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21.
The human tooth faces different stresses under environments of different loading conditions, these loading produces major factors in weakness of the tooth and bone structure. The need to save natural teeth has prompted the development of novel and complex techniques in endodontology, prosthodontics and periodontology. Despite a poor long-term prognosis and some prejudice to local bone, considerable efforts have been exerted for the realization of these techniques. Nowadays, the 3D finite element analysis (FEA) is one of the more recently used techniques for stress analysis in single human tooth under different loading cases. The von Mises stress distribution indicated that the greatest effort area of tooth lies at the base of crown up to the gingival line with varying intensities in the different loading cases. The highest stress in the cortical bone was predominantly found around the cervical region of the tooth and lowest in the cancellous bone and periodontal ligament (PDL). The PDL is a soft tissue, and it could function as an intermediate cushion element which absorbs the impact force and uniformly transfers the occlusal forces into the surrounding bone.  相似文献   
22.
To elaborate tailor‐made proton conducting materials showing an interesting range of flexibility, a series of conetworks combining poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid) (PAMPS) and poly(ethylene oxide) dimethacrylate (PEGDM) with various chain lengths was synthesized. The homogeneity of these conetworks was checked by differential scanning calorimetry and dynamic mechanical thermal analysis. The swelling behavior of these materials is strongly influenced by the amount of sulfonic acid groups and the endothermal peak temperature, characteristic of the presence of bound water in the conetwork, increases from 65 to 120°C when AMPS amount increases from 10 to 75 wt %. In addition, the proton conductivity of these materials varies from 10?3 to 10?1 S cm?1, depending on the AMPS amount. The storage moduli were found to be affected by both the AMPS content in the conetwork and its crosslinking density. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  相似文献   
23.
Hyperbranched polyesters of 2,2-bis(hydroxymethyl)propanoic acid (BMPA) with various molar ratios of tetra(hydroxymethyl)methane (PE) core molecule were characterized by NMR spectroscopy and MALDI-TOF mass spectrometry. In all polyesters, the formation of ether groups was observed. The extent of etherification increased with increasing PE content. This was assigned to a higher reactivity of PE towards etherification than BMPA. Intra- and intermolecular etherifications and intramolecular esterifications were detected by MALDI-TOF MS on the core molecule-containing polyesters, resulting in the formation of cycle-containing hyperbranched molecules. The ratio of cycle-containing molecules reached 50% at high reaction time for the polyester without core molecule, but was much lower for the polyesters containing a core molecule. As a consequence of these side reactions, the control of hyperbranched polyester molar mass by varying the core molecule (chain limiter) molar ratio is much more difficult than for linear polyesters.  相似文献   
24.
The underlying idea behind the classical Lévêque problem was to provide a simple asymptotic solution for the incipient development of the mass (heat) boundary layer flow in a round tube. Inspired by physical concepts, Lévêque assumed that the hydrodynamic boundary layer was confined to a thin annular region near the tube wall so that the fluid velocity varied linearly with y = R ? r, y being the distance measured from the wall. The present article addresses the Lévêque problem from a mathematical perspective, adhering to the original concentration conservation equation in cylindrical coordinates continually without making any hydrodynamic assumptions a priori. The approximate solution procedure to be pursued here combines the transversal method of lines (TMOL) with the Fröbenius power series method. The quality of the local and global mass transfer results obtained with the new TMOL/Fröbenius methodology surpasses the quality of the counterpart results determined by the traditional Lévêque approach.  相似文献   
25.
For three decades, hydrogen has been identified as a versatile potential fuel concurrent to the conventional fuel such as gasoline. In order to fully implement it and to develop the combustion based power devices that may supply much higher energy density, it is very essential to understand the mechanism of Hydrogen/Air combustion. In this work, Computational Fluid Dynamics (CFD) numerical simulations have been performed to study the combustion of non-premixed turbulent hydrogen-air mixture with different equivalence ratios and different mass flow rates and its effect on different species formation, peak temperature and NOx formation. The performance of the combustor is evaluated by using FLUENT software under adiabatic wall condition. Generalized finite rate chemistry model was used to analyze the hydrogen-air combustion system. The combustion is modeled using multi-step reaction mechanism with 14 species, until complete conversion of fuel to H2O. Through such a systematic analysis, a proper controlled operation condition for the combustor is suggested which may be used as a guideline for combustor design. Results reported in this work illustrate that the CFD simulation can be one of the most powerful, beneficial and economical tool for combustor design and for optimization and performance analysis. They are more sensitive to the model of the transport properties while the reasonable results can be achieved even with the use of global reaction mechanism and a simple turbulence model as k- ε, which are not excessively time and memory consuming. From an environmental point view, this study shows that the radical production (OH and NO) is very small although maximum temperature reached exceeded 2000 (K). The mass fraction of NO is much lower if we increase the air inlet velocity, which makes the cold reaction mixture do not promote the NO formation by dissociation.  相似文献   
26.
Pattern Analysis and Applications - Instance and variable selection involve identifying a subset of instances and variables such that the learning process will use only this subset with better...  相似文献   
27.
Journal of Mechanical Science and Technology - In order to estimate the seismic demand by using the nonlinear static procedure, different approximate methods have been developed. One of the most...  相似文献   
28.
Conclusions The use of four different indicators has been investigated in the titrimetric determination of the weight proportion of benzoic acid in molten caprolactam.It has been shown that the phenolphthalein indicator which is used at present for benzoic acid analysis is not suitable. Tropeolin 000 may be recommended for use instead of it.Translated from Khimicheskie Volokna, No. 5, pp. 56–57, September–October, 1987.  相似文献   
29.
Chikh  C. Mahdjoubi  K. Terret  C. 《Electronics letters》1995,31(22):1888-1889
An element by element method of mutual impedance correction is used to take into account the parasitic element effects. It assumes that the elements are characterised by a single radiation mode. The method is then extended to bipolarised arrays and validated experimentally  相似文献   
30.
In order to estimate the flexural behaviour of reinforced concrete members, the stress–strain behaviour of the constituent materials must be well established. The behaviour of confined concrete is important to the designer in order to determine the quantity of the confining steel required in reinforced concrete column sections to achieve the ultimate curvatures required in seismic design for ductility. The objective of this study is to develop an analytical model for the confinement mechanism in rectangular reinforced concrete columns. The proposed model was established on the basis of the observations derived from several experimental studies conducted in past years and encompasses some features of already established models. The main variables examined in the model include the volumetric ratio of lateral reinforcement, the characteristics of steel and concrete and the effectiveness confinement coefficient. The comparison with other existing models illustrates the validity of the proposed equations.
Résumé L’issue fondamentale permettant de définir la capacité flexionnelle des éléments en béton armé est la connaissance des lois contraintes déformations des matériaux constitutifs. Le comportement du béton confiné est donc l’élément capital qui devra permettre au concepteur d’estimer, par utilisation de l’armature transversale, la ductilité de courbure exigée pour une demande de ductilité désirée. L’objectif de cette étude est de développer un modèle analytique tenant compte du mécanisme de confinement dans les poteaux en béton armé. Le modèle est basé sur une analyse rigoureuse de modèles analytiques existants et une exploitation de données expérimentales réalisées durant les deux dernières décennies. L’étude a pris en considération l’influence des différents paramètres, notamment le rapport volumétrique des aciers transversaux, les caractéristiques mécaniques de l’acier et du béton et le coefficient efficace de confinement. La comparaison avec d’autres modèles existants confirme la validité des équations proposées.
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