全文获取类型
收费全文 | 3745篇 |
免费 | 133篇 |
国内免费 | 15篇 |
专业分类
化学 | 2346篇 |
晶体学 | 55篇 |
力学 | 45篇 |
数学 | 470篇 |
物理学 | 977篇 |
出版年
2022年 | 27篇 |
2021年 | 35篇 |
2020年 | 46篇 |
2019年 | 64篇 |
2018年 | 20篇 |
2017年 | 33篇 |
2016年 | 82篇 |
2015年 | 104篇 |
2014年 | 88篇 |
2013年 | 135篇 |
2012年 | 178篇 |
2011年 | 192篇 |
2010年 | 116篇 |
2009年 | 118篇 |
2008年 | 163篇 |
2007年 | 186篇 |
2006年 | 149篇 |
2005年 | 167篇 |
2004年 | 139篇 |
2003年 | 98篇 |
2002年 | 142篇 |
2001年 | 86篇 |
2000年 | 71篇 |
1999年 | 57篇 |
1998年 | 60篇 |
1997年 | 59篇 |
1996年 | 65篇 |
1995年 | 48篇 |
1994年 | 70篇 |
1993年 | 44篇 |
1992年 | 41篇 |
1991年 | 52篇 |
1990年 | 52篇 |
1989年 | 30篇 |
1988年 | 46篇 |
1987年 | 65篇 |
1986年 | 28篇 |
1985年 | 54篇 |
1984年 | 42篇 |
1983年 | 38篇 |
1982年 | 45篇 |
1981年 | 56篇 |
1980年 | 44篇 |
1979年 | 40篇 |
1978年 | 28篇 |
1977年 | 21篇 |
1976年 | 23篇 |
1975年 | 25篇 |
1974年 | 21篇 |
1973年 | 25篇 |
排序方式: 共有3893条查询结果,搜索用时 31 毫秒
1.
2.
Alloys of the systems Fe–Al (mixable over the whole concentration range) and Fe–Mg (insoluble with each other) were produced by implantation of Fe ions into Al and Mg, respectively. The implantation energy was 200 keV and the ion doses ranged from 1 × 1014 to 9 × 1017cm-2The obtained implantation profiles were determined by Auger electron spectroscopy depth profiling. Maximum iron concentrations reached were up to 60 at.% for implantation into Al and 94 at.% for implantation into Mg. Phase analysis of the implanted layers was performed by conversion electron Mössbauer spectroscopy and X‐ray diffraction. For implantation into Mg, two different kinds of Mössbauer spectra were obtained: at low doses paramagnetic doublets indicating at least two different iron sites and at high doses a dominant ferromagnetic six‐line‐pattern with a small paramagnetic fraction. The X‐ray diffraction pattern concluded that in the latter case a dilated αiron lattice is formed. For implantation into Al, the Mössbauer spectra were doublet structures very similar to those obtained at amorphous Fe–Al alloys produced by rapid quenching methods. They also indicated at least two different main iron environments. For the highest implanted sample a ferromagnetic six‐line‐pattern with magnetic field values close to those of Fe3Al appeared. 相似文献
3.
4.
F. Richter 《Analytical and bioanalytical chemistry》1940,119(3-4):109-118
5.
K. H. Geib J. Reitstötter R. E. Liesegang Thomas M. Richter Thierbach P. Krais 《Colloid and polymer science》1938,84(1):119-122
Ohne Zusammenfassung 相似文献
6.
Extending to r > 1 a formula of the authors, we compute the expected reflection distance of a product of t random reflections in the complex reflection group G(r, 1, n). The result relies on an explicit decomposition of the reflection distance function into irreducible G(r, 1, n)-characters and on the eigenvalues of certain adjacency matrices.Received December 8, 2003 相似文献
7.
8.
For a graph G and a positive integer m, G(m) is the graph obtained from G by replacing every vertex by an independent set of size m and every edge by m2 edges joining all possible new pairs of ends. If G triangulates a surface, then it is easy to see from Euler's formula that G(m) can, in principle, triangulate a surface. For m prime and at least 7, it has previously been shown that in fact G(m) does triangulate a surface, and in fact does so as a “covering with folds” of the original triangulation. For m = 5, this would be a consequence of Tutte's 5‐Flow Conjecture. In this work, we investigate the case m = 2 and describe simple classes of triangulations G for which G(2) does have a triangulation that covers G “with folds,” as well as providing a simple infinite class of triangulations G of the sphere for which G(2) does not triangulate any surface. © 2003 Wiley Periodicals, Inc. J Graph Theory 43: 79–92, 2003 相似文献
9.
10.
This is the second in a two-part series of articles in which we analyze a system similar in structure to the well-known Zakharov equations from weak plasma turbulence theory, but with a nonlinear conservation equation allowing finite time shock formation. In this article we analyze the incompressible limit in which the shock speed is large compared to the underlying group velocity of the dispersive wave (a situation typically encountered in applications). After presenting some exact solutions of the full system, a multiscale perturbation method is used to resolve several basic wave interactions. The analysis breaks down into two categories: the nonlinear limit and the linear limit, corresponding to the form of the equations when the group velocity to shock speed ratio, denoted by ε, is zero. The former case is an integrable limit in which the model reduces to the cubic nonlinear Schrödinger equation governing the dispersive wave envelope. We focus on the interaction of a “fast” shock wave and a single hump soliton. In the latter case, the ε=0 problem reduces to the linear Schrödinger equation, and the focus is on a fast shock interacting with a dispersive wave whose amplitude is cusped and exponentially decaying. To motivate the time scales and structure of the shock-dispersive wave interactions at lowest orders, we first analyze a simpler system of ordinary differential equations structurally similar to the original system. Then we return to the fully coupled partial differential equations and develop a multiscale asymptotic method to derive the effective leading-order shock equations and the leading-order modulation equations governing the phase and amplitude of the dispersive wave envelope. The leading-order interaction equations admit a fairly complete analysis based on characteristic methods. Conditions are derived in which: (a) the shock passes through the soliton, (b) the shock is completely blocked by the soliton, or (c) the shock reverses direction. In the linear limit, a phenomenon is described in which the dispersive wave induces the formation of a second, transient shock front in the rapidly moving hyperbolic wave. In all cases, we can characterize the long-time dynamics of the shock. The influence of the shock on the dispersive wave is manifested, to leading order, in the generalized frequency of the dispersive wave: the fast-time part of the frequency is the shock wave itself. Hence, the frequency undergoes a sudden jump across the shock layer.In the last section, a sequence of numerical experiments depicting some of the interesting interactions predicted by the analysis is performed on the leading-order shock equations. 相似文献