全文获取类型
收费全文 | 1070篇 |
免费 | 516篇 |
国内免费 | 141篇 |
专业分类
化学 | 119篇 |
晶体学 | 1篇 |
力学 | 9篇 |
综合类 | 6篇 |
数学 | 29篇 |
物理学 | 1563篇 |
出版年
2024年 | 7篇 |
2023年 | 17篇 |
2022年 | 50篇 |
2021年 | 67篇 |
2020年 | 47篇 |
2019年 | 39篇 |
2018年 | 47篇 |
2017年 | 30篇 |
2016年 | 57篇 |
2015年 | 32篇 |
2014年 | 111篇 |
2013年 | 96篇 |
2012年 | 108篇 |
2011年 | 123篇 |
2010年 | 130篇 |
2009年 | 124篇 |
2008年 | 155篇 |
2007年 | 112篇 |
2006年 | 97篇 |
2005年 | 72篇 |
2004年 | 49篇 |
2003年 | 48篇 |
2002年 | 25篇 |
2001年 | 16篇 |
2000年 | 18篇 |
1999年 | 10篇 |
1998年 | 4篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
排序方式: 共有1727条查询结果,搜索用时 15 毫秒
21.
22.
Ramanan Krishnamoorti William W. Graessley Achim Zirkel Dieter Richter Nikos Hadjichristidis Lewis J. Fetters David J. Lohse 《Journal of Polymer Science.Polymer Physics》2002,40(16):1768-1776
The unperturbed chain dimensions (〈R2〉o/M) of cis/trans‐1,4‐polyisoprene, a near‐atactic poly(methyl methacrylate), and atactic polyolefins were measured as a function of temperature in the melt state via small‐angle neutron scattering (SANS). The polyolefinic materials were derived from polydienes or polystyrene via hydrogenation or deuteration and represent structures not encountered commercially. The parent polymers were prepared via lithium‐based anionic polymerizations in cyclohexane with, in some cases, a polymer microstructure modifier present. The polyolefins retained the near‐monodisperse molecular weight distributions exhibited by the precursor materials. The melt SANS‐based chain dimension data allowed the evaluation of the temperature coefficients [dln 〈R2〉o/dT(κ)] for these polymers. The evaluated polymers obeyed the packing length (p)‐based expressions of the plateau modulus, G = kT/np3 (MPa), and the entanglement molecular weight, Me = ρNanp3 (g mol?1), where nt denotes the number (~21) of entanglement strands in a cube with the dimensions of the reptation tube diameter (dt) and ρ is the chain density. The product np3 is the displaced volume (Ve) of an entanglement that is also expressible as pd or kT/G. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1768–1776, 2002 相似文献
23.
Franois Fillaux 《Journal of Molecular Structure》2004,700(1-3):133-145
After a brief introduction to neutron scattering techniques, illustrated with the scattering function for harmonic oscillators, some new aspects of proton dynamics in the KHCO3 crystal are presented. The full scattering function for the proton modes measured on single crystals provides a graphic view of proton dynamics. Vibrational states are fully characterized with three quantum numbers. The effective oscillator mass of 1 amu confirms the decoupling of protons from the lattice. Combining infrared, Raman and inelastic neutron scattering techniques, the double minimum potential for the transfer of a single proton along hydrogen bonds is totally determined. Elastic neutron scattering techniques probe dynamics in the fully degenerate ground state. Quantum entanglement arising from normal coordinates gives rise to quantum interference. With diffraction techniques, the dynamical structure arising from large-scale quantum coherence is observed as ridges of intensity, well separated from Bragg's peaks. The vibrational wave function in the ground state must be regarded as a superposition of non-factorable macroscopic wave function. 相似文献
24.
Min-zhi Chen Xiao-liang Wang Fang-fang Tao Qi Xue Ping-chuan 《高分子科学》2007,(1):107-111
The concept of entanglement provides the basis of our current understanding of the flow behavior of polymer melts, Current techniques developed to investigate the degree of interpenetration of polymer chains only provide indirectly the information of the degree of entanglement in a relatively large scale (several to tens of nanometer). In this article, we report ^1H-NMR spectroscopy with dipolar filters under fast magic angle spinning for probing chain interpenetration of polymer glasses at the molecular level. 相似文献
25.
