全文获取类型
收费全文 | 205918篇 |
免费 | 1662篇 |
国内免费 | 519篇 |
专业分类
化学 | 106636篇 |
晶体学 | 3443篇 |
力学 | 10433篇 |
综合类 | 16篇 |
数学 | 22511篇 |
物理学 | 65060篇 |
出版年
2021年 | 2072篇 |
2020年 | 2134篇 |
2019年 | 2677篇 |
2018年 | 3764篇 |
2017年 | 3746篇 |
2016年 | 4942篇 |
2015年 | 2454篇 |
2014年 | 4433篇 |
2013年 | 8848篇 |
2012年 | 7059篇 |
2011年 | 8300篇 |
2010年 | 6616篇 |
2009年 | 6790篇 |
2008年 | 7836篇 |
2007年 | 7781篇 |
2006年 | 6848篇 |
2005年 | 6087篇 |
2004年 | 5761篇 |
2003年 | 5276篇 |
2002年 | 5253篇 |
2001年 | 5668篇 |
2000年 | 4168篇 |
1999年 | 3172篇 |
1998年 | 2727篇 |
1997年 | 2785篇 |
1996年 | 2559篇 |
1995年 | 2233篇 |
1994年 | 2346篇 |
1993年 | 2237篇 |
1992年 | 2530篇 |
1991年 | 2654篇 |
1990年 | 2558篇 |
1989年 | 2629篇 |
1988年 | 2537篇 |
1987年 | 2557篇 |
1986年 | 2421篇 |
1985年 | 3040篇 |
1984年 | 3111篇 |
1983年 | 2612篇 |
1982年 | 2572篇 |
1981年 | 2536篇 |
1980年 | 2338篇 |
1979年 | 2713篇 |
1978年 | 2674篇 |
1977年 | 2874篇 |
1976年 | 2874篇 |
1975年 | 2667篇 |
1974年 | 2603篇 |
1973年 | 2715篇 |
1972年 | 2086篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
131.
132.
Physics of Particles and Nuclei Letters - The problem of spontaneous isotopic symmetry breaking in Nambu–Jona-Lasinio quark models is considered. It is shown that, in models with light... 相似文献
133.
Doklady Physics - In this paper, we study the statistical characteristics of the Riemann wave and the integral of it. Such problems arise in the physics of fronts’ propagation, in particular,... 相似文献
134.
135.
136.
We consider the problem of estimating a large rank-one tensor u ⊗k ∈ (ℝn)⊗k , k ≥ 3 , in Gaussian noise. Earlier work characterized a critical signal-to-noise ratio λ Bayes = O(1) above which an ideal estimator achieves strictly positive correlation with the unknown vector of interest. Remarkably, no polynomial-time algorithm is known that achieved this goal unless λ ≥ Cn(k − 2)/4 , and even powerful semidefinite programming relaxations appear to fail for 1 ≪ λ ≪ n(k − 2)/4 . In order to elucidate this behavior, we consider the maximum likelihood estimator, which requires maximizing a degree-k homogeneous polynomial over the unit sphere in n dimensions. We compute the expected number of critical points and local maxima of this objective function and show that it is exponential in the dimensions n , and give exact formulas for the exponential growth rate. We show that (for λ larger than a constant) critical points are either very close to the unknown vector u or are confined in a band of width Θ(λ−1/(k − 1)) around the maximum circle that is orthogonal to u . For local maxima, this band shrinks to be of size Θ(λ−1/(k − 2)) . These “uninformative” local maxima are likely to cause the failure of optimization algorithms. © 2019 Wiley Periodicals, Inc. 相似文献
137.
138.
Ain Uddin Kyle N. Plunkett 《Journal of polymer science. Part A, Polymer chemistry》2020,58(22):3165-3169
A series of donor-acceptor copolymers with dicyclopenta[cd,jk]pyrene and dicyclopenta[cd,lm]perylene acceptor units was prepared via palladium catalyzed cyclopenta-annulation reactions. The acceptor units were paired with diethynyl containing donor groups based on benzo[1,2-b:4,5-b’]dithiophene, thieno[3,2-b]thiophene, and 4-octyl-4H-dithieno[3,2-b:2′,3′-d]pyrrole to create six polymer variants. The cyclopentannulation polymerization resulted in copolymers with molecular weights (Mn) of 6–14 kDa and broad light absorption in the visible region with band gaps of 1.38–1.85 eV. The synthetic methodology, as well as optoelectronic properties, including thin-film absorption and cyclic voltammetry, of the donor-acceptor copolymers are presented. 相似文献
139.
Doklady Mathematics - Integro-differential equations with unbounded operator coefficients in a Hilbert space are studied. The equations under consideration are abstract hyperbolic equations... 相似文献
140.
The structure, chemical composition, and magnetic properties of electrochemically deposited nanocrystalline Co-Ni-Fe films
were investigated using a number of techniques. A high saturation magnetic induction up to B
s
= 21 kG was attained. An enhancement of the saturation magnetization compared to the ideal anticipated one was revealed,
which correlated with the nonlinear behavior of the structural phase composition and lattice parameters with the change of
the composition.
The text was submitted by the authors in English. 相似文献