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71.
A.H. Ahmadi Motlagh S.H. Hashemabadi 《International Communications in Heat and Mass Transfer》2008,35(5):674-680
Two- and three-dimensional CFD modeling of heat transfer from discrete circular cylindrical particles in four different situations including A) infinite cylinder in cross-flow, B) cross-flow on finite cylinder with different aspect ratio in a rectangular duct, C) axial-flow on finite cylinder and D) axial-flow on finite cylinder with upstream turbulence have been investigated with the commercial CFD software, FEMLAB. The results were validated using experimental data from different research papers and also experimental correlations and show good quantitative and qualitative agreement with each other. In case B, a correction term has been proposed from CFD work which is applied to an experimental correlation to consider the aspect ratio influence on predicting the Nusselt number with an average error of 3.7%. 相似文献
72.
Shrinkage of repair material, especially in patching repairs, is the major factor inducing cracking in concrete repairs. Induced cracks in repair materials are due to restrained shrinkage. Although in usual practice, the free shrinkage of the repair mortar is measured, in reality, cracking is not due to free shrinkage. It is well known that cracking is due to restrained shrinkage. It is very hard to measure the restrained shrinkage; therefore, to overcome this problem a restraint factor (R) is used to modify the free shrinkage and come up with the restrained shrinkage. The restraint factor is influenced by the surface and boundary condition.In this study, the restraint factor for patching repair with different boundary conditions (with eaves and without eaves) and surface condition (rough and smooth) of the substrate concrete is investigated.The results show that the restraint factor R lies between 0.1 and 0.94; with an increase of restraint, the restraint factor is increased. In situations with a high level of restraint (eaves at the perimeter and a rough surface of substrate), the average R is 0.83. while with a low level of restraint (without eaves at the perimeter and a smooth surface of the substrate), the average R is 0.22. 相似文献
73.
Gh. Tahmasebipour Y. Hojjat V. Ahmadi A. Abdullah 《The International Journal of Advanced Manufacturing Technology》2009,44(1-2):80-90
This paper presents optimization of electrochemical etching parameters to achieve the optimum aspect ratio of the scanning tunneling microscopy/field ion microscopy tungsten nanotip by using Taguchi method. The combination of optimum level of process parameters was obtained by using the analysis of signal-to-noise ratio. The level of importance of the process parameters on the nanotip aspect ratio was determined by using analysis of variance. It was found that the optimum level of process parameters are electrolyte concentration of 2 M/lit, wire immersion length of 2.5 mm, cathode tube inner diameter of 40 mm, and voltage of 3.5 V. Within the range of experiments and the process parameters in terms of impact significance were found to be electrolyte concentration, process voltage, wire immersion length, and inner diameter of cathode tube, respectively. By using the optimum level of the process parameters, the nanotip aspect ratio was enhanced by 263% in comparison to the mean value of the experimental results. The nanotip aspect ratio of up to 163:1 was obtained in the present research. 相似文献
74.
Empirical evaluation of river basin sustainability affected by inter‐basin water transfer using composite indicators 下载免费PDF全文
Maryam Kefayati Bahram Saghafian Azadeh Ahmadi Hossein Babazadeh 《Water and Environment Journal》2018,32(1):104-111
In this study, a practical approach to evaluate the sustainability of river basins subjected to an inter‐basin water transfer project is developed. Selection of appropriate evaluation indicators is pivotal to such approach. To make use of huge amount of data, composite indicators of sustainability (CIS) should be utilised. The proposed approach relies on 15 sustainability indicators (SI) that cover three major criteria namely (economic, social and environmental), and aggregates them into eight different types of sustainability indices for a more robust outcome. Two scenarios were considered within the source and recipient basins. Furthermore, multivariate principal component analysis (PCA) was applied to determine principal and non‐principal indicators for the two river basins. The ability of CIS and PCA methods were verified via correlation and simple regression methods respectively. The results demonstrated that inter‐basin water transfer may improve sustainability, provided that a proper water resource management is enforced. 相似文献
75.
Supertough (Polyamide 6)/(acrylonitrile butadiene rubber) nano alloy through in situ polymerization of caprolactam in the presence of acrylonitrile butadiene rubber nanophase 下载免费PDF全文
Shervin Ahmadi Yousef Jahani Ghasem Naderi Amir Hossein Asadollahzadeh 《乙烯基与添加剂工艺杂志》2015,21(2):116-121
In this work, polymerization of caprolactam (CL) was carried out in the presence of acrylonitrile butadiene rubber (NBR) during the reactive melt‐mixing process. During shear mixing, NBR particles swelled and dissolved in the molten CL, which led to separation and distribution of rubber particles to nanoscale in the dissolution stage. Then, in an internal mixer, supertough Polyamide 6 was prepared via melt polymerization of CL/NBR mixture, sodium caprolactam as a catalyst, and hexamethylene diisocyanate as an activator. The effects of various concentrations of catalyst and activator on the initiation time of the reaction were determined. Physical and mechanical properties of different formulations prepared via reactive melt blending were determined by tensile and impact measurements, differential scanning calorimetry, Fourier‐transform infrared spectroscopy, X‐ray scattering techniques, transmission electron microscopy, and dynamic mechanical thermal analysis. Experimental results showed that a recipe with 3% nitrile rubber in a CL/NBR mixture enhances the physical and mechanical properties the best, compared with other formulations. This condition led to the formation of NBR nanospheres during melt polymerization of Polyamide 6 as well. J. VINYL ADDIT. TECHNOL., 21:116–121, 2015. © 2014 Society of Plastics Engineers 相似文献
76.
