全文获取类型
收费全文 | 470篇 |
免费 | 17篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 7篇 |
综合类 | 1篇 |
化学工业 | 93篇 |
金属工艺 | 11篇 |
机械仪表 | 17篇 |
建筑科学 | 23篇 |
矿业工程 | 1篇 |
能源动力 | 25篇 |
轻工业 | 44篇 |
水利工程 | 7篇 |
石油天然气 | 3篇 |
无线电 | 52篇 |
一般工业技术 | 99篇 |
冶金工业 | 15篇 |
原子能技术 | 3篇 |
自动化技术 | 91篇 |
出版年
2024年 | 3篇 |
2023年 | 8篇 |
2022年 | 23篇 |
2021年 | 25篇 |
2020年 | 20篇 |
2019年 | 21篇 |
2018年 | 27篇 |
2017年 | 16篇 |
2016年 | 21篇 |
2015年 | 14篇 |
2014年 | 22篇 |
2013年 | 38篇 |
2012年 | 33篇 |
2011年 | 39篇 |
2010年 | 19篇 |
2009年 | 18篇 |
2008年 | 21篇 |
2007年 | 15篇 |
2006年 | 14篇 |
2005年 | 14篇 |
2004年 | 7篇 |
2003年 | 2篇 |
2002年 | 13篇 |
2001年 | 4篇 |
2000年 | 1篇 |
1999年 | 3篇 |
1998年 | 5篇 |
1997年 | 11篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有492条查询结果,搜索用时 15 毫秒
481.
Previous CFD studies on pollution dispersion problems have largely centred on employing Reynolds-averaged Navier–Stokes (RANS) turbulence closure schemes, which have often been reported to overpredict pollutant concentration levels in comparison to wind tunnel measurement data. In addition, the majority of experimental and numerical investigations have failed to account for the aerodynamic effects of trees, which can occupy a significant proportion of typical urban street canyons. In the present work, the prediction accuracy of pollutant dispersion within urban street canyons of width to height ratio, W/H = 1 lined with avenue-like tree plantings are examined using two steady-state RANS models (the standard k-ε and RSM), and Large Eddy Simulation (LES) to compare their performance against wind tunnel experiments available on the online database CODASC [1]. Two cases of tree crown porosities are investigated, one for a loosely (Pvol = 97.5%) and another for a densely (Pvol = 96%) packed tree crown, corresponding to pressure loss coefficients of λ = 80 m−1 and λ = 200 m−1, respectively. Results of the tree-lined cases are then compared to a tree-free street canyon in order to demonstrate the impact of trees on the flow field and pollutant dispersion, and it is observed that the presence of trees reduces the in-canyon circulation and air exchange, and increases the overall concentration levels. Between the two numerical methods employed, LES performs better than RANS, because it captures the unsteady and intermittent fluctuations of the flow field, and hence, successfully resolves the transient mixing process within the canyons. 相似文献
482.
Salim Mohamed Salim Riccardo Buccolieri Andrew Chan Silvana Di Sabatino 《Journal of Wind Engineering & Industrial Aerodynamics》2011,99(2-3):103-113
Prediction accuracy of pollutant dispersion within an urban street canyon of width to height ratio W/H=1 is examined using two steady-state Reynolds-averaged Navier–Stokes (RANS) turbulence closure models, the standard k–ε and Reynolds Stress Model (RSM), and Large Eddy Simulation (LES) coupled with the advection–diffusion method for species transport. The numerical results, which include the statistical properties of pollutant dispersion, e.g. mean concentration distributions, time-evolution and three-dimensional spreads of the pollutant, are then compared to wind-tunnel (WT) measurements. The accuracy and computational cost of both numerical approaches are evaluated. The time-evolution of the pollutant concentration (for LES only) and the mean (time-averaged) values are presented. It is observed that amongst the two RANS models, RSM performed better than standard k–ε except at the centerline of the canyon walls. However, LES, although computationally more expensive, did better than RANS in predicting the concentration distribution because it was able to capture the unsteady and intermittent fluctuations of the flow field, and hence resolve the transient mixing process within the street canyon. 相似文献
483.
A comprehensive study on analysis and design of fiber reinforced plastic (FRP) composite deck-and-stringer bridges is presented. The FRP decks considered consist of contiguous thin-walled box sections and are fabricated by bonding side-by-side pultruded thin-walled box beams, which are placed transversely over FRP composite stringers. In this study, we review the modeling and experimental verification of FRP structural beams, including micro/macro-mechanics predictions of ply and laminate properties, beam bending response, shear-lag effect, and local and global buckling behaviors. A simplified design analysis procedure for cellular FRP bridge decks is developed based on a first-order shear deformation macro-flexibility (SDMF) orthotropic plate solution. The present approach can allow the designers to analyze, design and optimize material architectures and shapes of FRP beams, as well as various bridge deck configurations, before their implementation in the field. Experimental studies of cellular FRP bridge decks are conducted to obtain stiffness coefficients, and an example of a cellular FRP deck on optimized winged-box FRP stringers under actual track-loading is presented to illustrate the analytical method. The experimental-analytical approach presented in this study is used to propose simplified engineering design equations for new and replacement highway FRP deck-and-stringer bridges. 相似文献
484.
