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61.
Correlation between deformation bleaching and mechanoluminescence in coloured alkali halide crystals
The present paper reports the correlation between deformation bleaching of coloration and mechanoluminescence (ML) in coloured
alkali halide crystals. When the F-centre electrons captured by moving dislocations are picked up by holes, deep traps and other compatible traps, then deformation
bleaching occurs. At the same time, radiative recombination of dislocation captured electrons with the holes gives rise to
the mechanoluminescence. Expressions are derived for the strain dependence of the density of colour centres in deformed crystals
and also for the number of colour centres bleached. So far as strain, temperature, density of colour centres, E
a and volume dependence are concerned, there exists a correlation between the deformation bleaching and ML in coloured alkali
halide crystals. From the strain dependence of the density of colour centres in deformed crystals, the value of coefficient
of deformation bleaching D is determined and it is found to be 1.93 and 2.00 for KCl and KBr crystals, respectively. The value of (D+χ) is determined from the strain dependence of the ML intensity and it is found to be 2.6 and 3.7 for KCl and KBr crystals,
respectively. This gives the value of coefficient of deformation generated compatible traps χ to be 0.67 and 1.7 for KCl and KBr crystals, respectively. 相似文献
62.
Poonam Tandon V. D. Gupta O. Prasad Shantanu Rastogi V. P. Gupta 《Journal of Polymer Science.Polymer Physics》1997,35(14):2281-2292
Poly(L -methionine) (PMet) is one of the two sulfur containing polyamino acids. Raman, FTIR spectra, and heat capacity measurements of PMet have been well interpreted through the normal mode analysis and the density of states derived therefrom. Earlier interpretation of heat capacity data is limited because it is based on the Tarasov model, wherein the concept of group frequency and skeletal similarity are used. A special feature of some dispersion curves is their tendency to bunch in the neighborhood of the helix angle. This has been attributed to the presence of strong intramolecular interactions. Repulsion between the dispersion curves is also observed. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2281–2292, 1997 相似文献
63.
Navina Wadhwani Poonam Tandon Vishwambhar D. Gupta Shantanu Rastogi 《Macromolecular Symposia》1997,119(1):113-117
Among the synthetic polymers of commercial potential, poly-butadiene is an important rubbery material and it encompasses the bulk elastomers in use. To the best of our knowledge, a complete normal coordinate analysis with full phonon dispersion curves for cis 1,4 polybutadiene (CPBD) have not been reported so far. In the present communication, we report a complete normal coordinate analysis with full dispersion curves, density-of-states and calculation of heat capacity. The normal coordinate analysis has been carried out using the Urey-Bradley force field and the Wilson's GF matrix method as modified by Higgs. A comparison has been made with trans 1,4 polybutadiene (TPBD). The prominent features of the dispersion curves like crossing over and regions of zero-slope away from the zone centre are discussed. To check the validity of the force field used and the assignments, normal mode calculations are also performed for unsaturated C-deuterated and fully deuterated CPBD. 相似文献
64.
R. P. Rastogi Kehar Singh Ram Shabd B. M. Upadhyay 《Journal of colloid and interface science》1981,80(2):402-411
Electrical properties of cholesterol interfaces have been investigated. For this purpose electroosmotic and hydrodynamic permeation of water, sodium chloride, barium chloride, aluminum chloride, and urea solutions across a cholesterol plug have been investigated. Dependence of electroosmotic permeability on concentration of electrolytes has also been studied. Electrophoretic mobility of cholesterol particles of known size distribution and dispersed in solutions of varying concentrations of electrolytes and urea has also been studied. The data have been used to estimate ζ potentials in order to have a plausible picture of the electrical double layer at the cholesterol/ solution interfaces. 相似文献
65.
Holographic interferometry is proposed to detect the change in the mechanical responses of reed stems growing in eutrophic, as compared with those in healthy, water bodies. The detection of the difference in behaviour could be a sensitive way to index the degree of eutrophication. An interferometric method based on holomicroscopic moiré is developed and preliminary results obtained are presented. 相似文献
66.
