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71.
C.A. d’Azevedo F.M.S. Garrido M.E. Medeiros 《Journal of Thermal Analysis and Calorimetry》2006,83(3):649-655
Samples
of the MgO–Al2O3–SiO2
ternary system, constituted by 28.5 mol% ofMgO, 28.5 mol% of Al2O3
and 43mol%of SiO2, were activated in a roll mill and
calcined at different temperatures. The influence of the grinding time, the
used SiO2 precursor and activation medium, furthermore
the mass ratio between the powdered sample and zirconia cylinders was investigated
on the reactivity of the MgO–Al2O3–SiO2
ternary system. FTIR spectra and the X-ray powder diffraction patterns indicates
the formation of Mg(OH)2 at 393 K, of forsterite (MgSi2O5)
and enstatite (MgSiO3) at 1223 K and of spinel (MgAl2O4)
between 1223 and 1523 K in some samples. The presence of cordierite (Mg2Al2Si5O18) was observed at 1523 K, a reaction pathway concerning
its formation was proposed. 相似文献
72.
Summary The addition of organic solvents (light aliphatic, heavy aliphatic and aromatic hydrocarbons) in Brazilian gasoline is unfortunately very frequent, and this illicit practice impares gasoline quality. Gas chromatography (GC) and gas chromatography coupled to mass spectrometry (GC-MS) analyses can be used as a procedure to improve the detection of adulterated gasoline. The results showed that adulterated samples and also the type of organic solvent used in adulteration can be detected by comparison of chromatographic profiles (standard samples versus adulterated samples). However, a single GC analysis can detect an adulterated gasoline, and so decrease the number of adulterated samples approved as presenting good quality. 相似文献
73.
74.
L. J. Azevedo J. E. Schirber R. L. Greene E. M. Engler 《Molecular Crystals and Liquid Crystals》2013,570(1):479-484
Abstract The electron spin resonance of (TMTSF)2PF6 has been observed at low fields (Ho < 110 Oe) in the high pressure, metallic phase (p > 6.5 kbar) in the temperature range 1-4?K. The anisotropy in the g value is similar to that observed at ambient pressure above the metal-insulator transition. The linewidth is very narrow and the spin susceptibility strongly decreases as the superconducting transition is approached from above. We interpret this as evidence for singlet-paired superconductivity. Superconductivity is observed at 1.1 K and the critical field has angular dependence in the be plane. These observations lead us to conclude that (TMTSF)2PF6 is a singlet paired superconductor. 相似文献
75.
Cristiano A. Fonseca Gláucia C.S. Vaz Júlia P.A. Azevedo Felipe S. Semaan 《Microchemical Journal》2011,99(2):186-192
The present study reports some aspects of ion-pair formation between pyridoxine and dodecyl sulphate under suitable conditions of pH, and its application with analytical purposes. Electrochemical behavior of the analite onto a graphite-polyurethane electrode was assessed by both cyclic and square-wave voltammetries under different conditions (pH from 1.2 to 13.0, with and without surfactant), aiming to study its mechanisms and to define best parameters for such determination exploiting the association of electroanalytical variables and ion-pair formation; besides these, electrochemical impedance spectroscopy was also applied to evaluate ion-pair formation and its influence on interfacial fenomena. Best conditions were reach by square-wave voltammetry in pH 4.2 acetate buffer sweeping from + 0.7 to + 1.2 V (vs. Ag|AgClsat) in pulses of 50 mV amplitude and 10 mV step, in a frequency of 10 Hz. The concentration of sodium dodecyl sulphate was optimized being the optimal value a constant submicelar concentration of 3 mmol L-1. Under such conditions a linear dynamic range from 2 to 18 μmol L-1 was observed, providing faster, more selective and sensitive system. Interference studies were also carried out showing no relevant influence of thiamine, riboflavine and nicotinamide over the analysis of pyridoxine. The system was successfully applied to commercial parenteral samples containing thiamine and pyridoxine as purchased, without further treatment. 相似文献
76.
