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排序方式: 共有489条查询结果,搜索用时 15 毫秒
1.
Gabriel Tsechpenakis Dimitris Metaxas Carol Neidle 《Computer Vision and Image Understanding》2006,104(2-3):140
We present a data-driven dynamic coupling between discrete and continuous methods for tracking objects of high dofs, which overcomes the limitations of previous techniques. In our approach, two trackers work in parallel, and the coupling between them is based on the tracking error. We use a model-based continuous method to achieve accurate results and, in cases of failure, we re-initialize the model using our discrete tracker. This method maintains the accuracy of a more tightly coupled system, while increasing its efficiency. At any given frame, our discrete tracker uses the current and several previous frames to search into a database for the best matching solution. For improved robustness, object configuration sequences, rather than single configurations, are stored in the database. We apply our framework to the problem of 3D hand tracking from image sequences and the discrimination between fingerspelling and continuous signs in American Sign Language. 相似文献
2.
Dominic D. J. Chandar Jayanarayanan Sitaraman Dimitri Mavriplis 《The Journal of supercomputing》2014,67(1):47-68
The application of graphics processing units (GPU) to solve partial differential equations is gaining popularity with the advent of improved computer hardware. Various lower level interfaces exist that allow the user to access GPU specific functions. One such interface is NVIDIA’s Compute Unified Device Architecture (CUDA) library. However, porting existing codes to run on the GPU requires the user to write kernels that execute on multiple cores, in the form of Single Instruction Multiple Data (SIMD). In the present work, a higher level framework, termed CU++, has been developed that uses object oriented programming techniques available in C++ such as polymorphism, operator overloading, and template meta programming. Using this approach, CUDA kernels can be generated automatically during compile time. Briefly, CU++ allows a code developer with just C/C++ knowledge to write computer programs that will execute on the GPU without any knowledge of specific programming techniques in CUDA. This approach is tremendously beneficial for Computational Fluid Dynamics (CFD) code development because it mitigates the necessity of creating hundreds of GPU kernels for various purposes. In its current form, CU++ provides a framework for parallel array arithmetic, simplified data structures to interface with the GPU, and smart array indexing. An implementation of heterogeneous parallelism, i.e., utilizing multiple GPUs to simultaneously process a partitioned grid system with communication at the interfaces using Message Passing Interface (MPI) has been developed and tested. 相似文献
3.
Retrograde densification of pelletized calcines and glasses having an approximate (Bi,Pb)2 Sr2 Ca2 Cu3 O10 starting stoichiometry and sintered at ∼850°C can be described by first-order rate equations. Retrograde densification in the calcine precursors was largely due to the development of open pores, and was approximately proportional to the concentration of the (Bi,Pb)2 Sr2 CaCu3 O10 phase. In the glasses, retrograde densification is mainly caused by porosity accompanying the growth of a needlelike Sr─Ca─Cu─O phase, together with (Bi,Pb)2 Sr2 Ca2 Cu3 O10 and (Bi,Pb)2 Sr2 CaCu2 O8 . 相似文献
4.
Surrogate modeling approximation using a mixture of experts based on EM joint estimation 总被引:1,自引:1,他引:0
Dimitri Bettebghor Nathalie Bartoli Stéphane Grihon Joseph Morlier Manuel Samuelides 《Structural and Multidisciplinary Optimization》2011,43(2):243-259
An automatic method to combine several local surrogate models is presented. This method is intended to build accurate and
smooth approximation of discontinuous functions that are to be used in structural optimization problems. It strongly relies
on the Expectation−Maximization (EM) algorithm for Gaussian mixture models (GMM). To the end of regression, the inputs are
clustered together with their output values by means of parameter estimation of the joint distribution. A local expert is
then built (linear, quadratic, artificial neural network, moving least squares) on each cluster. Lastly, the local experts
are combined using the Gaussian mixture model parameters found by the EM algorithm to obtain a global model. This method is
tested over both mathematical test cases and an engineering optimization problem from aeronautics and is found to improve
the accuracy of the approximation. 相似文献
5.
