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排序方式: 共有223条查询结果,搜索用时 31 毫秒
21.
Ming Xia LI Yan Ming WANG Ru Ru CHEN* Research Institute of Elemento-Organic Chemistry Nankai University Tianjin Pittsburgh University Medical Center Pittsburgh PA U. S. A 《中国化学快报》2001,(6)
The chiral diols ((,(,((,((-Tetraaryl-1,3-dioxolane-4,5-dimethanols) have been used for the formation of cyclic titanates and similar derivatives of Mg, Al and Zr. These complexes of oxophilic metal centers were employed in catalytic and stiochiometric enantioselective reactions such as enantioselective addition reactions of carbon-centered nucleophiles to aldehydes1, [2+2] cycloadditions2, and Diels-Alder reactions3. So far, the two hydrogen atoms of all this type of diols are in trans form… 相似文献
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We consider diffraction by a semi-infinite crack located alonga fusion interface between two differing elastic media. Twotypes of crack, namely open and partially closed cracks, areinvestigated. An open crack is modelled by a stress-free contactboundary condition and a partially closed crack is modelledby a spring contact boundary condition. For the latter, thejump in the stress across the crack is assumed to be proportionalto the jump in the displacement across the crack. This situationarises in, for example, a K-weld where the fine grain of theparent material (for example, ferritic or forged austeniticsteel) is in stark contrast with the coarse-grained weld metal(for example, austenitic weld metal). In the metal weld thedirection of the grain axis varies through the metal. However,diffraction is a local phenomenon and so the austenitic steelis assumed to have a zonal axis so that it may be modelled bya transversely isotropic composite. The ferritic or forged austeniticsteel will be modelled as an isotropic material. 相似文献
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R. Andrew Sims Pankaj Kadwani Heike Ebendorff-Heideprem Lawrence Shah Tanya M. Monro Martin Richardson 《Applied physics. B, Lasers and optics》2013,111(2):299-304
We report femtosecond pulse generation and chirped pulse amplification in Tm:fiber. A mode-locked oscillator operating in the soliton regime produced 800 fs pulses with 5 nm spectral bandwidth, at 40 pJ pulse energy. This oscillator seeded a pre-amplifier that utilizes a Raman soliton self-frequency shift to produce wavelength tunable pulses with 3 nJ energy, reduced pulse duration of 150 fs, and increased bandwidth of 30 nm. For further amplification, the pulses were stretched up to 160 ps using a chirped Bragg grating (CBG). Stretched pulses were amplified to 85 nJ after compression in single-mode Tm:fiber and recompressed with the CBG as short as 400 fs. Compressed pulses were coupled into a highly nonlinear tellurite fiber to investigate the potential of this ultrashort pulse 2-μm fiber source as a pump for mid-IR supercontinuum generation. 相似文献
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Public Attitudes Toward Nanotechnology 总被引:5,自引:5,他引:0
Data from 3909 respondents to an Internet survey questionnaire provide the first insights into public perceptions of nanotechnology. Quantitative analysis of statistics about agreement and disagreement with two statements, one positive and the other negative, reveals high levels of enthusiasm for the potential benefits of nanotechnology and little concern about possible dangers. The respondents mentally connect nanotechnology with the space program, nuclear power, and cloning research, but rate it more favorably. In contrast, they do not associate nanotechnology with pseudoscience, despite its imaginative exploitation by science fiction writers. Qualitative analysis of written comments from 598 respondents indicates that many ideas about the value of nanotechnology have entered popular culture, and it provides material for an additional 108 questionnaire items that can be used in future surveys on the topic. The findings of this exploratory study can serve as benchmarks against which to compare results of future research on the evolving status of nanotechnology in society. 相似文献
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The unique halogenated monoterpene, 7-bromo-2,6-dimethyl-4,4,8-trichloro-1,5(z)-octadiene-3-one, was isolated from the marine red alga . 相似文献
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Sims JW Fillmore JP Warner DD Schmidt EW 《Chemical communications (Cambridge, England)》2005,(2):186-188
An iterative polyketide synthase-peptide synthetase hybrid assembles the HIV-1 integrase inhibitory tetramic acid, equisetin, in the filamentous fungus Fusarium heterosporum. 相似文献
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