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  • 1
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Zusammenfassung Lösungen nativer Dextrane sind schon in sehr geringer Konzentration getrübt und zeigen ein anomales Viskositätsverhalten. Das weist auf das Vorliegen großer strukturierter Assoziate hin. Mit der Annahme einer Helixstruktur für die native Dextrankette kann man die Bildung solcher Assoziate deuten. An Hand modellmäßiger Betrachtungen wird versucht, die makroskopischen Eigenschaften auf das Vorliegen bestimmter Konformationen zurückzuführen.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Zusammenfassung Es wird untersucht, inwieweit es möglich ist, die spezifischen, vorwiegend hydrophilen adsorptionseigenschaften von handelsüblichem Silikagel durch nachträgliche Veränderungen der chemischen Struktur, insbesondere an der inneren Oberfläche, womöglich in organophile Eigenschaften umzuwandeln. In der Annahme, daß die an der Oberfläche des Gels befindlichen Si−OH-Gruppen für die bevorzugte Wasseradsorption verantwortlich seien, wurden diese durch Substitution mit organischen Resten entfernt. Ferner wurde Silikagel bei drei verschiedenen Temperaturen behandelt, um auch diesen Effekt auf die Adsorptionseigenschaften zu studieren. Diese “Organogele” und die thermisch behandelten Gele wurden auf ihre Adsorptionsfähigkeit für Äthylen — als Beispiel eines relativ kleinen dipollosen organischen Moleküls — und für Wasser untersucht. Außerdem wurde die Zahl der Si−OH-Gruppen quantitativ bestimmt und die Größe der Oberfläche nach der BET-Methode durch Aufnahme der Adsorptionstherme von Argon bei—183° C ermittelt. Bei den Organogelen wurde die Adsorptionsfähigkeit für Äthylen und Wasserdampf etwa gleichmäßig verkleinert, während die Oberfläche wohl kleiner wurde, quantitativ jedoch einen anderen Verlauf zeigt. Auch für die thermisch behandelten Gele nahm die Adsorptionsfähigkeit ab, und zwar um so stärker, je höher die Temperatur war, der das Gel ausgesetzt war. Die Zahl der Si−OH-Gruppen nimmt ebenfalls sowohl bei der Substitution durch organische Gruppen als auch bei der thermischen Behandlung ab, doch zeigt die Abnahme in quantitativer Hinsicht einen anderen Verlauf. Daher scheint die Ansicht, daß die Wasseradsorption mit der Zahl der OH-Gruppen zusammenhängt, nicht berechtigt. Mit Hilfe von Infrarotspektren gelang es nachzuweisen, daß bei den Organogelen die Substitution wirklich an den Si−OH-Gruppen stattgefunden hat.
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  • 3
    ISSN: 1588-2837
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Abstract Были приготовлены катализаторы хрома на монолитных подлозках, некоторые из которых имели на поверхности радиоактивный Cr-51. Для сравнения каталитической активности радиоактивных и инактивных катализаторов била использована реакция гидрогенизации-дегирогенизации циклогексена. При низких температурах била замечена разница в распределении главных продуктов, а при высоких температурах — и главных, и побочных продуктов.
    Notes: Abstract Chromium catalysts were prepared on monolith supports, some of them with radioactive Cr-51 in the surface. The dehydrogenation-hydrogenation reaction of cyclohexene was used to compare the catalytic activities of the radioactive and inactive catalysts. Differences were observed in the distribution of the main products at low temperatures and of the byproducts also at high temperatures.
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  • 4
    ISSN: 1588-2837
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 215 (1967), S. 1383-1384 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The decrease in the activity of the enzyme in relation to the dose of irradiation is shown in Fig. 1. The resistance of the enzyme is very high, 800 krads being necessary for a 50 per cent reduction of activity, and the enzyme is completely destroyed by 2.5 Mrad. Because of the high radiation ...
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  • 6
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract 121-Sb Mössbauer data are reported for a number of organoantimony rings and catena-stibanes. These compounds are representative of RSb(Sb)2 and R2SbSb type of coordination, and spectral parameters are compared and discussed in relation to RSbCl2 and R2SbCl systems. Although the trend in isomer shift is similar, the present compounds show slightly less negative isomer shift values together with a remarkable reduction of the quadrupolar coupling constant. A rationalization of the quadrupolar interaction in the above series of compounds appears feasible by using point charge model calculations whose results, in terms of bonding, indicate a large contribution of p-electron density along Sb-Sb bonds.
