全文获取类型
收费全文 | 11010篇 |
免费 | 625篇 |
国内免费 | 416篇 |
专业分类
化学 | 1358篇 |
晶体学 | 15篇 |
力学 | 3522篇 |
综合类 | 56篇 |
数学 | 3811篇 |
物理学 | 3289篇 |
出版年
2023年 | 77篇 |
2022年 | 137篇 |
2021年 | 160篇 |
2020年 | 187篇 |
2019年 | 215篇 |
2018年 | 157篇 |
2017年 | 204篇 |
2016年 | 330篇 |
2015年 | 327篇 |
2014年 | 375篇 |
2013年 | 736篇 |
2012年 | 455篇 |
2011年 | 617篇 |
2010年 | 459篇 |
2009年 | 750篇 |
2008年 | 749篇 |
2007年 | 727篇 |
2006年 | 647篇 |
2005年 | 576篇 |
2004年 | 535篇 |
2003年 | 538篇 |
2002年 | 410篇 |
2001年 | 292篇 |
2000年 | 307篇 |
1999年 | 241篇 |
1998年 | 291篇 |
1997年 | 220篇 |
1996年 | 170篇 |
1995年 | 194篇 |
1994年 | 150篇 |
1993年 | 124篇 |
1992年 | 93篇 |
1991年 | 77篇 |
1990年 | 49篇 |
1989年 | 64篇 |
1988年 | 52篇 |
1987年 | 40篇 |
1986年 | 34篇 |
1985年 | 42篇 |
1984年 | 20篇 |
1983年 | 15篇 |
1982年 | 21篇 |
1981年 | 23篇 |
1980年 | 17篇 |
1979年 | 21篇 |
1978年 | 17篇 |
1977年 | 18篇 |
1976年 | 18篇 |
1973年 | 13篇 |
1971年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
31.
L. A. Utracki 《Journal of Polymer Science.Polymer Physics》2004,42(15):2909-2915
The Simha and Somcynsky (S–S) statistical thermodynamics theory was used to compute the solubility parameters as a function of temperature and pressure [δ = δ(T, P)], for a series of polymer melts. The characteristic scaling parameters required for this task, P*, T*, and V*, were extracted from the pressure–temperature–volume (PVT) data. To determine the potential polymer–polymer miscibility, the dependence of δ versus T (at ambient pressure) was computed for 17 polymers. Close proximity of the δ versus T curves for four miscible polymer pairs: PPE/PS, PS/PVME, and PC/PMMA signaled the usefulness of this approach. It is noteworthy, that the tabulated solubility parameters (derived from the solution data under ambient conditions) propounded the immiscibility of the PVC/PVAc pair. The computed values of δ also suggested miscibility for polymer pairs of unknown miscibility, namely PPE/PVC, PPE/PVAc, and PET/PSF. In recognizing the limitations of the solubility parameter approach (the omission of several thermodynamic contributions), these preliminary results are auspicious because they indicate a new route for estimating the miscibility of any polymeric material at a given temperature and pressure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2909–2915, 2004 相似文献
32.
利用量子统计方法 ,直接计算Barriola_Vilenkin黑洞背景下玻色场和费米场的配分函数 ,然后利用砖墙膜模型计算和讨论黑洞背景下玻色场和费米场的熵 相似文献
33.
Thomas H. Pate 《Linear and Multilinear Algebra》2003,51(3):263-278
If 1≤k≤n, then Cor(n,k) denotes the set of all n×n real correlation matrices of rank not exceeding k. Grone and Pierce have shown that if A∈Cor (n, n-1), then per(A)≥n/(n-1). We show that if A∈Cor(n,2), then , and that this inequality is the best possible. 相似文献
34.
汤旦林,王松柏.几种国际通用统计软件的比较,数理统计与管理,1997,16(1),48~53.本文对七种著名的国际通用统计软件作了扼要的介绍,并从用户的角度对它们的性能进行了具体的比较 相似文献
35.
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
36.
Y. Abe 《The European Physical Journal A - Hadrons and Nuclei》2002,13(1-2):143-148
Based on the theory of the compound nucleus reaction, a brief review is given on the special aspects of the reaction dynamics
in the synthesis of the superheavy elements (SHE), where the fusion probability is the most unknown factor. A new viewpoint
of the fusion reaction is proposed that it consists of two processes; the first process up to the contact of two nuclei of
the incident channel and the second one of a dynamical evolution to the spherical compound nucleus from the contact configuration.
The fusion probability is, thus, given as a product of a contact probability and a formation probability. Analytic studies
of the latter probability are discussed in the one-dimensional model, where a simple expression is given to the so-called
extra-push energy in terms of the reduced friction, the curvature parameter of the conditional saddle point and the nuclear
temperature. Preliminary results of numerical analyses of the contact probability are given, using the surface friction model
(SFM). Remarks are given on the present status of our knowledge and for future developments.
Received: 1 May 2001 / Accepted: 4 December 2001 相似文献
37.
The Existence of Solutions to Sturm-Liouville Boundary Value Problems with Laplacian-like Operator 总被引:2,自引:0,他引:2
Wei-ping Sun Wei-gao GeDepartment of Applied Mathematics Beijing Institute of Technology Beijing China 《应用数学学报(英文版)》2002,18(2):341-348
Abstract The existence of infinitely many solutions to Sturm-Liouville boundary value problem with aLaplacian-like operator is studied by applying generalized polar coordinates. 相似文献
38.
Consider the problem of rolling a dynamically asymmetric balanced ball (the Chaplygin ball) over a sphere. Suppose that the
contact point has zero velocity and the projection of the angular velocity to the normal vector of the sphere equals zero.
This model of rolling differs from the classical one. It can be realized, in some approximation, if the ball is rubber coated
and the sphere is absolutely rough. Recently, J. Koiller and K. Ehlers pointed out the measure and the Hamiltonian structure
for this problem. Using this structure we construct an isomorphism between this problem and the problem of the motion of a
point on a sphere in some potential field. The integrable cases are found.
相似文献
39.
本文给出了Banach空间广义分解定理的一个初等证明,并利用它来证明两个对称不等式.这是首次在Banach空间获得这样的不等式. 相似文献
40.
We consider the isothermal flow through a cylindrical flat chamber, a model of some particular heat exchanger, for which LDV measurements and a numerical simulation have been performed. Experimental results show the establishment of an important vortex zone, the secondary flow extending all along the chamber radius. This observation leads to an expected significant increase of the fluid mixing. Results issued from the numerical simulation appear to be in close agreement with experimental data. Nevertheless, the k–ε model used here must be improved to obtain a better approach near the vortex centre. To cite this article: S. Petitot et al., C. R. Mecanique 330 (2002) 593–599. 相似文献