全文获取类型
收费全文 | 6844篇 |
免费 | 551篇 |
国内免费 | 253篇 |
专业分类
化学 | 1221篇 |
晶体学 | 53篇 |
力学 | 230篇 |
综合类 | 40篇 |
数学 | 3165篇 |
物理学 | 2939篇 |
出版年
2023年 | 45篇 |
2022年 | 89篇 |
2021年 | 135篇 |
2020年 | 157篇 |
2019年 | 159篇 |
2018年 | 136篇 |
2017年 | 118篇 |
2016年 | 142篇 |
2015年 | 153篇 |
2014年 | 270篇 |
2013年 | 573篇 |
2012年 | 260篇 |
2011年 | 331篇 |
2010年 | 254篇 |
2009年 | 366篇 |
2008年 | 447篇 |
2007年 | 477篇 |
2006年 | 360篇 |
2005年 | 263篇 |
2004年 | 223篇 |
2003年 | 251篇 |
2002年 | 285篇 |
2001年 | 230篇 |
2000年 | 249篇 |
1999年 | 225篇 |
1998年 | 219篇 |
1997年 | 107篇 |
1996年 | 101篇 |
1995年 | 81篇 |
1994年 | 93篇 |
1993年 | 62篇 |
1992年 | 68篇 |
1991年 | 61篇 |
1990年 | 51篇 |
1989年 | 59篇 |
1988年 | 42篇 |
1987年 | 69篇 |
1986年 | 40篇 |
1985年 | 65篇 |
1984年 | 48篇 |
1983年 | 34篇 |
1982年 | 42篇 |
1981年 | 14篇 |
1980年 | 27篇 |
1979年 | 32篇 |
1978年 | 24篇 |
1977年 | 26篇 |
1976年 | 22篇 |
1974年 | 16篇 |
1973年 | 16篇 |
排序方式: 共有7648条查询结果,搜索用时 15 毫秒
131.
In this paper, by exploiting recent results on the pathwise behavior of the workload process in single server, work conserving queues of theG/G/1/ type, we show that the workload of multiserver, work conserving queues ofG/G/m/ (m<) (andG/G/) queues satisfies an o(t) growth condition, provided that the time average of the work brought into the system is less thanm form < (and finite form=). 相似文献
132.
P. Vieillefosse 《Journal of statistical physics》1994,74(5-6):1195-1209
The Coulomb pair density matrixG
(r, r) for attractive and repulsive potentials is not only interesting for determining the two-particle effective potentials, but it is also essential in numerical studies of quantum systems. A high-temperature approximation is obtained for logG
(r, r), in the form of simple integrals or series expansions; large-distance expansions are also given. 相似文献
133.
Michel Weber 《Journal of Theoretical Probability》1996,9(1):105-112
Let (Y,,,T) be an ergodic dynamical system. LetA be an nonempty subset ofL
2() such that
, whereA=sup{||sȒt||2
,s, tA} andN(A, u) is the smallest number ofL
2()-open balls of radiusu, centered inA, enough to coverA. Let
. We prove as a consequence of a more general result, thatC(A) is aGB subset ofL
2(). 相似文献
134.
Consider anM/M/1 queueing system with server vacations where the server is turned off as soon as the queue gets empty. We assume that the vacation durations form a sequence of i.i.d. random variables with exponential distribution. At the end of a vacation period, the server may either be turned on if the queue is non empty or take another vacation. The following costs are incurred: a holding cost ofh per unit of time and per customer in the system and a fixed cost of each time the server is turned on. We show that there exists a threshold policy that minimizes the long-run average cost criterion. The approach we use was first proposed in Blanc et al. (1990) and enables us to determine explicitly the optimal threshold and the optimal long-run average cost in terms of the model parameters. 相似文献
135.
B. Kaminski 《Proceedings of the American Mathematical Society》1996,124(5):1533-1537
It is shown that if an abelian countable group is such that is a finite group and every aperiodic positive entropy action of on a Lebesgue probability space has a countable Haar spectrum in the subspace , where denotes the Pinsker -
algebra of , then every aperiodic positive entropy action of on has the same property. A positive answer to the question of J.P. Thouvenot is obtained as a corollary.
algebra of , then every aperiodic positive entropy action of on has the same property. A positive answer to the question of J.P. Thouvenot is obtained as a corollary.
136.
The effect of geometry modifications of13C chemical shifts has been investigated in a small subset of molecules using both LO-INDO and Gaussian 70 (4–31) calculations. The Gaussian calculations, while known to give poor absolute shifts, compare well to the reparameterized semi-empirical INDO determinations in calculated shift changes. In virtually all cases the signs of the shift changes were found to be opposite to that of the changes in the calculated electronic energy. 相似文献
137.
Tin dioxide SnO2−δ is a pronounced n-type electron conductor due to its oxygen deficiency. This study investigates the rate of chemical diffusion of oxygen in SnO2−δ single crystals, which is a crucial step in the overall stoichiometry change of the material. The chemical diffusion coefficient Dδ was determined from conductivity- and EPR-relaxation methods. The temperature dependence was found to be . The dependence on crystal orientation, dopant content and oxygen partial pressure was below experimental error. The latter observation leads to the conclusion that the chemical diffusion coefficient is close to the diffusion coefficient of oxygen vacancies. Along with the relaxation process resulting from the chemical diffusion of oxygen, additional processes were observed. One of these was attributed to complications in the defect chemistry of the material. The relevance of the results for the kinetics of drift processes of Taguchi sensors is discussed. 相似文献
138.
J. Neveu 《Stochastic Processes and their Applications》1985,19(2):237-258
Given a stationary stochastic continuous demand of service σ(θtω) dt with ∫ σ(ω)P(dω) < 1, we construct real stationary point processes such that for a given constant D \2>0. These point processes correspond to a service discipline for which a single server services during the time intervals [Tn, Tn+1[ the demand of service accumulated during the proceding intervals [Tn?1, Tn[ and take a rest of fixed duration D. 相似文献
139.
140.
A. Rivaton B. Mailhot M. Lounaci J.-L. Gardette 《Polymer Degradation and Stability》2006,91(3):565-572
This paper is devoted to the analysis of the photochemical behaviour of copolymers with carbazole units exposed to long-wavelength radiation. These copolymers are constituted of two types of carbazolylethyl methacrylate units (CEM) with octyl methacrylate moieties (OMA). The exposure of copolymers and PVK to UV light results in dramatic modifications of the physical and photophysical properties of the polymer. These modifications can be correlated with modifications of the chemical structure of the matrix. The photoageing of copolymers and PVK has been analysed by fluorescence, ESR, UV-vis and infrared spectroscopies. The effects of crosslinking and chain scissions were determined by gel fraction measurements and size exclusion chromatography. 相似文献