全文获取类型
收费全文 | 1539篇 |
免费 | 107篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 10篇 |
综合类 | 1篇 |
化学工业 | 422篇 |
金属工艺 | 29篇 |
机械仪表 | 48篇 |
建筑科学 | 59篇 |
矿业工程 | 4篇 |
能源动力 | 53篇 |
轻工业 | 366篇 |
水利工程 | 9篇 |
石油天然气 | 19篇 |
无线电 | 51篇 |
一般工业技术 | 254篇 |
冶金工业 | 129篇 |
原子能技术 | 15篇 |
自动化技术 | 178篇 |
出版年
2024年 | 7篇 |
2023年 | 27篇 |
2022年 | 52篇 |
2021年 | 81篇 |
2020年 | 48篇 |
2019年 | 59篇 |
2018年 | 53篇 |
2017年 | 44篇 |
2016年 | 68篇 |
2015年 | 50篇 |
2014年 | 69篇 |
2013年 | 112篇 |
2012年 | 117篇 |
2011年 | 118篇 |
2010年 | 80篇 |
2009年 | 91篇 |
2008年 | 77篇 |
2007年 | 64篇 |
2006年 | 53篇 |
2005年 | 37篇 |
2004年 | 25篇 |
2003年 | 37篇 |
2002年 | 30篇 |
2001年 | 18篇 |
2000年 | 13篇 |
1999年 | 12篇 |
1998年 | 44篇 |
1997年 | 34篇 |
1996年 | 27篇 |
1995年 | 22篇 |
1994年 | 12篇 |
1993年 | 14篇 |
1992年 | 3篇 |
1991年 | 10篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有1647条查询结果,搜索用时 15 毫秒
101.
Eduardo Muñoz José L. Boldú Eduardo Andrade Octavio Novaro Xi. Bokhimi Tessy López Ricardo Gómez 《Journal of the American Ceramic Society》2001,84(2):392-98
Electron paramagnetic resonance (EPR) room-temperature observation of trivalent titanium in sol–gel titania has been reported. This unprecedented detection of stable paramagnetic signals in this titania, which was treated at 200°–800°C, occurred regardless of whether the atmosphere was reducing, inert, or oxidating. The possibility that the paramagnetic signals may originate from an metal impurity other than titanium was completely excluded by analyzing the samples using three different ion-beam-analysis techniques: Rutherford backscattering spectroscopy, particle-induced X-ray emission resonance, and energy-recoil detection analysis. The paramagnetic signals appeared at precisely the temperature range of the sample dehydroxylation, which suggests a mechanism for explaining these Ti3+ EPR spectra. 相似文献
102.
João Adriano Rossignolo 《Construction and Building Materials》2009,23(2):817-821
This paper deals with the effect of silica fume and styrene-butadiene latex (SBR) on the microstructure of the interfacial transition zone (ITZ) between Portland cement paste and aggregates (basalt). Scanning electron microscope (SEM) equipped with energy dispersive X-ray analysis system (EDX) was used to determine the ITZ thickness. In the plain concrete a marked ITZ around the aggregate particles (55 μm) was observed, while in concretes with silica fume or latex SBR the ITZ was less pronounced (35–40 μm). However, better results were observed in concretes with silica fume and latex SBR (20–25 μm). 相似文献
103.
The present paper describes the analysis of the melting process in a single vertical shell‐and‐tube latent heat thermal energy storage (LHTES), unit and it is directed at understanding the thermal performance of the system. The study is realized using a computational fluid‐dynamic (CFD) model that takes into account of the phase‐change phenomenon by means of the enthalpy method. Fluid flow is fully resolved in the liquid phase‐change material (PCM) in order to elucidate the role of natural convection. The unsteady evolution of the melting front and the velocity and temperature fields is detailed. Temperature profiles are analyzed and compared with experimental data available in the literature. Other relevant quantities are also monitored, including energy stored and heat flux exchanged between PCM and HTF. The results demonstrate that natural convection within PCM and inlet HTF temperature significantly affects the phase‐change process. Thermal enhancement through the dispersion of highly conductive nanoparticles in the base PCM is considered in the second part of the paper. Thermal behavior of the LHTES unit charged with nano‐enhanced PCM is numerically analyzed and compared with the original system configuration. Due to increase of thermal conductivity, augmented thermal performance is observed: melting time is reduced of 15% when nano‐enhanced PCM with particle volume fraction of 4% is adopted. Similar improvements of the heat transfer rate are also detected. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
104.
105.
Leonardo A. de Andrade Matheus R. U. Zingarelli Rodolfo R. Silva Rudinei Goularte 《Multimedia Tools and Applications》2014,71(3):1673-1697
This paper presents a new spatial compression method specifically designed for stereo videos. Different form current compressors, which simply apply known 2D compression techniques, the method proposed here was developed taking into account specificities of the components of the spatial compression process which may impact the correct depth visualization, named Chrominance Subsampling, Discrete WaveletTransform (DWT) and Quantization. Each component was evaluated analyzing where datalosses occur and proposing ways to provide a good balance between compression ratio and image quality, minimizing losses in depth perception. The evaluations were made using standard objective (PSNR) and subjective (DSCQS) metrics, applied to an anaglyphic stereoscopic video base. The results showedour method is competitive regarding compression rate and providessuperior image quality. 相似文献
106.
