全文获取类型
收费全文 | 927篇 |
免费 | 48篇 |
国内免费 | 8篇 |
学科分类
工业技术 | 983篇 |
出版年
2024年 | 3篇 |
2023年 | 16篇 |
2022年 | 24篇 |
2021年 | 45篇 |
2020年 | 40篇 |
2019年 | 56篇 |
2018年 | 37篇 |
2017年 | 37篇 |
2016年 | 46篇 |
2015年 | 22篇 |
2014年 | 47篇 |
2013年 | 97篇 |
2012年 | 58篇 |
2011年 | 71篇 |
2010年 | 44篇 |
2009年 | 41篇 |
2008年 | 37篇 |
2007年 | 31篇 |
2006年 | 23篇 |
2005年 | 13篇 |
2004年 | 14篇 |
2003年 | 14篇 |
2002年 | 16篇 |
2001年 | 10篇 |
2000年 | 6篇 |
1999年 | 12篇 |
1998年 | 14篇 |
1997年 | 10篇 |
1996年 | 10篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1966年 | 1篇 |
排序方式: 共有983条查询结果,搜索用时 328 毫秒
51.
Nema Ankita Bano Mustri Rai Mansi Shrivastava Kavya Dangi Sambhavna Singh Khan Farid 《Journal of Porous Materials》2022,29(2):459-471
Journal of Porous Materials - Silver monoliths using non-ionic surfactant Triton X-102 as reducing agent with and without additives such as Dextran and Ludox (SiNPs) were synthesized by modified... 相似文献
52.
T. Ahmadi A. Monshi V. Mortazavi M.H. Fathi S. Sharifi B. Hashemi Beni A. Moghare Abed M. Kheradmandfard A. Sharifnabi 《Ceramics International》2014
Nanosized hydroxyapatite (HA) powders exhibit a greater surface area than coarser crystals and are expected to show an improved bioactivity. In addition, properties of HA can be tailored over a wide range by incorporating different ions into HA lattice. The aim of this study was to prepare and characterize silicon and magnesium co-doped fluorapatite (Si–Mg–FA) with a chemical composition of Ca9.5Mg0.5 (PO4)5.5(SiO4)0.5F2 by the high-energy ball milling method. Characterization techniques such as X-ray diffraction analysis (XRD), Fourier transformed infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM) were utilized to investigate the structural properties of the obtained powders. Dissolution behavior was evaluated in simulated body fluid (SBF) and physiological normal saline solution at 37 °C for up to 28 days. The results of XRD and FTIR showed that nanocrystalline single-phase Si–Mg–FA powders were synthesized after 12 h of milling. In addition, incorporation of magnesium and silicon into fluorapatite lattice decreased the crystallite size from 53 nm to 40 nm and increased the lattice strain from 0.220% to 0.296%. Dissolution studies revealed that Si–Mg–FA in comparison to fluorapatite (FA), releases more Ca, P and Mg ions into SBF during immersion. 175 ppm Ca, 33.5 ppm P and 48 ppm Mg were detected in the SBF containing Si–Mg–FA after 7days of immersion, while for FA, it was 75 ppm Ca, 21.5 ppm P and 29 ppm Mg. Release of these ions could improve the bioactivity of the obtained nanopowder. It could be concluded that the prepared nanopowders have structural properties such as crystallite size (~40 nm), crystallinity degree (~40%) and chemical composition similar to biological apatite. Therefore, prepared Si–Mg–FA nanopowders are expected to be appropriate candidates for bone substitution materials and also as a phase in polymer or ceramic-based composites for bone regeneration in tissue engineering applications. 相似文献
53.
Farid H. Abed 《Mechanics of Time-Dependent Materials》2010,14(4):329-345
A constitutive relation is presented in this paper to describe the plastic behavior of ferritic steel over a broad range of
temperatures and strain rates. The thermo-mechanical behavior of high strength low alloy (HSLA-65) and DH-63 naval structural
steels is considered in this study at strains over 40%. The temperatures and strain rates are considered in the range where
dynamic strain aging is not effective. The concept of thermal activation analysis as well as the dislocation interaction mechanism
is used in developing the flow model for both the isothermal and adiabatic viscoplastic deformation. The flow stresses of
the two steels are very sensitive to temperature and strain rate, the yield stresses increase with decreasing temperatures
and increasing strain rates. That is, the thermal flow stress is mainly captured by the yield stresses while the hardening
stresses are totally pertained to the athermal component of the flow stress. The proposed constitutive model predicts results
that compare very well with the measured ones at initial temperature range of 77 K to 1000 K and strain rates between 0.001 s−1 and 8500 s−1 for both steels. 相似文献
54.
Farid C. Christo 《Renewable Energy》2012,39(1):356-366
This study reports on numerical predictions of velocity and pressure fields, and dust particles trajectories in steady and unsteady flows around a full-scale paraboloidal solar dish. Calculations are performed for three wind speeds of 4.16, 9.72, and 15.2 m s−1, and dish pitch angles from 0° to 180°. The flow field structure, lift and drag coefficients are calculated for each flow configuration. Using the predicted mean flow velocity field, analytical expressions for the aerodynamic coefficients, as a function of the pitch angle, are developed. The unsteady-state flow is characterised by formation of stable vortices behind the dish for most flow configurations, except at 60° and 150° pitch angles. At these angles vortex-shedding occurred with a strong flow oscillation extending downstream the dish. The calculations of dust particles trajectories provide a qualitative assessment of the deposition rate, dish orientation, and surface locations where dust accumulation is most likely to occur. The study also presents an initial assessment of the effectiveness of various windbreaks installed upstream of the dish in reducing aerodynamics drag. 相似文献
55.
