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排序方式: 共有205条查询结果,搜索用时 196 毫秒
1.
Alexandre S. Miranda Paula M. Marcos Jos R. Ascenso M. Paula Robalo Vasco D. B. Bonifcio Mrio N. Berberan-Santos Neal Hickey Silvano Geremia 《Molecules (Basel, Switzerland)》2021,26(6)
Direct O-alkylation of p-tert-butyldihomooxacalix[4]arene (1) with N-(bromopropyl)- or N-(bromoethyl)phthalimides and K2CO3 in acetonitrile was conducted under conventional heating (reflux) and using microwave irradiation and ball milling methodologies. The reactions afforded mono- and mainly distal di-substituted derivatives in the cone conformation, in a total of eight compounds. They were isolated by column chromatography, and their conformations and the substitution patterns were established by NMR spectroscopy (1H, 13C, COSY and NOESY experiments). The X-ray structures of four dihomooxacalix[4]arene phthalimide derivatives (2a, 3a, 3b and 5a) are reported, as well as their photophysical properties. The microwave (MW)-assisted alkylations drastically reduced the reaction times (from days to less than 45 min) and produced higher yields of both 1,3-di-substituted phthalimides (3a and 6a) with higher selectivity. Ball milling did not reveal to be a good method for this kind of reaction. 相似文献
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Yves Crama Michel Grabisch Silvano Martello 《4OR: A Quarterly Journal of Operations Research》2016,14(4):333-336
We recall some cases of ethical misconduct that occurred in the recent years, and we report a new trick that was recently attempted to cheat the journal in order to obtain the publication of an article through usurped identity. 相似文献
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Diazonium salts, precisely arenediazonium o-benzenedisulfonimides, have been used for the first time as efficient electrophilic partners in Negishi coupling reactions. The synthetic protocol was general, easy and gave biaryls in satisfactory yields (34 examples, average yield 69%). o-Benzenedisulfonimide was recovered at the end of the reactions and reused to prepare the starting salts once again. 相似文献
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Silvano Ellena Alessandra Viale Roberto Gobetto Silvio Aime 《Magnetic resonance in chemistry : MRC》2012,50(8):529-533
Para‐hydrogen–induced polarization effects have been observed in the 29Si NMR spectra of trimethylsilyl para‐hydrogenated molecules. The high signal enhancements and the long T1 values observed for the 29Si hyperpolarized resonances point toward the possibility of using 29Si for hyperpolarization applications. A method for the discrimination of multiple compounds and/or complex mixtures of hydroxylic compounds (such as steroids), consisting of the silylization of alcoholic functionalities with an unsaturated silylalkyl moiety and subsequent reaction with para‐H2, is proposed. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
8.
Maurizio Lusignoli Silvano Petrarca 《The European Physical Journal C - Particles and Fields》2011,71(3):1568
A brief up-to-date review of the long-range forces generated by two neutrino exchange is presented. The potential due to exchange
of a massive neutrino–antineutrino pair between particles carrying weak charge might be larger than expected if the neutrinos
have not only masses but also magnetic moments close to the present experimental bounds. It still remains too small to be
observable. 相似文献
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用于光电仪器和相关测量的自混合干涉技术(特邀) 总被引:1,自引:0,他引:1
回顾了一种全新结构的干涉仪—自混合干涉仪(SMI)的发展情况。SMI由于其在激光器外部无需任何光学元件且应用范围广泛而倍受关注。SMI可用于测量与光路长度有关的一些量(如位移、小幅度振动、速度),也可用于测量弱光的回波(即回波损耗和隔离因子的测量)并可表征与介质相互作用特性相关的物理参数(如激光线宽、相干长度以及α因子等)。SMI是一种相干探测方法,其工作在靠近接收场的量子极限处,目前对散射目标物的最小探测幅值可达槡20 pm/(Hz)~(1/2)甚至更高,使用角锥棱镜使其计数步长为半波长,在动态范围为2 m时其分辨率约为0.5μm。另外,SMI结构紧凑、易于现场安装且可用于MEMS测试、旋转机械振动测试和生物运行测试等各种实验。 相似文献