全文获取类型
收费全文 | 88篇 |
免费 | 1篇 |
国内免费 | 1篇 |
专业分类
化学 | 74篇 |
物理学 | 16篇 |
出版年
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2018年 | 2篇 |
2017年 | 4篇 |
2016年 | 3篇 |
2014年 | 2篇 |
2013年 | 2篇 |
2012年 | 2篇 |
2011年 | 7篇 |
2010年 | 3篇 |
2009年 | 5篇 |
2008年 | 6篇 |
2007年 | 4篇 |
2006年 | 4篇 |
2005年 | 7篇 |
2004年 | 5篇 |
2003年 | 1篇 |
2002年 | 2篇 |
2001年 | 1篇 |
2000年 | 5篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有90条查询结果,搜索用时 31 毫秒
1.
A series of commercial monomeric and polymeric C(18), C(27), and C(30) stationary phases were compared with immobilized poly(ethylene-co-acrylic acid) stationary phases synthesized in-house. The columns were characterized on the basis of methylene selectivity, silanol activity, metal activity, pore size, shape selectivity, and the ability to separate tocopherol isomers and carotenoid isomers. Monomeric and polymeric C(30) phases were shown to yield excellent separations of the tocopherol isomers while the polymeric C(30) and polyethylene phases were more appropriate to the separation of carotenoids. 相似文献
2.
High-speed counter-current chromatography was successfully applied for the first time to the isolation and purification of the bioactive carotenoid zeaxanthin from the cyanobacterium Microcystis aeruginosa. The crude zeaxanthin was obtained by extraction with organic solvents after the microalgal sample had been saponified. Preparative high-speed counter-current chromatography with a two-phase solvent system composed of n-hexane-ethyl acetate-ethanol-water (8:2:7:3, v/v/v/v) was successfully performed yielding zeaxanthin at 96.2% purity from 150 mg of the crude extract in a one-step separation. The recovery of zeaxanthin was 91.4%. This was also the first report that zeaxanthin was successfully separated and purified from microalgae. 相似文献
3.
Socaciu C Jessel R Diehl HA 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2000,56(14):133-2809
The carotenoids beta-carotene (BC), lycopene (LYC), lutein (LUT), zeaxanthin (ZEA), canthaxanthin (CTX) and astaxanthin (ASTA) have been incorporated into pig liver microsomes. Effective incorporation concentrations in the range of about 1-6 nmol/mg microsomal protein were obtained. A stability test at room temperature revealed that after 3 h BC and LYC had decayed totally whereas, gradually, CTX (46%), LUT (21%), ASTA (17%) and ZEA (5%) decayed. Biophysical parameters of the microsomal membrane were changed hardly by the incorporation of carotenoids. A small rigidification may occur. Membrane anisotropy seems to offer only a small tolerance for incorporation of carotenoids and seems to limit the achievable incorporation concentrations of the carotenoids into microsomes. Microsomes instead of liposomes should be preferred as a membrane model to study mutual effects of carotenoids and membrane dynamics. 相似文献
4.
Horst Pommer 《Angewandte Chemie (International ed. in English)》1977,16(7):423-429
The effects of a scientific discovery on industrial practice are illustrated with reference to the Wittig reaction. The aim of utilizing the Wittig reaction of linking terpenoid building blocks to give vitamin A and carotenoids on an industrial scale prompted extensive research and development work of a synthetic and chemical engineering nature. The importance of the Wittig reaction and its variants in the synthesis of active compounds and fine chemicals in industrial research is demonstrated in the present article. 相似文献
5.
Summary Reinvestigation by HPLC of the petals ofLilium tigrinum and the isolation of some minor compounds is reported. Using HPLC-controlled, preparative-column chromatography, 5,6-diakarpoxanthin
(6), 6-epikarpoxanthin (2), 5,6-diacapsokarpoxanthin (8), and 9Z-antheraxanthin (9Z-13) were isolated and characterized. Based on spectroscopic data the absolute configurations of6 and8 were identical with those originating from paprika, thus the 5,6-diakarpoxanthin (6) and 5,6-diacapsokarpoxanthin (8) have the 3S, 5S, 6S configuration and 6-epikarpoxanthin (2) has the 3S, 5R, 6S configuration.
Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997. 相似文献
6.
