全文获取类型
收费全文 | 2534篇 |
免费 | 79篇 |
国内免费 | 118篇 |
专业分类
化学 | 205篇 |
晶体学 | 1篇 |
力学 | 132篇 |
综合类 | 1篇 |
数学 | 1555篇 |
物理学 | 837篇 |
出版年
2024年 | 4篇 |
2023年 | 18篇 |
2022年 | 55篇 |
2021年 | 30篇 |
2020年 | 65篇 |
2019年 | 70篇 |
2018年 | 77篇 |
2017年 | 53篇 |
2016年 | 46篇 |
2015年 | 37篇 |
2014年 | 126篇 |
2013年 | 228篇 |
2012年 | 87篇 |
2011年 | 156篇 |
2010年 | 127篇 |
2009年 | 171篇 |
2008年 | 209篇 |
2007年 | 174篇 |
2006年 | 119篇 |
2005年 | 87篇 |
2004年 | 77篇 |
2003年 | 78篇 |
2002年 | 61篇 |
2001年 | 36篇 |
2000年 | 41篇 |
1999年 | 38篇 |
1998年 | 50篇 |
1997年 | 41篇 |
1996年 | 44篇 |
1995年 | 29篇 |
1994年 | 27篇 |
1993年 | 25篇 |
1992年 | 29篇 |
1991年 | 21篇 |
1990年 | 13篇 |
1989年 | 27篇 |
1988年 | 20篇 |
1987年 | 15篇 |
1986年 | 12篇 |
1985年 | 12篇 |
1984年 | 20篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1974年 | 3篇 |
排序方式: 共有2731条查询结果,搜索用时 15 毫秒
101.
Random coil phosphorus chemical shift of deoxyribonucleic acids 总被引:1,自引:0,他引:1
Random coil phosphorus chemical shift has been studied using 16 17-nucleotide DNA sequences. Due to the presence of residual base stacking in these sequences, the temperature and sequence effects were investigated at 50 and 55 degrees C. The phosphorus chemical shifts of random coil DNA sequences have been found to be independent of temperature. Sequence effect analysis shows that the phosphorus chemical shift of a nucleotide in a random coil DNA sequence depends on both its 5'- and 3'-nearest neighbors. A trimer model has been used to establish the random coil 31P chemical shift prediction protocol which shows an accuracy of 0.02 ppm. 相似文献
102.
Peter?EichelsbacherEmail author Matthias?L?we 《Probability Theory and Related Fields》2004,130(4):441-472
We derive moderate deviation principles for the overlap parameter in the Hopfield model of spin glasses and neural networks. If the inverse temperature is different from the critical inverse temperature c=1 and the number of patterns M(N) satisfies M(N)/N 0, the overlap parameter multiplied by N, 1/2 < < 1, obeys a moderate deviation principle with speed N1–2 and a quadratic rate function (i.e. the Gaussian limit for = 1/2 remains visible on the moderate deviation scale). At the critical temperature we need to multiply the overlap parameter by N, 1/4 < < 1. If then M(N) satisfies (M(N)6 log N M(N)2N4 log N)/N 0, the rescaled overlap parameter obeys a moderate deviation principle with speed N1–4 and a rate function that is basically a fourth power. The random term occurring in the Central Limit theorem for the overlap at c = 1 is no longer present on a moderate deviation scale. If the scaling is even closer to N1/4, e.g. if we multiply the overlap parameter by N1/4 log log N the moderate deviation principle breaks down. The case of variable temperature converging to one is also considered. If N converges to c fast enough, i.e. faster than the non-Gaussian rate function persists, whereas for N converging to one slower than the moderate deviations principle is given by the Gaussian rate. At the borderline the moderate deviation rate function is the one at criticality plus an additional Gaussian term.Research supported by the Volkswagen-Stiftung (RiP-program at Oberwolfach, Germany).Mathematics Subject Classification (2000): 60F10 (primary), 60K35, 82B44, 82D30 (secondary) 相似文献
103.
