全文获取类型
收费全文 | 545207篇 |
免费 | 28939篇 |
国内免费 | 19275篇 |
专业分类
化学 | 305674篇 |
晶体学 | 7612篇 |
力学 | 24667篇 |
综合类 | 88篇 |
数学 | 66497篇 |
物理学 | 188883篇 |
出版年
2020年 | 4271篇 |
2019年 | 4946篇 |
2018年 | 5434篇 |
2017年 | 6078篇 |
2016年 | 8996篇 |
2015年 | 7505篇 |
2014年 | 9412篇 |
2013年 | 24854篇 |
2012年 | 20475篇 |
2011年 | 25597篇 |
2010年 | 21287篇 |
2009年 | 21133篇 |
2008年 | 22016篇 |
2007年 | 21835篇 |
2006年 | 20860篇 |
2005年 | 19413篇 |
2004年 | 18632篇 |
2003年 | 16142篇 |
2002年 | 15847篇 |
2001年 | 17405篇 |
2000年 | 13250篇 |
1999年 | 10897篇 |
1998年 | 8959篇 |
1997年 | 8625篇 |
1996年 | 9008篇 |
1995年 | 8548篇 |
1994年 | 8543篇 |
1993年 | 8339篇 |
1992年 | 8538篇 |
1991年 | 8135篇 |
1990年 | 7462篇 |
1989年 | 7371篇 |
1988年 | 7502篇 |
1987年 | 6655篇 |
1986年 | 6533篇 |
1985年 | 8519篇 |
1984年 | 8749篇 |
1983年 | 6897篇 |
1982年 | 7832篇 |
1981年 | 7496篇 |
1980年 | 7191篇 |
1979年 | 7258篇 |
1978年 | 7404篇 |
1977年 | 7543篇 |
1976年 | 7857篇 |
1975年 | 6867篇 |
1974年 | 6820篇 |
1973年 | 7192篇 |
1972年 | 4938篇 |
1971年 | 3798篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Summary In this paper a Gauss-Jordan algorithm with column interchanges is presented and analysed. We show that, in contrast with Gaussian elimination, the Gauss-Jordan algorithm has essentially differing properties when using column interchanges instead of row interchanges for improving the numerical stability. For solutions obtained by Gauss-Jordan with column interchanges, a more satisfactory bound for the residual norm can be given. The analysis gives theoretical evidence that the algorithm yields numerical solutions as good as those obtained by Gaussian elimination and that, in most practical situations, the residuals are equally small. This is confirmed by numerical experiments. Moreover, timing experiments on a Cyber 205 vector computer show that the algorithm presented has good vectorisation properties. 相似文献
112.
113.
In the Bogoliubov theory, a condensate initially prepared in its ground state described by a stationary Bogoliubov vacuum and later perturbed by a time-dependent potential or interaction strength evolves into a time-dependent excited state which is a dynamical Bogoliubov vacuum. The dynamical vacuum has a simple diagonal form in a time-dependent orthonormal basis of single-particle modes. This diagonal representation leads to a Gaussian probability distribution for possible density-measurement outcomes in position and momentum space. 相似文献
114.
A. L. Chistov 《Journal of Mathematical Sciences》2006,138(3):5733-5752
Consider a projective algebraic variety W which is an irreducible component of the set of all common zeros of a family of
homogeneous polynomials of degrees less than d in n + 1 variables over a field of zero characteristic. Consider a dominant
rational morphism from W to W′ given by homogeneous polynomials of degree d′. We suggest algorithms for constructing objects
in general position related to this morphism. They generalize some algorithms from the first part of the paper to the case
dim W > dim W′. These algorithms are deterministic and polynomial in (dd′)n and the size of the input. Bibliography: 12 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 325, 2005, pp. 181–224. 相似文献
115.
116.
C.J. Wu 《Applied Acoustics》2002,63(10):1143-1154
This work formulates the double-layer structural-acoustic coupling problem for cylindrical shell by using a combination of the wave-number domain approach (WDA) and the boundary integral equation (BIE). Expressions for the spectral radial velocity of the outer surface of a finite fluid-filled/submerged (FFS) cylindrical thin shell are formulated by means of the transfer matrix equation in wave-number domain. It is shown that the spectral variables on the inner surface of the shell are related to those on the outer surface of the shell. The far field sound radiation from this kind of shell is numerically evaluated for various fluid cases. An experimental verification is performed, and a good correlation between the theoretical results and the experimental results shows that the theoretical study work in this paper is correct. 相似文献
117.
In this paper necessary and sufficient conditions of null-controllability and approximate null-controllability are obtained for the wave equation on a half-axis. Controls solving these problems are found explicitly. Moreover, bang-bang controls solving the approximate null-controllability problem are constructed with the aid of solutions of a frequency extinguishing problem in the restricted band (−a,a) for this equation and the Markov power moment problem. 相似文献
118.
We consider front solutions of the Swift–Hohenberg equation ∂
t
u= -(1+ ∂
x
2)2
u + ɛ2
u -u
3. These are traveling waves which leave in their wake a periodic pattern in the laboratory frame. Using renormalization techniques
and a decomposition into Bloch waves, we show the non-linear stability of these solutions. It turns out that this problem
is closely related to the question of stability of the trivial solution for the model problem ∂
t
u(x,t) = ∂
x
2
u (x,t)+(1+tanh(x-ct))u(x,t)+u(x,t)
p
with p>3. In particular, we show that the instability of the perturbation ahead of the front is entirely compensated by a diffusive
stabilization which sets in once the perturbation has hit the bulk behind the front.
Received: 23 February 2001 / Accepted: 27 August 2001 相似文献
119.
Let (\gnm)n,m ? \Zst(\gnm)_{n,m\in\Zst} be a Gabor frame for \LtR\LtR for given window gg. We show that the window \ho = \SQI g\ho=\SQI g that generates the canonically associated tight Gabor frame minimizes ||g-h||\|g-h\| among all windows hh generating a normalized tight Gabor frame. We present and prove versions of this result in the time domain, the frequency domain, the time-frequency domain, and the Zak transform domain, where in each domain the canonical \ho\ho is expressed using functional calculus for Gabor frame operators. Furthermore, we derive a Wiener--Levy type theorem for rationally oversampled Gabor frames. Finally, a Newton-type method for a fast numerical calculation of \ho\ho is presented. We analyze the convergence behavior of this method and demonstrate the efficiency of the proposed algorithm by some numerical examples. 相似文献
120.