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91.
Inés González-Rodríguez Camino R. Vela Jorge Puente 《Journal of Intelligent Manufacturing》2010,21(1):65-73
In this work we consider a multiobjective job shop problem with uncertain durations and crisp due dates. Ill-known durations
are modelled as fuzzy numbers. We take a fuzzy goal programming approach to propose a generic multiobjective model based on
lexicographical minimisation of expected values. To solve the resulting problem, we propose a genetic algorithm searching
in the space of possibly active schedules. Experimental results are presented for several problem instances, solved by the
GA according to the proposed model, considering three objectives: makespan, tardiness and idleness. The results illustrate
the potential of the proposed multiobjective model and genetic algorithm. 相似文献
92.
Iván García-Magariño Rubén Fuentes-Fernández Jorge J. Gómez-Sanz 《Information and Software Technology》2010,52(4):422-435
Computer-Aided Software Engineering (CASE) tools support modeling-related activities in development projects. Given the variety of tools and functionalities, it is quite common to work with several tools in the same project. However, data cannot usually be exchanged between these tools without loss of information. Recent approaches address this model interchange problem using metamodels to characterize the involved information and transformations to export/import it. Nevertheless, most of these solutions focus on the abstract syntax of models. They fail to consider aspects such as the presentation of models or tool-specific information, which are either disregarded or represented in ad-hoc ways that make difficult their processing. In order to overcome these limitations, this paper introduces a framework to define metamodels of CASE tools and a process to carry out the model interchange using them. The proposed metamodels have a modular organization with several internal metamodels. Each of them is aimed at describing some specific information about content, structure and presentation for both models and tools. The paper illustrates this approach with a case study used for comparison with existing works for this problem. 相似文献
93.
Cândida M. Pereira Jorge A. Ambrósio Amílcar L. Ramalho 《Multibody System Dynamics》2010,24(3):303-324
To overcome the difficulty on building manually complex models of chain drives, this work proposes a comprehensive methodology to build multibody models of any general chain drive automatically from a minimal set of data. The proposed procedure also evaluates the initial positions and velocities of all components of the drive that are consistent with the kinematic joints or with the contact pairs used in the model. In this methodology, all links and sprockets are represented by rigid bodies connected to each other either by ideal or by clearance revolute joints. The clearance revolute joint contact is further extended to handle the contact between the chain rollers and the sprocket teeth exact profiles. A suitable cylindrical continuous contact law is applied to describe the interaction on all contact pairs. One of the complexities of the computational study of roller chain drives is the large number of bodies in the system and the dynamics of the successive engagement and disengagement of the rollers with the sprockets. Each time a roller engages or disengages with a sprocket tooth, the number of rigid bodies in contact changes. The search for the contact pairs is recognized as one of the most time consuming task in contact analysis. This work proposes a procedure to specify the contact pairs and their update during the dynamic analysis optimizing the computational efficiency of the contact search. The methodologies adopted result in a general computer program that is applied and demonstrated in a generic chain drive that can be used in industrial machines, vehicle engines or any other type of mechanical system. 相似文献
94.
Navigational features have been largely recognized as fundamental for graph database query languages. This fact has motivated several authors to propose RDF query languages with navigational capabilities. In this paper, we propose the query language nSPARQL that uses nested regular expressions to navigate RDF data. We study some of the fundamental properties of nSPARQL and nested regular expressions concerning expressiveness and complexity of evaluation. Regarding expressiveness, we show that nSPARQL is expressive enough to answer queries considering the semantics of the RDFS vocabulary by directly traversing the input graph. We also show that nesting is necessary in nSPARQL to obtain this last result, and we study the expressiveness of the combination of nested regular expressions and SPARQL operators. Regarding complexity of evaluation, we prove that given an RDF graph G and a nested regular expression E, this problem can be solved in time O(|G||E|). 相似文献
95.
