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排序方式: 共有671条查询结果,搜索用时 15 毫秒
651.
This article concerns a ring property called pseudo-reduced-over-center that is satisfied by free algebras over commutative reduced rings.The properties of radicals of pseudo-reduced-over-center rings are investigated,especially related to polynomial rings.It is proved that for pseudo-reduced-over-center rings of nonzero characteristic,the centers and the pseudo-reduced-over-center property are preserved through factor rings modulo nil ideals.For a locally finite ring R,it is proved that if R is pseudo-reduced-over-center,then R is commutative and R/J(R) is a commutative regular ring with J(R) nil,where J(R) is the Jacobson radical of R. 相似文献
652.
Simulation study of blue InGaN multiple quantum well light-emitting diodes with different hole injection layers
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InGaN-based light-emitting diodes with p-GaN and p-AlGaN hole injection layers are numerically studied using the APSYS simulation software.The simulation results indicate that light-emitting diodes with p-AlGaN hole injection layers show superior optical and electrical performance,such as an increase in light output power,a reduction in current leakage and alleviation of efficiency droop.These improvements can be attributed to the p-AlGaN serving as hole injection layers,which can alleviate the band bending induced by the polarization field,thereby improving both the hole injection efficiency and the electron blocking efficiency. 相似文献
653.
Jun Chen Hai-Long Liu Xiao-Qin Hong Mu-Li Wang Cheng Cai Qian-Feng Zhang 《Colloid and polymer science》2012,290(18):1955-1963
Polystyrene/montmorillonite (PSt/MMT) nanocomposite latexes have been synthesized by soap-free emulsion polymerization using MMT clay platelets as stabilizer. Small amounts of methacrylic acid were used as auxiliary monomer to promote clay adhesion to the surface of the particles. Overall solids content of the composite latexes in complete absence of coagulation of up to 30.7?wt% are reported under batch conditions. The 3?wt% MMT clay platelets were sufficient to maintain the colloidal stability and increasing MMT clay content resulted in the increase of particle diameter due to the improved viscosity of reaction medium. Transmission electron microscopy results demonstrate the existence of MMT platelets on the particle surface. X-ray diffraction spectroscopy (XRD) results show that an exfoliated structure of PSt/MMT nanocomposites was obtained in this study with the absence of d001 diffraction peak of MMT in the XRD region. 相似文献
654.
655.
5,10,15,20-四(4-氯苯基)-2′,3′-二氰基[2,3-β]卟啉和4,5-二(丁烷氧基)邻二氰基苯在锂存在的条件下在正戊醇中回流四聚,然后用醋酸处理得到了一种新型的平面共轭酞菁二联体H4{[(DAPc(OC4H9)6][TClPP]}(1)(其中DAPc(OC4H9)6是2,3,9,10,16,17-六(丁烷氧基)-22,25-二氮杂酞菁的二价阴离子,TClPP是5,10,15,20-四(4-氯苯基)卟啉的二价阴离子)。这种二联体和Zn(OAc)2.2H2O在DMF和甲苯混合溶剂中反应得到双金属配合物Zn2{[(DAPc(OC4H9)6][(TClPP)]}(2)。质谱和核磁共振光谱等一系列的表征方法证明了这种双核的混杂四吡咯结构。电子吸收光谱和磁圆二色谱证明了酞菁发色团和卟啉发色团之间存在有效的分子内电子相互作用。这一结论进一步得到了理论计算的支持。 相似文献
656.
In this work, for the first time, we have systematically demonstrated that solvent plays crucial roles in both controllable synthesis of metal-organic frameworks (MOFs) and their structural transformation process. With solvent as the only variable, five new MOFs with different structures have been constructed, in which one MOF undergoes solvent-induced single-crystal to single-crystal (SCSC) transformation that involves not only solvent exchange but also the cleavage and formation of coordination bonds. Particularly, a significant crystallographic change has been realized through an unprecedented three-step SCSC transformation process. Furthermore, we have demonstrated that the obtained MOF could be an excellent host for chromophores such as Alq3 for modulated luminescent properties. 相似文献
657.
