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41.
Coherent Dynamics of Direct-Current-Driven Quantum-Dot-Array with Two Time-Dependent Embedded Impurities 下载免费PDF全文
The coherent dynamics of dc-driven quantum-dot array with two embedded time-dependent impurities is investigated, the exact crossings and avoided crossings in the quasienergies are associated with the evolution dynamics of the electron by the introduction of the envelope lines of the site's maximum returning probability. Through a perturbative scheme, the time-dependent Hamiltonian is replaced by an equivalent static one, whose structure reveals the new quantum tunnelling mechanism in the time-periodic driving system and sheds light on the alternative interpretation of dynamic localization and delocalization. 相似文献
42.
Ceren ATLA DNER Ceren G
KALP Bengü GETREN Atila YILDIZ Nuray YILDIZ 《Turkish Journal of Chemistry》2021,45(4):1248
Usnic acid (UA) was extracted from Usnea longissima (L.) Ach. in supercritical carbon dioxide (SC-CO2) medium. The selected process parameters were extraction temperature (35–45 °C), amount of co-solvent (0%–5%) and extraction time (5–9 h). These parameters were applied to Box-Behnken design (BBD) belonging to response surface methodology (RSM) to determine optimum process parameters for the highest amount of UA in the extract. g UA/100g lichen, extraction yield % and UA content values were calculated in the range of 0.045–0.317, 2.77–5.4 and 71%–82% in different experimental conditions, respectively. The optimum conditions were predicted as 42 °C, 4.3% (ethanol) and 7.48 h. It was determined that the predicted and experimental values of g UA/100g lichen were compatible, and the suggested model was valid. 相似文献
43.
Fillers have been reported to raise, have no effect upon, or to lower the glass transition temperature Tgof polymers. In those studies, comparisons have been made between filled and unfilled polymers having equal thermal histories. In the work report here, however, the thermal history (cooling rate) was also varied. Two systems, polystyrene-silica and epoxy-rubber were studied. The glass transitions were measured by using a differential scanning calorimeter and a method of analysis first described by Ellerstein and later elaborated upon by Flynn. The data could be represented by a linear plot of the log of cooling rate versus Tgor Tg ?1. For the polystyrene system, the filled material had a larger negative slope for the plot of log cooling rate versus Tg ?1 so that after fast cooling the filled material had a lower Tg than the unfilled material. However, when the cooling rate was lowered, the Tg of the filled and unfilled materials approached each other, and for very slow cooling (annealed samples) the filled material had a higher Tg than the unfilled one. For the epoxy-rubber system, the rubber lowered the Tg by an amount which increased with cooling rate. Thus the extent and even the direction of the change in Tg with filler is shown to be dependent upon thermal history. It is shown that the slope of the plot of log cooling rate versus Tg ?1 or Tg is related to an activation energy. A new simplified method of correcting Tg for DSC instrument thermal lag is described. 相似文献
44.
J. MEDINA YU. G. GUREVICH G. N. LOGVINOV P. RODRÍGUEZ G. GONZÁLEZ DE LA CRUZ 《Molecular physics》2013,111(19):3133-3138
The problem of the effective thermal diffusivity of two-layer systems is investigated using the photoacoustic spectroscopy. The experimental results are examined in terms of the effective thermal parameters of the composite system determined from a homogeneous material that produces the same physical response under an external perturbation in the detector device. It is shown that the effective thermal conductivity is not symmetric under exchange of the two layers of the composite, i.e. the effective thermal parameters depend upon which layer is illuminated in the photoacoustic experiments. Particular emphasis is given to the characterization of the interface thermal conductivity between the layer system. 相似文献
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This paper presents a robust control algorithm for plants involvingboth internal (i.e. in the state) and external (i.e. in theoutput or input) known point delays. Several stabilizing controllerstructures are given and analysed for the case of perfectlymodelled plants with known parameters. The parametrized partsof two of the controller structures involve delays, while thoseof the two remaining controllers are delay-free. However, auxiliarycompensating signals which weight the plant input and outputintegrals are incorporated in all the controller structuresfor stabilization and model matching purposes. 相似文献
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基于密度泛函理论(DFY)的第一性原理计算方法,对氢原子在过渡金属(Sc、Ti、Cr、Mn、Fe、Co、Ni、Cu、V、Zn)修饰的Mg(0001)表面扩散性能进行了研究.研究发现过渡金属元素Sc、Ti、V、Cr、Mn、Fe、Co、Ni和Cu选择替代在镁表面第二层稳定,而Zn则选择替代在第一层稳定.当镁表面掺杂Zn和Cu时,氢原子选择停留在表面稳定;当掺杂Sc、Ti、V、Cr、Mn、Fe、Co和Ni时,氢原子选择进入镁块体内部.值得一提的是氢原子通过从过渡金属顶部通道扩散进入镁块体内部的势垒大大降低,笔者用差分电荷密度分析后发现氢原子与过渡金属原子成键使扩散势垒降低.当氢原子进入镁块体内部后靠近Sc、Ti、V、Cu和Zn原子时,将与这些过渡金属原子成键,从而阻碍了氢原子继续向内部扩散;而氢原子靠近Cr、Mn、Fe、Co、Ni原子时,选择离开过渡金属从而促进了氢原子向块体内扩散,可以大幅改善镁基储氢材料的吸氢动力性能. 相似文献
50.
Cary DR Zaitseva NP Gray K O'Day KE Darrow CB Lane SM Peyser TA Satcher JH Van Antwerp WP Nelson AJ Reynolds JG 《Inorganic chemistry》2002,41(6):1662-1669
Bipyridine ligands containing pendant methyl, amino, and amino-boronic acid groups were synthesized. Coordination complexes of these ligands with rhenium were prepared straightforwardly and in good yield. The fluorescence behavior of the Re complexes was studied as a function of pH and exposure to various concentrations of glucose. The methyl bipyridine complex showed no change in fluorescence with pH, the amino derivative showed a rapid decrease from low pH to neutral, and the amino-boronate derivative showed little change from pH 4 to 10. Fluorescence quenching was observed at high pH as expected on the basis of a photoinduced electron transfer (PET) signaling mechanism. This behavior can be explained on the basis of the first oxidation and reduction potentials of these complexes. Glucose testing showed a significant dependence on the solvent system used. In pure methanol, the rhenium boronate complex exhibited a 55% fluorescence intensity increase upon increasing glucose concentration from 0 to 400 mg/dL. However, in 50 vol % methanol/phosphate buffered saline, none of the complexes showed significant response in the glucose range of physiological interest. 相似文献