全文获取类型
收费全文 | 498077篇 |
免费 | 6396篇 |
国内免费 | 2446篇 |
专业分类
化学 | 274012篇 |
晶体学 | 6997篇 |
力学 | 20643篇 |
综合类 | 68篇 |
数学 | 60401篇 |
物理学 | 144798篇 |
出版年
2020年 | 3755篇 |
2019年 | 3894篇 |
2018年 | 4322篇 |
2017年 | 4313篇 |
2016年 | 7390篇 |
2015年 | 5615篇 |
2014年 | 7742篇 |
2013年 | 21810篇 |
2012年 | 17353篇 |
2011年 | 21367篇 |
2010年 | 14024篇 |
2009年 | 13784篇 |
2008年 | 19732篇 |
2007年 | 20003篇 |
2006年 | 19256篇 |
2005年 | 17437篇 |
2004年 | 15685篇 |
2003年 | 13741篇 |
2002年 | 13624篇 |
2001年 | 14801篇 |
2000年 | 11387篇 |
1999年 | 8900篇 |
1998年 | 7231篇 |
1997年 | 7072篇 |
1996年 | 7221篇 |
1995年 | 6437篇 |
1994年 | 6286篇 |
1993年 | 6037篇 |
1992年 | 6644篇 |
1991年 | 6580篇 |
1990年 | 6151篇 |
1989年 | 5934篇 |
1988年 | 6117篇 |
1987年 | 5836篇 |
1986年 | 5705篇 |
1985年 | 7945篇 |
1984年 | 8102篇 |
1983年 | 6656篇 |
1982年 | 7264篇 |
1981年 | 7077篇 |
1980年 | 6691篇 |
1979年 | 6963篇 |
1978年 | 7133篇 |
1977年 | 7175篇 |
1976年 | 7157篇 |
1975年 | 6807篇 |
1974年 | 6746篇 |
1973年 | 6938篇 |
1972年 | 4590篇 |
1971年 | 3528篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Rainer Löwen 《Journal of Geometry》1989,36(1-2):110-116
We prove that a spread S over a locally compact nondlscrete field F defines a topological translation plane if and only if the spread is compact. For F=R, this is implicit in Breuning's thesis [Bre], cf. [B 2]. For the proof, we describe the point set of the projective translation plane as a quotient space of some projective space, with identifications taking place in one hyperplane. This is new even for F=R. 相似文献
42.
R. J. Vanderbei 《Mathematical Programming》1989,43(1-3):31-44
The affine-scaling modification of Karmarkar's algorithm is extended to solve problems with free variables. This extended primal algorithm is used to prove two important results. First the geometrically elegant feasibility algorithm proposed by Chandru and Kochar is the same algorithm as the one obtained by appending a single column of residuals to the constraint matrix. Second the dual algorithm as first described by Adler et al., is the same as the extended primal algorithm applied to the dual. 相似文献
43.
A piecewise linearization method based on the linearization of nonlinear ordinary differential equations in small intervals, that provides piecewise analytical solutions in each interval and smooth solutions everywhere, is developed for the study of the limit cycles of smooth and non-smooth, conservative and non-conservative, nonlinear oscillators. It is shown that this method provides nonlinear maps for the displacement and velocity which depend on the previous values through the nonlinearity and its partial derivatives with respect to time, displacement and velocity, and yields non-standard finite difference formulae. It is also shown by means of five examples that the piecewise linearization method presented here is more robust and yields more accurate (in terms of displacement, energy and frequency) solutions than the harmonic balance procedure, the method of slowly varying amplitude and phase, and other non-standard finite difference equations. 相似文献
44.
Aidan Mooney John G. Keating Daniel M. Heffernan 《Chaos, solitons, and fractals》2006,30(5):1088-1097
A digital watermark is a visible, or preferably invisible, identification code that is permanently embedded in digital media, to prove owner authentication and provide protection for documents. Given the interest in watermark generation using chaotic functions a detailed study of one chaotic function for this purpose is performed. In this paper, we present an approach for the generation of watermarks using the logistic map. Using this function, in conjunction with seed management, it is possible to generate chaotic sequences that may be used to create highpass or lowpass digital watermarks. In this paper we provide a detailed study on the generation of optically detectable watermarks and we provide some guidelines on successful chaotic watermark generation using the logistic map, and show using a recently published scheme, how care must be taken in the selection of the function seed. 相似文献
45.
I. J. Tchoupaeva 《Journal of Mathematical Sciences》2006,135(5):3409-3419
Some geometric theorems can be stated in coordinate-free form as polynomials in Grassman algebra and can be proven by the anticommutative Gröbner basis method. In this article, we analyze some properties of both sets of hypotheses and conclusions of the theorem. 相似文献
46.
R. J. Hinde 《Few-Body Systems》2006,38(2-4):187-191
We compute the vibrational coupling between two H2 molecules from ab initio quantum chemical calculations of the H2-H2 potential carried out at the full configuration interaction level of theory using the atom-centered aug-cc-pVTZ basis set
for hydrogen. We compare the full configuration interaction results with those obtained using two variants of coupled cluster
theory and find that a fully iterative treatment of connected triples may be required to estimate the H2-H2 vibrational coupling accurately using coupled cluster theory. 相似文献
47.
J. M. Rubi 《Journal of statistical physics》2006,123(2):497-498
48.
In this paper we study root system generalizations of the quantum Bose-gas on the circle with pair-wise delta-function interactions.
The underlying symmetry structures are shown to be governed by the associated graded algebra of Cherednik's (suitably filtered)
degenerate double affine Hecke algebra, acting by Dunkl-type differential-reflection operators. We use Gutkin's generalization
of the equivalence between the impenetrable Bose-gas and the free Fermi-gas to derive the Bethe ansatz equations and the Bethe
ansatz eigenfunctions. 相似文献
49.
J. Matkowski 《Aequationes Mathematicae》2002,64(3):297-303
Summary. Iteration semigroups of weighted quasi-arithmetic mean-type mappings are considered. Existence and uniqueness of a mean which is invariant with respect to a continuous semigroup of mean-type mapping is proved. 相似文献
50.
L. Aggoun 《Mathematical and Computer Modelling》2002,36(11-13)
In this paper, finite-dimensional recursive filters for space-time Markov random fields are derived. These filters can be used with the expectation maximization (EM) algorithm to yield maximum likelihood estimates of the parameters of the model. 相似文献