全文获取类型
收费全文 | 5455篇 |
免费 | 600篇 |
国内免费 | 394篇 |
专业分类
化学 | 1337篇 |
晶体学 | 56篇 |
力学 | 762篇 |
综合类 | 63篇 |
数学 | 2525篇 |
物理学 | 1706篇 |
出版年
2024年 | 8篇 |
2023年 | 62篇 |
2022年 | 124篇 |
2021年 | 138篇 |
2020年 | 140篇 |
2019年 | 132篇 |
2018年 | 135篇 |
2017年 | 187篇 |
2016年 | 220篇 |
2015年 | 176篇 |
2014年 | 281篇 |
2013年 | 382篇 |
2012年 | 308篇 |
2011年 | 313篇 |
2010年 | 290篇 |
2009年 | 352篇 |
2008年 | 328篇 |
2007年 | 329篇 |
2006年 | 288篇 |
2005年 | 259篇 |
2004年 | 239篇 |
2003年 | 228篇 |
2002年 | 228篇 |
2001年 | 155篇 |
2000年 | 151篇 |
1999年 | 124篇 |
1998年 | 138篇 |
1997年 | 114篇 |
1996年 | 100篇 |
1995年 | 59篇 |
1994年 | 58篇 |
1993年 | 53篇 |
1992年 | 51篇 |
1991年 | 34篇 |
1990年 | 36篇 |
1989年 | 17篇 |
1988年 | 25篇 |
1987年 | 35篇 |
1986年 | 19篇 |
1985年 | 20篇 |
1984年 | 21篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 11篇 |
1980年 | 13篇 |
1979年 | 8篇 |
1978年 | 18篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1975年 | 4篇 |
排序方式: 共有6449条查询结果,搜索用时 31 毫秒
61.
In this paper, a projection method is presented for solving the flow problems in domains with moving boundaries. In order to track the movement of the domain boundaries, arbitrary‐Lagrangian–Eulerian (ALE) co‐ordinates are used. The unsteady incompressible Navier–Stokes equations on the ALE co‐ordinates are solved by using a projection method developed in this paper. This projection method is based on the Bell's Godunov‐projection method. However, substantial changes are made so that this algorithm is capable of solving the ALE form of incompressible Navier–Stokes equations. Multi‐block structured grids are used to discretize the flow domains. The grid velocity is not explicitly computed; instead the volume change is used to account for the effect of grid movement. A new method is also proposed to compute the freestream capturing metrics so that the geometric conservation law (GCL) can be satisfied exactly in this algorithm. This projection method is also parallelized so that the state of the art high performance computers can be used to match the computation cost associated with the moving grid calculations. Several test cases are solved to verify the performance of this moving‐grid projection method. Copyright © 2004 John Wiley Sons, Ltd. 相似文献
62.
63.
In this work we consider computing and continuing connecting orbits in parameter dependent dynamical systems. We give details
of algorithms for computing connections between equilibria and periodic orbits, and between periodic orbits. The theoretical
foundation for these techniques is given by the seminal work of Beyn in 1994, “On well-posed problems for connecting orbits
in dynamical systems”, where a numerical technique is also proposed. Our algorithms consist of splitting the computation of
the connection from that of the periodic orbit(s). To set up appropriate boundary conditions, we follow the algorithmic approach
used by Demmel, Dieci, and Friedman, for the case of connecting orbits between equilibria, and we construct and exploit the
smooth block Schur decomposition of the monodromy matrices associated to the periodic orbits. Numerical examples illustrate
the performance of the algorithms.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
64.
