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81.
Sorting by Short Block-Moves 总被引:1,自引:0,他引:1
Sorting permutations by operations such as reversals and block-moves has received much interest because of its applications
in the study of genome rearrangements and in the design of interconnection networks. A short block-move is an operation on
a permutation that moves an element at most two positions away from its original position. This paper investigates the problem
of finding a minimum-length sorting sequence of short block-moves for a given permutation. A 4/3 -approximation algorithm
for this problem is presented. Woven double-strip permutations are defined and a polynomial-time algorithm for this class
of permutations is devised that employs graph matching techniques. A linear-time maximum matching algorithm for a special
class of grid graphs improves the time complexity of the algorithm for woven double-strip permutations.
Received June 1, 1997; revised July 25, 1998. 相似文献
82.
The problem of channel sharing by rate adaptive streams belonging to various classes is considered. Rate adaptation provides
the opportunity for accepting more connections by adapting the bandwidth of connections that are already in the system. However,
bandwidth adaptation must be employed in a careful manner in order to ensure that (a) bandwidth is allocated to various classes
in a fair manner (system perspective) and (b) bandwidth adaptation does not affect adversely the perceived user quality of
the connection (user quality). The system perspective aspect has been studied earlier. This paper focuses on the equally important
user perspective. It is proposed to quantify user Quality of Service (QoS) through measures capturing short and long-term
bandwidth fluctuations that can be implemented with the mechanisms of traffic regulators, widely used in networking for the
purpose of controlling the traffic entering or exiting a network node. Furthermore, it is indicated how to integrate the user
perspective metrics with the optimal algorithms for system performance metrics developed earlier by the authors. Simulation
results illustrate the effectiveness of the proposed framework.
Nikos G. Argiriou received the Diploma degree in Electrical Engineering from the Department of Electrical Engineering, Telecommunication Division, Aristotle University of Thessaloniki, Greece, in 1996. He worked as a researcher, on secure medical image transmission over networks, at the Image Processing Lab at the same university during 1996–1997. During 1998–2000 he was a researcher for the European Project Esprit Catserver concerning the use of advanced Quality of Service techniques in CATV networks. He received his Ph.D. degree at Aristotle University of Thessaloniki in 2007. His current research interests are in the development and implementation of QoS techniques for wired and wireless networks. Leonidas Georgiadis received the Diploma degree in Electrical Engineering from Aristotle University, Thessaloniki, Greece, in 1979, and his M.S. and Ph.D degrees both in Electrical Engineering from the University of Connecticut, in 1981 and 1986, respectively. From 1986 to 1987 he was Research Assistant Professor at the University of Virginia, Charlottesville. In 1987 he joined IBM T. J. Watson Research Center, Yorktown Heights as a Research Staff Member. Since October 1995, he has been with the Telecommunications Department of Aristotle University, Thessaloniki, Greece. His interests are in the area of wireless networks, high speed networks, routing, scheduling, congestion control, modeling and performance analysis. 相似文献
Leonidas GeorgiadisEmail: |
Nikos G. Argiriou received the Diploma degree in Electrical Engineering from the Department of Electrical Engineering, Telecommunication Division, Aristotle University of Thessaloniki, Greece, in 1996. He worked as a researcher, on secure medical image transmission over networks, at the Image Processing Lab at the same university during 1996–1997. During 1998–2000 he was a researcher for the European Project Esprit Catserver concerning the use of advanced Quality of Service techniques in CATV networks. He received his Ph.D. degree at Aristotle University of Thessaloniki in 2007. His current research interests are in the development and implementation of QoS techniques for wired and wireless networks. Leonidas Georgiadis received the Diploma degree in Electrical Engineering from Aristotle University, Thessaloniki, Greece, in 1979, and his M.S. and Ph.D degrees both in Electrical Engineering from the University of Connecticut, in 1981 and 1986, respectively. From 1986 to 1987 he was Research Assistant Professor at the University of Virginia, Charlottesville. In 1987 he joined IBM T. J. Watson Research Center, Yorktown Heights as a Research Staff Member. Since October 1995, he has been with the Telecommunications Department of Aristotle University, Thessaloniki, Greece. His interests are in the area of wireless networks, high speed networks, routing, scheduling, congestion control, modeling and performance analysis. 相似文献
83.
Databases are the core of Information Systems (IS). It is, therefore, necessary to ensure the quality of the databases in order to ensure the quality of the IS. Metrics are useful mechanisms for controlling database quality. This paper presents two metrics related to referential integrity, number of foreign keys (NFK) and depth of the referential tree (DRT) for controlling the quality of a relational database. However, to ascertain the practical utility of the metrics, experimental validation is necessary. This validation can be carried out through controlled experiments or through case studies. The controlled experiments must also be replicated in order to obtain firm conclusions. With this objective in mind, we have undertaken different empirical work with metrics for relational databases. As a part of this empirical work, we have conducted a case study with some metrics for relational databases and a controlled experiment with two metrics presented in this paper. The detailed experiment described in this paper is a replication of the later one. The experiment was replicated in order to confirm the results obtained from the first experiment.
