全文获取类型
收费全文 | 1243篇 |
免费 | 94篇 |
国内免费 | 13篇 |
专业分类
电工技术 | 34篇 |
综合类 | 9篇 |
化学工业 | 279篇 |
金属工艺 | 60篇 |
机械仪表 | 54篇 |
建筑科学 | 59篇 |
矿业工程 | 8篇 |
能源动力 | 54篇 |
轻工业 | 118篇 |
水利工程 | 23篇 |
石油天然气 | 25篇 |
无线电 | 123篇 |
一般工业技术 | 202篇 |
冶金工业 | 66篇 |
原子能技术 | 5篇 |
自动化技术 | 231篇 |
出版年
2024年 | 3篇 |
2023年 | 18篇 |
2022年 | 38篇 |
2021年 | 73篇 |
2020年 | 81篇 |
2019年 | 72篇 |
2018年 | 112篇 |
2017年 | 94篇 |
2016年 | 97篇 |
2015年 | 37篇 |
2014年 | 92篇 |
2013年 | 155篇 |
2012年 | 93篇 |
2011年 | 99篇 |
2010年 | 58篇 |
2009年 | 47篇 |
2008年 | 47篇 |
2007年 | 25篇 |
2006年 | 20篇 |
2005年 | 6篇 |
2004年 | 11篇 |
2003年 | 5篇 |
2002年 | 5篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1998年 | 10篇 |
1997年 | 1篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1982年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有1350条查询结果,搜索用时 15 毫秒
61.
The effect of bed-load transport on flow resistance of alluvial channels with undulated bed was experimentally investigated.
The experiments were carried out in a tilting flume 250mm wide and 12.5m long with glass-sides of rectangular cross-section
and artificial dune shaped floor that was made from Plexi-glass. Steady flow of clear as against sediment-laden water with
different flow depths and velocities were studied in the experiments with a fine sand (d
50 = 0.5mm). The results indicate that the transport of fine particles (d
50 = 0.5mm) can decrease the friction factor by 22% and 24% respectively for smooth and rough beds. Increasing the bed-load
size (d
50 = 2.84 mm) can decrease the friction factor by 32% and 39% respectively for smooth and rough beds. The decrease in flow resistance
is due to filling up of the troughs of dunes. This separation zone is responsible for increasing the flow resistance. On the
upstream side of dunes condition is similar to plane bed. Presence of bed-load causes to increase the shear velocity and hence
increasing flow resistance. But decreasing in flow resistance is more and it causes to decrease the total flow resistance.
Grains saturated the troughs in the bed topography, effectively helping in smoothening of bed irregularities. 相似文献
62.
Roozbeh Javad Kalbasi Majid Kolahdoozan Keinaz ShahabianFarzad Zamani 《Catalysis communications》2010,11(14):1109-1115
This work is concerned about the preparation and characterization of MnO4− supported poly (4-methyl vinylpyridinium)/SBA-15 which was effectively employed as a heterogeneous oxidant for oxidation of aromatic alcohols. P4MVPMnO4/SBA-15 exhibited excellent activity and selectivity under mild and solvent-less conditions. 相似文献
63.
M. Morakabati M. Aboutalebi Sh. Kheirandish A. Karimi Taheri S.M. Abbasi 《Intermetallics》2011,19(10):1399-1404
The deformation behavior of a 49.8 Ni-50.2 Ti (at pct) alloy was investigated using the hot compression test in the temperature range of 700 °C–1100 °C, and strain rate of 0.001 s?1 to 1 s?1. The hot tensile test of the alloy was also considered to assist explaining the related deformation mechanism within the same temperature range and the strain rate of 0.1 s?1. The processing map of the alloy was developed to evaluate the efficiency of hot deformation and to identify the instability regions of the flow. The peak efficiency of 24–28% was achieved at temperature range of 900 °C–1000 °C, and strain rates higher than 0.01 s?1 in the processing map. The hot ductility and the deformation efficiency of the alloy exhibit almost similar variation with temperature, showing maximum at temperature range of 900 °C–1000 °C and minimum at 700 °C and 1100 °C. Besides, the minimum hot ductility lies in the instability regions of the processing map. The peak efficiency of 28% and microstructural analysis suggests that dynamic recovery (DRV) can occur during hot working of the alloy. At strain rates higher than 0.1 s?1, the peak efficiency domain shifts from the temperature range of 850 °C–1000 °C to lower temperature range of 800 °C–950 °C which is desirable for hot working of the NiTi alloy. The regions of flow instability have been observed at high Z values and at low temperature of 700 °C and low strain rate of 0.001 s?1. Further instability region has been found at temperature of 1000 °C and strain rates higher than 1 s?1 and at temperature of 1100 °C and all range of strain rates. 相似文献
64.
Mohammad Javad Nasr Isfahani Marjaneh Jafari Fesharaki Vladimir Šepelák 《Ceramics International》2013,39(2):1163-1167
The bulk NiFe2?xBixO4 ferrites with various Bi3+ concentration (x=0, 0.1, 0.15) were synthesized via sol–gel procedure, starting from nickel, bismuth and iron nitrate powders, followed by the conventional thermal treatment. The structural and magnetic properties of the as-prepared ferrites were studied by means of X-ray diffraction, alternating gradient force magnetometry and Faraday balance. The anisotropy constant was determined by the law of approach to saturation (LAS) model. An increasing Bi3+ concentration in NiFe2?xBixO4 leads to a decrease in the saturation magnetization, Néel temperature and the anisotropy constant of the material. 相似文献
65.
