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391.
Ahmed Meskini Mustapha Raihane Chady Hakme Isabelle Stevenson Gérard Seytre 《European Polymer Journal》2009,45(3):804-812
In the frame of a research aiming at developing new dielectric polymers containing CCN and CF substituents with strong dipole moment, statistical copolymers based on cyano monomers such as acrylonitrile (AN), methacrylonitrile (MAN), methylvinylidene cyanide (MVCN) and 2,2,2-trifluoroethylmethacrylate (MATRIF), were synthesized and characterized. Elemental analysis has shown that the molar percentages of AN and MAN in the copolymers were 45 mol.%, while only 5 mol.% of MVCN was incorporated in the poly(MVCN-co-MATRIF) copolymer. These copolymers exhibit glass transition temperatures, Tg, in the range of 70-90 °C. The dynamic dielectric analyses and their complex permittivities of these copolymers were studied versus the temperature and the frequency. Evidence of an α-relaxation phenomenon in the glass transition region, which is confirmed by the Vogel-Fulcher-Tammann (VFT) temperature dependence of the relaxation times, was assigned to the cooperative reorientation motions of the cyano groups. The values of dielectric strength (Δε) for the copolymers based on MATRIF were determined by Havriliak-Negami (HN) fitting from the dispersion curves, and can be related to the polarity of the monomer unit and to the packing of the macromolecular chains. These relaxations are sometimes overlapped by conduction phenomena due to ionic impurities at low frequencies and high temperatures dipolar losses. In the glassy state, the permittivity values of AN and MAN copolymers show an increase of polarity which makes them candidates for some applications amongst advanced electrical materials such as dielectric layer for capacitors. 相似文献
392.
A. F. Jalbout M. Ali Naseri M. Fazli H. Raissi M. Rezaei A. Nowroozi A. de Leon 《International journal of quantum chemistry》2009,109(7):1481-1496
The intramolecular hydrogen bond, molecular structure, and vibrational frequencies of α‐chloro acetylacetone have been investigated. Fourier transform infrared and Fourier transform Raman spectra of this compound and its deuterated analogue were recorded in the regions 400–4,000 cm?1 and 50–4,000 cm?1, respectively. Rigorous normal coordinate analysis has been performed at the B3LYP/6‐311++G** level of theory for purposes of comparison. The complete vibrational assignment for TFAA has been made on the basis of the calculated potential energy distribution. We also applied the atoms in molecules theory and natural bond orbital method for the analysis of the hydrogen bond in α‐Chloro acetylacetone and acetylacetone. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 相似文献
393.
Mustapha El Gouri Abderrahim El Bachiri Salah Eddine Hegazi Mohamed Rafik Ahmed El Harfi 《Polymer Degradation and Stability》2009,94(11):2101-2106
Hexaglycidyl cyclotriphosphazene (HGCP) was synthesized, and characterized by FTIR, 31P, 1H, and 13C-NMR. This compound was used as a reactive flame retardant to blend with commercial epoxy resin DGEBA (Diglycidyl ether of bisphenol A). Its effect on the DGEBA decomposition pathways was characterized by studying both gas and solid phases produced during thermogravimetric analysis (TGA). The gases evolved during TGA in air were studied by means of thermogravimetry coupled with Fourier transform infrared spectroscopy (TG–FTIR), while the solid residues were analysed by FTIR and scanning electron microscopy (SEM). The results showed that HGCP presents a good dispersion in DGEBA, and the blend thermoset with 4,4′-methylene-dianiline (MDA) curing agent leads to a significant improvement of the thermal stability at elevated temperature with higher char yields compared with pure DGEBA thermoset with the same curing agent. Improvement has also been observed in the fire behaviour of blend sample. 相似文献
394.
We employ a piecewise-constant, discontinuous Galerkin method for the time discretization of a sub-diffusion equation. Denoting
the maximum time step by k, we prove an a priori error bound of order k under realistic assumptions on the regularity of the solution. We also show that a spatial discretization using continuous,
piecewise-linear finite elements leads to an additional error term of order h
2 max (1,logk
− 1). Some simple numerical examples illustrate this convergence behaviour in practice.
We thank the University of New South Wales for financial support provided by a Faculty Research Grant. 相似文献
395.
The reaction mechanism between AlX and HX (X = Br, Cl, and F) have been characterized in detail using DFT as well as the ab initio method. The reaction yielding AlX3 and molecular hydrogen was calculated to be highly exothermic. The present calculations also show that the possible routes
to the trihalides species start more favorable with the primary insertion product AlX2H than with the biadduct AlX(HX)2 one.
相似文献
396.
