全文获取类型
收费全文 | 832篇 |
免费 | 51篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 18篇 |
综合类 | 3篇 |
化学工业 | 227篇 |
金属工艺 | 22篇 |
机械仪表 | 27篇 |
建筑科学 | 38篇 |
矿业工程 | 2篇 |
能源动力 | 58篇 |
轻工业 | 50篇 |
水利工程 | 10篇 |
石油天然气 | 4篇 |
无线电 | 77篇 |
一般工业技术 | 156篇 |
冶金工业 | 27篇 |
原子能技术 | 16篇 |
自动化技术 | 157篇 |
出版年
2024年 | 7篇 |
2023年 | 14篇 |
2022年 | 37篇 |
2021年 | 58篇 |
2020年 | 64篇 |
2019年 | 46篇 |
2018年 | 90篇 |
2017年 | 51篇 |
2016年 | 51篇 |
2015年 | 33篇 |
2014年 | 59篇 |
2013年 | 104篇 |
2012年 | 60篇 |
2011年 | 64篇 |
2010年 | 42篇 |
2009年 | 35篇 |
2008年 | 12篇 |
2007年 | 16篇 |
2006年 | 15篇 |
2005年 | 4篇 |
2004年 | 5篇 |
2003年 | 5篇 |
2002年 | 1篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1994年 | 2篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1979年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有892条查询结果,搜索用时 15 毫秒
21.
Ehsan Mohammadi 《Scientometrics》2012,92(3):593-608
Nanoscience and technology (NST) is a relatively new interdisciplinary scientific domain, and scholars from a broad range of different disciplines are contributing to it. However, there is an ambiguity in its structure and in the extent of multidisciplinary scientific collaboration of NST. This paper investigates the multidisciplinary patterns of Iranian research in NST based on a selection of 1,120 ISI??indexed articles published during 1974?C2007. Using text mining techniques, 96 terms were identified as the main terms of the Iranian publications in NST. Then the scientific structure of the Iranian NST was mapped through multidimensional scaling, based upon the co-occurrence of the main terms in the academic publications. The results showed that the NST domain in Iranian publications has a multidisciplinary structure which is composed of different fields, such as pure physics, analytical chemistry, chemistry physics, material science and engineering, polymer science, biochemistry and new emerging topics. 相似文献
22.
We use numerical linked-cluster expansions to study finite-temperature properties of strongly interacting fermions in two-dimensional optical lattices, governed by the Hubbard model. We show the double occupancy and entropy for the infinite homogeneous system at temperatures significantly lower than those obtained by other exact methods at strong interactions. Employing a local density approximation, and using the high-precision results for the entropy, we study the density and nearest-neighbor spin correlation profiles of lattice fermions trapped in a harmonic potential during adiabatic processes. Starting with a trap that has a substantial band-insulator region at high temperatures, we show how one can access the Mott region at low temperatures by flattening the trapping potential. 相似文献
23.
Davood Iranshahi Ali Mohammad Bahmanpour Ehsan Pourazadi Mohammad Reza Rahimpour 《加拿大化工杂志》2012,90(5):1102-1111
In this study, the operating conditions of an axial flow spherical reactor have been optimised using a reliable optimisation technique and the results are compared with the results of non‐optimised conditions. The dynamic behaviour of the reactor has been considered in the optimisation process and orthogonal collocation method has been used in order to solve the obtained equations from mathematical modelling of the process. The goal of this study is to maximise the aromatics and hydrogen production rate. Therefore, the objective function is the combination of two terms which include the production rate of the mentioned components. The catalyst distribution for each reactor, the inlet pressure of the system, Length per radius for each reactor, the naphtha feed molar flow rate and the hydrogen mole fraction in the recycle stream as well as the inlet temperature of each reactor have been optimised in this study. © 2011 Canadian Society for Chemical Engineering 相似文献
24.
Ehsan Soleimani-Nasab Mehrdad Ardebilipour Ashkan Kalantari Behrad Mahboobi 《AEUE-International Journal of Electronics and Communications》2013,67(1):45-57
In this paper, we present the performance of multi-antenna selective combining decode-and-forward (SC-DF) relay networks over independent but non-identical Nakagami-m fading channels with imperfect channel estimation. The outage probability, moment generating function (MGF) and symbol error probability (SEP) will be derived in closed-form using the SNR statistical characteristics. To make the analysis trackable, we have derived the MGF and SEP for integer values of fading severity, m. Also, to make the relations more simple, we develop high signal to noise ratio (SNR) analysis for the performance metrics of our system. Subsequently, we propose optimal and adaptive power allocation algorithms along with the equal power allocation method. Finally, for comparison with analytical formulas, we perform some Monte-Carlo simulations. 相似文献
25.
Ehsan Eshtehardian Abbas Afshar Reza Abbasnia 《Construction Management & Economics》2013,31(7):679-691
Uncertainties should be considered in any time–cost trade‐off problems when minimizing project cost and duration, which leads to the so‐called stochastic time–cost trade‐off problem. A new approach to investigate stochastic time–cost trade‐off problems employing fuzzy logic theory is presented. The proposed approach fully embeds the fuzzy structure of the uncertainties in total direct cost into the model. An appropriate GA is used to develop a solution to the multi‐objective fuzzy time cost model. The accepted risk level of the project manager is defined through α cut approach for which a separate Pareto front with set of non‐dominated solutions has been developed. To compare the alternative set of options for any assumed project duration, associated fuzzy costs for different values of α cut are ranked employing two appropriate approaches for fuzzy costs comparison. The proposed models are applied to solve two benchmark test problems. It is shown that the models facilitate the decision‐making process by selecting specified risk levels and employing the associated Pareto front. 相似文献
26.