Abu Syed H. Kabir Xinjin Cao Javad Gholipour Priti Wanjara Jonathan Cuddy Anand Birur Mamoun Medraj 《Metallurgical and Materials Transactions A》2012,43(11):4171-4184
The effects of postweld heat treatment (PWHT) on 3.2-mm- and 5.1-mm-thick Ti-6Al-4V butt joints welded using a continuous wave (CW) 4-kW Nd:YAG laser welding machine were investigated in terms of microstructural transformations, welding defects, and hardness, as well as global and local tensile properties. Two postweld heat treatments, i.e., stress-relief annealing (SRA) and solution heat treatment followed by aging (STA), were performed and the weld qualities were compared with the as-welded condition. A digital image correlation technique was used to determine the global tensile behavior for the transverse welding samples. The local tensile properties including yield strength and maximum strain were determined, for the first time, for the laser-welded Ti-6Al-4V. The mechanical properties, including hardness and the global and local tensile properties, were correlated to the microstructure and defects in the as-welded, SRA, and STA conditions. 相似文献
66.
Ali Rahmatpour Mohammad Javad Shaibani 《Energy Sources, Part A: Recovery, Utilization, and Environmental Effects》2018,40(18):2236-2247
The pipeline gas pressure can be recovered as electricity by installing a turbo-expander in parallel with throttle valves at pressure reduction stations. This paper aims to provide a techno-economic assessment of electricity generation at a gas pressure reduction station. Owing to the gas flow rate of the station, technical assessment showed two installation capacities of 2853 kw (Case I) and 4169 kw (Case II). As a result, NPV and IRR for Case I is calculated €1,669,623.93 and 28.95%; and for Case II, NPV and IRR is €1,393,871.91 and 23.91% respectively. The analysis indicated case I is more profitable than case II. 相似文献
67.
The probability of fluidization regimes at high temperature was determined experimentally by frequency domain analysis of pressure fluctuations. Fluidization regime probabilities were calculated for various gas velocities and temperatures. By increasing the temperature, larger bubbles became more stable which resulted in postponing transition from bubbling to turbulent fluidization. Results showed that the transition velocity from bubbling to turbulent increases by raising the temperature. A probability model was proposed and compared with experimental data indicating good accordance. 相似文献
68.
Photonic-bandgap materials, with periodicity in one, two or three dimensions, offer control of spontaneous emission and photon localization. Low-threshold lasing has been demonstrated in two-dimensional photonic-bandgap materials, both with distributed feedback and defect modes. Liquid crystals with chiral constituents exhibit mesophases with modulated ground states. Helical cholesterics are one-dimensional, whereas blue phases are three-dimensional self-assembled photonic-bandgap structures. Although mirrorless lasing was predicted and observed in one-dimensional helical cholesteric materials and chiral ferroelectric smectic materials, it is of great interest to probe light confinement in three dimensions. Here, we report the first observations of lasing in three-dimensional photonic crystals, in the cholesteric blue phase II. Our results show that distributed feedback is realized in three dimensions, resulting in almost diffraction-limited lasing with significantly lower thresholds than in one dimension. In addition to mirrorless lasing, these self-assembled soft photonic-bandgap materials may also be useful for waveguiding, switching and sensing applications. 相似文献
69.
Cox W. Miles; Fadardi Javad Salehi; Pothos Emmanuel M. 《Canadian Metallurgical Quarterly》2006,132(3):443
Decisions about using addictive substances are influenced by distractions by addiction-related stimuli, of which the user might be unaware. The addiction-Stroop task is a paradigm used to assess this distraction. The empirical evidence for the addiction-Stroop effect is critically reviewed, and meta-analyses of alcohol-related and smoking-related studies are presented. Studies finding the strongest effects were those in which participants had strong current concerns about an addictive substance or such concerns were highlighted through experimental manipulations, especially those depriving participants of the substance. Theories to account for addiction-related attentional bias are discussed, of which the motivational theory of current concerns appears to provide the most complete account of the phenomenon. Recommendations are made for maximizing the precision of the addiction-Stroop test in future research. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
70.
In a conventional array, the location of each element must be known to an accuracy of aboutlambda/10 for phasing and scanning purposes. A larger tolerance on the element location results in the loss of gain and deterioration of the radiation pattern. In a self-cohering phased array, the phasing of the array elements is accomplished closed-loop and adaptively; therefore, no information on the element location is necessary. On the other hand, to scan the adaptively formed beam about the direction of the received wave, which has to be performed open-loop, one requires information on the element locations. In this paper, basic relations pertaining to the open-loop scanning of adaptive antenna arrays of arbitrary geometry are derived for both far-field and near-field scanning problems, and the transition between the two cases and the required accuracy in the knowledge of the same distance are explored. It is shown that the tolerance requirement on the element locations is the conventional tolerance divided by the maximum scan angle. In large systems designed for target imaging, it is shown that the tolerance on element location can be two or more orders of magnitude larger than that in a conventional array. 相似文献