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排序方式: 共有418条查询结果,搜索用时 142 毫秒
411.
Lacerda V da Silva GV Constantino MG Tormena CF Williamson RT Marquez BL 《Magnetic resonance in chemistry : MRC》2006,44(1):95-98
Detailed measurements of long-range heteronuclear spin-spin coupling constants, especially (2, 3)J(CH) spin-spin couplings for various cyclopentane derivatives, are reported. The measurements are based on a 2D heteronuclear correlation experiment named G-BIRD(R, X)-CPMG-HSQMBC. 相似文献
412.
S Bao C R Guttmann J P Mugler J R Brookeman L P Panych R A Kraft K Oshio D Jaramillo F A Jolesz D S Williamson R V Mulkern 《Magnetic resonance imaging》1999,17(8):1203-1210
Lipid characterization of bone marrow in vivo with proton magnetic resonance spectroscopy was performed using Spin-Echo Planar Spectroscopic Imaging sequences. The methods are shown capable of rapidly generating two-dimensional chemical shift imaging data sets suitable for measuring lipid indices that reflect unsaturation levels among triglycerides, as demonstrated in oil phantoms and bone marrow from a healthy volunteer. The volume coverage, spatial resolution, acquisition speed, and spectral characteristics of Spin-Echo Planar Spectroscopic Imaging should make it attractive for clinical studies of diseases affecting normal lipid chemical composition. 相似文献
413.
Gottschalk J.R. Shvydky O. Compaan A.D. Theodosiou C.E. Williamson W. Jr. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1999,27(3):772-777
We have used a commercially available monochrome plasma display panel (PDP) to study the electrical and optical properties of PDPs. The monochrome PDP was filled with helium at a pressure of 0.5 atm with the visible light emission observed directly from the gas discharge. The PDP is driven by an AC voltage source, operating at ~130 V at 50 kHz. With nanosecond resolution we have measured the current in the panel and the spectrally resolved light emission from the panel as a function of applied voltage. This study of a helium-filled conventional PDP is designed to provide data needed for improved modeling calculations of the plasma discharge. The ultimate goal is to achieve improved designs and efficacies for large-screen color PDP's 相似文献
414.
Clifton E. F. Rickard Warren R. Roper Alex Williamson L. James Wright 《Angewandte Chemie (International ed. in English)》1999,38(8):1110-1113
Support for key steps of the mechanism for the transition metal catalyzed hydroboration reaction is provided by the characterization and reactions of 1 , a cis-(boryl)(aryl) complex of osmium(II ). This compound readily eliminates o-tolylBcat to give the osmium(0) intermediate 2 , which in the presence of HBcat reestablishes the osmium–boron bond by forming 3 . R=o-tolyl, H2cat=catechol=1,2-(HO)2C6H4. 相似文献
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417.
The synthesis of high molecular weight star-shaped polymers comprising poly(1,3-cyclohexadiene-block-isoprene) diblock arms coupled to a divinyl benzene (DVB) core is reported. The number average molecular weights of the diblock arms were varied from 30000 to 50000 and the ratio of DVB to n-butyllithium (nBuLi) was systematically varied from 3:1 to 12:1. Size exclusion chromatography coupled with light scattering detection was utilized to detect the formation of star-shaped polymers and the presence of star-star coupling. The molecular weight distribution (<Mw>/<Mn>) of the star polymers ranged from 1.25 to 1.50. The effect of poly(1,3-cyclohexadiene) content on the mechanical properties of these novel elastomers is reported. The elastic modulus, elongation at break, and tensile strength of these elastomers were all found to be a function of the percentage of poly(1,3-cyclohexadiene). The glass transition temperatures were determined using both differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Atomic force microscopy was performed in the tapping mode (TMAFM) to verify the presence of microphase separation. 相似文献
418.
Jared S. Wood Guilherme Dal Poggetto Xiao Wang Mikhail Reibarkh R. Thomas Williamson Ryan D. Cohen 《Magnetic resonance in chemistry : MRC》2023,61(1):22-31
Chloride is the most common counterion used to improve aqueous solubility and enhance stability of small molecule active pharmaceutical ingredients. While several analytical techniques, such as titration, HPLC with charged aerosol detection, and ion chromatography, are currently utilized to assay the level of chloride, they have notable limitations, and these instruments may not be readily available. Here, we present a generally applicable 35Cl solution NMR method to assay the level of chloride in pharmaceutical compounds. The method uses KClO4 as an internal standard for improved accuracy in comparison with external standard methods, and it was found to be robust, linear over three orders of magnitude, precise (<3% RSD), and accurate (<0.5% absolute error). 相似文献