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排序方式: 共有206条查询结果,搜索用时 78 毫秒
161.
162.
Alves GA Amato S Anjos JC Appel JA Bracker SB Cremaldi LM Darling CL Dixon RL Errede D Fenker HC Gay C Green DR Jedicke R Kaplan D Karchin PE Kwan S Leedom I Lueking LH Luste GJ Mantsch PM de Mello Neto JR Metheny J Milburn RH de Miranda JM da Motta Filho H Napier A d'Olivera AB Rafatian A dos Reis AC Reucroft S Ross WR Santoro AF Sheaff M Souza MH Spalding WJ Stoughton C Streetman ME Summers DJ Takach SF Wu Z 《Physical review letters》1992,69(22):3147-3150
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164.
Heating 2-acyl-alkane-1,4-diones to temperatures above 120°C causes an acylgroupmigration leading to 3-acyl-alkane-1,4-diones. 相似文献
165.
De La Fuente JR Canete A Zanocco AL Saitz C Jullian C 《The Journal of organic chemistry》2000,65(23):7949-7958
The photophysical and photochemical behavior of 1-methyl-3-phenylquinoxalin-2-one (MeNQ) and 3-phenylquinoxalin-2-one (HNQ) in the presence of amines is reported. While HNQ fluorescence shows an auxochromic effect and a bathochromic shift with added amines, explained by association of HNQ with amine in the ground state and emission from both excited species HNQ and [HNQ-amine], both MeNQ and HNQ are photoreduced efficiently on irradiation in the presence of amines, leading to the semireduced quinoxalin-2-ones, MeNQH(-) and HNQH(-), respectively, via an electron-proton-electron transfer, with unit quantum yields at high amine concentrations. The semireduced quinoxalin-2-ones XNQH(-) (X = H, Me) revert almost quantitatively to the parent XNQ in a dark thermal reaction with an activation free energy for MeNQH(-) of 17.4 and 25.9 kcal/mol in acetonitrile and benzene, respectively. Kinetic and spectroscopic (UV and NMR) evidence supports the proposed reaction mechanism for the reversible photoreduction. 相似文献
166.
167.
Abstract— Absorption and emission spectra of several N-arylbenzamides have been measured. The quantum yields for their fluorescence were found to be dependent on matrix viscosity and temperature. Singlet-triplet splittings for these compounds were determined from their emission spectra and found to be abnormally small for π. π* states (˜ 1500 cm-1 ). Indeed, the phosphorescence maxima of N-arylbenzamides occur slightly to the blue relative to their fluorescence maxima. Intersystem crossing efficiencies were determined for several of these compounds and are consistent with S1 → S 0 radiationless decay. 相似文献
168.
Aitala EM Amato S Anjos JC Appel JA Ashery D Banerjee S Bediaga I Blaylock G Bracker SB Burchat PR Burnstein RA Carter T Carvalho HS Costa I Cremaldi LM Darling C Denisenko K Fernandez A Gagnon P Gerzon S Gobel C Gounder K Granite D Halling AM Herrera G Hurvits G James C Kasper PA Kondakis N Kwan S Langs DC Leslie J Lichtenstadt J Lundberg B Manacero A MayTal-Beck S Meadows B de Mello Neto JR Milburn RH de Miranda JM Napier A Nguyen A d'Oliveira AB O'Shaughnessy K Peng KC Perera LP Purohit MV 《Physical review letters》1996,76(3):364-367
169.
An optical waveguide acid vapor sensor 总被引:1,自引:0,他引:1
An optical waveguide sensor for the detection of acid vapors is described. The chemically sensitive reagent coating consists of bromothymol blue indicator suspended in a Nafion polymer film. The sensor uses a 562 nm LED source and a phototransistor detector. Response to hydrochloric acid and hydrogen sulphide vapours is both rapid and reversible, with an estimated detection limit for hydrogen sulphide of less than 15 ppm. The sensors exhibits generalized response to protonic acid vapours, but does not produce an indicator response to carbon dioxide, even at large concentrations (1100 mg/l.) in the presence of water vapor. The sensor exhibits a systematic interference from water vapor which may be corrected by a different approach, either using a reference sensor (Nafion/no indicator) or by monitoring sensor response at two wavelengths. 相似文献
170.
A mathematical model describing the coupling of electrical,optical and thermal effects in semiconductor lasers is introduced.Numerical and asymptotic solutions are derived, including expressionsfor key physical quantities such as the initial time delay,the frequency of spike oscillation and the temperature rise,together with its influence on the photon density, the electronconcentration and the threshold current. The consequences ofthermal effects in reducing efficiency are thus quantified. 相似文献