排序方式: 共有27条查询结果,搜索用时 15 毫秒
11.
Two new compounds,oleanolic acid 28-O- β-D-glucopyranosyl-3-O-α-L-arabinopyranosyl-(1→3)-(6′-butyl ester)-β-D-glucuropyranoside 1,oleanolic acid 28-O-β-D-glucopyranosyl(1→6)-β-D-glucopyranoside 2 have been isolated from the roots of Hemsleya penxianensis var.gulinensis.Their structures were determined on the bases of the spectral and chemical evidences. 相似文献
12.
本文在灵敏度、精密度、检出限、抗干扰能力,以及操作简易性和稳定性方面比较了流动注射氢化物发生法中膜分相器和U管分相器的分析性能。结果表明,两种分相器各有优缺点,均能满足地球化学样品分析的要求。但膜的寿命短,需经常更换,是膜分相器的不足之处。 相似文献
13.
CHIU Chris 《高等学校化学研究》2001,17(3)
In order to protect polymers or coatings from the damage by sun light, scientists have created the UV Absorber to complete the task. The first commercialized UV absorber (UVA) is based on a benzophenone structure and was developed by American Cyanamid (UV 531), circa 1955, and is still the leading UVA for flexible PVC. The most powerful UVA is of the triazine type, developed by American Cyanamid (UV 1164) and commercialized in 1987. 相似文献
14.
Kuo-Shou CHIU 《数学物理学报(B辑英文版)》2018,38(1):220-236
In this paper, we investigate the existence, uniqueness and the asymptotic equivalence of a linear system and a perturbed system of differential equations with piecewise alternately advanced and retarded argument of generalized type (DEPCAG). This is based in the study of an equivalent integral equation with Cauchy and Green matrices type and in a solution of a DEPCAG integral inequality of Gronwall type. Several examples are also given to show the feasibility of results. 相似文献
15.
The adaptive-passive vibration absorber shows promise for combining the stability and low complexity of passive tuned absorbers with the robust performance of active vibration control schemes. Previous adaptive tuned vibration absorbers (ATVA) had been complex and bulky. Shape memory alloys (SMA), with their variable material properties, offer an alternative adaptive mechanism. Heating an SMA causes a change in the elastic modulus of the material. An ATVA using spring elements composed of three pairs of SMA wires and one pair of steel wires was constructed and tested. On-off actuation of the SMA elements created an ATVA with four discrete tuned frequencies. Characterization testing of the absorber showed variation of the natural frequency of the ATVA of approximately 15%. The ATVA was applied to a primary system and the frequency response of the system at various states of ATVA actuation was determined. Manual tuning of the ATVA actuation during a stepped-sine base excitation of the primary system showed a wider notch of attenuation than was possible with a non-adaptive absorber. Results of the tests indicate that an adaptive absorber incorporating SMA as a tuning element has potential as a simple, high-performance adaptive-passive technique for vibration control. 相似文献
16.
YaCHEN MingHuaCHIU KunGU ZhongRongLI 《中国化学快报》2003,14(5):475-478
From rhizomes of Hemsleya giganthy collected in Shichuan of China,16 compounds were isolated.Among them,three compounds (8,9,15)are new natural products called Hemslecins G;Hemsgiganosides A and B;respectively.Their structures were elucidated as 7-hydroxy-23,24-dihydro-cucurbitacin F-25-O-acetate(8);3-O-(6‘‘‘‘‘‘‘‘-butyl ester-)-β-D-glu-curono-pyranosyl)-oleanolic acid-28-O-α-L-arabinopyranoside(9);3-O-β-D-glucuropyranosyl oleanolic acid-28-O-β-D-gluco pyranosyl-(1→6)-β-D-glucopyranoside(15)by spectroscopic and chemical means. 相似文献
17.
用从头算方法讨论了大气臭氧层主要破坏物ClONO2在光照下分解反应途径:ClONO2→ClO+NO2的反应机理.该反应的2个过渡态ClO…NOO(TS2a)和OCI…NOO(TS2b)中TS2a能垒较高,始态难于越过如此高的势垒;TS2b势垒较低,而产物到过渡态TS2b的能垒也仅有1.20 eV,故预测该反应为一个可逆反应. 相似文献
18.
SHA Chin-Kang CHIU Rei-Torng LIH Shinn-Horng SANTHOSH K. C. CHANG Ching-Jung TSENG Wei-Hong HO Wen-Yueh 《有机化学》2003,23(Z1):67-67
Intramolecular radical cyclization reactions are now used routinely to synthesize carbocyclic and heterocyclicstructures. We have reported that α-carbonyl radicals 1, generated from the corresponding iodo ketones or enones,underwent intramolecular radical cyclization smoothly to afford products 2. [1,2] 相似文献
19.
Vitamin E is widely used in pharmaceutical, food and cosmetic preparations.This paper discusses methods of preparing vitamin E emulsions by using sulfobetaine (SB) zwitterionic surfactants which have high electrolyte tolerance. The amount of vitamin E dissolved in water was analyzed by turbidity and UV absorption measurements. The emulsion droplet size was determined by laser light scattering. Microemulsions with small particle size and high resistance to oxidation in air can be obtained by solubilizing vitamin E in SB solutions at high concentrations (above %) The performance of a series of SB surfactants is compared in 1.5% solutions. A SB surfactant with a 12 carbon chain seems to be the most effective in dissolving vitamin E. The saturation value of vitamin E is increased about one order of magnitude by adding NaCl to the SB surfactant solutions. Emulsions formed in surfactant solutions containing NaCl (0 4-0.6 M) are stable at low surfactant concentrations such as 0.2-0.4 % The emulsion droplet sizes are below or around 200nm. 相似文献
20.
The purpose of this investigation is to study the convective heat transfer from a horizontal circular cylinder under the effect of a solid plane wall. The full Navier–Stokes and energy equations for two-dimensi onal steady flow are solved by a finite element method. The variations in surface shear stress, local pressure and Nusselt number around the surface of the cylinder as well as the predicted values of average Nusselt number, location of separation and some flow and temperature fields are presented. It is found that the average Nusselt number and drag force increase as the gap between the cylinder and the wall is increased. 相似文献