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41.
Immobilized sulfhydryl groups were prepared by partial thiolation of NH2-glass beads. The microenvironment of the immobilized SH groups was varied by different chemical modifications of neighboring
NH2 groups. Introduction of a strong charge in the surroundings of immobilized sulfhydryls results in their dramatic stabilization
against autooxidation. This effect is due to the salting of O2 from the surface microlayer of the thiolated beads. 相似文献
42.
Homogeneous mixed-metal oxides of the general formula (Bi/E/Si)O
x
, where E represents a dopant element (E=Sb, Sn, or Sb/Sn), can be prepared using typical sol-gel processing techniques. Reduction of the in-situ Bi(III) and E ions by hydrogen affords nanocomposites of Bi-Sb, Bi-Sn, or Bi-Sb-Sn widely dispersed throughout the silica xerogel matrix. The materials prepared have high Bi-E metal loading of 52–60 wt. % containing Bi-E alloy nanoclusters of 12–15 nm average diameter. These results demonstrate a convenient method for the production of practical quantities of nanostructured bismuth alloy ceramic composites at high metal content. 相似文献
43.
O. Penrose 《Journal of statistical physics》1995,78(1-2):267-283
The grand potentialP(z)/kT of the cluster model at fugacityz, neglecting interactions between clusters, is defined by a power series
n
Q
n
z
n
, whereQ
n
, which depends on the temperatureT, is the partition function of a cluster of sizen. At low temperatures this series has a finite radius of convergencez
s
. Some theorems are proved showing that ifQ
n
, considered as a function ofn, is the Laplace transform of a function with suitable properties, thenP(z) can be analytically continued into the complexz plane cut along the real axis fromz
s
to + and that (a) the imaginary part ofP(z) on the cut is (apart from a relatively unimportant prefactor) equal to the rate of nucleation of the corresponding metastable state, as given by Becker-Döring theory, and (b) the real part ofP(z) on the cut is approximately equal to the metastable grand potential as calculated by truncating the divergent power series at its smallest term. 相似文献
44.
We consider quantum unbounded spin systems (lattice boson systems) in -dimensional lattice space Z. Under appropriate conditions on the interactions we prove that in a region of high temperatures the Gibbs state is unique, is translationally invariant, and has clustering properties. The main methods we use are the Wiener integral representation, the cluster expansions for zero boundary conditions and for general Gibbs state, and explicitly -dependent probability estimates. For one-dimensional systems we show the uniqueness of Gibbs states for any value of temperature by using the method of perturbed states. We also consider classical unbounded spin systems. We derive necessary estimates so that all of the results for the quantum systems hold for the classical systems by straightforward applications of the methods used in the quantum case. 相似文献
45.
No modern theory of polymer excluded volume adequately describes the crossover from poor solvent to good solvent conditions; a fundamental difficulty is a singularity in the binary cluster integral. Mayer expansion techniques are applied to a model with a pair interaction between monomers to clarify the distinction between geometric and solvent contributions to excluded volume. Detailed calculations are undertaken for a hard-core potential and a mimic Lennard-Jones potential. The significance of the singularity in the binary cluster integral for calculations in the crossover regime is discussed. 相似文献
46.