Hayder Mohammed Salim Al-Maamori M. Hesham El Naggar Silvana Micic 《岩石力学与岩土工程学报(英文版)》2018,10(2):290-309
Effects of time-dependent deformation (TDD) on a tunnel constructed using the micro-tunneling technique in Queenston shale (QS) are investigated employing the finite element method. The TDD and strength parameters of the QS were measured from tests conducted on QS specimens soaked in water and lubricant fluids (LFs) used in micro-tunneling such as bentonite and polymer solutions. The numerical model was verified using the results of TDD tests performed on QS samples, field measurements of some documented projects, and the closed-form solutions to circular tunnels in swelling rock. The verified model was then employed to conduct a parametric study considering important micro-tunneling design parameters, such as depth and diameter of the tunnel, in situ stress ratio (Ko), and the time lapse prior to replacing LFs with permanent cement grout around the tunnel. It was revealed that the time lapse plays a vital role in controlling deformations and associated stresses developed in the tunnel lining. The critical case of a pipe or tunnel in which the maximum tensile stress develops at its springline occurs when it is constructed at shallow depths in the QS layer. The results of the parametric study were used to suggest recommendations for the construction of tunnels in QS employing micro-tunneling. 相似文献
485.
One challenge in designing a photovoltaic (PV) system is to predict its generation, given parameters such as location, meteorological conditions, and layout. A greater challenge is to predict the generation of such a system under snow-cover condition. Publicly available snowfall data provide records for horizontal surfaces. However, the effect of snow accumulated on a tilted PV module remains unknown. Hence, irradiance is insufficient for predicting the output of PV systems having any given layout configuration. The research in this paper aims to predict the daily generation of PV systems through the development of a predictive model flexible enough to accommodate different layout configurations based on long-term monitoring data collected from 85 sites. Snow coverage loss factors are derived empirically to enhance the performance of the model. A feed-forward artificial neural network model is developed and implemented with snow adjustments (snowfall data and snow coverage loss factors). Promising results are obtained and validated. 相似文献
486.
Tahir Iqbal Umair Shabbir Muhammad Sultan Muhammad Bilal Tahir Muhammad Farooq Muhammad Salim Mansha Mohsin Ijaz Mudassar Maraj 《国际能源研究杂志》2019,43(2):806-813
Low‐temperature solution process‐able perovskite solar cells are highly desirable for future photovoltaics. Chemical root was utilized to synthesize and optimize mixed halide‐based MAPbIBr2 light absorber perovskites on electron transport layer of TiO2 nanoparticles in ambient atmosphere. For the first time all synthesis work was performed in an ambient environment and observe material behavioral characteristics. To accurately control the film morphology, one‐step deposition technique was applied to investigate material's optoelectronic behavior. The role of the perovskite structure, physical, and optical properties in planner device architecture was studied through ultraviolet visible, X‐ray diffraction, X‐ray photoelectron spectroscopy, and scanning electron microscope characterization techniques to confirm a band gap of 1.76 eV with cubic crystalline structure having a particle size of 12.5–13.0 nm, which is highly suitable for perovskite solar cells. 相似文献
487.
Antioxidant activities of some dried fruits consumed in Algeria 总被引:1,自引:0,他引:1
Salim Ouchemoukh Said Hachoud Hamou Boudraham Abderrahmane Mokrani Hayette Louaileche 《LWT》2012,49(2):329-332
Dried fruits such as prune, apricots, raisins and figs are an important source of different antioxidants which can inhibit the harmful effects of the free radicals. They receive increasing attention for their potential role in prevention of human diseases. The aims of our study were the quantification of some antioxidants (carotenoïds, total phenolic compounds, anthocyanins, flavonoïds and proanthocyanidins) using colorimetric assays and the determination of antioxidant activities by three methods. Three aqueous solvents (distilled water, ethanol and methanol) were used for the extraction of some antioxidants. Apricots and figs had the highest concentration of carotenoïds (10.7 and 10.8 mg βCE/100 g, respectively). Raisins were the richest fruits in total phenolic concentration (1.18 g GAE/100 g) and proanthocyanidins (17.53 mg CE/100 g). Also, figs had the highest concentration of flavonoïds (105.6 mg QE/100 g) and anthocyanins (5.9 mg/100 g). Apricots and raisins possessed a good reducing power, while Agen prune showed significant antioxidant activity to the phosphomolybdate. There were significant correlations between total phenolic concentration and antiradical activity (r = 0.89; p < 0.001) of ethanolic extract and reducing power (r = 0.80; p < 0.01) of aqueous extract. 相似文献
488.
489.
Sihem Zitouni Khaled Rouabah Salim Attia Djamel Chikouche 《Wireless Personal Communications》2013,70(4):1397-1407
The mathematical formulation of the discriminator and the multipath error models presented by Harris and Lightsey contains some typing errors. In this comment, we review the formalism of aforementioned models and we fix and correct these typing errors. The simulation results show that the original analytical models, with these corrections, coincide with the numerical models. 相似文献
490.
Salim Barbhuiya 《Construction and Building Materials》2011,25(8):3301-3305
Fly ash and limestone powder are found to be the traditional materials to be used in controlling the segregation potential and deformability of fresh SCC. This research deals with the utilisation of an alternative material, dolomite powder, instead of limestone powder, for the production of SCC. Test results indicated that it is possible to manufacture SCC using fly ash and dolomite powder. The mix containing fly ash and dolomite powder in the ratio 3:1 was found to satisfy the requirements suggested by the European Federation of Producers and Contractors of Specialist Products for Structures (EFNARC) guide for making SCC. 相似文献