全文获取类型
收费全文 | 486250篇 |
免费 | 4572篇 |
国内免费 | 1440篇 |
专业分类
化学 | 254320篇 |
晶体学 | 7980篇 |
力学 | 21884篇 |
综合类 | 8篇 |
数学 | 54706篇 |
物理学 | 153364篇 |
出版年
2021年 | 3855篇 |
2020年 | 4145篇 |
2019年 | 4630篇 |
2018年 | 6157篇 |
2017年 | 6335篇 |
2016年 | 9075篇 |
2015年 | 5413篇 |
2014年 | 8796篇 |
2013年 | 22025篇 |
2012年 | 16188篇 |
2011年 | 19651篇 |
2010年 | 14229篇 |
2009年 | 14101篇 |
2008年 | 17655篇 |
2007年 | 17790篇 |
2006年 | 16462篇 |
2005年 | 14490篇 |
2004年 | 13496篇 |
2003年 | 11945篇 |
2002年 | 11884篇 |
2001年 | 14282篇 |
2000年 | 10843篇 |
1999年 | 8491篇 |
1998年 | 7042篇 |
1997年 | 6961篇 |
1996年 | 6652篇 |
1995年 | 5862篇 |
1994年 | 5742篇 |
1993年 | 5571篇 |
1992年 | 6330篇 |
1991年 | 6385篇 |
1990年 | 6192篇 |
1989年 | 6148篇 |
1988年 | 5869篇 |
1987年 | 6007篇 |
1986年 | 5628篇 |
1985年 | 7352篇 |
1984年 | 7366篇 |
1983年 | 6153篇 |
1982年 | 6430篇 |
1981年 | 6130篇 |
1980年 | 6018篇 |
1979年 | 6361篇 |
1978年 | 6656篇 |
1977年 | 6459篇 |
1976年 | 6387篇 |
1975年 | 6070篇 |
1974年 | 5990篇 |
1973年 | 6026篇 |
1972年 | 4178篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
Necessary conditions for the Gâteaux differentiability of the distance function to a set are considered. A series of characterizing results is obtained. 相似文献
44.
45.
The variational problem of contact equilibrium of a punch and an elastic body is considered. An equivalent formulation of the problem is given in variational inequality form. Existence and uniqueness of the solution is investigated in a particular case. A penalty method is proposed for approximate solution of the problem.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 56, pp. 97–103, 1985. 相似文献
46.
A method using third order moments for estimating the regression coefficients as well as the latent state scores of the reduced-rank regression model when the latent variable(s) are non-normally distributed is presented in this paper. It is shown that the factor analysis type indeterminacy of the regression coefficient matrices is eliminated. A real life example of the proposed method is presented. Differences of this solution with the reduced-rank regression eigen solution are discussed. 相似文献
47.
Exact closed-form solutions are exhibited for the Hopf equation for stationary incompressible 3D Navier-Stokes flow, for the cases of homogeneous forced flow (including a solution with depleted nonlinearity) and inhomogeneous flow with arbitrary boundary conditions. This provides an exact method for computing two- and higher-point moments, given the mean flow. 相似文献
48.
49.
In developing travel demand models it is generally assumed that the base-year data used in developing the parameters, as well as the forecasted data to be used as independent variables for the design year, are of acceptable quality. The purpose of this paper is to present the application of error propagation theory in assesing the predictive quality of one type of travel demand forecasting model (multinomial logit models) and to demonstrate how error considerations can be used as a tool for identifying the optimal model. The general conclusions of this study are that: (1) it is indeed possible to quantify errors in dependent variables in logit models as a consequence of errors in independent variables; and (2) error consideration can be used as a tool for identifying the optimal model from a set of candidate models. Further research is recommended to develop better insights into the phenomenon of error propagation so that the consideration of errors can be a factor in decisions on model selection. 相似文献
50.
H. Mazaheri 《分析论及其应用》2006,22(2):141-145
The concepts of quasi-Chebyshev and weakly-Chebyshev and σ-Chebyshev were defined [3 - 7], andas a counterpart to best approximation in normed linear spaces, best coapprozimation was introduced by Franchetti and Furi^[1]. In this research, we shall define τ-Chebyshev subspaces and τ-cochebyshev subspaces of a Banach space, in which the property τ is compact or weakly-compact, respectively. A set of necessary and sufficient theorems under which a subspace is τ-Chebyshev is defined. 相似文献