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31.
Summary The normal incidence reflectivity spectrum of excitons in GaAs/Ga1−x
Al
x
As multiple quantum wells is calculated within the local response approximation. It is shown that the reflectivity lineshape
strongly depends on the sample geometry. Using realistic parameters of a multiple quantum well structure, we obtain an excellent
fit of the experimental reflectivity curve, thus giving exciton energies, oscillator strengths and exciton broadening parameters.
Riassunto Lo spettro di riflettività ad incidenza normale degli eccitoni nei pozzi quantistici multipli di GaAs/Ga1−x Al x As è calcolato nell’ambito dell’approssimazione locale. Si mostra con la forma della linea di riflettività dipende in gran misura dalla forma geometrica del campione. Usando parametri realistici di una struttura a pozzi quantistici multipli, si ottiene un’ottima approssimazione della curva di riflettività sperimentale, che fornisce così energie eccitoniche, forze dell’oscillatore e parameri di ampliamento eccitonico.
Резюме В рамках приближения линейного отклика вычисляется спекрт отражательной способности экситонов при нормальном падении для множественных квантовых ям в GaAs/Ga1−x Al x As. Показывается, что форма линии отражательной способности сильно зависит от геометрии образца. Используя реалистические параметры структуры множественных квантовых ям, мы получаем хорошее соответствие с экспериментальной кривой для отражательной способности. Получаются энергии экситонов, силы осцилляторов и парам⪟тры экситонного уширения.相似文献
32.
In the first part of this review, the authors give a survey on the literature of vibrational spectroscopy of phenol, phenol derivatives, and other phenolic componds from the last decade of the last century through today. The classical and modern methods of vibrational spectroscopy are also introduced and a glossary is included to aid comprehension. The second part deals with the literature regarding the importance of vibrational spectroscopy in the investigation and identification of phenolic compounds in natural substances, the application of vibrational spectroscopy in composite and synthetic polymer chemistry, and following of chemical processes and investigating their resulting products. Vibrational spectroscopy is a very good tool for determination of molecular structures and is important in chemical analysis and in the chemical industry. 相似文献
33.
W. Ouerghui J. Martinez-Pastor J. Gomis M. A. Maaref D. Granados J. M. García 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(2):217-223
Exciton recombination dynamics in vertical stacks of InGaAs quantum rings have been studied by means of continuous wave and
time resolved
photoluminescence under low excitation density conditions. We have paid
special attention to the effect of the carrier coupling on the exciton
radiative lifetime: weak (14 nm spacer sample), intermediate (4.5 nm spacer
sample), where the size filtering effects (towards small rings) compensate
partially that arising from carrier coupling (towards lower energies), and
strong electron and hole coupling (1.5 nm spacer sample) between layers.
Experimental decay times in the latter two cases have been compared to the
times simulated with a multi-quantum well based model, which accounts for
the observed change of carrier coupling regime. The most important effect is
observed when the hole wave function overlap along the growth direction
becomes important (1.5 nm spacer sample). This situation makes important the
lateral tunneling of excitons between rings, given their large lateral size,
which is characterized by times around 5 ns at the emission peak energy
(rings with the most probable size of the distribution). 相似文献
34.
S. Pleutin A. Ovchinnikov 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(4):521-531
The static polarizability of cylindrical systems is shown to have a strong dependence on a uniform magnetic field applied
parallel to the tube axis. This dependence is demonstrated by performing exact numerical diagonalizations of simple cylinders
(rolled square lattices), armchair and zig-zag carbon nanotubes (rolled honeycomb lattices) for different electron-fillings.
At low temperature, the polarizability as function of the magnetic field has a discontinuous character where plateau-like
region are separated by sudden jumps or peaks. A one to one correspondence is pointed out between each discontinuity of the
polarizability and the magnetic-field induced cross-over between the ground state and the first excited state. Our results
suggest the possibility to use measurements of the static polarizability under magnetic field to get important informations
about excited states of cylindrical systems such as carbon nanotubes.
Received 29 March 2001 and Received in final form 8 August 2001 相似文献
35.
A. Komnik R. Egger 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(2):271-280
We study nonlinear transport for two coupled one-dimensional quantum wires or carbon nanotubes described by Luttinger liquid
theory. Transport properties are shown to crucially depend on the contact length L
c. For a special interaction strength, the problem can be solved analytically for arbitrary L
c. For point-like contacts and strong interactions, a qualitatively different picture compared to a Fermi liquid emerges, characterized
by zero-bias anomalies and strong dependence on the applied cross voltage. In addition, pronounced Coulomb drag phenomena
are important for extended contacts.
Received 28 July 2000 相似文献
36.
