全文获取类型
收费全文 | 258699篇 |
免费 | 18305篇 |
国内免费 | 9886篇 |
专业分类
化学 | 152168篇 |
晶体学 | 3298篇 |
力学 | 13211篇 |
综合类 | 519篇 |
数学 | 27680篇 |
物理学 | 90014篇 |
出版年
2023年 | 2378篇 |
2022年 | 4058篇 |
2021年 | 4511篇 |
2020年 | 4997篇 |
2019年 | 4589篇 |
2018年 | 4329篇 |
2017年 | 4002篇 |
2016年 | 6849篇 |
2015年 | 6219篇 |
2014年 | 7724篇 |
2013年 | 14347篇 |
2012年 | 14280篇 |
2011年 | 16061篇 |
2010年 | 10270篇 |
2009年 | 10240篇 |
2008年 | 12909篇 |
2007年 | 12160篇 |
2006年 | 11592篇 |
2005年 | 10181篇 |
2004年 | 8668篇 |
2003年 | 7238篇 |
2002年 | 6973篇 |
2001年 | 7717篇 |
2000年 | 6081篇 |
1999年 | 5254篇 |
1998年 | 4165篇 |
1997年 | 4150篇 |
1996年 | 4095篇 |
1995年 | 3580篇 |
1994年 | 3284篇 |
1993年 | 3002篇 |
1992年 | 3172篇 |
1991年 | 3068篇 |
1990年 | 2654篇 |
1989年 | 2496篇 |
1988年 | 2392篇 |
1987年 | 2262篇 |
1986年 | 2188篇 |
1985年 | 3023篇 |
1984年 | 2902篇 |
1983年 | 2322篇 |
1982年 | 2485篇 |
1981年 | 2325篇 |
1980年 | 2268篇 |
1979年 | 2188篇 |
1978年 | 2244篇 |
1977年 | 2199篇 |
1976年 | 2130篇 |
1975年 | 2118篇 |
1973年 | 2105篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
I. J. Lozada J. C. Osorio D. V. Griffiths M. Cerrolaza 《Numerical Methods for Partial Differential Equations》2006,22(2):296-316
The semi‐analytical integration of an 8‐node plane strain finite element stiffness matrix is presented in this work. The element is assumed to be super‐parametric, having straight sides. Before carrying out the integration, the integral expressions are classified into several groups, thus avoiding duplication of calculations. Symbolic manipulation and integration is used to obtain the basic formulae to evaluate the stiffness matrix. Then, the resulting expressions are postprocessed, optimized, and simplified in order to reduce the computation time. Maple symbolic‐manipulation software was used to generate the closed expressions and to develop the corresponding Fortran code. Comparisons between semi‐analytical integration and numerical integration were made. It was demonstrated that semi‐analytical integration required less CPU time than conventional numerical integration (using Gaussian‐Legendre quadrature) to obtain the stiffness matrix. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2006 相似文献
82.
C Falugi A Diaspro C Angelini M L Pedrotti M Raimondo M Robello 《Micron (Oxford, England : 1993)》2002,33(3):233-239
Confocal laser scanning microscopy (CLSM) was used to examine molecules related to the cholinergic neurotransmission system and detected at all the larval stages of Paracentrotus lividus, by histochemical and immunohistochemical methods. CLSM, providing spatial resolution of the cells located both at the larval surface and at depth, allows a complete mapping in a three-dimensional volumetric frame. At early larval stages acetylcholinesterase- as well as choline acetyltransferase-like molecules were found mainly in the gut wall cells, and along the ciliary bands of the arms, together with muscarinic acetylcholine receptors. At perimetamorphic stages, cholinergic molecules were present in the ciliate strands along the arms, in the larval body and in the rudiment. At metamorphosis, positivity to cholinergic molecules translocated to the juvenile, where a high frequency of mAChR- and ChAT-like positive cells was found. 相似文献
83.
84.
On Dirichlet Characters of Polynomials 总被引:1,自引:0,他引:1
The main purpose of this paper is to use the properties of Gaussiansums and the analytic method to study the problem of calculatingone kind of character sums modulo q, and to give an interestingidentity. 2000 Mathematics Subject Classification 11L10, 11L40. 相似文献
85.
A convective flow CO laser composed of polytetrafluoroethylene discharge tubes, nickel–chromium steel components, a cupric heat exchanger and other components is described. Operating in liquid nitrogen condition, output power of 60 W has been obtained from a non-selective cavity. 相似文献
86.
Liyue Liu Yingge Yang Yafei Zhang 《Physica E: Low-dimensional Systems and Nanostructures》2004,24(3-4):343-348
The electrical conductivity was investigated for multi-walled carbon nanotubes (MWNTs) dissolved in chloroform and toluene, respectively. The electrical conductivity remarkably increased with increase in the content of MWNTs, which is in accordance with Archie's equation . Furthermore, a hypothesis of the electronic transport process was proposed to explain the difference between the solution and the solid compound. In addition, the temperature dependence of the electrical conductivity shows that log σ vs. 1/T exist in a good linear relationship. The activation energy of the electrical conductivity decreased with increase in concentration and an inflexion was observed at 60 °C in MWNT/toluene solution. 相似文献
87.
88.
Equilibrium Problems with Applications to Eigenvalue Problems 总被引:5,自引:0,他引:5
In this paper, we consider equilibrium problems and introduce the concept of (S)+ condition for bifunctions. Existence results for equilibrium problems with the (S)+ condition are derived. As special cases, we obtain several existence results for the generalized nonlinear variational inequality studied by Ding and Tarafdar (Ref. 1) and the generalized variational inequality studied by Cubiotti and Yao (Ref. 2). Finally, applications to a class of eigenvalue problems are given. 相似文献
89.
90.