全文获取类型
收费全文 | 525253篇 |
免费 | 5911篇 |
国内免费 | 1460篇 |
专业分类
化学 | 279405篇 |
晶体学 | 8163篇 |
力学 | 23153篇 |
综合类 | 8篇 |
数学 | 61357篇 |
物理学 | 160538篇 |
出版年
2021年 | 4267篇 |
2020年 | 4695篇 |
2019年 | 5155篇 |
2018年 | 6996篇 |
2017年 | 6997篇 |
2016年 | 10315篇 |
2015年 | 6556篇 |
2014年 | 9910篇 |
2013年 | 24371篇 |
2012年 | 18907篇 |
2011年 | 22446篇 |
2010年 | 15867篇 |
2009年 | 15459篇 |
2008年 | 19998篇 |
2007年 | 20146篇 |
2006年 | 18567篇 |
2005年 | 16559篇 |
2004年 | 15257篇 |
2003年 | 13347篇 |
2002年 | 13118篇 |
2001年 | 14911篇 |
2000年 | 11384篇 |
1999年 | 8890篇 |
1998年 | 7347篇 |
1997年 | 7230篇 |
1996年 | 7013篇 |
1995年 | 6093篇 |
1994年 | 6029篇 |
1993年 | 5858篇 |
1992年 | 6638篇 |
1991年 | 6633篇 |
1990年 | 6428篇 |
1989年 | 6397篇 |
1988年 | 6066篇 |
1987年 | 6197篇 |
1986年 | 5789篇 |
1985年 | 7645篇 |
1984年 | 7650篇 |
1983年 | 6344篇 |
1982年 | 6696篇 |
1981年 | 6376篇 |
1980年 | 6237篇 |
1979年 | 6577篇 |
1978年 | 6855篇 |
1977年 | 6609篇 |
1976年 | 6604篇 |
1975年 | 6245篇 |
1974年 | 6193篇 |
1973年 | 6215篇 |
1972年 | 4257篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
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
82.
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
83.
84.
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
85.
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
86.
J. H. Eberly 《Laser Physics》2006,16(6):921-926
We examine the application of Schmidt mode analysis to pure-state entanglement. Several examples permitting exact analytic calculation of Schmidt eigenvalues and eigenfunctions are included, as well as evaluation of the associated degree of entanglement. 相似文献
87.
Debendra K. Mohapatra Dhananjoy Mondal Mukund S. Chorghade Mukund K. Gurjar 《Tetrahedron letters》2006,47(52):9215-9219
The non-proteinogenic amino acid 3-hydroxy-4-methylproline (HMP) is an active constituent of some potent antimicrobials including echinocandins, nostopeptins, pneumocandins, sporiofungin and mulundocandins. A synthesis has been achieved in 10 steps with 29% overall yield; the Evans’ aldol reaction using Crimmins’ modified method was pivotal to the success of the strategy. 相似文献
88.
S. N. Solov’ev K. A. Minasyan A. A. Korunov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(4):663-664
The enthalpies of reactions of La2CoO4(cr) and CoCl2(cr) with hydrochloric acid were measured with an isothermal-jacket calorimeter. The results obtained and the available literature data were used to calculate the standard enthalpy of formation of La2CoO4(cr) at 298.15 K, Δf H o = ?2179 ± 7 kJ/mol. 相似文献
89.
Johan Håstad 《Random Structures and Algorithms》2006,29(4):466-474
We show that the operations of permuting columns and rows separately and independently mix a square matrix in constant time. © 2006 Wiley Periodicals, Inc. Random Struct. Alg., 2006 相似文献
90.
An algorithm is proposed which allows one to construct higher symmetries of arbitrary order for some special classes of hyperbolic
systems possessing integrals. The Pohlmeyer-Lund-Regge system and the open two-dimensional Toda lattices are shown to belong
to the class of systems where our algorithm is applicable.
__________
Translated from Fundamental’naya i Prikladnaya Matematika (Fundamental and Applied Mathematics), Vol. 10, No. 1, Geometry
of Integrable Models, 2004. 相似文献