全文获取类型
收费全文 | 21626篇 |
免费 | 2673篇 |
国内免费 | 994篇 |
专业分类
化学 | 6611篇 |
晶体学 | 58篇 |
力学 | 1393篇 |
综合类 | 118篇 |
数学 | 7051篇 |
物理学 | 10062篇 |
出版年
2024年 | 9篇 |
2023年 | 172篇 |
2022年 | 248篇 |
2021年 | 466篇 |
2020年 | 540篇 |
2019年 | 494篇 |
2018年 | 411篇 |
2017年 | 570篇 |
2016年 | 829篇 |
2015年 | 676篇 |
2014年 | 1168篇 |
2013年 | 1685篇 |
2012年 | 1034篇 |
2011年 | 1183篇 |
2010年 | 962篇 |
2009年 | 1319篇 |
2008年 | 1577篇 |
2007年 | 1499篇 |
2006年 | 1287篇 |
2005年 | 1052篇 |
2004年 | 931篇 |
2003年 | 938篇 |
2002年 | 878篇 |
2001年 | 698篇 |
2000年 | 701篇 |
1999年 | 585篇 |
1998年 | 550篇 |
1997年 | 398篇 |
1996年 | 313篇 |
1995年 | 280篇 |
1994年 | 250篇 |
1993年 | 202篇 |
1992年 | 198篇 |
1991年 | 139篇 |
1990年 | 111篇 |
1989年 | 110篇 |
1988年 | 116篇 |
1987年 | 86篇 |
1986年 | 75篇 |
1985年 | 104篇 |
1984年 | 85篇 |
1983年 | 27篇 |
1982年 | 52篇 |
1981年 | 54篇 |
1980年 | 50篇 |
1979年 | 41篇 |
1978年 | 36篇 |
1977年 | 35篇 |
1976年 | 31篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
具有奇异值分解性质的代数 总被引:4,自引:0,他引:4
设F为一个域,R为一个带有对合的F-代数,如果R上每一个矩阵都有奇异值分解(简称SVD),则称R为一个有SVD性质的F-代数.本文指出:R为一个有SVD性质的F-代数的充要条件是:R同构于R~+,或R~+上二次扩域,或R~+上四元数体((-1,-1)/R~+),其中R~+为R的对称元集合,并且R~+为一个Galois序闭域. 相似文献
102.
In this paper, we present a unified treatment and analysis of a dynamic traffic network model with elastic demands formulated and studied as a projected dynamical system. We propose a travel route choice adjustment process that satisfies the projected dynamical system. Under certain conditions, stability and asymptotical stability of the equilibrium patterns are then derived. Finally, two discrete-time algorithms, the Euler method and the Heun method, are proposed for the computation of the solutions, and convergence results established. The convergence results depend crucially on stability analysis. The performance of the algorithms is then illustrated on several transportation networks. 相似文献
103.
提出了折射率温敏式光纤温度传感器的理论模型,包括子午光线和偏射光线的影响,讨论了多模光纤的弯曲损耗,理论的分析和结果与实验相当一致。 相似文献
104.
E. Hatta H. Hosoi H. Akiyama T. Ishii K. Mukasa 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):347-349
We have observed a remarkable two-armed spiral in the collapse process of a floating monolayer at the air-water interface
by phase contrast microscopy. This demonstrates that the floating monolayer as a form of soft condensed matter reorganizes
itself due to a certain kind of macroscopic or collective behavior of molecules as it collapses. This pattern formation is
caused by the breakdown of a critical dynamical balance between the deformation of solid domain and the applied surface pressure.
The fragility as well as the flexibility of the floating monolayer can be associated with the observed pattern growth. There
are also observed interesting, periodically arranged collections of molecules in numerous collapsed regions.
Received: 8 July 1997 / Accepted: 4 November 1997 相似文献
105.
用紫外光直接在光纤内写入布拉格反射光栅的实验研究 总被引:2,自引:0,他引:2
用紫外光直接在光纤内写入布拉格反射光栅的实验研究杜卫冲谭华耀*刘颂豪华南师范大学,激光生命科学研究所,广州510631*香港理工大学,电机系自1989年Meltaz[1]首次提出采用两束波长位于掺Ge-石英光纤吸收带内的相干紫外激光相干涉,从侧面照射... 相似文献
106.
L. A. Sakhnovich 《Functional Analysis and Its Applications》2002,36(3):205-211
The conjecture according to which the mean energy of an equilibrium system in quantum theory exceeds the mean energy of the corresponding classical system is considered. It is rigorously proved that the conjecture holds for the potential well. The estimates for the mean energy of the potential well at high and low temperatures are of special interest. 相似文献
107.
An effective residual interaction between particles and holes for shell model calculations around 208Pb, derived from the interaction between free nucleons, is compared with the measured properties of proton-hole neutron states
in 208Tl and the interaction between proton holes is adjusted to newly measured level energies in 206Hg. These interaction elements are particularly relevant for neutron-rich nuclei. The adjustment of two mixing elements reproduces
the known γ-decay data in 208Tl.
Received: 2 April 2002 / Accepted: 2 May 2002 相似文献
108.
We study the expected delay in cyclic polling models with general ‘branching-type’ service disciplines. For this class of
models, which contains models with exhaustive and gated service as special cases, we obtain closed-form expressions for the
expected delay under standard heavy-traffic scalings. We identify a single parameter associated with the service discipline
at each queue, which we call the ‘exhaustiveness’. We show that the scaled expected delay figures depend on the service policies
at the queues only through the exhaustiveness of each of the service disciplines. This implies that the influence of different
service disciplines, but with the same exhaustiveness, on the expected delays at the queues becomes the same when the system
reaches saturation. This observation leads to a new classification of the service disciplines. In addition, we show monotonicity
of the scaled expected delays with respect to the exhaustiveness of the service disciplines. This induces a complete ordering
in terms of efficiency of the service disciplines. The results also lead to new rules for optimization of the system performance
with respect to the service disciplines at the queues. Further, the exact asymptotic results suggest simple expected waiting-time
approximations for polling models in heavy traffic. Numerical experiments show that the accuracy of the approximations is
excellent for practical heavy-traffic scenarios.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
109.
Jrg Winkelmann 《Mathematische Nachrichten》1997,186(1):285-302
We investigate under which conditions an algebraic group G defined over a locally compact field k admitr a subgroup Γ? G(k) which is dense in the Zariski topology, but discerte in the topology induced by the locally compact topology on k. For non—solvable groups we provide a complete answer. 相似文献
110.
This paper describes a method and the corresponding algorithms for simplification of large-scale linear programming models. It consists of the elimination of the balance constraints (i.e. constraints with zero RHS term). The idea is to apply some linear transformations to the original problem in order to nullify the balance constraints. These transformations are able to simultaneously eliminate more balance rows. The core of this contribution is the introduction of the reduction matrix and the associated theorems on the equivalent linear programs (original and reduced). The numerical experiments with this method of simplification proved this approach to be beneficial for a large class of LP problems.This research work was done while the first author was at Duisburg University, Mess-, Steuer und Regelungstechnik, Germany, under the greatly appreciated financial assistance given by the Alexander-von-Humboldt Foundation. 相似文献