全文获取类型
收费全文 | 2199篇 |
免费 | 33篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 8篇 |
综合类 | 5篇 |
化学工业 | 118篇 |
金属工艺 | 31篇 |
机械仪表 | 33篇 |
建筑科学 | 7篇 |
能源动力 | 44篇 |
轻工业 | 79篇 |
水利工程 | 3篇 |
石油天然气 | 3篇 |
无线电 | 48篇 |
一般工业技术 | 138篇 |
冶金工业 | 1663篇 |
原子能技术 | 3篇 |
自动化技术 | 55篇 |
出版年
2023年 | 5篇 |
2022年 | 19篇 |
2021年 | 43篇 |
2020年 | 32篇 |
2019年 | 29篇 |
2018年 | 39篇 |
2017年 | 26篇 |
2016年 | 28篇 |
2015年 | 14篇 |
2014年 | 30篇 |
2013年 | 36篇 |
2012年 | 30篇 |
2011年 | 37篇 |
2010年 | 31篇 |
2009年 | 17篇 |
2008年 | 25篇 |
2007年 | 29篇 |
2006年 | 17篇 |
2005年 | 14篇 |
2004年 | 12篇 |
2003年 | 6篇 |
2002年 | 3篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 52篇 |
1998年 | 501篇 |
1997年 | 272篇 |
1996年 | 210篇 |
1995年 | 98篇 |
1994年 | 85篇 |
1993年 | 105篇 |
1992年 | 22篇 |
1991年 | 22篇 |
1990年 | 26篇 |
1989年 | 25篇 |
1988年 | 23篇 |
1987年 | 52篇 |
1986年 | 29篇 |
1985年 | 34篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 10篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 32篇 |
1976年 | 71篇 |
1975年 | 5篇 |
1955年 | 1篇 |
排序方式: 共有2238条查询结果,搜索用时 15 毫秒
131.
132.
Javaid Akhtar Muhammad Imran Yaqub Javed Iqbal Naseer Sheikh Tanzila Saba 《国际自然能源杂志》2018,39(8):904-908
In this review the energy potential of Pakistan from hydro, coal, wind, solar and nuclear sources has been discussed. The new projects that are being commissioned on coal, wind, solar, hydel and nuclear-based technologies have also been mentioned. The review has also explored the future prospects of the country’s energy requirements. Pakistan has potential to produce 100,000?MW of electricity from Thar coal for 20 years, 56,000?MW of hydroelectricity, 150,000?MW of wind energy and ~50,000?MW from solar sources. The coal-fired power generation is expected to 11,500?MW in period 2017–2019. The country is moving in the right direction to cater its energy needs. However, there is a need to find local and foreign investment in the country to meet high energy demands in the country in future. 相似文献
133.
Banyan tree saw dust powder (BSD) filled Polypropylene (PP) green composites have been fabricated with varying amounts viz., 0%, 20%, and 40% of BSD particulate filler by using a co‐rotating twin screw extruder followed by injection molding. The mechanical properties such as surface hardness, tensile behavior, and impact strength of the fabricated PP/BSD green composites have been studied in order to standardize the composites. Abrasive water jet (AWJ) machining has been reported mainly for ceramics, concrete, and glass but not much literature is available on AWJ machining of polymer composites. This research is aimed at examining the AWJ machining of green polymer composites. The effect of BSD loading on the AWJ machining behavior of the PP/BSD green composites has been investigated. Furthermore, the effect of addition of 4% maleic anhydride grafted PP (coupling agent) and 4% talc (mineral filler) on the machining behavior of PP/BSD composites has also been evaluated. Surface roughness and optical micrographs of the AWJ cut composite specimens were examined to assess the effect of BSD content, AWJ traverse speed and pressure on the machining behavior of the composites. In order to probe the mechanism of AWJ machining behavior of PP/BSD composites, the kerf width and taper have been measured and results are correlated. POLYM. COMPOS., 37:1754–1764, 2016. © 2014 Society of Plastics Engineers 相似文献
134.
