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951.
952.
A novel polymer‐bound alkaloid ligand QN–AQN–OPEG‐OMe, which was characterized by an anthraquinone core at the 9‐O position of quinine, was synthesized conveniently. It delivered up to 99% ees in the homogeneous catalytic asymmetric dihydroxylation of seven olefins, comparable to that reported for the homogeneous catalyst with free ligand (DHQ)2AQN. This ligand was recovered almost quantitatively by a simple filtration and reused for five cycles without obvious decreased enantioselectivities and catalytic activities. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
953.
三元对称形式的Schur分拆与不等式的可读证明 总被引:14,自引:0,他引:14
本文给出了一类三元对称形式(即对称齐次多项式)的一种分拆法,即将此类多项式表示成一类特定形式的正半定对称形式的线性组合,介绍分拆算法.并由此而给出了三元对称形式半正定的一个充分条件. 相似文献
954.
955.
Nanosized gold clusters were developed in a gold-doped soda-lime silicate glass after X-ray irradiation followed by annealing, which provided an alternative way of forming metallic nanoclusters in glass to ion implantation. The formation of gold nanoclusters can be controlled by irradiation time or annealing time. 相似文献
956.
Jian‐Qiang Meng Fu‐Sheng Du Ya‐Shu Liu Zi‐Chen Li 《Journal of polymer science. Part A, Polymer chemistry》2005,43(4):752-762
A detailed exploration of the atom transfer radical polymerization (ATRP) of a sugar‐carrying monomer, 6‐O‐methacryloyl‐1,2;3,4‐di‐O‐isopropylidene‐D‐galactopyranose (MAIPGal) was performed. The factors pertinent to ATRP, such as initiators, ligands, catalysts, and temperature were optimized to obtain good control over the polymerization. The kinetics were examined in detail when the polymerization was initiated by methyl 2‐bromoisopropionate (2‐MBP), ethyl 2‐bromoisobutyrate (2‐EBiB), or a macroinitiator, [α‐(2‐bromoisobutyrylate)‐ω‐methyl PEO] (PEO–Br), with bipyridine (bipy) as the ligand at 60 °C or by 2‐EiBB with N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) as the ligand at room temperature (23 °C). The effects of the catalysts (CuBr and CuCl) were also investigated. We demonstrate that the successful ATRP of MAIPGal can be achieved for 2‐EBiB/CuBr/bipy and 2‐MBP/CuCl/bipy at 60 °C and for 2‐EBiB/CuBr/PMDETA at room temperature. The initiation by 2‐EBiB at room temperature with PMDETA as the ligand should be the most optimum operation for its moderate condition and suppression of many side reactions. Chain extension of P(MAIPGal) prepared by ATRP with methyl methacrylate (MMA) as the second monomer was carried out and a diblock copolymer, P(MAIPGal)‐b‐PMMA, was obtained. Functional polymers, poly(D‐galactose 6‐methacrylate) (PGMA), PEO‐b‐PGMA, and PGMA‐b‐PMMA were obtained after removal of the protecting groups. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 752–762, 2005 相似文献
957.
958.
IntroductionVeryrecently ,twonewmosquitolarvicidalbuteno lidesI (1)andII (2 )wereisolatedbyKarunaratneetal.1fromtheleavesofallthreespeciesofHortonia (fam ilyMonimiaceae) (H .angustifolia ,H .floribundaandH .ovalifolia) .Bothbutenolidesexhibitedmosquitolar vicidalact… 相似文献
959.
The crystal structure of 1,4,8,11,15,18,22,25‐octaethyloxyphthalocyaninatocopper was determined by X‐ray diffraction. The ring skeleton distortion is shown, which not only attributed to inter‐molecular steric congestion of substituents but also to the less overlap of the skeletons. 相似文献
960.
在研究容错图像编码算法的基础上,针对图像压缩编码中复杂度较大和将图像分成多个小块而带来的图像重建中有分块痕迹等问题,在子带位平面编码(SBC)算法中加入了与图像无关的率失真优化编码并采用虚拟分块的方法,对SBC算法进行了改进,实验结果表明,在相同压缩倍数和相同误码率情况下,本算法与传统的图像压缩算法重建图像的峰值信噪比提高了1.0~1.5dB。 相似文献