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81.
Closed form expressions for the reflection of light in a dielectric waveguide incident on a grating with a nonlinear chirp are presented. The method is based on a direct integration of the coupled mode equations using the method of stationary phase. 相似文献
82.
Mössbauer emission spectra of57Co in solutions of the saccharide binding protein concanavalin A have been obtained between 90 K and 238 K. The spectra were analyzed taking into account after-decay effects and between 200 and 238 K, using the bound diffusion model. The mean square amplitude, ?x 2?, of the collective motion was found to be smaller in concanavalin A with saccharide, than in that without it. 相似文献
83.
Amnon Yariv 《Optics Communications》1982,40(6):401-404
The NH4Br crystal is irradiated simultaneously with a modulated red light and a steady UV light in the region of the fundamental absorption band. The resulting recombination luminescence of electrons with VK centers is phase-sensitively detected, and compared with the emission which is directly excited by UV light. From measurements of the excitation spectra for recombination luminescence, it is pointed out that the dissociation of free excitons occurs efficiently in NH4Br. 相似文献
84.
Li-, Na-, K-, Rb- and Cs-montmorillonites were saturated with benzidine, these organo-clay complexes heated under vacuum to 200°C and IR spectra recorded at various temperatures. Benzidine is mostly bound to interlayer cations through water molecules, except in Cs-clay where bonding to hydrophobic water and to water molecules which are hydrogen bonded to the oxygen plane predominates. During the thermal treatment water is lost and alkali, cations coordinate directly with benzidine. In Cs-, and to some extent also in Rb- and K-montmorillonite, benzidine is oxidized to semiquinone and quinoidal cation during the thermal treatment. 相似文献
85.
Amnon Yariv 《Optics Communications》1978,25(1):23-25
The phenomenon of four-wave optical mixing is an exact analog of the sequential operations of holographic recording and reconstruction. It should thus be possible to realize, in real time, holographic experiments and devices using such mixing. 相似文献
86.
87.
88.
The grinding of a mixture containing kaolinite and CsF was carried out by three different techniques, short manual grinding,
Fisher mechanical mortar and Retsch ball mill. In addition to different cesium aluminium silicates which were detected by
X-ray powder diffraction, a new type of intercalation complex was identified by FTIR spectroscopy. The X-ray diffractogram
of this complex did not show any basal spacing, which may characterize the complex but the 0.715 nm characteristic peak of
the untreated kaolinite became very weak. The Retsch ball mill led to a slight destruction of the kaolinite and the formation
of small amounts of the new intercalation complex. The delamination of book-like kaolinite assemblages was observed after
the manual and Fisher mortar grindings. In the latter grinding techniques the kaolin-like layers persisted and served as the
framework for the intercalation complexes.
Received: 4 February 1998 Accepted: 11 March 1998 相似文献
89.
Yermiyahu Z. Landau A. Zaban A. Lapides I. Yariv S. 《Journal of Thermal Analysis and Calorimetry》2003,72(2):413-441
The adsorption of the anionic dye congo-red (CR) by Na-, Cs-, Mg-, Al- and Fe-montmorillonite was studied by simultaneous
DTA-TG. Thermal analysis curves of adsorbed CR were compared with those of neat CR. The oxidation of neat CR is completed
below 570°C. Thermal analysis curves of adsorbed CR show three regions representing dehydration of the clay, oxidation of
the organic dye and dehydroxylation of the clay together with the oxidation of residual organic matter. The oxidation of the
dye begins at about 250°C with the transformation of organic H atoms into water and carbon into charcoal. Two types of charcoal
are obtained, low-temperature and high-temperature stable charcoal. The former gives rise to an exothermic peak in the second
region of the thermal analysis and the latter in the third region. The exchangeable metallic cation determines the ratio between
the low-temperature and high-temperature stable charcoal, which is formed. With increasing acidity of the exchangeable metallic
cation higher amounts of high-temperature stable charcoal are obtained. It was suggested that aromatic compounds p bonded
to the oxygen plane of the clay framework are converted into charcoal, which is burnt at about 550-700°C. With increasing
surface acidity of the clay more species of CR are protonated. Only protonated dye species can form p bonds with oxygen plane
and are converted to high-temperature stable charcoal during the thermal analysis. The thermal behavior of the dye complex
of Cu-montmorillonite is different probably due to the catalytic effect of Cu.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
90.
Z. Grauer S. Yariv L. Heller-Kallai D. Avnir 《Journal of Thermal Analysis and Calorimetry》1983,26(1):49-64
The nature of the adsorption complex formed between dibenzotropone (DBT) and montmorillonite at elevated temperatures is strongly dependent on the interlayer cations. This was shown by electronic and IR spectra, by X-ray diffraction, and by study of the effects of gradual heating of the samples on these analyses. All samples exhibited significant red shifts of the electronic spectra of DBT into the visible range. These red shifts are attributed to two factors, both contributing to the enhancement of the tropylium planar character of DBT: hydrogen-bonding of acidic interlayer water to the carbonyl group, imparting positive charge to the tropone ring; and π interactions between the aromatic moiety and the oxygen planes. The position of the maximum was temperature-dependent for Cu-, Ni-, Al- and Fe-montmorillonites, for which heating (100°) under vacuum increased the red shift. The organic molecule assumes a planar conformation and is oriented parallel to the clay layers. IR spectra confirming this conformational orientation of DBT are discussed. The basal spacings of the DBT montmorillonite associations depend on the number of water and DBT sheets present in the interlayers. Layers with one or two sheets of DBT and with up to two sheets of water could be distinguished, leading to a maximum spacing of 20.4 Å. 相似文献