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91.
Investigation into the physics of foaming has traditionally been focused on aqueous systems. Non-aqueous foams, by contrast, are not well understood, but have been the subject of a recent surge in interest motivated by the need to manage foaming across industrial applications. In this review, we provide a comprehensive discussion of the current state-of-the-art methods for characterizing non-aqueous foams, with a critical evaluation of the advantages and limitations of each. Subsequently, we present a concise overview of the current understanding of the mechanisms and methods used for stabilizing and destabilizing non-aqueous foams. We conclude the review by discussing open questions to guide future investigations. 相似文献
92.
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94.
讨论了非水毛细管电泳(NACE)的优势和缺点,分别评价了常用非水溶剂作为运行介质的潜力,非水介质中电渗流的产生原因与控制机理.对于 NACE 的分离机理,尤其是静电相互作用与疏溶剂相互作用对分离的影响进行了讨论.着重评述了 NACE 在电中性物质的分离以及离子对手性拆分方面的应用及其机制. 相似文献
95.
Zdena Křesinová Lucie Hostačná Jaroslava Medková Monika Čvančarová Tatiana Stella 《International journal of environmental analytical chemistry》2013,93(8):822-836
Chlorobenzoic acids (CBAs) are the major metabolite of aerobic bacterial degradation of polychlorinated biphenyls (PCBs). A rapid and simple simultaneous derivatisation method has been developed for gas chromatography-mass spectrometry determination in historically PCB-contaminated soils for 15 isomers of mono-, di-, tri-, tetra-, and pentachlorobenzoic acids in CBA mixtures. Two derivatisation agents (diazomethane and methyl chloroformate) and various conditions were evaluated (temperature, time, solvents, catalysts) in terms of efficiency. The optimised derivatisation method with diazomethane and 1% methanol running 1 hour at 5°C was used for derivatisation of extracts of soils and river sediment from historically PCB-contaminated sites; the extracts were prepared using accelerated solvent extraction by a previously described method. Methylated CBAs were separated by gas chromatography using a system with two different common columns, DB-5 and DB-200, in series-coupled (tandem) arrangement and detected by EI-MS. A clean-up with a gel permeation chromatography was carried out to remove soil interfering matrix compounds as well as major portion of PCBs. The limits of quantification ranged between 1 and 10 ng g?1 of individual CBA in the soil. The procedure was applied to various soil samples from Lhenice (Czech Republic) highly contaminated with PCBs. CBAs were found in all tested soils and also in the river sediment. The most contaminated soil contained all CBAs representatives under the study with a total concentration of 3.1 µg g?1 of dry soil. 相似文献
96.
《Analytical letters》2012,45(20):2497-2505
Abstract The behaviour of sodium salts of two heterocyclic sulphonamide derivatives (Sulphadimidine and sulphadiazine) in non-aqueous titrimetry was studied. Accordingly a simple and accurate procedure for their determination, based on their titration in acetic anhydride-acetic acid solvent system (5:1) with acetous perchloric acid solution is proposed. Results obtained agreed with those of a pharmacopoeial method. 相似文献
97.
Antonia María Carro Paula González Noelia Fajar Rosa Antonia Lorenzo Rafael Cela 《Analytical and bioanalytical chemistry》2009,394(3):893-901
The headspace solid-phase micro-extraction technique with on-fibre derivatisation followed by gas chromatography-tandem mass
spectrometry has been evaluated for the analysis of 1,3-dichloro-2-propanol in water. An asymmetric factorial design has been
performed to study the influence of five experimental factors: extraction time and temperature, derivatisation time and temperature
and pH. The best extraction performance is achieved in the headspace mode, with 5 mL stirred water samples (pH 4) containing
1.3 g of NaCl, equilibrated for 30 min at 25 °C, using divinylbenzene-carboxen-polydimethylsiloxane as the fibre coating.
On-fibre derivatisation has been used for the first time with 50 μL of bis(trimethylsilyl)trifluoroacetamide at 25 °C during
15 min, leading to effective yields. The proposed method provides high sensitivity, good linearity and repeatability (relative
standard deviation of 5.1% for 10 ng mL−1 and n = 5). The limits of detection and quantification were 0.4 and 1.4 ng mL−1, respectively. Analytical recoveries obtained for different water samples were approx. 100%. 相似文献
98.
