全文获取类型
收费全文 | 7319篇 |
免费 | 423篇 |
国内免费 | 596篇 |
专业分类
化学 | 2005篇 |
晶体学 | 76篇 |
力学 | 99篇 |
综合类 | 107篇 |
数学 | 4939篇 |
物理学 | 1112篇 |
出版年
2023年 | 61篇 |
2022年 | 127篇 |
2021年 | 163篇 |
2020年 | 145篇 |
2019年 | 241篇 |
2018年 | 258篇 |
2017年 | 183篇 |
2016年 | 206篇 |
2015年 | 144篇 |
2014年 | 296篇 |
2013年 | 590篇 |
2012年 | 287篇 |
2011年 | 386篇 |
2010年 | 325篇 |
2009年 | 425篇 |
2008年 | 478篇 |
2007年 | 496篇 |
2006年 | 445篇 |
2005年 | 366篇 |
2004年 | 327篇 |
2003年 | 293篇 |
2002年 | 268篇 |
2001年 | 179篇 |
2000年 | 183篇 |
1999年 | 185篇 |
1998年 | 187篇 |
1997年 | 115篇 |
1996年 | 162篇 |
1995年 | 130篇 |
1994年 | 107篇 |
1993年 | 95篇 |
1992年 | 77篇 |
1991年 | 58篇 |
1990年 | 24篇 |
1989年 | 42篇 |
1988年 | 31篇 |
1987年 | 23篇 |
1986年 | 13篇 |
1985年 | 43篇 |
1984年 | 25篇 |
1983年 | 12篇 |
1982年 | 16篇 |
1981年 | 15篇 |
1980年 | 20篇 |
1979年 | 15篇 |
1978年 | 14篇 |
1977年 | 13篇 |
1975年 | 9篇 |
1974年 | 7篇 |
1973年 | 12篇 |
排序方式: 共有8338条查询结果,搜索用时 15 毫秒
71.
S. -S. Chow 《Numerische Mathematik》1989,54(4):373-393
Summary In this paper we shall consider the application of the finite element method to a class of second order elliptic boundary value problems of divergence form and with gradient nonlinearity in the principal coefficient, and the derivation of error estimates for the finite element approximations. Such problems arise in many practical situations — for example, in shock-free airfoil design, seepage through coarse grained porous media, and in some glaciological problems. By making use of certain properties of the nonlinear coefficients, we shall demonstrate that the variational formulations associated with these boundary value problems are well-posed. We shall also prove that the abstract operators accompanying such problems satisfy certain continuity and monotonicity inequalities. With the aid of these inequalities and some standard results from approximation theory, we show how one may derive error estimates for the finite element approximations in the energy norm. 相似文献
72.
J. -P. Kauthen 《Numerische Mathematik》1989,56(5):409-424
Summary Integral equations of mixed Volterra-Fredholm type arise in various physical and biological problems. In the present paper we study continuous time collocation, time discretization and their global and discrete convergence properties. 相似文献
73.
The spectral structure of two parameter unbounded operator pencils of waveguide type is studied. Theorems on discreteness
of the spectrum for a fixed parameter are proved. Variational principles for real eigenvalues in some parts of the root zones
are established. In the case of n = 1 (quadratic pencils) domains containing the spectrum are described (see Fig. 1–3). Conditions in the definition of the
pencils of waveguide type arise naturally from physical problems and each of them has a physical meaning. In particular a
connection between the energetic stability condition and a perturbation problem for the coefficients is given. 相似文献
74.
证明了强平稳正相协列乘积和的重对数律与不同分布正相协列乘积和的强大数律,指出了部分和服从强大数律但乘积和未必服从强大数律这一事实,并讨论了定理2中一个条件的必要性. 相似文献
75.
Raiko P. Zaikov 《Letters in Mathematical Physics》1994,32(4):283-297
Higher spin extensions of the non-Abelian gauge symmetries for the classical WZNW model are considered. Both linear and nonlinear realizations of the extended affine Kac-Moody algebra are obtained. It is a characteristic property of the WZNW model that it admits a higher spin linear realization of the extended affine Kac-Moody algebra which is equivalent to the corresponding higher spin nonlinear realization of the same algebra. However, in both cases, the higher spin Noether currents do not span an invariant space with respect to their generating transformations. Here, the current space is extended to an invariant space which allows us to gauge the symmetry.Supported by Bulgarian Foundation on Fundamental Research under contract Ph-318/93-95. 相似文献
76.
Minoru Murata 《Journal of Functional Analysis》2002,194(1):53-141
We consider positive solutions of elliptic partial differential equations on non-compact domains of Riemannian manifolds. We explicitly determine Martin boundaries and Martin kernels for a class of elliptic equations in skew product form by exploiting and developing perturbation theory for elliptic equations and short/long-time estimates for fundamental solutions of parabolic equations. 相似文献
77.
78.
Here we prove that every compact differential manifold has a smooth algebraic model defined over Q. In dimension 2 we find an algebraic model (may be singular) defined over Q and birational over Q to the projective plane. 相似文献
79.
Nicolae Tomozeiu 《Applied Surface Science》2006,253(1):376-380
Thin films of a-SiOx (0 < x < 2) were prepared by reactive r.f. magnetron sputtering from a polycrystalline-silicon target in an Ar/O2 gas mixture. The oxygen partial pressure in the deposition chamber was varied so as to obtain films with different values of x. The plasma was monitored, during depositions, by optical emission spectroscopy (OES) system. Energy dispersive X-ray (EDX) measurements and infra-red (IR) spectroscopy were used to study the compositional and structural properties of the deposited layers.Structural modifications of SiOx thin films have been induced by UV photons’ bombardment (wavelength of 248 nm) using a pulsed laser. IR spectroscopy and X-ray photoemission spectroscopy (XPS) were used to investigate the structural changes as a function of x value and incident energy. SiOx phase separation by spinodal decomposition was revealed. The IR peak position shifted towards high wavenumber values when the laser energy is increased. Values corresponding to the SiO2 material (only Si4+) have been found for laser irradiated samples, independently on the original x value. The phase separation process has a threshold energy that is in agreement with theoretical values calculated for the dissociation energy of the investigated material.For high values of the laser energy, crystalline silicon embedded in oxygen-rich silicon oxide was revealed by Raman spectroscopy. 相似文献
80.
A review of the analysis of petroleum fuels, oils, tars and engine exhaust particulate extracts by on-line coupled LC-GC is presented. 相似文献