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681.
A. Lopez Molinero Alberto Morales Anselmo Villareal Juan R. Castillo 《Fresenius' Journal of Analytical Chemistry》1997,358(5):599-603
The generation of volatile species of silicon as a means to introduce silicon into an inductively coupled plasma has been
studied. It is based on the reaction between silicon and fluoride ions in sulfuric acid media and it was carried out using
different flow injection mountings. The first mounting works with an injection of 100 μL concentrated sulfuric acid and 150
μL silicon standard solution in a continuous 0.05 mol L–1 NaF solution flow. The method shows a linear response between the intensity of emission at 251.611 nm line and the silicon
concentration from 0.1 to 200 μg mL–1, with a reproducibility of 2% and a detection limit of 0.004 μg mL–1. The second mounting produces the volatile species by the reaction between two opposed aerosol flows in a home-made nebulization
chamber. This chamber has a Cross-Flow and a Meinhard nebulizer at either end. A linear response ranging from 0.1 to 1000
μg mL–1 of silicon solution is obtained and the reproducibility rises to 8%.The detection limit reached is 0.02 μg mL–1. The silicon content in real water samples was determined by applying both the above-mentioned methods and a third method
for reference.
Received: 6 November 1996 / Revised: 19 December 1996 / Accepted: 3 January 1997 相似文献
682.
A rapid spectrophotometric method for sulphate determination in a discontinuous mode is described. The method is based on sulphate reduction to hydrogen sulphide followed by its volatilization and absorption in an alkaline solution. The reduction is obtained when a sulphate sample is heated to 287 degrees C for 15 min, with a mixture of Fe(o)/KI and phosphoric acid. The resulting gas is swept by nitrogen flow into a 0.1 M sodium hydroxide solution and the absorbance of the sulphide ions is measured directly at 230 nm. The proposed method enabled us to determine 50-700 mug of total sulphate with a relative standard deviation of the order of 5%. The method has been applied for the determination of sulphates in liquid (mineral waters) and solid (gypsiferous soils) samples. 相似文献
683.
A method for the quantitative determination of the total available lysine in various foods is developed. The method is based on the reaction of the amino groups on the lysine molecule with fluorodinitrobenzene and is capable of furnishing simultaneous determination of the available intrachain lysine (known as N-epsilon-[2,4-dinitrophenyl]-L-lysine) or the available free and/or N-terminal lysine (known as N,N'-di-[2,4-dinitrophenyl]-L-lysine). Optimum conditions for separation and quantitation are studied. The results show the proposed method to be both accurate and precise and suitable for food samples containing hydrolyzed proteins. 相似文献
684.
A novel reactor design, sampling probe and wet collection system were used to investigate the combined effects of plasma operating
parameters and particle collection mechanisms on the synthesis of CeO2 particles from liquid precursors. The sampling of particles in-flight and the collection of particles at several reactor
regions were used to provide experimental evidence of particle size at different reactor locations at various plasma operating
conditions, i.e., power and plasma gas flow rates. This information provided a picture of how CeO2 particles were formed and how these particles were collected in various locations. The effect of adding water-soluble fuels
(alanine and glycine) to the original cerium nitrate solutions was also investigated. Fuel addition decreased the temperature
of CeO2 formation by acting as a local heat source as a result of fuel auto-ignition. Photographs of the particles in-flight were
taken using a fast speed CCD camera. 相似文献
685.
