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91.
M. Grifoni E. Paladino U. Weiss 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(4):719-729
The dynamics of the reduced density matrix of the driven dissipative two-state system is studied for a general diagonal/off-diagonal
initial state. We derive exact formal series expressions for the populations and coherences and show that they can be cast
into the form of coupled nonconvolutive exact master equations and integral relations. We show that neither the asymptotic
distributions, nor the transition temperature between coherent and incoherent motion, nor the dephasing rate and relaxation
rate towards the equilibrium state depend on the particular initial state chosen. However, in the underdamped regime, effects
of the particular initial preparation, e.g. in an off-diagonal state of the density matrix, strongly affect the transient dynamics. We find that an appropriately tuned external ac-field
can slow down decoherence and thus allow preparation effects to persist for longer times than in the absence of driving.
Received 23 October 1998 and Received in final form 26 February 1999 相似文献
92.
A. Ślebarski A. Jezierski M. Neumann S. Plogmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(4):519-523
The electronic structure of the Co2-xZrSn Heusler alloys has been studied by X-ray photoelectron spectroscopy (XPS). XPS valence band spectra can be compared with
ab initio electronic structure calculations using the linearized muffin-tin orbital (LMTO) method. The calculated magnetic moments
per Co atom agree well with the moments obtained from experiment. The LMTO calculations also show the energy shifts of the
Co, Zr and Sn valence electron states towards the Fermi level when the concentration of vacancies increases in these alloys.
Received 9 March 1999 and Received in final form 6 May 1999 相似文献
93.
Reflection of cold atoms from an array of current-carrying wires 总被引:1,自引:0,他引:1
D.C. Lau A.I. Sidorov G.I. Opat R.J. McLean W.J. Rowlands P. Hannaford 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,5(2):193-199
We report the realization of a new type of magnetostatic mirror for slowly moving atoms which comprises a planar array of
parallel wires alternately carrying electric current in opposite directions. One of the features of this atomic mirror is
that the magnetic field may be readily varied, switched or modulated by altering the current in the wires. Reflection signals
close to 100% at a pulsed current of 3 A are demonstrated for a beam of free-falling laser-cooled cesium atoms at normal incidence.
The current dependence of the reflection signals exhibits structure which is associated with the sequential onset of reflection
of cesium 62
S
1/2
, F=4 atoms in the m=+4, +3, +2 and +1 magnetic states. Measurements of the spatial distribution of the reflected atoms indicate the reflection
is predominantly specular at currents of 3 A.
Received: 31 August 1998 / Accepted: 6 October 1998 相似文献
94.
95.
C. Keller J. Schmiedmayer A. Zeilinger T. Nonn S. Dürr G. Rempe 《Applied physics. B, Lasers and optics》1999,69(4):303-309
We report experiments on the diffraction of atoms from a standing light wave in the channeling regime, characterized by long
interaction time and large potential height. The observed far-field diffraction patterns depend specifically on the way in
which the potential is switched on and off. For fast switching, the evolution is non-adiabatic and many diffraction orders
are populated. For slow switching, however, the evolution is adiabatic and the number of populated diffraction orders decreases
dramatically. The experiments are performed in two different setups employing rubidium and argon atoms, respectively. In one
of the setups, we study the dependence of the diffraction pattern on the interaction time, in the other setup that on the
incidence angle.
Received: 30 November 1998 / Revised version: 5 July 1999 / Published online: 8 September 1999 相似文献
96.
97.
Received: 30 May 1997/Revised version: 26 August 1997 相似文献
98.
Multi-nucleon transfer reactions56Fe(12C, X) have been studied at an incident12C energy of 60 MeV. Angular distributions of10Be and9Be corresponding to 2p and 2p 1n transfer reactions in transition to low-lying states in the residual nuclei have been measured. The angular distribution
data for 2p transfer have been analysed in terms of finite range DWBA calculations assuming a one-step transfer of two protons. The spectroscopic
factors for three low-lying transitions observed in56Fe(12C,10Be)58Ni have been extracted. Transfer probabilities for the ground state transition in two- and three-nucleon stripping channels
have been obtained and compared with the corresponding sequential transfer probabilities in order to emphasise the role of
direct transfer of nucleons vis-a-vis sequential transfer. 相似文献
99.
Experimental measurements of small-signal gain in an optically-pumped NH3 amplifier are carried out at pressures ranging from 40 Torr to 760 Torr, and the results are used to validate a rate-equation model describing the amplifier dynamics. The gain measurements show that dilute mixtures of <0.5% NH3 in N2 are reqired to minimize the problems of gas heating due to pump absorption. The model is used to extrapolate the results to gas pressures of several atmospheres, and to demonstrate the potential for highpressure operation of optically-pumped NH3 lasers. For a pump intensity of 100 MW/cm2, calculations indicate that operation of an NH3–N2 laser is feasible up to a pressure of 10 atm, which would provide a maximum continuous tuning range of 4 cm–1. High-resolution spectroscopy reveals that gain on a few NH3 transitions is eliminated at high pressures due to the presence of overlapping absorptions in other NH3 bands. 相似文献
100.
B. C. Curley G. Rossi R. Ferrando R. L. Johnston 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):53-56
Ag–Au bimetallic “nanoalloy” clusters with 38 atoms have been
studied using a Gupta many-body potential combined with a genetic
algorithm search technique. Clear changes in structure are observed as
a function of Ag/Au composition and there is a clear tendency for
surface segregation of the Ag atoms. Cluster stability is found to
increase with increasing number of Au-Au and Ag-Au bonds and the
segregation has been rationalised in terms of bonds strengths and
elemental surface energies. 相似文献