全文获取类型
收费全文 | 410篇 |
免费 | 23篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 10篇 |
综合类 | 6篇 |
化学工业 | 80篇 |
金属工艺 | 11篇 |
机械仪表 | 26篇 |
建筑科学 | 15篇 |
能源动力 | 17篇 |
轻工业 | 28篇 |
水利工程 | 6篇 |
石油天然气 | 13篇 |
无线电 | 50篇 |
一般工业技术 | 72篇 |
冶金工业 | 18篇 |
原子能技术 | 3篇 |
自动化技术 | 88篇 |
出版年
2024年 | 1篇 |
2023年 | 10篇 |
2022年 | 11篇 |
2021年 | 23篇 |
2020年 | 16篇 |
2019年 | 24篇 |
2018年 | 34篇 |
2017年 | 35篇 |
2016年 | 29篇 |
2015年 | 12篇 |
2014年 | 16篇 |
2013年 | 43篇 |
2012年 | 37篇 |
2011年 | 37篇 |
2010年 | 35篇 |
2009年 | 22篇 |
2008年 | 13篇 |
2007年 | 15篇 |
2006年 | 8篇 |
2005年 | 4篇 |
2004年 | 3篇 |
2003年 | 4篇 |
2002年 | 2篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1994年 | 4篇 |
排序方式: 共有443条查询结果,搜索用时 31 毫秒
81.
Bearing fault detection using wavelet packet transform of induction motor stator current 总被引:6,自引:0,他引:6
Induction motor vibrations, caused by bearing defects, result in the modulation of the stator current. In this research, bearing defect is detected using the stator current analysis via Meyer wavelet in the wavelet packet structure, with energy comparison as the fault index. The advantage of this method is in the detection of incipient faults. The presented method is evaluated using experimental signals. Sets of data are gathered before and after using defective bearings. Compared to conventional methods, the superiority of the proposed method is shown in the success of fault detection. 相似文献
82.
This paper presents a 3rd-order two-path continuous-time time-interleaved (CTTI) delta-sigma modulator which is implemented in standard 90 nm CMOS technology. The architecture uses a novel method to resolve the delayless feedback path issue arising from the sharing of integrators between paths. By exploiting the concept of the time-interleaving techniques and through the use time domain equations, a conventional single path 3rd-order discrete-time (DT) ΔΣ modulator is converted into a corresponding two-path discrete-time time-interleaved (DTTI) counterpart. The equivalent CTTI version derived from the DTTI ΔΣ modulator by determining the DT loop filters and converting them to the equivalent continuous-time loop filters through the use of the Impulse Invariant Transformation. Sharing the integrators between two paths of the reported modulator makes it robust to path mismatch effects compared to the typical time-interleaved modulators which have individual integrators in all paths. The modulator achieves a dynamic range of 12 bits with an OverSampling Ratio of 16 over a bandwidth of 10 MHz and dissipates only 28 mW of power from a 1.8-V supply. The clock frequency of the modulator is 320 MHz but integrators, quantizers and DACs operate at 160 MHz. 相似文献
83.
M. A. Jafar Mazumder L. K. M. O. Goni S. A. Ali M. K. Nazal 《Iranian Polymer Journal》2018,27(12):979-995
Ethyl ester hydrochloride of amino acid l-methionine 1 was converted to cationic monomers N,N-diallyl methionine ethyl ester hydrochloride 2 and hydrochloride salt of N,N-diallylmethionine 3. Cationic monomers 2 and 3 underwent alternate copolymerization with SO2 in dimethyl sulfoxide to give terpolymers 4 and 5, respectively, both having?≈?1:1 ratio of sulfide and sulfoxide motifs owing to O transfer from dimethyl sulfoxide to the S. The sulfide groups in 5 have been oxidized with H2O2 to give polymer sulfoxide 6. In the presence of a small concentration of 35.2 µM (~?11?±?1 ppm) of each of the polymers 4, 5 and 6, the inhibition efficiency against mild steel corrosion in 1.0 M HCl at 60 °C was determined to be 90.8, 98.7 and 93.0%, respectively. The inhibition efficiency obtained from gravimetric weight loss was corroborated by the findings of potentiodynamic polarization and electrochemical impedance spectroscopy methods. Adsorption of polymer compounds onto the mild steel surface followed a mixture of chemisorption and physisorption processes and obeyed Langmuir, Temkin and Freundlich adsorption isotherms. The X-ray photoelectron spectroscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy techniques further confirmed that the synthesized compounds formed a protective film onto the metal surface and prove it against further corrosion attack. 相似文献
84.
