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991.
In this paper, we present an iterative technique based on Monte Carlo simulations for deriving the optimal control of the infinite horizon linear regulator problem of discrete-time Markovian jump linear systems for the case in which the transition probability matrix of the Markov chain is not known. We trace a parallel with the theory of TD(λ) algorithms for Markovian decision processes to develop a TD(λ) like algorithm for the optimal control associated to the maximal solution of a set of coupled algebraic Riccati equations (CARE). It is assumed that either there is a sample of past observations of the Markov chain that can be used for the iterative algorithm, or it can be generated through a computer program. Our proofs rely on the spectral radius of the closed loop operators associated to the mean square stability of the system being less than 1. 相似文献
992.
Stack filters are a special case of non-linear filters. They have a good performance for filtering images with different types of noise while preserving edges and details. A stack filter decomposes an input image into several binary images according to a set of thresholds. Each binary image is filtered by a Boolean function. The Boolean function that characterizes an adaptive stack filter is optimal and is computed from a pair of images consisting of an ideal noiseless image and its noisy version. In this work the behavior of adaptive stack filters on synthetic aperture radar (SAR) data is evaluated. With this aim, the equivalent number of looks for stack filtered data are calculated to assess the speckle noise reduction capability of this filter. Then a classification of simulated and real SAR images is carried out on data filtered with a stack filter trained with selected samples. The results of a maximum likelihood classification of these data are evaluated and compared with the results of classifying images previously filtered using the Lee and the Frost filters. 相似文献
993.
994.
A major problem in monitoring the online reputation of companies, brands, and other entities is that entity names are often ambiguous (apple may refer to the company, the fruit, the singer, etc.). The problem is particularly hard in microblogging services such as Twitter, where texts are very short and there is little context to disambiguate. In this paper we address the filtering task of determining, out of a set of tweets that contain a company name, which ones do refer to the company. Our approach relies on the identification of filter keywords: those whose presence in a tweet reliably confirm (positive keywords) or discard (negative keywords) that the tweet refers to the company.We describe an algorithm to extract filter keywords that does not use any previously annotated data about the target company. The algorithm allows to classify 58% of the tweets with 75% accuracy; and those can be used to feed a machine learning algorithm to obtain a complete classification of all tweets with an overall accuracy of 73%. In comparison, a 10-fold validation of the same machine learning algorithm provides an accuracy of 85%, i.e., our unsupervised algorithm has a 14% loss with respect to its supervised counterpart.Our study also shows that (i) filter keywords for Twitter does not directly derive from the public information about the company in the Web: a manual selection of keywords from relevant web sources only covers 15% of the tweets with 86% accuracy; (ii) filter keywords can indeed be a productive way of classifying tweets: the five best possible keywords cover, in average, 28% of the tweets for a company in our test collection. 相似文献
995.
We apply current theorem proving technology to certified code in the domain of abstract algebra. More concretely, based on
a formal proof of the Basic Perturbation Lemma (a central result in homological algebra) in the prover Isabelle/HOL, we apply various code generation techniques, which
lead to certified implementations of the associated algorithm in ML. In the formal proof, algebraic structures occurring in
the Basic Perturbation Lemma are represented in a way, which is not directly amenable to code generation with the available
tools. Interestingly, this representation is required in the proof, while for the algorithm simpler data structures are sufficient.
Our approach is to establish a link between the non-executable setting of the proof and the executable representation in the
algorithm, which is to be generated. This correspondence is established within the logical framework of Isabelle/HOL—that
is, it is formally proved correct. The generated code is applied to and illustrated with a number of examples. 相似文献
996.
Julio E. Normey-Rico Jose Luis Guzman Sebastin Dormido Manuel Berenguel Eduardo F. Camacho 《Control Engineering Practice》2009,17(10):1234-1244
This paper presents an interactive tool for dead-time compensator design. The tool is based on an unified dead-time compensator and considers models commonly used in industrial process control. The main contribution of this work is that the proposed tool and controller are simple to analyze and tune as they are based on an unique modified structure of the Smith predictor valid for every type of dead-time process (including integrating and unstable systems). Simple frequency analysis and block diagram transformations are used together with simulations to illustrate the main problems associated to the control of dead-time processes. Several examples of typical processes are presented to illustrate the fundamental concepts associated to the control of these systems. The interactive tool is not only useful for designing and analyzing but also for training and educational purposes. 相似文献
997.
Pablo Picazo-Sanchez Lara Ortiz-Martin Pedro Peris-Lopez Julio Cesar Hernandez-Castro 《The Journal of supercomputing》2013,65(2):949-960
Internet of Things is a paradigm that enables communication between different devices connected to a local network or to Internet. Identification and communication between sensors used in Internet of Things and devices like smart-phones or tablets are established using radio frequency identification technology. However, this technology still has several security and privacy issues because of its severe computational constraints. In 2011, Jeong and Anh proposed the combined use of an authentication radio frequency identification protocol together with a ticket issuing system for bank services (in J. Supercomput. 55:307, 2011). In this paper we show that their message generation is weak, because it abuses the XOR operation and the use of a counter, which leaks too much secret protocol information. Our analysis shows important security faults that ruin most of the security properties claimed in the original paper. More precisely, information privacy (via a disclosure and leakage attack) and location privacy (traceability attack) are both compromised. Moreover, an attacker can disrupt the proper working of the system by exploiting the fact that message integrity is not properly checked. 相似文献
998.
Julio?AbascalEmail author Simone?D.?J.?Barbosa Colette?Nicolle Panayiotis?Zaphiris 《Universal Access in the Information Society》2016,15(2):179-182
The universal accessibility concept is usually formulated in terms that ignore the socioeconomic and sociopolitical contexts. Therefore, it has impact only on a small fraction of the global population of people with disabilities. This issue raises the need for a comprehensive approach that takes into account issues related to literacy, availability of technology, digital literacy, the use of minority languages, etc. 相似文献
999.
Markel Vigo Amaia Aizpurua Myriam Arrue Julio Abascal 《Universal Access in the Information Society》2011,10(1):33-49
Conformance metrics for the mobile web can play a crucial role as far as engineering mobile websites are concerned, especially
if they are automatically obtained. In this way, developers can have an idea in numeric terms of how suitable their developments
are for mobile devices. However, there are a plethora of devices with their own particular features (screen size, formats
support, etc.) that restrict a unified automatic assessment process. This paper proposes a tool-supported method for device-tailored
assessment in terms of conformance with Mobile Web Best Practices 1.0, including the definition of five quantitative metrics
for automatically measuring mobile web conformance: Navigability, Page layout, Page definition, User input and Overall score.
The behaviour of these metrics was analysed for different devices and different web paradigms, both mobile web pages and their
equivalent desktop pages. As expected, the results show that mobile web pages on more capable devices score higher. In addition,
20 users took part in an experiment aimed at discovering how conformance-based scores relate to usability dimensions. The
results demonstrate that automatic scoring approaches strongly correlate with usability scores obtained by direct observation,
such as task completion time and user satisfaction. This correlation is even stronger for the device-tailored assessment than
the one that assumes a general profile for all devices. For instance, results show a strong negative correlation between Overall
score and task completion time: ρ (9) = −0.81, (p < 0.05) for the generalist approach and ρ (9) = −0.88 for the device-tailored one, entailing that mobile web guidelines and
the metrics based on their conformance capture usability aspects. This result challenges the widely accepted belief that conformance
to guidelines does not imply more usable web pages, at least for web accessibility conformance. 相似文献
1000.