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91.
High‐temperature superconductivity and long‐range order in strongly correlated electronic systems
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Lawrence J. Dunne 《International journal of quantum chemistry》2015,115(20):1443-1458
A selective review of the question of how repulsive electron correlations might give rise to off‐diagonal long‐range order (ODLRO) in high‐temperature superconductors is presented. The article makes detailed explanations of the relevance to superconductivity of reduced electronic density matrices and how these can be used to understand whether ODLRO might arise from Coulombic repulsions in strongly correlated electronic systems. Time‐reversed electron pairs on alternant Cuprate and the iron‐based pnictide and chalcogenide lattices may have a weak long‐range attractive tail and much stronger short‐range repulsive Coulomb interaction. The long‐range attractive tail may find its origin in one of the many suggested proposals for high‐Tc superconductivity and thus has an uncertain origin. A phenomenological Hamiltonian is invoked whose model parameters are obtained by fitting to experimental data. A detailed summary is given of the arguments that such interacting electrons can cooperate to produce a superconducting state in which time‐reversed pairs of electrons effectively avoid the repulsive hard‐core of the Coulomb interaction but reside on average in the attractive well of the long‐range potential. Thus, the pairing of electrons itself provides an enhanced screening mechanism. The alternant lattice structure is the key to achieving robust high‐temperature superconductivity with dx2‐y2 or sign alternating s‐wave or s± condensate symmetries in cuprates and iron‐based compounds. Some attention is also given to the question first raised by Leggett as to where the Coulombic energy is saved in the superconducting transition in cuprates. A mean‐field‐type model in which the condensate density serves as an order parameter is discussed. Many of the observed trends in the thermal properties of cuprate superconductors are reproduced giving strong support for the proposed model for high‐temperature superconductivity in such strongly correlated electronic systems. © 2015 Wiley Periodicals, Inc. 相似文献
92.
93.
Xian Tao 《Journal of organometallic chemistry》2011,696(13):2681-2666
The preparation of {[(MeO)3P]n·AgO3SCH3} (n = 1, 2a; n = 2, 2b) is described. The molecular structure of 2a was determined by using X-ray single crystal analysis. Complex 2a contains an Ag4 rectangular make-up, the centroid of which constitutes an inversion center. Complex 2b was used as precursor in the deposition of silver films using metal organic chemical vapor deposition (MOCVD) technique for the first time. The silver films obtained were characterized using scanning electron microscopy (SEM) and energy-dispersion X-ray (EDX) analysis. 相似文献
94.
Results of ab initio electronic structure calculations on the compound MgB2 using the FPLAPW method employing GGA for the exchange-correlation energy are presented. Total energy minimization enables
us to estimate the equilibrium volume, c/a ratio and the bulk modulus, all of which are in excellent agreement with experiment. We obtain the mass enhancement parameter
by using our calculated D (E
F) and the experimental specific heat data. The T
c is found to be 24.7 K. 相似文献
95.
96.
Bixiang Wang 《Journal of Mathematical Analysis and Applications》2002,266(1):1-20
This paper deals with the time-dependent Ginzburg-Landau equations of superconductivity in three spatial dimensions. The uniqueness of global weak solutions is established for this model with initial data of the order parameter in L4 and magnetic potential in L3. 相似文献
97.
98.
Highly c-axis oriented MgB2 thin films with Tc^onset of 39.6K were fabricated by magnesium diffusing into pulsedlaser-deposited boron precursors.The estimation of critical current density Jc,using hysteresis loops and the Bean model,has given the value of 10^7A/cm^2(15K,0T),which is one of the highest values ever reported.The x-ray photoemission study of the MgB2 thin films has revealed that the binding energies of Mg 2p and B 1s are at 49.4eV and 186.9eV,which are close to those of metallic Mg and transition-metal diborides,respectively. 相似文献
99.
Specific contact resistances of vacuum-evaporated silver contacts on new oxide superconductors, YBa2Cu3O7 are measured using a modified Kelvin test structure. Contact resistivity increases continuously as the temperature decreases
down to zero resistance point. AtT
c, its value is ∼0.15 ohm cm2 which is high for technological applications. The nature of contacts appears different from that of semiconductor metal structures. 相似文献
100.
K.-U. Neumann F. Kusmartsev H.-J. Lauter O. Schärpf T.J. Smith K.R.A. Ziebeck 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(1):5-9
A polarized neutron scattering investigation of the flux line lattice in the type-II superconductor niobium is reported. A
modulation of the nuclear lattice has been detected, and the magnitude of the first Fourier component of the lattice distortion
established relative to the magnitude of the magnetic scattering. This constitutes the first experimental observation of lattice
distortions due to the presence of magnetic flux lines within the bulk of a type-II superconductor. Using a simple microscopic
model the lattice distortion in niobium is estimated. A new mechanism is suggested for the coupling of the flux line lattice
to the crystallographic lattice. The experimental technique opens up the possibility of investigating the microscopic mechanism
of flux line - nuclear lattice interactions, in particular the pinning of flux lines within the bulk of a type-II superconductor.
Received: 8 August 1997 / Accepted: 16 October 1997 相似文献