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1.
A europium complex Eu (DBM)3 TPPO (Eu tris(benzoylmethide)-(triphenylphosphine oxide)) and silicon nanoparticles have been hybridized.The hybridization can evidently change the photoluminescence (PL) characteristics of the Eu complex in the following aspects:under an excitation of 390nm,the intensity of the PL peak at 611nm due to the ^5Du-^7F2 transition of the Eu^3 ions has been increased by 30%,and thc integrated PL intensity in the visible range has been increased by nearly 3 times;the PL excitation efficiency beyond 440nm has been improved cvidently;the peak in the PL excitation spectrum shifts from 408nm to 388nm,and the PL decay time decreases from 2.07 to 0.96μs,The experimental results indicatde that in the PL process,the photoexcited energy may transfer from the silicon nanoparticlcs to the Eu^3 ions. 相似文献
2.
The possible defect models of Y^3+:PbWO4 crystals are discussed by defect chemistry and the most possible substituting positions of the impurity Y^3+ ions are studied by using the general utility lattice program (GULP). The calculated results indicate that in the lightly doped Y^3+ :PWO crystal, the main compensating mechanism is [2Ypb^+ + VPb^2-], and in the heavily doped Y^3+ :PWO crystal, it will bring interstitial oxygen ions to compensate the positive electricity caused by YPb^+, forming defect clusters of [2Ypb^+ +Oi^2-] in the crystal. The electronic structures of Y3+ :PWO with different defect models are calculated using the DV-Xα method. It can be concluded from the electronic structures that, for lightly doped cases, the energy gap of the crystal would be broadened and the 420nm absorption band will be restricted; for heavily doped cases, because of the existence of interstitial oxygen ions, it can bring a new absorption band and reduce the radiation hardness of the crystal. 相似文献
3.
V.I. Anisimov I.A. Nekrasov D.E. Kondakov T.M. Rice M. Sigrist 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(2):191-201
The electronic structures of the metallic and insulating phases of the alloy series Ca2-xSrxRuO4 ( 0 ?
x
? 2) are calculated using LDA, LDA+U and Dynamical Mean-Field Approximation methods. In the end members the groundstate respectively
is an orbitally non-degenerate antiferromagnetic insulator (x
= 0) and a good metal (x
= 2). For x
> 0.5 the observed Curie-Weiss paramagnetic metallic state which possesses a local moment with the unexpected spin S
= 1/2, is explained by the coexistence of localized and itinerant Ru-4d-orbitals. For 0.2 <
x
< 0.5 we propose a state with partial orbital and spin ordering. An effective model for the localized orbital and spin degrees
of freedom is discussed. The metal-insulator transition at x
= 0.2 is attributed to a switch in the orbital occupation associated with a structural change of the crystal.
Received 27 July 2001 相似文献
4.
B. Freisinger U. Kogelschatz J. H. Schäfer J. Uhlenbusch W. Viöl 《Applied physics. B, Lasers and optics》1989,49(2):121-129
Ozone is generated in pure oxygen (p5 kPa), synthetic air (p7 kPa) and oxygen-argon mixtures (p3 kPa) by irradiation of these gases with the VUV light of a repetitively pulsed (f
L15 Hz) F2-laser at =157.6 nm with maximum about 4 mJ/pulse. An absorption photometer measurement operating at 253.7 nm (Hg line) determines the ozone concentration as a function of oxygen and/or additive gas pressure, the repetition frequency of the laser and the wall temperature of the reaction chamber. The temporal development of the ozone concentration as a function of these parameters is calculated by means of rate equations for the species O(3
P), O2(X
3
g
–
), O3(1
A
1), O(1
D), O2(a
1g), O2(b
1
g
+
) and vibrationally excited O
3
*
(1
A
1) and the photon distribution. The maximum concentration of O3 in the sealed-off chamber reaches 1.6% in pure O2, 4.1% in air and 1.2% in a 1:5 O2-Ar mixture at 3 kPa. The annihilation of O3 by the wall and temperature dependent volume processes (300 KT395 K) is studied and the experimental and theoretical results are compared. 相似文献
5.
R. Slater 《Applied physics. B, Lasers and optics》1987,42(1):17-20
The rate of build-up of N2 was measured in electron-beam-irradiated Ne/Xe/NF3 mixtures using mass spectroscopy. the amount of N2 produced indicated that N2 is the primary nitrogen bearing stable species created in these mixtures. The rate constant for dissociative electron attachment to the NF2 fragments produced in electron attachment to NF3 is estimated to be 5×10–8 cm3/s in order to explain the amount of N2 produced.This work was supported by DARPA under Contract No. DAA01-82-C-A125 and monitored by MICOM 相似文献
6.
