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A new and simple method, based entirely on a physical approach, was proposed to produce activated carbon from longan fruit seed with controlled mesoporosity. This method, referred to as the OTA, consisted of three consecutive steps of (1) air oxidation of initial microporous activated carbon of about 30% char burn-off to introduce oxygen surface functional groups, (2) the thermal destruction of the functional groups by heating the oxidized carbon in a nitrogen atmosphere at a high temperature to increase the surface reactivity due to increased surface defects by bond disruption, and (3) the final reactivation of the resulting carbon in carbon dioxide. The formation of mesopores was achieved through the enlargement of the original micropores after heat treatment via the CO2 gasification, and at the same time new micropores were also produced, resulting in a larger increase in the percentage of mesopore volume and the total specific surface area, in comparison with the production of activated carbon by the conventional two-step activation method using the same activation time and temperature. For the activation temperatures of 850 and 900 °C and the activation time of up to 240 min, it was found that the porous properties of activated carbon increased with the increase in activation time and temperature for both preparation methods. A maximum volume of mesopores of 0.474 cm3/g, which accounts for 44.1% of the total pore volume, and a maximum BET surface area of 1773 m2/g was achieved using three cycles of the OTA method at the activation temperature of 850 °C and 60 min activation time for each preparation cycle. The two-step activation method yielded activated carbon with a maximum mesopore volume of 0.270 cm3/g (33.0% of total pore volume) and surface area of 1499 m2/g when the activation temperature of 900 °C and a comparable activation time of 240 min were employed. Production of activated carbon by the OTA method is superior to the two-step activation method for better and more precise control of mesopore development.  相似文献   
2.
为提高龙眼愈伤组织中单宁的提取率,采用超声波辅助浸提法,基于乙醇浓度(A)、超声波功率(B)与提取时间(C) 3个单因素试验,通过响应面试验优化设计,建立了龙眼愈伤组织单宁提取工艺。 研究结果表明,龙眼愈伤组织中单宁的最佳提取条件为乙醇浓度61%、超声波功率140 W,提取时间54 min,提取温度60 ℃,在此工艺条件下,提取量为7.53 mg·g-1。  相似文献   
3.
From the extracts of Dimocarpus longan Lour leaves, 2 unusual flavonol glycosides, quercetin 3-O-(3″-O-2?-methyl-2?-hydroxylethyl)-β-d-xyloside (1) and quercetin 3-O-(3″-O-2?-methyl-2?-hydroxylethyl)-α-l-rhamnopyranoside (2), as well as 10 known compounds including 2 flavonol glycosides, afzelin (3) and kaempferol-3-O-α-l-rhamnopyranoside (4), 2 flavans, ( ? )-epicatechin (5) and proanthocyanidin A-2 (6), 3 triterpenoids, friedelin (7), epifriedelanol (8) and β-amyrin (9), a peptide, N-benzoylphenylalanyl-N-benzoylphenylalaninate (10), and 2 sterols, β-sitosterol (11) and daucosterol (12) were isolated and identified by using combination of mass spectrometry and various 1D and 2D NMR techniques. This is the first report of flavonoid glycosides possessing a 2-methyl-2-hydroxylethoxyl group in sugar moiety from D. longan.  相似文献   
4.
A large quantity of longan fruits (Dimocarpus longan Lour.) produced annually are processed into many products, one of which is black longan, from which the dried, dark-brown meat has been used medicinally in traditional medicine, while the starch-containing seeds are discarded. In this study, starch samples (BLGSs) were isolated from seeds of black longan fruits prepared using varied conditions. The in vitro digestibility was determined in comparison with those extracted from fresh (FLGS) and dried (DLGS) seeds. Scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy were employed to evaluate the starch properties. The results showed that the yields of FLGS, DLGS, and BLGSs were 20%, 23%, and 16–22% w/w, respectively. SEM images showed starch granules of mixed shapes, with sizes up to 15 µm in all samples. XRD patterns confirmed an A-type crystallinity for FLGS and DLGS, with strong refraction peaks at 2θ = 15°, 17°, 18°, and 23°, while BLGSs also showed detectable peaks at 2θ = 10° and 21°, which suggested V-type structures. Thermal properties corroborated the changes by showing increases in peak gelatinization temperature (Tp) and enthalpy energy (ΔH) in BLGSs. The paste viscosity of BLGSs (5% w/w) decreased by 20–58% from that of FLGS. The FTIR peak ratio at 1045/1022 and 1022/995 cm−1 also indicated an increase in ordered structure in BLGSs compared to FLGS. The significant increase in the amounts of slowly digestible starch (SDS) and resistant starch (RS) in BLGSs compared to FLGS, especially at a prolonged incubation time of 20 (4.2×) and 30 days (4.1×), was proposed to be due to the heat-induced formation of starch inclusion with other components inside the seed during the black longan production process. Thus, black longan seed could be a new source of starch, with increased RS content, for potential use in the food and related industries.  相似文献   
5.
龙眼三萜-A的晶体结构   总被引:3,自引:0,他引:3  
用直接法测定了龙眼三萜-A的晶体结构。晶体属单斜晶系, 空晶群C2, 晶胞参数:a=1.3419(4), b=0.6422(2), c=2.9586(7)nm, β=91.91(2)°, Vc=2.548(1)nm^3;z=4, Dc=1.12g/cm^3, Dm=1.10g/cm^3, F(000)=960。结构在MICRO VAX 计算机上用TEXSAN程序包求解、晶体结构用全矩阵最小二乘法修正, 得到最后的偏离因子R=0.068。  相似文献   
6.
In this study, longan juice was subjected to a high pressure of 500 MPa for 30 min and compared with a juice pasteurized at 90°C/2 min. Probiotic Lactobacillus casei 01 was fortified into both juices and the shelf life of these products was studied. Their bioactive components such as ascorbic acid, gallic acid and ellagic acid were analyzed by High Performance Liquid Chromatography (HPLC). Total phenolic compounds and 2,2-Diphenyl-1-picrythydrazyl radical-scavenging activity were determined by colorimetric and spectrophotometric methods. It was found that the pressurized longan juice retained higher amounts of bioactive compounds than the pasteurized juice. In terms of storage stability, bioactive compounds in both processed juices decreased according to the increase in storage time. The survivability of probiotic L. casei 01 in both processed juices declined from 9 to 6 log CFU/mL after 4 weeks of storage.  相似文献   
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