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排序方式: 共有244条查询结果,搜索用时 31 毫秒
1.
Manjin Kim Qinfen Gu Tanveer Hussain Yahia Ali Trevor B. Abbott Kazuhiro Nogita 《International Journal of Hydrogen Energy》2021,46(53):27096-27106
With superior properties of Mg such as high hydrogen storage capacity (7.6 wt% H/MgH2), low price, and low density, Mg has been widely studied as a promising candidate for solid-state hydrogen storage systems. However, a harsh activation procedure, slow hydrogenation/dehydrogenation process, and a high temperature for dehydrogenation prevent the use of Mg-based metal hydrides for practical applications. For these reasons, Mg-based alloys for hydrogen storage systems are generally alloyed with other elements to improve hydrogen sorption properties. In this article, we have added Na to cast Mg–La alloys and achieved a significant improvement in hydrogen absorption kinetics during the first activation cycle. The role of Na in Mg–La has been discussed based on the findings from microstructural observations, crystallography, and first principles calculations based on density functional theory. From our results in this study, we have found that the Na doped surface of Mg–La alloy systems have a lower adsorption energy for H2 compared to Na-free surfaces which facilitates adsorption and dissociation of hydrogen molecules leading to improvement of absorption kinetic. The effect of Na on the microstructure of these alloys, such as eutectic refinement and a density of twins is not highly correlated with absorption kinetics. 相似文献
2.
Modeling of musculoskeletal structures requires accurate data on anatomical parameters such as muscle lengths (MLs), moment arms (MAs) and those describing the upper limb position. Using a geometrical model of planar arm movements with three degrees of freedom, we present, in an analytical form, the available information on the relationship between MAs and MLs and joint angles for thirteen human upper limb muscles. The degrees of freedom included are shoulder flexion/extension, elbow flexion/extension, and either wrist flexion/extension (the forearm in supination) or radial/ulnar deviation (the forearm in mid-pronation). Previously published MA/angle curves were approximated by polynomials. ML/angle curves were obtained by combining the constant values of MLs (defined by the distance between the origin and insertion points for a specific upper limb position) with a variable part obtained by multiplying the MA (joint radius) and the joint angle. The MAs of the prime wrist movers in radial/ulnar deviation were linear functions of the joint angle (R2 > or = 0.9954), while quadratic polynomials accurately described their MAs during wrist flexion/extensions. The relationship between MAs and the elbow angle was described by 2nd, 3rd or 5th-order polynomials (R2 > or = 0.9904), with a lesser quality of fit for the anconeus (R2 = 0.9349). In the full range of angular displacements, the length of wrist, elbow and shoulder muscles can change by 8.5, 55 and 200%, respectively. 相似文献
3.
Mechanical stimulation, as provided by physiotherapy or controlled motion is essentially the only factor able to improve anterior cruciate ligament (ACL) healing. We investigate the cellular effects of such stimulus. Two types of stimulations are applied on canine ACL fibroblasts: repetitive stretch of an elastomeric adhesion substrate and a laminar flow of culture media over the culture surface. Cell orientation, proliferation rate, synthesis and type of collagen as well as proteoglycans (PG) synthesis and hydrodynamic characteristics have been studied. According to our results, the fibroblasts tend to align perpendicularly to the deformation axis of their substrate, and along a laminar flow. The shear stress induced by the laminar flow does not modify significantly proliferation rate nor extracellular matrix synthesis. Substrate stretching however, increases proliferation rate, collagen synthesis, mostly type III, and PG synthesis, principally of small sizes. The characteristics of fibroblasts submitted to repeated deformation match those of fibroblasts from ligament scar tissues. Their orientation perpendicular to substratum deformation differs from the one usually encountered in the undamaged tissue: aligned on the ligament axis. 相似文献
4.
Yahia Lebbah 《Artificial Intelligence》2002,139(1):109-132
Search algorithms for solving Numeric CSPs (Constraint Satisfaction Problems) make an extensive use of filtering techniques. In this paper1 we show how those filtering techniques can be accelerated by discovering and exploiting some regularities during the filtering process. Two kinds of regularities are discussed, cyclic phenomena in the propagation queue and numeric regularities of the domains of the variables. We also present in this paper an attempt to unify numeric CSPs solving methods from two distinct communities, that of CSP in artificial intelligence, and that of interval analysis. 相似文献
5.
The success of several constraint-based modeling languages such as OPL, ZINC or COMET, appeals for better software engineering
practices, particularly in the testing phase. This paper introduces a testing framework enabling automated test case generation
for constraint programming. We propose a general framework of constraint program development which supposes that a first declarative
and simple constraint model is available from the problem specifications analysis. Then, this model is refined using classical
techniques such as constraint reformulation, surrogate, redundant, implied, global constraint and symmetry-breaking to form
an improved constraint model that must be thoroughly tested before being used to address real-sized problems. We think that
most of the faults are introduced in this refinement step and propose a process which takes the first declarative model as
an oracle for detecting non-conformities and derive practical test purposes from this process. We implemented this approach
in a new tool called CPTEST that was used to automatically detect non-conformities on classical benchmark programs, such as the Golomb rulers, n-queens,
social golfer and the car-sequencing problems. 相似文献
6.
