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71.
A new coupling of one-dimensional random walks is describedwhich tries to control the coupling by keeping the separationof the two random walks of constant sign. It turns out thatamong such monotone couplings there is an optimal one-step couplingwhich maximises the second moment of the difference (assumingthis is finite), and this coupling is fast inthe sense that for a random walk with a unimodal step distributionthe coupling time achieved by using the new coupling at eachstep is stochastically no larger than any other coupling. Thisis applied to the case of symmetric unimodal distributions. 相似文献
72.
This paper studies the dynamics of members of the two-parameter family of maps x → μx(1 ? xv), emphasizing the evolution from snapback repeller to crisis bifurcations. The example of the square root map is taken to represent the subfamily where v is fixed and taken from the range . A map from such a subfamily is shown to be conjugate with a map with negative Schwarzian derivative. This allows a characterization of crisis as the demise of a snapback repeller on a proper subinterval. 相似文献
73.
J. L. Lundberg E. J. Mooney C. E. Rogers 《Journal of Polymer Science.Polymer Physics》1969,7(5):947-962
Diffusion coefficients and solubilities of methane in polyisobutylene have been measured at four temperatures between 102 and 188°C. in the pressure range 23–341 atm. Diffusion coefficients extrapolated to atmospheric pressure range from 1.72 × 10?6 cm.2/sec. at 102°C. to 1.5 × 10?5 cm.2/sec. at 188°C. corresponding to an activation energy for diffusion of 8.7 ± 0.4 kcal./mole. Solubilities are small, about one molecule of methane for every forty carbon atoms in the polyisobutylene at 300 atm. partial pressure of methane. Solubilities vary little with temperature, but show an apparent minimum between 127 and 188°C. With improved methods of data analysis, diffusion coefficients and solubilities have been recalculated from previously reported studies on nitrogen in branched polyethylene and methane in branched polyethylene, linear polyethylene, and polystyrene. Recalculated diffusion coefficients are essentially the same as those reported previously, but the recalculated solubilities are decreased from 2 to 30%. The solubilities of all five systems show strong deviations from Henry's law, i.e., increases in partial pressure of methane and nitrogen with respect to solubility exceed linearity. The partial pressure (or fugacity)—solubility data may be interpreted in terms of a sorption model in which sorbed molecules are accommodated in widely dispersed, unoccupied volumes or sites in the polymer. An almost equivalent, solution model in which the first sorbed molecules to enter the polymer are accommodated to a large extent in existing volumes in the polymer, with successively sorbed molecules swelling the polymer to a greater extent (i.e., partial molal volume of sorbed molecules, V 1, increasing with concentration) can also account for these data. 相似文献
74.
Leucine aminopeptidase activity was measured using l-[U-14C]leucinamide as substrate. The leucine freed by hydrolysis was separated by high voltage electrophoresis and estimated in a scintillation counter. The method was especially useful for studying the production of LAP during the molting of infective juveniles of the nematodes, H. contortus, because activity could be measured without purifying or concentrating the enzyme. 相似文献
75.
The heats of combustion of 95 samples of oil shale from the Nevis Valley have been determined from DTA peak areas obtained by combustion in 1.5 atm oxygen. The heats of combustion of the oil shale ranged from 0.2 to 8.5 MJ kg−1, with an average of 2.6 MJ kg−1, while that of the kerogen was calculated to be 34.2 MJ kg−1. Up to four peaks were obtained in the DTA combustion curve, suggesting that different parts of the kerogen molecule were being oxidised at different temperatures.
In nitrogen, DTA endotherms were observed due to decarbonation of siderite (ca. 455°C), and dehydroxylation of kaolinite (ca. 570°C) and chlorite (ca. 760°C), and an exotherm due to formation of mullite (ca. 980°C). 相似文献
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Many of the proprietary additive formulations that have been proposed to control the properties of metal electrodeposits include water soluble macromolecules. Among these are the hydrodynamically interesting polyethylene glycols ‘Polyox’. In the course of a rotating disk electrode study of the effects of additives in copper electrodeposition the present authors had cause to try the effects of low concentrations of Polyox in an acid copper sulphate plating solution. In the presence of an essential trace of chloride ion Polyox very strongly inhibited deposition below a critical overpotential at which current density rises extremely rapidly with increasing overpotential. These results suggest that below the critical overpotential chloride ions hold a film of Polyox onto the electrode surface and may also give the film some lateral cohesion. The film may be a Polyox-cuprous chloride complex. Striking spiral patterns form at the critical overpotential. Their characteristics are explained as the consequences of electrodeposition on a surface containing submicroscopic protrusions and depressions in conditions where current density increases very rapidly with potential. 相似文献