56.
Ahmed Reda Yeddou Boubakeur Nadjemi Farid Halet Aïssa Ould-Dris Richard Capart 《Minerals Engineering》2010,23(1):32-39
This work is dedicated to the removal of the very toxic free cyanide from aqueous solution by oxidation with hydrogen peroxide H2O2 in the presence of activated carbon prepared from olive stones. Effects of the initial molar ratio [H2O2]0/[CN?]0, the initial cyanide concentration, the activated carbon concentration and the temperature on cyanide removal have been examined. The removal of free cyanide in absence of activated carbon showed very slow kinetics. The presence of activated carbon has increased the reaction rate showing thus a catalytic activity. The kinetics of cyanide removal has been found to be of pseudo-first-order with respect to cyanide and the rate constants have been determined for different values of the aforementioned parameters. The apparent activation energy has been determined from tests carried out at three different temperatures. It was found equal to 46.2 kJ/mol in the presence of activated carbon, which is about half of the 82.7 kJ/mol found for the oxidation in absence of the activated carbon.This process can be interesting for the cyanide removal from processed solutions because it does not use soluble metal catalyst and it consumes only hydrogen peroxide as chemical product. 相似文献
57.
Influence of the deposition duration and electrolyte concentration on the structural and morphological features of the ZnO thin films, grown by cathodic electrodeposition on zinc substrate followed by annealing in air at 400 °C, have been investigated. The surface morphology of the as-synthesized films shows two distinct features, presence of ‘2-dimensional nanosheets’ on the area near the electrolyte-air interface and ‘granular’ nanostructures, below the interface region. However, upon annealing, the formation of ZnO nanowires, possessing length of several microns and diameter less than 20 nm, on the entire substrate is observed. The X-ray and selected area electron diffraction patterns clearly confirm the polycrystalline nature of the ZnO nanowires. 相似文献
58.
Arvin Farid Akram N. Alshawabkeh Carey M. Rappaport 《Canadian Metallurgical Quarterly》2009,135(9):1209-1218
This paper explains and evaluates the potential and limitations of conducting cross-well radar (CWR) in sandy soils. Implementing the experiment and data collection in the absence of any scattering object, and in the presence of an acrylic plate [a representative of dielectric objects, such as dense nonaqueous phase liquid (DNAPL) pools, etc.], as a contrasting object in a water-saturated soil is also studied. To be able to image the signature of any object, more than one pair of receiving and transmitting antennas are required. The paper describes a method to achieve repeatable, reliable, and reproducible laboratory results for different transmitter-receiver combinations. Different practical methods were evaluated for collecting multiple-depth data. Similarity of the corresponding results and problems involved in each method are studied and presented. The data show that the frequency response of a saturated coarse-grained soil is smooth due to the continuous and dominant nature of water in saturated soils. The repeatability and potential symmetry of patterns across some borehole axes provide a valuable tool for validation of experimental results. The potential asymmetry across other borehole axes is used as a tool to evaluate the strength of the perturbation on the electromagnetic field due to hidden objects and to evaluate the feasibility of detecting dielectric objects (such as DNAPL pools, etc.) using CWR. The experimental simulation of this paper models a real-life problem in a smaller scale, in a controlled laboratory environment, and within homogeneous soils that are uniformly dry or fully water saturated, with a uniform dielectric property contrast between the inclusion and background. The soil in the field will not be as homogeneous and uniform. The scaling process takes into consideration that as the size is scaled down; the frequency needs to be scaled up. It is noteworthy that this scaling process needs to be extensively studied and validated for future extension of the models to real-field applications. For example, to extend the outcome of this work to the real field, the geometry (antenna size, their separation and inclusion size) needs to be scaled up back to the field size, while soil grains will not. Therefore, soil, water, and air coupling effects and interactions observed at the laboratory scale do not scale up in the field, and may have different unforeseen effects that require extensive study. 相似文献
59.
Ahmad Farid Abidin Azah Mohamed Hussain Shareef 《Expert systems with applications》2011,38(12):14969-14975
The conventional power swing schemes used in distance relay operation are not fast enough to detect and distinguish a fault, stable swing and unstable swing and this may lead to unintended tripping of protection devices. Therefore, there is a need for fast detection of unstable swings so as to improve the reliability of distance relay operation. This paper presents an intelligent approach for detecting unstable swings during distance relay operation using the S-transform signal processing technique and artificial neural networks. To illustrate the effectiveness of the proposed approach, simulations were carried out on the IEEE 39 bus test system using the PSS/E software. Test results showed that the proposed approach using S-transform, multi layer perceptron network and probabilistic neural network can accurately detect and classify fault, stable swing, unstable swing, fault clearance and post fault events for correct distance relay operation. 相似文献
60.