全文获取类型
收费全文 | 23445篇 |
免费 | 2838篇 |
国内免费 | 3269篇 |
专业分类
化学 | 8978篇 |
晶体学 | 104篇 |
力学 | 2016篇 |
综合类 | 177篇 |
数学 | 7736篇 |
物理学 | 10541篇 |
出版年
2024年 | 71篇 |
2023年 | 255篇 |
2022年 | 390篇 |
2021年 | 594篇 |
2020年 | 754篇 |
2019年 | 696篇 |
2018年 | 702篇 |
2017年 | 789篇 |
2016年 | 940篇 |
2015年 | 835篇 |
2014年 | 1207篇 |
2013年 | 2023篇 |
2012年 | 1303篇 |
2011年 | 1547篇 |
2010年 | 1217篇 |
2009年 | 1578篇 |
2008年 | 1625篇 |
2007年 | 1673篇 |
2006年 | 1394篇 |
2005年 | 1185篇 |
2004年 | 961篇 |
2003年 | 980篇 |
2002年 | 912篇 |
2001年 | 720篇 |
2000年 | 737篇 |
1999年 | 620篇 |
1998年 | 567篇 |
1997年 | 428篇 |
1996年 | 293篇 |
1995年 | 285篇 |
1994年 | 237篇 |
1993年 | 199篇 |
1992年 | 182篇 |
1991年 | 159篇 |
1990年 | 161篇 |
1989年 | 153篇 |
1988年 | 130篇 |
1987年 | 127篇 |
1986年 | 99篇 |
1985年 | 106篇 |
1984年 | 99篇 |
1983年 | 37篇 |
1982年 | 74篇 |
1981年 | 69篇 |
1980年 | 56篇 |
1979年 | 64篇 |
1978年 | 55篇 |
1977年 | 65篇 |
1976年 | 58篇 |
1973年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
51.
C Premkumar Yesudian 《Pramana》1989,33(6):651-657
An extended technicolour grand unification model based on the gauge groupE
6×SU(7) extended technicolour is presented. The symmetry-breaking based on extended technicolour theory is discussed. It is
shown that the existing phenomenology is well explained by the model. The strangeness changing neutral currents may not be
a problem with this model. 相似文献
52.
应用密度泛函理论,本文系统地研究了O在Au(111)表面上的吸附能、吸附结构、功函数、电子密度和投影态密度,给出了覆盖度从0.11ML到1.0ML的范围内,O的吸附特性随覆盖度变化的规律.研究发现O的稳定吸附位为3重面心立方(fcc)洞位,O在fcc洞位的吸附能对覆盖度比较敏感,其值随着覆盖度的增加而减小;O诱导Au(111)表面功函数的变化量与覆盖度成近线性关系,原因是Au表面电子向O偏移,形成表面偶极子;O—Au的相互作用形成成键态和反键态,且反键态都被占据,造成O—Au键很弱,O吸附能较小.
关键词:
表面吸附
Au(111)表面
密度泛函理论
电子特性 相似文献
53.
54.
It is long known that the Fokker-Planck equation with prescribed constant coefficients of diffusion and linear friction describes
the ensemble average of the stochastic evolutions in velocity space of a Brownian test particle immersed in a heat bath of
fixed temperature. Apparently, it is not so well known that the same partial differential equation, but now with constant
coefficients which are functionals of the solution itself rather than being prescribed, describes the kinetic evolution (in
the N→∞ limit) of an
isolated
N-particle system with certain stochastic interactions. Here we discuss in detail this recently discovered interpretation.
An erratum to this article can be found at 相似文献
55.
