全文获取类型
收费全文 | 8366篇 |
免费 | 1243篇 |
国内免费 | 577篇 |
专业分类
化学 | 3436篇 |
晶体学 | 122篇 |
力学 | 462篇 |
综合类 | 39篇 |
数学 | 1314篇 |
物理学 | 4813篇 |
出版年
2024年 | 19篇 |
2023年 | 79篇 |
2022年 | 173篇 |
2021年 | 183篇 |
2020年 | 244篇 |
2019年 | 232篇 |
2018年 | 196篇 |
2017年 | 195篇 |
2016年 | 291篇 |
2015年 | 243篇 |
2014年 | 333篇 |
2013年 | 692篇 |
2012年 | 416篇 |
2011年 | 471篇 |
2010年 | 382篇 |
2009年 | 515篇 |
2008年 | 448篇 |
2007年 | 550篇 |
2006年 | 482篇 |
2005年 | 380篇 |
2004年 | 377篇 |
2003年 | 344篇 |
2002年 | 386篇 |
2001年 | 300篇 |
2000年 | 336篇 |
1999年 | 260篇 |
1998年 | 254篇 |
1997年 | 166篇 |
1996年 | 152篇 |
1995年 | 138篇 |
1994年 | 133篇 |
1993年 | 100篇 |
1992年 | 105篇 |
1991年 | 67篇 |
1990年 | 48篇 |
1989年 | 43篇 |
1988年 | 53篇 |
1987年 | 38篇 |
1986年 | 54篇 |
1985年 | 49篇 |
1984年 | 52篇 |
1983年 | 13篇 |
1982年 | 24篇 |
1981年 | 32篇 |
1980年 | 22篇 |
1979年 | 16篇 |
1978年 | 28篇 |
1977年 | 24篇 |
1976年 | 17篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
61.
Various tests have been carried out in order to compare the performances of several methods used to solve the non-symmetric linear systems of equations arising from implicit discretizations of CFD problems, namely the scalar advection-diffusion equation and the compressible Euler equations. The iterative schemes under consideration belong to three families of algorithms: relaxation (Jacobi and Gauss-Seidel), gradient and Newton methods. Two gradient methods have been selected: a Krylov subspace iteration method (GMRES) and a non-symmetric extension of the conjugate gradient method (CGS). Finally, a quasi-Newton method has also been considered (Broyden). The aim of this paper is to provide indications of which appears to be the most adequate method according to the particular circumstances as well as to discuss the implementation aspects of each scheme. 相似文献
62.
T. Grenet J. Delahaye M. Sabra F. Gay 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(3):183-197
We present a study of non-equilibrium phenomena observed
in the electrical conductance of insulating granular aluminium thin films.
An anomalous field effect and its slow relaxation are studied in some
detail. The phenomenology is very similar to the one already observed in
indium oxide. The origin of the phenomena is discussed. In granular systems,
the present experiments can naturally be interpreted along two different
lines. One relies on a slow polarisation in the dielectric surrounding the
metallic islands. The other one relies on a purely electronic mechanism: the
formation of an electron Coulomb glass in the granular metal. More selective
experiments and/or quantitative predictions about the Coulomb glass
properties are still needed to definitely distinguish between the two
scenarios. 相似文献
63.
B. V. Pal’tsev I. I. Chechel’ 《Computational Mathematics and Mathematical Physics》2006,46(5):820-847
The convergence rate of a fast-converging second-order accurate iterative method with splitting of boundary conditions constructed by the authors for solving an axisymmetric Dirichlet boundary value problem for the Stokes system in a spherical gap is studied numerically. For R/r exceeding about 30, where r and R are the radii of the inner and outer boundary spheres, it is established that the convergence rate of the method is lower (and considerably lower for large R/r) than the convergence rate of its differential version. For this reason, a really simpler, more slowly converging modification of the original method is constructed on the differential level and a finite-element implementation of this modification is built. Numerical experiments have revealed that this modification has the same convergence rate as its differential counterpart for R/r of up to 5 × 103. When the multigrid method is used to solve the split and auxiliary boundary value problems arising at iterations, the modification is more efficient than the original method starting from R/r ~ 30 and is considerably more efficient for large values of R/r. It is also established that the convergence rates of both methods depend little on the stretching coefficient η of circularly rectangular mesh cells in a range of η that is well sufficient for effective use of the multigrid method for arbitrary values of R/r smaller than ~ 5 × 103. 相似文献
64.
