全文获取类型
收费全文 | 8533篇 |
免费 | 592篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 114篇 |
综合类 | 24篇 |
化学工业 | 2189篇 |
金属工艺 | 96篇 |
机械仪表 | 187篇 |
建筑科学 | 905篇 |
矿业工程 | 14篇 |
能源动力 | 351篇 |
轻工业 | 1430篇 |
水利工程 | 46篇 |
石油天然气 | 44篇 |
无线电 | 557篇 |
一般工业技术 | 1221篇 |
冶金工业 | 289篇 |
原子能技术 | 69篇 |
自动化技术 | 1600篇 |
出版年
2024年 | 9篇 |
2023年 | 85篇 |
2022年 | 319篇 |
2021年 | 341篇 |
2020年 | 230篇 |
2019年 | 235篇 |
2018年 | 273篇 |
2017年 | 297篇 |
2016年 | 342篇 |
2015年 | 243篇 |
2014年 | 408篇 |
2013年 | 693篇 |
2012年 | 529篇 |
2011年 | 628篇 |
2010年 | 503篇 |
2009年 | 506篇 |
2008年 | 473篇 |
2007年 | 381篇 |
2006年 | 304篇 |
2005年 | 267篇 |
2004年 | 227篇 |
2003年 | 207篇 |
2002年 | 235篇 |
2001年 | 134篇 |
2000年 | 124篇 |
1999年 | 125篇 |
1998年 | 143篇 |
1997年 | 94篇 |
1996年 | 89篇 |
1995年 | 88篇 |
1994年 | 82篇 |
1993年 | 63篇 |
1992年 | 67篇 |
1991年 | 50篇 |
1990年 | 39篇 |
1989年 | 57篇 |
1988年 | 37篇 |
1987年 | 29篇 |
1986年 | 17篇 |
1985年 | 20篇 |
1984年 | 21篇 |
1983年 | 8篇 |
1982年 | 19篇 |
1981年 | 12篇 |
1980年 | 15篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 11篇 |
1975年 | 8篇 |
1973年 | 6篇 |
排序方式: 共有9136条查询结果,搜索用时 15 毫秒
101.
Antonio M. Ortiz Fernando Royo Teresa Olivares Jose Carlos Castillo Luis Orozco‐Barbosa 《Expert Systems》2014,31(2):154-162
ZigBee is the primary standard solution for wireless sensor networks, implementing the Ad hoc On‐Demand Distance Vector (AODV) protocol in the network layer and supported by the standard IEEE 802.15.4. This study is focused on mesh topologies and the critical problems encountered when AODV is executed in conjunction with the Carrier Sense Multiple Access with Collision Avoidance protocol. These problems are mainly related to the packet overhead required to carry out route creation. To perform preliminary experiments to be able to implement AODV in a real network, a new metric is proposed herein. This metric uses fuzzy logic to help in the decision‐making process. The objective of the fuzzy routine is to determine, during the route‐discovery process, the best node to forward request/reply packets, with the aim of reducing packet overhead and energy consumption. Moreover, minor changes are also added to the discovery procedure of AODV to improve the performance of the route‐creation process. This intelligent version of AODV has provided promising experimental results, greatly reducing the number of packets required, with the consequent energy saving while selecting the best nodes to be part of the routes. 相似文献
102.
