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981.
The fabrication of a periodic domain inversion in LiTaO3 and LiNbO3 using direct ion-beam writing is presented. The polarization of these materials can be reversed at room temperature by irradiating Si2+ ions into +c faces. A first-order periodic domain inversion with a 50% duty cycle, a depth of 300μ, and an interaction length of 1 mm was realized in LiTaO3. Using this structure, 300μW of blue light was generated for a conversion efficiency of 0.25%/W. 相似文献
982.
The (111)B surface of GaAs has been investigated using scanning tunneling microscopy (STM) and a number of different reconstructions have been found at different surface stoichiometries. In accordance with electron diffraction studies, we find the series (2 × 2), (1 × 1)LT, (
) and (1 × 1)HT with increasing annealing temperature, corresponding to decreasing surface As concentration. The (1 × 1)LT is of particular interest, since it only occurs in a narrow temperature window between the two more established reconstructions, the (2 × 2) and the (
). We find the (1 × 1)LT to take the form of a mixture of the local structures of both the (2 × 2) and (
) phases, rather than having a distinct structure. This is behaviour consistent with a kinetically limited system, dominated by the supply of As adatoms to the surface, and may be an example of a continuous phase transition. Above the (1 × 1)LT transition, atomic resolution images of the (
) surface reveal only a three-fold symmetry of the hexagonal structural units, brought about by inequivalent surface bonding due to the 23.4° rotation of the surface unit cell relative to the substrate. This is responsible for the disorder found in the (
) reconstruction, since the structure may form in one of two domains. At lower surface As concentration, the (1 × 1)HT surface adopts a structure combining small domains of a
19.1° structure and random disorder. There is no apparent similarity between the (1 × 1)LT and (1 × 1)HT structures, which may be due to our measurements being conducted at room temperature and without an As flux to control the surface As concentration. 相似文献
983.
T. Tsuruoka Y. Ohizumi R. Tanimoto R. Arafune S. Ushioda 《Applied Surface Science》2002,190(1-4):275-278
We have investigated the electron diffusion process in Al0.3Ga0.7As/GaAs quantum well (QW) structures by means of scanning tunneling microscope light emission (STM-LE) spectroscopy. The optical measurements were performed on a cleaved (1 1 0) surface at room temperature. The STM-LE spectra were measured by injecting hot electrons from the tip positioned at different distances from the QWs. The emission intensity from individual wells as a function of the tip-well distance was found to decay with two distinct decay constants. From comparison with Monte Carlo simulations for hot electron relaxation, we found that the intervalley scattering from the Γ valley to the L and X valleys has the most significant effect on the diffusion process of the injected electrons. 相似文献
984.
Properties of GaAs single crystals grown at low temperatures by molecular beam epitaxy (LTMBE GaAs) have been studied. The
results show that excessive arsenic atoms of about 1020 cm−3 exist in LTMBE GaAs in the form of arsenic interstitial couples, and cause the dilation in lattice parameter of LTMBE GaAs.
The arsenic interstitial couples will be decomposed, and the excessive arsenic atoms will precipitate during the annealing
above 300°C. Arsenic precipitates accumulate in the junctions of epilayers with the increase in the temperature of annealing.
The depletion regions caused by arsenic precipitates overlap each other in LTMBE GaAs, taking on the character of high resistivity,
and the effects of backgating or sidegating are effectively restrained. 相似文献
985.
Semiconducting thin films of cadmium selenide have been grown by conventional thermal evaporation technique on glass substrate. Films evaporated at substrate temperature equal 523 K are stoichiometric and homogeneous. Effect of various growth parameters like rate of deposition and substrate temperature on the electrical properties has been studied in details. Also, the annealed at 673 K under vacuum for 1 h films have been analyzed for resistivity and Hall effect. 相似文献
986.
