全文获取类型
收费全文 | 20930篇 |
免费 | 883篇 |
国内免费 | 98篇 |
专业分类
化学 | 13992篇 |
晶体学 | 129篇 |
力学 | 463篇 |
数学 | 3160篇 |
物理学 | 4167篇 |
出版年
2023年 | 120篇 |
2022年 | 149篇 |
2021年 | 271篇 |
2020年 | 385篇 |
2019年 | 405篇 |
2018年 | 257篇 |
2017年 | 270篇 |
2016年 | 637篇 |
2015年 | 591篇 |
2014年 | 686篇 |
2013年 | 1111篇 |
2012年 | 1162篇 |
2011年 | 1346篇 |
2010年 | 785篇 |
2009年 | 691篇 |
2008年 | 1136篇 |
2007年 | 1112篇 |
2006年 | 1046篇 |
2005年 | 930篇 |
2004年 | 835篇 |
2003年 | 693篇 |
2002年 | 654篇 |
2001年 | 344篇 |
2000年 | 336篇 |
1999年 | 301篇 |
1998年 | 260篇 |
1997年 | 246篇 |
1996年 | 277篇 |
1995年 | 275篇 |
1994年 | 239篇 |
1993年 | 234篇 |
1992年 | 219篇 |
1991年 | 188篇 |
1990年 | 189篇 |
1989年 | 202篇 |
1988年 | 167篇 |
1987年 | 147篇 |
1986年 | 148篇 |
1985年 | 206篇 |
1984年 | 193篇 |
1983年 | 154篇 |
1982年 | 182篇 |
1981年 | 177篇 |
1980年 | 156篇 |
1979年 | 162篇 |
1978年 | 191篇 |
1977年 | 139篇 |
1976年 | 129篇 |
1975年 | 145篇 |
1974年 | 110篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
Summary We prove convergence and error estimates in Sobolev spaces for the collocation method with tensor product splines for strongly elliptic pseudodifferential equations on the torus. Examples of applications include elliptic partial differential equations with periodic boundary conditions but also the classical boundary integral operators of potential theory on torus-shaped domains in three or more dimensions. For odd-degree splines, we prove convergence of nodal collocation for any strongly elliptic operator. For even-degree splines and midpoint collocation, we find an additional condition for the convergence which is satisfied for the classical boundary integral operators. Our analysis is a generalization to higher dimensions of the corresponding analysis of Arnold and Wendland [4]. 相似文献
32.
33.
34.
David Stanovský 《Czechoslovak Mathematical Journal》2007,57(1):191-200
We investigate the variety of residuated lattices with a commutative and idempotent monoid reduct. 相似文献
35.
The Dantzig-Wolfe reformulation principle is presented based on the concept of generating sets. The use of generating sets allows for an easy extension to mixed integer programming. Moreover, it provides a unifying framework for viewing various column generation practices, such as relaxing or tightening the column generation subproblem and introducing stabilization techniques. 相似文献
36.
37.
Martin Loebl 《Advances in Mathematics》2007,211(2):546-565
We define a q-chromatic function and q-dichromate on graphs and compare it with existing graph functions. Then we study in more detail the class of general chordal graphs. This is partly motivated by the graph isomorphism problem. Finally we relate the q-chromatic function to the colored Jones function of knots. This leads to a curious expression of the colored Jones function of a knot diagram K as a chromatic operator applied to a power series whose coefficients are linear combinations of long chord diagrams. Chromatic operators are directly related to weight systems by the work of Chmutov, Duzhin, Lando and Noble, Welsh. 相似文献
38.
Quantitative H–Al distances in acid sites of two zeolites with MFI and IFR framework topology were obtained by numerical simulation of 1H{27Al} rotational echo adiabatic passage double resonance (REAPDOR) experiments. A 27Al offset-dependent data set yields for each resolved 1H NMR line a corresponding nuclear electric quadrupole coupling constant of the neighboring 27Al site. This information is used for analyzing a second data set for on-resonance irradiation, where the dipolar evolution time (number of rotor cycles) was varied, to yield the 1H–27Al dipolar coupling constant. Numerical simulations indicate that the REAPDOR method does not depend significantly on the polar angles, defining the orientation of the electric field gradient tensor of 27Al with respect to the Al–H dipolar vector. In contrast, the transfer of populations in double resonance sequence is sensitive to these angles, and it can be thus used to measure them. 相似文献
39.
40.
Jiří Čtyroký 《Optical and Quantum Electronics》2006,38(1-3):45-62
The bi-directional mode expansion propagation algorithm (BEP) is known to be an accurate and efficient method for modelling field distribution in high-index contrast waveguide structures with strong back-reflections like Bragg gratings and photonic crystals. The main difficulty of this method is that for lossy structures, the propagation constants of modes are to be searched in the complex plane. To speed-up this procedure, a two-step algorithm for eigenmode calculation based on the expansion into the modes of an empty metallic waveguide has recently been proposed. Proper truncation rules possessing good convergence of the expansion method for both TE and TM modes have also been recently published. In this contribution, both these approaches are combined in the development of an extremely simple version of the two-dimensional BEP method that makes use of the field expansion into the eigenmodes of a parallel-plate waveguide. The method is strictly reciprocal and appeared to be computationally reliable also for strongly lossy structures. High numerical stability is ensured using the scattering matrix formalism, and an efficient method of calculating Bloch modes for symmetric as well as asymmetric periodic waveguide structures is adopted. A wide range of applicability of the method is demonstrated by a few examples. 相似文献