全文获取类型
收费全文 | 28327篇 |
免费 | 806篇 |
国内免费 | 230篇 |
专业分类
化学 | 19288篇 |
晶体学 | 129篇 |
力学 | 648篇 |
综合类 | 1篇 |
数学 | 5387篇 |
物理学 | 3910篇 |
出版年
2022年 | 183篇 |
2021年 | 277篇 |
2020年 | 347篇 |
2019年 | 313篇 |
2018年 | 276篇 |
2017年 | 292篇 |
2016年 | 600篇 |
2015年 | 621篇 |
2014年 | 659篇 |
2013年 | 1407篇 |
2012年 | 1408篇 |
2011年 | 1708篇 |
2010年 | 952篇 |
2009年 | 815篇 |
2008年 | 1467篇 |
2007年 | 1466篇 |
2006年 | 1553篇 |
2005年 | 1394篇 |
2004年 | 1328篇 |
2003年 | 1099篇 |
2002年 | 1048篇 |
2001年 | 454篇 |
2000年 | 408篇 |
1999年 | 396篇 |
1998年 | 385篇 |
1997年 | 432篇 |
1996年 | 399篇 |
1995年 | 361篇 |
1994年 | 392篇 |
1993年 | 344篇 |
1992年 | 321篇 |
1991年 | 320篇 |
1990年 | 278篇 |
1989年 | 280篇 |
1988年 | 260篇 |
1987年 | 218篇 |
1986年 | 246篇 |
1985年 | 362篇 |
1984年 | 370篇 |
1983年 | 315篇 |
1982年 | 348篇 |
1981年 | 316篇 |
1980年 | 338篇 |
1979年 | 270篇 |
1978年 | 300篇 |
1977年 | 279篇 |
1976年 | 227篇 |
1975年 | 191篇 |
1974年 | 195篇 |
1973年 | 167篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
For linear statistical ill-posed problems in Hilbert spaces we introduce an adaptive procedure to recover the unknown solution from indirect discrete and noisy data. This procedure is shown to be order optimal for a large class of problems. Smoothness of the solution is measured in terms of general source conditions. The concept of operator monotone functions turns out to be an important tool for the analysis.
103.
104.
Peter Enders 《Optical and Quantum Electronics》1989,21(3):167-181
The small-signal analysis of a simple model of three rate equations is performed rigorously by means of both the Routh-Hurwitz theorem and Descartes' sign rule, and the relationship between bistable behaviour and self-sustained pulsations (SSPs) is investigated. Because one eigenvalue of the Jacobian of the model system is always negative, small-amplitude, sinusoidal SSPs can be described in terms of Haken's dressed-mode variables on a two-dimensional centre manifold. Possible simplifications for the switching modelling are also mentioned. 相似文献
105.
Empirical minimization 总被引:3,自引:0,他引:3
We investigate the behavior of the empirical minimization algorithm using various methods. We first analyze it by comparing
the empirical, random, structure and the original one on the class, either in an additive sense, via the uniform law of large
numbers, or in a multiplicative sense, using isomorphic coordinate projections. We then show that a direct analysis of the
empirical minimization algorithm yields a significantly better bound, and that the estimates we obtain are essentially sharp.
The method of proof we use is based on Talagrand's concentration inequality for empirical processes.
Research partially supported by NSF under award DMS-0434393.
Research partially supported by the Australian Research Council Discovery Porject DP0343616. 相似文献
106.
107.
108.
Symmetry is one of the most important aesthetic criteria in graph drawing because it reveals structure in the graph. To draw
graphs symmetrically, we employ two steps. The first step is to find appropriate automorphisms. The second step is to draw
the graph to display the automorphisms. Our aim in this paper is to construct maximally symmetric straight line drawings of
triconnected planar graphs in linear time. Previously known algorithms run in quadratic time. We show that an algorithm of
Fontet can be used to find an embedding in the plane with the maximum number of symmetries, and present a new algorithm for
finding a straight line drawing that achieves that maximum. Both algorithms run in linear time. 相似文献
109.
110.
We consider the M(t)/M(t)/m/m queue, where the arrival rate λ(t) and service rate μ(t) are arbitrary (smooth) functions of time. Letting pn(t) be the probability that n servers are occupied at time t (0≤ n≤ m, t > 0), we study this distribution asymptotically, for m→∞ with a comparably large arrival rate λ(t) = O(m) (with μ(t) = O(1)). We use singular perturbation techniques to solve the forward equation for pn(t) asymptotically. Particular attention is paid to computing the mean number of occupied servers and the blocking probability
pm(t). The analysis involves several different space-time ranges, as well as different initial conditions (we assume that at t = 0 exactly n0 servers are occupied, 0≤ n0≤ m). Numerical studies back up the asymptotic analysis.
AMS subject classification: 60K25,34E10
Supported in part by NSF grants DMS-99-71656 and DMS-02-02815 相似文献