Dan Lin Prathima Rao Elisa Bertino Ninghui Li Jorge Lobo 《International Journal of Information Security》2010,9(4):253-273
Policy integration and inter-operation is often a crucial requirement when parties with different access control policies
need to participate in collaborative applications and coalitions. Such requirement is even more difficult to address for dynamic
large-scale collaborations, in which the number of access control policies to analyze and compare can be quite large. An important
step in policy integration and inter-operation is to analyze the similarity of policies. Policy similarity can sometimes also
be a pre-condition for establishing a collaboration, in that a party may enter a collaboration with another party only if
the policies enforced by the other party match or are very close to its own policies. Existing approaches to the problem of
analyzing and comparing access control policies are very limited, in that they only deal with some special cases. By recognizing
that a suitable approach to the policy analysis and comparison requires combining different approaches, we propose in this
paper a comprehensive environment—EXAM. The environment supports various types of analysis query, which we categorize in the
paper. A key component of such environment, on which we focus in the paper, is the policy analyzer able to perform several
types of analysis. Specifically, our policy analyzer combines the advantages of existing MTBDD-based and SAT-solver-based
techniques. Our experimental results, also reported in the paper, demonstrate the efficiency of our analyzer. 相似文献
96.
Manuel Silva Jorge Júlvez Cristian Mahulea C. Renato Vázquez 《Discrete Event Dynamic Systems》2011,21(4):427-497
As a preliminary overview, this work provides first a broad tutorial on the fluidization of discrete event dynamic models,
an efficient technique for dealing with the classical state explosion problem. Even if named as continuous or fluid, the relaxed models obtained are frequently hybrid in a technical sense. Thus,
there is plenty of room for using discrete, hybrid and continuous model techniques for logical verification, performance evaluation
and control studies. Moreover, the possibilities for transferring concepts and techniques from one modeling paradigm to others
are very significant, so there is much space for synergy. As a central modeling paradigm for parallel and synchronized discrete
event systems, Petri nets (PNs) are then considered in much more detail. In this sense, this paper is somewhat complementary
to David and Alla (2010). Our presentation of fluid views or approximations of PNs has sometimes a flavor of a survey, but also introduces some new
ideas or techniques. Among the aspects that distinguish the adopted approach are: the focus on the relationships between discrete and continuous PN models, both for untimed, i.e., fully non-deterministic abstractions, and timed versions; the use of structure theory of (discrete) PNs, algebraic and graph based concepts and results; and the bridge to Automatic Control Theory. After discussing
observability and controllability issues, the most technical part in this work, the paper concludes with some remarks and
possible directions for future research. 相似文献
97.
Bruno R. de Araújo Tiago Guerreiro Manuel J. Fonseca Joaquim A. Jorge João M. Pereira Monica Bordegoni Francesco Ferrise Mario Covarrubias Michele Antolini 《Journal of Real-Time Image Processing》2010,5(2):73-90
Currently, the design of aesthetic products is a process that requires a set of activities where digital models and physical
mockups play a key role. Typically, these are modified (and built) several times before reaching the desired design, increasing
the development time and, consequently, the final product cost. In this paper, we present an innovative design environment
for computer-aided design (CAD) surface analysis. Our system relies on a direct visuo-haptic display system, which enables
users to visualize models using a stereoscopic view, and allows the evaluation of sectional curves using touch. Profile curves
are rendered using an haptic device that deforms a plastic strip, thanks to a set of actuators, to reproduce the curvature
of the shape co-located with the virtual model. By touching the strip, users are able to evaluate shape characteristics, such
as curvature or discontinuities (rendered using sound), and to assess the surface quality. We believe that future computer-aided
systems (CAS)/CAD systems based on our approach will contribute in improving the design process at industrial level. Moreover,
these will allow companies to reduce the product development time by reducing the number of physical mockups necessary for
the product design evaluation and by increasing the quality of the final product, allowing a wider exploration and comparative
evaluation of alternatives in the given time. 相似文献
98.
