全文获取类型
收费全文 | 427873篇 |
免费 | 4784篇 |
国内免费 | 1391篇 |
专业分类
化学 | 232757篇 |
晶体学 | 5927篇 |
力学 | 18206篇 |
综合类 | 13篇 |
数学 | 49286篇 |
物理学 | 127859篇 |
出版年
2020年 | 2914篇 |
2019年 | 2954篇 |
2018年 | 3227篇 |
2017年 | 3135篇 |
2016年 | 5900篇 |
2015年 | 4480篇 |
2014年 | 6350篇 |
2013年 | 18917篇 |
2012年 | 14327篇 |
2011年 | 17845篇 |
2010年 | 11435篇 |
2009年 | 11459篇 |
2008年 | 16430篇 |
2007年 | 16767篇 |
2006年 | 16068篇 |
2005年 | 14631篇 |
2004年 | 13108篇 |
2003年 | 11653篇 |
2002年 | 11516篇 |
2001年 | 12937篇 |
2000年 | 9944篇 |
1999年 | 7859篇 |
1998年 | 6505篇 |
1997年 | 6319篇 |
1996年 | 6217篇 |
1995年 | 5733篇 |
1994年 | 5446篇 |
1993年 | 5181篇 |
1992年 | 5845篇 |
1991年 | 5752篇 |
1990年 | 5433篇 |
1989年 | 5235篇 |
1988年 | 5478篇 |
1987年 | 5062篇 |
1986年 | 4917篇 |
1985年 | 6886篇 |
1984年 | 7046篇 |
1983年 | 5775篇 |
1982年 | 6229篇 |
1981年 | 6216篇 |
1980年 | 5938篇 |
1979年 | 6213篇 |
1978年 | 6312篇 |
1977年 | 6222篇 |
1976年 | 6182篇 |
1975年 | 6040篇 |
1974年 | 5949篇 |
1973年 | 6098篇 |
1972年 | 3667篇 |
1971年 | 2909篇 |
排序方式: 共有10000条查询结果,搜索用时 20 毫秒
31.
A piecewise linearization method based on the linearization of nonlinear ordinary differential equations in small intervals, that provides piecewise analytical solutions in each interval and smooth solutions everywhere, is developed for the study of the limit cycles of smooth and non-smooth, conservative and non-conservative, nonlinear oscillators. It is shown that this method provides nonlinear maps for the displacement and velocity which depend on the previous values through the nonlinearity and its partial derivatives with respect to time, displacement and velocity, and yields non-standard finite difference formulae. It is also shown by means of five examples that the piecewise linearization method presented here is more robust and yields more accurate (in terms of displacement, energy and frequency) solutions than the harmonic balance procedure, the method of slowly varying amplitude and phase, and other non-standard finite difference equations. 相似文献
32.
I. J. Tchoupaeva 《Journal of Mathematical Sciences》2006,135(5):3409-3419
Some geometric theorems can be stated in coordinate-free form as polynomials in Grassman algebra and can be proven by the anticommutative Gröbner basis method. In this article, we analyze some properties of both sets of hypotheses and conclusions of the theorem. 相似文献
33.
R. J. Hinde 《Few-Body Systems》2006,38(2-4):187-191
We compute the vibrational coupling between two H2 molecules from ab initio quantum chemical calculations of the H2-H2 potential carried out at the full configuration interaction level of theory using the atom-centered aug-cc-pVTZ basis set
for hydrogen. We compare the full configuration interaction results with those obtained using two variants of coupled cluster
theory and find that a fully iterative treatment of connected triples may be required to estimate the H2-H2 vibrational coupling accurately using coupled cluster theory. 相似文献
34.
J. M. Rubi 《Journal of statistical physics》2006,123(2):497-498
35.
In this paper we study root system generalizations of the quantum Bose-gas on the circle with pair-wise delta-function interactions.
The underlying symmetry structures are shown to be governed by the associated graded algebra of Cherednik's (suitably filtered)
degenerate double affine Hecke algebra, acting by Dunkl-type differential-reflection operators. We use Gutkin's generalization
of the equivalence between the impenetrable Bose-gas and the free Fermi-gas to derive the Bethe ansatz equations and the Bethe
ansatz eigenfunctions. 相似文献
36.
J. Matkowski 《Aequationes Mathematicae》2002,64(3):297-303
Summary. Iteration semigroups of weighted quasi-arithmetic mean-type mappings are considered. Existence and uniqueness of a mean which is invariant with respect to a continuous semigroup of mean-type mapping is proved. 相似文献
37.
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
38.
A. R. Volkov B. V. Shul'gin T. I. Polupanova V. N. Lebedev A. A. Nagornyi V. L. Petrov Yu. F. Kargin 《Journal of Applied Spectroscopy》1991,54(6):585-590
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 6, pp. 970–975, June, 1991. 相似文献
39.
In a twisted nematic liquid crystal cell we report and study the self-transparency effect induced by the creation of an isotropic droplet. A simple theoretical model is presented and good agreement with experimental data is found. In a two beams configuration transistor-like behavior is observed and theoretically discussed. 相似文献
40.