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111.
The infrared spectra of a linear (Cs) and a cyclic (Ci) water dimer and a linear (Cs) and a cyclic (C2h) ammonia dimer have been calculated, at the second order level of MØller-Plesset perturbation theory, using the 6-31G** basis set. The calculated spectra have been compared with the spectra of water and ammonia isolated in nitrogen and argon matrices. In the case of water, theory predicts the linear to be the more stable isomer, and the observed spectrum can only be interpreted in terms of the linear structure. For ammonia, while the experimentally determined spectrum fits the calculated spectrum of the linear dimer fairly closely, the prediction of which is the more stable structure is still ambiguous. 相似文献
112.
113.
We have developed a general and highly efficient method for the preparation of diverse [small omega]-formyl-[small alpha],[small beta]-unsaturated carbonyl compounds and optimized the conditions for the intramolecular Baylis-Hillman reactions of these compounds to provide various biologically important polycyclic compounds. 相似文献
114.
[structure: see text] A new cavitand bearing four imidazolium groups was synthesized for the recognition of anions through (C-H)+...X- hydrogen bond formation. The binding properties toward various anions including dicarboxylates were examined on the basis of 1H NMR spectroscopic experiments. 相似文献
115.
We study the annealed complexity of the m-vector spin glasses in the Sherrington-Kirkpatrick limit. The eigenvalue spectrum of the Hessian matrix of the Thouless-Anderson-Palmer free energy is found to consist of a continuous band of positive eigenvalues in addition to an isolated eigenvalue and (m-1) null eigenvalues due to rotational invariance. Rather surprisingly, the band does not extend to zero at any finite temperature. The isolated eigenvalue becomes zero in the thermodynamic limit, as in the Ising case (m=1), indicating that the same supersymmetry breaking recently found in Ising spin glasses occurs in vector spin glasses. 相似文献
116.
Yeo LY Matar OK Perez de Ortiz ES Hewitt GF 《Journal of colloid and interface science》2002,248(2):443-454
A speculative study on the conditions under which phase inversion occurs in agitated liquid-liquid dispersions is conducted using a Monte Carlo technique. The simulation is based on a stochastic model, which accounts for fundamental physical processes such as drop deformation, breakup, and coalescence, and utilizes the minimization of interfacial energy as a criterion for phase inversion. Profiles of the interfacial energy indicate that a steady-state equilibrium is reached after a sufficiently large number of random moves and that predictions are insensitive to initial drop conditions. The calculated phase inversion holdup is observed to increase with increasing density and viscosity ratio, and to decrease with increasing agitation speed for a fixed viscosity ratio. It is also observed that, for a fixed viscosity ratio, the phase inversion holdup remains constant for large enough agitation speeds. The proposed model is therefore capable of achieving reasonable qualitative agreement with general experimental trends and of reproducing key features observed experimentally. The results of this investigation indicate that this simple stochastic method could be the basis upon which more advanced models for predicting phase inversion behavior can be developed. 相似文献
117.
A theoretical model for the instability of turbulent boundary layer over compliant surfaces is described. The investigation
of instability is carried out from a time-asymptotic space-time perspective that classifies instabilities as either convective
or absolute. Results are compared against experimental observations of surface waves on elastic and viscoelastic compliant
layers. 相似文献
118.
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120.
An experimental investigation of the three-dimensional boundary layer induced by a Rankine-like vortex with its axis normal
to a stationary disk is described. The velocity field through the boundary layer was measured for Reynolds number Re (based on the tangential velocity and radius at the disk edge) ranging from 10 000 to 25 000 at various radial distances
by means of a 4-beam, 2-component Laser Doppler Anemometer. Our results show that the nature of the boundary layer is affected
by two factors: an inflexional instability caused by the crossflow velocity profile and a stability factor caused by the favorable
pressure gradient. At lower Reynolds number, the radial pressure gradient has a very strong stabilizing effect on the boundary
layer and acts to revert it to its laminar state upstream of the effusing core. At higher Re the inflexional instability caused by the crossflow velocity dominates while the stabilizing influence of the favorable pressure
gradient recedes. As such, laminar reversion likely occurs closer to the effusion core. Thus, the point of laminar reversion
moves closer to the effusion core as the Reynolds number is increased.
Received 23 May 1996 / Accepted 29 July 1996 相似文献