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101.
Zero shear viscosity in miscible polymer blends of polystyrene and poly(2,6-dimethylphenylene ether)
The dynamic viscosities of blends of high molecular weight, narrowmolecular-weight distributed polystyrene and poly(2, 6-dimethylphenylene ether) are studied. The zero shear viscosity ηo depends on the weight average molecular weight M̄w and on the average entanglement molecular weight M̄e in the blend according to ηo ≈︁ M̄3.4 w(blend)/M̄2.4e(blend). 相似文献
102.
V. J. Fernandes Jr. A. S. Araujo G. J. T. Fernandes J. R. Matos M. Ionashiro 《Journal of Thermal Analysis and Calorimetry》2001,64(2):585-589
High density poly(ethylene) has been submitted to thermal degradation alone, and in the presence of silicoaluminophosphate
SAPO-37. The processes were carried out in a reactor connected on line to a gas chromatograph/mass spectrometer in order to
analyze the evolved products. Polymer degradation was also evaluated by thermogravimetry, from room temperature until 800°C,
under nitrogen dynamic atmosphere, with multiple heating rates. From TG curves, the activation energy related to degradation
process was calculated using the Flynn and Wall multiple heating rate kinetic model for pure polymer (PE) and for polymer
in the presence of catalyst (PE/S37). SAPO-37 showed good selectivity for low molecular mass hydrocarbons in PE catalytic
degradation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
103.
S. A. Araujo M. Ionashiro V. J. Fernandes Jr. A. S. Araujo 《Journal of Thermal Analysis and Calorimetry》2001,64(2):801-805
MCM-41 material was synthesized starting from hydrogel containing colloidal fumed silica, sodium silicate, cetyltetramethylammonium
bromide(CTMABr) as surfactant, and distilled water as solvent. These reactants were mixed to obtain a gel with the following
composition: 4SiO2:1Na2O:1CTMABr:200H2O. The hydrogel with pH=14 was hydrothermally treated at100°C, for 4 days. Each day, the pH was measured, and then adjusted
to 9.5–10 by using 30%acetic acid solution. Thermogravimetry was the main technique, which was used to monitor the participation
of the surfactant on the MCM-41 nanophase, being possible to determine the temperature ranges relative to water desorption
as well as the surfactant decomposition and silanol condensation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
104.
Rinaldo A. M. Vieira Leticia S. V. S. Su?é Carlos A. M. Pires Antonio O. S. Silva Marcelo J. B. Souza Antonio S. Araujo 《Reaction Kinetics and Catalysis Letters》2006,88(1):119-126
Summary The catalytic oxidation of phenol over CuZSM-12 (SAR = 200) has been studied using a semi-batch slurry reactor at temperatures
of 110; 120 and 130oC, and acidic neutral and basic pH. At 130oC, the phenol undergoes total conversion to carbon dioxide and water in 1.5 h. The kinetic parameters were evaluated using
a modified homogeneous-heterogeneous model for the experimental data. Using this modified model, the activation energy for
the catalytic oxidation process was ca. 90 kJ mol-1. 相似文献
105.
Carolina Araujo 《Geometriae Dedicata》2009,139(1):289-297
In this paper we characterize smooth complex projective varieties that admit a quadric bundle structure on some dense open
subset in terms of the geometry of certain families of rational curves.
相似文献
106.
Joint rolling-horizon scheduling of materials processing and lot-sizing with sequence-dependent setups 总被引:3,自引:0,他引:3
A lot sizing and scheduling problem from a foundry is considered in which key materials are produced and then transformed
into many products on a single machine. A mixed integer programming (MIP) model is developed, taking into account sequence-dependent
setup costs and times, and then adapted for rolling horizon use. A relax-and-fix (RF) solution heuristic is proposed and computationally
tested against a high-performance MIP solver. Three variants of local search are also developed to improve the RF method and
tested. Finally the solutions are compared with those currently practiced at the foundry. 相似文献
107.
R. Fermento D.C. Leitao J.M. Teixeira A.M. Pereira F. Carpinteiro J. Ventura J.P. Araujo J.B. Sousa 《Journal of Non》2008,354(47-51):5279-5281
Magnetic nanostructures display new and interesting physical phenomena and are currently used in a large variety of applications. We studied the structural, magnetic and transport properties of Co thin films deposited by ion beam sputtering. We probed the influence of the buffer layer material (Al, Cu, Ru or Ta) and thickness (10–100 Å) on the structural properties of Co thin films. Using X-ray diffraction we observed that textured fcc Co films can be grown on amorphous Ta as thin as 20 Å but for the other buffer layers no texture is observed. We also studied by magneto-optical Kerr effect (MOKE) the magnetic properties of the Co thin films as a function of Co thickness (100–1000 Å). Finally, the electrical resistivity and anisotropic magnetoresistance (AMR) of our Co thin films (on a Ta buffer) was obtained as a function of Co thickness. 相似文献
108.