Jorge Cortés Author vitae 《Automatica》2009,45(12):2754-2762
This paper proposes a simple, distributed algorithm that achieves global stabilization of formations for relative sensing networks in arbitrary dimensions with fixed topology. Assuming the network runs an initialization procedure to equally orient all agent reference frames, convergence to the desired formation shape is guaranteed even in partially asynchronous settings. We characterize the algorithm robustness against several sources of errors: link failures, measurement errors, and frame initialization errors. The technical approach combines algebraic graph theory, multidimensional scaling, and distributed linear iterations. 相似文献
99.
Jorge Navarro-Ortiz Pablo Ameigeiras Juan J. Ramos-Munoz Juan M. Lopez-Soler 《Computer Communications》2009,32(11):1281-1297
In this paper we present a solution for the IEEE 802.11e HCCA (Hybrid coordination function Controlled Channel Access) mechanism which aims both at supporting strict real-time traffic requirements and, simultaneously, at handling TCP applications efficiently. Our proposal combines a packet scheduler and a dynamic resource allocation algorithm. The scheduling discipline is based on the Monolithic Shaper-Scheduler, which is a modification of a General Processor Sharing (GPS) related scheduler. It supports minimum-bandwidth and delay guarantees and, at the same time, it achieves the optimal latency of all the GPS-related schedulers. In addition, our innovative resource allocation procedure, called the territory method, aims at prioritizing real time services and at improving the performance of TCP applications. For this purpose, it splits the wireless channel capacity (in terms of transmission opportunities) into different territories for the different types of traffic, taking into account the end-to-end network dynamics. In order to give support to the desired applications, we consider the following traffic classes: conversational, streaming, interactive and best-effort. The so called territories shrink or expand depending on the current quality experienced by the corresponding traffic class. We evaluated the performance of our solution through extensive simulations in a heterogeneous wired-cum-wireless scenario under different traffic conditions. Additionally, we compare our proposal to other HCCA scheduling algorithms, the HCCA reference scheduler and Fair Hybrid Coordination Function (FHCF). The results show that the combination of the MSS and the territory method obtains higher system capacity for VoIP traffic (up to 32 users) in the simulated scenario, compared to FHCF and the HCCA reference scheduler (13 users). In addition, the MSS with the territory method also improves the throughput of TCP sources (one FTP application achieves between 6.1 Mbps without VoIP traffic and 2.1 Mbps with 20 VoIP users) compared to the reference scheduler (at most 388 kbps) and FHCF (with a maximum FTP throughput of 4.8 Mbps). 相似文献
100.
Nina P.G. Salau Gustavo Alberto Neumann Jorge O. Trierweiler Argimiro R. Secchi 《Journal of Process Control》2009,19(3):530-538
In an industrial gas-phase polyethylene reactor, the safe operating range of temperature is rather narrow. Even within this temperature range, temperature excursions must be avoided because they can result in low catalyst productivity and significant changes in product properties. If the manipulated variable for temperature control saturates (i.e., the cooling water valve position is completely open), then the reactor operates without a feedback temperature controller, leading to oscillatory behavior and limit cycles. In this work, it has been demonstrated that the saturation in the manipulated variable and the complex non-linear dynamic behavior are removed when auxiliary manipulated variables, obtained by bifurcation analysis, are used in a multivariable control strategy for the reactor temperature control. Two control structures are proposed and compared considering their impact in the reactor production and polymer melt index. In the first control structure, the designed PID controller for the reactor temperature is considered and a switching strategy with a PI controller for the auxiliary manipulated variables is included. In the second control structure, the designed PID controller for the reactor temperature is also used, however, a MPC controller for the auxiliary manipulated variables is considered. The results suggest that the use of gain-scheduling strategy in the PID temperature controller with a MPC controller for the auxiliary manipulated variables avoids the saturation of the manipulated variable and, hence, the undesired non-linear dynamic behavior, reducing the production loss and improving the product quality. 相似文献