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951.
3-Arylsydnone-4-carbonitrile oxides may undergo 1,3-dipolar cycloadditions with alkenes to produce the corresponding 3-aryl-4-(5-substituted-isoxazolin-3-yl)sydnones. The direct reaction of 3-arylsydone-4-carbohydroximic acid chlorides with alkenes may also give the same products, and with higher yield. 相似文献
952.
Daniel T. W. Chu 《Journal of heterocyclic chemistry》1985,22(4):1033-1034
An efficient and regiospecific synthesis of 1-methylamino-6-fluoro-7-(4-methylpiperizin-1-yl)-1,4-dihydro-4-oxoquinoline-3-carboxylic acid ( 3 ) via an intramolecular nucleophilic displacement cyclization reaction is reported. 相似文献
953.
Jiang Xu Yuexia Chen Tingxiang Chu Shoujian Peng Dan Feng Chaolin Zhang 《Transport in Porous Media》2017,116(2):645-662
Physical simulations of coalbed methane (CBM) drainage using different initial gas pressures and different crustal stresses were conducted, and the gas pressures were obtained. The permeability evolutions were calculated based on a permeability model that used the same preconditions and parameters that were obtained from experiments. The permeability decreased rapidly during the initial phase of CBM drainage and then recovered slowly with time. During the initial phase of CBM drainage, the permeability decreased more rapidly near the borehole than further away. The distributions of \(k/k_0 (k\) is permeability, \(k_{0}\) is initial permeability) on the section, surface and longitudinal section that were analyzed were all funnel-shaped, and the distributions were shaped like circular rings, circular cones and circular cones, respectively. After a period of time, the permeability near the borehole recovered slightly, and the distributions of \(k/k_0\) reversed. At the end of CBM drainage, the values of \(k/k_0\) on the section, surface and longitudinal section were almost equal. The higher the crustal stress, the more slowly the permeability decreased, and the higher the initial gas pressure, the more rapidly the permeability decreased. 相似文献
954.
Lin YC Liu KK Wu CY Chu CW Wang JT Liang CT Li LJ 《Physical chemistry chemical physics : PCCP》2012,14(9):3083-3088
We report that copper thin films deposited on top of graphene oxide (GO) serve as an effective catalyst to reduce GO sheets in a diluted hydrogen environment at high temperature. The reduced GO (rGO) sheets exhibit higher effective field-effect hole mobility, up to 80 cm(2) V(-1) s(-1), and lower sheet resistance (13 kΩ □(-1)) compared with those reduced by reported methods such as hydrazine and thermal annealing. Raman and XPS characterizations are addressed to study the reduction mechanism on graphene oxide underneath copper thin films. The level of reduction in rGO sheets is examined by Raman spectroscopy and it is well correlated with hole mobility values. The conductivity enhancement is attributed to the growth of the graphitic domain size. This method is not only suitable for reduction of single GO sheets but also applicable to lower the sheet resistance of Langmuir-Blodgett assembled GO films. 相似文献
955.
Wei Gao Yaxin Qin Yaping Zang Jiaming Zhu Wei Chen Shengqiang Tong Yuqun Zeng Chu Chu 《Journal of separation science》2023,46(17):2300164
Accurate quantitative analysis of trace analytes in a complicated matrix is a challenge in modern analytical chemistry. An appropriate analytical method is considered to be one of the most common gaps during the whole process. In this study, a green and efficient strategy based on miniaturized matrix solid-phase dispersion and solid-phase extraction combined with capillary electrophoresis was first proposed for extracting, purifying and determining target analytes from complicated matrix, using Wubi Shanyao Pill as an example. In detail, 60 mg of samples were dispersed on MCM-48 to obtain high yields of analytes, then the extract was purified with a solid-phase extraction cartridge. Finally, four analytes in the purified sample solution were determined by capillary electrophoresis. The parameters affecting the extraction efficiency of matrix solid-phase dispersion, purification efficiency of solid-phase extraction and separation effect of capillary electrophoresis were investigated. Under the optimized conditions, all analytes demonstrated satisfactory linearity (R2>0.9983). What's more, the superior green potential of the developed method for the determination of complex samples was confirmed by the Analytical GREEnness Metric Approach. The established method was successfully applied in the accurate determination of target analytes in Wubi Shanyao Pill and thus provided reliable, sensitive, and efficient strategy support for its quality control. 相似文献
956.
基于傅里叶变换的高精度条纹细分方法 总被引:2,自引:1,他引:2
针对传统傅里叶变换法在提取条纹图相位中存在的能量泄漏问题,提出了条纹图整周期裁剪的方法,可有效抑制能量泄漏对检相精度的影响,提高傅里叶变换法相位计算的精度。在此基础上,提出了一种基于傅里叶变换时移特性的叠栅条纹细分新方法。与传统傅里叶变换法相比,该方法求取相邻两帧条纹图间的相移,只需经过两次傅里叶变换,不需要截取条纹图的基频再逆变换回空域,因此计算量至少减少了一倍,计算速度大大提高。数值计算结果表明,对两束单色平面波形成的条纹,理想条件下细分精度高达10-12量级;对高斯包络调制的条纹,细分精度至少可达10-3量级。 相似文献
957.
958.
959.
Efficient control of regioselectivity is a key concern in transition-metal-catalyzed direct C–H functionalization reactions. Various strategies for regiocontrol have been established by tuning the selectivity of the C–H activation step as a common mode. Herein, we present our study on an alternative mode of regiocontrol, in which the selectivity of the C–H activation step is no longer a key concern. We found that, in a reaction where the C–H activation step exhibits a different regio-preference from the subsequent functionalization step, a ligand-enabled switch of the regioselectivity-determining step could provide efficient regiocontrol. This mode has been exemplified by the Pd(ii)-catalyzed aerobic oxidative Heck reaction of indoles, in which a ligand-controlled C3-/C2-selectivity was achieved for the first time by the development of sulfoxide-2-hydroxypyridine (SOHP) ligands.Ligand-enabled switch of the regioselectivity-determining step allowed for efficient regiocontrol in the aerobic oxidative Heck reaction of indole. 相似文献
960.
C. Gao J. Yang X. J. Meng T. Lin J. H. Ma J. L. Sun J. H. Chu 《Applied Physics A: Materials Science & Processing》2011,104(1):123-128
The dielectric properties of fresh and aged Ba(Zr0.25Ti0.75)O3 thin films have been investigated. It is found that the aged sample shows a significant decrease in the dielectric constant
compared to the fresh one. Furthermore, the aged sample also exhibits abnormal double-peaks-shape butterfly C–V characteristics, which indicates the defect-dipole stabilized domain and/or domain-wall motions. Meanwhile, we found that
double-peaks-shape butterfly C–V characteristics become weak and even disappear with increasing of applied electric field and temperature. The present results
are discussed in light of the symmetry-conforming principle of point defects. 相似文献