首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   47篇
  免费   3篇
  国内免费   1篇
化学   45篇
综合类   3篇
物理学   3篇
  2022年   7篇
  2021年   1篇
  2020年   1篇
  2019年   1篇
  2018年   3篇
  2017年   1篇
  2015年   3篇
  2014年   1篇
  2013年   1篇
  2012年   3篇
  2011年   2篇
  2010年   1篇
  2009年   3篇
  2008年   5篇
  2007年   2篇
  2006年   4篇
  2005年   1篇
  2004年   4篇
  2002年   2篇
  2000年   1篇
  1997年   2篇
  1995年   1篇
  1992年   1篇
排序方式: 共有51条查询结果,搜索用时 46 毫秒
1.
In the present work, the extraction process of total flavonoids (TFs) from X. sorbifolia flowers by ultrasound-assisted extraction was optimized under the response surface methodology (RSM) on the basis of single-factor experiments. The optimal extraction conditions were as follows: ethanol concentration of 80%, solid–liquid ratio of 1:37 (g/mL), temperature of 84 °C, and extraction time of 1 h. Under the optimized conditions, the extraction yield of the TFs was 3.956 ± 0.04%. The radical scavenging capacities of TFs against 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) were much greater than that of rutin. The results of antibacterial experiments indicated that the TFs displayed strong inhibitory activities on E. coli, S. aureus and Bacillus subtilis. Therefore, X. sorbifolia flowers can be used as a novel source of natural flavonoids, and the TFs have potential applications as natural antioxidants or antibacterial agents in the food and pharmaceutical industries.  相似文献   
2.
Salvia miltiorrhiza Bunge (SM) has been extensively used in Alzheimer’s disease treatment, the permeability through the blood-brain barrier (BBB) determining its efficacy. However, the transport mechanism of SM components across the BBB remains to be clarified. A simple, precise, and sensitive method using LC-MS/MS was developed for simultaneous quantification of tanshinone I (TS I), dihydrotanshinone I (DTS I), tanshinone IIA (TS IIA), cryptotanshinone (CTS), protocatechuic aldehyde (PAL), protocatechuic acid (PCTA), and caffeic acid (CFA) in transport samples. The analytes were separated on a C18 column by gradient elution. Multiple reaction monitoring mode via electrospray ionization source was used to quantify the analytes in positive mode for TS I, DTS I, TS IIA, CTS, and negative mode for PAL, PCTA, and CFA. The linearity ranges were 0.1–8 ng/mL for TS I and DTS I, 0.2–8 ng/mL for TS IIA, 1–80 ng/mL for CTS, 20–800 ng/mL for PAL and CFA, and 10–4000 ng/mL for PCTA. The developed method was accurate and precise for the compounds. The relative matrix effect was less than 15%, and the analytes were stable for analysis. The established method was successfully applied for transport experiments on a BBB cell model to evaluate the apparent permeability of the seven components.  相似文献   
3.
A simple and accurate HPLC method with refractive index detection was developed to determine the main fatty acid methyl esters in biodiesel produced from yellow horn oil. Methyl linoleate, methyl linolenate, methyl arachidate, methyl stearate, methyl palmitate and methyl oleate were separated on a HIQ SIL C18W column using methanol as mobile phase. The method has good repeatability and precision, the intraday and interday RSD for both retention time and peak area was less than 3.2%. The LOD (S/N = 3) and LOQ (S/N = 9) were less than 0.004 and 0.015 mg mL−1, respectively.  相似文献   
4.
利用响应面法研究了翻白草总黄酮的微波辅助提取工艺.在单因素试验的基础上,以乙醇体积分数、液固比、提取温度、微波时间为自变量,总黄酮的得率为响应值,研究各因素及其交互作用对黄酮得率的影响.结果表明其最佳提取条件是:乙醇体积分数55%、液固比32 m L/g、温度82℃、微波时间10 min.此条件下,翻白草中黄酮的提取率为6.96 mg/g,与理论预测值基本吻合.  相似文献   
5.
The structure of the new cycloartane glycoside cyclomacroside D, which was isolated from Astragalus macropus Bunge (Leguminosae) and is 24R-cycloartan-1α,3β,7β,24,25-pentaol 3-O-α-L-rhamnopyranoside–24-O-β-D-xylopyranoside, was proved. Presented at the 7th International Symposium on the Chemistry of Natural Compounds (SCNC, Tashkent, Uzbekistan, October 16–18, 2007). Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 48–50, January–February, 2009.  相似文献   
6.
