全文获取类型
收费全文 | 294275篇 |
免费 | 2216篇 |
国内免费 | 900篇 |
专业分类
化学 | 151363篇 |
晶体学 | 4403篇 |
力学 | 13233篇 |
综合类 | 21篇 |
数学 | 38214篇 |
物理学 | 90157篇 |
出版年
2019年 | 2303篇 |
2018年 | 4250篇 |
2017年 | 4514篇 |
2016年 | 5153篇 |
2015年 | 3179篇 |
2014年 | 4723篇 |
2013年 | 11314篇 |
2012年 | 10995篇 |
2011年 | 12024篇 |
2010年 | 8656篇 |
2009年 | 8213篇 |
2008年 | 9818篇 |
2007年 | 10063篇 |
2006年 | 9421篇 |
2005年 | 12268篇 |
2004年 | 11134篇 |
2003年 | 8888篇 |
2002年 | 7108篇 |
2001年 | 7557篇 |
2000年 | 5744篇 |
1999年 | 4489篇 |
1998年 | 3966篇 |
1997年 | 3910篇 |
1996年 | 3633篇 |
1995年 | 3380篇 |
1994年 | 3536篇 |
1993年 | 3221篇 |
1992年 | 3789篇 |
1991年 | 3778篇 |
1990年 | 3698篇 |
1989年 | 3536篇 |
1988年 | 3636篇 |
1987年 | 3514篇 |
1986年 | 3318篇 |
1985年 | 4393篇 |
1984年 | 4655篇 |
1983年 | 3898篇 |
1982年 | 4022篇 |
1981年 | 3940篇 |
1980年 | 3920篇 |
1979年 | 3900篇 |
1978年 | 4213篇 |
1977年 | 4121篇 |
1976年 | 4239篇 |
1975年 | 3878篇 |
1974年 | 3927篇 |
1973年 | 4090篇 |
1972年 | 2886篇 |
1971年 | 2396篇 |
1970年 | 2203篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
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
52.
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
53.
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
54.
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
55.
We build a metric space which is homeomorphic to a Cantor set but cannot be realized as the attractor of an iterated function system. We give also an example of a Cantor set K in R3 such that every homeomorphism f of R3 which preserves K coincides with the identity on K. 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.