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31.
V. Piccirillo J. M. Balthazar B. R. Jr. Pontes J. L. P. Felix 《Nonlinear dynamics》2009,55(1-2):139-149
In this paper, an optimal linear control is applied to control a chaotic oscillator with shape memory alloy (SMA). Asymptotic stability of the closed-loop nonlinear system is guaranteed by means of a Lyapunov function, which can clearly be seen to be the solution of the Hamilton–Jacobi–Bellman equation, thus guaranteeing both stability and optimality. This work is presented in two parts. Part I considers the so-called ideal problem. In the ideal problem, the excitation source is assumed to be an ideal harmonic excitation. 相似文献
32.
Electrochemical cells containing an iron rotating disk electrode which is dissolved in the electrolyte, an 1 M H2SO4 solution present a current instability in the plateau region, where the current is controlled by the mass transport. Dissolution of the electrode gives rise to a thin concentration boundary layer, due to a Schmidt number Sc = 2000. This boundary layer, together with the potential applied to the electrode, leads to an increase in the fluid viscosity and in a decrease in the diffusion coefficient, coupling the concentration and the chemical species field. Since the current is proportional to the concentration gradient at the interface, an instability of the coupled fields at Reynolds numbers attained in experimental conditions could be responsible for the current instability. Mangiavacchi [1] performed a linear stability analysis of the problem and showed that this is indeed the case. In this paper we review the main results of the stability analysis and present the main features of the FEM code recently developed in our group, to proceed with the investigation of the current instability observed in electrochemical cells. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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María S. Di Nezio Marcelo F. Pistonesi Wallace D. Fragoso Mrcio J.C. Pontes Hctor C. Goicoechea Mrio C.U. Araujo e Beatriz S. Fernndez Band 《Microchemical Journal》2007,85(2):194-200
This paper proposes an analytical method to determine directly and simultaneously five phenolic compounds (4-nitrophenol, 2-nitrophenol, phenol, 2,4,6-trichlorophenol and 4-chlorophenol) in sea water (Ria de Bahía Blanca, Argentine). The advantages of this method is that only requires spectrophotometric measurements (separation steps and derivatization reagents are avoided) and chemometric modelling (PLS and MLR–SPA).The statistical comparison between PLS — a well established multivariate method — and MLR–SPA — a recently presented chemometric modelling — demonstrated better analytical performance for the later one. This fact is indicative of the potentiality of MLR–SPA for solving complex analytical problems. 相似文献
35.
Pontes F. M. L. Oliveira S. F. Espínola J. G. P. Arakaki L. N. H. Fonseca M. G. Airoldi C. 《Journal of Thermal Analysis and Calorimetry》2004,75(3):975-988
Solid adducts SbX3·L-pic (X=Cl, I and L=α-, β- and γ-picolines) were synthesized and characterized by elemental analysis, 1H and 13C NMR, IR spectroscopy and thermal analysis. The infrared spectroscopy and the magnetic resonance for 1H and 13C nuclei of these compounds suggest that the ligands coordinate through nitrogen atom. Kinetic studies were accomplished by
means of thermogravimetric data, through isothermal and non-isothermal techniques. The best adjusting models for adducts thermal
decomposition were R1 for isothermal and R1 and R2 for the non-isothermal methods. The energy of activation values obtained by isothermal method indicate the following orders
of thermal stability for adducts: i) SbCl3·α-pic>SbCl3·β-pic>SbCl3·γ-pic and ii) SbI3·β-pic>SbI3·γ-pic>SbI3·α-pic. The activation energy values obtained by non-isothermal were higher than those from isothermal methods, showing the
order of stability:iii) SbCl3·α-pic<SbCl3·β-pic<SbCl3·γ-pic and iv) SbI3·β-pic>SbI3·α-pic=SbI3··γ-pic. These obtained data through R1 model presented the kinetic compensation effect for trichloride adducts, which could be associated to both isothermal and
non-isothermal processes.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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S. H. Leal J. C. Sczancoski L. S. Cavalcante M. T. Escote J. M. E. Matos M. R. M. C. Santos F. M. Pontes E. Longo J. A. Varela 《Journal of Sol-Gel Science and Technology》2010,53(1):21-29
Pb1−x
Sr
x
)TiO3 powders with different compositions (x = 0, 0.10, 0.50, 0.90 and 1) were synthesized by the polymeric precursor method and heat treated at 800 °C for 2 h under
air atmosphere. The thermogravimetric and differential scanning calorimetry analyses were performed in the range from 25 to
800 °C in order to estimate the stages corresponding to the water evaporation, organic decomposition and crystallization of
these materials. X-ray diffraction patterns and Rietveld analyses showed that the (Pb1−x
Sr
x
)TiO3 phases with strontium content up to x = 0.1 crystallize in a tetragonal structure. The micrographs obtained by scanning electron microscopy and transmission electron
microscopy showed that the powders have agglomerated nature, presenting irregular morphologies and polydisperse particle size
distribution. The energy dispersive X-ray spectrometry indicated the presence of pure (Pb0.50Sr0.50)TiO3 phase. 相似文献
39.
Pistonesi MF Di Nezio MS Centurión ME Lista AG Fragoso WD Pontes MJ Araújo MC Band BS 《Talanta》2010,83(2):320-323
In this study, a novel, simple, and efficient spectrofluorimetric method to determine directly and simultaneously five phenolic compounds (hydroquinone, resorcinol, phenol, m-cresol and p-cresol) in air samples is presented. For this purpose, variable selection by the successive projections algorithm (SPA) is used in order to obtain simple multiple linear regression (MLR) models based on a small subset of wavelengths. For comparison, partial least square (PLS) regression is also employed in full-spectrum. The concentrations of the calibration matrix ranged from 0.02 to 0.2 mg L−1 for hydroquinone, from 0.05 to 0.6 mg L−1 for resorcinol, and from 0.05 to 0.4 mg L−1 for phenol, m-cresol and p-cresol; incidentally, such ranges are in accordance with the Argentinean environmental legislation. To verify the accuracy of the proposed method a recovery study on real air samples of smoking environment was carried out with satisfactory results (94-104%). The advantage of the proposed method is that it requires only spectrofluorimetric measurements of samples and chemometric modeling for simultaneous determination of five phenols. With it, air is simply sampled and no pre-treatment sample is needed (i.e., separation steps and derivatization reagents are avoided) that means a great saving of time. 相似文献
40.
Célia?Fonseca?Guerra Tushar?van der?Wijst F.?Matthias?BickelhauptEmail author 《Structural chemistry》2005,16(3):211-221
We have theoretically analyzed Watson–Crick AT and GC base pairs in which purine C8 and/or pyrimidine C6 positions carry a substituent X = H, F, Cl or Br, using the generalized gradient approximation (GGA) of density functional theory at BP86/TZ2P. The purpose is to study the effects on structure and hydrogen bond strength if X = H is substituted by a halogen atom. Furthermore, we wish to explore the relative importance of electrostatic attraction versus orbital interaction in the above multiply hydrogen-bonded systems, using a quantitative bond energy decomposition scheme. We find that replacing X = H by a halogen atom has relatively small yet characteristic effects on hydrogen bond lengths, strengths and bonding mechanism. In general, it reduces the hydrogen-bond-accepting- and increases the hydrogen-bond-donating capabilities of a DNA base. The orbital interaction component in these hydrogen bonds is found for all substituents (X = H, F, Cl, and Br) to contribute about 41% of the attractive interactions and is thus of the same order of magnitude as the electrostatic component, which provides the remaining 59% of the attraction. 相似文献