The chemical derivatization of bilirubin oxidase (BOx) with a fluorescein derivative (FS) yields a chemically modified enzyme (BOx-FS), with excitation and emission maxima at 487 and 520 nm, respectively. During the oxygen oxidation reaction of bilirubins, in the presence of the modified enzyme, the change in the fluorescence of the modified enzyme depends on the concentration and type of bilirubin. This effect can be used for analytical purposes. Firstly, a theoretical-experimental study of the analytical system was carried out. The mechanism responsible for the fluorescence variation was clarified, a mathematical model developed and the variables affecting the fluorescence changes optimized. The concentration ranges in which the model can be applied (up to 12 mg bilirubin l(-1)), and the precision of the measurement (about 4%) were established for the three bilirubins. The application of the methodology to the simultaneous determination of direct and total bilirubins were studied by applying multivariate calibration methods to the whole kinetic profiles. A reduced calibration matrix (derived from a 5(3) base matrix) is proposed for calibration and different numerical methods were tested: Principal Components Regression (PCR), Partial Least Squares Regression (PLS) and Artificial Neural Networks (ANN). The simultaneous determination of direct and total bilirubin (average validation errors of about 9 and 10%, respectively) can be carried out from a single run. Furthermore, a semi-quantitative speciation of the three bilirubins (free, conjugated and albumin-bonded bilirubin) may be simultaneously obtained. 相似文献
686.
Flores G Blanch GP Ruiz del Castillo ML Herraiz M 《Journal of separation science》2005,28(17):2333-2338
Characteristic aroma compounds in plants and essential oils of Lavandula from different varieties were examined. The study of the qualitative and quantitative composition of the major volatile components was faced by developing a method based on the use of supercritical fluid extraction-GC-MS (SFE-GC-MS). The optimization of a variety of parameters affecting SFE extraction enabled RSDs from three replicates lower than 2% to be achieved. Equally, recoveries of up to 59% were obtained by applying the proposed method. The use of multidimensional GC was necessary to enantiomerically resolve the target compounds. The obtained results showed enantiomeric purities >90% for all studied compounds in all varieties considered, proving the natural invariability of the enantiomeric composition of the compounds of interest. This information can be useful in authenticity studies as well as in selecting natural sources of enantiomerically pure compounds. 相似文献
687.
Contaminated industrial effluents often contain a variety of organic pollutants that can disturb the development of the endocrine system and the organs that respond to endocrine signals in organisms. Total characterisation of the effluents to detect all these potential endocrine disruptors by standard GC-MS methods is difficult since this technique often misses the more polar or non-volatile fraction of these organic compounds. The wide spectrum of endocrine-toxic substances and their low concentrations require powerful analytical approaches like LC-MS for their identification. Furthermore, the methods for the detection of endocrine effects developed up to now do not show all the possible oestrogenic effects and results of the different tests are not comparable to one another. Therefore, further ecotoxicological research should be carried out so that new strategies can be proposed. In this article, an overview of the analytical methods for determining organic contaminants in industrial effluents and tests for the identification of endocrine disruptors and their effects is presented. 相似文献
688.
Manuel Castillo Ana Criado Elias Ramirez Julio Criado Benigno Macias 《Transition Metal Chemistry》1987,12(2):184-185
Summary Oxidation of L-serine occurs on degradation of bis(L-serinato)copper(II) and at the same time copper is reduced. 相似文献
689.
A method for quantifying of ethinylestradiol (ETE) and levo-norgestrel (LEV) in pharmaceutical products by micellar electrokinetic chromatography (MEKC) is described. The separation was carried out at 25 degrees C and 25 kV, using a 20 mM borate buffer (pH 9.2), 15 mM sodium dodecylsulfate (SDS) in 30% acetonitrile/water (v/v). Under these conditions the analysis takes about 7 min. The method has been applied for quantifying both compounds in six different commercial contraceptives and the proposed method gave good results when compared with a reference liquid chromatographic (LC) method. 相似文献
690.
Hilda Castillo Matthew Yarger Melissa Rappleye Carol Parish 《Journal of Molecular Structure》2004,710(1-3):73-76
The LM:MC conformational search method was used to identify the low energy structures on the OPLS-AA/GBSA(water) and AMBER*/GBSA(water) surfaces for a diastereomeric series of cyclic urea molecules that have been shown to be potent inhibitors of the HIV-1 protease enzyme. The lowest energy structures from each search were then subjected to geometry optimization and frequency analysis using the HF/6-311G** method in conjunction with the self-consistent reaction field (SCRF) treatment for water. A comparison of the diastereomeric energies and structures indicates that the OPLSAA/GBSA(water) surface is in good agreement with the HF/6-311G**/SCRF(water) surface. 相似文献