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991.
992.
A convenient, 40% overall yield synthesis of 2,3,17β-triacetoxy-1,3,5(10)-estratriene is described, which involves epoxidation of 19-nortestosterone and subsequent acetylation, lead tetra-acetate acetoxylation of the so-formed 17β-acetoxy-4β,5-epoxy-5β-estran-3-one, and aromatization of ring A, by means of acidic alumina, of the resulting 2α and 2β epimers of 2,17β-diacetoxy-4β,5-epoxy-5β-estran-3-one. 相似文献
993.
994.
M. Chvojka V. Hermoch B. Králiková J. Krása L. Láska K. Mašek J. Musil S. Polák K. Rohlena J. Schmiedberger J. Skála J. Sulek 《Czechoslovak Journal of Physics》1988,38(12):1337-1356
The photodissociation iodine laser system PERUN I is described. The laser generates and amplifies the subnanosecond pulse with the energy about 80 J of the fundamental wavelength 1·315 μm and beam diameter 10 cm. The physical principles of this type of the high power laser are briefly explained and the laser system and its characteristics are described from the physical and technical point of view. Special attention is paid to the realization of such system with the slow optical pumping (≈300 μs). 相似文献
995.
Miroslav Holub Miloš Buděšínský Zdeňka Smítalovǎ David Šaman Urszula Rychlewska 《Tetrahedron letters》1984,25(34):3755-3758
The newly established structures of sesquiterpene lactones from Laser trilobum showed that these lactones belong among the stereostructural types of germacranolides, guaianolides, eudesmanolides and elemanolides. 相似文献
996.
997.
An alternative, concise proof of the general form of Hohenberg-Kohn theorem is presented. 相似文献
998.
Z. V. Popović C. Thomsen M. Cardona R. Liu G. Stanišić W. König 《Zeitschrift für Physik B Condensed Matter》1988,72(1):13-16
We report both Raman and infrared reflectivity spectra of M2Cu2O5 (M=Y, Ho) at room temperature in the spectral range of 30–1000 cm–1.37 (31) ir and 18 (15) Raman active modes of Y2Cu2O5 (Ho2Cu2O5) are observed. A factor group analysis has been performed to identify the symmetries of the observed modes. Comparing the vibrational spectra of these compounds we conclude that the phonons above 300 cm–1 originate from the Cu–O vibrations and those under 300 cm–1 from M–O vibrations.Alexander von Humboldt Foundation fellow 相似文献
999.
F. Macášek 《Journal of Radioanalytical and Nuclear Chemistry》1996,208(1):5-21
A method for determination of the composition of binary mixtures of a metal or radionuclide species by optimized repeated two-phase separations (SORTS) was proposed and theoretically substantiated. Its principle consists in repeated equilibration of two immiscible phases, one being the original liquid or solid matrix with minimal adjustment of its composition and varying the phase ratio (separation stage cut) as the optimized parameter. The batch separation technique may consist in the repeated solvent extraction or aqueous biphasic distribution, or in the replicate equilibration with solvent or leaching solution. Results of SORTS can be presented e.g. by Tukey box diagrams as the characteristic fingerprints of original species composition. 相似文献
1000.
By DS calorimetry of Ge30S70(a), Ge20S80(b), Ge20Sb2.5S77.5(c) and Ge20Bi5S75(d) crystalline sulphur was identified in (b), (c) and (d) glasses, respectively. It means that these compositions are heterogeneous. Thus the application of the Phillips topological model for estimation of the “ideal” glassy composition in GexS1?x system seems to be open. 相似文献