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51.
Irradiation in acetonitrile of any one of the six isomers of dimethylbenzotrifluoride 8 resulted in efficient photoisomerization to the others. The dominant processes in these phototransposition reactions divides the isomers into two triads. The first consists of 8-2,6 (2,6-dimethylbenzotrifluoride), 8-2,3, and 8-3,4; the second consists of 8-3,5, 8-2,4, and 8-2,5. Moreover, irradiation of 2,6-dideuterio-4-methylbenzotrifluoride 5-d(2) resulted in formation of 5,6-dideuterio-3-methylbenzotrifluoride 6-d(2). These observations demonstrate that it is the trifluoromethyl-substituted carbon that is the migratory one in these reactions. 相似文献
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Obadiah G. Reid Jennifer A. Nekuda Malik Gianluca Latini Smita Dayal Nikos Kopidakis Carlos Silva Natalie Stingelin Garry Rumbles 《Journal of Polymer Science.Polymer Physics》2012,50(1):27-37
The influence of solid‐state microstructure on the optoelectronic properties of conjugated polymers is widely recognized, but still poorly understood. Here, we show how the microstructure of conjugated polymers controls the yield and decay dynamics of long‐lived photogenerated charge in neat films. Poly(3‐hexylthiophene) was used as a model system. By varying the molecular weight, we drive a transition in the polymer microstructure from nonentangled, chain‐extended, paraffinic‐like to entangled, semicrystalline (MW = 5.5–347 kg/mol). The molecular weight range at which this transition occurs (MW = 40–50 kg/mol) can be deduced from the drastic change in elongation at break found in tensile tests. Linear absorption measurements of free‐exciton bandwidth and time‐resolved microwave conductivity (TRMC) measurements of transient photoconductance track the concomitant evolution in optoelectronic properties of the polymer as a function of MW. TRMC measurements show that the yield of free photogenerated charge increases with increasing molecular weight in the paraffinic regime and saturates at the transition into the entangled, semicrystalline regime. This transition in carrier yield correlates with a sharp transition in free‐exciton bandwidth and decay dynamics at a similar molecular weight. We propose that the transition in microstructure controls the yield and decay dynamics of long‐lived photogenerated charge. The evolution of a semicrystalline structure with well‐defined interfaces between amorphous and crystalline domains of the polymer is required for spatial separation of the electron and hole. This structural characteristic not only largely controls the yield of free charges, but also serves as a recombination center, where mobile holes encounter a bath of dark electrons resident in the amorphous phase and recombine with quasi first‐order kinetics. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011 相似文献
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The lattice dynamics of CaF2 has been studied on the basis of a noncentral model using CGW type angular forces. The experimental data agree with the data
obtained for the dispersion curves. The model has also been used to calculate lattice specific heat and Debye-Waller factors. 相似文献
59.
The effect of γ-irradiation on the transport and structural properties of polycrystalline Bi1.2 Pb0.33 Sr1.54 Ca2.06 Cu3 O10+δ superconductor, synthesized by nitrate route is studied. The sample has been irradiated by γ-ray upto a dose 400 MR using a 60Co isotope source of 2 kCi strength with a dose-rate of 6.26 Gy/min. Its X-ray diffraction pattern, resistivity–temperature behaviour as well as elemental and morphological analyses using scanning electron microscope have been examined before and after the irradiation. It is observed that the normal state resistivity increases as the dose is increased. The transition width of the sample is found to get broadened with the increasing dose. Using the theories of Aslamazov–Larkin and Maki–Thompson, we present an analysis of the excess conductivity of our sample and the effect of γ-irradiation on it. It is found that the coherence length of the sample gets increased with the increase of the irradiation dose. 相似文献
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Anil Kumar Singh Dayal Singh Mehra Utpal Kumar Niyogi Sunil Sabharwal Rakesh Kumar Khandal 《Radiation Physics and Chemistry》2012,81(5):547-552
Polyurethane based pressure sensitive adhesive using monofunctional urethane acrylate and difunctional urethane acrylate has been made using electron beam irradiation. The effect of varying electron beam doses on the adhesion properties viz., peel adhesion, shear adhesion and initial tack has been studied. Effect of tackifier and crosslinkers viz., polymeric methylene diphenyl diisocynate, carbodiimide modified methylene diphenyl diisocynate and triallyl cynurate on adhesion properties as well as on moisture vapor transmission rate and gel content of the polyurethane based pressure sensitive adhesive has also been studied. It was found that with increasing dose, tackifier and crosslinkers concentration, all the adhesion properties viz., peel adhesion, shear adhesion strength and initial tack were increased upto a certain dose, concentration of tackifier and crosslinkers, reached a plateau and then levelled off with further increasing the dose, tackifier and crosslinkers concentration. Similarly, moisture vapor transmission rate was decreased and the gel content increased with increasing dose of electron beam. 相似文献