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61.
Robert D. Lotz Brian E. Thompson Christopher A. Konings Farhad Davoudzadeh 《国际流体数值方法杂志》1997,24(4):355-373
Numerical uncertainties are quantified for calculations of transonic flow around a divergent trailing edge (DTE) supercritical aerofoil. The Reynolds-averaged Navier–Stokes equations are solved using a linearized block implicit solution procedure and mixing-length turbulence model. This procedure has reproduced measurements around supercritical aerofoils with blunt trailing edges that have shock, boundary layer and separated regions. The present effort quantifies numerical uncertainty in these calculations using grid convergence indices which are calculated from aerodynamic coefficients, shock location, dimensions of the recirculating region in the wake of the blunt trailing edge and distributions of surface pressure coefficients. The grid convergence index is almost uniform around the aerofoil, except in the shock region and at the point where turbulence transition was fixed. The grid convergence index indicates good convergence for lift but only fair convergence for moment and drag and also confirms that drag calculations are more sensitive to numerical error. © 1997 by John Wiley and Sons, Ltd. 相似文献
62.
63.
A variety of alcohols and phenols are efficiently acetylated with acetic anhydride in the presence of a catalytic amount of V(HSO4)3 in solution and under solvent free conditions.Mild reaction conditions,high yields of the products,easy procedure and selective acetylation of alcohols and phenols in the presence of amines and thiols are the main advantages of this procedure. 相似文献
64.
Farhad Shirini Mohammad Ali Zolfigol Masoumeh Abedini 《Monatshefte für Chemie / Chemical Monthly》2009,141(10):61-64
Abstract
Saccharin sulfonic acid was easily prepared by the reaction of saccharin with neat chlorosulfonic acid at room temperature. This reagent is efficiently able to catalyze the chemoselective trimethylsilylation of alcohols with hexamethyldisilazane in the presence of amines and thiols. 相似文献65.
The reaction of dithiocarbamate salts ( IV a − c ) with bis(naphthalene chloroacetates) ( II a,b ) and bis(naphthalene ethoxybromide) ( II c ) in dimethylformamide (DMF) furnished corresponding podands as V a − i in high to excellent yields. Three reacting ligands, ( II a,b ) and ( II c ), were obtained in the reaction of bis(naphthalene) ( I a,b ) with chloroacetylchloride and 1,2‐dibromoethane. Dynamic NMR spectroscopic data of three series of podands ( V a − c , V d−f , and V g − i ) are discussed, and their free energy of activation (Δ GC≠) at coalescence temperatures are figured out. The Δ GC≠ s of these podands were attributed to conformational isomerization in the range of 14.5–18.3 kcal mol−1 due to rotation and resonance effects about thioamide C N bond. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:659–668, 2011; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20730 相似文献
66.
Experimental and theoretical investigation on the microstructure of aluminum alloys during extrusion
The purpose of this work is the investigation of the material behavior of aluminum alloys during extrusion and cooling. In particular, the alloys of the 6000 series (Al–Mg–Si) and 7000 series (Al–Zn–Mg) are relevant here. Under the corresponding conditions, their behavior is controlled mainly by dynamic recovery during the extrusion and static recrystallization during cooling. For the development of a suitable material model EBSD measurements are done on different parts of an extruded Al6060 specimen. For this sample a microstructure picture is generated and a statistical analysis is performed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
67.
Hassan Bassereh Vahid Salari Farhad Shahbazi Tapio Ala-Nissila 《The European Physical Journal B - Condensed Matter and Complex Systems》2017,90(6):111
We consider quantum excitation energy transport (EET) in a network of two-state nodes in the Markovian approximation by employing the Lindblad formulation. We find that EET from an initial site, where the excitation is inserted to the sink, is generally inefficient due to the inhibition of transport by localization of the excitation wave packet in a symmetric, fully-connected network. We demonstrate that the EET efficiency can be significantly increased up to ≈100% by perturbing hopping transport between the initial node and the one connected directly to the sink, while the rate of energy transport is highest at a finite value of the hopping parameter. We also show that prohibiting hopping between the other nodes which are not directly linked to the sink does not improve the efficiency. We show that external dephasing noise in the network plays a constructive role for EET in the presence of localization in the network, while in the absence of localization it reduces the efficiency of EET. We also consider the influence of off-diagonal disorder in the hopping parameters of the network. 相似文献
68.
Farhad Darabi 《Central European Journal of Physics》2014,12(9):678-686
The dynamics of large scale gravitational structures like galaxies, local groups and clusters is studied based on the so-called Liquid-Droplet model describing the saturation property of the nuclear force. Using the assumption that the gravitational force is also saturated over large scale structures, it is argued that the Newtonian gravitational potential may be replaced by an effective Machian gravitational potential. Application of this new potential at these large scale structures may give the rotation curves in good agreement with observations. Then, the virial theorem for this kind of gravitational interaction is developed and also the Tully-Fisher relation is obtained. A physical explanation is given for the so-called constant acceleration in the MOND as the effective gravitational strength of these structures. Finally, a brief argument is given for comparison with dark matter models. 相似文献
69.
In this paper we proposed optical NOR and NAND gates. By combining nonlinear Kerr effect with photonic crystal ring resonators first we designed a structure, whose optical behavior can be controlled via input power intensity. The switching power threshold obtained for this structure equal to 2 kW/μm2. For designing the proposed optical logic gates we employed two resonant rings with the same structures, both rings at the logic gates were designed such that their resonant wavelength be at λ = 1550 nm. Every proposed logic gate has one bias and two logic input ports. We used plane wave expansion and finite difference time domain methods for analyzing the proposed structures. 相似文献
70.
Photonic crystal ring resonators are promising candidates for realizing all optical filters with acceptable transmission efficiency and quality factor values. In this paper, by putting a12-fold quasi crystal at the middle of on 7 × 7 square cavity we created a ring resonator structure and designed a T-shaped channel drop filter. The drop wavelength of our filter is at 1551 nm, with transmission efficiency and quality factor equal to 90% and 387. Our structure is composed of dielectric rods immersed in air. Because in this kind of structures the dominant band gap is in TM mode, all of our simulations have been done in TM mode. The total footprint of our filter is 242.4 μm2, which makes it suitable for all optical integrated circuits. 相似文献