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• 2018-11-29 15:29發(fā)布了問答

  1953年沃森和克里克通過x射線衍射分析研究提出什么模式理論？

  　

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• 2018-11-24 12:46發(fā)布了問答

  包裹體的研究方法

  　

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• 2018-11-22 19:33發(fā)布了問答

  德國布魯克x射線衍射儀波長

  　

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• 2017-09-19 16:18發(fā)布了問答

  xrd粉末衍射方法能測無定型的材料嗎

  　

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• 2017-02-21 11:54發(fā)布了問答

  經(jīng)過研磨后再電鏡和能譜分析 砂紙的成分會影響結(jié)果嗎

  　

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• 2014-12-12 21:20發(fā)布了問答

  x射線衍射儀多少錢？

  　

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• 2011-07-11 08:40發(fā)布了問答

  什么是分子

  　

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• 2009-08-20 06:27發(fā)布了問答

  X射線能量定標(biāo)問題

  我研究生期間正在做一套能量色散X射線熒光分析儀，其中高壓電源和燈絲電源是自己做的，X光管在丹東買的，半導(dǎo)體探測器、放大器、多道分析器都是美國AMPTEK公司的。整個系統(tǒng)已經(jīng)構(gòu)建完成，現(xiàn)在正要做X光管的能譜分析，目前的問題是不知道如何定標(biāo)，想用Cs137和... 我研究生期間正在做一套能量色散X射線熒光分析儀，其中高壓電源和燈絲電源是自己做的，X光管在丹東買的，半導(dǎo)體探測器、放大器、多道分析器都是美國AMPTEK公司的。整個系統(tǒng)已經(jīng)構(gòu)建完成，現(xiàn)在正要做X光管的能譜分析，目前的問題是不知道如何定標(biāo)，想用Cs137和Co60，但好像不太適合。我應(yīng)該怎樣定標(biāo)呢？ 展開

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• 2007-03-16 05:16發(fā)布了問答

  化學(xué)專業(yè)翻譯2

  Summarizing the experimental data available today， thiol-capped CdTe nanocrystals synthesized in aqueous solution represent a kind of stable highly luminescent core-shell QD system with a naturally sulfur-capped surface (CdS shell) created ... Summarizing the experimental data available today， thiol-capped CdTe nanocrystals synthesized in aqueous solution represent a kind of stable highly luminescent core-shell QD system with a naturally sulfur-capped surface (CdS shell) created by mercapto- groups covalently attached to the surface cadmium atoms. All chemicals used were of analytical grade or of the highestpurity available. Al2Te3 (lumps) used as a source of H2Te waspurchased from CERAC Inc.， WI. Milli-Q water (Millipore)was used as a solvent. UV-vis absorption spectra were recorded with a Cary 50 spectrophotometer (Varian). Photoluminescence (PL) measurements were performed at room temperature using a FluoroMax-2 spectrofluorimeter (Instruments SA). The room-temperature PL quantum efficiency (QE) of CdTe nanocrystals was estimated following the procedure of ref 41 by comparison with Rhodamine 6G (laser grade， Lambda Physik) in ethanol (Uvasol) assuming its PL QE as 95%.42 High-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray analysis (EDX) were performed on a Philips CM-300 microscope operating at 300 kV. TEM samples were prepared by dropping diluted solutions of transferred in toluene (by surface exchange of capping agent with 1-dodecanethiol) CdTe nanocrystals onto 400-mesh carbon-coated copper grids with the excessive solvent immediately evaporated. Powder X-ray diffraction (XRD) measurements were carried out with a Philips X￠Pert diffractometer (Cu KR-radiation， variable entrance slit， Bragg-Brentano geometry， secondary monochromator). Samples for this study were prepared by placing finely dispersed powders of CdTe nanocrystals on standard Si supports. To investigate the photostability of CdTe QDs， dilute colloidal solutions were irradiated for different time intervals with light of a 450 W xenon lamp cut around 400 nm by a band-pass filter having a bandwidth of _40 nm and a peak transmission of _40%. a “Stable” means here that colloidal solutions of CdTe QDs are stable for months and even years being stored under air in the dark at room temperature. “Moderate” means that colloidal solutions coagulate occasionally during the storage; however， they are generally stable for months as well. Independent of the stabilizer nature， CdTe QDs are generally stable (no oxidation， no or only very minor changes of the optical properties) for years in powder form and in closely packed or nanocrystal/polymer films being kept in the dark under air. b The charge of nanocrystals was evaluated from ú-potential measurements with employment of oppositely charged latex beads. The experimental conditions were chosen so that the ú-potential of the beads changed its sign after adsorption of a monolayer of nanoparticles. 展開

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