全文获取类型
收费全文 | 262篇 |
免费 | 20篇 |
专业分类
化学 | 205篇 |
力学 | 4篇 |
数学 | 26篇 |
物理学 | 47篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 13篇 |
2021年 | 20篇 |
2020年 | 11篇 |
2019年 | 10篇 |
2018年 | 8篇 |
2017年 | 18篇 |
2016年 | 22篇 |
2015年 | 12篇 |
2014年 | 24篇 |
2013年 | 10篇 |
2012年 | 25篇 |
2011年 | 27篇 |
2010年 | 20篇 |
2009年 | 16篇 |
2008年 | 17篇 |
2007年 | 7篇 |
2006年 | 8篇 |
2005年 | 1篇 |
2003年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
排序方式: 共有282条查询结果,搜索用时 15 毫秒
31.
Hollow fiber liquid-phase microextraction and CE were applied for the determination of albendazole sulfoxide (ASOX) enantiomers in liquid culture medium after a fungal biotransformation study. The analytes were extracted from 1 mL of liquid culture medium spiked with the internal standard (rac-hydroxychloroquine) and buffered with 0.50 mol/L phosphate buffer, pH 10. The analytes were extracted into 1-octanol impregnated in the pores of the hollow fiber, and into an acid acceptor solution inside the polypropylene hollow fiber. The electrophoretic separations were carried out in 0.05 mol/L tris(hydroxymethyl)aminomethane buffer, pH 9.3, containing 3.0% w/v sulfated-β-CD (S-β-CD) with a constant voltage of +15 kV and detection at 220 nm. The method was linear over the concentration range of 250-5000 ng/mL for each ASOX enantiomer. Within-day and between-day assay precision and accuracy for the analytes were studied at three concentration levels and the values of RSD% and relative error % were lower than 15%. The developed method was applied for the determination of ASOX after a biotransformation study employing the endophytic fungus Penicillium crustosum (VR4). This study showed that the endophytic fungus was able to metabolize the albendazole to ASOX enantioselectively. In addition, it was demonstrated that hollow fiber liquid-phase microextraction coupled to CE can be an excellent and environmentally friendly technique for the analysis of samples obtained in biotransformation studies. 相似文献
32.
Jacqueline Arguello Hérica A. Magosso Thiago C. Canevari Richard Landers Yoshitaka Gushikem 《Electroanalysis》2011,23(2):334-338
Selective electroanalytical responses for ascorbic acid, dopamine and uric acid at a carbon modified electrode based on 3‐n‐propyl‐1‐azonia‐4‐azabicyclo[2.2.2]octane silsesquioxane chloride (SiDbCl) is reported. The overlapped peaks observed at an unmodified electrode are resolved into three well defined voltammetric peaks allowing the simultaneous determination of the three species. Detection limits of 37, 0.3 and 0.1 μmo L−1 of ascorbic acid, dopamine and uric acid, respectively, were calculated from calibration curves based on differential pulse voltammetric experiments performed in Britton ‐ Robinson buffer solution at pH 7.04. 相似文献
33.
In this work a method is proposed and demonstrated for the analysis of the macrocyclic lactones abamectin, doramectin, eprinomectin, ivermectin and moxidectin in bovine milk by liquid chromatography coupled to mass spectrometry (LC-MS/MS) and liquid chromatography with fluorescence detection (LC-FL). The method is based on liquid-liquid extraction followed by a low temperature purification (LLE-LTP) step. Moreover, the proposed method was validated according to the Commission Decision 2002/657/EC, using LC-MS/MS and LC-FL for confirmatory and quantitative analysis, respectively. For LC-MS/MS the recovery rates observed ranged from 101.2 to 141.6% with coefficient of variation from 2.6 to 19.8%. For LC-FL the recovery rates observed ranged from 100.2 to 105% and coefficient of variations from 2.9 to 8.8%. Matrix effects were negligible due to the low temperature purification step. The quantification limits were far below the maximum limits established by regulations of all countries consulted. The proposed method proved to be simple, easy, and adequate for high-throughput analysis of a large number of samples per day at low cost. 相似文献
34.
