全文获取类型
收费全文 | 15067篇 |
免费 | 990篇 |
国内免费 | 886篇 |
专业分类
化学 | 240篇 |
晶体学 | 4篇 |
力学 | 1481篇 |
综合类 | 186篇 |
数学 | 13863篇 |
物理学 | 1169篇 |
出版年
2024年 | 32篇 |
2023年 | 149篇 |
2022年 | 193篇 |
2021年 | 220篇 |
2020年 | 340篇 |
2019年 | 352篇 |
2018年 | 405篇 |
2017年 | 405篇 |
2016年 | 388篇 |
2015年 | 294篇 |
2014年 | 626篇 |
2013年 | 1213篇 |
2012年 | 672篇 |
2011年 | 795篇 |
2010年 | 701篇 |
2009年 | 977篇 |
2008年 | 1041篇 |
2007年 | 1052篇 |
2006年 | 951篇 |
2005年 | 721篇 |
2004年 | 614篇 |
2003年 | 687篇 |
2002年 | 599篇 |
2001年 | 448篇 |
2000年 | 458篇 |
1999年 | 412篇 |
1998年 | 376篇 |
1997年 | 334篇 |
1996年 | 253篇 |
1995年 | 213篇 |
1994年 | 149篇 |
1993年 | 122篇 |
1992年 | 121篇 |
1991年 | 106篇 |
1990年 | 79篇 |
1989年 | 43篇 |
1988年 | 41篇 |
1987年 | 38篇 |
1986年 | 41篇 |
1985年 | 54篇 |
1984年 | 53篇 |
1983年 | 28篇 |
1982年 | 29篇 |
1981年 | 27篇 |
1980年 | 18篇 |
1979年 | 22篇 |
1978年 | 15篇 |
1977年 | 15篇 |
1976年 | 9篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
We argue that QCD belongs to a topologically ordered phase similar to many well-known condensed matter systems with a gap such as topological insulators or superconductors. Our arguments are based on an analysis of the so-called “deformed QCD” which is a weakly coupled gauge theory, but nevertheless preserves all the crucial elements of strongly interacting QCD, including confinement, nontrivial θ dependence, degeneracy of the topological sectors, etc. Specifically, we construct the so-called topological “BF” action which reproduces the well known infrared features of the theory such as non-dispersive contribution to the topological susceptibility which cannot be associated with any propagating degrees of freedom. Furthermore, we interpret the well known resolution of the celebrated U(1)A problem where the would be η′ Goldstone boson generates its mass as a result of mixing of the Goldstone field with a topological auxiliary field characterizing the system. We then identify the non-propagating auxiliary topological field of the BF formulation in deformed QCD with the Veneziano ghost (which plays the crucial role in resolution of the U(1)A problem). Finally, we elaborate on relation between “string-net” condensation in topologically ordered condensed matter systems and long range coherent configurations, the “skeletons”, studied in QCD lattice simulations. 相似文献
132.
It is of engineering importance to accurately predict the surface cooling characteristics in bath quenching of metals and alloys. In this investigation, the surface cooling characteristics in quenching of Wolfson probe are estimated with reasonable accuracy by solving an inverse heat conduction problem. Regularization method is used for smoothening the input temperature measurements at probe center, for superior inversion estimates. The reverse pool-boiling curve is captured on bath quenching characteristic, plotted as cooling velocity versus surface temperature. The prime advantage is the bypassing of convection coefficients, which are uncertain in pool boiling. 相似文献
133.
A numerical/experimental inverse procedure was employed to estimate the temperature-dependent thermal conductivity of a solid body in which 1D heat conduction in a top heated cylindrical sample is assumed. The emphasis is focused on the issue of sensitivity of results to selected assumptions made in inverse calculations. It has been found that the accuracy of heat capacity evaluation brings the largest contribution to final errors (up to 74%). Density accounts for one-fourth to one-third of the total error of determination. The failure to ensure unidirectional heat conduction in a sample during an experiment is important only at elevated temperatures. 相似文献
134.