Our model is a generalized linear programming relaxation of a much studied random K-SAT problem. Specifically, a set of linear constraints on K variables is fixed. From a pool of n variables, K variables are chosen uniformly at random and a constraint is chosen from also uniformly at random. This procedure is repeated m times independently. We are interested in whether the resulting linear programming problem is feasible. We prove that the feasibility property experiences a linear phase transition, when n and m = cn for a constant c. Namely, there exists a critical value c* such that, when c < c*, the problem is feasible or is asymptotically almost feasible, as n, but, when c>c*, the distance to feasibility is at least a positive constant independent of n. Our result is obtained using the combination of a powerful local weak convergence method developed in Aldous [Ald92], [Ald01], Aldous and Steele [AS03], Steele [Ste02] and martingale techniques. By exploiting a linear programming duality, our theorem implies the following result in the context of sparse random graphs G(n, cn) on n nodes with cn edges, where edges are equipped with randomly generated weights. Let (n, c) denote maximum weight matching in G(n, cn). We prove that when c is a constant and n , the limit limn (n, c)/n, exists, with high probability. We further extend this result to maximum weight b-matchings also in G(n, cn). 相似文献
104.
In this paper we consider random perturbations of dynamical systems and diffusion processes with a first integral. We calculate, under some assumptions, the limiting behavior of the slow component of the perturbed system in an appropriate time scale for a general class of perturbations. The phase space of the slow motion is a graph defined by the first integral. This is a natural generalization of the results concerning random perturbations of Hamiltonian systems. Considering diffusion processes as the unperturbed system allows to study the multidimensional case and leads to a new effect: the limiting slow motion can spend non-zero time at some points of the graph. In particular, such delay at the vertices leads to more general gluing conditions. Our approach allows one to obtain new results on singular perturbations of PDEs.
Mathematics Subject Classification (2001): 60H10; 34C29; 35B20 相似文献
105.
FengDejun WangYang 《分析论及其应用》2003,19(4):312-331
The Bernoulli convolution Vλ measure is shown to be absolutely continuous with L^2 density for almost all 1/2<λ<1, and singular if λ^-1 is a Pisot number. It is an open question whether the Pisot type Bernoulli conuolutions are the only singular ones. In this paper, we construct a family of non-Pisot type Bernoulli convo-lutions Vλ such that their density functions, if they exist, are not L^2. We also construct other Bernolulli convo-lutions whose density functions if they exist, behave rather badly. 相似文献
106.
LiuYanyan WuJun 《分析论及其应用》2003,19(4):342-354
A set is called regular if its Hausdorff dimension and upper box-counting dimension coincide. In this paper, we prove that the random self-con formal set is regular almost surely. Also we determine the dimen-sions for a class of random self-con formal sets. 相似文献
107.
We derive an elementary formula for Janossy densities for determinantal point processes with a finite rank projection-type kernel. In particular, for =2 polynomial ensembles of random matrices we show that the Janossy densities on an interval I can be expressed in terms of the Christoffel–Darboux kernel for the orthogonal polynomials on the complement of I. 相似文献
108.
Gady Kozma Alexander Olevskii 《Proceedings of the American Mathematical Society》2003,131(6):1901-1906
We show that the spectra of frequencies obtained by random perturbations of the integers allows one to represent any measurable function on by an almost everywhere converging sum of harmonics:
109.
110.
B. Podobnik D. F. Fu H. E. Stanley P. Ch. Ivanov 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(1):47-52
We develop a stochastic process with two coupled variables where
the absolute values of each variable exhibit long-range power-law
autocorrelations and are also long-range cross-correlated. We investigate how
the scaling exponents characterizing power-law autocorrelation and long-range
cross-correlation behavior in the absolute values of the generated variables
depend on the two parameters in our model. In particular, if the
autocorrelation is stronger, the cross-correlation is also stronger. We test
the utility of our approach by comparing the autocorrelation and
cross-correlation properties of the time series generated by our model with
data on daily returns over ten years for two major financial indices, the
Dow Jones and the S&P500, and on daily returns of two well-known
company stocks, IBM and Microsoft, over five years. 相似文献