We deal with the reconstruction of surfaces that deform under a variety of conditions. The deformation can range from no extension to a certain degree of extensibility. The deformed surface is reconstructed from a single image, given a 3D reference shape. This shape corresponds to the undeformed state of the surface and can be computed using any appropriate technique. In particular, we use homographies defined from two views of the surface. To proceed with the 3D reconstruction of the deformed surface, we assume that the deformations are locally homogeneous and that the overall surface deformation can be obtained by combining the local homogeneous deformations. For this purpose, the surface is split into small patches. For each patch, a mapping between the undeformed and the deformed shapes is computed. The mapping is specified by using the quadratic deformation model Fayad et al. (Proceedings of British Machine Vision Conference (BMVC), 2004). As a result, given the undeformed shape, we define an optimization procedure whose goal is to estimate the 3D positions of deformed points in each image. The optimization is performed on each patch, independently of the others. The experimental results show that this approach allows precise reconstruction of a wide class of real deformations. 相似文献
85.
A high step‐up half‐bridge DC/DC converter with a special coupled inductor for input current ripple cancelation and extended voltage doubler circuit for power conditioning of fuel cell systems
下载免费PDF全文
![点击此处可从《International Journal of Circuit Theory and Applications》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Hadi Moradisizkoohi Jafar Milimonfared Meghdad Taheri Sina Salehi 《International Journal of Circuit Theory and Applications》2016,44(6):1290-1307
This paper presents a high step‐up soft switched dc–dc converter having the feature of current ripple cancelation in the input stage that is specialized for power conditioning of fuel cell systems. The converter comprises a special half‐bridge converter and a rectifier stage based upon the voltage‐doubler circuit, in which the coupled‐inductor technology is amalgamated with switched‐capacitor circuit. The input current with no ripple is the principal characteristics of this topology that is achieved by utilizing a small coupled inductor. In addition, the low clamped voltage stress across both power switches and output diodes is another advantage of the proposed converter, which allows employing the metal–oxide–semiconductor field‐effect transistors with minuscule on‐state resistance and diodes with lower forward voltage‐drop, and thereby, the semiconductors' conduction losses diminish considerably. The inherent nature of this topology handles the switching scheme based on the asymmetrical pulse width modulation in order for switches to establish the zero voltage switching, leading to lower switching losses. Besides, because of the absence of the reverse‐recovery phenomenon, all diodes turn off with zero current switching. At last, a 250‐W laboratory prototype with the input voltage 24 V and output voltage 380 V is implemented to verify the especial features of the proposed converter. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
86.
A novel application of nanoparticles of paramagnetic magnetite (Fe3O4) as an efficient catalyst for carbon‐carbon bond formation via the Sonogashira–Hagihara reaction under heterogeneous ligand‐free conditions in ethylene glycol (EG) is described. By using this catalyst, arylalkynes are produced from the reaction of aryl iodides and activated heteroaryl bromides with alkynes. The results are reproducible using the catalyst, which was prepared from different sources. The catalyst is easily separated by an external magnetic field from the reaction mixture. The separated catalyst can be recycled for several consecutive runs without appreciable loss of its catalytic activity. 相似文献
87.
