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21.
This work has been developed using a sylvestral fruit tree, native to the Brazilian forest, the Eugenia uniflora L., one of the Mirtaceae family. The main goal of the analytical study was focused on extraction methods themselves. The method development pointed to the Clevenger extraction as the best yield in relation to SFE and Soxhlet. The SFE method presented a good yield but showed a big amount of components in the final extract, demonstrating low selectivity. The essential oil extracted was analyzed by GC/FID showing a large range of polarity and boiling point compounds, where linalool, a widely used compound, was identified. Furthermore, an analytical solid phase extraction method was used to clean it up and obtain separated classes of compounds that were fractionated and studied by GC/FID and GC/MS. 相似文献
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Mendes Isolda C. Teixeira Letícia R. Lima Rejane Carneiro Tânia G. Beraldo Heloisa 《Transition Metal Chemistry》1999,24(6):655-658
Seven platinum(II) complexes isolated from thiosemicarbazones derived from 2-, 3- and 4-formylpyridine and 2-, 3-, and 4-acetylpyridine have been characterised by microanalyses, molar conductivities and by their i.r. and 1H-n.m.r. spectra. 相似文献
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Alexandru L. Let Colin J. Rix Pandiyan Murugaraj 《Journal of Physics and Chemistry of Solids》2007,68(7):1428-1435
Titanium tetraisopropoxide reacts with hydrogen sulfide in butylamine solvent at room temperature to form an amorphous titanium alkoxy-sulfide which can be converted to crystalline titanium disulfide by heat treatment in a flowing hydrogen sulfide gas stream. The reaction has been studied using infrared and Raman spectroscopy, gas chromatography-mass spectrometry, X-ray diffractometry and energy-dispersive X-ray analysis measurements. Based on these studies, it is shown that a partially thiolysed alkoxide precursor forms through the replacement of a limited number of alkoxy groups by hydrosulfide moieties. This alkoxy-hydrosulfide is believed to form following a thiolysis-condensation mechanism similar to the hydrolysis-condensation process that occurs during the corresponding oxide sol-gel reaction. The alkoxy-hydrosulfide species can then be completely thiolysed at 800 °C in a stream of hydrogen sulfide to yield pure, hexagonal titanium disulfide in either film or particulate form. 相似文献
26.
Biosynthesis of Bromoroquefortines in a High Saline Medium by Penicillium chrysogenum,a Terrestrial Endophyte Collected from Coffea arabica
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José Vinicius da Silva Taicia Pacheco Fill Letícia Veras Lotufo Cláudia do Ó. Pessoa Edson Rodrigues‐Filho 《Helvetica chimica acta》2014,97(10):1345-1353
Roquefortine C ( 1 ) and 11‐bromoroquefortine C ( 4 ) were isolated from Penicillium chrysogenum, an endophyte obtained from green leaves of Coffea arabica, during induction experiments by adding halide salts to the culture media. In our studies, 11‐bromoroquefortine D and 11‐bromo‐17‐hydroxybromoroquefortine C were identified by LC/HR‐MS. It is the first time that bromoroquefortine C and D are described as halogenated natural products. These halo alkaloids were shown to be biosynthesized from brominated tryptophan as the biosynthetic precursor. Cytotoxic and antibiotic assays using roquefortine C and 11‐bromoroquefortine C showed that the presence of the 11‐Br substituent impairs some biological activities of this alkaloid. 相似文献
27.
A new high-performance liquid chromatographic method was developed and validated for clopidogrel determination in pharmaceutical formulations. The system consisted of an ACE 5 octadecylsilane (C18; 150 x 4.6 mm id), 5.0 microm particle size column; methanol-0.1% triethylamine (75 + 25, v/v), pH 5.3, mobile phase at a flow rate of 1.2 mL/min; and a diode array detector set at 220 nm. Specificity, linearity, precision, accuracy, and robustness were the parameters evaluated. The retention time for clopidogrel was 6.8 min. To estimate specificity, an aqueous sample solution was subjected to degradation by ultraviolet light and by acid, alkaline, and oxidation media. The peaks of degradation products did not interfere with the compound signal, and there was no interference when a placebo solution was analyzed. Linearity over a concentration range of 10.0 to 90.0 microg/mL was shown (correlation coefficient = 0.9998). Low values of relative standard deviation indicated the adequate intraday and interday precision. The average recovery was found as 99.16%. In the robustness test, small modifications to the mobile phase composition did not affect the determination of clopidogrel. The proposed method proved to be simple, fast, and cost efficient for the intended use. 相似文献
28.
A new approach to the enzymatic production of conjugated linoleic acid (CLA) ascorbyl ester with a remarkably high volumetric productivity (120-200 g L(-1)) has been developed, in which strong solvation by tOMA.TFA (methyltrioctylammonium trifluoroacetate) enables a high concentration of ascorbic acid to be applied, and in which t-butanol enhances conversion by changing the equilibrium constant of the activity coefficients. This work has experimentally demonstrated the practicability of achieving efficient reactions of polar compounds at high concentrations in ionic liquids without significant loss of enzyme activity. 相似文献
29.
Nogueira FH Goulart Lde P César Ida C de Campos LM Pianetti GA 《Journal of AOAC International》2011,94(4):1089-1093
A simple HPLC method for determination of mefloquine hydrochloride in tablets was developed and validated. The separation was carried out on an Xterra RP18 (250 x 4.6 mm id, 5 pm particle size) analytical column. The mobile phase was 0.05 M monobasic potassium phosphate buffer (pH 3.5)-methanol (40 + 60, v/v). The flow rate and wavelength were set to 1 mL/min and 283 nm, respectively. The method was specific for mefloquine hydrochloride in the presence of hydrolytic, oxidative, and photolytic degradation products. It was also linear, precise, accurate, and robust, being suitable for routine QC analyses and stability studies. The developed HPLC method was compared to a previously described spectrophotometric method. 相似文献
30.
Determination of parabens in shampoo using high performance liquid chromatography with amperometric detection on a boron-doped diamond electrode 总被引:1,自引:0,他引:1
Martins I Carreira FC Canaes LS de Souza Campos Junior FA da Silva Cruz LM Rath S 《Talanta》2011,85(1):1-7
Methylparaben (MePa), ethylparaben (EtPa) and propylparaben (PrPa) have been widely used, among others, as chemical preservatives in cosmetics, drugs and foods. As these compounds are linked with allergies, dermatitis and estrogenic properties, it is necessary to control the concentration of these substances in different matrices. The aim of this paper are: to evaluate the electrochemical behavior of parabens on the boron-doped diamond (BDD) electrode and the development of a chromatographic method, with electrochemical detection (HPLC-ED), for determination of parabens in shampoo. A BDD (8000 ppm) electrode was adapted in a thin layer mode analytical cell consisting of a stainless steel and a platinum wire as reference and auxiliary electrodes, respectively. Chromatographic separations were obtained with a reversed phase C8 analytical column and a mobile phase of 0.025 mol L−1 disodium phosphate, pH 7.0, and acetonitrile (40:60, v/v), delivered at a flow rate of 1.0 mL min−1. Sample preparation was performed by solid phase extraction using C18 cartridges and acetonitrile for elution. Benzylparaben was employed as internal standard. The HPLC-ED method developed, using the BDD electrode, was validated for the determination of parabens in shampoos and presented adequate linearity (>0.999), in the range of 0.0125-0.500% (w/w), detectability 0.01% (w/w), precision (RSD of 2.3-9.8%) and accuracy (93.1-104.4%) and could be applied for routine quality control of shampoos containing MePa, EtPa and PrPa. 相似文献