When setting up a meeting, meeting participants need to reach a mutual agreement to hold the meeting subject to their personal constraints and preferences. It is a time-consuming process, and a variety of calendaring applications are in use assisting users to schedule meetings. Software applications failed to overcome the constraints of the traditional-scheduling process and works as a supporting tool for managing meeting information. One of the main constraints in automated scheduling is the unavailability of a standard structured communication protocol. In addition, automated scheduling requires other issues to be considered such as automated decision-making paradigm, negotiation strategy selection mechanism, etc. This paper proposes a personal meeting scheduling agent (PMSA) and a personal meeting scheduling protocol (PMSP). PMSP is embedded in the PMSA for handling bilateral and multilateral negotiations. PMSA is designed using model-based, goal-based methodology. Additionally, PMSP is designed following a structured negotiation protocol influenced by simultaneous response protocol. To evaluate all meeting invitations and to make decisions subject to users’ preferences, participants’ profiles, and the schedule availability, this paper utilizes the naïve Bayes model of maximum likelihood Estimation. The PMSP goal is to automatically make decisions and select the appropriate negotiation strategies to avoid or resolve possible meeting conflicts. To demonstrate the feasibility of the proposed PMSP, a simulation environment with experimental results is presented. 相似文献
7.
8.
Elhadi Shakshuki Hsiang-Hwa Koo Darcy Benoit Daniel Silver 《Journal of Computer and System Sciences》2008,74(2):279-296
Electronic calendars are important tools that are used by consumers on a daily basis. However, scheduling a meeting that involves persons with different commitments and preferences remains a difficult task. Meeting scheduling is difficult because current calendaring applications cannot handle the responsibility of automatically and autonomously managing time slots. This paper presents a distributed multi-agent system architecture in which each person is represented by an agent. These agents automatically and autonomously work together to assist different users to book meetings on their behalf. Each agent has the capability to manage, negotiate and schedule tasks, meetings, events, appointments for its assigned user. In this multi-agent system, the agents coordinate their activities and negotiate on behalf of their associated users to find a solution that satisfies the users' meeting requirements and preferences. A prototype of this system is implemented to demonstrate how the agents can automatically book meetings. 相似文献
9.
Moussa Yahia Pascal Acco Malek Benslama 《International Journal of Control, Automation and Systems》2011,9(6):1021-1027
This paper proposes to decompose the nonlinear dynamic of a chaotic system with Chebyshev polynomials to improve performances
of its estimator. More widely than synchronization of chaotic systems, this algorithm is compared to other nonlinear stochastic
estimator such as Extended Kalman Filter (EKF) and Unscented Kalman Filter (UKF). Chebyshev polynomials orthogonality properties
is used to fit a polynomial to a nonlinear function. This polynomial is then used in an Exact Polynomial Kalman Filter (ExPKF)
to run real time state estimation. The ExPKF offers mean square error optimality because it can estimate exact statistics
of transformed variables through the polynomial function. Analytical expressions of those statistics are derived so as to
lower ExPKF algorithm computation complexity and allow real time applications. Simulations under the Additive White Gaussian
Noise (AWGN) hypothesis, show relevant performances of this algorithm compared to classical nonlinear estimators. 相似文献
10.
Tarek Sheltami Anas Al-Roubaiey Elhadi Shakshuki Ashraf Mahmoud 《Multimedia Systems》2009,15(5):273-282
Mobile Ad-hoc NETworks (MANET) are infrastructureless networks where self-configuring mobile nodes are connected by wireless
links. Because of its decentralized operation, these nodes rely on each other to store and forward packets. Video transmission
over MANETs is more challenging than over conventional wireless networks due to rapid topology changes and lack of central
administration. Most of the proposed MANET protocols assume that all nodes are working within a cooperative and friendly network
context. However, misbehaving nodes that exhibit abnormal behaviors can disrupt the network operation and affect the network
availability by refusing to cooperate to route packets due to their selfish or malicious behavior. In this paper, we examine
the effect of packet dropping attacks on video transmission over MANETs. We also study the effects of mitigation using intrusion
detection systems to MANET in presence of video traffic. To the best of our knowledge, this is the first attempt to study
multimedia over such environments. We propose a novel intrusion detection system, which is an adaptive acknowledgment scheme
(AACK) with the ability to detect misbehaved nodes and avoid them in other transmissions. The aim of AACK scheme is to overcome
watchdog weaknesses due to collisions and limited transmission power and also to improve TWOACK scheme. To demonstrate the
performance of our proposed scheme, simulation experiments are performed. The results of our experiments show that MPEG4 is
more suitable for our simulation environment than H264 video traffic. The simulation results show that AACK scheme provides
better network performance with less overhead than other schemes; it also shows that AACK outperforms both TWOACK and watchdog
in video transmission applications in the presence of misbehaving nodes. 相似文献