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151.
Shoaib Ahmad 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(3):309-318
The mechanisms and processes of the formation of the regenerative soot in a graphite hollow cathode discharge that produces
and emits carbon clusters are presented. Mass spectrometry with a specially designed E×B velocity filter analyzes the entire range of the charged clusters from C
1 to ∼C
4300. The state of the carbon vapour within the source is evaluated by using the characteristic line emissions from the carbonaceous
discharge whose formative mechanisms depend upon the kinetic and potential sputtering of the sooted cathode. The carbonaceous
discharge generates atomic and ionic C and its clusters C
m (m≥ 2), noble gas metastable atoms and ions, energetic electrons and photons in the cavity of the graphite hollow cathode. The
parameters of soot formation and its recycling depend critically on the discharge parameters, the geometry of the hollow cathode
and 3D profile of the cusp magnetic field contours.
Received 2nd July 2001 and Received in final form 10 September 2001 相似文献
152.
153.
154.
U. Galster P. Kaminski M. Beckert H. Helm U. Müller 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(3):307-318
We have performed kinematically complete investigations of molecular photodissociation of triatomic hydrogen in a fast beam
translational spectrometer recently built in Freiburg. The apparatus allows us to investigate laser-induced dissociation of
neutral molecules into two, three, or more neutral products. The fragments are detected in coincidence and their vectorial
momenta in the center-of-mass frame are determined. We demonstrate the potential of the method at the fragmentation of the
3 s
2
A
1
′
(
N
= 1,
K
= 0) state of triatomic hydrogen. In this state, three-body decay into ground state hydrogen atoms H+H+H, two-body predissociation
into H+H
2
(v
,
J), and photoemission to the H
3
ground state surface with subsequent two-body decay are competing channels. In the case of two-body predissociation, we determine
the rovibrational population in the H
2
(v
,
J) fragment. The vibrational distribution of H
2
is compared with approximate theoretical predictions. For three-body decay, we measure the six-fold differential photodissociation
cross-section. To determine accurate final state distributions, the geometric collection efficiency of the apparatus is calculated
by a Monte Carlo simulation, and the raw data are corrected for apparatus efficiency. The final state momentum distribution
shows pronounced correlation patterns which are characteristic for the dissociation mechanism. For a three-body decay process
with a discrete kinetic energy release we have developed a novel data reduction procedure based on the detection of two fragments.
The final state distribution determined by this independent method agrees extremely well with that observed in the triple-coincidence
data. In addition, this method allows us to fully explore the phase space of the final state and to determine the branching
ratios between the two- and three-body decay processes.
Received 29 March 2001 相似文献
155.
A. Perali M. Sindel G. Kotliar 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):487-503
A number of normal state transport properties of cuprate superconductors are analyzed in detail using the Boltzmann equation.
The momentum dependence of the electronic structure and the strong momentum anisotropy of the electronic scattering are included
in a phenomenological way via a multi-patch model. The Brillouin zone and the Fermi surface are divided in regions where scattering between the electrons
is strong and the Fermi velocity is low (hot patches) and in regions where the scattering is weak and the Fermi velocity is
large (cold patches). We present several motivations for this phenomenology starting from various microscopic approaches.
A solution of the Boltzmann equation in the case of N patches is obtained and an expression for the distribution function away from equilibrium is given. Within this framework,
and limiting our analysis to the two patches case, the temperature dependence of resistivity, thermoelectric power, Hall angle,
magnetoresistance and thermal Hall conductivity are studied in a systematic way analyzing the role of the patch geometry and
the temperature dependence of the scattering rates. In the case of Bi-based cuprates, using ARPES data for the electronic
structure, and assuming an inter-patch scattering between hot and cold states with a linear temperature dependence, a reasonable
agreement with the available experiments is obtained.
Received 3 August 2001 and Received in final form 1st November 2001 相似文献
156.
157.
The electron-stimulated desorption (ESD) of D− and H− ions from condensed D2O and H2O films is investigated. Three low-energy peaks are observed in the ESD anion yield, which are identified as arising from excitation of 2B1, 2A1 and 2B2 dissociative electron attachment (DEA) resonances. Additional structure is observed between 18 and 32 eV, which may be due to ion pair formation or to DEA resonances involving the 2a1 orbital. The ion yield resulting from excitation of the 2B1 resonance increases as the film is heated. We attribute the increase in the ion yield to thermally induced hydrogen bond breaking near the surface, which enhances the lifetimes of the excited states that lead to desorption. 相似文献
158.
We have measured time-of-flight (TOF) distributions of Br atoms desorbed from thin (less than 1000 Å) epitaxial films of KBr on (100) InSb with a 2 keV electron beam. Although the general structure of the TOF spectra was similar to that obtained previously for the thick crystals, both the fast and the slow (thermal) components of the distribution were strongly dependent on the film thickness. We argue that this dependence is due to two different diffusion processes involved in the transport of the primary excitation products from the bulk to the surface. By measuring the velocity resolved ESD yield for films of various thicknesses, we determined that a diffusion length of the carriers responsible for the thermal ESD component varied from 30 to 700 Å with temperature in the range 20–300°C. In contrast, for the non-thermal desorption we found the carrier diffusion length of about 140 Å which did not depend significantly on the temperature. 相似文献
159.
G. Doucas M. F. Kimmitt Th. Kormann G. Korschinek C. Wallner 《International Journal of Infrared and Millimeter Waves》2003,24(6):829-845
Spontaneous Smith-Purcell radiation at wavelengths of 100 and 220m has been observed. The angles of observation were 17° and 28° and the electron beam energies 1.9 and 1.56MeV, respectively. The radiated power was about 320nW at 17° and 92nW at 28°. These values are in reasonable agreement with what is theoretically expected if the emission process is due to the acceleration of image charges induced on the grating surface by the electrons of the beam. 相似文献
160.
K.N. Joshipura M. Vinodkumar B.K. Antony N.J. Mason 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(1):81-90
Total ionization cross-sections of electron impact are calculated for the molecular targets CHx, CFx, SiHx, SiFx (x = 1-4) and CCl4 at incident energies 20-3 000 eV. The calculation is based on Complex Scattering Potential approach, as developed by us recently.
This leads to total inelastic cross-sections, from which the total ionization cross-sections are extracted by reasonable physical arguments. Extensive comparisons are made here with the previous theoretical
and experimental data. The present results are satisfactory except for the CFx and SiFx (x = 1-3) radicals, for which the experimental data are lower than most of the theories by more than 50%.
Received 23 May 2002 / Received in final form 24 October 2002 Published online 21 January 2003
RID="a"
ID="a"e-mail: knjoshipura@yahoo.com 相似文献