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排序方式: 共有803条查询结果,搜索用时 171 毫秒
711.
An emission excitation source comprising a high-frequency diode-pumped Q-switched Nd:YAG laser and a radio-frequency powered glow discharge lamp is proposed. In this system sample atoms ablated by the laser irradiation are introduced into the lamp chamber and subsequently excited by the helium glow discharge plasma. The pulsed operation of the laser can produce a cyclic variation in the emission intensities of the sample atoms whereas the plasma gas species emit the radiation continuously. The salient feature of the proposed technique is the selective detection of the laser modulation signal from the rest of the continuous background emissions, which can be achieved with the phase sensitive detection of the lock-in amplifier. The arrangement may be used to estimate the emission intensity of the laser ablated atom, free from the interference of other species present in the plasma. The experiments were conducted with a 13.56 MHz radio-frequency (rf) generator operated at 80 W power to produce plasma and the laser at a wavelength of 1064 nm (pulse duration:34 ns, repetition rate:7 kHz and average pulse energy of about 0.36 mJ) was employed for sample ablation. The measurements resulted in almost complete removal of nitrogen molecular bands (N2+ 391.44 nm). Considerable reduction (about 75%) in the emission intensity of a carbon atomic line (C I 193.03 nm) was also observed. 相似文献
712.
Majid M. Heravi Mahmood Tajbakhsh Amir N. Ahmadi Bagher Mohajerani 《Monatshefte für Chemie / Chemical Monthly》2006,137(2):175-179
Summary. A superior method of synthesis of 2-substituted benzimidazoles by means of the heterogeneous catalysis of synthetic and natural
zeolites in the reaction of 1,2-diaminobenzene with acid chlorides is described. 相似文献
713.
The origin of observed interference effects is investigated by comparing signals obtained for lead and bismuth before and after the addition of different matrix components. It is concluded that the applicability of the solid-sampling technique should be related to the solubility of the impurity in the matrix components and to the volatilities of the impurity and matrix. The extent to which trace elements are removed from steels is similarly established by using steels and graphite pieces to which the element was added. The samples are introduced under isothermal conditions and peak areas are evaluated. It is found that 80% of lead or bismuth is recovered from stainless steel at 2100°C. Thus standardization against aqueous solutions gives inaccurate results for solid samples. 相似文献
714.
Alam MS Kim IJ Ling Z Mahmood AH O'Neill JJ Severini H Sun CR Timm S Wappler F Duboscq JE Fulton R Fujino D Gan KK Honscheid K Kagan H Kass R Lee J Sung M White C Wanke R Wolf A Zoeller MM Fu X Nemati B Richichi SJ Ross WR Skubic P Wood M Bishai M Fast J Gerndt E Hinson JW Miao T Miller DH Modesitt M Shibata EI Shipsey IP Wang PN Gibbons L Johnson SD Kwon Y Roberts S Thorndike EH Jessop CP Lingel K Marsiske H Perl ML Schaffner SF Wang R Coan TE Dominick J Fadeyev V Korolkov I Lambrecht M 《Physical review letters》1996,76(15):2637-2641
715.
Kubota Y Lattery M Nelson JK Patton S Poling R Riehle T Savinov V Wang R Alam MS Kim IJ Ling Z Mahmood AH O'Neill JJ Severini H Sun CR Timm S Wappler F Crawford G Duboscq JE Fulton R Fujino D Gan KK Honscheid K Kagan H Kass R Lee J Sung M White C Wanke R Wolf A Zoeller MM Fu X Nemati B Ross WR Skubic P Wood M Bishai M Fast J Gerndt E Hinson JW Miao T Miller DH Modesitt M Shibata EI Shipsey IP Wang PN Gibbons L Johnson SD Kwon Y Roberts S Thorndike EH Coan TE Dominick J Fadeyev V Korolkov I 《Physical review D: Particles and fields》1996,54(5):2994-3005
716.
Mahmood Tajbakhsh Iraj Mohammadpoor-Baltork Kamal Alimohammadi 《Monatshefte für Chemie / Chemical Monthly》2003,39(9):1571-1575
Various kinds of aliphatic (cyclic and acyclic), aromatic, and heterocyclic thiols are converted into the corresponding disulfides by quinolinium fluorochromate (QFC) on silica-gel in excellent yields. Selective oxidation of thiols in the presence of sulfides is also achieved under solid phase conditions. 相似文献
717.
A simple, rapid, cost effective and extraction‐free spectrophotometric method has been developed for the determination of zolmitriptan in pharmaceutical raw and dosage forms. The method is based on the charge‐transfer reaction of zolmitriptan in acetonitrile medium with 0.2% 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone to form a colored product peaking at 555 nm. Beer's law is obeyed in the concentration range 10‐250 μg mL?1 with molar absorptivity of 1.7 × 103 L mole?1 cm?1. The effects of variables such as reagent concentration, time of reaction, color stability and interferences have been investigated to optimize the procedure. The results have been validated analytically and statistically. The proposed method has been successfully applied for the determination of zolmitriptan in pharmaceutical formulations. Results indicate that the method is accurate, precise and reproducible (relative standard deviation < 2%). 相似文献
718.
Delawar M Gehrhus B Hitchcock PB 《Dalton transactions (Cambridge, England : 2003)》2005,(17):2945-2953
An unusual product formation is observed for the insertion reaction of the thermally stable silylene Si[(NCH(2)Bu(t))(2)C(6)H(4)-1,2][abbrev. as Si(NN)] into the carbon-halogen bond of alkyl or aryl halides RHal (Hal=Cl, Br). In general, depending on the halogen, the reaction either results in a disilane of type (NN)Si(Hal)-(R)Si(NN) for Hal=Cl or a mixture of disilane and the monosilane (NN)Si(R)(Hal) for Hal=Br. The results are put into context to previously suggested mechanisms. The disilane (NN)Si(Hal)-(R)Si(NN)(Hal=Cl or Br) is thermally labile and mild thermolysis yields the corresponding monosilane (NN)Si(R)(Hal) and silylene 1. Additionally, strong evidence is presented for a radical pathway for the reaction of 1 and RHal. 相似文献
719.
Avery P Freyberger A Lingel K Prescott C Rodriguez J Yang S Yelton J Brandenburg G Cinabro D Liu T Saulnier M Wilson R Yamamoto H Bergfeld T Eisenstein BI Ernst J Gladding GE Gollin GD Palmer M Selen M Thaler JJ Edwards KW McLean KW Ogg M Bellerive A Britton DI Hyatt ER Janicek R MacFarlane DB Patel PM Spaan B Sadoff AJ Ammar R Baringer P Bean A Besson D Coppage D Copty N Davis R Hancock N Kotov S Kravchenko I Kwak N Kubota Y Lattery M Momayezi M Nelson JK Patton S Poling R Savinov V Schrenk S 《Physical review letters》1995,75(24):4364-4368
720.
Ammar R Baringer P Bean A Besson D Coppage D Copty N Davis R Hancock N Kelly M Kotov S Kravchenko I Kwak N Lam H Kubota Y Lattery M Momayezi M Nelson JK Patton S Poling R Savinov V Schrenk S Wang R Alam MS Kim IJ Ling Z Mahmood AH O'Neill JJ Severini H Sun CR Wappler F Crawford G Daubenmier CM Fulton R Fujino D Gan KK Honscheid K Kagan H Kass R Lee J Sung M White C Wolf A Zoeller MM Butler F Fu X Nemati B Ross WR Skubic P Wood M Bishai M Fast J Gerndt E Hinson JW McIlwain RL Miao T Miller DH 《Physical review letters》1995,74(18):3534-3537