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排序方式: 共有626条查询结果,搜索用时 15 毫秒
41.
Peter Haider Bertram Kimmerle Frank Krumeich Wolfgang Kleist Jan-Dierk Grunwaldt Alfons Baiker 《Catalysis Letters》2008,125(3-4):169-176
The effect of the size of gold particles deposited on CeO2 and TiO2 supports on their catalytic behavior in the aerobic oxidation of benzyl alcohol in different solvents (mesitylene, toluene, and supercritical carbon dioxide) has been investigated. The size of supported gold particles deposited via a colloidal route was in the range 1.3–11.3 nm, as determined by means of EXAFS and HAADF-STEM measurements. The catalytic performance of the supported gold catalysts in the different solvents revealed a significant effect of the gold particle size. Optimal activity was observed for catalysts with medium particle size (ca. 6.9 nm) whereas smaller and bigger particles showed inferior activity. Identical trends for the activity–particle size relationship were found using Au/CeO2 and Au/TiO2 for the reaction at atmospheric pressure in conventional solvents (mesitylene, toluene) as well as under supercritical conditions (scCO2). Selectivity to benzaldehyde was only weakly affected by the gold particle size and mainly depended on reaction conditions. In supercritical CO2 (scCO2) selectivity was higher than in the conventional solvents under atmospheric pressure. All catalysts tested with particle sizes ranging from 1.3 to 11.3 nm showed excellent selectivity of 99% or higher under supercritical conditions. 相似文献
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Chahan Yeretzian Alfons Jordan Raphael Badoud Werner Lindinger 《European Food Research and Technology》2002,214(2):92-104
Volatile organic compounds (VOCs), emitted from green coffee beans, during coffee roasting and from a cup of coffee, were all analysed by proton-transfer-reaction mass spectrometry. Firstly, the headspace (HS) of green beans was investigated. Alcohols dominate the HS, but aldehydes, hydrocarbons and organic acids were also abundant. Secondly, we roasted coffee under two different conditions and monitored on-line the VOCs emitted during the process. In a first roasting series, a batch of beans was roasted. After an initial drying phase, dominated by evaporation of water and methanol, the HS concentrations of VOCs such as acetic acid, acetaldehyde, pyridine and methylbutanal rapidly increased and went through a maximum at medium roast level. In a second series, just six beans were roasted. We observed sporadic bursts of some volatiles (furans, butanal, 2,3-pentanedione), coinciding with popping sounds. Other VOCs showed smooth time-intensity profiles (pyridine, pyrazine). These experiments gave a real-time insight into the complex processes taking place during roasting. Finally, the HS of coffee extracts, prepared from beans roasted to different roast levels, were analysed. Most VOCs showed a maximum concentration at medium roast level (e.g. pentanedione, furfural, 5-methyl furfural), while others showed a gradual increase (e.g. pyrrol) or decrease (e.g. methanol). 相似文献
44.
Hans Lück und Alfons Pavlik 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1962,119(1):30-38
Zusammenfassung Sowohl bei der UV-Bestrahlung der Milch als auch der des Milchserums (etwa 0,01 W/ml) wird im Gegensatz zur Bestrahlung wäßriger Lösungen reiner Aminosäuren insgesamt eine Zunahme an freien Aminosäuren beobachtet. Der Effekt, der auf einer Spaltung von Peptid-Bindungen beruht, ist bei der unter molkereimäßigen Bedingungen durchgeführten UV-Bestrahlung zum Zwecke der Vitamin D-Anreicherung so gering, daß er ernährungsphysiologisch ohne Bedeutung sein dürfte. Die Aminosäuren wurden durch Säulenchromatographie nachMoore undStein bestimmt. 相似文献
45.
The eye movements of young and older adults were tracked as they read sentences varying in syntactic complexity. In Experiment 1, cleft object and object relative clause sentences were more difficult to process than cleft subject and subject relative clause sentences; however, older adults made many more regressions, resulting in increased regression path fixation times and total fixation times, than young adults while processing cleft object and object relative clause sentences. In Experiment 2, older adults experienced more difficulty than young adults while reading cleft and relative clause sentences with temporary syntactic ambiguities created by deleting the that complementizers. Regression analyses indicated that readers with smaller working memories need more regressions and longer fixation times to process cleft object and object relative clause sentences. These results suggest that age-associated declines in working memory do affect syntactic processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
46.
Ernst Büchel Karlheinz Lohau Hermann Bosch Manfred Espenhahn Alfons Nikoleizig 《国际钢铁研究》1978,49(6):307-311
Entwicklung eines automatisierfähigen Gerätes (Hydrevometer) zur schnellen Bestimmung der Auflagen an feueraluminiertem Feinblech. Kontinuierliche Messung des Wasserstoffdruckes und des elektrochemischen Potentials während der schichtweisen Auflösung. Seitendifferenzierende Bestimmung der Aluminiumdeckschicht und der Legierungsschicht. Funktionsweise des Gerätes. Ermittelte Standardabweichungen. Einsatzmöglichkeiten. 相似文献
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