In this study the levels of aflatoxin M1 (AFM1) in UHT milk samples were determined in May, August and November and February. Two hundred and ten UHT milk samples were obtained from supermarkets in Tehran, Iran. The occurrence and concentration range of AFM1 in the samples were investigated by competitive enzyme-linked immunoabsorbent assay (ELISA) method. AFM1 was found in 116 (55.2%) of 210 UHT milk samples examined. The levels of AFM1 in 70 (33.3%) samples were higher than the maximum tolerance limit (0.05 μg/l) accepted by some European countries while none of the samples exceeded the prescribed limit of US regulations. The highest mean concentration of AFM1 was recorded in February (0.087 μg/l). The lowest mean concentration of AFM1 was recorded in August (0.021 μg/l). Statistical evaluation showed that there were significant difference (P < 0.01) between the mean concentrations of AFM1 of UHT milk samples taken in February with May and August. AFM1 contents of milk samples taken in February were not higher than UHT milk samples taken in November (P < 0.01). The AFM1 incidence of exceeding legal limit in UHT milk samples (33.3%) was relatively much higher than some other countries. It was therefore concluded that, the levels of AFM1 in UHT milk samples consumed in Iran were high and seemed to pose a threat to public health. 相似文献
88.
Samaneh Shahgaldi Zahira Yaakob Dariush Jafar Khadem Wan Ramli Wan Daud 《International Journal of Hydrogen Energy》2012
In the present work, titania-coated (TiO2) boron nitride nanofibers were produced by the electrospinning method, and the effect of heat treatment on the nanofibers was studied. Electrospinning method is often adopted for the synthesis of one-dimensional nanofibers due to high productivity, simplicity, and cost-effectiveness. In this study, boric oxide was deposited on co-electrospun polyacrylonitrile and TiO2. TiO2-coated boron nitride nanofibers, with a diameter of 100 nm, were obtained after heat treatment and nitridation. The effects of heat treatment on the morphology, surface area and hydrogen storage capacity were studied extensively. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM) showed long, bead-free nanofibers and the presence of TiO2 nanoparticles on the nanofibers. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy depicted hexagonal structures of boron nitride. The hydrogen uptake capacities of the nanofibers were investigated by pressure composition isotherm (PCI) in the pressure range of 1–70 bar at room temperature. 相似文献
89.
Zahira Yaakob Dariush Jafar Khadem Samaneh Shahgaldi Wan Ramli Wan Daud Siti Masrinda Tasirin 《International Journal of Hydrogen Energy》2012
Pure and doped ZnO nanofibers with Al and Mg were successfully synthesized via an electrospinning method using a sol–gel containing Polyvinylpyrrolidone as a spinning aid and a zinc nitrate precursor. Calcination of the doped and undoped electrospun nanofibers was conducted at 500 °C in air, and the resultant structures were analyzed by X-ray diffraction (XRD) and Raman spectroscopy. The diameter of the doped nanofibers decreased with increasing viscosity and conductivity, as measured by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Energy dispersive spectroscopy (EDS) showed that Mg and Al are present in ZnO nanofibers. The pressure composition isotherm (PCI) demonstrated that the capacity of hydrogen storage in pure zinc oxide nanofibers is a factor of two greater than that of zinc oxide nanoparticles. However, Al-doped ZnO nanofibers have the highest capacity of hydrogen storage (2.81 wt%) at room temperature. 相似文献
90.
Multiple-step martensitic transformations of an aged Ni51Ti49 single crystal using calorimetric method were investigated. Results show that for short aging times (10–45 min) multiple-step
martensitic transformations on cooling occur in two steps. Applying intermediate aging times (1.25–4 h) results in three steps
and long aging times (more than 8 h) lead to two-step martensitic transformations again. This behavior has not been recognized
in NiTi single crystals in literatures. It can be related to the heterogeneity of composition and stress fields around Ni4Ti3 precipitates. 相似文献