Chen J  Wang F  Lee FS  Wang X  Xie M 《Talanta》2006,69(1):172-179
High-speed counter-current chromatography (HSCCC) technique in semi-preparative scale has been applied to separate and purify salvianolic acids from the water extract of Danshen, Salvia miltiorrhiza Bunge. High efficiency HSCCC separation was achieved on a two-phase solvent system composed of a mixture of n-hexane-ethyl acetate-water-methanol (1.5:5:5:1.5, v/v) by eluting the lower mobile phase at a flow-rate of 1.7 ml/min and a revolution of 850 rpm. A total of five well separated peaks were obtained in the HSCCC chromatogram, and their purities determined by HPLC-UV absorption. These peaks were characterized by UV-vis spectra and ESI-MS, and the data compared with the reference standards. Salvianolic acid B was positively identified as one of the major peaks. Three of the remaining four peaks were also tentatively identified as rosmarinic acid, lithospermic acid, and salvianolic acid E, an isomer of salvianolic acid B, all are members of the salvianolic acids group. In a typical run, tens of milligrams of samples can be separated with high efficiency to yield tens of milligrams of purified materials with over 98% purity. HSCCC thus provides a cost-effective alternative to preparative scale HPLC for the semi-preparative scale separation and purification of salvianolic acids in Danshen. With appropriate modifications, the technique should also be applicable to other herbs in general.  相似文献   
7.
测定七叶树制剂中七叶皂苷Ia含量的高效液相色谱法   总被引:4,自引:0,他引:4  
建立了利用七叶皂苷Ia作为指标性成分测定制剂中七叶皂苷含量的方法,采用ODS柱,乙腈-0.02%(ф)磷酸(体积比37:63)为流动相,在210nm进行测定;该法的回收率为96%-98%,RSD为0.8%(n=5);实验表明该法简便、快速、适用性好。  相似文献   
8.
用GC/MS分析几种葱属植物挥发油中的有机硫化物   总被引:3,自引:0,他引:3  
采用蒸汽蒸馏的方法,分别提取了大葱(Allium fistulosum L)、薤白(Allium macrostemonBunge)和大蒜(Allium sativum L)中的挥发油,用GC/MS方法鉴别了它们中的主要硫化合物,并进行了比较。  相似文献   
9.
Sedum sarmentosum Bunge (SSB) is a traditional Chinese herbal medicine containing multiple components that has been extensively used clinically to treat chronic viral hepatitis and some inflammatory diseases. Total flavonoids are major pharmacologically active components of SSB. To gain a deeper understanding of SSB resources, we analyzed eight chemical constituents in 33 batches of SSB from 11 regions in China. An accurate, precise and sensitive ultra‐high‐performance liquid chromatography coupled with triple quadrupole electrospray tandem mass spectrometry method was developed for the determination of eight flavonoids in SSB. Under the optimized chromatographic conditions, good separation for the eight target components was obtained on an Agilent Zobax SB C18 (50 × 2.1 mm, 5 μm) column within 4 min. The established methods were validated with good linearity (r ≥ 0.9988), precision (RSD ≤ 2.68%), stability (1.43–3.28%) and repeatability (1.14–2.89%). Moreover, the average recoveries were 95.91–100.68%, and the RSDs were 1.50–3.80%. In addition, the analytical conditions of UPLC–ESI–MS/MS provided better sensitivity with a shorter analysis time when compared with the HPLC–DAD method. Hierarchical clustering analysis and principal component analysis were performed to estimate and classify these samples based on the contents of the eight chemical constituents. This study provided the theoretical basis and scientific evidence for the development and utilization of SSB resources.  相似文献   
10.
浙江槭属植物新记录   总被引:1,自引:0,他引:1  
作为浙江槭属植物区系的补充,报道了浙闽槭Acer johnedwardianum F.P.Metcalf、乳源槭A. chunii Fang和九江三角枫A. buergerianum Miq. var. jiujiangense Z.X. Yu 3个植物分布新记录;补充描述了浙闽槭、乳源槭花的形态特征;恢复了浙闽槭的种级地位。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号