Approximate policy iteration: a survey and some new methods 总被引:2,自引:0,他引:2
Dimitri P. BERTSEKAS 《控制理论与应用(英文版)》2011,9(3):310-335
We consider the classical policy iteration method of dynamic programming(DP),where approximations and simulation are used to deal with the curse of dimensionality.We survey a number of issues:convergence and rate of convergence of approximate policy evaluation methods,singularity and susceptibility to simulation noise of policy evaluation,exploration issues,constrained and enhanced policy iteration,policy oscillation and chattering,and optimistic and distributed policy iteration.Our discussion of policy evaluation is couched in general terms and aims to unify the available methods in the light of recent research developments and to compare the two main policy evaluation approaches:projected equations and temporal differences(TD),and aggregation.In the context of these approaches,we survey two different types of simulation-based algorithms:matrix inversion methods,such as least-squares temporal difference(LSTD),and iterative methods,such as least-squares policy evaluation(LSPE) and TD(λ),and their scaled variants.We discuss a recent method,based on regression and regularization,which recti?es the unreliability of LSTD for nearly singular projected Bellman equations.An iterative version of this method belongs to the LSPE class of methods and provides the connecting link between LSTD and LSPE.Our discussion of policy improvement focuses on the role of policy oscillation and its effect on performance guarantees.We illustrate that policy evaluation when done by the projected equation/TD approach may lead to policy oscillation,but when done by aggregation it does not.This implies better error bounds and more regular performance for aggregation,at the expense of some loss of generality in cost function representation capability.Hard aggregation provides the connecting link between projected equation/TD-based and aggregation-based policy evaluation,and is characterized by favorable error bounds. 相似文献
6.
Xiaoying Wu Dimitri Theodoratos Calisto Zuzarte 《The VLDB Journal The International Journal on Very Large Data Bases》2010,19(5):661-686
The streaming evaluation is a popular way of evaluating queries on XML documents. Besides its many advantages, it is also
the only option for a number of important XML applications. Unfortunately, existing algorithms focus almost exclusively on
tree-pattern queries (TPQs). Requirements for flexible querying of XML data have motivated recently the introduction of query
languages that are more general and flexible than TPQs. These languages are not supported by existing algorithms. In this
paper, we consider a partial tree-pattern query (PTPQ) language which generalizes and strictly contains TPQs. PTPQs can express
a fragment of XPath which comprises reverse axes and the node identity equality (is) operator, in addition to forward axes, wildcards and predicates. They constitute an important subclass of XPath, which is
very useful in practice. Unfortunately, previous streaming algorithms for TPQs cannot be applied to PTPQs. PTPQs can be represented
as dags enhanced with constraints. We explore this representation to design an original polynomial time streaming algorithm
for PTPQs. Our algorithm aggressively filters incoming data that is irrelevant to the query and wisely avoids processing redundant
query matches (i.e., matches of the query dag that do not contribute to new solutions). Our algorithm is the first one to
support the streaming evaluation of such a broad fragment of XPath. We provide an analysis of it, and conduct an extensive
experimental evaluation of its performance and scalability. Compared to the only known streaming algorithm that supports TPQs
extended with reverse axes, our algorithm performs better by orders of magnitude while consuming a much smaller fraction of
memory space. Current streaming applications have stringent requirements on query response time and memory consumption because
of the large (possibly unbounded) size of data they handle. In order to keep memory usage and CPU consumption low for the
PTPQ streaming evaluation, we design another streaming algorithm called Eager PSX for PTPQs. Its key feature is that it applies an eager evaluation strategy to quickly determine when node matches should
be returned as solutions to the user and also to proactively detect redundant matches. We theoretically analyze Eager PSX, and experimentally test its time and space performance and scalability. We compare it with PSX. Our results show that Eager PSX not only achieves better space performance without compromising time performance, but it also greatly improves query response
time for both simple and complex queries, in many cases, by orders of magnitude. 相似文献
7.
Xiaoying Wu Dimitri Theodoratos Stefanos Souldatos Theodore Dalamagas Timos Sellis 《World Wide Web》2010,13(4):441-474
Finding the occurrences of structural patterns in XML data is a key operation in XML query processing. Existing algorithms
for this operation focus almost exclusively on path patterns or tree patterns. Current applications of XML require querying
of data whose structure is complex or is not fully known to the user, or integrating XML data sources with different structures.
