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排序方式: 共有173条查询结果,搜索用时 15 毫秒
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Joseph M. Levy Eugene Storozynsky Robert M. Ravey 《Journal of separation science》1991,14(10):661-666
A key feature differentiating analytical supercritical fluid extraction (SFE) from conventional liquid extraction is the possibility of varying the solvent strength of a supercritical fluid to achieve selective extractions of specific target compounds, or functional classes of compound, from complex matrices. This can be accomplished by using supercritical fluids other than carbon dioxide, for example, sulfur hexafluoride, nitrous oxide, or sulfur hexafluoride-modified carbon dioxide. The use of these fluids will be demonstrated by the characterization of complex environmental and petroleum matrices by directly coupled SFE – capillary GC. On-line SFE-GC involves the decompression of pressurized extraction fluid directly into the heated, unmodified capillary split injection port of the chromatograph. This paper will also show how, by adjustment of the extraction temperature and pressure, SFE selectivity may be further enhanced. 相似文献
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《Arabian Journal of Chemistry》2022,15(2):103603
Heterogeneous catalysts, named SPS (sodium potassium silicates), were synthesized with an alternative silica (MPI silica) obtained from beach sand. In this work, the MPI was modified with NaOH and KOH producing silicate-based catalyst for biodiesel synthesis from waste cooking oil (WCO). The obtained catalyst was characterized by XRD, CO2-TPD, the Hammett basicity test, XRF, FESEM, EDX, FTIR and TG/DTG. The results confirmed the presence of K2O/Na2O oxides and their silicates, the main active sites responsible for the catalytic action. CO2-TPD and the Hammett basicity data suggested the presence of weak, medium and strong basic sites. Biodiesel yield was about 92% and the SPS catalyst was reused for five cycles. The biodiesel conversion by NMR 1H was about 93.89%. The DTG deconvolution revealed the decomposition of four typical biodiesel compounds (R2 = 0.9987). The method applied for the WCO biodiesel production using SPS catalyst represents an environmentally friendly process, based on low-cost material and reuse of waste biomass. 相似文献
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以正十四烷为内标,采用气相色谱-质谱(GC/MS)联用技术对中药甘草(GUF)、甘遂(EKL)单味药材,以及其组成的药对(GUF-EKL)的挥发成分进行测定,基于一种新的化学计量学方法——转换移动窗口因子分析法(AMWFA)和直观推导式演进特征投影法(HELP)对产生的二维色谱/质谱数据同时进行分辨和解析,获取各个组分的纯色谱曲线和质谱,根据分辨得到的纯质谱在质谱库中进行相似检索以实现对组分的定性。利用AMWFA对组合前后的成分进行归属分析,然后采用面积归一法进行定量。分别在甘草、甘遂及其药对中鉴定出52、51和63个成分,占各自挥发油成分的84%、90%和75%。 相似文献
45.
将人的诱导型一氧化氮合成酶(hiNOS)启动子构建在带荧光素酶基因的载体pGL3-basic上, 构建成用荧光素酶为系统的启动子, 以研究载体p8.3iNOS. 结果显示, 肾母细胞肿瘤抑制因子(WT1)能够有效地抑制hiNOS启动子的转录; 且WT1的4个选择性剪接本的抑制效果有所不同, 其中WT1(-/-)在两种肝癌细胞(HepG2和Hep3B)中对hiNOS的表达均具有最强的抑制作用, 并且抑制效果具有剂量依赖性, 用Western blot检测结果进一步证实HepG2细胞中WT1(-/-)过量表达能下调hiNOS表达. 以上结果说明WT1在肝癌细胞中对人的hiNOS具有转录调节作用. 相似文献
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S. Capozziello V. I. Man’ko G. Marmo C. Stornaiolo 《General Relativity and Gravitation》2008,40(12):2627-2647
The probability representation, in which cosmological quantum states are described by a standard positive probability distribution,
is constructed for minisuperspace models selected by Noether symmetries. In such a case, the tomographic probability distribution
provides the classical evolution for the models and can be considered an approach to select “observable” universes. Some specific
examples, derived from Extended Theories of Gravity, are worked out. We discuss also how to connect tomograms, symmetries
and cosmological parameters. 相似文献
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Dr. Jan Schwabedissen Timo Glodde Dr. Yury V. Vishnevskiy Dr. Hans-Georg Stammler Lukas Flierl Prof. Dr. Andreas J. Kornath Prof. Dr. Norbert W. Mitzel 《ChemistryOpen》2020,9(9):921-928
The refrigerant trans-1,3,3,3-tetrafluoropropene (HFO-1234ze) is used as a replacement for former cooling agents that have been phased-out due to their global warming potential or ozone depleting potential. Although it is used on a large scale, only a few vibrational data and no structural data of HFO-1234ze are known. We report structure determinations based on low-temperature single-crystal X-ray diffraction data as well as gas-phase diffraction data of HFO-1234ze and HFO-1234yf (2,3,3,3-tetrafluoropropene). Furthermore, vibrational spectra of HFO-1234ze in all phases are described. The results are discussed together with quantum-chemical calculations on the PBE0/cc-pVTZ level of theory. Combustion experiments of HFO-1234ze show carbonyl difluoride, carbon dioxide and hydrogen fluoride to be the main combustion products. 相似文献