全文获取类型
收费全文 | 76983篇 |
免费 | 4336篇 |
国内免费 | 11177篇 |
专业分类
化学 | 65190篇 |
晶体学 | 1310篇 |
力学 | 1136篇 |
综合类 | 540篇 |
数学 | 10844篇 |
物理学 | 13476篇 |
出版年
2024年 | 76篇 |
2023年 | 603篇 |
2022年 | 1226篇 |
2021年 | 1413篇 |
2020年 | 1702篇 |
2019年 | 2630篇 |
2018年 | 1671篇 |
2017年 | 2938篇 |
2016年 | 2319篇 |
2015年 | 2033篇 |
2014年 | 2758篇 |
2013年 | 6081篇 |
2012年 | 5088篇 |
2011年 | 4347篇 |
2010年 | 3400篇 |
2009年 | 4560篇 |
2008年 | 4841篇 |
2007年 | 4976篇 |
2006年 | 4540篇 |
2005年 | 4057篇 |
2004年 | 3905篇 |
2003年 | 3149篇 |
2002年 | 3834篇 |
2001年 | 2656篇 |
2000年 | 2474篇 |
1999年 | 2260篇 |
1998年 | 1927篇 |
1997年 | 1541篇 |
1996年 | 1285篇 |
1995年 | 1247篇 |
1994年 | 1043篇 |
1993年 | 851篇 |
1992年 | 848篇 |
1991年 | 571篇 |
1990年 | 470篇 |
1989年 | 483篇 |
1988年 | 345篇 |
1987年 | 253篇 |
1986年 | 278篇 |
1985年 | 224篇 |
1984年 | 223篇 |
1983年 | 109篇 |
1982年 | 195篇 |
1981年 | 172篇 |
1980年 | 180篇 |
1979年 | 191篇 |
1978年 | 163篇 |
1977年 | 107篇 |
1976年 | 96篇 |
1974年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Summary. Let be a square matrix dependent on parameters and , of which we choose as the eigenvalue parameter. Many computational problems are equivalent to finding a point such that has a multiple eigenvalue at . An incomplete decomposition of a matrix dependent on several parameters is proposed. Based on the developed theory two new algorithms are
presented for computing multiple eigenvalues of with geometric multiplicity . A third algorithm is designed for the computation of multiple eigenvalues with geometric multiplicity but which also appears to have local quadratic convergence to semi-simple eigenvalues. Convergence analyses of these methods
are given. Several numerical examples are presented which illustrate the behaviour and applications of our methods.
Received December 19, 1994 / Revised version received January 18, 1996 相似文献
42.
Addition of functionalized zinc-copper reagents to the title complexes proceeds in a highly diastereoselective fashion to afford dienol complexes. The relative configurations of adducts 3d were determined by single X-ray diffraction analysis. 相似文献
43.
Double Michael additions of lithium enolaie of 1,4-dioxaspiro[4.5]dec-6-en-8-one to four acrylates afforded bicyclo[2.2.2]octan-2-ones with high regio- and stereoselectivities in moderate yields. 相似文献
44.
The Schwinger representation of the SO(8) fermion pair algebra in terms ofd and quasispin vector (u, s, v) bosons is used in deriving a microscopic boson coherent state having both particle-hole and pair excitations. The coherent
state is the exact boson image of the HFB variational solution. We can study the shape phase transition and pairing behaviour
of the nuclear ground states using the coherent states. 相似文献
45.
Summary In the analysis of discretization methods for stiff intial value problems, stability questions have received most part of the attention in the past.B-stability and the equivalent criterion algebraic stability are well known concepts for Runge-Kutta methods applied to dissipative problems. However, for the derivation ofB-convergence results — error bounds which are not affected by stiffness — it is not sufficient in many cases to requireB-stability alone. In this paper, necessary and sufficient conditions forB-convergence are determined.This paper was written while J. Schneid was visiting the Centre for Mathematics and Computer Science with an Erwin-Schrödinger stipend from the Fonds zur Förderung der wissenschaftlichen Forschung 相似文献
46.
Summary We present an approximation method of a space-homogeneous transport equation which we prove is convergent. The method is very promising for numerical computation. Comparison of a numerical computation with an exact solution is given for the Master equation. 相似文献
47.
K. Y. Lin 《Journal of statistical physics》1987,49(1-2):269-279
The spontaneous magnetization of the Ising model on a 4–8 lattice with six different coupling constants and two different magnetic moments is studied. A formula for the spontaneous magnetization is proposed. The result agrees with the exact low-temperature series expansions up to the 12th order. 相似文献
48.
本文用密度泛函理论(DFT)的总能计算研究了一氧化碳和氢原子在Ni(111)表面上p(2×2)共吸附系统的原子结构和电子态,结果表明CO和H原子分别被吸附于两个对角p(1×1)元胞的hcp和fcc位置.以氢分子和CO分子作为能量参考点,总吸附能为2.81 eV,相应的共吸附表面功函数φ为6.28 eV.计算得到的C—O,C—Ni和H—Ni的键长分别是1.19?, 1.96?和 1.71?,并且CO分子以C原子处于hcp的谷位与金属衬底原子结合.衬底Ni(111)的最外两层的晶面间距在吸附后的相对变化分别是
关键词:
Fisher-Tropsch反应
催化作用
Ni(111) p(2×2)/(CO+H)
共吸附 相似文献
49.
50.