全文获取类型
收费全文 | 297472篇 |
免费 | 2882篇 |
国内免费 | 855篇 |
专业分类
化学 | 162269篇 |
晶体学 | 4365篇 |
力学 | 12635篇 |
综合类 | 9篇 |
数学 | 34670篇 |
物理学 | 87261篇 |
出版年
2020年 | 2532篇 |
2019年 | 2727篇 |
2018年 | 3466篇 |
2017年 | 3457篇 |
2016年 | 5243篇 |
2015年 | 3333篇 |
2014年 | 5027篇 |
2013年 | 12276篇 |
2012年 | 9746篇 |
2011年 | 12010篇 |
2010年 | 8122篇 |
2009年 | 7797篇 |
2008年 | 11118篇 |
2007年 | 11322篇 |
2006年 | 10652篇 |
2005年 | 9745篇 |
2004年 | 8853篇 |
2003年 | 7975篇 |
2002年 | 7811篇 |
2001年 | 7692篇 |
2000年 | 6021篇 |
1999年 | 4682篇 |
1998年 | 4170篇 |
1997年 | 4166篇 |
1996年 | 4021篇 |
1995年 | 3641篇 |
1994年 | 3764篇 |
1993年 | 3439篇 |
1992年 | 3902篇 |
1991年 | 3888篇 |
1990年 | 3786篇 |
1989年 | 3650篇 |
1988年 | 3773篇 |
1987年 | 3641篇 |
1986年 | 3449篇 |
1985年 | 4688篇 |
1984年 | 4946篇 |
1983年 | 4095篇 |
1982年 | 4290篇 |
1981年 | 4222篇 |
1980年 | 4175篇 |
1979年 | 4133篇 |
1978年 | 4413篇 |
1977年 | 4311篇 |
1976年 | 4353篇 |
1975年 | 4037篇 |
1974年 | 4079篇 |
1973年 | 4232篇 |
1972年 | 2925篇 |
1971年 | 2443篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
David K Bisset 《国际流体数值方法杂志》2002,39(10):961-977
Turbulent flow simulation methods based on finite differences are attractive for their simplicity, flexibility and efficiency, but not always for accuracy or stability. This paper demonstrates that a good compromise is possible with the advected grid explicit (AGE) method. Starting from the same initial field as a previous spectral DNS, AGE method simulations of a planar turbulent wake were carried out as DNS, and then at three levels of reduced resolution. The latter cases were in a sense large‐eddy simulations (LES), although no specific sub‐grid‐scale model was used. Results for the two DNS methods, including variances and power spectra, were very similar, but the AGE simulation required much less computational effort. Small‐scale information was lost in the reduced resolution runs, but large‐scale mean and instantaneous properties were reproduced quite well, with further large reductions in computational effort. Quality of results becomes more sensitive to the value chosen for one of the AGE method parameters as resolution is reduced, from which it is inferred that the numerical stability procedure controlled by the parameter is acting in part as a sub‐grid‐scale model. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
52.
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
53.
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
54.
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
55.
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
56.
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
57.
The direct regioselective C–H arylation of 3-methoxythiophene and 3,4-ethylenedioxythiophene (EDOT) was performed successfully under ‘Heck-type’ experimental conditions. This novel synthetic methodology has been used to prepare in a more simple way a series of oligothiophenes interesting for the electronic industry to build new synthetic organic materials. 相似文献
58.
The synthesis of rigid spirocyclic bislactams derived from pyroglutamic acid has been established. 相似文献
59.
60.