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81.
82.
83.
Ole Toft Sørensen 《Journal of Thermal Analysis and Calorimetry》2005,80(3):793-794
Summary An enormous development has taken place within the last five years in synchronous teaching over the Internet, i.e. both the teacher and the students are simultaneously in direct communication with each other as in a normal class-room or auditorium. With this concept it is possible to communicate orally, to exchange Power Point Presentations, documents, programmes and live web-camera pictures. It is even possible to use an electronic black board on which both the teacher and the students can work simultaneously. The great advantage with this type of teaching is that it is not restricted to a single class-room/auditorium with limited access, but in a virtual room accessible to everybody in principle all over the world, and which certainly open up new possibilities in teaching. The purpose of this paper is to present and to discuss the concept of virtual class-room teaching, how the system operates in practice, its advantages and, finally, how its inherent limitations can be overcome. 相似文献
84.
Some new complexes between thecis-4,4′-dinitrodibenzo-18-crown-6 and rare earth chlorides LnCl3 (Ln=Nd, Gd, Yb) were synthesized in acetonitrile. Ligandcis-4,4′-dinitrodibenzo-18-crown-6 and its complexes were identified by infrared spectroscopy, X-ray diffraction and thermal
analysis (TG and DTA). Acis-trans isomerisation of the complexed ligand is observed about 148°C when heating the rare earth complex.
相似文献
85.
86.
High-resolution 17O NMR spectra have been collected for crystalline samples of lanthanum new phase, La3Si8N11O4. In conjunction with previously published 29Si and 15N spectra obtained for this phase, and in the light of the high-quality crystal structure data reported recently, a more detailed interpretation of the NMR spectra is presented than was possible in previous studies. The non-bridging oxygens in the structure are responsible for the single sharp peak seen in the 17O spectrum at 188 ppm; the remaining oxygens, occupying bridging sites shared with nitrogen, show up only weakly on the 17O spectrum as a broad diffuse band centered around zero ppm. The peak at −57.3 ppm on the 29Si spectrum is believed to correspond to an overlap of [SiN4] and [SiON3] environments, with the −68.2 ppm peak corresponding to an [SiO2N2] environment. 相似文献
87.
I. M. Krukovskii M. S. Molchanova A. V. Evtushenko V. A. Shlyapochnikov 《Russian Chemical Bulletin》1998,47(7):1266-1273
The ratio between the numbers of structural formulas of C,H,N,O-containing energetic compounds belonging to the classes of
fuels (low values of the oxygen coefficientA), explosives (mediumA), and oxidants (highA values) was studied by a computer generation procedure. The number of the theoretically possible structural formulas was
found to decrease rapidly on going from fuels to explosives and then to oxidants; this observation agrees with the data on
the numbers of various energetic compounds currently used and proposed. The strategy of the search for new compounds with
the specified properties is described in brief, and its applicability to the search for explosives and oxidants with a small
(up to 12) number of atoms in a molecule is evaluated.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1304–1310, July, 1998. 相似文献
88.
Green Chemistry and Modern Technology 总被引:4,自引:0,他引:4
The basic principles, approaches, and early achievements of green chemistry are considered. The definition of green chemistry as a branch of chemistry that studies the laws of passing of chemical reactions and the properties of substances participating in such reactions, with the aim of acquiring basic knowledge that provides a basis for designing chemical technologies that eliminate (sharply curtail) the use and production of materials that pose a risk to the environment. 相似文献
89.
A new compound of 4,4'-diamino-N,N'-diethyl bisbenzenesulfamide (C18H26N4O4S2,Fw = 426.55) has been synthesized and its structure was determined by X-ray crystallography method. The crystal belongs to the monoclinic system, space group P21/c with a = 10.0623(9), b =13.6759(13), c =15.5309(14) (A),β = 100.482(2)°, V= 2101.6(3)(A)3, Dc = 1.348 g/cm3, F(000) = 904,μ = 0.285 mm-1, Z = 4, the final R = 0.0512 and wR = 0.1363 for 3485 observed reflections with I >2σ(Ⅰ). The structure of the title compound is pseudo secondary axisymmetric, and the two sulfamide-groups show distorted tetrahedral configurations. 相似文献
90.
Ilaria Serafini Livia Lombardi Claudia Fasolato Manuel Sergi Francesca Di Ottavio Fabio Sciubba 《Natural product research》2019,33(7):1040-1051
AbstractIn this paper, the application of a multi-analytical approach for the characterisation of synthetic and natural dyes in a historical textile is presented. The work is focused on a historical dress of a Sicilian noblewoman, dating from about 1865–1870. Firstly, SERS on fibre was performed, in order to individuate the classes of dyes employed. The SERS spectra suggested the presence of two main dyes: mauveine and orcein. In order to confirm these preliminary results, two different extraction protocols were applied. The extracts obtained were analysed by ESI-MS, MALDI-ToF and UHPCL-MS analyses, confirming the SERS results. In particular, the application of the ammonia mild extraction technique allowed to selectively extract the phenoxazonic dyes, separating them already in the extraction step from the synthetic ones. Thanks to this multi-analytical approach, this dress could be considered as one of the first examples of employment of synthetic dyes in association with natural ones. 相似文献