Ribeiro EA Sidooski T Nandi LG Machado VG 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,81(1):745-753
2,6-Diphenyl-4-(2,4,6-triphenylpyridinium-1-yl)phenolate (1a) and 4-[(1-methyl-4(1H)-pyridinylidene)-ethylidene]-2,5-cyclohexadien-1-one (2a) were protonated in organic solvents (dichloromethane, acetonitrile, and DMSO) to form 1b and 2b, respectively. The appearance of the solvatochromic bands of 1a and 2a was studied UV-vis spectrophotometrically by deprotonation of 1b and 2b in solution in the presence of the following amines: aniline (AN), N-methylaniline (NMAN), N,N-dimethylaniline (NDAN), n-butylamine (BA), diethylamine (DEA), and triethylamine (TEA). Titrations of 1b and 2b with the amines were carried out and the binding constants were determined from the titration curves in each solvent, using a mathematical model adapted from the literature which considers the simultaneous participation of two dye: amine stoichiometries, 1:1 and 1:2. The data obtained showed the following base order for the two compounds in DMSO: BA>DEA>TEA, while aromatic amines did not cause any effect. In dichloromethane, the following base order for 1b was verified: TEA>DEA>BA?NDAN, while for 2b the order was: TEA>DEA>BA, suggesting that 1b is more acidic than 2b. The data in acetonitrile indicated for 1b and 2b the following order for the amines: DEA>TEA>BA. The diversity of the experimental data were explained based on a model that considers the level of interaction of the protonated dyes with the amines to be dependent on three aspects: (a) the basicity of the amine, which varies according to their molecular structure and the solvent in which it is dissolved, (b) the molecular structure of the dye, and (c) the solvent used to study the system. 相似文献
35.
Hellyda K. T. A. Silva Thiago Chellappa Fabíola C. Carvalho Edjane F. B. Silva Tarcísio A. Nascimento Antônio S. Araújo Valter J. FernandesJr. 《Journal of Thermal Analysis and Calorimetry》2011,106(3):731-733
Biodiesel is defined as a mixture of mono- or di-alquil esters of vegetable oil or animal fats. During long-term storage,
oxidation caused by contact with air (autoxidation) presents a legitimate concern in relation to monitoring and maintaining
fuel quality. Extensive oxidative degradation may compromise the quality by adversely affecting kinematic viscosity, acid
value, or peroxide value. The oxidation susceptibility of biodiesel, due to the presence of triacilglycerides of poly-unsaturated
fatty acids, was evaluated in this study. Samples of sunflower, castor, and soybean biodiesels were obtained through the transesterification
reaction, with the intention of achieving the thermal stability study through thermogravimetrical analyses and differential
scanning calorimetry high pressure. It was furthermore observed through thermogravimetry and pressure differential scanning
calorimetry curves that castor biodiesel exhibited the highest thermal and oxidative stability. 相似文献
36.
Osorio Ana C. P. de Sena Rodrigo C. Araújo Thiago de O. de Almeida Marcelo D. 《Accreditation and quality assurance》2019,24(5):387-394
Accreditation and Quality Assurance - The production of Certified Reference Materials (CRMs) is one of the essential activities of the National Institute of Metrology, Quality and Technology... 相似文献
37.
38.
39.
40.
Mohallem JR Coura Tde O Diniz LG de Castro G Assafrão D Heine T 《The journal of physical chemistry. A》2008,112(38):8896-8901
The adiabatic finite-nuclear-mass-correction (FNMC) to the electronic energies and wave functions of atoms and molecules is formulated for density-functional theory and implemented in the deMon code. The approach is tested for a series of local and gradient corrected density functionals, using MP2 results and diagonal-Born-Oppenheimer corrections from the literature for comparison. In the evaluation of absolute energy corrections of nonorganic molecules the LDA PZ81 functional works surprisingly better than the others. For organic molecules the GGA BLYP functional has the best performance. FNMC with GGA functionals, mainly BLYP, show a good performance in the evaluation of relative corrections, except for nonorganic molecules containing H atoms. The PW86 functional stands out with the best evaluation of the barrier of linearity of H2O and the isotopic dipole moment of HDO. In general, DFT functionals display an accuracy superior than the common belief and because the corrections are based on a change of the electronic kinetic energy they are here ranked in a new appropriate way. The approach is applied to obtain the adiabatic correction for full atomization of alcanes C(n)H(2n+2), n = 4-10. The barrier of 1 mHartree is approached for adiabatic corrections, justifying its insertion into DFT. 相似文献