As a result of all the experimental works, we can conclude that the NFK metric is a good indicator of relational database complexity. However, we cannot draw such firm conclusions regarding the DRT metric. 相似文献
84.
In this paper I describe how confidence in a software inspection can be obtained through calculating an estimate of its effectiveness. The method uses a Bayesian Belief Network to model the software inspection process and calculates the inference on how effective a particular inspection was. This technique was selected as it provides a means of initialising the model with inspectors' experience and has the ability to learn and optimise performance. This technique provides answers to some of the questions and limitations raised by current models used to predict inspection effectiveness. The application of the model to a major software project is discussed, covering the initial practitioner survey, model initialisation, model calibration and verification results obtained. 相似文献
85.
T.?LimEmail author J.?M.?Ritchie R.?G.?Dewar J.?R.?Corney P.?Wilkinson M.?Calis M.?Desmulliez J.-J.?Fang 《Virtual Reality》2007,11(4):241-252
Current computer-aided assembly systems provide engineers with a variety of spatial snapping and alignment techniques for
interactively defining the positions and attachments of components. With the advent of haptics and its integration into virtual
assembly systems, users now have the potential advantage of tactile information. This paper reports research that aims to
quantify how the provision of haptic feedback in an assembly system can affect user performance. To investigate human–computer
interaction processes in assembly modeling, performance of a peg-in-hole manipulation was studied to determine the extent to which haptics and stereovision may impact on task completion time. The
results support two important conclusions: first, it is apparent that small (i.e. visually insignificant) assembly features
(e.g. chamfers) affect the overall task completion at times only when haptic feedback is provided; and second, that the difference
is approximately similar to the values reported for equivalent real world peg-in-hole assembly tasks. 相似文献
86.
87.
Subjective evaluation of software evolvability using code smells: An empirical study 总被引:2,自引:2,他引:0
This paper presents the results of an empirical study on the subjective evaluation of code smells that identify poorly evolvable
structures in software. We propose use of the term software evolvability to describe the ease of further developing a piece
of software and outline the research area based on four different viewpoints. Furthermore, we describe the differences between
human evaluations and automatic program analysis based on software evolvability metrics. The empirical component is based
on a case study in a Finnish software product company, in which we studied two topics. First, we looked at the effect of the
evaluator when subjectively evaluating the existence of smells in code modules. We found that the use of smells for code evaluation
purposes can be difficult due to conflicting perceptions of different evaluators. However, the demographics of the evaluators
partly explain the variation. Second, we applied selected source code metrics for identifying four smells and compared these
results to the subjective evaluations. The metrics based on automatic program analysis and the human-based smell evaluations
did not fully correlate. Based upon our results, we suggest that organizations should make decisions regarding software evolvability
improvement based on a combination of subjective evaluations and code metrics. Due to the limitations of the study we also
recognize the need for conducting more refined studies and experiments in the area of software evolvability.
相似文献
Casper LasseniusEmail: |
88.
H.V. Jagadish Olga Kapitskaia Raymond T. Ng Divesh Srivastava 《The VLDB Journal The International Journal on Very Large Data Bases》2000,9(3):214-230
With the increasing importance of XML, LDAP directories, and text-based information sources on the Internet, there is an
ever-greater need to evaluate queries involving (sub)string matching. In many cases, matches need to be on multiple attributes/dimensions,
with correlations between the multiple dimensions. Effective query optimization in this context requires good selectivity
estimates. In this paper, we use pruned count-suffix trees (PSTs) as the basic data structure for substring selectivity estimation.
For the 1-D problem, we present a novel technique called MO (Maximal Overlap). We then develop and analyze two 1-D estimation
algorithms, MOC and MOLC, based on MO and a constraint-based characterization of all possible completions of a given PST.
For the k-D problem, we first generalize PSTs to multiple dimensions and develop a space- and time-efficient probabilistic algorithm
to construct k-D PSTs directly. We then show how to extend MO to multiple dimensions. Finally, we demonstrate, both analytically and experimentally,
that MO is both practical and substantially superior to competing algorithms.
Received April 28, 2000 / Accepted July 11, 2000 相似文献
89.
Taghi M. Khoshgoftaar Xiaojing Yuan Edward B. Allen 《Empirical Software Engineering》2000,5(4):313-330
Software product and process metrics can be useful predictorsof which modules are likely to have faults during operations.Developers and managers can use such predictions by softwarequality models to focus enhancement efforts before release.However, in practice, software quality modeling methods in theliterature may not produce a useful balance between the two kindsof misclassification rates, especially when there are few faultymodules.This paper presents a practical classificationrule in the context of classification tree models that allowsappropriate emphasis on each type of misclassification accordingto the needs of the project. This is especially important whenthe faulty modules are rare.An industrial case study using classification trees, illustrates the tradeoffs.The trees were built using the TREEDISC algorithm whichis a refinement of the CHAID algorithm. We examinedtwo releases of a very large telecommunications system, and builtmodels suited to two points in the development life cycle: theend of coding and the end of beta testing. Both trees had onlyfive significant predictors, out of 28 and 42 candidates, respectively.We interpreted the structure of the classification trees, andwe found the models had useful accuracy. 相似文献
90.