Héctor Rosas Leidy Erika Sarmiento Vito Lubes María Goncalves Mary Lorena Araujo Felipe Brito 《Journal of solution chemistry》2008,37(5):701-711
The complex species formed between vanadium(III) cysteine and small blood serum bioligands: lactic, oxalic, citric and phosphoric
acids were studied in aqueous solution by means of electromotive force measurements, Emf(H), at 25 °C and 3.0 mol⋅dm−3 KCl as the ionic medium. The ternary complexes were studied by potentiometric measurements and the data analyzed using the
least-squares computational program LETAGROP to obtain the respective stability constants and stoichiometric coefficients.
The UV-Vis spectrophotometric measurements were done in order to make a qualitative characterization of the complexes formed
in aqueous solution. 相似文献
109.
Interaction of catechol and gallic acid with titanium dioxide in aqueous suspensions. 1. Equilibrium studies 总被引:1,自引:0,他引:1
Araujo PZ Morando PJ Blesa MA 《Langmuir : the ACS journal of surfaces and colloids》2005,21(8):3470-3474
The adsorption isotherms of catechol (1,2-dihydroxybenzene) and gallic acid (3,4,5-trihydroxybenzoic acid) onto titanium dioxide (Degussa P-25) were measured at various pH values and room temperature using attenuated total reflection Fourier transform infrared (FTIR-ATR) data, processed by singular value decomposition. The affinity is largely pH independent, although the deprotonatation of the carboxylic group in gallic acid might produce a slight increase in the affinity. Catechol was shown to form two complexes, with Langmuir stability constants log K of 4.66 (strong mode) and 3.65 (weak mode). Both complexes have the same spectral signature, and mononuclear and binuclear chelate structures are proposed for them. Gallic acid chemisorbs by complexation through two -OH groups and forms one complex only, log K = 4.70. The third -OH and the pendant carboxylate do not influence much the stability of the surface complex. Comparison with literature data demonstrates that the affinity of 4-chlorocatechol is also similar, whereas 2,3-dihidroxynaphthalene and 4-nitrocatechol form more stable complexes, probably because of the solvation contribution to the overall Gibbs adsorption energy. All quoted constants refer to the surface complexation equilibria written as follows: ([triple bond]Ti-OH)2 + H2L = ([triple bond]Ti)2-L + 2H2O, i.e., as electroneutral processes. The FTIR-ATR spectra of the surface complexes are also discussed. 相似文献
110.
Dos Santos WN da Silva EG Fernandes MS Araujo RG Costa AC Vale MG Ferreira SL 《Analytical and bioanalytical chemistry》2005,382(4):1099-1102
Chocolate is a complex sample with a high content of organic compounds and its analysis generally involves digestion procedures that might include the risk of losses and/or contamination. The determination of copper in chocolate is important because copper compounds are extensively used as fungicides in the farming of cocoa. In this paper, a slurry-sampling flame atomic-absorption spectrometric method is proposed for determination of copper in powdered chocolate samples. Optimization was carried out using univariate methodology involving the variables nature and concentration of the acid solution for slurry preparation, sonication time, and sample mass. The recommended conditions include a sample mass of 0.2 g, 2.0 mol L–1 hydrochloric acid solution, and a sonication time of 15 min. The calibration curve was prepared using aqueous copper standards in 2.0 mol L–1 hydrochloric acid. This method allowed determination of copper in chocolate with a detection limit of 0.4 g g–1 and precision, expressed as relative standard deviation (RSD), of 2.5% (n=10) for a copper content of approximately 30 g g–1, using a chocolate mass of 0.2 g. The accuracy was confirmed by analyzing the certified reference materials NIST SRM 1568a rice flour and NIES CRM 10-b rice flour. The proposed method was used for determination of copper in three powdered chocolate samples, the copper content of which varied between 26.6 and 31.5 g g–1. The results showed no significant differences with those obtained after complete digestion, using a t-test for comparison. 相似文献