We present a theoretical analysis of corrugated long-period gratings in planar waveguides. In particular, we calculate the transmission spectra for both the TE and TM polarizations and highlight the polarization-independence conditions. 相似文献
67.
Nileshkumar Kukalyekar Luigi Balzano Gerrit W. M. Peters Sanjay Rastogi John C. Chadwick 《大分子反应工程》2009,3(8):448-454
Bimodal polyethylenes comprising varying proportions of high‐ and low‐molecular‐weight fractions are synthesized in a single polymerization stage, via the co‐immobilization of a chromium and an iron catalyst on an MgCl2/AlEtn(OEt)3?n support. Changes observed in the viscoelastic response of the polymer melt with increasing content of the high‐molecular‐weight fraction indicate effective mixing in the bimodal blend. In flow, chains in the high‐molecular weight fraction tend to orient and stretch under shear. Due to the longer relaxation time of the high‐molecular‐weight component, X‐ray diffraction and scattering reveal that shear‐induced crystallization takes place at temperatures close to the equilibrium melting point of linear polyethylene. The so‐crystallized high‐molecular‐weight component suppresses the nucleation barrier for further crystallization, leading to the formation of a “shish‐kebab” polymer morphology.
68.
Prodigiosin, a metabolite isolated from Serratia bacteria, is a potent anti-cancer agent. The goal of this research was to determine if prodigiosin could bind to G-quadruplex DNA. We found by using UV–vis spectroscopy that the G-quadruplex K+√d[TG4T]4, but not the single-stranded Li+√d[TG4T], increased the water solubility of prodigiosin. In addition, we found that prodigiosin's fluorescence was strongly enhanced in the presence of K+√d[TG4T]4, further evidence for quadruplex-ligand binding. Using 1H and 31P NMR experiments, we confirmed that prodigiosin binds at the 3′-end of K+√d[TG4T]4. Saturation transfer difference NMR experiments, done by irradiating the G5 H8 signal in K+√d[TG4T]4, indicated specific interactions between the G-quadruplex and prodigiosin's A and B rings. This study raises the possibility that G-quadruplex DNA may well be a target for the anti-cancer agent prodigiosin. 相似文献
69.
Rastogi VK Jain V Palafox MA Singh DN Yadav RA 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2001,57(2):209-216
Raman spectrum of 2,4-dichlorobenzonitrile (2,4-DCBN) in powder form has been recorded in the region 50-4000 cm(-1) on a Jasco K-500 Raman spectrophotometer using the 488.0 nm radiation from an argon laser. FTIR spectra in the region 200-4000 cm(-1) have been recorded in KBr pellet and nujol mull on a Nicolet DX spectrometer. Using the observed Raman and IR frequencies, normal co-ordinate analysis has been carried out to support the vibrational analysis and to determine the planar and non-planar force fields. 相似文献
70.
The kinetics of metal exchange between copper(II) and tetramethylenediaminetetraacetatonickel(II), [Ni(TMDTA)] has been studied
between pH 3.4 and 4.8 at an ionic strength of 1.25 M (NaClO4) and a temperature of 25.0 ± 0.1 °C. The reaction is first order in [Ni(TMDTA)]. The reaction order in [Cu2+] varies from first to zero and then back to first as [Cu2+] is increased. At low copper concentration, the first-order rate constant is pH independent and represents the attack of
copper on the nickel complex through a pathway in which TMDTA is partially uncoordinated before reaction with copper. Evidence
is presented for a stepwise dechelation mechanism followed by attack of copper to give a dinuclear intermediate. The zero-order
rate is pH dependent. At higher [Cu2+], the swing back to first order is due to the formation of a weak copper-tetramethylenediaminetetraacetatonickelate complex
which then converts to products through a dinuclear intermediate. A plausible mechanism, consistent with all the kinetic data,
is presented. 相似文献