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排序方式: 共有9094条查询结果,搜索用时 15 毫秒
991.
992.
Kim SH Kim JH Kang BK Uhm HS 《Langmuir : the ACS journal of surfaces and colloids》2005,21(26):12213-12217
Stable superhydrophobic coatings on various substrates are attained with an in-line atmospheric rf plasma process using CF4, H2, and He. The coating layer is composed of CFx nanoparticulates and has an average roughness of approximately 10 nm. This roughness is much smaller than other surfaces reported for superhydrophobicity in the literature. The superhydrophobic coatings are produced on both metallic and insulating substrates without any need of separate microroughening or vacuum lines. 相似文献
993.
Phytochemical investigation of Ginkgo biloba (Ginkgoaceae) has resulted in the isolation of two new biflavone glucosides, ginkgetin 7'-O-beta-D-glucopyranoside (1) and isoginkgetin 7-O-beta-D-glucopyranoside (2). The structures were determined on the basis of chemical and spectroscopic evidences. 相似文献
994.
Interaction between cationic surfactants and montmorillonites under nonequilibrium condition 总被引:2,自引:0,他引:2
Surfactant adsorption by two different montmorillonites was characterized by examining the time dependence of surfactant behavior on clay surfaces. Surfactants with different micelle concentrations were conducted in our experiment to observe a nonequilibrium activity of cationic surfactant on the clay over reaction periods ranging from 0.1 min to 11 days. Compared with Ca-montmorillonite (SAz), a more active intrusion of surfactant molecules into the interlayers was found in Na-montmorillonite (SWy). During a short "initiation" stage, the basal spacing of SWy montmorillonite increased rapidly with logarithmic time. For SAz montmorillonite, however, the abrupt basal spacing increase occurred at a later stage of the reaction. From the results, it is assumed that the difference in the adsorption behavior exhibited by the two montmorillonite types partly arises from their intrinsic nature; that is, inorganic cations originally existed on the clay surfaces. Additionally, the micelle concentration of the surfactants affects the development of organomontmorillonite, especially in the intercalant formation and stabilization under nonequilibrium. 相似文献
995.
Lee SA Lee KM Park WY Kim B Nam J Yoo KY Noh DY Ahn SH Hirvonen A Kang D 《Experimental & molecular medicine》2005,37(2):86-90
To evaluate the relationship of genetic polymorphisms of ERCC2 and ERCC4 genes, both involved in nucleotide excision repair (NER), and the risk of breast cancer, a hospital-based case-control study was conducted in Korea. Histologically confirmed breast cancer cases (n = 574) and controls (n = 502) with no present or previous history of cancer were recruited from three teaching hospitals in Seoul during 1995-2001. Information on selected characteristics was collected by interviewed questionnaire. ERCC2 Asp(312)Asn (G>A) was genotyped by single-base extension assay and ERCC4 Ser(835)Ser (T>C) by dynamic allele-specific hybridization system. Although no significant association was observed between the genetic polymorphisms and the risk of breast cancer, women with both ERCC2 A allele- and ERCC4 C allele-containing genotypes showed a 2.6-fold risk (95% CI: 1.02-6.48) of breast cancer compared to women concurrently carrying the ERCC2 GG and ERCC4 TT genotypes. The breast cancer risk increased as the number of "at risk" genotypes increased with a borderline significance (P for trend = 0.07). Interactive effect was also observed between ERCC4 genotype and body mass idnex (BMI) for the breast cancer risk; the ERCC4 C allele containing genotypes posed a 1.7-fold (95% CI: 0.96-2.93) breast cancer risk in obese women (BMI>25 kg/m(2)) with a borderline significance. Our finding suggests that the combined effect of ERCC2 Asp(312)Asn and ERCC4 Ser(835)Ser genotypes might be associated with breast cancer risk in Korean women. 相似文献
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999.
Huah Chu Shou-Jen Hu Ming-chang Kang 《Proceedings of the American Mathematical Society》2005,133(10):2865-2871
Let be a linearly reductive group over a field , and let be a -algebra with a rational action of . Given rational --modules and , we define for the induced -action on Hom a generalized Reynolds operator, which exists even if the action on Hom is not rational. Given an -module homomorphism , it produces, in a natural way, an -module homomorphism which is -equivariant. We use this generalized Reynolds operator to study properties of rational - modules. In particular, we prove that if is invariantly generated (i.e. ), then is a projective (resp. flat) -module provided that is a projective (resp. flat) -module. We also give a criterion whether an -projective (or -flat) rational --module is extended from an -module.
1000.
This study investigates how to dynamically allocate resources with a given budget for advertising through Web portals using keyword-activated banner ads on the Internet. Identifying the factors that affect the potential number of banner ad clickthroughs in each portal, we show that the process of budget allocation between the two types of portals (generic vs specialized) that leads to the largest banner clicksthrough in the long run is an optimal control problem. Using techniques of dynamic programming, we find analytical solutions for the optimal budgeting decisions. Our analysis shows that an advertisers optimal portal budgeting depends nonlinearly on the number of visitors who type the same trigger keyword and the average clicksthrough rates, as well as on the advertiser and ad effectiveness. Further, we find that the maximal number of banner clickthroughs from both portals, at time t, depends on the remaining budget until the end of the planning period. The analytical results have useful managerial insight. One of the interesting features of our solution shows that, while a large visitor base may favor the generic portal, other parameters may affect it unfavorably: e.g., lower clickthrough rates of keyword banners from a more heterogeneous audience. Using a specificaction that is consistent with empirical observations, we show that, in the long run, an advertiser must always spend more ad money at the specialized portal. 相似文献