Guido Consonni Piero Veronese Eduardo Gutirrez-Pea 《Journal of multivariate analysis》2004,88(2):335-364
Reference analysis is one of the most successful general methods to derive noninformative prior distributions. In practice, however, reference priors are often difficult to obtain. Recently developed theory for conditionally reducible natural exponential families identifies an attractive reparameterization which allows one, among other things, to construct an enriched conjugate prior. In this paper, under the assumption that the variance function is simple quadratic, the order-invariant group reference prior for the above parameter is found. Furthermore, group reference priors for the mean- and natural parameter of the families are obtained. A brief discussion of the frequentist coverage properties is also presented. The theory is illustrated for the multinomial and negative-multinomial family. Posterior computations are especially straightforward due to the fact that the resulting reference distributions belong to the corresponding enriched conjugate family. A substantive application of the theory relates to the construction of reference priors for the Bayesian analysis of two-way contingency tables with respect to two alternative parameterizations. 相似文献
65.
Huang H. X. Liang Z. A. Pardalos P. M. 《Journal of Optimization Theory and Applications》2004,120(1):53-71
A flow search approach is presented in this paper. In the approach, each iterative process involves a subproblem, whose variables are the stepsize parameters. Every feasible solution of the subproblem corresponds to some serial search stages, the stepsize parameters in different search stages may interact mutually, and their optimal values are determined by evaluating the total effect of the interaction. The main idea of the flow search approach is illustrated via the minimization of a convex quadratic function. Based on the flow search approach, some properties of the m-step linear conjugate gradient algorithm are analyzed and new bounds on its convergence rate are also presented. Theoretical and numerical results indicate that the new bounds are better than the well-known ones. 相似文献
66.
Giovanna Idone 《Journal of Mathematical Analysis and Applications》2004,290(1):147-170
Hölder regularity up to the boundary of the solutions to the Dirichlet problem for second order elliptic systems with nonlinearity q>2 and with controlled growth is proved when n?q+2. 相似文献
67.
Stewart S. J. Mercader R. C. Punte G. Desimoni J. Cernicchiaro G. Scorzelli R. B. 《Hyperfine Interactions》2004,158(1-4):89-93
In this paper we analyze trend of EFG values measured at Cd impurity in a group of semiconducting delafossites with chemical
formula CuBO2 (B = Al, Fe, Cr, Nd). We conclude that this trend reveals one of the most subtle details in electronic spectrum of the compounds:
if impurity states are formed within or out of the band gap. In CuAlO2 and CuFeO2 the Cd EFG exhibits larger value than in CuCrO2 and CuNdO2, when Cd substitutes the Cu atom. This occurs because in the first two compounds the Cd forms shallow band within the gap,
and in the second two compounds does not. When Cd occupies the B position it exhibits almost the same EFG in all delafossites.
In this case, Cd does not form its states within the gap in none of the compounds. To arrive to these conclusions we analyzed
and calculated various systems (Cd-doped CuAlO2 and CuCrO2 compounds, fictitious molecules), using the FP-LAPW method. 相似文献
68.
Let Hn be an n-dimensional Haar subspace of
and let Hn−1 be a Haar subspace of Hn of dimension n−1. In this note we show (Theorem 6) that if the norm of a minimal projection from Hn onto Hn−1 is greater than 1, then this projection is an interpolating projection. This is a surprising result in comparison with Cheney and Morris (J. Reine Angew. Math. 270 (1974) 61 (see also (Lecture Notes in Mathematics, Vol. 1449, Springer, Berlin, Heilderberg, New York, 1990, Corollary III.2.12, p. 104) which shows that there is no interpolating minimal projection from C[a,b] onto the space of polynomials of degree n, (n2). Moreover, this minimal projection is unique (Theorem 9). In particular, Theorem 6 holds for polynomial spaces, generalizing a result of Prophet [(J. Approx. Theory 85 (1996) 27), Theorem 2.1]. 相似文献
69.
70.
The line search method incorporating the Wolfe conditions is modified to ensure that a descent algorithm terminates in a finite number of steps at an approximate stationary point where the second-order conditions of optimality are satisfied. A simple procedure based on conjugate directions is proposed to determine directions of negative curvature. 相似文献