排序方式: 共有46条查询结果,搜索用时 15 毫秒
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IntroductionTherehasbeenrecentresearchinterestincrystalen gineeringandthedesignofsupramoleculararchitectures .1Byselectingthechemicalstructureofligandsandtheco ordinationgeometryoftransitionmetalions ,theorganic/inorganichybridmaterialsmayyieldaseriesofn… 相似文献
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基于彩色扫描仪的图像光谱重构 总被引:5,自引:0,他引:5
针对彩色扫描仪的特点,采用主元分析法(PCA)和反向传播(BP)人工神经网络(ANN)相结合的方法对图像光谱重构进行研究。选择IT8.7/2标准色卡作为训练样本,将该色卡中的另一组色靶作为检验样本以讨论不同网络结构以及不同主元数和训练样本数对光谱重构的影响,再以自然色系统(NCS)色卡为检验样本来分析不同种类的训练和检验样本与光谱重构性能的关系。实验结果表明,采用3-14-6网络结构和6个主元数是最佳选择,训练样本和扫描目标之间的一致性是基于彩色扫描仪图像光谱重构的关键所在。 相似文献
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The syn and anti isomers of cis,cis-tricyclo[5.3.0.02,6]dec-3-ene derivatives have been synthesized and their 1H and 13C NMR spectra unequivocally analyzed. Both their structures and their 1H and 13C NMR chemical shifts were calculated by DFT, the latter two calculations employing the GIAO perturbation method. Additionally, calculated NMR shielding values were partitioned into Lewis and non-Lewis contributions from the bonds and lone pairs involved in the molecules by accompanying NBO and NCS analyses. The differences between the syn and anti isomers were evaluated with respect to steric and spatial hyperconjugation interactions. 相似文献
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W. Witko 《Molecular Crystals and Liquid Crystals》2013,570(1):161-168
Abstract Raman spectra for isotropic phase of PAA, PAP and HOAB were recorded. Three benzene rings vibrations were chosen for quantitative analysis and the choice is discussed for different PAA deuteration. The separation of vibrational and rotational relaxation was performed. Vibrational relaxation is a dominating process, but ca. 10% of total bandshape can be attributed to rotational relaxation. Rotational correlation times τ2 were calculated for all studied substances to be of the order 10?11 s. τ2 is connected with the rotation around the long molecular axis and supports the correlation time τ1 received from the dielectric relaxation measurements. 相似文献
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Thilini D. Kondasinghe Hasina Y. Saraha Shane T. Jackowski Jennifer L. Stockdill 《Tetrahedron letters》2019,60(1):23-28
α4/7-Conotoxin LvIA is an isoform-selective inhibitor of the α3β2 nicotinic acetylcholine receptor. An efficient strategy for the synthesis of this toxin is critical to advancing its utility as a probe for receptor function and as a potential pharmaceutical lead target. On-resin methods for peptide synthesis offer potential synthetic advantages; however, strategies for on-resin formation of multiple disulfides have historically been low-yielding. Here, we harness the reactivity of the Allocam protecting group and employ a 3-amino acid spacer strategy to synthesize α4/7-conotoxin LvIA via three different on-resin strategies, each of which results in an isolated yield higher than previous fully on-resin approaches. 相似文献
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NCS自由基与NO反应动力学的理论研究 总被引:7,自引:1,他引:6
用量子化学密度泛函理论B3LYP/6-31+G*和高级电子相关校正的偶合簇[CCSD(T)/6-311+G*]方法,对NCS自由基与NO反应的机理和动力学进行了理论研究,得到了体系的势能面信息和可能的反应机理.计算了反应的热力学参数及反应能垒.采用传统过渡态理论计算了各反应通道的速率常数.研究结果表明,NCS自由基与NO反应中存在4个反应通道,产物分别为OCS+N2,CS+N2O,ONS+CN和ONCNS.从能量变化和反应速率两方面考虑,NCS+NOOCS+N2应为主反应通道. 相似文献
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Cody Timmons Dianjun Chen C. Elizabeth Barney Sameer Kirtane Guigen Li 《Tetrahedron》2004,60(52):12095-12099
A new nitrogen source combination was found for the regio- and stereoselective diamination of α,β-unsaturated ketones. This combination employs the readily available and inexpensive combination of NCS and 2-NsNH2 as the electrophilic nitrogen source, and acetonitrile as the nucleophilic nitrogen source, respectively. The reaction is easily performed by mixing olefin, 2-NsNH2, NCS and 4 Å molecular sieves in freshly distilled acetonitrile at room temperature. The reaction is chemoselective without the formation of any haloamine side products. A new aziridinium ion formed from enones and 2-NsNHCl is suggested to exist and to react with nitrile via a [2+3] cycloaddition mechanism, which is responsible for the excellent regio-, stereoselectivity of the resulting diamination products. 相似文献