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51.
V. Crozatier 《Journal of luminescence》2007,127(1):104-109
We report on the demonstration of the chirp transform algorithm for the instantaneous optical frequency analysis of wide band radiofrequency signals. The process exploits photon echoes in an Er3+:YSO crystal at 1536 nm. The analysis covers a 1.6 GHz instantaneous bandwidth together with more than 24,000 independent channels. These performances require a frequency agile laser source that is phase-locked in order to take advantage of the tens of μs of coherence time offered by the crystal optical transition. 相似文献
52.
We study near-field fluorescence images of samples composed of aggregates of 100 nm dye-doped latex spheres. These images have been performed by a reflection Apertureless Scanning Near-field Optical Microscope (A-SNOM). We show that the near-field distribution in fluorescence A-SNOM images arises from coherent scattering phenomena between all spheres. This is a consequence of the coherent nature of the fluorescence emission of each single sphere. The results shown here are significant for all fluorescent samples characterised by a nonnegligible topography. 相似文献
53.
We give a comprehensive overview on passive mode locking of solid-state lasers with slow saturable absorbers, based on analytical
and numerical calculations. For picosecond lasers, we present a simple equation to estimate the obtained pulse duration and
compare the results to those for mode locking with fast saturable absorbers. We also discuss how much shorter the pulse duration
can be compared to the absorber recovery time and present a simple rule. The effect of self-phase modulation is found to be
qualitatively different compared to the case of a fast saturable absorber, and the effect of phase changes in the absorber
is also discussed. Finally, we discuss various issues concerning soliton mode-locked lasers.
Received: 20 July 2001 / Revised version: 28 September 2001 / Published online: 7 November 2001 相似文献
54.
Ch. Kegler N. Büttgen H.-A. Krug von Nidda A. Krimmel L. Svistov B.I. Kochelaev A. Loidl A. Prokofiev W. Aßmus 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(3):321-326
EPR and 7Li NMR measurements were performed in the distorted inverse spinel V(LiCu)O4 down to 1.5 K. Anisotropy effects on magnetic resonance spectra due to the Jahn-Teller distortion of the oxygen octahedra
surrounding the copper ions are discussed. The estimation of the spin-spin interactions deduced from the EPR-relaxation rate
Δ
H reveals a situation comparable to the prototypical one-dimensional S
= 1/2 Heisenberg antiferromagnet CuGeO3. Approaching three-dimensional antiferromagnetic order ( T
N
≈ 2 K) from above, both magnetic relaxation rates, Δ
H
EPR
and
7
(1/
T
1
), respectively, exhibit nearly the same critical divergence reminding to the onset of three-dimensional order in two-dimensional
layered systems.
Received 22 January 2001 and Received in final form 6 May 2001 相似文献
55.
We develop a continuum theory of linear viscoelastic response in oriented monodomain nematic elastomers. The expression for
the dissipation function is analogous to the Leslie-Ericksen version of anisotropic nematic viscosity; we propose the relations
between the anisotropic rubber moduli and new viscous coefficients. A new dimensionless number is introduced, which describes
the relative magnitude of viscous and rubber-elastic torques. In an elastic medium with an independently mobile internal degree
of freedom, the nematic director with its own relaxation dynamics, the model shows a dramatic decrease in the dynamic modulus
in certain deformation geometries. The degree to which the storage modulus does not altogether drop to zero is shown to be
both dependent on frequency and to be proportional to the semi-softness, the non-ideality of a nematic network. We consider
the most interesting geometry for the implementation of the theory, calculating the dynamic response to an imposed simple
shear and making predictions for effective moduli and (exceptionally high) loss factors.
Received 16 October 2000 and Received in final form 10 December 2000 相似文献
56.
With a reflective single-walled carbon nanotube as the saturable absorber, a laser diode-pumped passively mode-locked Nd:YVO4 laser at 1064 nm was realized for the first time. The pulse duration of 12 ps was produced with a repetition rate of 83.7 MHz. The peak power and the single pulse energy of the mode-locking laser were 1.28 kW and 15.4 nJ, respectively. 相似文献
57.
H. -J. Reyher B. Faust M. Maiwald H. Hesse 《Applied physics. B, Lasers and optics》1996,63(4):331-337
The analysis of EPR spectra obtained from iron doped KTaO3 crystals in the as-grown state revealed three dominant iron centers: Fe3+-OI, axial Fe-centers with spinS = 3/2 and rhombic Fe3+. By comparison with data from literature possible assignments for the center withS = 3/2 are discussed. For the rhombic species the temperature dependence of the main parameters of the Spin- Hamiltonian was measured. The result makes it most plausible that only one rhombic iron center exists in KTaO3, in contrast with literature. The understanding of the EPR spectra allows us to assign transitions, observed at very low magnetic fields by optically detected magnetic resonance (ODMR), to this rhombic Fe center. On this basis, the magnetic circular dichroism (MCD) of this defect could be identified using the method of tagged-MCD. This spectrum is compared to the tagged-MCD of Fe3+-O1 and of axial Fe4+ centers, which may be generated metastably by optical charge transfer. Considerably different structures in the MCD spectra of both Fe3+ centers indicate different local surroundings and electronic states.Dedicated to O. F. Schirmer on the occasion of his 60th birthday 相似文献
58.
The active mode-locking process of the multimode laser with an external pump modulation is theoretically investigated in the frequency domain within the framework of the continuous-mode approximation. Intermode interaction and mode-coupling effects, including both AM and FM modulations, are naturally considered in a hierarchical equation of the mode components derived from the multimode Maxwell-Bloch equations. It is reduced to a continuous-mode equation that can be solved analytically in a stationary case, and used to discuss the spectral line shape and the phase dynamics of mode-components as a function of modulation amplitude and detuning of the modulation frequency. We predict a novel oscillation existing below the threshold of the ordinary complete mode-locking: The intensity of the total electric field yields a stable pulse train but its phase varies irregularly in time. This semi-locked state is characterized by a nonlinear chirping, an asymmetric spectrum, and drifting phases of the field mode-components. 相似文献
59.
S. P. Ng D. Y. Tang J. Kong L. J. Qin X. L. Meng Z. J. Xiong 《Applied physics. B, Lasers and optics》2005,80(4-5):475-477
We report a diode-pumped Nd:Gd0.64Y0.36VO4 laser passively mode locked by using a GaAs saturable absorber mirror. Both the Q-switched and continuous-wave (CW) mode locking were experimentally realized. The CW mode-locked pulses have a pulse width of about 8.8 ps at a repetition rate of 161.3 MHz. Limited by the available pump power, a maximum output power of 2.47 W was obtained for the CW mode-locked pulses with a slope efficiency of about 26.6%. 相似文献
60.
O. Probst S. Grafström J. Fritz S. Dey J. Kowalski R. Neumann M. Wörtge G. zu Putlitz 《Applied Physics A: Materials Science & Processing》1994,59(2):109-113
By irradiation of the tunneling junction of a scanning tunneling microscope with intensity-modulated laser light a gap-width modulation due to thermal expansion of tip and sample was produced. Photothermal images were obtained by spatial mapping of the resulting modulation of the tunneling current or its logarithm. The various mechanisms responsible for the observed contrast are discussed quantitatively. In case of a highly corrugated gold film on mica the contrast arises mainly from either the current variations caused by the non-zero reaction time of the current control loop or from a geometry factor. In both cases the images reflect certain properties of the sample topography. On the other hand, for a liquid-crystal film adsorbed on graphite a contrast on a molecular scale was found which is attributed to variations of the effective barrier height. 相似文献