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31.
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
32.
33.
This letter develops a framework for EEG analysis and similar applications based on polyharmonic splines. This development overcomes a basic problem with the method of splines in the Euclidean setting: that it does not work on low-degree algebraic surfaces such as spherical and ellipsoidal scalp models. The method's capability is illustrated through simulations on the three-sphere model and using empirical data. 相似文献
34.
Alvaro E. Cuno Parari Claudio Esperança Antonio A. F. Oliveira 《The Visual computer》2009,25(10):911-922
This work presents methods for deforming meshes in a shape-sensitive way using Moving Least Squares (MLS) optimization. It
extends an approach for deforming space (Cuno et al. in Proceedings of the 27th Computer Graphics International Conference,
pp. 115–122, 2007) by showing how custom distance metrics may be used to achieve deformations which preserve the overall mesh shape. Several
variant formulations are discussed and demonstrated, including the use of geodesic distances, distances constrained to paths
contained in the mesh, the use of skeletons, and a reformulation of the MLS scheme which makes it possible to affect the bending
behavior of the deformation. Finally, aspects of the implementation of these techniques in parallel architectures such as
GPUs (graphics processing units) are described and compared with CPU-only implementations. 相似文献
35.
Hub-and-spoke networks are widely studied in the area of location theory. They arise in several contexts, including passenger airlines, postal and parcel delivery, and computer and telecommunication networks. Hub location problems usually involve three simultaneous decisions to be made: the optimal number of hub nodes, their locations and the allocation of the non-hub nodes to the hubs. In the uncapacitated single allocation hub location problem (USAHLP) hub nodes have no capacity constraints and non-hub nodes must be assigned to only one hub. In this paper, we propose three variants of a simple and efficient multi-start tabu search heuristic as well as a two-stage integrated tabu search heuristic to solve this problem. With multi-start heuristics, several different initial solutions are constructed and then improved by tabu search, while in the two-stage integrated heuristic tabu search is applied to improve both the locational and allocational part of the problem. Computational experiments using typical benchmark problems (Civil Aeronautics Board (CAB) and Australian Post (AP) data sets) as well as new and modified instances show that our approaches consistently return the optimal or best-known results in very short CPU times, thus allowing the possibility of efficiently solving larger instances of the USAHLP than those found in the literature. We also report the integer optimal solutions for all 80 CAB data set instances and the 12 AP instances up to 100 nodes, as well as for the corresponding new generated AP instances with reduced fixed costs. 相似文献
36.
Claudio Schepke Nicolas Maillard Philippe O. A. Navaux 《International journal of parallel programming》2009,37(6):593-611
This paper presents and discusses a blocked parallel implementation of bi- and three-dimensional versions of the Lattice Boltzmann
Method. This method is used to represent and simulate fluid flows following a mesoscopic approach. Most traditional parallel
implementations use simple data distribution strategies to parallelize the operations on the regular fluid data set. However,
it is well known that block partitioning is usually better. Such a parallel implementation is discussed and its communication
cost is established. Fluid flows simulations crossing a cavity have also been used as a real-world case study to evaluate
our implementation. The presented results with our blocked implementation achieve a performance up to 31% better than non-blocked
versions, for some data distributions. Thus, this work shows that blocked, parallel implementations can be efficiently used
to reduce the parallel execution time of the method. 相似文献
37.
Arilo Claudio Dias-Neto Guilherme Horta Travassos 《Information and Software Technology》2009,51(11):1487-1504
Selecting software technologies for software projects represents a challenge to software engineers. It is known that software projects differ from each other by presenting different characteristics that can complicate the selection of such technologies. This is not different when considering model-based testing. There are many approaches with different characteristics described in the technical literature that can be used in software projects. However, there is no indication as to how they can fit a software project. Therefore, a strategy to select model-based testing approaches for software projects called Porantim is fully described in this paper. Porantim is based on a body of knowledge describing model-based testing approaches and their characterization attributes (identified by secondary and primary experimental studies), and a process to guide by adequacy and impact criteria regarding the use of this sort of software technology that can be used by software engineers to select model-based testing approaches for software projects. 相似文献
38.
39.
Mihai Tanase Juan de la Riva Fernando Pérez-Cabello 《Remote sensing of environment》2011,115(8):2075-2085
Disturbed forests may need decades to reach a mature stage and optically-based vegetation indices are usually poorly suited for monitoring purposes due to the rapid saturation of the signal with increasing canopy cover. Spaceborne synthetic aperture radar (SAR) data provide an alternate monitoring approach since the backscattered microwave energy is sensitive to the vegetation structure. Images from two regions in Spain and Alaska were used to analyze SAR metrics (cross-polarized backscatter and co-polarized interferometric coherence) from regrowing forests previously affected by fire. TerraSAR-X X-band backscatter showed the lowest sensitivity to forest regrowth, with the average backscatter increasing by 1-2 dB between the most recent fire scar and the unburned forest. Increased sensitivity (around 3-4 dB) was observed for C-band Envisat Advanced Synthetic Aperture (ASAR) backscatter. The Advanced Land Observing Satellite (ALOS) Phased Array-type L-band Synthetic Aperture Radar (PALSAR) L-band backscatter presented the highest dynamic range from unburned to recently burned forests (approximately 8 dB). The interferometric coherence showed low sensitivity to forest regrowth at all SAR frequencies. For Mediterranean forests, five phases of forest regrowth were discerned whereas for boreal forest, up to four different regrowth phases could be discerned with L-band SAR data. In comparison, the Normalized Difference Vegetation Index (NDVI) provided reliable differentiation only for the most recent development stages. The results obtained were consistent in both environments. 相似文献
40.
Mario A. S. Lizi��r Marcelo F. Siqueira Joel Daniels II Claudio T. Silva L. Gustavo Nonato 《The Visual computer》2011,27(10):887-903
This paper describes a novel template-based meshing approach for generating good quality quadrilateral meshes from 2D digital
images. This approach builds upon an existing image-based mesh generation technique called Imeshp, which enables us to create a segmented triangle mesh from an image without the need for an image segmentation step. Our
approach generates a quadrilateral mesh using an indirect scheme, which converts the segmented triangle mesh created by the
initial steps of the Imesh technique into a quadrilateral one. The triangle-to-quadrilateral conversion makes use of template meshes of triangles. To
ensure good element quality, the conversion step is followed by a smoothing step, which is based on a new optimization-based
procedure. We show several examples of meshes generated by our approach, and present a thorough experimental evaluation of
the quality of the meshes given as examples. 相似文献