We address in this paper the problem of finding an optimal strategy for dealing with bottleneck machines and bottleneck parts in the cell formation process in group technology. Three types of economic decisions are considered: subcontracting, machine duplication and intercell moves. The problem is formulated as a minimum weighted node covering problem in a hypergraph, and we show that it can be solved in polynomial time by finding a maximum weighted stable set in a bipartite graph. We extend this result to cellular manufacturing systems in which the sequence of operations of each part is known in advance. 相似文献
135.
G. A. Watson 《Advances in Computational Mathematics》1994,2(4):393-405
The orthogonal Procrustes problem involves finding an orthogonal matrix which transforms one given matrix into another in
the least-squares sense, and thus it requires the minimization of the Frobenius matrix norm. We consider, the solution of
this problem for a family of orthogonally invariant norms which includes the Frobenius norm as a special case. 相似文献
136.
A new method for a class of linear variational inequalities 总被引:14,自引:0,他引:14
In this paper we introduce a new iterative scheme for the numerical solution of a class of linear variational inequalities. Each iteration of the method consists essentially only of a projection to a closed convex set and two matrix-vector multiplications. Both the method and the convergence proof are very simple.This work is supported by the National Natural Science Foundation of the P.R. China and NSF of Jiangsu. 相似文献
137.
The linear complementarity problem is to find nonnegative vectors which are affinely related and complementary. In this paper we propose a new complementary pivoting algorithm for solving the linear complementarity problem as a more efficient alternative to the algorithms proposed by Lemke and by Talman and Van der Heyden. The algorithm can start at an arbitrary nonnegative vector and converges under the same conditions as Lemke's algorithm.This research is part of the VF-program Competition and Cooperation. 相似文献
138.
The distribution of the likelihood ratio for mixtures of densities from the one-parameter exponential family 总被引:2,自引:0,他引:2
Dankmar Böhning Ekkehart Dietz Rainer Schaub Peter Schlattmann Bruce G. Lindsay 《Annals of the Institute of Statistical Mathematics》1994,46(2):373-388
We here consider testing the hypothesis ofhomogeneity against the alternative of a two-component mixture of densities. The paper focuses on the asymptotic null distribution of 2 log
n
, where
n
is the likelihood ratio statistic. The main result, obtained by simulation, is that its limiting distribution appears pivotal (in the sense of constant percentiles over the unknown parameter), but model specific (differs if the model is changed from Poisson to normal, say), and is not at all well approximated by the conventional
(2)
2
-distribution obtained by counting parameters. In Section 3, the binomial with sample size parameter 2 is considered. Via a simple geometric characterization the case for which the likelihood ratio is 1 can easily be identified and the corresponding probability is found. Closed form expressions for the likelihood ratio
n
are possible and the asymptotic distribution of 2 log
n
is shown to be the mixture giving equal weights to the one point distribution with all its mass equal to zero and the 2-distribution with 1 degree of freedom. A similar result is reached in Section 4 for the Poisson with a small parameter value (0.1), although the geometric characterization is different. In Section 5 we consider the Poisson case in full generality. There is still a positive asymptotic probability that the likelihood ratio is 1. The upper precentiles of the null distribution of 2 log
n
are found by simulation for various populations and shown to be nearly independent of the population parameter, and approximately equal to the (1–2)100 percentiles of
(1)
2
. In Sections 6 and 7, we close with a study of two continuous densities, theexponential and thenormal with known variance. In these models the asymptotic distribution of 2 log
n
is pivotal. Selected (1–) 100 percentiles are presented and shown to differ between the two models. 相似文献
139.
M. A. Pinsky 《Applied Mathematics and Optimization》1994,30(2):171-174
By working with suitable test functions, we obtain an upper bound for the principal eigenvalue of a geodesic ball on a sphere of arbitrary dimension. This bound is sharp in the limiting case when the radius of the ball approaches the diameter of the sphere.This research was supported by ARO Grant 28905-MA. 相似文献
140.
The mapping in a nonlinear complementarity problem may be discontinuous. The integral global optimization algorithm is proposed to solve a nonlinear complementarity problem with a robust piecewise continuous mapping. Numerical examples are given to illustrate the effectiveness of the algorithm. 相似文献