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101.
Petr A. Kalinin Vitaly V. Kocharovsky Vladimir V. Kocharovsky 《Solid State Communications》2012,152(12):1008-1011
We consider exciton recombination lasing in heterostructure traps for Bose–Einstein condensation of dipolar excitons. We show that such structures suit well for class D lasers where cavity decay strongly exceeds polarization decay. We evaluate lasing threshold taking into account specific inhomogeneous broadening of the exciton spectral line owing to Bose–Einstein condensation phenomenon under quasi-equilibrium conditions.It is found that narrowing of the exciton momentum distribution just before the condensation onset considerably lowers lasing threshold. At the same time, it is pointed out that a subsequent formation of condensate itself does not help lasing much. We conclude that it is possible to achieve lasing on polariton modes in nowadays experiments aimed on Bose–Einstein condensation of excitons. 相似文献
102.
In this paper we establish hypercyclicity of continuous linear operators on \({H(\mathbb{C})}\) that satisfy certain commutation relations. 相似文献
103.
A theory is developed providing a rational framework for spatial scale- dependent fluid’s flow and heat transfer, and mass
of a component migrating with it through porous media. Introducing the assumption of a non-Brownian type motion and referring
to asymptotic expansion in powers of a small defined parameter, we develop a novel approach associated with macroscopic balance
equations obtained by averaging over a Representative Elementary Volume (REV). We prove that these equations can be decomposed
into a primary part that refers to the REV length scale and a secondary part valid at a length scale smaller than that of
the corresponding REV length. Further to our previous development, we obtain two general forms of the primary and secondary
macroscopic balance equations. One is based on the assumption that the advective flux of the extensive quantity is dominant
over that of the dispersive flux, whereas the other disregards this assumption. Moreover we also introduce the primary and
secondary macroscopic forms for the fluid heat- transfer equation. Considering a Newtonian fluid, the resulting primary Navier–Stokes
equation can vary from a nonlinear wave equation to a drag-dominant equation at the fluid–solid interface (Darcy’s law). The
secondary momentum balance equation describes a wave equation governing the concurrent propagation of the intensive momentum
and the dispersive momentum flux, deviating from their corresponding average terms. The primary macroscopic fluid heat-transfer
equation accounts for advective and dispersive heat fluxes and the secondary macroscopic heat-transfer equation involves the
simultaneous advection of heat deviating from its corresponding intensive average quantity. The primary macroscopic solute
mass balance equation accounts for advection and hydrodynamic dispersion. The secondary macroscopic component mass balance
equation is in the form of pure advection governing migration of the deviation from the average component concentration. At
this stage, we focus on establishing the viability of the developed theory. We do this by arguing that field observations
of motion at small spatial scales are coherent with the hyperbolic characteristics of the secondary balance equations. Field
observations under natural gradient flow conditions show excessive high concentration (average of 50 mg/L) of colloids under
land irrigated by sewage effluents. We argue that this displacement of condensed colloidal parcels manifests the theoretical
findings for the smaller spatial scale. Further evidence show the accumulation of particles moving behind the front of an
emitted shockwave. We consider this as an experimental proof reinforcing the argument that colloidal migration is subject
to the action of a shockwave in the fluid and pure advection transport, governed by the respective suggested hyperbolic macroscopic
balance equations of fluid momentum and component mass at the smaller spatial scale. 相似文献
104.
Leonid E. Gusel'nikov Vitaly G. Avakyan Stephan L. Guselnikov 《Heteroatom Chemistry》2007,18(7):704-720
Ab initio and DFT thermochemical study of diradical mechanism of 2 + 2 cycloreversion of parent heterocyclobutanes and 1,3‐diheterocyclobutanes, cyclo‐(CH2CH2CH2X), and cyclo‐(CH2XCH2X), where X = NH, O, SiH2, PH, S, was undertaken by calculating closed‐shell singlet molecules at three levels of theory: MP4/6‐311G(d)//MP2/6‐31G(d)+ZPE, MP4/6‐311G(d,p)//MP2/6‐31G (d,p)+ZPE, and B3LYP/6‐311+G(d,p)+ZPE. The enthalpies of 2 + 2 cycloreversion decrease on going from group 14 to group 16 elements, being substantially higher for the second row elements. Normally endothermic 2 + 2 cycloreversion is predicted to be exothermic for 1,3‐diazetidine and 1,3‐dioxtane. Strain energies of the four‐membered rings were calculated via the appropriate homodesmic reactions. The enthalpies of ring opening via the every possible one‐bond homolysis that results in the formation of the corresponding 1,4‐diradical were found by subtracting the strain energies from the central bond dissociation energies of the heterobutanes CH3CH2—CH2XH, CH3CH2—XCH3, and HXCH2—XCH3. The latter energies were determined via the enthalpies of the appropriate dehydrocondensation reactions, using C—H and X—H bond energies in CH3XH calculated at G2 level of theory. Except 1,3‐disiletane, in which ring‐opening enthalpy attains 69.7 kcal/mol, the enthalpies of the most economical ring openings do not exceed 60.7 kcal/mol. The 1,4‐diradical decomposition enthalpies found as differences between 2 + 2 cycloreversion and ring‐opening enthalpies were negative, the least exothermicity was calculated for ⋅ CH2SiH2CH2CH2. The only exception was 1,3‐disiletane, which being diradical, CH2SiH2CH2SiH2, decomposed endothermically. Since decomposition of the diradical containing two silicon atoms required extra energy, raising the enthalpy of the overall reaction to 78.9 kcal/mol, 1,3‐disiletane was predicted to be highly resisting to 2 + 2 cycloreversion. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:704–720, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20377 相似文献
105.
106.
107.
Jatinder N.D. Gupta Christos P. Koulamas George J. Kyparisis Chris N. Potts Vitaly A. Strusevich 《Annals of Operations Research》2004,129(1-4):171-185
This paper considers a variant of the classical problem of minimizing makespan in a two-machine flow shop. In this variant, each job has three operations, where the first operation must be performed on the first machine, the second operation can be performed on either machine but cannot be preempted, and the third operation must be performed on the second machine. The NP-hard nature of the problem motivates the design and analysis of approximation algorithms. It is shown that a schedule in which the operations are sequenced arbitrarily, but without inserted machine idle time, has a worst-case performance ratio of 2. Also, an algorithm that constructs four schedules and selects the best is shown to have a worst-case performance ratio of 3/2. A polynomial time approximation scheme (PTAS) is also presented. 相似文献
108.
109.
Vyacheslav I. Boyko Anna A. Podoprigorina Anton V. Yakovenko Vladimir V. Pirozhenko Vitaly I. Kalchenko 《Journal of inclusion phenomena and macrocyclic chemistry》2004,50(3-4):193-197
An effective method of 5,11,17,23-tetra-tert-butyl-25,26-dialkoxy-27,28-dihydroxy-calix[4]arenes and 25,26,27,28-tetraalkoxycalix[4]arenes synthesis by alkylation of tetrahydroxycalix[4]arenes in a DMSO-NaOH medium was developed. 相似文献
110.
Vitaly Vologodsky 《Proceedings of the American Mathematical Society》2004,132(11):3159-3165
We study the minimal toric resolution of the extended Prym map. We describe the blowup at certain singular points of the indeterminacy locus of the extended Prym map.