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1.
J.Z. Wu S.H. Yoo T. Aytug A. Gapud B.W. Kang S. Wu W. Zhou 《Journal of Superconductivity》1998,11(1):169-171
The effect of Na- and Li-doping in Hg-based cuprates has been studied. It has been found that superconductivity can be achieved in samples containing small amount of Na or Li. While little change is found in the crystalline structure, the formed superconducting phase have the onset Tc typically above 140 K and zero-resistance Tc up to 136K. More interestingly, the processing temperature for the doped Hg-1223 can be reduced significantly to near 700 °C which is promising for thin films growth on many technologically compatible substrates. 相似文献
2.
IthasbenwelknownthatsomelanthanidescanreplaceytriuminYBCOsuperconductorswithoutappreciablechangingthetransitiontemperature.N... 相似文献
3.
N. Guskos V. Lyvkodimos C. A. Londos A. Kondos S. M. Paraskevas A. Koufoudakis C. Mitros H. Gamari-Seale D. Niarchos I. Kruk 《Journal of Superconductivity》1992,5(5):457-461
EPR, XRD, and magnetic studies are presented for Pr0.5Re0.5Ba2Cu3O7– compounds (Re= La, Nd, Sm, Eu, Gd, Dy, Ho, Y, Er, Tm, Yb, and Lu) in the orthorhombic and tetragonal (large oxygen deficiency) phase. For the samples with Re=Dy, Ho, Y, Er, Tm, Yb, and Lu in the orthorhombic phase, the transition to the superconducting state has been observed in the temperatures rangeT
c
between 18 and 40 K. For the samples with Nd and Yb in the tetragonal phase, EPR spectra coming from trivalent rare earth ions have been recorded. In the nonoxygenated sample Pr0.5La0.5Ba2Cu3O7–
the EPR spectrum arising from the non-Kramers trivalent praseodymium ion has been observed. A broad EPR line appearing in all our samples was attributed to superexchange interaction between copper ions over oxygen (O
2
–
) bridges. Interestingly, for the Pr0.5Re0.5Ba0.5Cu3O7– (Re = Er and Lu) compounds in the tetragonal phase at liquid-nitrogen temperature, a nonresonant microwave absorption in low magnetic fields has been detected. 相似文献
4.
The electronic momentum distribution n(k) of the two dimensional Hubbard model is studied for different values of the coupling U/t, electronic density n , and temperature, using quantum Monte Carlo techniques. A detailed analysis of the data on 8 × 8 clusters shows that features consistent with hole pockets at momenta k=(±/2,±/2,) appear as the system is doped away from half-filling. Our results are consistent with recent experimental data for the cuprates discussed by Aebi et al. (Phys. Rev. Lett.72, 2757 (1994)). In the range of couplings studied, the depth of the pockets is maximum at n approximately 0.9, and it increases with decreasing temperature. The apparent absence of hole pockets in previous numerical studies of this model is explained. 相似文献
5.
The charge-transfer hypothesis is shown to be inconsistent with data for YBa2Cu3Ox: (i) The two-step behavior ofT
c(x) (with jumps from zero to 60 K and then to 90 K) is not reflected as a similar, statistically significant two-step behavior in the bond-valence-sum charge of cuprate-plane Cu ions (as once believed), (ii) as a consequence of the law of conservation of charge, the derivatives of the layer charges with respect to oxygen contentx for both the Ba-O layers and the charge-reservoir Cu-O chains have the opposite signs to those predicted, and (iii) the charge-transfer observed for superconducting YBa2Cu3Ox is not sufficient to produce superconductivity, as demonstrated by insulating PrBa2Cu3Ox, which has virtually the same layer charges. 相似文献
6.