Alain Valla Benoist Valla Régis Le Guillou Dominique Cartier Laurent Dufossé Roger Labia 《Helvetica chimica acta》2007,90(3):512-520
Since the C15 β‐end‐group aldehyde 10 ((β‐ionylidene)acetaldehyde), an excellent intermediate in the syntheses of retinoids, can be synthesized in many ways from β‐ionone, and since the corresponding acyclic C15 ψ‐end‐group aldehyde 5 can easily be synthesized from citral ( 1 ) (Scheme 3), we applied the C15+C5 route to the syntheses of γ‐retinal ((all‐E)‐ 8 ) (Scheme 3) and retinal ((all‐E)‐ 13 ) (Scheme 4), and therefore, by coupling (2×C20→C40), to the preparation of lycopene ( 14 ) and β‐carotene ( 15 ) (Scheme 5). Our new syntheses of retinal ((all‐E)‐ 13 ) and γ‐retinal ((all‐E)‐ 8 use an extended aldol reaction with a C6 building block that incorporates a C5 unit after decarboxylation. 相似文献
7.
In this work, different extracts from the microalga Spirulina platensis are obtained using pressurized liquid extraction (PLE) and four different solvents (hexane, light petroleum, ethanol and water). Different extraction temperatures (115 and 170 degrees C) were tested using extraction times ranging from 9 to 15 min. The antioxidant activity of the different extracts is determined by means of an in vitro assay using a free radical method. Moreover, a new and fast method is developed using micellar electrokinetic chromatography with diode array detection (MEKC-DAD) to provide a preliminary analysis on the composition of the extracts. This combined application (i.e., in vitro assays plus MEKC-DAD) allowed the fast characterization of the extracts based on their antioxidant activity and the UV-vis spectra of the different compounds found in the extracts. To our knowledge, this work shows for the first time the great possibilities of the combined use of PLE-in vitro assay-MEKC-DAD to investigate natural sources of antioxidants. 相似文献
8.
《Electrophoresis》2017,38(6):886-896
This paper describes an analytical approach, based on LC‐diode array detector‐MS/MS (LC‐DAD‐MS/MS), for characterizing the fat‐soluble micronutrient fraction in rainbow trout (Oncorhynchus mykiss ). Two different procedures were applied to isolate the analytes from liver and muscle tissue: overnight cold saponification to hydrolyze bound forms and to simplify the analysis; matrix solid‐phase dispersion to avoid artifacts and to maintain unaltered the naturally occurring forms. Analytes were separated on a C30 analytical column by using a nonaqueous reversed mobile phase compatible with the atmospheric pressure chemical ionization. Compared to other works, the most relevant advantage of the here illustrated method is the large amount of information obtained with few analytical steps: nine fat‐soluble vitamins (3,4‐dehydroretinol, retinol, cholecalciferol, ergocalciferol, α‐tocopherol, γ‐tocopherol, δ‐tocopherol, phylloquinone, and menaquinone‐4) and eight carotenoids (all‐trans ‐lutein, all‐trans ‐astaxanthin, all‐trans ‐zeaxanthin, all‐trans ‐β‐cryptoxanthin, all‐trans ‐canthaxanthin, all‐trans ‐ζ‐carotene, all‐trans ‐β‐carotene, and all‐trans ‐γ‐carotene) were quantified after the method validation, while other untargeted carotenoids were tentatively identified by exploiting the identification power of the LC‐DAD‐MS/MS hyphenation. 相似文献
9.
Stefanie Breukers Christer L. Øpstad Hans‐Richard Sliwka Vassilia Partali 《Helvetica chimica acta》2009,92(9):1741-1747
The oft‐claimed ‘good’ water solubility of the food color norbixin ( 3 ) could not be confirmed. In contrast, the potassium salt 5 of norbixin formed suitable dispersions. The surface and aggregation properties of salt 5 were investigated and compared with other naturally occurring and synthetic hydrophilic carotenoids (Table). 相似文献
10.
Antonio J. Meléndez‐Martínez Maria L. Escudero‐Gilete Isabel M. Vicario Francisco J. Heredia 《Journal of separation science》2009,32(11):1838-1848
The efficiency of C30 stationary phases in the separation of carotenes and diverse hydroxycarotenoids has been the subject of several studies. However, little is known concerning their ability to resolve epoxycarotenoids isomers, whose study is of great importance due to the functions they serve and the information they can reveal concerning the processing of foods. We have concluded that C30 columns provide an excellent separation of structural, geometrical and optical isomers of epoxycarotenoids and that the presence of 5,8‐epoxide groups leads to a better shape recognition, to the extent that over 10 geometrical–optical isomers of 5,8‐epoxycarotenoids have been separated. Additionally, it was observed that these carotenoids elute later than their 5,6‐epoxide counterparts, albeit the latter have a longer chromophore. 相似文献