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81.
    
The phenomenon of system churn degrades the lookup performance of distributed hash table (DHT) systems greatly. To handle the churn, a number of approaches have been proposed to date. However, there is a lack of theoretical analysis to direct how to make design choices under different churn rates and how to configure their parameters optimally. In this paper, we analytically study three important aspects on optimizing DHT lookup performance under churn, i.e. lookup strategy, lookup parallelism and lookup key replication. Our objective is to build a theoretical basis for designers to make better design choices in the future. We first compare the performance of two representative lookup strategies—recursive routing and iterative routing—and explore the existence of better alternatives. Then we study the effectiveness of lookup parallelism in systems with different churn rates and show how to select the optimal degree of parallelism. Owing to the importance of key replication on lookup performance, we also analyze the reliability of the replicated key under two different replication policies, and show how to perform proper configuration. Besides the analytical study, our results are also validated by simulation, and Kad is taken as a case to show the meaningfulness of our analysis. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
82.
    
Abstract— The De Montfort University (DMU) autostereoscopic 3‐D display, intended for television applications, is described. It provides freedom of viewer movement over a typical “living room” sized area, with no restrictions on viewer's head positions. The display is capable of supplying 3‐D images to multiple viewers who do not need to wear special glasses. It operates by producing regions (exit pupils) in the viewing field where either a left or a right image is perceived. The positions of the exit pupils are steered to the viewers' eyes by the use of head tracking. Design issues that became apparent during the construction of a first prototype, and the findings from tests on it, are described. In addition, the current status of a more advanced prototype is reported.  相似文献   
83.
    
Abstract— Under the European Union funded Advanced Three‐dimensional Television System Technologies (ATTEST) project, De Montfort University (DMU) is developing a 3D display system targeted specifically at domestic television applications. This system uses a modified transmissive LCD panel together with novel backlighting and optics to project multiple viewing regions, or exit pupils, into the viewing space. These exit pupils are located in space using a head tracker. The display accommodates multiple viewers simultaneously and imposes no physical constraints, such as special eyewear. Viewers may move freely over a “typical” room‐sized area. The design of the backlighting facilitates many other display regimes beyond the “standard” 3DTV mode in which each viewer sees the same image pair.  相似文献   
84.
85.
The effects of frusemide on the urinary excretion of dopamine and 5-hydroxytryptamine (5-HT) were investigated in eight healthy male subjects in a randomized, placebo-controlled, cross-over study. Frusemide produced the expected rise in urinary dopamine excretion but it did not affect 5-HT excretion when compared with placebo. The lack of an effect on 5-HT excretion in man contrasts with studies in the rat which have reported a marked increase in 5-HT excretion after administration of this loop diuretic.  相似文献   
86.
Two experiments tested an information-processing model of causal judgment proposed by D. L. Hamilton, P. D. Grubb, D. A. Acorn, T. K. Trolier, and S. Carpenter (1990). In Exp 1 the explanatory quality (plausibility, sufficiency, and likelihood) of context information pertaining to a behavioral event was varied independently of its implications for internal or external causality. In Exp 2 perceivers performed tasks requiring either item-specific elaboration or relational encoding of the information in addition to making external versus internal causal attributions. Results imply that (a) perceivers encode the causal potency of individual information items even when the judgment task requires only a general internal versus external attribution and (b) perceivers engage in multiple modes of encoding information, depending on the implicational structure of the information array and on the explanatory quality of the context items. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
87.
The fracture toughness under mixed-mode I/III loading conditions was evaluated for a quaternary 8090 Al-Li-Cu-Mg alloy in underaged and peak-aged conditions. The mixed-mode fracture behavior was found to be significantly different for the two aging conditions. Super-imposed mode III component lowered the fracture resistance of the alloy in underaged condition, whereas it had no significant effect in peak-aged condition. The results obtained have been discussed in the light of the prevalent fracture processes, namely, transgranular shear and ductile intergranular fracture mechanisms. Further, these results are analyzed in terms of different frac-ture criteria and they were found to deviate significantly from those predicted by the energy release rate criterion. On leave from the Defense Metallurgical Research Laboratory, Hyderbad  相似文献   
88.
Multiple scale meshfree methods for damage fracture and localization   总被引:7,自引:0,他引:7  
The Reproducing Kernel Particle Method (RKPM), which utilizes the fundamental notions of the convolution theorem, multiresolution analysis and meshfree properties, is reviewed. The multiple-scale RKPMs are then proposed as an alternative to commonly used numerical methods such as the finite element method. The elimination of a mesh, combined with the filtering properties of window functions, makes a particle method suitable for problems with large deformations, high gradients, and localization problems. This class of methods has been applied to shear band problems, and large deformation fracture and damage problems.  相似文献   
89.
A novel microstrip ring hybrid incorporating a PBG cell   总被引:1,自引:0,他引:1  
An experimental investigation of a novel compact microstrip 180° ring hybrid incorporating a one-dimensional (1-D) slow-wave structure, in the form of perforations on the ring itself, is presented. The size of the hybrid is reduced by 23% due to the slow-wave effect, and this size reduction technique has potential applications in MICs and MMICs. The measured insertion loss is comparable to that of a conventional microstrip hybrid  相似文献   
90.
In this paper, we examined mixing of various two-fluid flows in a silicon/glass microchannel based on the competition of dominant forces in a flow field, namely viscous/elastic, viscous/viscous and viscous/inertial. Experiments were performed over a range of Deborah and Reynolds numbers (0.36 < De < 278, 0.005 < Re < 24.2). Fluorescent dye and microshperes were used to characterize the flow kinematics. Employing abrupt convergent/divergent channel geometry, we achieved efficient mixing of two-dissimilar viscoelastic fluids at very low Reynolds number. Enhanced mixing was achieved through elastically induced flow instability at negligible diffusion and inertial effects (i.e. enormous Peclet and Elasticity numbers). This viscoelastic mixing was achieved over a short effective mixing length and relatively fast flow velocities.  相似文献   
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