Manuel J. Castro José M. Gallardo Antonio Marquina 《Journal of scientific computing》2014,60(2):363-389
In this paper we propose a new class of incomplete Riemann solvers, based on approximations in the \(L^\infty \) -norm to the absolute value function in \([-1,1]\) by means of rational functions, for the numerical approximation of the solution of hyperbolic systems of conservation laws. The main idea relies on the construction of a numerical approximation to the viscosity matrix by using an appropriate rational real function \(R(x)\) , that approximates the function \(|x|\) uniformly in \([-1,1]\) , evaluated at the Jacobian of the fluxes of the hyperbolic system computed at some average value (for example, Roe averages). In addition to the Jacobians of the fluxes we shall use either the maximum in absolute value of the characteristic speeds in each cell or an upper bound of them. Thus, the resulting approximate Riemann solver is incomplete in the sense that we do not use the complete spectral decomposition of the Jacobian. Moreover, the new class of Riemann solvers consists of a hierarchy of schemes running from the more dissipative to the less dissipative ones, and having as limiting case a Roe-like scheme. According to the order of the approximation of the generating rational function used, the degree of dissipation can be dosed for particular applications. We study different rational approximations: Newman-type functions, iterative generated Halley functions, and also Chebyshev polynomial approximants. We test our basic algorithms for different initial value Riemann problems for ideal gas dynamics (HD) and magnetohydrodynamics (MHD) to observe their behavior with respect to challenging scenarios in numerical simulations, including some standard numerical pathologies (e. g., heat conduction, postshock oscillations and overheating) and the formation of compound waves in ideal MHD. We also examine our proposed schemes, by computing the numerical approximation of different initial value problems for nonconservative multilayer shallow water equations, where it has been observed that intermediate waves can be properly captured for an appropriate degree of approximation of the generating rational function used. Our numerical tests indicate that the proposed schemes are robust, running stable and accurate with a satisfactory time step restriction (CFL constant), and the computational cost is more advantageous with respect to schemes that use a complete spectral decomposition of the Jacobians. 相似文献
103.
Electrochemical destruction of chlorophenoxy herbicides by anodic oxidation and electro-Fenton using a boron-doped diamond electrode 总被引:1,自引:0,他引:1
Enric Brillas Birame Boye José Antonio Garrido Conchita Arias Christos Comninellis 《Electrochimica acta》2004,49(25):4487-4496
The degradation of herbicides 4-chlorophenoxyacetic acid (4-CPA), 4-chloro-2-methylphenoxyacetic acid (MCPA), 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) in aqueous medium of pH 3.0 has been comparatively studied by anodic oxidation and electro-Fenton using a boron-doped diamond (BDD) anode. All solutions are totally mineralized by electro-Fenton, even at low current, being the process more efficient with 1 mM Fe2+ as catalyst. This is due to the production of large amounts of oxidant hydroxyl radical (OH) on the BDD surface by water oxidation and from Fenton’s reaction between added Fe2+ and H2O2 electrogenerated at the O2-diffusion cathode. The herbicide solutions are also completely depolluted by anodic oxidation. Although a quicker degradation is found at the first stages of electro-Fenton, similar times are required for achieving overall mineralization in both methods. The decay kinetics of all herbicides always follows a pseudo first-order reaction. Reversed-phase chromatography allows detecting 4-chlorophenol, 4-chloro-o-cresol, 2,4-dichlorophenol and 2,4,5-trichlorophenol as primary aromatic intermediates of 4-CPA, MCPA, 2,4-D and 2,4,5-T, respectively. Dechlorination of these products gives Cl−, which is slowly oxidized on BDD. Ion-exclusion chromatography reveals the presence of persistent oxalic acid in electro-Fenton by formation of Fe3+-oxalato complexes, which are slowly destroyed by OH adsorbed on BDD. In anodic oxidation, oxalic acid is mineralized practically at the same rate as generated. 相似文献
104.
Maria?Antonietta BresciaEmail author Vincenzo?Mazzilli Angela?Sgaramella Stefano?Ghelli Francesco?Paolo Fanizzi Antonio?Sacco 《Journal of the American Oil Chemists' Society》2004,81(5):431-436
Characterization of the lipid fraction of raw cow and buffalo milk samples, collected in different breeding areas in Apulia,
a region of southern Italy, were performed by means of 1H NMR. The aim of this work was to establish whether FA composition data obtained by 1H NMR can be used in the differentiation of buffalo and cow milk samples according to species. A complete assignment of the
signals present in the spectrum was attempted by COSY, heteronuclear coherence spectra. Quantification of FA was carried out
by inserting the integrals of particular peaks in suitable calculations. Multivariate statistical analysis, conducted on the
results of the quantification, permitted buffalo and cow milks to be distinguished. 相似文献
105.
