全文获取类型
收费全文 | 914篇 |
免费 | 14篇 |
国内免费 | 9篇 |
专业分类
化学 | 288篇 |
晶体学 | 2篇 |
力学 | 16篇 |
数学 | 311篇 |
物理学 | 320篇 |
出版年
2020年 | 8篇 |
2019年 | 8篇 |
2018年 | 13篇 |
2017年 | 14篇 |
2016年 | 21篇 |
2015年 | 9篇 |
2014年 | 18篇 |
2013年 | 42篇 |
2012年 | 33篇 |
2011年 | 36篇 |
2010年 | 22篇 |
2009年 | 14篇 |
2008年 | 30篇 |
2007年 | 36篇 |
2006年 | 47篇 |
2005年 | 44篇 |
2004年 | 27篇 |
2003年 | 30篇 |
2002年 | 24篇 |
2001年 | 10篇 |
2000年 | 17篇 |
1999年 | 15篇 |
1998年 | 8篇 |
1997年 | 12篇 |
1996年 | 20篇 |
1995年 | 15篇 |
1994年 | 21篇 |
1993年 | 19篇 |
1992年 | 23篇 |
1991年 | 13篇 |
1990年 | 21篇 |
1989年 | 15篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 13篇 |
1985年 | 19篇 |
1984年 | 21篇 |
1983年 | 13篇 |
1982年 | 18篇 |
1981年 | 16篇 |
1980年 | 10篇 |
1979年 | 15篇 |
1978年 | 10篇 |
1977年 | 11篇 |
1976年 | 8篇 |
1975年 | 15篇 |
1974年 | 11篇 |
1973年 | 7篇 |
1972年 | 4篇 |
1967年 | 5篇 |
排序方式: 共有937条查询结果,搜索用时 24 毫秒
101.
A.C.A. Oliveira R. Rosenfeld 《Physics letters. [Part B]》2011,702(4):201-204
In this Letter we study a novel effect of a hidden sector coupling to the standard model Higgs boson: an enhancement of the Higgs pair production cross section near threshold due to bound state effects. After summing the ladder contributions of the hidden sector to the effective ggHH coupling, we find the amplitude for gluon-gluon scattering via a Higgs loop. We relate this amplitude to the double Higgs production cross section via the optical theorem. We find that enhancements of the O(100) for the partonic cross section near the threshold region can be obtained for a hidden sector strongly coupled to the Higgs boson. The corresponding cross section at the LHC can be as large as O(10) times the SM result for extreme values of the coupling. The detection of such an effect could in principle lead to important information about the hidden sector. 相似文献
102.
103.
Vladimir R. Rosenfeld Douglas J. Klein Josep M. Oliva 《Journal of mathematical chemistry》2012,50(7):2012-2022
Various sorts of isomer enumeration problems are addressed in the context of polycarboranes, with special illustrative focus on the case of dicarboranes, for which then various numerical results are given. A systematic and general Pólya-theoretic methodology is used to make the computations, including some new techniques being applicable to a wide range of nano-structures built from a framework of like local subunits. 相似文献
104.
Ad Cohen Geoffrey W. Coates Moshe Kol 《Journal of polymer science. Part A, Polymer chemistry》2013,51(3):593-600
The activities of C1‐symmetric dibenzyl zirconium complexes of Salan ligands that bear a halo‐substituted phenolate ring and an alkyl‐substituted phenolate ring in propylene polymerization with methylaluminoxane as cocatalyst were studied. These {ONNO′}ZrBn2‐type catalysts exhibited moderate‐to‐high activities and yielded polypropylene of low molecular weight. The degree of tacticity was found to depend on the steric bulk of the substituents on both phenolate rings and ranged from practically atactic to substantially isotactic (74–78% [mmmm] for polymerizations at room temperature by Lig5ZrBn2). Hemi‐isotactic polypropylene was not obtained, despite the diastereotopicity of the two positions. The pattern of stereo errors was consistent with the enantiomorphic site control of propylene insertion typically observed for C2‐symmetric catalysts and implied a facile site‐averaging mechanism. A regular 1,2‐insertion and a β‐H transfer to an incoming monomer correspond to the main propagation and termination processes, respectively. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 相似文献
105.
106.
Moshe Gitterman 《Journal of statistical physics》1994,74(5-6):1327-1328
107.
Moshe Marcus 《Calculus of Variations and Partial Differential Equations》1998,6(2):123-142
We consider the problem of minimizing functionals of the form , for small , subject to the constraint . (Here is typically a double well potential.) We study structural properties of minimizers that are shared by all minimizers of
the problem, for sufficiently small values of . It is shown that the average ‘mass’ and ‘energy’ of minimizers, over intervals of length , is almost uniformly distributed (depending on ), for all sufficiently small . Here is a constant depending on the degree of ‘uniformity’, but independent of .
Received May 5, 1996 / Accepted October 28, 1996 相似文献
108.
It is shown that if R is a finitely generated integral domain of zero characteristic, then for every n there exist elements of R which are not sums of at most n units. This applies in particular to rings of integers in finite extensions of the rationals. On the other hand there are
many infinite algebraic extensions of the rationals in which every integer is a sum of two units. 相似文献
109.
We study the message queueing delays in a node of a communication system, where a message consists of a block of consecutive packets. The message delay is defined as the time elapsing between the arrival epoch of the first packet of the message to the system until after the transmission of the last packet of that message is completed. We distinguish between two types of message generation processes. The message can be generated as abatch or it can bedispersed over time. In this paper we focus on the dispersed generation model. The main difficulty in the analysis is due to the correlation between the system states observed by different packets of the same message. This paper introduces a new technique to analyze the message delay in such systems for different arrival models and different number of sessions. For anM/M/1 system with variable size messages and for the bursty traffic model, we obtain an explicit expression for the Laplace-Stieltjes transform (LST) of the message delay. Derivations are also provided for anM/G/1 system, for multiple session systems and for fixed message sizes. We show that the correlation has a strong effect on the performance of the system, and that the commonly usedindependence assumption, i.e., the assumption that the delays of packets are independent from packet to packet, can lead to wrong conclusions. 相似文献
110.
Michael Shapiro Vladislav Dudko Victor Royzen Yuri Krichevets Samuel Lekhtmakher Victor Grozubinsky Moshe Shapira Moti Brill 《Particle & Particle Systems Characterization》2004,21(4):268-275
The thermal conductivity of ceramic powder packed beds was measured at temperatures below 100 °C for various powder sizes and compositions and under different gas atmospheres. Measurements at low pressures (down to 10 Pa) combined with a theoretical model allowed the elucidation of geometrical and thermal resistance parameters for the contact points between granules. The gap thickness and contact point size were found to be well correlated with the mean particle size. The thermal conductivities of all powders at low pressure were found to differ at most by a factor of two, whereas the solid‐phase conductivities of the powder materials differed by more than one order of magnitude. A theoretical model accounting for the size‐dependence of contact point conductivity is incorporated to rationalize this trend. 相似文献