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排序方式: 共有4919条查询结果,搜索用时 15 毫秒
21.
Heinrich Heydt Philipp Eisenbarth Karin Feith Klaus Urgast Gerhard Maas Manfred Regitz 《Israel journal of chemistry》1986,27(1):96-104
Amino-substituted cyclopropenylium salts ( 11a,b ) react with diazomethyl compounds ( 12a-i ) in dichloromethane or acetonitrile in the presence of a base (ethyldiisopropylamine, 1,5-diazabicyclo[4.3.0] non-5-ene) to form 4-aminopyridazines ( 13a-i ) specifically. The reaction is interpreted in terms of an initial electrophilic diazoalkane substitution to give diazomethylcyclopropenes ( 11 + 12 → 14 ) which undergo a [1.5]-cyclisation to form the betaines 16 which, in turn, isomerise with opening of the bridging bond to give the aminopyridazines 13 . In a similar manner, the tris[amino] cyclopropenylium salts 8a,b and 10a-c are converted to the 3,4,5-tris[amino]-pyridazines ( 21a-k ) by treatment with diazomethyl compounds ( 12a, c-f ). 相似文献
22.
23.
Crystallization of Polymer-Derived Silicon Carbonitride at 1873 K under Nitrogen Overpressure 总被引:1,自引:0,他引:1
Martin Friess Joachim Bill Jerzy Golczewski re Zimmermann Fritz Aldinger Ralf Riedel Rishi Raj 《Journal of the American Ceramic Society》2002,85(10):2587-2589
The chemical stability of an amorphous silicon carbonitride ceramic, having the composition 0.57SiC·0.43Si3 N4 ·0.49C is studied as a function of nitrogen overpressure at 1873 K. The ceramic suffers a weight loss at p N2 < 3.5 bar (1 bar = 100 kPa), does not show a weight change from 3.5 to 11 bar, and gains weight above 11 bar. The structure of the ceramic changes with pressure: it is crystalline from 1 to 6 bar, amorphous at ∼10 bar, and is crystalline above ∼10 bar. The weight-loss transition, at 3.5 bar, is in excellent agreement with the prediction from thermodynamic analysis when the activities of carbon, SiC, and Si3 N4 are set equal to those of the crystalline forms; this implies that the material crystallizes before decomposition. The amorphous to crystalline transition that occurs at ∼10 bar, and which is accompanied by weight gain, is likely to have taken place by a different mechanism. A nucleation and growth reaction with the atmospheric nitrogen is proposed as the likely mechanism. The supersaturation required to nucleate α-Si3 N4 crystals is calculated to be 30 kJ/mol. 相似文献
24.
Klaus Fröhlich Öve Gerfried Zeichen 《e & i Elektrotechnik und Informationstechnik》1998,115(4):226-226
Ohne Zusammenfassung 相似文献
25.
Riedel S.A. Harris G.F. Jizzine H.A. 《IEEE engineering in medicine and biology magazine》1992,11(4):42-47
Results of tests undertaken to identify which measures of seated posture control are most effective in two areas, distinguishing differences in the x and y direction control strategies for a given task and distinguishing differences in overall control strategies for pairs of different tasks, are presented. The test platform, calibration tests, test protocol, and data analysis method are described. The results of statistical analyses performed on the data are summarized 相似文献
26.
The current density used in electrochemical machining can be increased only up to a certain value, above which the formation of electric sparks on the cathode (tool) is observed, whereby the latter is damaged and the anode surface becomes rough. The present work is devoted to the measurement of this critical density for small metal cathodes placed on the wall of a flow-through channel for Reynolds numbers from 1265 up to 5902 and static pressures ranging from 0.1 up to 1.0 MPa. The results are correlated by criterion equations which gave values of critical (sparking) cathodic current density,j
s, with an average error of 7.1 % for laminar flow and 4.1 % for turbulent flow. The equations can be used for the calculation of the sparking current density for industrial flow-through cells for electrochemical machining. 相似文献
27.
Prof. Dr.-Ing. Klaus Gersten 《Forschung im Ingenieurwesen》1992,58(5):113-118
Zusammenfassung Es wird ein allgemeines Widerstandsgesetz für Stufendiffusoren hergeleitet, bei dem die Widerstandszahl den Zusatzverlust
gegenüber den Verlusten der bis zum Kontursprung reichenden fiktiven Kanal- bzw. Rohrstr?mungen in der Zu- und Abstr?mung
beschreibt. Unter vereinfachenden Annahmen reduziert sich dieses Gesetz auf die bekannte Carnot-Formel. Insbesondere wird
dabei der Anteil des Zusatzverlustes, der vom Unterdruck an der Stufe und von der Wandschubspannungs?nderung unmittelbar hinter
der Stufe herrührt, vernachl?ssigt. Die Berücksichtigung dieses Anteils führt zu einem gegenüber der Carnot-Formel verbesserten
Widerstandsgesetz.
Herrn Prof. Dr.-Ing. Martin Fiebig zum 60. Geburtstag 相似文献
28.
Klaus Lorenz 《化学,工程师,技术》1992,64(4):341-348
29.
Joern Ploennigs Mario Neugebauer Klaus Kabitzsch 《International Journal on Software Tools for Technology Transfer (STTT)》2006,8(6):607-620
Large technical systems need to be designed both reliable and efficient. Specialized design tools offer therefore a simplified,
abstract design and extend details autonomously in the background. Analytic and simulation based models could improve the
quality by testing and dimensioning the design before implementation, but setting up the necessary models is time-consuming
and expensive. Therefore many developers ask for analysis tools which are able to create their models from the available information
in the design tools. This paper presents such an automated modeling approach basing on an existing design database at the
example of a network analysis for building automation fieldbuses. The process of automated modeling is unfolded, and the potentials
and limitations are discussed. 相似文献
30.
Klaus G. Johannsen 《International Journal of Satellite Communications and Networking》1987,5(3):233-247
Several domestic satellite systems have been more than 10 years in operation. During this time, the world has experienced a dramatic growth in communication. While the demand for more telephony and data circuits and television channels is still on the rise, new methods of signal transmission and circuit compression have been developed which may balance or reduce the need for more satellite trunk capacity. And while whole national networks are converting to digital transmission, new transmission media like optical fibre, are finding application, and may take over some of the heavy traffic routes previously carried by satellite. On the other side, business data communication between roof-top terminals, thin route traffic to remote users, television distribution by direct satellite broadcasting are becoming more popular and satellite land mobile communication may soon be a reality. Thus the domestic satellite's role appears to be slowly changing towards thin route and mobile traffic and DBS-type distribution and perhaps even radio position determination. System planners are adapting to the new trends in satellite communication and are trying to accommodate the various service payloads on a single satellite. This article discusses some aspects of the emerging multi-purpose domestic satellite, which carries fixed and mobile services, TV direct broadcasting and radio position determination, in view of network digitalization, network expansion, circuit compression, synchronization. The discussion centres on transponder supply and demand, satellite replenishment, Ku-band vs. C-band for TV direct satellite broadcasting, choice of modulation/multiple access for mobile communication, and expected accuracy in radio position determination. 相似文献