Feng L Wakahara T Nakahodo T Tsuchiya T Piao Q Maeda Y Lian Y Akasaka T Horn E Yoza K Kato T Mizorogi N Nagase S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(21):5578-5586
The reaction of La@C82 with diethyl bromomalonate in the presence of base (the Bingel reaction) generated five monoadducts which have been fully characterized. It was found that four of them (mono-A, -B, -C, and -D) are ESR-inactive, suggesting singly bonded regioisomers. In contrast, the fifth product (mono-E) is ESR-active, indicating that it possesses a cyclic moiety between the appended malonate group and the fullerene cage, analogous to conventional Bingel adducts. The differences in the molecular structures of mono-A, -B, -C, and -E result in varying thermal stabilities and electrochemical behavior. In particular, the singly bonded monoadducts undergo the retro-Bingel reaction either under thermal treatment or during electron transfer on the cyclic voltammetric timescale. However, mono-E shows remarkable thermal stability and perfect reversibility under the same experimental conditions. 相似文献
658.
HanQing Ge Yan Leng FuMin Zhang JiaRui Piao ChangJiang Zhou Jun Wang 《中国科学B辑(英文版)》2009,52(8):1264-1269
Pyridine(Py)-modified Keggin-type vanadium-substituted heteropoly acids (Py
n
PMo10V2O40, n=1 to 5) were prepared by a precipitation method as organic/inorganic hybrid catalysts for direct hydroxylation of benzene
to phenol in a pressured batch reactor and their structures were detected by FT-IR. Among various catalysts, Py3PMo10V2O40 exhibits the highest catalytic activity (yield of phenol, 11.5%), without observing the formation of catechol, hydroquinone
and benzoquinone in the reaction with 80 vol% aqueous acetic acid, molecular oxygen and ascorbic acid used as the solvent,
oxidant and reducing reagent, respectively. Influences of reaction temperature, reaction time, oxygen pressure, amount of
ascorbic acid and catalyst on yield of phenol were investigated to obtain the optimal reaction conditions for phenol formation.
Pyridine can greatly promote the catalytic activity of the Py-free catalyst (H5PMo10V2O40), mostly because the organic π electrons in the hybrid catalyst may extend their conjugation to the inorganic framework of
heteropoly acid and dramatically modify the redox properties, at the same time, pyridine adsorbed on heteropoly acids can
promote the effect of “pseudo-liquid phase”, thus accounting for the enhancement of phenol yield.
Supported by the National Natural Science Foundation of China (Grant Nos. 20476046 and 20776069) and the “Qinglan” Project
of Jiangsu Province for Young Researchers 相似文献
659.
Enhanced recognition of non-complementary hybridization by single-LNA-modified oligonucleotide probes 总被引:1,自引:0,他引:1
XianYu Piao Ying Yan Jing Yan YiFu Guan 《Analytical and bioanalytical chemistry》2009,394(6):1637-1643
Locked nucleic acid (LNA) is a deoxyribonucleotide analogue with an unusual ‘locked’ furanose conformation. LNA-modified oligonucleotide
probes have demonstrated an enhanced binding affinity towards their complementary strands; however, their potential to discriminate
non-complementary hybridization of mismatches has not been explored. In this study, we investigated the effect of the chemical
nature of LNA nucleobases on the hybridization stability and the capability of LNA-modified oligonucleotides to discriminate
the LNA:DNA mismatched base pairs. It was observed that LNA modification indeed improves the discrimination capability of
oligonucleotides by increasing the melting temperature differences between the complementary duplexes and hybrids containing
mismatches. Particularly, LNA purines offer a greater potential to recognize the mismatches than LNA pyrimidines and DNA purines.
Real-time PCR experiments further confirmed that LNA modifications at the 3′-end are more effective. The results and conclusions
in this study provide useful information for hybridization-based nucleic acid analysis where designing sound oligonucleotide
probes is crucial to the success of the analyses.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
660.
应用基于α-型硅钼黄显色的分光光度法进行草类原料蒸煮黑液中硅含量的测定。测定波长360nm,pH 4.0,时间10min。实验中采用过氧化氢-硝酸消解法消除样品中木素成分对光度检测的干扰。研究表明:该方法的相对偏差及回收率分别为0.9%和99.0%~102%。该方法具有操作简便、快速,稳定性好,准确性高,试剂干扰少的优点,可用于黑液中高硅含量的日常快速分析。 相似文献