We consider the covariance matrix,G
mm
=q
2<(x,m);(y,m)>, of thed-dimensionalq-states Potts model, rewriting it in the random cluster representation of Fortuin and Kasteleyn. In any of theq ordered phases, we identify the eigenvalues of this matrix both in terms of representations of the unbroken symmetry group of the model and in terms of random cluster connectivities and covariances, thereby attributing algebraic significance to these stochastic geometric quantities. We also show that the correlation length corresponding to the decay rate of one of the eigenvalues is the same as the inverse decay rate of the diameter of finite clusers. For dimensiond=2, we show that this correlation length and the correlation length of the two-point function with free boundary conditions at the corresponding dual temperature are equal up to a factor of two. For systems with first-order transitions, this relation helps to resolve certain inconsistencies between recent exact and numerical work on correlation lengths at the self-dual point o. For systems with second order transitions, this relation implies the equality of the correlation length exponents from above and below threshold, as well as an amplitude ratio of two. In the course of proving the above results, we establish several properties of independent interest, including left continuity of the inverse correlation length with free boundary conditions and upper semicontinuity of the decay rate for finite clusters in all dimensions, and left continuity of the two-dimensional free boundary condition percolation probability at o. We also introduce DLR equations for the random cluster model and use them to establish ergodicity of the free measure. In order to prove these results, we introduce a new class of events which we call decoupling events and two inequalities for these events. The first is similar to the FKG inequality, but holds for events which are neither increasing nor decreasing; the second is similar to the van den Berg-Kesten inequality in standard percolation. Both inequalities hold for an arbitrary FKG measure. 相似文献
47.
M. Slemrod 《Journal of statistical physics》1996,83(5-6):1067-1108
A discrete-velocity Boltzmann model is introduced. It is based on two principles: (i) clusters of particles move in 3 with seven fixed momenta; (ii) clusters may gain or lose particles according to the rules of Becker-Döring cluster equations. The model provides a kinetic representation of evaporation and condensation. The model is used to obtain macroscopic fluid equations which are valid into the metastable fluid regime,
, where is any positive number, is the inelastic Knudsen number, and
s
is the saturation density. 相似文献
48.
Polymer enhanced ultrafiltration (PEUF) is a newly developed method for the removal of heavy metals from aqueous solutions. This method was applied for the removal of mercury and cadmium with the presence of polyethyleneimine (PEI) as a water soluble polymer. After ultrafiltration experiments for metal–polymer mixtures, two separate streams, namely, retentate and permeate, former of which contains mainly metal–polymer complex and free polymer molecules while latter of which mainly contains free metal ions, were obtained. At the end of PEUF experiments, performance of operation was determined by concentration analyses which was achieved by atomic absorption spectroscopy (AAS) applied in a different way for permeate and retentate streams considering the effect of presence of polymer. For mercury analysis, cold vapor AAS was applied. It was observed that the presence of PEI did not affect the atomic absorption signal when 10% HCl was added to the sample solutions. For calcium and cadmium, flame AAS was used. It was observed that change in PEI concentration results in change in measured concentration of calcium and cadmium. Therefore, two new approaches were developed for accurate measurement of concentrations of calcium and cadmium. It was also observed that presence of other metals did not affect the accuracy of the measurement of a particular metal in the concentration range studied. 相似文献
49.
50.
Reactions of 1,2,3,4-tetraphenyl-1,2,3,4-tetraphospholane (I) with triruthenium dodecacarbonyl at different temperatures result in the cleavage of P-P bonds and even P-C bond(s) in I to afford a series of new ruthenium cluster derivatives containing phosphido and phosphinidene ligands: a penta-ruthenium wing-tip bridged butterfly cluster [Ru5(CO)11(μ4-PPh)(μ3-PPh){(μ4-η2-(PPh)2CH2}] (1), a hepta-ruthenium polyhedral (consisting of two fused square pyramids with a co-apex) cluster [Ru7(CO)15(μ4-PPh)2{(μ2-PPh)2CH2}](2), a linked penta-ruthenium cluster [Ru4(CO)10(μ4-PPh)(μ3-PPh)2(μ3-η2-PPhCH2)Ru(CO)3] (3), and a hepta-nuclear polyhedral (consisting of two fused square pyramids with different apexes) cluster [Ru7(CO)15(μ4-PPh)2{(μ2-PPh)2CH2}](4). Clusters 2 and 4 are isomeric and differ only in the connection of the two square pyramids in the Ru7 polyhedron. All the newly obtained clusters have been fully characterized by spectroscopic (IR, FABMS, 1H- and 31P-NMR spectroscopy) and analytical techniques, and their molecular structures are established by single crystal X-ray diffraction analysis. 相似文献