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排序方式: 共有250条查询结果,搜索用时 109 毫秒
1.
Let [a, b] be any interval and let p0, p1, pk be any three polynomials of degrees 0, 1, k, respectively, where k 2. A set of necessary and sufficient conditions for the existence of an f in C[a, b] such that pi is the best approximation to f from the space of all polynomials of degree less than or equal to i, for all i = 0, 1, k, is given. 相似文献
2.
3.
A simple spectrophotometric method for determination of isoxsuprine hydrochloride in pharmaceuticals
A spectrophotometric method has been developed for the determination of isoxsuprine hydrochloride and its dosage forms, based on its coupling reaction with diazotized sulphanilic acid. The yellow chromophore has an absorption maximum at 440 nm. Beer's law holds over the range 0.8-8 mu/ml in the final solution. 相似文献
4.
[reaction: see text] Direct asymmetric catalytic Michael reactions have been performed using chiral-amine/acid bifunctional catalysts. Performed with 0.3 equiv of (S)-(+)-1-(2-pyrrolidinylmethyl)pyrrolidine and 0.3 equiv of trifluoroacetic acid as the catalyst, the reaction of alpha,alpha-dialkylaldehydes with (E)-beta-nitrostyrene provided the alpha,alpha-dialkyl Michael products in up to 96% yield with up to 91% ee. With respect to enantioselectivity, l-proline was a poor catalyst of this class of Michael reactions. 相似文献
5.
J. Ravichandran C. M. Lakshmanan B. Sivasankar 《Reaction Kinetics and Catalysis Letters》1996,59(2):301-308
Treatment of montmorillonite and vermiculite with hydrochloric acid results in an overall increase in acidity and acidic sites. IR and DSC studies of base adsorbed catalysts have revealed the heterogeneity of surface acidity on the activated catalysts. Clay catalysts have been found to dehydrate 1-butanol to 1-butene, which directly isomerizes tocis- andtrans-2-butenes, confirming the presence of Lewis and Brönsted acid sites. Cumene cracking studies using the clay catalyst also confirm the presence of Brönsted acid sites. The temperature and concentration of acid have been found to have a significant influence on the catalytic activity. 相似文献
6.
Glass-ceramic was prepared by sol–gel method using Ca(NO3)2·4H2O and P2O5 as Ca and P precursors, respectively. In order to improve the bioactivity of the implant material, glass-ceramic (β-Ca2P2O7) coating was developed on 316L SS substrate by spin coating method. Coating was annealed at different temperatures and its
corrosion resistance was evaluated by electrochemical polarization and impedance analysis using Ringer’s solution as electrolyte.
The results from the present study, show excellent corrosion resistance for coated 316L SS, corroborated by the high values
of charge transfer resistance from impedance analysis and higher breakdown and repassivation potential with the corresponding
lower current density from polarization measurements. Based on the results, the glass-ceramic coating on 316L SS can be considered
as a corrosion resistant material. 相似文献
7.
D. Ravichandran K. Yamakawa A.S. Bhalla R. Roy 《Journal of Sol-Gel Science and Technology》1997,9(1):95-101
Phase pure powder and thin films of the novel ferroelectric materials SrBi2Ta2O9 (SBT) have been prepared using the organic precursors. The xero-gel formed was dried and characterized using TGA and DTA
to determine the organic burn out and crystallization temperature of SBT. Powder X-ray diffraction was used systematically
to check the crystallinity of SBT. Phase pure SBT powder was formed as low as 650°C and thin films at 600°C in comparison
to other earlier reported work. SEM micrographs show a grain size of ≈0.1 μm and show crack free films with a film thickness
of 2 μm. 相似文献
8.
The effect of repeated loading from mechanically simulated hull slamming on foam core sandwich composites was investigated
utilizing a novel technique that simultaneously measured temperature and displacement while cyclic loading occurred. Thermoelastic
Stress Analysis (TSA) and Digital Image Correlation (DIC) techniques were combined using a single infrared camera for characterization
of the foam core. Improved stress fields with TSA results were found through deformation compensation. Initial work approximating
hull slamming conditions mechanically utilizing a custom device were performed. Mechanically loading offers several benefits
over water impact investigations, including easy access to the sample during the slamming event, an unobstructed optical path,
and accelerated testing. Evolving stress fields under long-duration, repeated simulated hull slamming loading were observed
around a growing delamination crack between the foam core and skin. 相似文献
9.
Priyanka Lohar Manish Kumar Sharma Amit Kumar Sahu Rajeswari Rathod Pinaki Sengupta 《Biomedical chromatography : BMC》2019,33(12)
The combination of acebrophylline (ABP), levocetirizine (LCZ) and pranlukast (PRN) is used to treat allergic rhinitis, asthma, hay‐fever and other conditions where patients experience difficulty in breathing. This study was carried out with the aim of developing and validating a reverse‐phase high‐performance liquid chromatographic bioanalytical method to simultaneously quantitate ABP, LCZ and PRN in rat plasma. The objective also includes determination of the pharmacokinetic interaction of these three drugs after administration via the oral route after individual and combination treatment in rat. Optimum resolution between the analytes was observed with a C18 Kinetex column (250 mm × 4.6 mm × 5 μm). The chromatography was performed in a gradient elution mode with a 1 mL/min flow rate. The calibration curves were linear over the concentration range of 100–1600 ng/mL. The intra‐ and inter‐day precision and accuracy were found to be within acceptable limits as specified in US Food and Drug Administration guideline for bioanalytical method validation. The analytes were stable on the bench‐top (8 h), after three freeze–thaw cycles, in the autosampler (8 h) and as a dry extract (?80°C for 48 h). The statistical results of the pharmacokinetic study in Sprague–Dawley rats showed a significant change in pharmacokinetic parameters for PRN upon co‐administration of the three drugs. 相似文献
10.
Seth Sheeba Thavamani Murugesan Sudharsan Anitha Santhana Mariya Devarajan Suresh Arlin Jose Amali Sanniyasi Rajeswari Thomas Peter Amaladhas 《应用有机金属化学》2020,34(9):e5752
The catalytic activity of CeO2 and palladium nanoparticles supported fly ash zeolite (CeO2/Pd@FAZ) for Csp2-Csp2 bond formation was studied. CeO2/Pd@FAZ was characterized by FTIR, XRD, EDAX and TEM studies. In the Suzuki-Miyauracross-coupling reaction, biphenyl derivatives with excellent yields were obtained, and the reaction conditions were optimized. The catalytic activity was explored using a wide variety of diversely substituted aryl bromides and chlorides with aryl boronic acid under optimized reaction conditions. The recyclability of the catalyst was established for three cycles, with the conversion rate from 99 to 40%, which gained the advantage of heterogeneous catalysis. 相似文献