全文获取类型
收费全文 | 3326篇 |
免费 | 99篇 |
国内免费 | 22篇 |
专业分类
化学 | 2109篇 |
晶体学 | 12篇 |
力学 | 145篇 |
数学 | 495篇 |
物理学 | 686篇 |
出版年
2024年 | 4篇 |
2023年 | 35篇 |
2022年 | 82篇 |
2021年 | 117篇 |
2020年 | 101篇 |
2019年 | 82篇 |
2018年 | 58篇 |
2017年 | 45篇 |
2016年 | 130篇 |
2015年 | 92篇 |
2014年 | 137篇 |
2013年 | 169篇 |
2012年 | 227篇 |
2011年 | 254篇 |
2010年 | 148篇 |
2009年 | 125篇 |
2008年 | 200篇 |
2007年 | 194篇 |
2006年 | 207篇 |
2005年 | 195篇 |
2004年 | 146篇 |
2003年 | 129篇 |
2002年 | 127篇 |
2001年 | 51篇 |
2000年 | 23篇 |
1999年 | 29篇 |
1998年 | 34篇 |
1997年 | 38篇 |
1996年 | 36篇 |
1995年 | 21篇 |
1994年 | 23篇 |
1993年 | 17篇 |
1992年 | 8篇 |
1991年 | 16篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 13篇 |
1987年 | 9篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 14篇 |
1980年 | 7篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1975年 | 9篇 |
排序方式: 共有3447条查询结果,搜索用时 15 毫秒
81.
We study the energy diffusion in a chain of anharmonic oscillators where the Hamiltonian dynamics is perturbed by a local energy conserving noise. We prove that under diffusive rescaling of space–time, energy fluctuations diffuse and evolve following an infinite dimensional linear stochastic differential equation driven by the linearized heat equation. We also give variational expressions for the thermal diffusivity and some upper and lower bounds. 相似文献
82.
Caterina Viglianisi Stefano Menichetti Giulio Assanelli Maria Carmela Sacchi Incoronata Tritto Simona Losio 《Journal of polymer science. Part A, Polymer chemistry》2012,50(22):4647-4655
A new family of ethylene‐based copolymers with controlled amounts of a norbornene comonomer (NArOH) bearing a stabilizing antioxidant functionality (2,6‐di‐tert‐butyl phenol) was prepared. Due to unavoidable exo/endo equilibrium operative in NArOH comonomer, a complete and detailed NMR assignment of the structure of the prepared ethylene/NArOH copolymers was carried out for the determination of the exo/endo ratio inside the polymer. These novel functionalized comonomers can be considered suitable starting material for preparing ethylene‐based copolymers, with tunable comonomer content, as non‐releasing macromolecular antioxidant additives for specific application in safe food and/or drug packaging © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
83.
SBV REGULARITY OF GENUINELY NONLINEAR HYPERBOLIC SYSTEMS OF CONSERVATION LAWS IN ONE SPACE DIMENSION
Stefano Bianchini 《数学物理学报(B辑英文版)》2012,32(1)
The problem of the presence of Cantor part in the derivative of a solution to a hyperbolic system of conservation laws is considered.An overview of the techniques involved in the proof is given,and a c... 相似文献
84.
Cristiana Cesari Iacopo Ciabatti Cristina Femoni Maria Carmela Iapalucci Stefano Zacchini 《Journal of Cluster Science》2017,28(4):1963-1979
The reactions of [Ni16(C2)2(CO)23]4? and [Ni38C6(CO)42]6? with CuCl afforded mixtures of the previously reported [HNi42C8(CO)44(CuCl)]7? bimetallic octa-carbide cluster and the new [HNi43C8(CO)45]7? and [HNi44C8(CO)46]7? homo-metallic octa-carbides. The three species have very similar properties resulting always in co-crystals such as [NMe4]7[HNi42+2xC8(CO)44+2x(CuCl)1?x]·6.5MeCN (x = 0.14) (86% [HNi42C8(CO)44(CuCl)]7?, 14%[HNi43C8(CO)45]7?/[HNi44C8(CO)46]7?) and [NMe4]7[HNi42+2xC8(CO)44+2x(CuCl)1?x]·5.5MeCN (x = 0.30) (70% [HNi42C8(CO)44(CuCl)]7?, 30% [HNi43C8(CO)45]7?/[HNi44C8(CO)46]7?). The new homo-metallic octa-carbides can be obtained free from the Ni–Cu octa-carbido cluster by reacting [Ni10(C2)(CO)16]2? in thf with a stoichiometric amount of CuCl, and crystals of [NMe4]6[H2Ni43+xC8(CO)45+x]·6MeCN (x = 0.72), which contain [H2Ni44C8(CO)46]6? (72%) and [H2Ni43C8(CO)45]6? (28%), have been obtained. Despite the different charges and compositions, these anions display almost identical structures, which are also closely related to those previously reported for the bimetallic Ni–Cd octa-carbido clusters [Ni42+xC8(CO)44+x(CdCl)]7? and [HNi42+xC8(CO)44+x(CdBr)]6?. Indeed, all these clusters are based on the same Ni42C8 cage decorated by miscellaneous [CdX]+ (X = Cl, Br), [CuCl] and [Ni(CO)] fragments. 相似文献
85.
86.
Coherent tunneling by adiabatic passage (CTAP) is a well-established technique for robust spatial transport of quantum particles in linear chains. Here we introduce two exactly-solvable models where the CTAP protocol can be extended to two-dimensional lattice geometries. Such bi-dimensional lattice models are synthesized from time-dependent second-quantization Hamiltonians, in which the bosonic field operators evolve adiabatically like in an ordinary three-level CTAP scheme thus ensuring adiabatic passage in Fock space. 相似文献
87.
Stefano Bernardi J. S. Hansen Federico Frascoli B. D. Todd Carl P. Dettmann 《Journal of statistical physics》2012,148(6):1156-1169
We analyze the dynamics of a gas particle moving through a nanopore of adjustable width with particular emphasis on ergodicity. We give a measure of the portion of phase space that is characterized by quasiperiodic trajectories which break ergodicity. The interactions between particle and wall atoms are mediated by a Lennard-Jones potential, so that an analytical treatment of the dynamics is not feasible, but making the system more physically realistic. In view of recent studies, which proved non-ergodicity for systems with scatterers interacting via smooth potentials, we find that the non-ergodic component of the phase space for energy levels typical of experiments, is surprisingly small, i.e. we conclude that the ergodic hypothesis is a reasonable approximation even for a single particle trapped in a nanopore. Due to the numerical scope of this work, our focus will be the onset of ergodic behavior which is evident on time scales accessible to simulations and experimental observations rather than ergodicity in the infinite time limit. 相似文献
88.
89.
90.
Arenediazonium o-benzenedisulfonimides have been used as efficient electrophilic partners in Au(I) catalysed Suzuki coupling reactions. The synthetic protocol is general, easy and produced either biaryls or heteroaryl arenes in good yields (51 positive examples, average yield 80%). o-Benzenedisulfonimide was recovered at the end of the reactions and was reused to prepare the starting salts for further reactions. Mechanistic insights suggest that the o-benzenedisulfonimide anion act as an electron transfer agent and promotes a catalytic cycle which does not require the presence of photocatalysts or external oxidants. 相似文献