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991.
W. Apel H.-U. Everts U. Körner 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):317-324
A coherent state representation for the electrons of ordered antiferromagnets is used to derive effective Hamiltonians for
the dynamics of holes in such systems. By an appropriate choice of these states, the constraint of forbidden double occupancy
can be implemented rigorously. Using these coherent states, one arrives at a path integral representation of the partition
function of the systems, from which the effective Hamiltonians can be read off. We apply this method to the t-J model on the square lattice and on the triangular lattice. In the former case, we reproduce the well-known fermion-boson
Hamiltonian for a hole in a collinear antiferromagnet. We demonstrate that our method also works for non-collinear antiferromagnets
by calculating the spectrum of a hole in the triangular antiferromagnet in the self-consistent Born approximation and by comparing
it with numerically exact results.
Received: 23 December 1997 / Accepted: 17 March 1998 相似文献
992.
Zhang Ying Li Ziping Li Ziping Zhang Ying 《International Journal of Theoretical Physics》2004,43(5):1231-1240
The fractional spin of a system with Chern–Simons (CS) term coupled to a polaron at the quantum level is studied. The Faddeev–Senjanovic (FS) scheme for path-integral quantization of constrained Hamiltonian systems is applied. The quantal conserved angular momentum and the fractional spin at the quantum level of this system are presented based on the quantal Noether theorem. The fractional spin is also presented for the system with Maxwell kinetic term. 相似文献
993.
P. Ruján 《Journal of statistical physics》1984,34(3-4):615-646
The methods presented in the first two articles of this series are simplified and generalized by growing stationary stochastic crystals from a given Ansatz layer. On the disorder trajectory the free energy, correlation functions, and multicritical points are calculated explicitly for a large class of models with competing interactions, including the staggered eight-vertex model, the general sixteen-vertex model, theq-state Potts model on a triangular lattice, a generalZ(q) model, and restricted spin glass models in two dimensions. 相似文献
994.
Monte Carlo simulations are performed for pure and site-diluted Ising ferro- and ferrimagnets on a simple cubic lattice with up to 403 sites and with impurity concentrationx. For the diluted ferromagnet (x=0.2) the exponent= 0.392±0.03 is definitely larger than the pure model value of=0.304±0.03. In contrast, for ferrimagnetic systems (x=0, 0.1, 0.2) the values appear to be independent ofx and within the error limits consistent with the value for the pure ferromagnet, possibly because the width of the asymptotic random critical regime (or of the crossover regime) is even smaller than in the case of ferromagnets. 相似文献
995.
The Steven’s method of molecular orbitals for octahedral complexes containing transition metal ions has been used for estimating
the binding parameters and interpreting theg factors of VO
2
+
ion in single crystals. The expressions forg factors have been given in terms ofK
‖ andK
⊥ taking into account the tetragonal crystalline field and covalent binding effects. Computations show thatK
⊥ should be less than 0.066 in order to fit the experimentalg values. The ground state wave function (GSWF) of VO
2
+
ion doped in different single crystals has been estimated using crystal field theory. The GSWF is found to be ind
xy state with slight admixture of the excited states
,d
xz andd
yz. The hyperfine interaction parameterP and Fermi contact termX have also been estimated. 相似文献
996.
997.
《Comptes Rendus Chimie》2018,21(12):1095-1120
The piezochromic properties of spin-crossover complexes have been recognized for a long time, with increasing pressure favouring the low spin state due to its smaller volume and therefore shifting the spin equilibrium towards higher temperatures and accelerating the relaxation at a given temperature. However, the interpretation and quantification of pressure-induced changes have been several times compromised by the relatively poor and incomplete spectral and structural information provided by the detection methods or due to the experimental difficulties related to the need for hydrostatic conditions at low temperatures. The present review is therefore primarily focused on these experimental aspects of high-pressure spin crossover research providing an overview of methods of pressure generation and associated detection methods as well as on selected recent results. 相似文献
998.
The spectrum of the hydrogen atom confined in a spherical impenetrable box of radius Rc has been investigated by many authors up to date, but not at the level of relativistic corrections. It is well known that, as Rc diminishes, all energy levels and the pressure increase very rapidly, whereas the polarizability goes to zero. In this report, we have computed the relativistic corrections that underlie the fine structure of the confined hydrogen atom, as a function of Rc. Such corrections correspond to relativistic kinetic energy, spin‐orbit coupling and the Darwin term, which are calculated in the frame of time‐independent perturbation theory, for which, use was made of the exact confined hydrogen atom wave functions. We show that for a confinement radius of 0.5 au the relativistic corrections increase up to three orders of magnitude with respect to those corresponding to the free atom. As Rc decreases, the kinetic energy correction and the spin‐orbit coupling for become negative whereas their absolute value and the Darwin term, which is positive, increase very rapidly. 相似文献
999.
R. Raghavan Christopher L. Henley Scott L. Arouh 《Journal of statistical physics》1997,86(3-4):517-550
We define two new models on the square lattice in which each allowed configuration is a superposition of a covering by white dimers and one by black dimers. Each model maps to a solid-on-solid (SOS) model in which the height field is two dimensional. Measuring the stiffness of the SOS fluctuations in the rough phase provides critical exponents of the dimer models. Using this height representation, we have performed Monte Carlo simulations. They confirm that each dimer model has critical correlations and belongs to a new universality class. In the dimer-loop model (which maps to a loop model) one height component is smooth, but has unusual correlated fluctuations; the other height component is rough. In the noncrossing-dimer model the heights are rough, having two different elastic constants; an unusual form of its elastic theory implies anisotropic critical correlations. 相似文献
1000.
A general method for automated de novo deduction of protein structure from 2D NMR has been developed. The algorithms which extract simple spin coupling topologies from MQF-COSY, construct more complicated spin coupling topologies based upon MQ spectrum including all possible pathways, and extract spin coupling topological fragments for amino acids of a protein, have been implemented in C~(++) language and run on a SUN 4/280 work station. Compared with the manual assignments for melittin, the total identity of the automated de novo method is 86.3%. 相似文献