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排序方式: 共有369条查询结果,搜索用时 46 毫秒
1.
2.
The a.c. conductivity of the proteins lysozyme and subtilisin, both in their active and inactive or inhibited forms were determined theoretically. For this, quantum mechanical calculations and a random walk theory were used. The conclusions are that these enzymatic proteins can easily transport electrons which is most probably important in their role as catalysators of biochemical reactions. The electron transport is sensitive to three-dimensional changes of the active sites of these enzymes which have more flexibility than the whole molecule. Therefore, the flexibility of the active sites of enzyme catalysts is not only important for the conformational fitting with the reactants, but also strongly influences the transport in biochemical reactions. 相似文献
3.
E Di Cesare M Sabatini A Splendiani C Masciocchi 《Canadian Metallurgical Quarterly》1998,96(1-2):113-115
A wandering spleen and splenic cysts are uncommon conditions in children. A combination of both entities has only rarely been reported in the literature. Another case of this complex pathology in 12-year-old girl is presented. She was initially referred for evaluation of a large abdominal mass. Diagnostic studies raised the suspicion of a hematoma in an abnormally located spleen, but the definitive diagnosis was established at laparotomy. Successful surgical management consisted of total cystectomy and splenopexy. 相似文献
4.
Nanoindentation Characterization of Submicro- and Nano-Sized Liquid-Phase-Sintered SiC Ceramics 总被引:1,自引:0,他引:1
Stefano Guicciardi Diletta Sciti Cesare Melandri Alida Bellosi 《Journal of the American Ceramic Society》2004,87(11):2101-2107
Submicro- and nano-sized liquid-phase-sintered SiC ceramics were mechanically tested by nanoindentation in the peak load range 5–400 mN. The submicro-sized sample showed a marked indentation size effect which the nano-sized samples did not exhibit. The relevance of indentation depth with respect to the microstructural scale has been outlined. In the investigated grain-size range, the hardness dependence on the grain size could be described by a load-dependent inverse Hall–Petch relation. Young's modulus was less microstructure- and load-dependent. Because of the very fine microstructure, the nano-sized SiC materials gave lower elastic values than the submicro-sized SiC ceramic. 相似文献
5.
K. J. Williams A. B. Boffa M. Salmeron A. T. Bell G. A. Somorjai 《Catalysis Letters》1991,9(5-6):415-426
Submonolayer deposits of titania on a Rh foil have been found to increase the rate of CO2 hydrogenation. The primary product, methane, exhibits a maximum rate at a TiO
x
coverage of 0.5 ML which is a factor of 15 higher than that over the clean Rh surface. The rate of ethane formation displays a maximum which is 70 times that over the unpromoted Rh foil; however, the selectivity for methane remains in excess of 99%. The apparent activation energy for methane formation and the dependence of the rate on H2 and CO2 partial pressure have been determined both for the bare Rh surface and the titania-promoted surface. These rate parameters show very small variations as titania is added to the Rh catalyst. The methanation of CO2 is proposed to start with the dissociation of CO2 into CO(a) and O(a), and then proceed through steps which are identical to those for the hydrogenation of CO. The increase in the rate of CO2 hydrogenation in the presence of titania is attributed to an interaction between the adsorbed CO, released by CO2 dissociation, and Ti3+ ions located at the edge of TiO
x
islands covering the surface. Differences in the effects of titania promotion on the methanation of CO2 and CO are discussed in terms of the mechanisms that have been proposed for these two reactions. 相似文献
6.
Sub-monolayer quantities of metal oxides are found to influence CO hydrogenation, CO2 hydrogenation, acetone hydrogenation, ethylene hydroformylation, ethylene hydrogenation, and ethane hydrogenolysis over Rh foils. The metal oxides investigated include AlOx, TiOx, VOx, FeOx, ZrOx, NbOx, TaOx, and WOx. Only those reactions involving the hydrogenation of C-O bonds are enhanced by the oxide overlayers. The coverage at which maximum rate enhancement occurs is approximately 0.5 ML for each oxide promoter. Titanium, niobium, and tantalum oxides are the most effective promoters. XPS measurements after reaction show that of the oxides studied titanium, niobium, and tantalum oxide overlayers are stable in the highest oxidation states. The trend in promotion effectiveness is attributed to the direct relationship between oxidation state and Lewis acidity. For the oxide promoters, bonding at the metal oxide/metal interface between the O-end of adsorbed CO and the Lewis acidic oxide is postulated to facilitate C-O bond dissociation and subsequent hydrogenation. 相似文献
7.
RESTful Web service composition with BPEL for REST 总被引:4,自引:0,他引:4
8.
9.
Commiphora myrrha (Nees) Engl. extracts: evaluation of antioxidant and antiproliferative activity and their ability to reduce microbial growth on fresh‐cut salad
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Luisa Boffa Arianna Binello Valentina Boscaro Margherita Gallicchio Gabriella Amisano Stefania Fornasero Giancarlo Cravotto 《International Journal of Food Science & Technology》2016,51(3):625-632
With the aim to develop natural preservatives displaying also chemopreventive activity, different Commiphora myrrha (Nees) Engl. extracts were studied. Myrrh essential oils, obtained by steam distillation and microwave‐assisted hydrodistillation, and several other extracts, obtained by sequential procedures with petroleum ether (PE), ethanol, ethyl acetate and butanol, have been screened for their antioxidant (DPPH· scavenging assay) and antiproliferative activity (on both nontumour and colon cancer cell lines) without previous purification. Considering that the colon cancer cell lines were more sensitive to PE and ethanol extracts, the latter of which showed the highest antioxidant activity (EC50 = 0.160 ± 0.008 mg mL?1), both have been selected for further antibacterial/antifungal activity tests using an antimicrobial diffusion test and a growth inhibition test on salads. Results showed that the ethanol extract possessed the higher antibacterial and antifungal activity. Compared to untreated product, fresh‐cut salads treated with these two myrrh extracts displayed a significant lower bacterial growth. Although further investigation is required, these promising results offer hints as how to improve the shelf life of fresh‐cut salad. 相似文献
10.
George D. Quinn Cesare Melandri Goffredo de Portu 《Journal of the American Ceramic Society》2013,96(7):2283-2291
The edge chipping test was used to measure the fracture resistance of alumina/alumina‐zirconia laminated structures. Tailored, symmetrical laminated structures were prepared with a variety of layer thickness. The laminates had a significantly greater edge chipping resistance. Laminates with thin layers were just as effective in impeding edge chips as laminates with thick layers. 相似文献