排序方式: 共有80条查询结果,搜索用时 31 毫秒
21.
大晶粒钛硅沸石TS-1晶貌的离子蚀刻改性 总被引:2,自引:0,他引:2
钛硅沸石 TS- 1 [1] 的微孔体系由同是十元氧环的直通道和“Z”字形通道相交而成 ,孔径 0 .5 1~ 0 .5 6nm,晶体结构与硅铝 ZSM- 5沸石的 MFI结构相同 .TS- 1能以稀双氧水为氧源 ,使烃类发生选择氧化 ,生成含氧化合物 [2~ 8] .并已在催化苯酚羟基化和环己酮氨氧化方面实现了工 相似文献
22.
利用二维晶格模型和相分离模型,由正规溶液理论首先推导出了二元表面活性剂形成混合胶束的分子交换能(ε~m)与混合胶束中组分A的超额化学位(μ^E~m~,~A)的关系式:μ^E~m~,~A=ε~m~gN~0(1-x~A)^2。然后导出ε~m与混合胶束中表面活性剂分子间的相互作用参数(β~m)的关系:ε~m=gRTβ~m/N~0。用该结论对皂荚素(GS)与十二烷基磺酸钠(C~1~2H~2~5SO~3Na)、十二烷基聚氧乙烯醚硫酸钠[C~1~2H~2~5(OC~2H~4)~3SO~4Na]、全氟辛酸钠(C~7F~1~5CO~2Na)、十二烷基脂肪醇聚氧乙烯(9)醚[C~1~2H~2~5(EO)~9OH]、辛基酚聚氧乙烯(10)醚[C~8H~1~7Ph(EO)~1~0OH]及十六烷基三甲基溴化铵(C~1~6H~3~3NMe~3Br)等表面活性剂混合体系的研究和计算表明:含皂荚素的二元表面活性剂形成的混合胶束,ε~m均为负值,表面活性剂分子间具有较强的协同效应。 相似文献
23.
Study of the surface and far fields of terahertz radiation generated by large-aperture photoconductive antennas 总被引:3,自引:0,他引:3 下载免费PDF全文
We have studied analytically the temporal characteristics of terahertz radiation emitted from a biased largeaperture photoconductive antenna triggered by an ultrashort optical pulse. We have included the effects of the finite lifetime and transient mobility dynamics of photogenerated carriers in the analysis. Succinct explicit expressions are obtained for the emitted radiation in the surface field and in the far field. The dependence of the waveforms of the radiated field on the fluence and duration of triggering optical pulse, carrier relaxation time and carrier lifetime are discussed in detail using the obtained expressions. 相似文献
24.
Dr. Shi-Lin Luo Dr. Li-Jun Hu Dr. Xiao-Jun Huang Dr. Jun-Cheng Su Dr. Xue-Hua Shao Dr. Lei Wang Prof. Dr. Han-Hong Xu Prof. Dr. Chuang-Chuang Li Prof. Dr. Ying Wang Prof. Dr. Wen-Cai Ye 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(49):11104-11108
A phloroglucinol-terpene adduct (PTA) collection consisting of twenty-four molecules featuring three skeletons was discovered from Baeckea frutescens. Inspired by its biosynthetic hypothesis, we synthesized this PTA collection by reductive activation of stable phloroglucinol precursors into highly reactive ortho-quinone methide (o-QM) intermediates and subsequently Diels–Alder cycloaddition. We also demonstrated, for the first time, the generation process of the active o-QM by performing dynamic NMR and HPLC-MS monitoring experiments. Moreover, the PTA collection showed significant antifeedant effect toward the Plutella xylostella larvae. 相似文献
25.
Based on a modified retrieving method, we demonstrate that hyperbolic metamaterials(HMs) have considerable robustness against disorders, even when the disorder strength is quite large. Our retrieval method is more precise when retrieving the parameters for anisotropic metamaterials. We also show that the light’s negative refraction of an HM is nearly unaffected when relatively large disorders exist. These results help us to understand the HMs and they have a direct significance for experiments. 相似文献
26.
The influence of hydrothermal treatment on the total acidity and the acidity distribution of γ-Al2O3 were studied in this paper. The experimental results indicated that the hydrothermal treatment of γ-Al2O3 at moderate condition (140 °C, 1.0-24.0 h) led to the formation of the plate-like γ-AlOOH crystallites with different morphologies, which resulted in the change of the surface acidity of the corresponding γ-Al2O3 supports. The increase of the reaction time in the period of 1.0-2.0 h led to the increase of the specific surface area, the surface OH, the total acidity and the ratio of the weak acidity in the acidity distribution of γ-Al2O3. The further prolongation of reaction time caused the overgrowth of γ-AlOOH crystallites, leading to the decrease of the specific surface area, the surface OH and the total acidity of the corresponding γ-Al2O3. 相似文献
27.
Synthesis of isoxazoline N-oxides and its application in the formal synthesis of dehydroclausenamide
A protocol for the synthesis of isoxazoline N-oxides and its application in the formal synthesis of dehydroclausenamide are described. Sulfonium salt 1 reacts with substituted nitroalkenes smoothly to generate isoxazoline N-oxides in high to excellent yields with dr higher than 99/1. Its asymmetric version has been developed by using cinchona alkaloid-derived ammonium salts 6a and 6b instead of sulfonium salt 1 and higher than 96% ee values are achieved. This method has also been successfully applied to the formal synthesis of dehydroclausenamide. 相似文献
28.
Techniques capable of assessing microstructure length scale are potentially useful in probing the integrity of biologic tissue at the microscopic level. Although the magnetic resonance (MR) diffusion-diffraction technique has been proposed for years, its realization in an undissected brain has not been reported on. In this study, validation of this method in a phantom simulating a series of repeated sheets of water with regular spacing was first performed. The same technique was applied to the corpus callosum of fixed rat brains of different ages (range, 21-84 days). The phantom was constructed with a pile of transparencies immersed in water doped with Gd-DTPA. The measured signal showed diffraction-like coherence peaks, the modulation of which was influenced by the gap distance and the center-to-center distance of the adjacent gaps. The measured distances were consistent with the actual values. In five 84-day-old rats, the diffusion length scale derived from the diffractogram was highly reproducible. In the course of brain maturation, the measured size decreased with age. Electron microscopy showed that axons on day 21 were smaller in diameter and less myelinated as compared with those on day 84. Progressive decrease in the diffusion length scale observed during brain maturation might reflect a gradual decrease in transmembrane permeability due to myelination. In conclusion, MR diffusion-diffraction can be observed in the corpus callosum of fixed rat brains. This technique might be useful in probing the status of myelination in the development of disease. 相似文献
29.
30.