Ternary gas permeation through synthesized pdms membranes: Experimental and CFD simulation basedon sorption‐dependent system using neural network model 下载免费PDF全文
Ehsan Farno Mashallah Rezakazemi Toraj Mohammadi Norollah Kasiri 《Polymer Engineering and Science》2014,54(1):215-226
In this study, a predictive model for the separation of gases via a polydimethylsiloxane (PDMS) membrane has been developed. This model takes into account the effects of gas composition and pressure at the membrane surfaces on the gas sorption and diffusion coefficients in the membrane. Computational fluid dynamics (CFD) modeling has been employed in order to predict the behavior of a gas mixture containing C3H8, CH4, and H2 at various operating conditions and three zones (upstream, downstream, and membrane body). Artificial neural network (ANN) modeling has been applied to predict sorption and diffusion coefficients of each component of the gas mixture in the membrane. A procedure of calculation has been applied to combine the CFD modeling and the ANN modeling in order to predict sorption, diffusion, and composition of each component at various sites of the membrane. The results determined using the developed prediction model have been found to be in agreement with those determined using experimental investigations with an average error of 10.21%. POLYM. ENG. SCI., 54:215–226, 2014. © 2013 Society of Plastics Engineers 相似文献
27.
The research was carried out to develop geopolymers mortars and concrete from fly ash and bottom ash and compare the characteristics deriving from either of these products. The mortars were produced by mixing the ashes with sodium silicate and sodium hydroxide as activator solution. After curing and drying, the bulk density, apparent density and porosity, of geopolymer samples were evaluated. The microstructure, phase composition and thermal behavior of geopolymer samples were characterized by scanning electron microscopy, XRD and TGA-DTA analysis respectively. FTIR analysis revealed higher degree of reaction in bottom ash based geopolymer. Mechanical characterization shows, geopolymer processed from fly ash having a compressive strength 61.4 MPa and Young's modulus of 2.9 GPa, whereas bottom ash geopolymer shows a compressive strength up to 55.2 MPa and Young's modulus of 2.8 GPa. The mechanical characterization depicts that bottom ash geopolymers are almost equally viable as fly ash geopolymer. Thermal conductivity analysis reveals that fly ash geopolymer shows lower thermal conductivity of 0.58 W/mK compared to bottom ash geopolymer 0.85 W/mK. 相似文献
28.
29.
Sadaqat Ali Bilal Anjum Ahmed Hafiz Muzammil Irshad Akolade Idris Bakare Abbas Saeed Hakeem Muhammad Qamaruddin Muhammad Ali Ehsan Sameer Ali Muhammad Umar Azam 《International Journal of Applied Ceramic Technology》2020,17(4):1948-1958
The thermomechanical behavior of micro/nano-alumina (Al2O3) ceramics reinforced with 1-5 wt.% of acid-treated oil fly ash (OFA) was investigated. Composites were sintered using spark plasma sintering (SPS) technique at a temperature of 1400°C by applying a constant uniaxial pressure of 50 MPa. It was evaluated that the fracture toughness of micro- and nanosized composites improved in contrast with the monolithic alumina. Highest fracture toughness value of 4.85 MPam1/2 was measured for the nanosized composite reinforced with 5 wt.% OFA. The thermal conductivity of the composites (nano-/microsized) decreased with the increase in temperature. However, the addition of OFA (1-5 wt.%) in nanosized alumina enhanced the thermal conductivity at an evaluated temperature. Furthermore, a minimum thermal expansion value of 6.17 ppm*K−1 was measured for nanosized Al2O3/5 wt.% OFA composite. Microstructural characterization of Al2O3-OFA composites was done by x-ray diffraction and Raman spectroscopy. Oil fly ash particles were seen to be well dispersed within the alumina matrix. Moreover, the comparative analysis of the nano-/microsized Al2O3/OFA composites shows that the mechanical and thermal properties were improved in nanosized alumina composites. 相似文献
30.
Lipase-catalysed interesterification between canola oil and fully hydrogenated canola oil in contact with supercritical carbon dioxide 总被引:1,自引:0,他引:1
The processing parameters in enzymatic reactions using CO2-expanded (CX) lipids have strong effects on the physical properties of liquid phase, degree of interesterification, and physicochemical properties of the final reaction products. CX-canola oil and fully hydrogenated canola oil (FHCO) were interesterified using Lipozyme TL IM in a high pressure stirred batch reactor. The effects of immobilised enzyme load, pressure, substrate ratio and reaction time on the formation of mixed triacylglycerols (TG) from trisaturated and triunsaturated TG were investigated. The optimal immobilised enzyme load, pressure, substrate ratio and time for the degree of interesterification to reach the highest equilibrium state were 6% (w/v) of initial substrates, 10 MPa, blend with 30% (w/w) of FHCO and 2 h, respectively. The physicochemical properties of the initial blend and interesterified products with different FHCO ratios obtained at optimal reaction conditions were determined in terms of TG composition, thermal behaviour and solid fat content (SFC). The amounts of saturated and triunsaturated TG decreased while the amounts of mixed TG increased as a result of interesterification. Thus, the interesterified product had a lower melting point, and broader melting and plasticity ranges compared to the initial blends. These findings are important for better understanding of CX-lipid reactions and for optimal formulation of base-stocks of margarine and confectionary fats to meet industry demands. 相似文献