全文获取类型
收费全文 | 354156篇 |
免费 | 2298篇 |
国内免费 | 971篇 |
专业分类
化学 | 149697篇 |
晶体学 | 5110篇 |
力学 | 20814篇 |
综合类 | 5篇 |
数学 | 71526篇 |
物理学 | 110273篇 |
出版年
2021年 | 1672篇 |
2020年 | 1810篇 |
2019年 | 2013篇 |
2018年 | 18808篇 |
2017年 | 19298篇 |
2016年 | 12163篇 |
2015年 | 3782篇 |
2014年 | 4020篇 |
2013年 | 9492篇 |
2012年 | 13972篇 |
2011年 | 27867篇 |
2010年 | 16968篇 |
2009年 | 17281篇 |
2008年 | 22648篇 |
2007年 | 27653篇 |
2006年 | 8090篇 |
2005年 | 14353篇 |
2004年 | 10832篇 |
2003年 | 10459篇 |
2002年 | 7670篇 |
2001年 | 6780篇 |
2000年 | 5463篇 |
1999年 | 3958篇 |
1998年 | 3247篇 |
1997年 | 3184篇 |
1996年 | 3088篇 |
1995年 | 2797篇 |
1994年 | 2609篇 |
1993年 | 2487篇 |
1992年 | 2796篇 |
1991年 | 2783篇 |
1990年 | 2702篇 |
1989年 | 2517篇 |
1988年 | 2581篇 |
1987年 | 2575篇 |
1986年 | 2399篇 |
1985年 | 3086篇 |
1984年 | 3344篇 |
1983年 | 2752篇 |
1982年 | 2922篇 |
1981年 | 2890篇 |
1980年 | 2752篇 |
1979年 | 2847篇 |
1978年 | 2950篇 |
1977年 | 2863篇 |
1976年 | 2961篇 |
1975年 | 2729篇 |
1974年 | 2693篇 |
1973年 | 2866篇 |
1972年 | 1809篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
It is demonstrated theoretically that the initial (both elastic and viscous) magnetic susceptibility components for nanocrystalline
magnets caused by the processes of rotations (in the region of linear response) have resonant rather than relaxation character
typical already for the susceptibility component caused by displacements of domain boundaries.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 88–92, June, 2007. 相似文献
993.
Ji-hong SU & Yi-cai ZHAO LMAM Department of Mathematics Jinan University Guangzhou China 《中国科学A辑(英文版)》2007,50(4):495-502
Let X be a smooth projective variety of dimension 2k-1 (k≥3) over the complex number field. Assume that fR: X→Y is a small contraction such that every irreducible component Ei of the exceptional locus of fR is a smooth subvariety of dimension k. It is shown that each Ei is isomorphic to the k-dimensional projective space Pk, the k-dimensional hyperquadric surface Qk in Pk 1, or a linear Pk-1-bundle over a smooth curve. 相似文献
994.
The central observation of this paper is that if εn random arcs are added to any n‐node strongly connected digraph with bounded degree then the resulting graph has diameter 𝒪(lnn) with high probability. We apply this to smoothed analysis of algorithms and property testing. Smoothed Analysis: Recognizing strongly connected digraphs is a basic computational task in graph theory. Even for digraphs with bounded degree, it is NL‐complete. By XORing an arbitrary bounded degree digraph with a sparse random digraph R ∼ 𝔻n,ε/n we obtain a “smoothed” instance. We show that, with high probability, a log‐space algorithm will correctly determine if a smoothed instance is strongly connected. We also show that if NL ⫅̸ almost‐L then no heuristic can recognize similarly perturbed instances of (s,t)‐connectivity. Property Testing: A digraph is called k‐linked if, for every choice of 2k distinct vertices s1,…,sk,t1,…,tk, the graph contains k vertex disjoint paths joining sr to tr for r = 1,…,k. Recognizing k‐linked digraphs is NP‐complete for k ≥ 2. We describe a polynomial time algorithm for bounded degree digraphs, which accepts k‐linked graphs with high probability, and rejects all graphs that are at least εn arcs away from being k‐linked. © 2007 Wiley Periodicals, Inc. Random Struct. Alg., 2007 相似文献
995.
996.
997.
The article concerns heterojunction resonant cavity-enhanced (RCE) Schottky photodiodes with GaAs in the absorption layer. The quantum efficiency and linear pulse response have thoroughly been analysed. For the first time, the response of a heterojunction photodiode has been modelled by the phenomenological model for a two-valley semiconductor. The results obtained have shown that the satellite valleys, as well as the parasitic time constant, significantly influence the response and, accordingly, have to be taken into account when analysing and optimizing RCE photodetectors. 相似文献
998.
We present the results of a study and substantiation of the method of polygaussian approximation of an electrocardiographic (ECG) signal against interference background during computer analysis of that signal. It is proposed to use adaptive processing of ECG signals, which allows one to increase the signal-to-interference ratio by over 7 dB. 相似文献
999.
René Meziat Diego Patiño Pablo Pedregal 《Computational Optimization and Applications》2007,38(1):147-171
We propose an alternative method for computing effectively the solution of non-linear, fixed-terminal-time, optimal control
problems when they are given in Lagrange, Bolza or Mayer forms. This method works well when the nonlinearities in the control
variable can be expressed as polynomials. The essential of this proposal is the transformation of a non-linear, non-convex
optimal control problem into an equivalent optimal control problem with linear and convex structure. The method is based on
global optimization of polynomials by the method of moments. With this method we can determine either the existence or lacking
of minimizers. In addition, we can calculate generalized solutions when the original problem lacks of minimizers. We also
present the numerical schemes to solve several examples arising in science and technology. 相似文献
1000.
N. B. Valetova L. L. Semenycheva I. S. Il’ichev A. N. Artemov D. F. Grishin 《Russian Journal of Applied Chemistry》2007,80(5):818-821
Features of radical polymerization of styrene in the presence of (diphenylbutadiene)tricarbonylchromium were studied. 相似文献