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101.
102.
Polyanna Silveira Hornung Layse do Prado Cordoba Simone Rosa da Silveira Lazzarotto Egon Schnitzler Marcelo Lazzarotto Rosemary Hoffmann Ribani 《Journal of Thermal Analysis and Calorimetry》2017,127(3):1869-1877
Determination of the characteristics of native starches is crucial in order to select their best application in various industrial fields. Thus, two different types of non-traditional native starches from the Dioscoreaceas species (Dioscorea sp. and Dioscorea piperifolia Humb. var. Wild) were studied regarding their thermal, structural and rheological properties. The results were contrasted with traditional commercial starch sources (potato, cassava and corn). From the thermogravimetric results (TG/DTG), D. piperifolia starch obtained the highest thermal stability of the samples, except for potato starch. Furthermore, using differential scanning calorimetry and viscoamylograph profiles (RVA), it was found that the Dioscoreaceas starches presented a higher onset (T o) temperature and susceptibility to retrogradation. They also showed lower values in relation to relative crystallinity, which was calculated from their X-ray patterns and tendency to white (L*) colour. The shapes of the Discoreaceas starch granules were determined using electron microscopy; it was found that as the potato starch the Dioscoreaceas starches showed a wide range of particle size. 相似文献
103.
Although alkyl carbonic acids (ACAs) and their salts are referred to as instable species in aqueous medium, we demonstrate that a monoalkyl carbonate (MAC) can in fact be easily formed from bicarbonate and an alcohol even in the presence of a high amount of water. A CE system with two capacitively coupled contactless conductivity detectors (C?Ds) was used to obtain different parameters about these species and their reactions. Based on the mobilities obtained for a series of alcohols ranging from 1 to 5 carbons, the coefficients of diffusion and the hydrodynamic radii were calculated. When compared with the equivalent carboxylates, MACs have radii systematically smaller. Although the precise pK(a) values of the ACAs could not be obtained, because of the fast decomposition in acid medium, it was possible, for the first time, to show that they are below 4.0. This result suggests that the acidity of an ACA is quite similar to the first hydrogen of H?CO?. Using a new approach to indirectly calibrate the C?D, the kinetic constants and the equilibrium constants of formation were also obtained. The results suggest that the increase in the chain length makes the MACs less stable and more inert. 相似文献
104.
Eliane S. C. Temba Aluísio S. Reis Júnior Ângela Maria Amaral Roberto P. G. Monteiro 《Journal of Radioanalytical and Nuclear Chemistry》2011,290(3):631-635
A methodology for the determination of 90Sr in low- and intermediate-level radioactive wastes from nuclear power plants is presented in this work. It is a part of
a methodology developed for the sequential radiochemical separation of radionuclides difficult-to-measure directly by gamma
spectrometry in these radioactive wastes. The separation procedure was carried out using precipitation and extraction chromatography
with Sr Resin, from Eichrom and the 90Sr was measured by liquid scintillation counting (LSC). Optimum conditions for the pretreatment, separation and LSC measurements
were determined using simulated samples, which were prepared using standard solutions and carriers. The procedure showed to
be rapid and achieved a good chemical yield, in the range 60–90%, and a detection limit of 6.0 × 10−4 Bq g−1. The method was also tested by participation in a national intercomparison program, with aqueous samples, with good agreement
of results. 相似文献
105.
Lucimara Mendonça CostaEmerson Schwingel Ribeiro Mariana Gava SegatelliDanielle Raphael do Nascimento Fernanda Midori de OliveiraCésar Ricardo Teixeira Tarley 《Spectrochimica Acta Part B: Atomic Spectroscopy》2011,66(5):329-337
The present study describes the adsorption characteristic of Cd(II) onto Nb2O5/Al2O3 mixed oxide dispersed on silica matrix. The characterization of the adsorbent has been carried out by infrared spectroscopy (IR), scanning electronic microscopy (SEM), energy dispersive spectroscopy (EDS), energy dispersive X-ray fluorescence analysis (EDXRF) and specific surface area (SBET). From batch experiments, adsorption kinetic of Cd(II) was described by a pseudo-second-order kinetic model. The Langmuir linear isotherm fitted to the experimental adsorption isotherm very well, and the maximum adsorption capacity was found to be 17.88 mg g−1. Using the effective material, a method for Cd(II) preconcentration at trace level was developed. The method was based on on-line adsorption of Cd(II) onto SiO2/Al2O3/Nb2O5 at pH 8.64, in which the quantitative desorption occurs with 1.0 mol L−1 hydrochloric acid towards FAAS detector. The experimental parameters related to the system were studied by means of multivariate analysis, using 24 full factorial design and Doehlert matrix. The effect of SO42−, Cu2+, Zn2+ and Ni2+ foreign ions showed no interference at 1:100 analyte:interferent proportion. Under the most favorable experimental conditions, the preconcentration system provided a preconcentration factor of 18.4 times, consumption index of 1.08 mL, sample throughput of 14 h−1, concentration efficiency of 4.35 min−1, linear range from 5.0 up to 35.0 μg L−1 and limits of detection and quantification of 0.19 and 0.65 μg L−1 respectively. The feasibility of the proposed method for Cd(II) determination was assessed by analysis of water samples, cigarette sample and certified reference materials TORT-2 (Lobster hepatopancreas) and DOLT-4 (Dogfish liver). 相似文献
106.
Manuel A.V. Ribeiro da Silva Luísa M.P.F. Amaral 《The Journal of chemical thermodynamics》2011,43(1):1-8
The standard (p° = 0.1 MPa) molar enthalpies of formation, in the gaseous state, at T = 298.15 K, for 2,5-dimethyl-3-furancarboxylic acid, 3-acetyl-2,5-dimethylfuran, and 4,5-dimethyl-2-furaldehyde were derived from the values of the standard molar enthalpies of formation, in the condensed phase, and the standard molar enthalpies of phase transition from the condensed to the gaseous state. The values of the standard molar enthalpies of formation of the compounds in the condensed phases were calculated from the measurements of the standard massic energies of combustion obtained by static bomb combustion calorimetry. The enthalpies of vaporization/sublimation were measured by Calvet high temperature microcalorimetry. For 2,5-dimethyl-3-furancarboxylic acid the standard enthalpy of sublimation was also calculated, by the application of the Clausius–Clapeyron equation, to the temperature dependence of the vapor pressures measured by the Knudsen effusion technique.
Compound | |||
---|---|---|---|
Calvet | Knudsen | ||
2,5-Dimethyl-3-furancarboxylic acid (cr) | 600.4 ± 1.5 | 99.0 ± 1.7 | 100.9 ± 0.5 |
3-Acetyl-2,5-dimethylfuran (l) | 352.1 ± 1.8 | 57.5 ± 1.5 | |
4,5-Dimethyl-2-furaldehyde (l) | 294.5 ± 1.7 | 57.7 ± 0.6 |