全文获取类型
收费全文 | 12992篇 |
免费 | 1600篇 |
国内免费 | 668篇 |
专业分类
化学 | 6478篇 |
晶体学 | 100篇 |
力学 | 797篇 |
综合类 | 158篇 |
数学 | 3607篇 |
物理学 | 4120篇 |
出版年
2024年 | 22篇 |
2023年 | 127篇 |
2022年 | 256篇 |
2021年 | 373篇 |
2020年 | 545篇 |
2019年 | 402篇 |
2018年 | 315篇 |
2017年 | 361篇 |
2016年 | 506篇 |
2015年 | 480篇 |
2014年 | 576篇 |
2013年 | 875篇 |
2012年 | 669篇 |
2011年 | 652篇 |
2010年 | 519篇 |
2009年 | 669篇 |
2008年 | 734篇 |
2007年 | 841篇 |
2006年 | 690篇 |
2005年 | 565篇 |
2004年 | 482篇 |
2003年 | 559篇 |
2002年 | 499篇 |
2001年 | 454篇 |
2000年 | 422篇 |
1999年 | 368篇 |
1998年 | 351篇 |
1997年 | 206篇 |
1996年 | 199篇 |
1995年 | 152篇 |
1994年 | 153篇 |
1993年 | 139篇 |
1992年 | 122篇 |
1991年 | 122篇 |
1990年 | 102篇 |
1989年 | 86篇 |
1988年 | 84篇 |
1987年 | 65篇 |
1986年 | 62篇 |
1985年 | 70篇 |
1984年 | 76篇 |
1983年 | 32篇 |
1982年 | 37篇 |
1981年 | 43篇 |
1980年 | 37篇 |
1979年 | 34篇 |
1978年 | 31篇 |
1977年 | 24篇 |
1976年 | 21篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
We develop a production policy that controls work-in-process (WIP) levels and satisfies demand in a multistage manufacturing system with significant uncertainty in yield, rework, and demand. The problem addressed in this paper is more general than those in the literature in three aspects: (i) multiple products are processed at multiple workstations, and the capacity of each workstation is limited and shared by multiple operations; (ii) the behavior of a production policy is investigated over an infinite-time horizon, and thus the system stability can be evaluated; (iii) the representation of yield and rework uncertainty is generalized. Generalizing both the system structure and the nature of uncertainty requires a new mathematical development in the theory of infinite-horizon stochastic dynamic programming. The theoretical contributions of this paper are the existence proofs of the optimal stationary control for a stochastic dynamic programming problem and the finite covariances of WIP and production levels under the general expression of uncertainty. We develop a simple and explicit sufficient condition that guarantees the existence of both the optimal stationary control and the system stability. We describe how a production policy can be constructed for the manufacturing system based on the propositions derived. 相似文献
32.
33.
An effective residual interaction between particles and holes for shell model calculations around 208Pb, derived from the interaction between free nucleons, is compared with the measured properties of proton-hole neutron states
in 208Tl and the interaction between proton holes is adjusted to newly measured level energies in 206Hg. These interaction elements are particularly relevant for neutron-rich nuclei. The adjustment of two mixing elements reproduces
the known γ-decay data in 208Tl.
Received: 2 April 2002 / Accepted: 2 May 2002 相似文献
34.
35.
F. Rubio F. García H. D. Burrows A. A. C. C. Pais A. J. M. Valente M. J. Tapia J. M. García 《Journal of polymer science. Part A, Polymer chemistry》2007,45(9):1788-1799
The interaction between trivalent lanthanide ions and poly(1,4,7,10,13‐pentaoxacyclopentadecan‐2‐yl‐methyl methacrylate), PCR5, in aqueous solution and in the solid state have been studied. In aqueous solution, evidence of a weak interaction between the lanthanides and PCR5 comes from the small red shift of the Ce(III) emission spectra and the slight broadening of the Gd(III) EPR spectra. From the Tb(III) lifetimes in the presence of H2O and D2O the loss of one or two water coordinated molecules is confirmed when Tb(III) is bound to PCR5. An association constant of the order of 200 M?1 was obtained for a 1:1 (lanthanide:15‐crown‐5) complex from the shift of the polymer NMR signals induced by Tb(III). A similar association constant is obtained from the differences of the molar conductivity of Ce(III) solution at various concentrations in presence and absence of PCR5. When Tb(III) is adsorbed on PCR5 membranes, lifetime experiments in H2O and D2O confirm the loss of 5 or 6 water coordinated molecules indicating that in solid state the lanthanide(III)‐PCR5 interaction is stronger than in solution. The adsorption of Ce(III) in PCR5 membranes shows a Langmuir type isotherm, from which an equilibrium constant of 39 M?1 has been calculated. SEM shows that the membrane morphology is not much affected by lanthanide adsorption. Support for lanthanide ion–crown interactions comes from ab initio calculations on 15‐crown‐5/La(III) complex. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1788–1799, 2007 相似文献
36.
引入了随机环境中双移民生灭过程的概念,定义了过程的模态指示函数,在此基础上研究了其转移矩阵的平稳分布,给出了平稳分布众数的位置与模态指示函数之间的关系.研究了平稳分布的众数与边界关系. 相似文献
37.
We introduce a random perturbed version of the classical fidelity and we show that it converges with the same rate of decay
of correlations, but not uniformly in the noise. This makes the classical fidelity unstable in the zero-noise limit. 相似文献
38.
We derive a moderate deviation principle for the lower tail probabilities of the length of a longest increasing subsequence in a random permutation. It refers to the regime between the lower tail large deviation regime and the central limit regime. The present article together with the upper tail moderate deviation principle in Ref. 12 yields a complete picture for the whole moderate deviation regime. Other than in Ref. 12, we can directly apply estimates by Baik, Deift, and Johansson, who obtained a (non-standard) Central Limit Theorem for the same quantity. 相似文献
39.
Robert J. Rubin 《Journal of statistical physics》1991,65(5-6):1207-1216
A one-dimensional lattice random walk in the presence ofm equally spaced traps is considered. The step length distribution is a symmetric exponential. An explicit analytic expression is obtained for the probability that the random walk will be trapped at thejth trapping site. 相似文献
40.
研究了平面上系数{Xn,n≥0}为(?)-混合序列在满足,(q>1)等条件下的随机级数的增长性及值分布,得到了比较好的结果. 相似文献