Electrokinetic effects are those that take place by application of an electric field to porous materials, with the zeta potential
as the key parameter. Specifically, in the case of contaminated construction materials, the generation of an electroosmotic
flux, with the corresponding dragging due to water transport, is a crucial mechanism to succeed in the treatment of decontamination.
Therefore, it is of great interest trying to optimize the treatment by the addition of specific electrolytes enhancing the
electrokinetic phenomena. Most of the data of zeta potential found in literature for construction materials are based in micro-electrophoresis
measurements, which are quite far of the real conditions of application of the remediation treatments. In this paper, electrophoretic
and electroosmotic experiments, with monolithic and powdered material respectively, have been carried out for mortar, brick
and granite clean and contaminated with Cs, Sr, Co, Cd, Cu and Pb. The electrolytes tested have been distilled water (DW),
Na2–EDTA, oxalic acid, acetic acid and citric acid. The zeta potential values have been determined through the two different
techniques and the results compared and critically analysed. 相似文献
107.
Adriano Pinto Mariano Caliane Bastos Borba Costa Dejanira de Franceschi de Angelis Francisco Maugeri Filho Daniel Ibraim Pires Atala Maria Regina Wolf Maciel Rubens Maciel Filho 《Chemical Engineering Research and Design》2010,88(5-6):562-571
Factorial design and response surface techniques were used in combination with mathematical modelling and computational simulation to optimise an innovative industrial bioprocess, the production of biobutanol employing the flash fermentation technology. A parametric analysis performed by means of a full factorial design at two levels determined the influence of operating variables on butanol yield and productivity. A second set of simulations were carried out based on the central composite rotatable design. This procedure generated simplified statistical models that describe butanol yield and productivity as functions of the significant operating variables. From these models, response surfaces were obtained and used to optimise the process. For a range of substrate concentration from 130 to 180 g/l, the optimum operating ranges ensure butanol productivity between 7.0 and 8.0 g/l h, butanol yield between 19 and 22%, substrate conversion above 90% and final butanol concentration around 25 g/l. 相似文献
108.
Adriano Pinto Mariano Caliane Bastos Borba CostaEduardo Coselli Vasco de Toledo Delba Nisi Cosme MeloRubens Maciel Filho 《Computers & Chemical Engineering》2011,35(12):2741-2749
The Particle Swarm Optimization (PSO) method was employed to optimize an industrial chemical process characterized by being difficult to be optimized by conventional deterministic methods. The chemical process is a three phase catalytic slurry reactor (tubular geometry) in which the reaction of the hydrogenation of o-cresol producing 2-methyl-cyclohexanol is carried out. The optimization problem was formulated considering as input variables the operating conditions of the reactor and as objective function the maximization of productivity, subject to the environmental constraint of conversion. The process was represented by a multivariable non-linear rigorous mathematical model and in order to solve the optimization problem, the performance of the PSO algorithm was evaluated considering four sets of parameters values suggested by the literature. PSO demonstrated to be efficient and robust to solve the constrained optimization problem, independently of the values of the PSO parameters. The solution of the rigorous mathematical model of the reactor was associated with a high computational burden, and although the PSO algorithm presented high rate of convergence, the attempt to make possible the optimization in a timeframe suitable to real time applications failed because the algorithm lost robustness (fraction of the number of runs the algorithm reached the optimization goal) when run with a reduced number of function evaluations. Therefore, if this type of application is desired, simplified mathematical models with fast and simple numerical methods must be preferred. 相似文献
109.
Orlando Soares Henrique Gonçalves António Martins Adriano Carvalho 《Renewable Energy》2010,35(8):1662-1670
This paper describes the models of a wind power system, such as the turbine, generator, power electronics converters and controllers, with the aim to control the generation of wind power in order to maximize the generated power with the lowest possible impact in the grid voltage and frequency during normal operation and under the occurrence of faults. The presented work considers a wind power system equipped with the doubly-fed induction generator and a vector-controlled converter connected between the rotor and the grid. The paper presents comparative results between proportional-integral controllers and neural networks based controllers, showing that better dynamic characteristics can be obtained using neural networks based controllers. 相似文献
110.
Effect of Ni on Pt/C and PtSn/C prepared by the Pechini method 总被引:1,自引:0,他引:1
T.S. AlmeidaK.B. Kokoh A.R. De Andrade 《International Journal of Hydrogen Energy》2011,36(6):3803-3810
Different compositions of Pt, PtNi, PtSn, and PtSnNi electrocatalysts supported on carbon Vulcan XC-72 were prepared through thermal decomposition of polymeric precursors. The nanoparticles were characterized by morphological and structural analyses (XRD, TEM, and EDX). XRD results revealed a face-centered cubic structure for platinum, and there was evidence that Ni and Sn atoms are incorporated into the Pt structure. The electrochemical investigation was carried out in slightly acidic medium (H2SO4 0.05 mol L−1), in the absence and in the presence of ethanol. Addition of Ni to Pt/C and PtSn/C catalysts significantly shifted the onset of ethanol and CO oxidations toward lower potentials, thus enhancing the catalytic activity, especially in the case of the ternary PtSnNi/C composition. Electrolysis of ethanol solutions at 0.4 V vs. RHE allowed for determination of acetaldehyde and acetic acid as the reaction products, as detected by HPLC analysis. Due to the high concentration of ethanol employed in the electrolysis experiments (1.0 mol L−1), no formation of CO2 was observed. 相似文献