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排序方式: 共有346条查询结果,搜索用时 15 毫秒
321.
Hong Wei Wang Ying Ping Jia Da Bin Gao Jing Mei Yin Guang-Yun-Zhou Shen Min Li 《中国化学快报》2007,18(7):795-798
The photo-promoted carbonylation of chloroalkanes with carbon monoxide was carried out under ambient conditions with copper and cadmium salts catalysts. The results indicated that the corresponding esters were produced with three salt catalysts, i.e. CuBr2, CuCl2 and CdI2. Among these catalysts, CdI2 was the most efficient in terms of ester yield and selectivity, particularly, 60% yield and 75% selectivity in the carbonylation of chlorocyclohexane were achieved. Furthermore, the yield and selectivity of the ester can be improved greatly by adding tri-n-butylamine in the CuBr2 and CuCl2 catalyst systems. On the other hand, the carbonylation did not proceed with single CdCl2, however, the catalytic activity of CdCl2 was increased greatly with NaIá2H2O as additive. As a result, we suggest that iodide ion plays an important role in the catalyst system of the cadmium salts. 相似文献
322.
Haixue Kuang Bingyou Yang Ling Tang Yonggang Xia Deqiang Dou 《Helvetica chimica acta》2009,92(7):1315-1323
In search for bioactive compounds from the flower of Datura metel L., three new withanolide glucosides, namely baimantuoluosides A, B, and C ( 1 – 3 , resp.) were isolated. Enzymatic hydrolysis of 1 – 3 afforded the corresponding aglycones 1a, 2a , and 3a , respectively. The structures of the new compounds were elucidated as (5α,6α,7α,12β,22R)‐5,12‐dihydroxy‐1,26‐dioxo‐6,7 : 22,26‐diepoxyergosta‐2,24‐dien‐27‐yl β‐D ‐glucopyranoside ( 1 ), (5α,6α,7α,12α,22R)‐5,12‐dihydroxy‐1,26‐dioxo‐6,7 : 22,26‐diepoxyergosta‐2,24‐dien‐27‐yl β‐D ‐glucopyranoside ( 2 ), (5α,6α,7α,22R)‐5‐hydroxy‐1,26‐dioxo‐6,7 : 22,26‐diepoxyergosta‐2,24‐dien‐27‐yl β‐D ‐glucopyranoside ( 3 ) on the basis of chemical and physicochemical evidence, and are further confirmed by the structure determination by X‐ray diffraction of withanolide aglycone 1a . 相似文献
323.
Numerical study on the thermo-stress of ZrO2 thermal and barrier coatings by high-intensity pulsed ion beam irradiation 下载免费PDF全文
This paper studies numerically the thermo-mechanical effects of ZrO2 thermal barrier coatings (TBCs) irradiated by a high-intensity pulsed ion beam in consideration of the surface structure.Taking the deposited energy of ion beams in TBCs as the source term in the thermal conduction equation,the distribution of temperature in TBCs was simulated.Then,based on the distribution,the evolution of thermal stress was calculated by the finite element method.The results show that tensile radial stress formed at the valley of TBC surfaces after irradiation by HIPIB.Therefore,if cracks happen,they must be at valleys instead of peaks.As for the stress waves,no matter whether through peak or valley position,tensile and compressive stresses are present alternately inside TBCs along the depth direction,and the strength of stress decreases with time. 相似文献
324.
本文弥补了文[4]中主要定理的不足之处,并且推广了文[5]的结果 相似文献
325.
The stability of a series of hydrogen-bonded duplexes was studied using molecular mechanics method with a modified AMBER GAFF force field, in which the original atomic charges were replaced by ones that are more appropriate for non-polar solvents. The free energy change of dimerization was calculated in vacuo and good agreement with experimental data was found. It is also shown that the stability of these duplexes increases linearly with the number of hydrogen bonds, in agreement with experimental data. 相似文献
326.
327.
Experimental results indicate that propagation paths of cracks in concrete are often irregular, producing rough fracture surfaces which are fractal. Based on dynamic analysis of microcrack coalescence, this paper presents a statistical fractal model to describe the damage evolution of concrete. The model demonstrates that the mechanism of fracture surfaces formed in concrete is closely related to the dynamic processes of the cascade coalescence of microcracks. A unimodal relation between the fractal dimension and the coalescence threshold can qualitatively explain the relation between fractal dimension and fracture energy. 相似文献
328.
矩阵对策的公平性研究 总被引:3,自引:1,他引:2
众所周知,零和二人有限对策也称为矩阵对策。设做一个矩阵对策的两个局中人都希望对策结果尽可能公平。当两个局中人使用对策解中的策略进行对策时,如果对策结果最公平,那么这个对策解称为最优的。本文证明了最优对策解集的一些性质,然后给出矩阵对策公平度的概念并证明了它的一些有趣的性质。 相似文献
329.
单模激光Lorenz系统反同步控制研究 总被引:1,自引:1,他引:0
提出了一种实现异结构混沌系统反同步控制的方法。根据Lyapunov 稳定性理论给出控制器的结构。以单模激光Lorenz系统和Rossler系统为例,验证了这种控制器的有效性。进一步研究了不确定混沌系统的反同步,并以不确定单模激光Lorenz系统和Rossler系统为例,实现了混沌反同步控制,同时系统中不确定参数得到识别。仿真模拟结果验证了这种方法的有效性。设计的反同步控制方法可用于任意混沌系统,具有一定的普适性。 相似文献
330.
《Chaos, solitons, and fractals》2005,23(4):1363-1369
The global exponential stability of cellular neural networks (CNNs) with time-varying delays is analyzed. Two new sufficient conditions ensuring global exponential stability for delayed CNNs are obtained. The conditions presented here are related to the size of delay. The stability results improve the earlier publications. Two examples are given to demonstrate the effectiveness of the obtained results. 相似文献