Th. Cabioc'h S. Camelio L. Henrard Ph. Lambin 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(3):535-540
Concentric-shell fullerenes, also called carbon onions, produced by carbon ion implantation into silver thin films, and subsequently
deposited on a silica substrate, were studied by optical transmission spectroscopy in the wavelength range 0.2 - 1.2 μm. In
this interval, the strongest absorption is due to the π-plasmon of sp2-like carbon. The position of the plasmon absorption band clearly evolved from 265 nm at low fluence to 230 nm at high implantation
fluences. A simulation of the optical spectra based on dielectric models of the concentric-shell fullerenes layer allowed
us to identify the first peak as due to disordered graphite and the latter to the carbon onions. The concentration of residual
graphite and the filling fraction of the carbon onions produced at high fluences could be estimated by fitting the optical
spectra with computed transmittance curves.
Received 13 July 2000 相似文献
37.
Fluid and plastic flow dynamics of the critical state for a strongly pinned 2D superconductor 总被引:2,自引:0,他引:2
D. Monier L. Fruchter 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(2):201-205
The frequency of the Raman active A1g radial breathing mode has been widely used as a tool to estimate the distribution of diameters of single wall carbon nanotubes
(SWNT). However, the relation between frequency and diameter is not straightforward and results are model-dependent. Because
most of the experiments are performed on bundles and not on isolated tubes, the model should especially take into account
the van der Waals intertube interactions. Here, we use a pair-potential approach to account for such interactions and we derive
a nonlinear relation between the SWNT diameter and the frequency of the A1g radial breathing modes. We demonstrate a good agreement between calculations and the diameters derived from diffraction experiments
on the same samples.
Received 22 December 1999 and Received in final form 17 July 2000 相似文献
38.
M. Combescot 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(3):289-303
We reconsider the procedure
developed for atoms a few decades ago by Girardeau, in the light of
the composite-boson many-body theory we recently proposed. The
Girardeau's procedure makes use of a so called “unitary Fock-Tani
operator” which in an exact way transforms one composite bound
atom into one bosonic “ideal” atom. When used to transform the
Hamiltonian of interacting atoms, this operator generates an extremely
complex set of effective scatterings between ideal bosonic atoms and free
fermions which makes the transformed Hamiltonian impossible to write
explicitly, in this way forcing to some truncation. The scatterings
restricted to the ideal-atom subspace are shown to read rather simply in
terms of the two elementary scatterings of the composite-boson many-body
theory, namely, the energy-like direct interaction scatterings
— which describe fermion interactions without fermion exchange — and
the dimensionless Pauli scatterings — which describe fermion exchanges
without fermion interaction. We here show
that, due to a fundamental difference in the scalar products of
elementary and composite bosons, the Hamiltonian expectation
value for N ground state atoms
obtained by staying in the ideal-atom subspace and working
with boson operators only, differ from the exact ones even for N = 2 and
a mapping to the ideal-atom subspace performed, as advocated, from
the fully antisymmetrical atomic state, i.e., the state which obeys the
so-called “subsidiary condition”. This shows that, within this
Girardeau's procedure too, we cannot completely forget the underlying
fermionic components of the particles if we want to correctly describe
their interactions. 相似文献
39.
O. Betbeder-Matibet M. Combescot 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(1):17-29
We study the interaction of an exciton with a distant metal, which is the simplest problem on interacting excitons: The semiconductor
and metal electrons being “different” species, we do not have to worry about the tricky consequences of Pauli exclusion between
identical carriers, which appear in any other problem on interacting excitons. We show how the exciton absorption, in the
presence of semiconductor-metal interaction, can be derived in a very simple and transparent way from an exciton diagram procedure,
provided that we use the appropriate exciton-metal interaction vertex, which contains the scattering from an exciton state
to another exciton state under a Coulomb excitation. We also show that the resolution of this problem using standard electron-hole
diagrams is dreadfully complicated at the lowest order in the semiconductor-metal interaction already, preventing a full calculation
of the exciton-metal coupling from this usual technique.
Received 26 February 2001 相似文献
40.
Ding Changgeng Yang Jinlong Cui Xiangyuan Wang Kelin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(1):123-126
Geometrical and electronic structures of C35X fullerenes with , N and Si as substitutional dopants have been studied. Three non-equivalent sites in the D6h structure of C36 have been considered for the substitution. We have found that the dopant has a strong tendency to substitute at sites where
the carbon atom contributes significantly to the frontier orbitals of C36 and has the weakest interaction with its nearest-neighbor atoms. The relative stability of C35Si and C35B (C35N) has been investigated and high chemical reactivity of C35Si has been predicted.
Received 8 July 1999 and Received in final form 4 October 1999 相似文献