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991.
Thin films of pentacene were deposited by vacuum sublimation onto amorphous carbon, glass, silicon and mica substrates, then characterized by X-ray and electron diffraction, transmission electron microscopy (TEM) and atomic-force microscopy (AFM). Sub-monolayer films consist of dendritic islands, which change to more compact fractal shapes upon transforming to a multilayer structure (with decrease in surface area) prior to complete coverage of the substrate. Increased crystallite size was obtained by heating the substrate during deposition and by post-deposition annealing. Irradiation with 200-keV electrons was found to destroy the crystallinity of the films after a dose of 0.6?C/cm2 (or 2?C/cm2 if the specimen is cooled to 90?K during TEM observation). We argue that, despite this moderate radiation sensitivity, TEM under near-optimal conditions can image monolayers of pentacene with sub-nm resolution. 相似文献
992.
Rational Design of an Ultrasensitive and Highly Selective Chemodosimeter by a Dual Quenching Mechanism for Cysteine Based on a Facile Michael‐Transcyclization Cascade Reaction
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Xiangmin Li Yongjun Zheng Hongjuan Tong Rui Qian Dr. Lin Zhou Prof. Dr. Guixia Liu Prof. Dr. Yun Tang Prof. Dr. Hao Li Prof. Dr. Kaiyan Lou Prof. Dr. Wei Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(27):9247-9256
Differentiation of biologically important thiols, such as cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) is still a challenging task. Herein, we present a novel fluorescent chemodosimeter capable of selectively detecting Cys over other biothiols including Hcy and GSH and other amino acids by a facile thiol‐Michael addition/transcyclization rearrangement cascade click process. The unique transcyclization step is critical for the selectivity as a result of the kinetically favorable formation of a six‐membered ring with the Cys Michael adduct. Moreover, the probe adopts a distinctive dual quenching mechanism—photoinduced electron transfer (PET) and photoinduced intramolecular charge transfer (ICT) to deliver a drastic turn‐on fluorescence response only at the Cys‐selective transcylization step. The judicious selection of strong electron‐withdrawing naphthalimide fluorophore with maleimide group enhances the electrophilicity and thus reactivity for the cascade process leading to fast detection and ultrasensitivity with a detection limit of 2.0 nm (S/N=3). The probe has demonstrated its practical utility potential in Cys imaging in live cells. 相似文献
993.
Lin-Song Cui Shou-Cheng Dong Yuan Liu Mei-Feng Xu Qian Li Zuo-Quan Jiang Liang-Sheng Liao 《Organic Electronics》2013,14(7):1924-1930
This study investigated the use of a novel modification in molecular design to get two new electron-transport host materials, SF3PO and BSF3PO. By linking the phosphine oxide moieties at meta-position of spirobifluorene rings, higher triplet energies could be easily achieved for these two new materials. The steric spirobifluorene structures could guarantee their good thermal stabilities. According to these properties, their applications as host materials for deep blue phosphorescent organic light-emitting diodes (PHOLEDs) were explored. As expected, the deep blue emitting devices with Ir-complex FIr6 as phosphorescent dopants and SF3PO and BSF3PO as hosts had been fabricated and showed high efficiency of 28.5 and 22.0 cd/A, respectively, which were significantly higher than that of the para-linked analogue SPPO1. 相似文献
994.
Recently, it has been seen that the ensemble classifier is an effective way to enhance the prediction performance. However, it usually suffers from the problem of how to construct an appropriate classifier based on a set of complex data, for example, the data with many dimensions or hierarchical attributes. This study proposes a method to constructe an ensemble classifier based on the key attributes. In addition to its high-performance on precision shared by common ensemble classifiers, the calculation results are highly intelligible and thus easy for understanding. Furthermore, the experimental results based on the real data collected from China Mobile show that the key-attributes-based ensemble classifier has the good performance on both of the classifier construction and the customer churn prediction. 相似文献
995.
Xusheng Shao Xinglong Huang Qian Shi Zhong Li Liming Tao Gonghua Song 《Journal of heterocyclic chemistry》2012,49(5):1136-1142
The chlorothiazolyl moiety was an effective bioisoster of chloropyridyl in pesticide molecular design. Replacement of chloropyridyl in cis‐nitromethylene neonicotinoids with chlorothiazolyl generated the chlorothiazolyl counterpart of nitromethylene neonicotinoids with tetrahydropyridine fixed cis‐configuration. Bioassay against cowpea aphis (Aphis craccivora) indicated that the chlorothiazolyl analogs could maintain the high insecticidal activity. 相似文献
996.
997.
作为电子信息技术与管理的有机结合,电子政务已成为当代信息化的重要领域之一。在此背景下,网络舆论对政府决策发挥着举足轻重的作用。网络舆论传播的快捷性、内容的丰富性、主体的平民化和复杂性等特点,既可以促进政府决策的科学化、民主化,同时也带来了许多不利因素。分析研究网络舆论对政府决策的影响,既能促使公众有序参政,提高电子政务的效能,又能维持政府决策的相对自主性。 相似文献
998.
Three octacyanometallate‐based hetero‐bimetallic complexes, [Ln(H2O)4(CH3CN)2][M(CN)8] · CH3CN [Ln = La, M = Mo( 1 ), W( 2 ); Ln = Ce, M = W( 3 )], were synthesized and characterized structurally. Single‐crystal X‐ray analysis reveals that 1 – 3 are isomorphous and consist of infinite one‐dimensional (1D) 3,3 rope‐ladder chains, in which the 12‐membered puckered square Ln2M2(CN)4 is the basic building unit. The 1D chains are further linked through interchain hydrogen bonds, resulting in a three‐dimensional (3D) supramolecular network. 相似文献
999.
Yankuan Liu Han Wang Yongchun Zhu Xiaoqing Wang Xiaoyan Liu Haibo Li Yitai Qian 《Solid State Communications》2009,149(37-38):1514-1518
The concentration of the Mn(NO3)2 solution has significant influence on the morphologies and the phases of the MnO2 products. A large number of ε- MnO2 nanowires were prepared via a simple pyrolysis under lower reaction concentration. The nanowires have lengths up to tens of micrometers and diameters in the range of 20–100 nm. The β- MnO2 nanobundles and nanoflowers were prepared by increasing the concentration of Mn(NO3)2 solution. The superparamagnetism of ε- MnO2 nanowires and paramagnetism of β- MnO2 nanoflowers indicate their potential applications in magnetic materials. 相似文献
1000.
Numerical pseudodifferential operator and Fourier regularization 总被引:1,自引:0,他引:1
The concept of numerical pseudodifferential operator, which is an extension of numerical differentiation, is suggested. Numerical
pseudodifferential operator just is calculating the value of the pseudodifferential operator with unbounded symbol. Many ill-posed
problems can lead to numerical pseudodifferential operators. Fourier regularization is a very simple and effective method
for recovering the stability of numerical pseudodifferential operators. A systematically theoretical analysis and some concrete
examples are provided. 相似文献