全文获取类型
收费全文 | 85043篇 |
免费 | 5282篇 |
国内免费 | 4316篇 |
专业分类
化学 | 47726篇 |
晶体学 | 1444篇 |
力学 | 4493篇 |
综合类 | 304篇 |
数学 | 7567篇 |
物理学 | 33107篇 |
出版年
2023年 | 606篇 |
2022年 | 1451篇 |
2021年 | 1453篇 |
2020年 | 1503篇 |
2019年 | 1543篇 |
2018年 | 1513篇 |
2017年 | 1475篇 |
2016年 | 2167篇 |
2015年 | 1960篇 |
2014年 | 2642篇 |
2013年 | 4534篇 |
2012年 | 4771篇 |
2011年 | 5501篇 |
2010年 | 4039篇 |
2009年 | 3979篇 |
2008年 | 4665篇 |
2007年 | 4365篇 |
2006年 | 4115篇 |
2005年 | 3493篇 |
2004年 | 2949篇 |
2003年 | 2523篇 |
2002年 | 2376篇 |
2001年 | 3636篇 |
2000年 | 2698篇 |
1999年 | 2025篇 |
1998年 | 1429篇 |
1997年 | 1363篇 |
1996年 | 1144篇 |
1995年 | 1032篇 |
1994年 | 931篇 |
1993年 | 788篇 |
1992年 | 1094篇 |
1991年 | 1078篇 |
1990年 | 968篇 |
1989年 | 835篇 |
1988年 | 803篇 |
1987年 | 847篇 |
1986年 | 715篇 |
1985年 | 930篇 |
1984年 | 847篇 |
1983年 | 586篇 |
1982年 | 581篇 |
1981年 | 539篇 |
1980年 | 503篇 |
1979年 | 628篇 |
1978年 | 653篇 |
1977年 | 662篇 |
1976年 | 576篇 |
1975年 | 481篇 |
1974年 | 522篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
121.
In this paper, we study a problem central to crossdocking that aims to eliminate or minimize storage and order picking activity using JIT scheduling. The problem is modelled naturally as a machine scheduling problem. As the problem is NP-hard, and for real-time applications, we designed and implemented two heuristics. The first uses Squeaky Wheel Optimization embedded in a Genetic Algorithm and the second uses Linear Programming within a Genetic Algorithm. Both heuristics offer good solutions in experiments where comparisons are made with the CPLEX solver. 相似文献
122.
In 1983, a preconditioner was proposed [J. Comput. Phys. 49 (1983) 443] based on the Laplace operator for solving the discrete Helmholtz equation efficiently with CGNR. The preconditioner is especially effective for low wavenumber cases where the linear system is slightly indefinite. Laird [Preconditioned iterative solution of the 2D Helmholtz equation, First Year's Report, St. Hugh's College, Oxford, 2001] proposed a preconditioner where an extra term is added to the Laplace operator. This term is similar to the zeroth order term in the Helmholtz equation but with reversed sign. In this paper, both approaches are further generalized to a new class of preconditioners, the so-called “shifted Laplace” preconditioners of the form Δφ−k2φ with
. Numerical experiments for various wavenumbers indicate the effectiveness of the preconditioner. The preconditioner is evaluated in combination with GMRES, Bi-CGSTAB, and CGNR. 相似文献
123.
124.
125.
本文考虑一带有人工粘性的二维定常等熵无旋平面流方程组的初-边值问题. 在一定的假设下,我们证明其驻波解是渐近稳定的. 相似文献
126.
Y. A. Coutinho J. A. Martins Simões C. M. Porto 《Zeitschrift fur Physik C Particles and Fields》1997,73(4):705-709
In this paper we investigate the effects of heavy Majorana neutrinos in the reaction e + e ? → W + W ?. We consider neutrino masses in the 1–10 TeV region. We show that at LEP II and NLC energies it is possible to use this processes to verify indirect evidence of heavy neutral particles with mixing angles of the order sin2 α = 0.01. We discuss the unitarity restrictions that can be obtained for vector singlet and fermion-mirror-fermion models. 相似文献
127.
In this article we have studied the nonlinear interaction between ellipticity and dissipation in a set of model equations (1.1) and established the relation between this interaction and chaos. In addition to theoretical investigations, extensive numerical simulations with these equations have been made, and different routes to chaos have been found. The numerical studies have revealed the chaotic nature of the solutions. 相似文献
128.
报道了KDP晶体中的三倍频产生的实验研究,计算了比较了直接三倍频过程和级联过程对KDP晶体三阶有效非线性系数的贡献,并探讨了KDP作为非线性晶体材料三阶非线性系数测量基准的可行性。 相似文献
129.
High resolution finite difference schemes for solving the nonlinear model Boltzmann equations are presented for the computations of rarefied gas flows. The discrete ordinate method is first applied to remove the velocity space dependency of the distribution function which renders the model Boltzmann equation in phase space to a set of hyperbolic conservation laws with source terms in physical space. Then a high order essentially nonoscillatory method due to Harten et al. (J. Comput. Phys. 71, 231, 1987) is adapted and extended to solve them. Explicit methods using operator splitting and implicit methods using the lower-upper factorization are described to treat multidimensional problems. The methods are tested for both steady and unsteady rarefied gas flows to illustrate its potential use. The computed results using model Boltzmann equations are found to compare well both with those using the direct simulation Monte Carlo results in the transitional regime flows and those with the continuum Navier-Stokes calculations in near continuum regime flows. 相似文献
130.
L.-Q. Han S.-Y. Zhao Y.-D. Zhou P.-L. Zhang 《Applied physics. B, Lasers and optics》1997,65(3):399-402
Received: 18 June 1996/Revised version: 3 January 1997 相似文献