A. Chandrasekhar Rao B. Natarajan H. Anandhalakshmi 《Journal of Physics and Chemistry of Solids》2007,68(2):305-310
Single crystal EPR studies of Cu(II) incorporated in magnesium rubidium sulphate hexahydrate are carried out at RT and 77 K. Since the hyperfine lines are not resolved at RT, single crystal rotations have been carried out at 77 K. The spin Hamiltonian parameters calculated from the 77 K spectra are: g11=2.133, g22=2.137, g33=2.327, A11=0.01, A22=1.44 and . The impurity ion occupies an interstitial position in this crystal lattice, which is not very common for copper ion. In addition, the low hyperfine coupling constant is explained by considering an admixture of dx2-y2 ground state with dz2 excited state. Bonding parameters, κ=0.254, , α2=0.706, α=0.8406 have also been calculated. The present study has helped to understand the static nature of JT, for which the present system is an example. 相似文献
987.
We apply unrestricted Hartree-Fock to modelling two systems:
- (1)
- We calculate the spin structure and addition spectra of small symmetric quantum dots (often called 2D “artificial atoms”), improving the accuracy considerably by including, for the first time, second-order correlation corrections. We compare the results to experiment and to previous numerical works, and find that our spin structure in some cases disagrees with that calculated within mean-field theories, such as Hartree-Fock without correlation corrections, or density-functional theory [C. Sloggett, O.P. Sushkov, Phys. Rev. B 71 (2005) 235326].
- (2)
- We model the well-known 0.7 anomaly in the conductance of a quantum point contact. We calculate the conductance using direct calculation of scattering phases on a ring, within Hartree-Fock. We observe strong localisation of the Fermi electrons on the barrier, and suggest a mechanism for the observed temperature-dependent conductance anomaly.
988.
Based on Timoshenko beam model, a theoretical model of radially polarized piezoelectric ceramic tubes is investigated. In the model, the piezoelectric effects are considered, and the shear correction factor is introduced which reveals effects of the size of the cross-section and Poisson’s ratio. Based on the model, the particular attentions are devoted to effects of the boundary conditions at two ends on flexural resonance frequencies of the piezoelectric ceramic tubes. Changing the sizes of the tubes and the mass loads at both free ends, the variations of the flexural resonance frequencies of free–free piezoelectric ceramic tubes are calculated theoretically. Besides, the flexural resonance frequencies of the piezoelectric ceramic tube cantilevers with mass loads at one free end are also investigated theoretically. To verify accuracy of the theoretical mode, the flexural resonance frequencies for different lengths of the piezoelectric ceramic tubes and different loaded masses are measured experimentally. The theoretical results agree well with the experimental measurement, which demonstrates that the model is accurate for analyzing the flexural resonance frequencies of the piezoelectric ceramic tubes with mass loads. 相似文献
989.
Hai Gou Huang 《Surface science》2007,601(5):1184-1192
The adsorption configurations of pyrimidine and triazine on Si(1 1 1)-7 × 7 were investigated using high-resolution electron energy loss spectroscopy (HREELS) X-ray photoelectron spectroscopy and density functional theory calculations. The HREELS spectra of chemisorbed monolayer show the coexistence of the C(sp2)-H and C (sp3)-H stretching modes together with the observation of the unconjugated CN(C) vibrational feature suggesting that the carbon atom and its para-nitrogen atom of pyrimidine and triazine directly participate in binding with the surface to form Si-C and Si-N σ-linkages. The core levels of the C-atom and its opposite nitrogen atom directly binding with Si-atoms experience a down-shifting by 1.8-1.9 and 1.4-1.6 eV, respectively. These experimental findings are consistent with the density functional theory calculations indicating that the carbon atom and its para-nitrogen atom favorably link with the adjacent adatom and rest atom pair to form C-Si and N-Si linkages. 相似文献
990.
The structure, growth and stoichiometry of heteroepitaxial Pr2O3 films on Si(1 1 1) were characterized by a combined RHEED, XRD, XPS and UPS study in view of future applications as a surface science model catalyst system. RHEED and XRD confirm the growth of a (0 0 0 1) oriented hexagonal Pr2O3 phase on Si(1 1 1), matching the surface symmetry by aligning the oxide in-plane direction along the Si azimuth. After an initial nucleation stage RHEED growth oscillation studies point to a Frank-van der Merwe growth mode up to a thickness of approximately 12 nm. XPS and UPS prove that the initial growth of the Pr2O3 layer on Si up to ∼1 nm thickness is characterized by an interface reaction with Si. Nevertheless stoichiometric Pr2O3 films of high crystalline quality form on top of these Pr-silicate containing interlayers. 相似文献