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991.
铋系层状半导体材料凭借其独特的表面特性在光催化领域得到广泛的研究及应用,然而在光催化反应过程中光生电荷迁移及其表界面动态变化却鲜见报道。本文中,我们利用准原位X射线光电子能谱仪(QIS-XPS)系统研究超薄Bi2MoO6纳米片光催化CO2还原过程中光生电荷迁移及其表界面演变过程。研究结果表明:在暗态条件下CO2分子吸附于(010)暴露面Bi活性位,由于CO2分子强的拉电子能力,导致内层出现高价态Mo(6 x) 。当光照射至样品表面上时,*CO2峰显著降低,*CO峰明显升高,表明CO2分子在Bi活性位发生活化断键,并与光生电子反应形成*CO,使得高价态Mo(6 x) 含量增大。活性测试表明超薄Bi2MoO6纳米片的CO产量活性为41.8 ?mol g-1 h-1,其比块体Bi2MoO6活性高4.2倍,并且展现出优异的光催化稳定性。该工作为二维层状材料高效光催化CO2还原机理研究提供了一种全新的研究思路。 相似文献
992.
993.
课程评价是课程编制的一项重要工作。为适应我国中学化学课程改革的需要,我们提出了一个化学课程评价的理论模式——OCPP模式。在本刊1994年第8期上个绍了OCPP模式的基本涵义,本文将主要讨论OCPP模式的评价标准和方法。 相似文献
994.
995.
简单记叙了德国化学家李比希和维勒的研究风格和在化学上的主要贡献,介绍了他们终生不渝的伟大友谊和相互关心、互相支持、不计个人名利的崇高精神,藉以说明在科学研究中团结协作的重要性. 相似文献
996.
Formal acceptance of the results of chemical laboratories is increasingly organized through a) accreditation of measuring laboratories nationally and b) mutual recognition of accreditation internationally (through formal Multilateral Recognition Agreements, MRAs). However, real comparability of results of measurements is realized by using common (internationally agreed) measurement scales which make these results traceable to this scale, i.e. “traceable” to the same (internationally agreed) value of the unit of that scale. In addition, the criterion against which the evaluation is done, should be “external” to the measurement laboratories which are being evaluated. This is realized in IRMM’s International Measurement Evaluation Programme (IMEP) where evaluation is performed against values which are anchored using “metrology”, the science of measurement with its own rules, which offers a sound foundation for measurement in all scientific disciplines. It is argued in this paper that the demonstration of measurement capability against values on such scales provides a result-oriented rather than a procedure-oriented evaluation. Thus, competence can be “demonstrated” rather than just “designated” and this can be shown to both customers and regulators. It inspires more confidence. 相似文献
997.
Several TiO2 and γ‐Al2O3 supported catalyst systems were prepared by a novel way and characterized by X‐ray diffraction, Raman spectroscopy and BET surface area measurement. The results show: (1) all the samples, including MoO3/TiO2, WO3/TiO2, V2O5/TiO2, FeSO4/γ‐Al2O3, Al2 (SO4)3/γ‐Al2O3, K2CO3/‐Al2O3 and so on, prepared by impregnating TiO2·H2O or pseudo‐boehmite AlO(OH) with the active components then calcining at a high temperature exhibit much larger surface areas than that of pure TiO2 or γ‐Al2O3 calcined at the same temperature; (2) the surface area of the sample increases with the increase in the coverage of active component on the surface of the support; (3) when the content of active component reaches its utmost monolayer dispersion capacity, the surface area of the sample is the largest, and then decreases when the content of active component exceeds its dispersion threshold. 相似文献
998.
Xiao Chuan CHEN Wen Xin GU Xiao Bi JING Xin Fu PAN* Department of Chemistry National Laboratory of Applied Organic Chemistry Lanzhou University Lanzhou 《中国化学快报》2001,(2)
1-(4-hydroxy-3-methoxyphenyl)-2-(4-formyl-2-methoxyphenoxy)-propane-1,3-diol 9, a natural 8-O-4' neolignan, was isolated as a mixture of erythro and threo isomers from wood of Larix leptolesis1. This kind of neolignans have shown various biological activities2-4.As reported previously, the synthesis of 8-O-4' neolignans was mainly achieved using oxidative coupling of monolignols4,5 and reduction of ketones which were prepared from bromoketone and phenols in basic conditions6, But these method… 相似文献
999.
探讨了PCR法鉴定牛早期胚胎性别时所用的引物,反应缓冲液中Mg2+浓度,循环反应的次数及可能造成污染的各种因素对性别鉴定结果的影响.并对18个胚胎进行了性别鉴定,移植38枚性别鉴定后的胚胎,成功产下2头与预测性别一致的牛犊,胚胎性别可鉴率为94.1%,预测性别符合率为100%. 相似文献
1000.
A double pendulum system is studied for analyzing the dynamic behaviour near a critical point characterized by nonsemisimple 1:1 resonance. Based on normal form theory, it is shown that two phase-locked periodic solutions may bifurcate from an initial equilibrium, one of them is unstable and the other may be stable for certain values of parameters. A secondary bifurcation from the stable periodic solution yields a family of quasi-periodic solutions lying on a two-dimensional torus. Further cascading bifurcations from the quasi-periodic motions lead to two chaoses via a period-doubling route. It is shown that all the solutions and chaotic motions are obtained under positive damping. 相似文献