Evandro Eduardo Broday Antonio Augusto de Paula XavierReginaldo de Oliveira 《International Journal of Industrial Ergonomics》2014
The incorrect determination of metabolic rate can be linked to discrepancies between the model of the PMV (Predicted Mean Vote) and real thermal sensation collected in field studies. Aiming to improve the correlation of the PMV model and the real thermal sensation, this work established new values for the metabolic rate: one way being called “calculated” using Newton's Method and the other called "measured" using a metabolic analyzer. Welder's activities were evaluated, through the measurements of environmental and personal variables. New values of metabolic rate were determined for this activity. The values found for the calculated form and the measured one were, respectively, 178.63 and 145.46 W/m2, different from the range provided by the table of ISO 8996 (2004) for this activity (75–125 W/m2). In order to verify which of the values of the metabolic rate was closer to the real thermal sensation of PMV, a linear regression was made between the PMV and the real thermal sensation in three ways: S × PMVtabulated (R2 = 0.1749), S × PMVcalculated (R ² = 0.7481) and S × PMVmeasured (R2 = 0.7854). It was found that the values measured by the instrument gave a higher coefficient of determination which was chosen for the correction of the table. The correction of the table provides a value of Mpredicted, that is a value of metabolic rate that corrects the values provided by the tables of ISO 8996 (2004), by means of a correction coefficient. For the welder's activities in a metal-mechanics industry, tabulated values can be multiplied by the correction coefficient 1.4648 in order to minimize inaccuracies. The PMVpredicted, obtained through the Mpredicted, when related to the actual thermal sensation, provides a coefficient of determination of 0.7511, thereby improving the model of the PMV. 相似文献
106.
A complete and efficient CUDA-sharing solution for HPC clusters 总被引:1,自引:0,他引:1
Antonio J. Peña Carlos Reaño Federico Silla Rafael Mayo Enrique S. Quintana-Ortí José Duato 《Parallel Computing》2014
In this paper we detail the key features, architectural design, and implementation of rCUDA, an advanced framework to enable remote and transparent GPGPU acceleration in HPC clusters. rCUDA allows decoupling GPUs from nodes, forming pools of shared accelerators, which brings enhanced flexibility to cluster configurations. This opens the door to configurations with fewer accelerators than nodes, as well as permits a single node to exploit the whole set of GPUs installed in the cluster. In our proposal, CUDA applications can seamlessly interact with any GPU in the cluster, independently of its physical location. Thus, GPUs can be either distributed among compute nodes or concentrated in dedicated GPGPU servers, depending on the cluster administrator’s policy. This proposal leads to savings not only in space but also in energy, acquisition, and maintenance costs. The performance evaluation in this paper with a series of benchmarks and a production application clearly demonstrates the viability of this proposal. Concretely, experiments with the matrix–matrix product reveal excellent performance compared with regular executions on the local GPU; on a much more complex application, the GPU-accelerated LAMMPS, we attain up to 11x speedup employing 8 remote accelerators from a single node with respect to a 12-core CPU-only execution. GPGPU service interaction in compute nodes, remote acceleration in dedicated GPGPU servers, and data transfer performance of similar GPU virtualization frameworks are also evaluated. 相似文献
107.