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  • 7
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 5 (1967), S. 423-430 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: According to the proposed mechanism for the enzymatic formation of dextran, branches of different length are formed in a reaction between a so-called acceptor dextran molecule and an active reaction complex; propagation of the dextran chain occurs by an insertion-type polymer growth. To investigate this branching reaction, radioactive labeled acceptor dextran of relatively low molecular weight was added to a dextran synthesizing system and the native high molecular weight dextran separated by a fractionation method. From the specific radioactivity of the isolated native dextran, and assuming a molecular weight of 2.5 × 105, the average number of acceptor molecules incorporated into native dextran is calculated to be about unity, as predicted by the proposed mechanism. Analogous results have been obtained in the reaction of two different dextran sucrases from Leuconostoc mesenteroides B512F and B1307, respectively.
    Additional Material: 3 Ill.
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  • 8
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Redox valence of oxygen on nickel specimens in 1 n hydrochloric and sulfuric acidsThe ratio of dissolved nickel to oxygen consumption was studied for the corrosion of nickel in oxigen containing acid. In air saturated 1 N H2SO4 4 electrons are accepted per molecule of oxygen (reduction to water). In air-saturated 1 N HCL only 2 electrons are reacting per molecule of oxygen (reduction to hydrogenperoxide) at the beginning of the reaction, in the course of the reaction (times greater than 2 hours) this value rises to 3 electrons per molecule of oxygen, according to a stationary hydrogenperoxide concentration of 7 · 10-4 moles/l in both acid, however, the oxygen reduction leads to hydrogen peroxide as an intermediate product which in the presence of chloride ions is desorbed faster from the metal surface than it is reduced. with increasing chlorid concentration the corrosion rate decreases from H2SO4 to HCL solutions.It is proposed that this effect is due to different mechanisms for the anodic dissolution of the nickel.
    Notes: Bei der Korrosion von Nickel in sauerstoffhaltiger Säure wurde das Verhältnis der in lösung gegangenen Nickelmenge zum Sauerstoffverbrauch untersucht. In luftgesättigter 1 N H2SO4werden pro reduziertem Sauerstoffmolekül 4 Elektronen verbraucht (Reduktion zu Wasser). In luftgesättigter 1 N HCL reagieren zu Beginn der Reaktion 2 Elektronen pro Molekül Sauerstoff (Bildung von Wasserstoffperoxiden), für Reaktionszeiten von mehr als 2 Stunden steigt der Wert auf 3 Elektronen an, entsprechend einer stationären Peroxidkonzentration im Elektrolyten von 7 · 40-4moles/l. Sowohl in H2SO4 als auch in HCL verläuft der Mechanismus der Sauerstoffreduktion über Wasserstoffperoxid als Zwischenprodukt, das in Gegenwart von Chloridionen schneller von der Metalloberfläche desorbiert wird als es weiterreagiert. Mit zunehmendem Chloridgehalt sinkt die Korrosionsgeschwindigkeit beim Übergang von Schwefelsäure in Salzsäure; dies wird auf unterschiedliche Mechanismen für die Nickelauflösung in den beiden Säuren zurückgeführt.
    Additional Material: 6 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the pyrolysis of n-hexane was studied in a conventional static reactor over a temperature range of 650-840 K. The overall reaction is essentially first order with the kinetic parameters A = 1013.92 s-1 and EA = 260.3 kJ/mol. The distributions of the main products were analyzed by gas chromatography. A reaction model involving 240 elementary reactions was developed to describe the experimental rate data. The agreement of the model with experimental data was surprisingly good over a wide range of temperatures and pressures and up to medium extents of conversion. Methods for sensitivity studies based upon the quasi-stationary-state assumption (QSSA) were developed, and for a number of more detailed effects, such as self-inhibition, explanations could be given. It was also shown that the hexyl isomerization reactions influence strongly the product distribution. The outstanding capability of kinetic modeling with computer simulations in handling complex kinetic systems is demonstrated.
    Additional Material: 11 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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