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排序方式: 共有129条查询结果,搜索用时 250 毫秒
31.
Ziad Khattari Mufeed MaghrabiTony McNally Saadi Abdul Jawad 《Physica B: Condensed Matter》2012,407(4):759-764
The dielectric behavior of polymethyl methacrylate/multi-walled carbon nanocomposites (PMMA/MWCNTs) was investigated using impedance spectroscopy technique. The composites were prepared using melt mixing with MWCNTs loading ranging from 0.01 to 10 wt%. The experimental results showed that the measured impedance reflects the insulating behavior of the host material (PMMA) with no appreciable effects of the filler less than 8.5 wt%. However, for the sample containing 10 wt%, the calculated value of dc conductivity increases with increasing temperature from 2.0×10−6 (Ω m)−1 to attain a value of 4.8×10−6 (Ω m)−1 at 110 °C. The percolation threshold derived from the dielectric data was estimated to be higher than 8.5 wt% and lower than 10 wt%. A temperature dependent electrical relaxation phenomenon was only observed in the sample containing 10 wt% of MWCNTs. The frequency dependence of the ac conductivity data followed a power law. 相似文献
32.
M. H. Abdallah Y. Ramaden S. A. Jawad M. Hassan M. S. Ahmad A. M. Zihlif 《Applied Physics A: Materials Science & Processing》1995,60(5):437-440
The effect of annealing on the electrical properties and the refractive index of red mercuric iodide (HgI2) single crystals is investigated. The ac-impedance and phase angle were measured in the frequency range from 100 Hz to 10 kHz at different annealing temperatures. The ac-conductivity, dielectric constants, loss tangent and the refractive index as a function of frequency are determined. The results are discussed in terms of structural changes taking place as a result of the heat treatment of the HgI2 single crystals. 相似文献
33.
Brett D. Martin Jawad Naciri Martin H. Moore Daniel A. Lowy Michael A. Dinderman Erica C. Pehrsson Banahalli Ratna 《Electrochemistry communications》2009,11(1):169-173
We describe a nanoscale gating effect by an atypical tether-containing polythiophene, [poly(thiophene-3-carboxylic acid 2-(2-(2-(2-ethoxy-ethoxymethyl sulfonate)-ethoxy)-ethoxy)-amide], referred to as poly(TP-OEG-SO4). Cyclic voltammetry data permitted us to calculate liquid-phase ion diffusivities in the polymer as a function of its oxidation state. Diffusivities are more than 350 times higher in the oxidized state versus the reduced state. As a control, poly 3′,4′-dimethyl-[2,2′;5′,2″] terthiophene (DMPT) was synthesized and characterized. On comparing both polymers in the reduced state, we find diffusivities in poly(TP-OEG-SO4) to be more than 4500 times lower than in poly(DMPT). To explain this behavior, we propose a model that features a charge-balancing mechanism by the sulfonate tethers in poly(TP-OEG-SO4), which causes nanoporous regions around the polymer main chains to be opened and closed, leading to the large observed differences in diffusivities. These data suggest that the polymer poly(TP-OEG-SO4) is evidently able to act as a reversible “nanogate” with an open pore structure when oxidized, and a closed one when reduced. 相似文献
34.
Lund Liaquat Ali Omar Zurni Raza Jawad Khan Ilyas 《Journal of Thermal Analysis and Calorimetry》2021,143(2):915-927
Journal of Thermal Analysis and Calorimetry - This study shows multiple solutions, heat transfer characteristics, and stability analysis of the magnetohydrodynamic (MHD) flow of hybrid nanofluid... 相似文献
35.
P. S. Pereira Silva Raza Murad Ghalib Sayed Hasan Mehdi Rokiah Hashim Othman Sulaiman Ali Jawad 《Journal of chemical crystallography》2010,40(12):1150-1154
Abstract
Cyclohexyl N-phenylcarbamate, C13H17NO2 (I), which is a useful target for biotransformations by fungi, has been synthesized and the structure has been solved by X-ray diffraction. The crystals are triclinic, space group P [`1] \bar{1} , with a = 5.2581 (2) ?, b = 9.5080 (3) ?, c = 12.6165 (4) ?, α = 70.544 (2)°, β = 89.075 (2)°, γ = 80.447 (2)°, M r = 219.28, V = 585.96 (3) ?3, Z = 2 and R = 0.065. In the title compound the phenyl ring makes a dihedral angle of 30.68(7)° with the carbamate group The molecules are linked into infinite chains via N–H···O hydrogen bonds along the a axis. These hydrogen-bonded chains are further linked by weaker C–H···π interactions. Quantum-mechanical ab initio calculations for the free molecule reproduce well the observed bond lengths and valency angles but show that the crystal packing might be responsible for the rotation of the phenyl ring out of the carbamate plane in the solid state conformation. 相似文献36.
