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排序方式: 共有349条查询结果,搜索用时 15 毫秒
71.
72.
Jahn U 《Chemical communications (Cambridge, England)》2001,(17):1600-1601
The combination of anionic Michael addition of lithium ester enolates with radical 5-exo cyclizations through SET oxidation gives highly functionalized cyclopentanes. 相似文献
73.
F. H. Vupré P. V. Vupré A. Gerasimow R. Bahr Fr. Grützmacher J. H. Walton R. C. Judd A. Stock K. Friederici W. Schuen M. Plüss Th. Paul Poda Jan von Zawidzki M. H. Palo Th. W. Richards G. D. Osgood R. Fänder J. G. Royd H. M. Atkinson W. R. Bousfield A. Whitaker S. H. Collins A. Slator J. Livingston R. Morgan Edy Björnsson Stéphan Jahn Ernest Esclangon P. B. Davis F. W. J. Boekhout H. Albrecht Alex L. Feild H. H. Bunzel H. Hasselbring Christ. gob & Co. 《Analytical and bioanalytical chemistry》1917,56(10-11):511-521
74.
L. A. Gomez Jahn J. J. Kasinski R. J. Dwayne Miller 《Applied Physics A: Materials Science & Processing》1987,43(1):41-46
The compression of the output of a Q-switched, mode-locked Nd:YAG (130 ps, 1.06 m) is reported for a number of different core-size single mode, multimode and polarization preserving fibers at power levels near the damage threshold. In maximizing the energy throughput, the main limitations are dielectric breakdown and nonlinear induced birefringence. Compressed pulse stability is found to depend critically on core size at this power level. An optimized compressor has been obtained capable of compression factors up to 35 (3.7 ps) with peak power in excess of 2 MW. Second-harmonic generation has been observed in polarization preserving fibers. 相似文献
75.
DISTRIBUTION OF 5-AMINOLEVULINIC ACID-INDUCED PORPHYRINS IN NODULOULCERATIVE BASAL CELL CARCINOMA 总被引:6,自引:0,他引:6
Qian Peng Trond Warloe Johan Moan Helen Heyerdahl Harald B. Steen Jahn M. Nesland Karl-Erik Giercksky 《Photochemistry and photobiology》1995,62(5):906-913
Abstract— Microscopic fluorescence photometry incorporating a light-sensitive thermo-electrically cooled charge-coupled device (CCD) camera was employed to investigate the fluorescence distribution of 5-aminolevulinic acid (ALA)-induced porphyrins in 22 patients with a total number of 52 noduloul-cerative basal cell carcinomas (BCC) after topical ALA application with or without dimethylsulfoxide (DMSO)/ethylenediaminetetraacetic acid (EDTA) or after intravenous administration of ALA. Both localization patterns and amounts of ALA-induced porphyrins in the BCC were studied. The ALA-induced porphyrins were localized only in the superficial layers of the noduloulcerative BCC lesions after topical application of 20% ALA alone for 3 h. However, both the penetration of ALA into deep lesions and the production of the ALA-induced porphyrin fluorescence were increased after topical administration of 20% ALA and 20% DMSO/4% EDTA for 3 h. Prior treatment with 99% DMSO for 15 min further enhanced the ALA penetration into the BCC lesions after topical application of the ALA/DMSO/EDTA mixture and produced more ALA-induced porphyrins by a factor of about three compared with those treated with ALA alone. The penetration of ALA into the deep BCC lesions could also be increased by prolonging the time of topical application of 20% ALA/4% EDTA to 29–48 h (without DMSO). Intravenous injection of ALA led to a more homogeneous distribution of the ALA-derived porphyrins in the whole noduloulcerative BCC lesions. 相似文献
76.
The profusion of resources, mostly on the Internet, makes the issue of their quality more and more pressing. Teachers often find themselves unable to choose from among them those that would be the most relevant to their educational goal and to the context of their classes. In our previous work, we claimed that acquiring resource analysis skills is one of the keys to the teachers’ professional development supporting the integration of dynamic geometry systems. Based on this assumption, we have designed a quality questionnaire for the i2geo repository aiming at framing the analysis of available resources by the platform users. The research reported in this paper, which is a continuation of this work, explores the way the quality criteria are taken into account in the design and use of resources by members of the community that has emerged around the repository and sheds light on possible evolutions of teachers’ and teacher educators’ professional practices due to their involvement in the resource quality evaluation. 相似文献
77.
Dr. Hans Jahn 《Monatshefte für Chemie / Chemical Monthly》1882,3(1):176-194
Ohne Zusammenfassung 相似文献
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A method is presented to allow the calculation of the dipole polarizabilities of ions and molecules in a condensed-phase coordination environment. These values will be useful for understanding the optical properties of materials and for developing simulation potentials which incorporate polarization effects. The reported values are derived from plane wave density functional theory calculations, though the method itself will apply to first-principles calculations on periodic systems more generally. After reporting results of test calculations on atoms to validate the procedure, values for the polarizabilities of the oxide ion and various cations in a range of materials are reported and compared with experimental information as well as previous theoretical results. 相似文献