Nejmeddine Jaballah Mejed Chemli Khaled Hriz Jean-Louis Fave Mohamed Jouini Mustapha Majdoub 《European Polymer Journal》2011,47(1):78-87
New conjugated polymers based on separated PPV-type chromophores and incorporating different types of solubilizing side-groups (ethoxy: P1, hexyloxy: P2, dodecyloxy: P3 and benzyloxy: P4) were synthesized via Wittig polycondensation, using a series of bisphenol A-derived di(triphenylphosphonium) salts as starting monomers. The polymers are soluble in common organic solvents and their structures were confirmed by 1H NMR, 13C NMR and FTIR spectroscopies. The optical properties of these materials were investigated by UV–vis absorption and fluorescence spectroscopies. In dilute solution, quasi-identical fluorescence spectra were obtained and all the polymers showed a blue emission (420, 445 nm) and a narrow spectrum. In thin solid films, the polymers show side-group-dependent optical behavior and, whereas the emission remains blue in the case of P2, P3 and P4, a green fluorescence was observed for the ethoxylated polymer P1. From cyclic voltammetry analysis, the electrochemical band gaps were estimated to be 2.99, 3.07, 3.15 and 3.06 eV for P1, P2, P3 and P4, respectively. Single-layer diode devices of the [indium tin oxide/polymer/aluminum] configuration have been fabricated and show relatively low turn-on voltages between 2.6 and 4.9 V. 相似文献
397.
Muhammad Imran Khan Zafar Iqbal Lateef Ahmad Yasar Shah Shabnam Nazir Abbas Khan Fazli Nasir 《Chromatographia》2011,73(9-10):929-939
A highly sensitive, precise, and accurate reversed-phase high-performance liquid-chromatography/electrochemical detection method for simultaneous determination of the endogenous free ??-lipoic acid and dihydrolipoic acid in biological matrices was developed and validated. The two analytes were extracted from the samples with acetonitrile/10% metaphosphoric acid solution(aqueous) (50/50 v/v). To determine the total lipoic acid, samples were treated with tris(2-carboxyethyl)phosphine solution in phosphate buffer, pH 2.5 with 85% orthophosphoric acid prior to deproteination. The two analytes were separated on a C18 (150 × 4.6 mm, 5 ??m) analytical column using acetonitrile-50 mM phosphate buffer, pH 2.5 with 85% orthophosphoric acid (35/65 v/v) as the isocratic mobile phase pumped at a flow rate of 2.0 mL min?1 at the column oven temperature of 35 °C. The column eluents were monitored at a potential of 0.9 V. These analytes were efficiently resolved in <7 min. The present method was sufficiently robust and specific for simultaneous determination of the two analytes and demonstrated acceptable values for linearity (r 2 = 0.999 in the range of 0.1?C500 and 0.25?C1,000 ng mL?1 for ??-lipoic acid and dihydrolipoic acid, respectively), recovery (>97%), precision (RSD% <2), and sensitivity (on column limit of detection, 150 and 375 fg for ??-lipoic acid and dihydrolipoic acid, respectively and limit of quantification: 0.5 and 1.25 pg for ??-lipoic acid and dihydrolipoic acid, respectively), indicating that the proposed method was more sensitive, precise, economical, and versatile, and has higher throughput than the previously reported methods for simultaneous determination of the two analytes. 相似文献
398.
Mustapha Chellali Teresa W. Haynes Stephen T. Hedetniemi Alice McRae 《Discrete Applied Mathematics》2013
A subset S⊆V in a graph G=(V,E) is a [j,k]-set if, for every vertex v∈V?S, j≤|N(v)∩S|≤k for non-negative integers j and k, that is, every vertex v∈V?S is adjacent to at least j but not more than k vertices in S. In this paper, we focus on small j and k, and relate the concept of [j,k]-sets to a host of other concepts in domination theory, including perfect domination, efficient domination, nearly perfect sets, 2-packings, and k-dependent sets. We also determine bounds on the cardinality of minimum [1, 2]-sets, and investigate extremal graphs achieving these bounds. This study has implications for restrained domination as well. Using a result for [1, 3]-sets, we show that, for any grid graph G, the restrained domination number is equal to the domination number of G. 相似文献
399.
Kasmi-Mir S Djafri A Paquin L Hamelin J Rahmouni M 《Molecules (Basel, Switzerland)》2006,11(8):597-602
A rapid and easy solvent free one-pot synthesis of 5-arylidene-2-imino-4-thiazolidinones by condensation of the thioureas with chloroacetic acid and an aldehyde under microwave-irradiation is described. 相似文献
400.
B. Bialecki M. Ganesh K. Mustapha 《Numerical Methods for Partial Differential Equations》2006,22(5):1052-1069
We propose and analyze a Crank–Nicolson quadrature Petrov–Galerkin (CNQPG) ‐spline method for solving semi‐linear second‐order hyperbolic initial‐boundary value problems. We prove second‐order convergence in time and optimal order H2 norm convergence in space for the CNQPG scheme that requires only linear algebraic solvers. We demonstrate numerically optimal order Hk, k = 0,1,2, norm convergence of the scheme for some test problems with smooth and nonsmooth nonlinearities. © 2006 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2006 相似文献