全文获取类型
收费全文 | 17849篇 |
免费 | 1954篇 |
国内免费 | 1056篇 |
专业分类
化学 | 5815篇 |
晶体学 | 42篇 |
力学 | 1621篇 |
综合类 | 152篇 |
数学 | 9319篇 |
物理学 | 3910篇 |
出版年
2023年 | 193篇 |
2022年 | 198篇 |
2021年 | 293篇 |
2020年 | 543篇 |
2019年 | 422篇 |
2018年 | 389篇 |
2017年 | 392篇 |
2016年 | 641篇 |
2015年 | 615篇 |
2014年 | 830篇 |
2013年 | 1475篇 |
2012年 | 955篇 |
2011年 | 1034篇 |
2010年 | 756篇 |
2009年 | 1149篇 |
2008年 | 1110篇 |
2007年 | 1156篇 |
2006年 | 1061篇 |
2005年 | 812篇 |
2004年 | 749篇 |
2003年 | 715篇 |
2002年 | 631篇 |
2001年 | 592篇 |
2000年 | 538篇 |
1999年 | 492篇 |
1998年 | 469篇 |
1997年 | 357篇 |
1996年 | 360篇 |
1995年 | 236篇 |
1994年 | 204篇 |
1993年 | 186篇 |
1992年 | 129篇 |
1991年 | 122篇 |
1990年 | 106篇 |
1989年 | 83篇 |
1988年 | 98篇 |
1987年 | 65篇 |
1986年 | 76篇 |
1985年 | 68篇 |
1984年 | 85篇 |
1983年 | 37篇 |
1982年 | 55篇 |
1981年 | 51篇 |
1980年 | 38篇 |
1979年 | 48篇 |
1978年 | 52篇 |
1977年 | 54篇 |
1976年 | 48篇 |
1975年 | 18篇 |
1974年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
Formalization for problems of multicriteria decision making under uncertainty is constructed in terms of guaranteed and weak
estimates. A relevant definition of the vector maximinimax value is given. Parameterization and approximation of maximum,
minimax, and maximinimax values based on the inverse logical convolution are suggested. An application for multicommodity
networks is considered.
Received: December 13, 2000 / Accepted: August 21, 2001?Published online May 8, 2002 相似文献
22.
P.A. Ramachandran 《Numerical Methods for Partial Differential Equations》2006,22(4):831-846
Time‐dependent differential equations can be solved using the concept of method of lines (MOL) together with the boundary element (BE) representation for the spatial linear part of the equation. The BE method alleviates the need for spatial discretization and casts the problem in an integral format. Hence errors associated with the numerical approximation of the spatial derivatives are totally eliminated. An element level local cubic approximation is used for the variable at each time step to facilitate the time marching and the nonlinear terms are represented in a semi‐implicit manner by a local linearization at each time step. The accuracy of the method has been illustrated on a number of test problems of engineering significance. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2006 相似文献
23.
Elena Kardash-Strochkova Yakov I. Tur’yan I. Kuselman Naphtali Brodsky 《Accreditation and quality assurance》2002,7(6):250-254
The results of two interlaboratory comparisons of acid number determinations in used motor oils are discussed. It is shown
that the comparability of the measurement results is not as good as that required by known standards for petroleum products.
The problem is motor oil contaminants which accumulated during use, and which are the source of a matrix effect in the acid
number determination. The standard methods’ drawbacks are analyzed and some improvements are proposed. Repeatability and accuracy
of the improved methods are evaluated.
Received: 11 December 2001 Accepted: 15 February 2002 相似文献
24.
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
25.
26.
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
27.
28.
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
29.
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
30.
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