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排序方式: 共有66条查询结果,搜索用时 15 毫秒
61.
S. Kukolja R. D. Miller D. C. Duckworth D. E. Dorman L. L. Huckstep Norbert Neuss S. W. Quenner 《Helvetica chimica acta》1984,67(3):876-884
Pure pencillin N α-sulfoxide ( 1 ) and penicillin N β-sulfoxide ( 2 ) were obtained by HPLC and tested as substrates for deacetoxycephalosporin C synthetase (DXCS). Neither one of the sulfoxides was utilized under conditions of conversion of penicillin N ( 8 ) to deacetoxycephalosporin C ( 9 ). The cephalosporin C α and β-sulfoxides ( 3 and 4 , resp.) were also prepared. Relative stabilities of the sulfoxides 3 and 4 are discussed by interpretation of the 13C-NMR spectra. 相似文献
62.
63.
L. I. Dorman 《Physics of Atomic Nuclei》2000,63(6):989-992
With effective heliolatitude L eff(n) for each solar-neutrino run n we separate all available Homestake experimental data for more than two solar cycles (1970–1994) on three zones SOUTH, EQUATORIAL, and NORTH in dependence on the heliolatitude (where detected neutrinos cross the Sun’s surface). For each latitudinal zone, we determine the average solar electron neutrino flux and correlations with effective solar-activity parameters for asymmetrical latitudinal belts. The obtained results indicate that neutrino should have nonzero mass and nonzero magnetic moment. 相似文献
64.
J M Lindholm M Dorman B E Taylor M T Hannley 《The Journal of the Acoustical Society of America》1988,83(4):1608-1614
The effects of mild-to-moderate hearing impairment on the perceptual importance of three acoustic correlates of stop consonant place of articulation were examined. Normal-hearing and hearing-impaired adults identified a stimulus set comprising all possible combinations of the levels of three factors: formant transition type (three levels), spectral tilt type (three levels), and abruptness of frequency change (two levels). The levels of these factors correspond to those appropriate for /b/, /d/, and /g/ in the /ae/ environment. Normal-hearing subjects responded primarily in accord with the place of articulation specified by the formant transitions. Hearing-impaired subjects showed less-than-normal reliance on formant transitions and greater-than-normal reliance on spectral tilt and abruptness of frequency change. These results suggest that hearing impairment affects the perceptual importance of cues to stop consonant identity, increasing the importance of information provided by both temporal characteristics and gross spectral shape and decreasing the importance of information provided by the formant transitions. 相似文献
65.
Dorman SC O'Brien RA Lewis AT Salter EA Wierzbicki A Hixon PW Sykora RE Mirjafari A Davis JH 《Chemical communications (Cambridge, England)》2011,47(32):9072-9074
A boronium-based paraquat analog undergoes reductions at more negative potentials than paraquat itself, making it a promising building block for electroactive materials. 相似文献
66.
Xiaolei Li Frank L. Dorman Paul A. Helm Sonya Kleywegt Andr Simpson Myrna J. Simpson Karl J. Jobst 《Molecules (Basel, Switzerland)》2021,26(22)
Gas chromatography–high-resolution mass spectrometry (GC–HRMS) is a powerful nontargeted screening technique that promises to accelerate the identification of environmental pollutants. Currently, most GC–HRMS instruments are equipped with electron ionization (EI), but atmospheric pressure ionization (API) ion sources have attracted renewed interest because: (i) collisional cooling at atmospheric pressure minimizes fragmentation, resulting in an increased yield of molecular ions for elemental composition determination and improved detection limits; (ii) a wide range of sophisticated tandem (ion mobility) mass spectrometers can be easily adapted for operation with GC–API; and (iii) the conditions of an atmospheric pressure ion source can promote structure diagnostic ion–molecule reactions that are otherwise difficult to perform using conventional GC–MS instrumentation. This literature review addresses the merits of GC–API for nontargeted screening while summarizing recent applications using various GC–API techniques. One perceived drawback of GC–API is the paucity of spectral libraries that can be used to guide structure elucidation. Herein, novel data acquisition, deconvolution and spectral prediction tools will be reviewed. With continued development, it is anticipated that API may eventually supplant EI as the de facto GC–MS ion source used to identify unknowns. 相似文献