M. Shamshi Hassan M. Shaheer Akhtar Kyung-Bo Shim O-Bong Yang 《Nanoscale research letters》2010,5(4):735-740
Highly crystalline Pr6O11 nanorods were prepared by a simple precipitation method of triethylamine complex at 500°C. Synthesized Pr6O11 nanorods were uniformly grown with the diameter of 12–15 nm and the length of 100–150 nm without any impurities of unstable
PrO2 phase. The Pr6O11 nanorod electrodes attained a high electrical conductivity of 0.954 Scm−1 with low activation energy of 0.594 eV at 850°C. The electrochemical impedance study showed that the resistance of electrode
was significantly decreased at high temperature, which resulted from its high conductivity and low activation energy. The
reduced impedance and high electrical conductivity of Pr6O11 nanorod electrodes are attributed to the reduction of grain boundaries and high space charge width. 相似文献
135.
Mohammad Akhtar 《电信科学》2010,26(11)
LTE是目前大部分电信运营商首选的下一代移动通信技术,已有100多家运营商承诺将于2010年开始部署LTE.不过,在非成对频段部署LTE的商机却常被忽略. 相似文献
136.
A thermophilic microorganism, SBS-4S, was isolated from a hot spring located in Gilgit, Northern Areas of Pakistan. It was found to be an aerobic, gram-positive, rod-shaped, thermophilic bacterium that grew on various sugars, carboxylic acids and hydrocarbons at temperatures between 45°C and 75°C. Complete 16S rRNA gene sequence of the microorganism exhibited homology to various species of genus Geobacillus. A highest homology of 99.8% was found with Geobacillus kaustophilus. A partial (0.7 kbp) chaperonin gene sequence also showed a highest homology of 99.4% to that of G. kaustophilus whereas biochemical characteristics of the microorganism were similar to Geobacillus uzenensis. Based on biochemical characterization, 16S rRNA and chaperonin gene sequences, we identified SBS-4S as a strain of genus Geobacillus. Strain SBS-4S produced several extracellular enzymes including amylase, protease and lipase. The lipase encoding gene was cloned, expressed in Escherichia coli and the gene product was characterized. The recombinant lipase was optimally active at 60°C with stability at wide pH range (6-12). The enzyme activity was enhanced remarkably in the presence of Ca(+2). The K(m) and the V(max) for the hydrolysis of p-nitrophenyl acetate were 3.8mM and 2273 μmol min(-1)mg(-1), respectively. The ability of the recombinant enzyme to be stable at a wide pH range makes it a potential candidate for use in industry. 相似文献
137.
138.
Ştefan Ţălu Samah Boudour Idris Bouchama Bandar Astinchap Hamta Ghanbaripour Muhammad Saeed Akhtar Sarwat Zahra 《Microscopy research and technique》2022,85(4):1213-1223
A multifractal analysis has been performed on the 3D (three-dimensional) surface microtexture of magnesium-doped zinc oxide (ZnO:Mg) thin films with doping concentration of 0, 2, 4, and 5%. Thin films were deposited onto the glass substrates via the sol–gel spin coating method. The effect of magnesium doping, on the crystal structure, morphology, and band gap for ZnO:Mg thin films has been analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV–Vis spectroscopy. It has been observed that the surface of ZnO thin films is multifractal in nature. However, multifractality and complexity observed to decrease with increasing content of Mg in ZnO thin films due to formation of islands on the surface in accordance with Volmer–Weber growth mechanism. The investigations revealed that crystallinity, microtexture, morphology, and optical properties of the thin films can be tuned by controlling the Mg content within the ZnO lattice. In particular, their optical band gap energies were 3.27, 3.31, 3.34, and 3.33 eV at 0, 2, 4, and 5%, respectively. The prepared thin films of ZnO:Mg with tuned characteristics would have promising applications in optoelectronic devices. 相似文献
139.
The use of visual occlusion as a cue to altitude maintenance in low-altitude flight (LAF) was investigated. The extent to which the ground surface is occluded by 3-D objects varies with altitude and depends on the height, radius, and density of the objects. Participants attempted to maintain a constant altitude during simulated flight over an undulating terrain with trees of various heights, radii, and densities. As would be predicted if participants used occlusion, root-mean-square error was related to the product of tree height and tree density (Experiment 1) and to the product of tree radius and tree density (Experiment 2). This relationship was also found for simulated terrains with a more realistic mixture of tree heights (Experiment 4). The authors present a modification to an occlusion model (T. Leung & J. Malik, 1997) that can be used to approximate occlusion in the context of LAF, and they evaluate the modified model using the present LAF data. On a practical level, simulating 3-D objects is computationally expensive. The present results suggest that performance may be maintained with fewer objects if their size is increased. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
140.