Jesse Noffsinger Feliciano Giustino Brad D. Malone Cheol-Hwan Park Steven G. Louie Marvin L. Cohen 《Computer Physics Communications》2010,181(12):2140-2148
EPW (Electron–Phonon coupling using Wannier functions) is a program written in Fortran90 for calculating the electron–phonon coupling in periodic systems using density-functional perturbation theory and maximally localized Wannier functions. EPW can calculate electron–phonon interaction self-energies, electron–phonon spectral functions, and total as well as mode-resolved electron–phonon coupling strengths. The calculation of the electron–phonon coupling requires a very accurate sampling of electron–phonon scattering processes throughout the Brillouin zone, hence reliable calculations can be prohibitively time-consuming. EPW combines the Kohn–Sham electronic eigenstates and the vibrational eigenmodes provided by the Quantum ESPRESSO package (see Giannozzi et al., 2009 [1]) with the maximally localized Wannier functions provided by the wannier90 package (see Mostofi et al., 2008 [2]) in order to generate electron–phonon matrix elements on arbitrarily dense Brillouin zone grids using a generalized Fourier interpolation. This feature of EPW leads to fast and accurate calculations of the electron–phonon coupling, and enables the study of the electron–phonon coupling in large and complex systems.
Program summary
Program title: EPWCatalogue identifier: AEHA_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEHA_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: GNU Public LicenseNo. of lines in distributed program, including test data, etc.: 304 443No. of bytes in distributed program, including test data, etc.: 1 487 466Distribution format: tar.gzProgramming language: Fortran 90Computer: Any architecture with a Fortran 90 compilerOperating system: Any environment with a Fortran 90 compilerHas the code been vectorized or parallelized?: Yes, optimized for 1 to 64 processorsRAM: Heavily system dependent, as small as a few MBSupplementary material: A copy of the “EPW/examples” directory containing the phonon binary files can be downloadedClassification: 7External routines: MPI, Quantum-ESPRESSO package [1], BLAS, LAPACK, FFTW. (The necessary Blas, Lapack and FFTW routines are included in the Quantum-ESPRESSO package [1].)Nature of problem: The calculation of the electron–phonon coupling from first-principles requires a very accurate sampling of electron–phonon scattering processes throughout the Brillouin zone; hence reliable calculations can be prohibitively timeconsuming.Solution method: EPW makes use of a real-space formulation and combines the Kohn–Sham electronic eigenstates and the vibrational eigenmodes provided by the Quantum-ESPRESSO package with the maximally localized Wannier functions provided by the wannier90 package in order to generate electron–phonon matrix elements on arbitrarily dense Brillouin zone grids using a generalized Fourier interpolation.Running time: Single processor examples typically take 5–10 minutes.References:[1]
P. Giannozzi, et al., J. Phys. Condens. Matter 21 (2009), 395502, http://www.quantum-espresso.org/.
7.
8.
Ekkehard Krüger 《Journal of Superconductivity and Novel Magnetism》2005,18(4):433-454
The symmetry of the Bloch functions in the conduction band of tetragonal and orthorhombic La2CuO4 is examined for the existence of symmetry-adapted and optimally localizable (usual or spin-dependent) Wannier functions.
It turns out that such Wannier functions do not exist in the tetragonal phase. In the orthorhombic phase, on the other hand,
the Bloch functions can be unitarily transformed in three different ways into optimally localizable Wannier functions: they
can be chosen to be adapted to each of the three phases observed in the pure or doped material, that is, to the antiferromagnetic
phase, to the superconducting phase or to the phase evincing neither magnetism nor superconductivity. This group-theoretical
result is proposed to be interpreted within a nonadiabatic extension of the Heisenberg model. Within this model, atomic-like
states represented by these Wannier functions are responsible for the stability of each of the three phases. However, all
the three atomic-like states cannot exist in the tetragonal phase, but are stabilized by the orthorhombic distortion of the
crystal. A simple model is proposed which may explain the physical properties of La2−x
Sr
x
CuO4 as a function of the Sr concentrationx. 相似文献
9.
10.