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排序方式: 共有1368条查询结果,搜索用时 62 毫秒
131.
J.S. Yadav Saibal Das J. Satyanarayana Reddy N. Thrimurtulu A.R. Prasad 《Tetrahedron letters》2010,51(31):4050-4052
The first total synthesis of (3R),(5R)-5-hydroxy-de-O-methyllasiodiplodin and its epimer is reported from malic acid. The adopted approach is highly convergent and stereoselective. The strategy utilizes syn selective reduction and ring-closing metathesis as key steps. 相似文献
132.
The synthesis of C1-C12 and C13-C22 fragments of (−)-callystatin A is accomplished employing desymmetrization strategy for the creation of five chiral centres of the polypropionate fragment and application of cross-metathesis (CM) reaction for the first time for this molecule. 相似文献
133.
B.V. Subba Reddy B. Bramha Reddy K.V. Raghavendra Rao J.S. Yadav 《Tetrahedron letters》2012,53(20):2500-2503
A tandem cycloisomerization/Friedel–Crafts alkylation of indoles has been achieved in a one-pot process to produce 2,5-disubstituted furans using gallium-catalyzed sequential nucleophilic addition onto metal-activated 1-alkynyl-2,3-epoxy acetates. The reaction proceeds efficiently under mild conditions with complete regioselectivity to afford the substituted furan derivatives in good yields with high diversity. 相似文献
134.
Bianchi Type-IX viscous fluid cosmological model is investigated. To get a deterministic model, we have assumed the conditiona = b
m(m is a constant) between metric potentials andη ∞θ whereη is the coefficient of shear viscosity andθ the scalar of expansion in the model. The coefficient of bulk viscosity (ς) is taken as constant. The physical and geometrical
aspects of the model are also discussed. 相似文献
135.
Mahesh Kumar Yadav Anju Rai Anirudh Pradhan 《International Journal of Theoretical Physics》2007,46(11):2677-2687
We investigate the integrability of cosmic strings in Bianchi III space-time in presence of a bulk viscous fluid by applying
a new technique. The behavior of the model is reduced to the solution of a single second order nonlinear differential equation.
We show that this equation admits an infinite family of solutions. Some physical consequences from these results are also
discussed. 相似文献
136.
PANI/PMMA composite was synthesized by emulsion polymerization pathway and the composite thin film was obtained by vacuum evaporation. The effect of vapour chopping and varying PMMA concentration was also studied. The FTIR spectra showed that the PANI/PMMA composite thin film deposited as a short chain oligomers. Increase in transmittance and decrease in refractive index was obtained with increasing concentration of PMMA, which further increased the adhesion and decreased intrinsic stress. The vapour chopping improved its optical as well as mechanical properties and produced smoother surface morphology. Increase of PMMA made the film more amorphous and does not change its band gap. 相似文献
137.
Dr. Vitthal N. Yadav Prof. Angiolina Comotti Prof. Piero Sozzani Dr. Silvia Bracco Prof. Tore Bonge‐Hansen Dr. Martin Hennum Prof. Carl Henrik Görbitz 《Angewandte Chemie (International ed. in English)》2015,54(52):15684-15688
Dipeptides with two hydrophobic side chains have proved to be an exceptional source of microporous organic materials, but since previous structures were limited to the incorporation of only proteinogenic residues, their full potential as adsorbents has remained unexplored. Single‐crystal XRD data for ten new compounds with non‐proteinogenic L ‐2‐aminobutanoic acid and/or L ‐2‐amino‐pentanoic acid are presented. The gas‐phase accessibility of their crystal pores, with cross‐sections of 2.3 to 5.1 Å, was monitored by CO2 and CH4 adsorption isotherms. Included CO2 was also detected spectroscopically by 2D MAS NMR. An extensive conformational analysis reveals that the use of linear rather than branched side chains (such as L ‐valine and L ‐isoleucine) affords peptides with a greater degree of conformational freedom and yields more‐flexible channel surfaces that may easily adapt to a series of potential guest molecules. 相似文献
138.
An Efficient Enantioselective Synthesis of Natural Gingerols,the Active Principles of Ginger 下载免费PDF全文
A. Ramesh Reddy Sachin B. Wadavrao J. S. Yadav A. Venkat Narsaiah 《Helvetica chimica acta》2015,98(7):1009-1017
A straightforward synthesis of (S)‐gingerols 1 – 3 has been described. The requisite stereogenic center in the target molecules was introduced by Sharpless asymmetric dihydroxylation using a chiral complex, AD‐mix β. This route is simple and efficient to prepare the products in very good yields. 相似文献
139.
Harshika Agarwal Shweta Yadav Gautam Jaiswar 《Journal of Thermal Analysis and Calorimetry》2017,129(3):1471-1479
The thermal, morphological and optical studies of BaSO4 and MMT (nanoclay) embedded in PVDF were investigated. Nanocomposites samples of PVDF–BaSO4–MMT were prepared by varying the loadings (1–4 mass%) in case of BaSO4 and MMT nanomaterials, respectively. Polyvinylidene fluoride–barium sulfate-montmorillonite (PVDF–BaSO4–MMT) nanocomposites were prepared by solvent-mixing technique. Nanoparticles were synthesized by in situ deposition technique with the help of nonionic polymeric surfactant, and the particle size of nanoparticles was recognized by scanning electron microscopy (SEM) analysis which confirms that the particle has diameter of 80–90 nm. As prepared, nanocomposites films (thickness, 25 μm) were characterized by Fourier transform infrared microscopy (FTIR), SEM and electron diffraction spectroscopy (EDS). FTIR shows that all the chemical constituents were present in the nanocomposites, whereas SEM analysis suggested that the nanofillers dispersed well in polymer matrix and EDS showed the elemental composition of nanocomposite samples. Thermal properties of nanocomposites were studied by using TG/DTA/DTG. TG/DTA studies showed decomposition temperature of pure PVDF is 473.5 °C. The decomposition temperature (T d) of nanocomposites was increased by 93 °C in case of nanocomposites with addition of both BaSO4 and MMT nanomaterials. The difference in the thermal degradation temperature was found to be 1.2% higher in case of addition of BaSO4 nanoparticle as compared to nanoclay. The obtained transparent nanocomposite films were characterized by using UV–Vis spectrophotometer which shows that transparencies of nanocomposites are maintained in visible region, the intensity of absorption band in UV region is increased with the addition of BaSO4 nanoparticles, while in case of addition of nanoclay the UV region does not show drastic changes. Addition of both nanoparticle and nanoclay shows higher absorption in comparison with the individual samples. But further, doubling the amount of nanoparticle and nanoclay shows decrease in UV absorption. Overall, the results of thermal studies show that the incorporation of BaSO4 and MMT could significantly improve the thermal properties of nanocomposites. 相似文献
140.
Om Prakash Yadav Ram Jiwari 《Numerical Methods for Partial Differential Equations》2017,33(5):1652-1677
In this article, the authors present finite element analysis and approximation of Burgers’‐Fisher equation. Existence and uniqueness of weak solution is proved by Galerkin's finite element method for non‐smooth initial data. Next, a priori error estimates of semi‐discrete solution in norm, are derived and the convergence of semi‐discrete solution is established. Then, fully discretization of the problem is done with the help of Euler's backward method. The nonlinearity is removed by lagging it to previous known level. The scheme is found to be convergent. Positivity of fully discrete solution is discussed, and bounds on time step are discovered for which the solution preserves its positivity. Finally, numerical experiments are performed on some examples to demonstrate the effectiveness of the scheme. The proposed scheme found to be fast, easy and accurate.© 2017 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 33: 1652–1677, 2017 相似文献