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排序方式: 共有566条查询结果,搜索用时 15 毫秒
91.
《Journal of magnetic resonance. Series B》1993,101(3):229-239
New pulse sequences for the selective excitation and editing of NMR spectra of protons directly bonded to carbon-13 in CH, CH2, and CH3 groups are described. Experimental results as well as theoretical calculations demonstrate that these sequences have excitation profiles of about ±0.5JCH or less and require no pulse shaping or special hardware to implement. After the isotope-directed excitation of the protons has been generated, the proton magnetization may be relayed to other protons via an isotropic mixing sequence to yield 1D HOHAHA subspectra or 2D COSY subspectra. Examples of applications to compounds containing carbon-13 either at natural abundance or with enrichment are shown. 相似文献
92.
93.
94.
Atmospheric pressure needle-to-plane discharges have been explored experimentally in electrode gaps from 100 μm to 400 μm. These discharges can be self-sustained and follow the form of existing empirical formulae describing the current-voltage characteristics of corona discharge. The discharge can also be self-sustained by its lower sustaining voltage applied between the two electrodes once it is ignited by the initial high output voltage from power supply. The experiments of charging aerosol particles by the self-sustaining discharge operating with a lowered power have shown that for particles with a diameter of 46 nm, the charging efficiency attained 43.6%. 相似文献
95.
对4种二烯丙基甲基烷基(n=12,14,16,18)溴化铵(标记为C12,C14,C16,C18)的性质与性能进行了研究。 通过测定其热稳定性、表面活性和絮凝性能,考察产物结构对其性质与性能的影响规律。 结果表明,季铵盐C12~C18的主要分解温度分别为170~300 ℃、172~303 ℃、170~293 ℃和170~310 ℃,对应失重率分别为92.8%、92.6%、96.4%和87.4%;临界胶束浓度(cmc)和临界胶束浓度下的表面张力(γcmc)分别为5.2、3.5、1.4、1.1 mmol/L和26.6、25.2、33.8、35.8 mN/m,显示出较高的表面活性;季铵盐C16的发泡与稳泡性能最好,C12的Krafft点<0 ℃,C14、C16和C18的Krafft点分别为1、8和19 ℃; C12和C14分别对膨润土和高岭土的絮凝能力最强,表明单体的絮凝性能具有结构选择性。 相似文献
96.
Ling Zhou Bing-hua Sun Zhong-ying Jiang Jian-guo Zhang Hai-ying Gu 《Physica A》2009,388(15-16):3093-3099
We construct a functional for amphiphile–polymer mixtures and investigate the demixing transition by using a proposed version of density functional theory. It is found that increase of the amphiphilic size ratio and polymer length can effectively promote phase separation of the systems. Phase diagrams are plotted to clarify these influences. The results provide an effective way of controlling the stability of the fluid–fluid phase equilibrium of the mixtures. 相似文献
97.
98.
多孔硅拉曼光谱随激发功率变化的研究 总被引:2,自引:0,他引:2
用阳极氧化法新制备了多孔硅样品,以457.5nm固体激光器为激发光源,在不同激发功率下,获得了拉曼谱图和一些谱峰参量随激光功率的变化关系。解释了520cm^-1和300cm^-1附近拉曼峰随功率变化的一系列可逆的实验现象:随激光功率升高出现的红移和非对称性展宽,主要是由于样品局域平均粒径变小而受量子限域效应的影响导致的;样品局域平均粒径在表面上的二维减小与随激光功率升高而导致的局域温升并不违背基本的热力学定律;高功率时520cm^-1附近双峰的出现是由于多孔硅样品局域平均粒径达到一定阈值而导致的纵模和横模双声子模的分裂。 相似文献
99.
The effects of temperature and common ions on binding of puerarin to bovine serum albumin (BSA) are investigated. The binding
constants (K
a) between puerarin and BSA are 1.13×104 L⋅mol−1 (20 °C) and 1.54×104 L⋅mol−1 (30 °C), and the number of binding sites (n) is (0.95±0.02). However, at a higher temperature (40 °C) the stability of the puerarin–BSA system decreases, which results
in a lower binding constant (1.58×103 L⋅mol−1) and number of binding sites (n=0.73) of the puerarin–BSA system. However, the presence of Cu2+ and Fe3+ ions increases the binding constants and the number of binding sites in the puerarin–BSA complex. 相似文献
100.
Hui Cao Donghui Wu Hongxian Wang Ming Xu 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,73(5):972-975
In this paper, two flavonoid aglycones (baicalein, quercetin) and their glycosides (baicalin, quercitrin) were studied for their ability to bind protein by quenching the protein intrinsic fluorescence. From the spectra obtained, the bimolecular quenching constants, the apparent static binding constants, and binding sites values were calculated. The glycosylation of flavonoids decreases the binding affinity with protein. For quercetin and quercitrin, the binding constants for BSA were 3.65 × 107 and 6.47 × 103 L mol−1, respectively. For baicalein and baicalin, the binding constants were 4.54 × 108 and 1.63 × 106 L mol−1, respectively. 相似文献