Signed graphs for portfolio analysis in risk management 总被引:1,自引:0,他引:1
Harary Frank; Lim Meng-Hiot; Wunsch Donald C. 《IMA Journal of Management Mathematics》2002,13(3):201-210
We introduce the notion of structural balance for signed graphsin the context of portfolio analysis. A portfolio of securitiescan be represented as a signed graph with the nodes denotingthe securities and the edges representing the correlation betweenthe securities. With signed graphs, the characteristics of aportfolio from a risk management perspective can be uncoveredfor analysis purposes. It is shown that a portfolio characterizedby a signed graph of positive and negative edges that is structurallybalanced is characteristically more predictable. Investors whoundertake a portfolio position with all positively correlatedsecurities do so with the intention to speculate on the upside(or downside). If the portfolio consists of negative edges andis balanced, then it is likely that the position has a hedgingdisposition within it. On the other hand, an unbalanced signedgraph is representative of an investment portfolio which ischaracteristically unpredictable. 相似文献
56.
Johan Helsing 《BIT Numerical Mathematics》2006,46(2):307-323
A sparse mesh-neighbour based approximate inverse preconditioner is proposed for a type of dense matrices whose entries come
from the evaluation of a slowly decaying free space Green’s function at randomly placed points in a unit cell. By approximating
distant potential fields originating at closely spaced sources in a certain way, the preconditioner is given properties similar
to, or better than, those of a standard least squares approximate inverse preconditioner while its setup cost is only that
of a diagonal block approximate inverse preconditioner. Numerical experiments on iterative solutions of linear systems with
up to four million unknowns illustrate how the new preconditioner drastically outperforms standard approximate inverse preconditioners
of otherwise similar construction, and especially so when the preconditioners are very sparse.
AMS subject classification (2000) 65F10, 65R20, 65F35, 78A30 相似文献
57.
We investigate the dynamics of the Λ system driven by two resonant laser fields in presence of dissipation for coupling strengths where the rotating‐wave approximation starts to break down. This regime is characterised by Rabi frequencies being approximately equal or smaller than the field frequencies. A systematic procedure to obtain an expansion for the solution of the Bloch evolution equations of the system is presented. The lowest contribution results to be the well‐known rotating‐wave approximation. The method is based on a semi‐classical treatment of the problem, and its predictions are interpreted fully quantum mechanically. The theory is illustrated by a detailed study of the disappearance of coherent population trapping as the intensities of the fields increase. 相似文献
58.
GU Bai-Ping REN Zhong-Zhou 《理论物理通讯》2005,44(2):337-342
The Dirac optical potential for p-^14 Be elastic scattering is evaluated by the relativistic impulse approximation. Each of the real part and the imaginary part of the potential shows a pronounced “long tail” for the proton elastic scattering from halo nucleus ^14Be compared with the potentials for proton scattering from its adjacent nuclei ^12C and ^16O, which do not have halo structures.This kind of “long tail” phenomenon suggests another signature for halo nuclei. 相似文献
59.
By further generalizing the skew-symmetric triangular splitting iteration method studied by Krukier, Chikina and Belokon (Applied Numerical Mathematics, 41 (2002), pp. 89–105), in this paper, we present a new iteration scheme, called the modified skew-Hermitian triangular splitting iteration method, for solving the strongly non-Hermitian systems of linear equations with positive definite coefficient matrices. We discuss the convergence property and the optimal parameters of this new method in depth. Moreover, when it is applied to precondition the Krylov subspace methods like GMRES, the preconditioning property of the modified skew-Hermitian triangular splitting iteration is analyzed in detail. Numerical results show that, as both solver and preconditioner, the modified skew-Hermitian triangular splitting iteration method is very effective for solving large sparse positive definite systems of linear equations of strong skew-Hermitian parts. 相似文献
60.
We study a model of a queueing system with two complementary products/services. In our model, there is one M/M/1 system and another facility that provides instantaneous service. The two services are complementary and the customer has no benefit from obtaining just one of them. We investigate the model under various price structures and ownership assumptions.AMS subject classification: 90B22, 91A10The authors are equal in their contribution to this paper. This paper is submitted by the first author to the Tokyo Institute of Technology as partial fulfillment of the requirements for the Ph.D. program in the Department of Value and Decision Sciences, and the order of names was chosen in compliance with program conditions. This research was supported by the Israel Science Foundation (grant No. 237/02). 相似文献