We study the spherically symmetric collapsing star in terms of dynamical instability. We take the framework of extended teleparallel gravity with a non-diagonal tetrad, a power-law form of the model presenting torsion and a matter distribution as a non-dissipative anisotropic fluid. The vanishing shear scalar condition is adopted to gain insight in a collapsing star. We apply a first order linear perturbation scheme to the metric, the matter, and f(T) functions. The dynamical equations are formulated under this perturbation scheme to develop collapsing equation for finding dynamical instability limits in two regimes, such as the Newtonian and the post-Newtonian regime. We obtain a constraint-free solution of a perturbed time dependent part with the help of a vanishing shear scalar. The adiabatic index exhibits the instability ranges through the second dynamical equation which depend on physical quantities such as the density, the pressure components, the perturbed parts of the symmetry of the star, etc. We also develop some constraints on the positivity of these quantities and obtain instability ranges to satisfy the dynamical instability condition. 相似文献
37.
Anwar Ja’afar Mohamad Jawad Anjan Biswas 《Applied mathematics and computation》2010,216(11):3370-3377
This paper carries out the integration of Burgers equation by the aid of tanh method. This leads to the complex solutions for the Burgers equation, KdV-Burgers equation, coupled Burgers equation and the generalized time-delayed Burgers equation. Finally, the perturbed Burgers equation in (1+1) dimensions is integrated by the ansatz method. 相似文献
38.
This paper reflects the implementation of a reliable technique which is called modified simple equation method (MSEM) for solving evolution equations. The proposed algorithm has been successfully tested on two very important evolution equations namely Fitzhugh-Nagumo equation and Sharma-Tasso-Olver equation. Numerical results are very encouraging. 相似文献
39.
Qishun Li Shahid Zaman Wanting Sun Jawad Alam 《International journal of quantum chemistry》2020,120(9):e26154
Let L n denote a linear pentagonal chain with 2n pentagons. The penta-graphene (penta-C), denoted by R n is the graph obtained from L n by identifying the opposite lateral edges in an ordered way, whereas the pentagonal Möbius ring is the graph obtained from the L n by identifying the opposite lateral edges in a reversed way. In this paper, through the decomposition theorem of the normalized Laplacian characteristic polynomial and the relationship between its roots and the coefficients, an explicit closed-form formula of the multiplicative degree-Kirchhoff index (resp. Kemeny's constant, the number of spanning trees) of R n is obtained. Furthermore, it is interesting to see that the multiplicative degree-Kirchhoff index of R n is approximately of its Gutman index. Based on our obtained results, all the corresponding results are obtained for . 相似文献
40.
NaSMe in toluene leads to regioselective de-C-silylation of the bis[(trimethylsilyl)ethynyl]saccharide 2 , but to decomposition of butadiynes such as 1 or 12 . We have, therefore, combined the known reagent-controlled, regioselective desilylation of 2 and of 12 (AgNO2/KCN) with a substrate-controlled regioselective de-C-silylation, based on C-silyl groups of different size. This combination was studied with the fully protected 3 which was mono-desilylated to 4 or to 5 (Scheme 1). Triethylsilylation of 5 (→ 6 ) was followed by removal of the Me3Si group (→ 7 ), introduction of a (t-Bu)Me2Si group (→ 8 ) and removal of the Et3Si group yielded 9 ; these high-yielding transformations proceed with a high degree of selectivity. Iodination of 4 gave 10 . The latter was coupled with 5 to the homodimer 11 and the heterodimer 12 , which was desilylated to 13 . The second building block for the tetramer was obtained by coupling 14 (from 7 ) with 5 , leading to 15 and 16 . Removal of the Me3Si group (→ 17 ) and iodination led to 18 which was coupled with 13 to the homotetramer 20 and the heterotetramer 19 (Scheme 2). Deprotection of 19 gave 21 , which was, on the one hand, iodinated to 22 , and, on the other hand, protected by the (t-Bu)Me2Si group (→ 23 ). Removal of the Et3Si group (→ 24 ) and coupling afforded the homooctamer 26 and the heterooctamer 25 . Yields of iodination, silylation, and desilylation were consistently high, while heterocoupling proceeded in only 50–55%. Cleavage of the (i-Pr)3SiC and MeOCH2O groups of 11 (→ 27 ), 15 (→ 28 ), 20 (→ 29 ) and 26 (→ 30 ) proceeded in high yields (Scheme 3). Complete deprotection in two steps of the heterocoupling products 16 (→ 31 → 32 ), 19 (→ 33 → 34 ), and 25 (→ 35 → 36 ) gave the unprotected dimer 32 , tetramer 34 , and octamer 36 in high yields (Scheme 4). Only the dimer 32 is soluble in H2O; the 1H-NMR spectra of 32 , 34 , and 36 in (D6)DMSO (relatively low concentration) show no signs of association. 相似文献