Saharnaz Ahmadi Maryam Farokhi Parisa Padidar Mojtaba Falahati 《International journal of molecular sciences》2015,16(8):17289-17302
In this study the effect of surface modification of mesoporous silica nanoparticles (MSNs) on its adsorption capacities and protein stability after immobilization of beta-lactoglobulin B (BLG-B) was investigated. For this purpose, non-functionalized (KIT-6) and aminopropyl-functionalized cubic Ia3d mesoporous silica ([n-PrNH2-KIT-6]) nanoparticles were used as nanoporous supports. Aminopropyl-functionalized mesoporous nanoparticles exhibited more potential candidates for BLG-B adsorption and minimum BLG leaching than non-functionalized nanoparticles. It was observed that the amount of adsorbed BLG is dependent on the initial BLG concentration for both KIT-6 and [n-PrNH2-KIT-6] mesoporous nanoparticles. Also larger amounts of BLG-B on KIT-6 was immobilized upon raising the temperature of the medium from 4 to 55 °C while such increase was undetectable in the case of immobilization of BLG-B on the [n-PrNH2-KIT-6]. At temperatures above 55 °C the amounts of adsorbed BLG on both studied nanomaterials decreased significantly. By Differential scanning calorimetry or DSC analysis the heterogeneity of the protein solution and increase in Tm may indicate that immobilization of BLG-B onto the modified KIT-6 results in higher thermal stability compared to unmodified one. The obtained results provide several crucial factors in determining the mechanism(s) of protein adsorption and stability on the nanostructured solid supports and the development of engineered nano-biomaterials for controlled drug-delivery systems and biomimetic interfaces for the immobilization of living cells. 相似文献
77.
Mazeyar Parvinzadeh Naser Memari Mohammad Shaver Bashir Katozian Saeed Ahmadi Issa Ziadi 《Journal of surfactants and detergents》2010,13(2):135-141
In recent years, the textile industry has been forced to develop new technologies to reduce energy and water consumption.
The use of ultrasound in textile wet processing is one solution to this problem. The aim of this work was to investigate the
effects of ultrasonic energy on the processing of cotton with a cationic softener. For this purpose, cotton fabric was treated
with a fatty acid amide derivative cationic softener in water using ultrasonic energy during treatment. The physical properties
of the fabrics treated under different conditions are discussed. The results show that the treatment of fabrics with softeners
in an ultrasound bath is more effective compared to conventional methods and that it enhances the physical properties of the
cotton. 相似文献
78.
79.
Optimization of Output Power and Thermal Efficiency of Solar‐Dish Stirling Engine Using Finite Time Thermodynamic Analysis 下载免费PDF全文
This paper presents an investigation on finite time thermodynamic (FTT) evaluation of a solar‐dish Stirling heat engine. FTTs has been applied to determine the output power and the corresponding thermal efficiency, exergetic efficiency, and the rate of entropy generation of a solar Stirling system with a finite rate of heat transfer, regenerative heat loss, conductive thermal bridging loss, and finite regeneration process time. Further imperfect performance of the dish collector and convective/radiative heat transfer mechanisms in the hot end as well as the convective heat transfer in the heat sink of the engine are considered in the developed model. The output power of the engine is maximized while the highest temperature of the engine is considered as a design parameter. In addition, thermal efficiency, exergetic efficiency, and the rate of entropy generation corresponding to the optimum value of the output power is evaluated. Results imply that the optimized absorber temperature is some where between 850 K and 1000 K. Sensitivity of results against variations of the system parameters are studied in detail. The present analysis provides a good theoretical guidance for the designing of dish collectors and operating the Stirling heat engine system. 相似文献
80.
M. Shiraly M. Shamanian M. R. Toroghinejad M. Ahmadi Jazani 《Journal of Materials Engineering and Performance》2014,23(2):413-420
In this study, the friction stir spot welding of Al/Cu composite produced by accumulative roll-bonding process was performed using a triangular pin with no features. The influence of tool rotation rate on the microstructure, surface hardness, and tensile shear strength was examined. The results indicated that the weld made at lower tool rotation rate was not bonded because there was no intermixing between the upper and lower sheets. The maximum shear failure load increased with the increasing tool rotation rate, and reached a maximum value at 1400 rpm, which can be ascribed to the increasing area and effective length (d) of stir zone (SZ). The experimental observations showed the presence of the intermetallic compounds (Al2Cu and AlCu3) in the SZ. It was concluded that the intermetallic compounds, accompanied by the material crushing, increased the hardness of the SZ. 相似文献