A. H. Parente E. T. A. Marques W. M. Azevedo F. B. Diniz E. H. M. Melo J. L. Lima Filho 《Applied biochemistry and biotechnology》1992,37(3):267-273
A biosensor for glucose utilizing kinetics of glucose oxidase (EC 1.1.3.4.) was developed. The enzyme was immobilized on polyaniline
by covalent bonding, using glutaraldehyde as a bifunctional agent. The system showed a linear response up to 2.2 mM of glucose
with a response time of 2.5–4.0 min. In addition, the immobilized enzyme had a higher activity between pH 6.5 and 7.5. The
system retained 50% of its activity after 30 d of daily use. The optical absorption spectra of the polyaniline/glucose oxidase
electrode after glucose had been added to the buffer solution showed that the absorption band around 800 nm had changed considerably
when glucose was allowed to react with the electrode. This optical variation makes polyaniline a very promising polymer for
use as a support in optical sensor for clinical application. 相似文献
77.
Maria de Ftima Vieira Marques Carla Camargo Pombo Rodrigo Azevedo Silva Anunciata Conte 《Journal of polymer science. Part A, Polymer chemistry》2002,40(17):2979-2986
In this work, propylene was polymerized with isospecific and syndiospecific catalysts in homogeneous and heterogeneous systems. The binary metallocene system of both isospecific and syndiospecific catalysts in the heterogeneous system was also used. Besides the type of catalyst, parameters such as polymerization temperature and pressure were varied to achieve the better conditions for the polymerization. The objective of this work is to investigate the influence of these parameters on the characteristics of the produced polymer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2979–2986, 2002 相似文献
78.
Andrade Breno Henrique da Silva Caluête Rafael Evaristo de Oliveira Danniel Ferreira Gomes Rodinei Medeiros Melo Tadeu Antônio de Azevedo 《Journal of Thermal Analysis and Calorimetry》2020,139(2):905-911
Journal of Thermal Analysis and Calorimetry - Cu–Al–Be polycrystalline SMAs modified with the addition of inoculants show improved ductility, which accredits them for technological... 相似文献
79.
A. Alencar S. Azevedo M. Machado 《Applied Physics A: Materials Science & Processing》2011,102(3):583-591
Interaction of one iron atom with pristine zigzag boron nitride nanotubes with different diameters, ranging from (8,0) to
(12,0), have been investigated using density functional theory calculations. Departing from four initial configurations, considering
each of them interacting with the tubes’ walls either from inside or outside, we have analyzed the adsorbate migration to
the most favorable positions together with the related binding energies and the equilibrium distances as well as the electronic
structure of the final systems. It was observed that the smaller the radius of the tube the lower is the binding energy for
all studied structures, and also that the inner configuration is more stable than the outer one for small radius. For the
preferred position for the iron atom, it was seen that it varies according to the starting configuration and that the iron-first-nitrogen-neighbor
bond length works as a constraint in determining the most favorable position for the adsorbate. Finally, for the electronic
structure, it was observed that the presence of the dopant introduces localized levels at the band gap of the nanotubes and
that those levels are mostly related to the orbitals 3d and 4s of the iron atom. For the inside case, as a consequence of
higher hybridization and a confinement effect, the gap closure is more pronounced for small diameter tubes. For all studied
structures, it was observed a net-spin-polarization equal to 4 μ
B. 相似文献
80.
Wladimir de Azevedo Pribitkin 《Proceedings of the American Mathematical Society》2008,136(9):3089-3094
Under what conditions do the (possibly complex) coefficients of a general Dirichlet series exhibit oscillatory behavior? In this work we invoke Laguerre's Rule of Signs and Landau's Theorem to provide a rather simple answer to this question. Furthermore, we explain how our result easily applies to a multitude of functions.