Nominally undoped AlxGa1–xAs grown by molecular beam epitaxy from As4 species at elevated substrate temperatures of 670°C exhibits well-resolved excitonic fine structure in the low-temperature photoluminescence spectra, if the effective As-to-(Al+Ga) flux ratio on the growth surface is kept within a rather narrow range of clearly As-stabilized conditions. In contrast to previous results on AlxGa1–xAs of composition 0.15not to shift in energy by changing the excitation intensity. This implies a simple freeelectron carbon-acceptor recombination mechanism for the line without any participation of a donor. In AlxGa1–xAs of composition close to the direct-to-indirect cross-over point, two distinct LO-phonons separated by 34 and 48 meV from the (D
0,C
0) peak position at x=0.43 were observed which were before only detectable by Raman scattering experiments. The intensity of the carbon-impurity related luminescence lines in bulk-type AlxGa1–xAs and GaAs layers was found to be strongly reduced, as compared to the excitonic recombination lines, if the respective active layer was covered by a very thin confinement layer of either GaAs on top of AlxGa1–xAs or vice versa grown in the same growth cycle. 相似文献
7.
The crystal structure of the quasi-one-dimensional oxide PbNi1.88Mg0.12V2O8 has been studied by Rietveld analysis of combined high-resolution neutron and X-ray powder diffraction data at 300 K and at low temperatures. The (Ni/Mg)O6 octahedral units share a common edge and form spiral chains along the c-axis of the tetragonal unit cell, without deviating the I41cd (Z=8) symmetry upon cooling. DC magnetic susceptibility measurements show that the system undergoes a magnetic phase transition below TN≅3.4 K. Rietveld analysis of the medium resolution neutron powder diffraction data confirms that impurity-induced antiferromagnetic order (with propagation vector, ) takes over from the Haldane ground state of the parent compound. The power-law [β=0.31(3)] temperature evolution of the strongest magnetic Bragg peak intensity indicates three-dimensional Ising-type magnetic interactions, while the reduced magnitude of the Ni2+ moment [〈μ〉=0.98(3) μB] suggests important zero-point spin fluctuations. Structural considerations are consistent with small changes in the interatomic distances around the bridging tetrahedral VO4 entities separating the chains. However, no bulk structural phase transition concurrent to the Néel ordering is found. We show that the modification of intra- and inter-chain Ni-Ni distances upon cooling promotes the magnetic coupling of the end-of-chain liberated S=1/2 spins and leads to antiferromagnetic ordering. 相似文献
8.
C. Lavoie M. Meunier R. Izquierdo S. Boivin P. Desjardins 《Applied Physics A: Materials Science & Processing》1991,53(4):339-342
Large area excimer laser induced deposition of titanium on fused silica from TiCl4 is studied with an emphasis on process modeling. We show that several TiCl4 monolayers can be adsorbed if the surface is adequately prepared and that the Ti thin film growth occurs through the photodecomposition of this adsorbed TiCl4 layer. We propose two growth regimes. During an initiation phase, up to 3 nm in thickness, the adsorbed layer is photochemically decomposed giving a growth rate of 0.015 nm/pulse. In a second phase, the deposition rate increases to between 2 and 7 nm/pulse due to the laser heating of the preceding photochemically deposited titanium film. Between consecutive pulses, TiCl4 molecules primarily from the adsorbed layer diffuse to the reaction zone leading to a new adsorbed layer ready to be transformed to solid titanium. 相似文献
9.
Effects of doping Na on the structure, electrical and magnetic properties of La2/3Ca1/3MnO3 are investigated. A structural phase transition from orthorhombic to rhombohedral structure takes place at y=0.375. All samples show metal-insulator (M-I) transition at the transition temperature and undergo the transition from paramagnetism to ferromagnetism at the Curie temperature TC. and TC increase monotonically with increasing Na content. However the Na-doped samples have a shoulder in their electrical transport curves found below and shows a widened magnetic transition process. On the other hand, intrinsic colossal magnetoresistance (CMR) peaks are observed in all the samples, but samples with y around 0.25 show two MR peaks which can be attributed to magnetic inhomogeneity induced by the doped Na+ ions. Here we propose a method to broaden the CMR peak of perovskite manganite, which is beneficial for practical applications. 相似文献
10.
We derive nonperturbatively — within the meanfield version of the Landau-Ginzburg-Wilson theory — the expressions for the constrained order parameter, for the coefficient of surface stiffness, and for the effective interface potential of a fluctuating interface in the presence of a flat substrate. The derived expressions display the typical dependence on the distancel between the interface and the substrate; the exponentially decaying contributions are multiplied by polynomials inl. We show that the expressions for the coefficient of surface stiffness and for the effective interface potential have identical form as those proposed recently by Jin and Fisher (Phys. Rev.B 47, 7365 (1993)).Dedicated to Herbert Wagner on the occasion of his 60th birthday 相似文献