S. C. Tiwari 《Foundations of Physics Letters》2006,19(1):51-62
Advances in gauge theories and unified theories have not thrown light on the meaning of electron. The problem of the origin
of electronic charge is made precise, new insights gained from Weyl space are summarized, and the origin of charge in terms
of fractional spin is suggested. A new perspective on the abelian Chern-Simons theory is presented to explain charge. 相似文献
65.
D. Abouelaoualim 《Pramana》2006,66(2):455-465
We develop a theoretical model to the scattering time due to the electron-confined LO-phonon in GaAs-AlxGa1-xAs superlattice taking into account the sub-band parabolicity. Using the new analytic wave function of electron miniband conduction
of superlattice and a reformulation slab model for the confined LO-phonon modes, an expression for the electron-confined LO-phonon
scattering time is obtained. In solving numerically a partial differential equation for the phonon generation rate, our results
show that forx = 0.45, the LO-phonon in superlattice changes from a bulk-like propagating mode to a confined mode. The dispersion of the
relaxation time due to the emission of confined LO-phonons depends strongly on the total energy. 相似文献
66.
Abstract In [16] a visco-elastic relaxation system, called the relaxed Burnett system, was proposed by Jinand Slemrod as a moment approximation to the Boltzmann equation. The relaxed Burnett system is weaklyparabolic, has a linearly hyperbolic convection part, and is endowed with a generalized eotropy inequality. Itagrees with the solution of the Boltzmann equation up to the Burnett order via the Chapman-Enskog expansion. We develop a one-dimensional non-oscillatory numerical scheme based on the relaxed Burnett system forthe Boltzmann equation. We compare numerical results for stationary shocks based on this relaxation scheme,and those obtained by the DSMC (Direct Simulation Monte Carlo), by the Navier-Stokes equations and bythe extended thermodynamics with thirteen moments (the Grad equations). Our numerical experiments showthat the relaxed Burnett gives more accurate approximations to the shock profiles of the Boltzmann equationobtained by the DSMC, for a range of Mach numbers for hypersonic flows, th 相似文献
67.
Applied Biochemistry and Biotechnology - 相似文献
68.
All-electron full-potential linearized augmented plane-wave calculations of the surface energy, work function, and interlayer spacings of close-packed metal surfaces are presented, in particular, for the free-electron-like metal surfaces, Mg(0 0 0 1) and Al(1 1 1), and for the transition metal surfaces, Ti(0 0 0 1), Cu(1 1 1), Pd(1 1 1), and Pt(1 1 1). We investigate the convergence of the surface energy as a function of the number of layers in the slab, using the Cu(1 1 1) surface as an example. The results show that the surface energy, as obtained using total energies of the slab and bulk from separate calculations, converges well with respect to the number of layers in the slab. Obviously, it is necessary that bulk and surface calculations are performed with the same high accuracy. Furthermore, we discuss the performance of the local-density and generalized gradient approximations for the exchange-correlation functional in describing the various surface properties. 相似文献
69.
磁电子学器件应用原理 总被引:13,自引:0,他引:13
本文介绍几种重要的磁电子器件的基本结构和工作原理,包括巨磁电阻与隧穿磁电阻传感器、巨磁电阻隔离器、巨磁电阻与隧穿磁电阻硬盘读出磁头、磁电阻随机存取存储器、自旋转移磁化反转与微波振荡器。自旋晶体管作为未来磁电子学或自旋电子学时代的基本元素,目前大都还处在概念型阶段,本文也将对几种自旋晶体管的大致原理作简要介绍。 相似文献
70.
First, this paper deals with lagrangean heuristics for the 0-1 bidimensional knapsack problem. A projected subgradient algorithm is performed for solving a lagrangean dual of the problem, to improve the convergence of the classical subgradient algorithm. Secondly, a local search is introduced to improve the lower bound on the value of the biknapsack produced by lagrangean heuristics. Thirdly, a variable fixing phase is embedded in the process. Finally, the sequence of 0-1 one-dimensional knapsack instances obtained from the algorithm are solved by using reoptimization techniques in order to reduce the total computational time effort. Computational results are presented. 相似文献