Ginés D. Guerrero José M. Cecilia Antonio Llanes José M. García Martyn Amos Manuel Ujaldón 《The Journal of supercomputing》2014,69(1):318-329
The rapidly growing field of nature-inspired computing concerns the development and application of algorithms and methods based on biological or physical principles. This approach is particularly compelling for practitioners in high-performance computing, as natural algorithms are often inherently parallel in nature (for example, they may be based on a “swarm”-like model that uses a population of agents to optimize a function). Coupled with rising interest in nature-based algorithms is the growth in heterogenous computing; systems that use more than one kind of processor. We are therefore interested in the performance characteristics of nature-inspired algorithms on a number of different platforms. To this end, we present a new OpenCL-based implementation of the Ant Colony Optimization algorithm, and use it as the basis of extensive experimental tests. We benchmark the algorithm against existing implementations, on a wide variety of hardware platforms, and offer extensive analysis. This work provides rigorous foundations for future investigations of Ant Colony Optimization on high-performance platforms. 相似文献
108.
Kenton O’Hara Gerardo Gonzalez Graeme Penney Abigail Sellen Robert Corish Helena Mentis Andreas Varnavas Antonio Criminisi Mark Rouncefield Neville Dastur Tom Carrell 《Computer Supported Cooperative Work (CSCW)》2014,23(3):299-337
While surgical practices are increasingly reliant on a range of digital imaging technologies, the ability for clinicians to interact and manipulate these digital representations in the operating theatre using traditional touch based interaction devices is constrained by the need to maintain sterility. To overcome these concerns with sterility, a number of researchers are have been developing ways of enabling interaction in the operating theatre using touchless interaction techniques such as gesture and voice to allow clinicians control of the systems. While there have been important technical strides in the area, there has been little in the way of understanding the use of these touchless systems in practice. With this in mind we present a touchless system developed for use during vascular surgery. We deployed the system in the endovascular suite of a large hospital for use in the context of real procedures. We present findings from a study of the system in use focusing on how, with touchless interaction, the visual resources were embedded and made meaningful in the collaborative practices of surgery. In particular we discuss the importance of direct and dynamic control of the images by the clinicians in the context of talk and in the context of other artefact use as well as the work performed by members of the clinical team to make themselves sensable by the system. We discuss the broader implications of these findings for how we think about the design, evaluation and use of these systems. 相似文献
109.
José I. Ronda Antonio Valdés Guillermo Gallego 《Journal of Mathematical Imaging and Vision》2014,50(3):179-198
In 3D reconstruction, the recovery of the calibration parameters of the cameras is paramount since it provides metric information about the observed scene, e.g., measures of angles and ratios of distances. Autocalibration enables the estimation of the camera parameters without using a calibration device, but by enforcing simple constraints on the camera parameters. In the absence of information about the internal camera parameters such as the focal length and the principal point, the knowledge of the camera pixel shape is usually the only available constraint. Given a projective reconstruction of a rigid scene, we address the problem of the autocalibration of a minimal set of cameras with known pixel shape and otherwise arbitrarily varying intrinsic and extrinsic parameters. We propose an algorithm that only requires 5 cameras (the theoretical minimum), thus halving the number of cameras required by previous algorithms based on the same constraint. To this purpose, we introduce as our basic geometric tool the six-line conic variety (SLCV), consisting in the set of planes intersecting six given lines of 3D space in points of a conic. We show that the set of solutions of the Euclidean upgrading problem for three cameras with known pixel shape can be parameterized in a computationally efficient way. This parameterization is then used to solve autocalibration from five or more cameras, reducing the three-dimensional search space to a two-dimensional one. We provide experiments with real images showing the good performance of the technique. 相似文献
110.
The radical polymerization of the macromonomer poly(ethyleneglycol) methyl ether methacrylate with ammonium persulfate at 60°C was carried out. The polymer was completely soluble in water. Yield was 75%. The polymacromonomer was characterized by Fourier transform infrared, proton nuclear magnetic resonance (NMR), and 13C NMR spectroscopy. Mn, Mw, and the polydispersity were determined by gel permeation chromatography. The polymacromonomer showed a high thermal stability with a TDT50% of 420°C. The metal ion binding capacity of this polychelatogen with respect to different metal ions was investigated through the liquid‐phase polymer‐based retention (LPR) technique. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2929–2934, 2002 相似文献