Vernix caseosa is a greasy biofilm formed on the skin of the human fetus in the last period of pregnancy. This matrix is known to contain a range of uncommon branched chain fatty acids. In this study, we studied the fatty acid composition of vernix caseosa by non-aqueous reversed phase high performance liquid chromatography (RP-HPLC) fractionation followed by gas chromatography-electron ionization mass spectrometry (GC/EI-MS) of the fractions. For this purpose the fatty acids from vernix caseosa were converted into the corresponding methyl esters. These were fractionated by non-aqueous RP-HPLC using three serially connected C(18)-columns and pure methanol as the eluent. Aliquots of the HPLC fractions were directly analyzed by GC/EI-MS in the selected ion monitoring mode. Data analysis and visualization were performed by the creation of a two dimensional (2D) contour plot, in which GC retention times were plotted against the HPLC fractions. Inspection of the plot resulted in the detection of 133 different fatty acids but only 16 of them contributed more than 1% to the total fatty acids detected. Identification was based on HPLC and GC retention data, GC/MS-SIM and full scan data, as well as plotting the logarithmic retention times against the longest straight carbon chain. In selected cases, aliquots of the HPLC fractions were hydrogenated or studied by means of the picolinyl esters. Using these techniques, the number of double bonds could be unequivocally assigned to all fatty acids. Moreover, the number of methyl branches, and in many cases the positions of methyl branches could be determined. The enantioselective analysis of chiral anteiso-fatty acids resulted in the dominance of the S-enantiomers. However, high proportions of R-a13:0, R-a15:0, and R-a17:1 were also detected while a17:0 was virtually S-enantiopure. 相似文献
99.
7,12-Dimethylbenz[a]anthracene (DMBA), is a widely studied polycyclic aromatic hydrocarbon that has long been recognized as a very potent carcinogen. Initially, the electrochemical oxidation of DMBA at the glassy carbon and pencil graphite electrodes in non-aqueous media (dimethylsulphoxide with lithium perchlorate) was studied by cyclic voltammetry. DMBA was irreversibly oxidized in two steps at high positive potentials, resulting in the ill-resolved formation of a couple with a reduction and re-oxidation wave at much lower potentials. Special attention was given to the use of adsorptive stripping voltammetry together with a medium exchange procedure on disposable pencil graphite electrode in aqueous solutions over the pH range of 3.0-9.0. The response was characterized with respect to pH of the supporting electrolyte, pre-concentration time and accumulation potential. Using square-wave stripping mode, the compound yielded a well-defined voltammetric response in acetate buffer, pH 4.8 at +1.15 V (vs. Ag/AgCl) (a pre-concentration step being carried out at a fixed potential of +0.60 V for 360 s). The process could be used to determine DMBA concentrations in the range 2-10 nM, with an extremely low detection limit of 0.194 nM (49.7 ng L−1). The applicability to assay of spiked human urine samples was also illustrated. Finally, the interaction of DMBA with fish sperm double-stranded DNA based on decreasing of the oxidation signal of adenine base was studied electrochemically by using differential pulse voltammetry with a pencil graphite electrode at the surface and also in solution. The favorable signal-to-noise characteristics of biosensor resulted in low detection limit (ca. 46 nM) following a 300-s interaction. These results displayed that the electrochemical DNA-based biosensor could be used for the sensitive, rapid, simple and cost effective detection of DMBA-DNA interaction. 相似文献
100.
Highly crystalline metal oxide nanoparticles of TiO2, WO3, and V2O5 were synthesized in just a few minutes by reacting transition metal chloride with benzyl alcohol using ultrasonic irradiation under argon atmosphere in a non-aqueous solvent. The sonochemical process was conducted at a relatively low temperature, 363 K. A unique crystallization process of these nanoparticles has been observed and characterized by powder X-ray diffraction (PXRD), high resolution scanning electron microscopy (HRSEM), and BET. The particles’ size and shape measured from HRSEM reveal “quasi” zero-dimensional, spherical TiO2 particles in the range of 3–7 nm. The V2O5 particles have a “quasi” one-dimensional ellipsoidal morphology, with lengths in the range of 150–200 nm and widths varying between 40 and 60 nm. The WO3 particles were obtained as “quasi” two-dimensional platelets with square shapes having facets ranging from 30 to 50 nm. The thickness of these platelets was between 2 and 7 nm. The mechanism of the reactions leading to these three metal oxide nanoparticles in a non-aqueous system is substantiated by Nuclear Magnetic Resonance (NMR), and Electron Spin Resonance (ESR). 相似文献