全文获取类型
收费全文 | 12774篇 |
免费 | 1260篇 |
国内免费 | 689篇 |
专业分类
化学 | 987篇 |
晶体学 | 27篇 |
力学 | 821篇 |
综合类 | 214篇 |
数学 | 8184篇 |
物理学 | 4490篇 |
出版年
2023年 | 125篇 |
2022年 | 144篇 |
2021年 | 288篇 |
2020年 | 323篇 |
2019年 | 315篇 |
2018年 | 275篇 |
2017年 | 358篇 |
2016年 | 386篇 |
2015年 | 301篇 |
2014年 | 521篇 |
2013年 | 1016篇 |
2012年 | 517篇 |
2011年 | 615篇 |
2010年 | 483篇 |
2009年 | 656篇 |
2008年 | 777篇 |
2007年 | 788篇 |
2006年 | 684篇 |
2005年 | 575篇 |
2004年 | 514篇 |
2003年 | 544篇 |
2002年 | 578篇 |
2001年 | 493篇 |
2000年 | 490篇 |
1999年 | 417篇 |
1998年 | 359篇 |
1997年 | 281篇 |
1996年 | 225篇 |
1995年 | 158篇 |
1994年 | 193篇 |
1993年 | 124篇 |
1992年 | 127篇 |
1991年 | 133篇 |
1990年 | 90篇 |
1989年 | 88篇 |
1988年 | 94篇 |
1987年 | 77篇 |
1986年 | 55篇 |
1985年 | 77篇 |
1984年 | 86篇 |
1983年 | 42篇 |
1982年 | 47篇 |
1981年 | 40篇 |
1980年 | 34篇 |
1979年 | 46篇 |
1978年 | 37篇 |
1977年 | 30篇 |
1976年 | 24篇 |
1975年 | 15篇 |
1973年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
1.
2.
3.
4.
5.
Renny Mathew Karolina A. Uchman Lydia Gkoura Chris J. Pickard Maria Baias 《Magnetic resonance in chemistry : MRC》2020,58(11):1018-1025
A combined experimental and computational approach was used to distinguish between different polymorphs of the pharmaceutical drug aspirin. This method involves the use of ab initio random structure searching (AIRSS), a density functional theory (DFT)-based crystal structure prediction method for the high-accuracy prediction of polymorphic structures, with DFT calculations of nuclear magnetic resonance (NMR) parameters and solid-state NMR experiments at natural abundance. AIRSS was used to predict the crystal structures of form-I and form-II of aspirin. The root-mean-square deviation between experimental and calculated 1H chemical shifts was used to identify form-I as the polymorph present in the experimental sample, the selection being successful despite the large similarities between the molecular environments in the crystals of the two polymorphs. 相似文献
6.
《Stochastic Processes and their Applications》2020,130(5):2596-2638
In this paper we introduce a new generalisation of the relative Fisher Information for Markov jump processes on a finite or countable state space, and prove an inequality which connects this object with the relative entropy and a large deviation rate functional. In addition to possessing various favourable properties, we show that this generalised Fisher Information converges to the classical Fisher Information in an appropriate limit. We then use this generalised Fisher Information and the aforementioned inequality to qualitatively study coarse-graining problems for jump processes on discrete spaces. 相似文献
7.
Nonclassical light states are important for both conceptual and practical reasons: they are basic ingredients in testing and exploring quantum foundations, and are crucial resources in quantum technologies. Various useful criteria have been developed to detect nonclassicality in the literature, and several meaningful measures of nonclassicality have been introduced and measured experimentally. In this work, by use of a non-Hermitian generalization of the Wigner-Yanase-Dyson skew information and playing with operator ordering in evaluating average photon number, we develop a novel family of criteria for detecting nonclassicality of light based on Lieb's concavity, which is a deep and powerful result concerning interaction between quantum states and observables. We elucidate the information-theoretic as well as the physical meaning of the criteria, and illustrate their effectiveness in capturing and quantifying nonclassicality of various important light states. 相似文献
8.
We give a sheaf theoretic interpretation of Potts models with external magnetic field, in terms of constructible sheaves and their Euler characteristics. We show that the polynomial countability question for the hypersurfaces defined by the vanishing of the partition function is affected by changes in the magnetic field: elementary examples suffice to see non-polynomially countable cases that become polynomially countable after a perturbation of the magnetic field. The same recursive formula for the Grothendieck classes, under edge-doubling operations, holds as in the case without magnetic field, but the closed formulae for specific examples like banana graphs differ in the presence of magnetic field. We give examples of computation of the Euler characteristic with compact support, for the set of real zeros, and find a similar exponential growth with the size of the graph. This can be viewed as a measure of topological and algorithmic complexity. We also consider the computational complexity question for evaluations of the polynomial, and show both tractable and NP-hard examples, using dynamic programming. 相似文献
9.
10.
Lu Chuanrong 《数学年刊B辑(英文版)》1997,18(1):71-78
Let $\{\xi_{\bold t}, {\bold t}
\in {\bold Z}^d\}$ be a nonuniform $\varphi$-mixing strictly stationary
real random field with
$E\xi_{\bold 0}=0, E|\xi_{\bold 0}|^{2+\delta}<\infty$ for some
$0<\delta<1$. A sufficient
condition is given for the sequence of partial sum set-indexed process
$\{Z_n(A),\ A\in \Cal A\}$ to converge to Brownian motion. By a direct
calculation, the author shows
that the result holds for a more general class of set index ${\Cal A}$, where
${\Cal A}$ is assumed only to have the metric entropy exponent $r, 0相似文献