排序方式: 共有18条查询结果,搜索用时 15 毫秒
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Ewalds R Eggeling EB Hewat AC Kamer PC van Leeuwen PW Vogt D 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(8):1496-1504
New chiral aminophosphine phosphinite ligands with a stereogenic center at the aminophosphine phosphorus atom were prepared based on (R,S)-ephedrine as the chiral auxiliary and backbone. Substituents at the chiral aminophosphine as well as at the phosphinite phosphorus atom were varied. These new ligands were applied to the rhodium-catalyzed asymmetric hydroformylation of vinyl arenes. The enantiomeric excess reached up to 77%. 1H and 31P NMR studies of the Rh complexes under syngas pressure reveal that [HRh(CO)2(PP)] complexes with the NP* moiety in an axial position are responsible for enantioselectivity. 相似文献
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Liang Di Chapman David C. Li Youli Oakley Douglas C. Napoleone Tony Juodawlkis Paul W. Brubaker Chad Mann Carl Bar Hanan Raday Omri Bowers John E. 《Applied Physics A: Materials Science & Processing》2011,102(1):213-217
β-SiC nanowires were synthesized by a simple carbothermal reduction of carbonaceous silica xerogel. The morphology and structure
of the nanowires were investigated by X-ray diffraction, scanning electron microscope and transmission electron microscopy.
The results showed that the nanowires were hexagonal prism-shaped hierarchical nanostructures. The typical stacking faults
and twin defects of SiC nanowires were also observed. Band-gap characterization and photoluminescence properties of SiC nanowires
were investigated by UV-vis absorption spectroscopy and fluorescence photometry, respectively. The results showed the SiC
nanowire was an indirect transition semiconductor and the band gap energy for the SiC nanowires was 2.85 eV. The photoluminescence
peak value at 470 nm (2.64 eV) originating from the SiC nanowires was a little higher than the value of band-gap energy. 相似文献
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We report the demonstration of a 1.5 microm InGaAsP mode-locked slab-coupled optical waveguide laser (SCOWL) producing 10 ps pulses with energies of 58 pJ and average output powers of 250 mW at a repetition rate of 4.29 GHz. To the best of our knowledge, this is the first passively mode-locked slab-coupled optical waveguide laser. The large mode and low confinement factor of the SCOWL architecture allows the realization of monolithic mode-locked lasers with high output power and pulse energy. The laser output is nearly diffraction limited with M2 values less than 1.2 in both directions. 相似文献