These applications have motivated recently the introduction of query languages that allow a partial specification of path
patterns in a query. In this paper, we consider partial path queries, a generalization of path pattern queries, and we focus
on their efficient evaluation under the indexed streaming evaluation model. Our approach explicitly deals with repeated labels
(that is, multiple occurrences of the same label in a query). We show that partial path queries can be represented as rooted
dags for which a topological ordering of the nodes exists. We present three algorithms for the efficient evaluation of these
queries. The first one exploits a structural summary of data to generate a set of path patterns that together are equivalent
to a partial path query. To evaluate these path patterns, we extend a previous algorithm for path-pattern queries so that
it can work on path patterns with repeated labels. The second one extracts a spanning tree from the query dag, uses a stack-based
algorithm to find the matches of the root-to-leaf paths in the tree, and merge-joins the matches to compute the answer. Finally,
the third one exploits multiple pointers of stack entries and a topological ordering of the query dag to apply a stack-based
holistic technique. We analyze our algorithms and perform extensive experimental evaluations. Our experimental results show
that the holistic algorithm outperforms the other ones. Our approaches are the first ones to efficiently evaluate this class
of queries in the indexed streaming model. 相似文献
8.
Ioannis Basdekis Iosif Klironomos Ioannis Metaxas Constantine Stephanidis 《Universal Access in the Information Society》2010,9(2):185-190
This communication reports on the results of a web accessibility audit of public Web sites in Greece. The audit was conducted
in 2008 by the Human Computer Interaction Laboratory of the Institute of Computer Science of FORTH, in its capacity as the
Greek National Contact Centre of the European Design for All e-Accessibility Network. In an earlier e-Accessibility study
in 2004, that evaluated approximately 250 public and commercial Web sites in Greece, 73% of the sample failed to meet the
most basic requirements for web accessibility (). Four years later, in the context of a re-audit, a similar sample was examined for compliance with the same web accessibility
standard (WCAG 1.0), as set by the Web Accessibility Initiative of the World Wide Web Consortium. The accessibility checks
were conducted during the period from March to September 2008. A comparison of the results indicates that although new web
development technologies may have been employed, instead of improving the overall status of e-accessibility, this has resulted
in a serious deterioration in overall accessibility levels. Such findings—85% of sites failed to comply with Level A—suggest
that Greek Web sites are likely to present even more significant access barriers to people with disability than in the past.
As Web Accessibility is poorly understood and, until today, new platforms have failed to deliver products that conform to
WCAG, the need emerges for a concrete legislative framework to set accessibility specifications for all public Web sites in
Greece. 相似文献
9.
We present a new approach for the analysis of the left ventricular shape and motion based on the development of a new class of volumetric deformable models. We estimate the deformation and complex motion of the left ventricle (LV) in terms of a few parameters that are functions and whose values vary locally across the LV. These parameters capture the radial and longitudinal contraction, the axial twisting, and the long-axis deformation. Using Lagrangian dynamics and finite-element theory, we convert these volumetric primitives into dynamic models that deform due to forces exerted by the datapoints. We present experiments where we used magnetic tagging (MRI-SPAMM) to acquire datapoints from the LV during systole. By applying our method to MRI-SPAMM datapoints, we were able to characterize the 3-D shape and motion of the LV both locally and globally, in a clinically useful way. In addition, based on the model parameters we were able to extract quantitative differences between normal and abnormal hearts and visualize them in a way that is useful to physicians. 相似文献
10.
Dimitri Papukashvili Nino Rcheulishvili Cong Liu Yang Ji Yunjiao He Peng George Wang 《International journal of molecular sciences》2022,23(21)
Messenger RNA (mRNA) technology has already been successfully tested preclinically and there are ongoing clinical trials for protein replacement purposes; however, more effort has been put into the development of prevention strategies against infectious diseases. Apparently, mRNA vaccine approval against coronavirus disease 2019 (COVID-19) is a landmark for opening new opportunities for managing diverse health disorders based on this approach. Indeed, apart from infectious diseases, it has also been widely tested in numerous directions including cancer prevention and the treatment of inherited disorders. Interestingly, self-amplifying RNA (saRNA)-based technology is believed to display more developed RNA therapy compared with conventional mRNA technique in terms of its lower dosage requirements, relatively fewer side effects, and possessing long-lasting effects. Nevertheless, some challenges still exist that need to be overcome in order to achieve saRNA-based drug approval in clinics. Hence, the current review discusses the feasibility of saRNA utility for protein replacement therapy on various health disorders including rare hereditary diseases and also provides a detailed overview of saRNA advantages, its molecular structure, mechanism of action, and relevant delivery platforms. 相似文献