The bipartite entanglement in pure and mixed states of a quantum spin-1 Heisenberg dimer with exchange and uniaxial single-ion anisotropies is quantified through the negativity in a presence of the external magnetic field. At zero temperature the negativity shows a marked stepwise dependence on a magnetic field with two abrupt jumps and plateaus, which can be attributed to the quantum antiferromagnetic and quantum ferrimagnetic ground states. The magnetic-field-driven phase transition between the quantum antiferromagnetic and quantum ferrimagnetic ground states manifests itself at nonzero temperatures by a local minimum of the negativity, which is followed by a peculiar field-induced rise of the negativity observable in a range of moderately strong magnetic fields. The rising temperature generally smears out abrupt jumps and plateaus of the negativity, which cannot be distinguished in the relevant dependencies above a certain temperature. It is shown that the thermal entanglement is most persistent against rising temperature at the magnetic field, for which an energy gap between a ground state and a first excited state is highest. Besides, temperature variations of the negativity of the spin-1 Heisenberg dimer with an easy-axis single-ion anisotropy may exhibit a singular point-kink, at which the negativity has discontinuity in its first derivative. The homodinuclear nickel complex [Ni(Medpt)(-ox)(HO)](ClO)·2HO provides a suitable experimental platform of the antiferromagnetic spin-1 Heisenberg dimer, which allowed us to estimate a strength of the bipartite entanglement between two exchange-coupled Ni magnetic ions on the grounds of the interaction constants reported previously from the fitting procedure of the magnetization data. It is verified that the negativity of this dinuclear compound is highly magnetic-field-orientation dependent due to presence of a relatively strong uniaxial single-ion anisotropy. 相似文献
26.
We present an efcient faithful multipartite polarization entanglement distribution protocol over an arbitrary noisy channel.The spatial degree of freedom is used to carry the entanglement during the transmission.We describe the principle by distributing n-qubit Greenberge–Horne–Zeilinger state and n-qubit W state.Our scheme can be used to distribute arbitrary n-qubit entangled states to n distant locations.The remote parties can obtain maximally entangled states deterministically on the polarization of photons.Only passive linear optics are employed in our setup,which makes our scheme more feasible and efcient for practical application in long distance quantum communication. 相似文献
27.
28.
We construct a quantum circuit to produce a task-oriented partially entangled state and use it as the quantum channel for controlled joint remote state preparation. Unlike most previous works, where the parameters of the quantum channel are given to the receiver who can accomplish the task only probabilistically by consuming auxiliary resource, operation and measurement, here we give them to the supervisor. Thanks to the knowledge of the task-oriented quantum channel parameters, the supervisor can carry out proper complete projective measurement, which, combined with the feed-forward technique adapted by the preparers, not only much economizes (simplifies) the receiver's resource (operation) but also yields unit total success probability. Notably, such apparent perfection does not depend on the entanglement degree of the shared quantum channel. Our protocol is within the reach of current quantum technologies. 相似文献
29.
30.
Meng-Yue Guo Gen Li Shuai-Liang Yang Ran Bu Xian-Qing Piao Prof. En-Qing Gao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(66):16415-16421
The assembly of two tripyridinium-tricarboxylate ligands and different metal ions leads to seven isostructural MOFs, which show novel 2D→2D supramolecular entanglement featuring catenane-like interlocking of tricyclic cages. The MOFs show tripyridinium-afforded and metal-modulated photoresponsive properties. The MOFs with d10 metal centers ( 1-Cd , 1-Zn , 2-Cd , 2-Zn ) show fast and reversible photochromism and concomitant fluorescence quenching, 1-Ni displays slower photochromism but does not fluoresce, and 1-Co and 2-Co are neither photochromic nor fluorescent. It is shown here that the network entanglement dictates donor-acceptor close contacts, which enable fluorescence originated from interligand charge transfer. The contacts also allow photoinduced electron transfer, which underlies photochromism and concomitant fluorescence response. The metal dependence in fluorescence and photochromism can be related to energy transfer through metal-centered d-d transitions. In addition, 1-Cd is demonstrated to be a potential fluorescence sensor for sensitive and selective detection of UO22+ in water. 相似文献