomogeneous magnetic field.
Received: 12 June 2001/Accepted: 27 October 2001 相似文献
42.
43.
C. Kimberling 《Aequationes Mathematicae》2002,63(1-2):158-167
44.
Nuclear Magnetic Resonance (NMR) was used to investigate the extrusion behaviour of PTFE pastes in a ram extruder. By means
of 1H-NMR imaging (MRI) it is possible to determine the local proton density and therefore, the local fluid concentration. The
19F-MRI provides the local solid concentration. Thus the local saturation and the local porosity can be calculated with the
information of the local fluid and solid concentration. Furthermore displacement profiles can be derived from NMR images by
means of correlation techniques without any preparation or marking of the pastes.
Received: 8 May 2000 Accepted: 1 May 2001 相似文献
45.
Two families of functions constructed by a system of n scalar Muckenhoupt weights are studied. Criteria are given under which these families are unconditional bases. From the point of view of the spectral operator theory, the problem is reduced to the study of the structure of n-dimensional perturbations of the integration operator. Weighted estimates for the Hilbert transform in the spaces of vector-functions are applied to construct an operator mapping functions of the studied families to vector-valued rational functions. The concept of the Carleson series is used in the study of the following problem: when do vector-valued rational functions form an unconditional basis? Bibliography: 8 titles. 相似文献
46.
A simple scheme is developed for treatment of vertical bed topography in shallow water flows. The effect of the vertical step on flows is modelled with the shallow water equations including local energy loss terms. The bed elevation is denoted with zb‐ for the left and zb+ for the right values at each grid point, hence exactly representing a discontinuity in the bed topography. The surface gradient method (SGM) is generalized to reconstruct water depths at cell interfaces involving a vertical step so that the fluxes at the cell interfaces can accurately be calculated with a Riemann solver. The scheme is verified by predicting a surge crossing a step, a tidal flow over a step and dam‐break flows on wet/dry beds. The results have shown good agreements compared with analytical solutions and available experimental data. The scheme is efficient, robust, and may be used for practical flow calculations. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
47.
In the following we find all of the three-dimensional flat spacetimes which are static and rotationally symmetric. 相似文献
48.
A method using third order moments for estimating the regression coefficients as well as the latent state scores of the reduced-rank regression model when the latent variable(s) are non-normally distributed is presented in this paper. It is shown that the factor analysis type indeterminacy of the regression coefficient matrices is eliminated. A real life example of the proposed method is presented. Differences of this solution with the reduced-rank regression eigen solution are discussed. 相似文献
49.
E. V. Zakharov A. G. Davydov Yu. V. Pimenov G. M. Tikhonov 《Computational Mathematics and Modeling》1991,2(1):79-84
Translated from Chislennye Metody Resheniya Obratnykh Zadach Matematicheskoi Fiziki, pp. 119–127. 相似文献
50.
We demonstrate a method that permits to obtain generalized solutions for some quasilinear equations and systems of hyperbolic
type. The corresponding variational principle is constructed using the theory of equilibrium of a potential in an external
field.
Dedicated to the memory of B. M. Levitan
Supported by RFBR grants Nos. 05-01-00522 and NSh-1551.2003.1, by Program No. 1 of the Branch of Mathematics, Russian Academy
of Sciences, and by INTAS project No. 03-51-6637. 相似文献