全文获取类型
收费全文 | 12620篇 |
免费 | 1373篇 |
国内免费 | 536篇 |
专业分类
化学 | 5601篇 |
晶体学 | 30篇 |
力学 | 1428篇 |
综合类 | 42篇 |
数学 | 4982篇 |
物理学 | 2446篇 |
出版年
2023年 | 162篇 |
2022年 | 132篇 |
2021年 | 275篇 |
2020年 | 465篇 |
2019年 | 342篇 |
2018年 | 296篇 |
2017年 | 272篇 |
2016年 | 506篇 |
2015年 | 503篇 |
2014年 | 624篇 |
2013年 | 1037篇 |
2012年 | 717篇 |
2011年 | 716篇 |
2010年 | 498篇 |
2009年 | 775篇 |
2008年 | 758篇 |
2007年 | 759篇 |
2006年 | 675篇 |
2005年 | 527篇 |
2004年 | 490篇 |
2003年 | 469篇 |
2002年 | 395篇 |
2001年 | 392篇 |
2000年 | 345篇 |
1999年 | 296篇 |
1998年 | 307篇 |
1997年 | 240篇 |
1996年 | 251篇 |
1995年 | 177篇 |
1994年 | 132篇 |
1993年 | 136篇 |
1992年 | 90篇 |
1991年 | 86篇 |
1990年 | 70篇 |
1989年 | 57篇 |
1988年 | 58篇 |
1987年 | 42篇 |
1986年 | 56篇 |
1985年 | 34篇 |
1984年 | 47篇 |
1983年 | 17篇 |
1982年 | 29篇 |
1981年 | 29篇 |
1980年 | 23篇 |
1979年 | 28篇 |
1978年 | 41篇 |
1977年 | 41篇 |
1976年 | 40篇 |
1975年 | 16篇 |
1974年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Y. Wardi 《Journal of Optimization Theory and Applications》1989,61(3):473-485
A stochastic algorithm for finding stationary points of real-valued functions defined on a Euclidean space is analyzed. It is based on the Robbins-Monro stochastic approximation procedure. Gradient evaluations are done by means of Monte Carlo simulations. At each iteratex
i
, one sample point is drawn from an underlying probability space, based on which the gradient is approximated. The descent direction is against the approximation of the gradient, and the stepsize is 1/i. It is shown that, under broad conditions, w.p.1 if the sequence of iteratesx
1,x
2,...generated by the algorithm is bounded, then all of its accumulation points are stationary. 相似文献
22.
This paper is concerned with the implementation and testing of an algorithm for solving constrained least-squares problems. The algorithm is an adaptation to the least-squares case of sequential quadratic programming (SQP) trust-region methods for solving general constrained optimization problems. At each iteration, our local quadratic subproblem includes the use of the Gauss–Newton approximation but also encompasses a structured secant approximation along with tests of when to use this approximation. This method has been tested on a selection of standard problems. The results indicate that, for least-squares problems, the approach taken here is a viable alternative to standard general optimization methods such as the Byrd–Omojokun trust-region method and the Powell damped BFGS line search method. 相似文献
23.
F. Iachello S. Oss 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(3):307-314
We present a brief review of algebraic techniques developed and applied in molecular spectroscopy in the last five years.
We also outline perspectives for new applications of the Lie algebraic method in the first decade of the new century.
Received 21 November 2001 相似文献
24.
通过改变带细玻璃管的烧瓶中水的温度导致水位变化来粗略演示水的收缩情况.为较准确测定水最大密度时的温度,将2个温度计放在水下较浅处和较深处,分别测量当温度经由4℃升高时和由4℃降低时两温度计的示数,进而验证水的反常热膨胀特性. 相似文献
25.
E. A. Bailov N. Temirgaliev 《Computational Mathematics and Mathematical Physics》2006,46(9):1515-1525
Sharp estimates (in the power scale) are obtained for the discretization error in the solutions to Poisson’s equation whose right-hand side belongs to a Korobov class. Compared to the well-known Korobov estimate, the order is almost doubled and has an ultimate value in the power scale. 相似文献
26.
Piotr Garbaczewski 《Journal of statistical physics》2006,123(2):315-355
We analyze the functioning of Gibbs-type entropy functionals in the time domain, with emphasis on Shannon and Kullback-Leibler entropies of time-dependent continuous probability distributions. The Shannon entropy validity is extended to probability distributions inferred from L
2(R
n
) quantum wave packets. In contrast to the von Neumann entropy which simply vanishes on pure states, the differential entropy quantifies the degree of probability (de)localization and its time development. The associated dynamics of the Fisher information functional quantifies nontrivial power transfer processes in the mean, both in dissipative and quantum mechanical cases.
PACS NUMBERS: 05.45.+b, 02.50.-r, 03.65.Ta, 03.67.-a 相似文献
27.
28.
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
29.
The effect of the amount of desorbed water on the mechanical properties of composites based on low-density polyethylene and linen yarn production waste (LW) is analyzed by statistical methods. It is shown that the amount of absorbed water decreases during the desorption process at room temperature both for specimens modified and unmodified with diphenylmethane diisocyanate (DIC.) The most sensitive to the action of water is the elastic modulus, which decreases considerably under the effect of water and is fully restored in the desorption process. The tensile strain also increases with the amount of absorbed water. It is found that the elastic modulus of the unmodified composite correlates linearly with the amount of desorbed water. Between the amount of desorbed water and the tensile strain, as well the specific work of deformation, a negative linear correlation is revealed. After water desorption, all strength and deformation characteristics of both the modified and unmodified composites are fully recovered.__________Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 4, pp. 515–524, July–August, 2005. 相似文献
30.
We consider a useful modification of the inexact implicit method with a variable parameter in Wang et al. J Optim Theory 111:
431–443 (2001) for generalized mixed monotone variational inequalities. One of the contributions of the proposed method in
this paper is that the restrictions imposed on the variable parameter are weaker than the ones in Wang et al. J Optim Theory
111: 431–443 (2001). Another contribution is that we establish a sufficient and necessary condition for the convergence of
the proposed method to a solution of the general mixed monotone variational inequality. 相似文献