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21.
We show that the nonlinear equation that describes nonparaxial Kerr propagation, together with the already reported bright-soliton solutions, admits of (1 + 1)D dark-soliton solutions. Unlike their paraxial counterparts, dark solitons can be excited only if their asymptotic normalized intensity u2infinity is below 3/7; their width becomes constant when u2infinity approaches this value. 相似文献
22.
We recently analyzed a new class of laser amplifier based on transverse Bragg reflection. We show that the unique properties of Bragg confinement make it possible through modal loss discrimination to achieve single-transverse-mode operation with transverse modal size that is an order of magnitude larger than in lasers that depend on total internal reflection for transverse confinement. 相似文献
23.
We study a model for the denaturation transition of DNA in which the molecules are considered as being composed of a sequence of alternating bound segments and denaturated loops. We take into account the excluded-volume interactions between denaturated loops and the rest of the chain by exploiting recent results on scaling properties of polymer networks of arbitrary topology. The phase transition is found to be first order in d = 2 dimensions and above, in agreement with experiments and at variance with previous theoretical results, in which only excluded-volume interactions within denaturated loops were taken into account. Our results agree with recent numerical simulations. 相似文献
24.
Calcination of sepiolite and of two sepiolite/CsCl mixtures, unground and air-ground was investigated by thermo-XRD-analysis.
At 200 °C sepiolite, neat, mixed or air-ground with CsCl lost interparticle and zeolitic water. The framework of sepiolite
persisted during the dehydration but became defected, mainly in the air-ground mixture, less in the unground mixture and little
in the neat clay. At 500 °C, with the loss of bound water, the neat clay was folded and transformed into sepiolite anhydride.
In sepiolite/CsCl mixtures the dehydrated variety persisted but the degree of crystal-imperfection increased in the air-ground
mixture more than in the unground mixture. At 700 °C the neat clay remained crystallized, but the CsCl mixtures became amorphous.
Some crystalline dehydrated sepiolite or sepiolite anhydride persisted in the unground and air-ground CsCl mixtures, respectively.
At 850 °C, the neat clay crystallized into protoenstatite with some enstatite and clinoenstatite. The amorphous fraction of
sepiolite in the unground sepiolite/CsCl mixtures crystallized into pollucite and forsterite and the crystalline fraction
was transformed into enstatite, protoenstatite, and clinoenstatite. In the air-ground mixture, the amorphous phase was transformed
into pollucite with some forsterite and the crystalline fraction into enstatite. 相似文献
25.
F. Burstein M. Borisover I. Lapides S. Yariv 《Journal of Thermal Analysis and Calorimetry》2008,92(1):35-42
In the present research we studied the effect of the solvent used, whether it was polar water or a non-polar organic solvent
(n-hexane or n-hexadecane), on the basal-spacing and bulk structure of the sorbate-sorbent complexes obtained by the secondary adsorption
of nitrobenzene and m-nitrophenol by two types of organo-montmorillonites. X-ray measured basal spacings before and after thermal treatments up
to 360°C. The organo-clays were synthesized, with 41 and 90% replacement of the exchangeable Na+ by hexadecyltrimethylammonium (HDTMA), with mono-and bilayers of HDTMA cations in the interlayer space, labelled OC-41 and
OC-90, respectively. After heating at 360°C both organo-clays showed spacing at 1.25–1.28 nm, due to the presence of interlayer-charcoal,
indicating that in the preheated organo-clays the HDTMA was located in the interlayer.
The thermo-XRD-analysis of Na-clay complexes showed that from organic solvents both sorbates were adsorbed on the external
surface but from water they were intercalated. m-Nitrophenol complexes of both organo-clays obtained in aqueous suspensions contain water molecules. Spacings of nitrobenzene
complexes of OC-41 and OC-90 and those of nitrophenol complexes of OC-41 showed that the adsorbed molecules were imbedded
in cavities in the HDTMA layers. Adsorption of m-nitrophenol by OC-90 from water and n-hexane resulted in an increase of basal spacing (0.21 and 0.29 nm, respectively) suggesting the existence of a layer of nitrophenol
molecules sandwiched between two parallel HDTMA layers. 相似文献
26.
Stokes-flow reversibility is violated in electrolyte solutions by a streaming-potential mechanism, where nonuniform convective currents within Debye layers surrounding charged particles induce electric fields in the electroneutral Ohmic bulk. We demonstrate the irreversibility consequences of this phenomenon for the problem of particle-pair sedimentation, where the two particles experience a repulsive force driven by bulk Maxwell stresses. At small separations the force scales inversely with the third power of separation distance. This singular behavior is associated with the counterrotation of the two torque-free particles, which leads through a lubrication mechanism to an intense electric field in the narrow gap between them. At large separations the force follows an inverse dependence upon the fourth power of separation, now associated with rectilinear particle motion. 相似文献
27.
Thermal Intercalation of Alkali Halides into Kaolinite 总被引:2,自引:0,他引:2
S. Yariv I. Lapides K.H. Michaelian N. Lahav 《Journal of Thermal Analysis and Calorimetry》1999,56(2):865-884
Solid state intercalation of alkali halides into kaolinite takes place by heating pressed disks of dimethylsulfoxide (DMSO)-kaolinite
complex ground in different alkali halides. This reaction involves diffusion of the DMSO outside the interlayer space and
the alkali halide into the interlayer space. IR and Raman spectroscopy reveal two types of intercalation complexes: (i) almost
non-hydrous, obtained during thermal treatment of the DMSO complex; and (ii) hydrated, obtained by regrinding the disk in
air. The strength of the hydrogen bonds between intercalated water or halide anions and the inner surface hydroxyls decreases
in the order Cl−>Br−>I−. Chlorides penetrate the ditrigonal holes and form hydrogen bonds with the inner OH groups.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
28.
29.
Y. Kafri D. Mukamel L. Peliti 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(1):135-146
Existing experimental studies of the thermal denaturation of DNA yield sharp steps in the melting curve suggesting that the
melting transition is first order. This transition has been theoretically studied since the early sixties, mostly within an
approach in which the microscopic configurations of a DNA molecule consist of an alternating sequence of non-interacting bound
segments and denaturated loops. Studies of these models neglect the repulsive, self-avoiding, interaction between different
loops and segments and have invariably yielded continuous denaturation transitions. In the present study we take into account
in an approximate way the excluded-volume interaction between denaturated loops and the rest of the chain. This is done by
exploiting recent results on scaling properties of polymer networks of arbitrary topology. We also ignore the heterogeneity
of the polymer. We obtain a first-order melting transition in d = 2 dimensions and above, consistent with the experimental results. We also consider within our approach the unzipping transition,
which takes place when the two DNA strands are pulled apart by an external force acting on one end. We find that the under
equilibrium condition the unzipping transition is also first order. Although the denaturation and unzipping transitions are
thermodynamically first order, they do exhibit critical fluctuations in some of their properties. For instance, the loop size
distribution decays algebraically at the transition and the length of the denaturated end segment diverges as the transition
is approached. We evaluate these critical properties within our approach.
Received 21 August 2001 and Received in final form 26 January 2002 相似文献
30.