全文获取类型
收费全文 | 305篇 |
免费 | 5篇 |
国内免费 | 11篇 |
专业分类
化学 | 60篇 |
力学 | 3篇 |
数学 | 133篇 |
物理学 | 125篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 5篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 11篇 |
2015年 | 7篇 |
2014年 | 8篇 |
2013年 | 11篇 |
2012年 | 20篇 |
2011年 | 18篇 |
2010年 | 18篇 |
2009年 | 8篇 |
2008年 | 21篇 |
2007年 | 13篇 |
2006年 | 10篇 |
2005年 | 18篇 |
2004年 | 9篇 |
2003年 | 10篇 |
2002年 | 5篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 8篇 |
1997年 | 5篇 |
1996年 | 16篇 |
1995年 | 1篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 1篇 |
1989年 | 4篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1970年 | 2篇 |
排序方式: 共有321条查询结果,搜索用时 33 毫秒
11.
12.
13.
We study the abelian sandpile growth model, where n particles are added at the origin on a stable background configuration in ? d . Any site with at least 2d particles then topples by sending one particle to each neighbor. We find that with constant background height h≤2d?2, the diameter of the set of sites that topple has order n 1/d . This was previously known only for h<d. Our proof uses a strong form of the least action principle for sandpiles, and a novel method of background modification. We can extend this diameter bound to certain backgrounds in which an arbitrarily high fraction of sites have height 2d?1. On the other hand, we show that if the background height 2d?2 is augmented by 1 at an arbitrarily small fraction of sites chosen independently at random, then adding finitely many particles creates an explosion (a sandpile that never stabilizes). 相似文献
14.
Or Dishi Yuval Rahav Dr. Raanan Carmieli Prof. Ori Gidron 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(62):e202202082
Macrocyclic furans are predicted to switch between global aromaticity and antiaromaticity, depending on their oxidation states. However, the macrocyclic furans reported to date are stabilized by electron withdrawing groups, which result in inaccessible oxidation states. To circumvent this problem, a post-macrocyclization approach was applied to introduce methylene-substituted macrocyclic furans, which display an extremely low oxidation potential of −0.23 vs. Fc/Fc+, and are partially oxidized in ambient conditions. Additional oxidation to the dication results in aromaticity switching to a global 30πe− aromatic state, as indicated by the formation of a strong diatropic current observed in the 1H NMR spectrum. NICS and ACID calculations support this trend and provide evidence for a different pathway for the global current in the neutral and dicationic states. According to these findings, macrocyclic furans can be rendered as promising p-type materials with stable oxidation states. 相似文献
15.
We investigate the geometric phase or Berry phase acquired by a spin half which is both subject to a slowly varying magnetic field and weakly coupled to a dissipative environment (either quantum or classical). We study how this phase is modified by the environment and find that the modification is of a geometric nature. While the original Berry phase (for an isolated system) is the flux of a monopole field through the loop traversed by the magnetic field, the environment-induced modification of the phase is the flux of a quadrupolelike field. We find that the environment-induced phase is complex, and its imaginary part is a geometric contribution to dephasing. Its sign depends on the direction of the loop. Unlike the Berry phase, this geometric dephasing is gauge invariant for open paths of the magnetic field. 相似文献
16.
Let be a random -CNF formula formed by selecting uniformly and independently out of all possible -clauses on variables. It is well known that if , then is unsatisfiable with probability that tends to 1 as . We prove that if , where , then is satisfiable with probability that tends to 1 as .
Our technique, in fact, yields an explicit lower bound for the random -SAT threshold for every . For our bounds improve all previously known such bounds.
17.
Lamed R Kenig R Morag E Yaron S Shoham Y Bayer EA 《Applied biochemistry and biotechnology》2001,90(1):67-73
Previous work from our group [Morag (Morgenstern), E., Bayer, E. A., and Lamed, R. (1991), Appl. Biochem. Biotechnol.
30, 129–136] has demonstrated an anomalous electrophoretic mobility pattern for scaffoldin, the 210-kDa cellulosome-integrating
subunit of Clostridium thermocellum. Subsequent evidence [Morag, E., Bayer, E. A., and Lamed, R. (1992), Appl. Biochem. Biotechnol.
33, 205–217] indicated that the effect could be attributed to a nonproteolytic fragmentation of the subunit into a defined series
of lowermolecular-weight bands. In the present work, a recombinant segment of the scaffoldin subunit was employed to determine
the site(s) of bond breakage. An Asp-Pro sequence within the cohesin domain was identified to be the sensitive peptide bond.
This sequence appears quite frequently in the large cellulosomal proteins, and the labile bond may be related to an as yet
undescribed physiological role in the hydrolysis of cellulose by cellulosomes. 相似文献
18.
Yuval Z. Flicker 《Israel Journal of Mathematics》2001,122(1):61-77
The torsorP
δ=Hom⊗ (H
DR,H
σ) under the motivic Galois groupG
σ=Aut⊗
H
δ of the Tannakian category
generated by one-motives related by absolute Hodge cycles over a field κ with an embedding σ:k↪ℂ is shown to be determined by its projectionP
σ→P
σ/G
σ
0
to a Gal(
)-torsor, and by its localizationsP
σ⊕k
k
ξ at a dense subset of orderings ϕ of the field κ, provided κ has virtual cohomological dimension (vcd) one. This result is
an application of a recent local-global principle for connected linear algebraic groups over a field κ of vcd ≤1. 相似文献
19.
Yuval Peres Michal Rams Ká roly Simon Boris Solomyak 《Proceedings of the American Mathematical Society》2001,129(9):2689-2699
A compact set is self-conformal if it is a finite union of its images by conformal contractions. It is well known that if the conformal contractions satisfy the ``open set condition' (OSC), then has positive -dimensional Hausdorff measure, where is the solution of Bowen's pressure equation. We prove that the OSC, the strong OSC, and positivity of the -dimensional Hausdorff measure are equivalent for conformal contractions; this answers a question of R. D. Mauldin. In the self-similar case, when the contractions are linear, this equivalence was proved by Schief (1994), who used a result of Bandt and Graf (1992), but the proofs in these papers do not extend to the nonlinear setting.
20.
We study coherence of electron transport through interacting quantum dots and discuss the relation of the coherent part to the flux-sensitive conductance for three different types of Aharonov-Bohm interferometers. Contributions to transport in first and second order in the intrinsic linewidth of the dot levels are addressed in detail. We predict an asymmetry of the interference signal around resonance peaks as a consequence of incoherence associated with spin-flip processes. Furthermore, we show by strict calculation that first-order contributions can be partially or even fully coherent. This contrasts with the sequential-tunneling picture which describes first-order transport as a sequence of incoherent processes. 相似文献