全文获取类型
收费全文 | 3314篇 |
免费 | 262篇 |
国内免费 | 80篇 |
专业分类
电工技术 | 43篇 |
综合类 | 333篇 |
化学工业 | 643篇 |
金属工艺 | 91篇 |
机械仪表 | 83篇 |
建筑科学 | 1639篇 |
矿业工程 | 45篇 |
能源动力 | 106篇 |
轻工业 | 90篇 |
水利工程 | 158篇 |
石油天然气 | 21篇 |
武器工业 | 8篇 |
无线电 | 52篇 |
一般工业技术 | 276篇 |
冶金工业 | 29篇 |
原子能技术 | 13篇 |
自动化技术 | 26篇 |
出版年
2024年 | 11篇 |
2023年 | 65篇 |
2022年 | 70篇 |
2021年 | 106篇 |
2020年 | 99篇 |
2019年 | 81篇 |
2018年 | 83篇 |
2017年 | 97篇 |
2016年 | 87篇 |
2015年 | 80篇 |
2014年 | 173篇 |
2013年 | 238篇 |
2012年 | 231篇 |
2011年 | 224篇 |
2010年 | 189篇 |
2009年 | 239篇 |
2008年 | 221篇 |
2007年 | 260篇 |
2006年 | 208篇 |
2005年 | 165篇 |
2004年 | 121篇 |
2003年 | 119篇 |
2002年 | 89篇 |
2001年 | 69篇 |
2000年 | 74篇 |
1999年 | 45篇 |
1998年 | 50篇 |
1997年 | 32篇 |
1996年 | 23篇 |
1995年 | 18篇 |
1994年 | 12篇 |
1993年 | 15篇 |
1992年 | 9篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 11篇 |
1988年 | 4篇 |
1987年 | 11篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有3656条查询结果,搜索用时 31 毫秒
71.
In this paper, the influence of single walled carbon nano tubes (SWCNTs) addition on the tribological properties of the polyimide
(PI) films on silicon substrate was studied. PI films, with and without SWCNTs, were spin coated onto the Si surface. Coefficient
of friction and wear durability were characterized using a ball-on-disk tribometer by employing a 4 mm diameter Si3N4 ball sliding against the film, at a contact pressure of ∼370 MPa, and a sliding velocity of 0.042 ms−1. Water contact angle, AFM topography, and nano-indentation tests were conducted to study the physical and mechanical properties
of the films. SWCNTs marginally increased the water contact angle of PI film. The addition of SWCNTs to PI has increased the
hardness and elastic modulus of pristine PI films by 60–70%. The coefficient of friction of PI films increased slightly (∼20%)
after the addition of SWCNTs, whereas, there was at least two-fold increase in the wear life of the film based on the film
failure condition of coefficient of friction higher than 0.3. However, the film did not show any sign of wear even after 100,000
cycles of rotation indicating its robustness. This increase in the wear durability due to the addition of the SWCNTs is believed
to be because of the improvement in the load-bearing capacity of the composite film and sliding induced microstructural changes
of the composite film. 相似文献
72.
73.
介绍疏水化合孔栓成分的工作机理,结合其特征,在每立方米混凝土中掺入30L疏水化合孔栓成分,配制出东华大桥主墩承台大体积高性能防水抗腐蚀混凝土,采取循环冷却水管降温的方法确保了基础混凝土的施工质量,凝结后混凝土表现出的憎水性显著。 相似文献
74.
75.
该文是对一台退役的汽车轮毂寿命测试设备进行数字化控制系统改造的成功案例的介绍。对退役或仍在使用中的老旧设备用数字控制器加传感器进行改造,是一个既能发挥老设备功能、节省地球资源,又能提高设备效率和精度的好办法。该文即展示了这样的一个实例。通过用DELTA运动控制器对该退役设备进行改造,成本只有新设备的25%,而取得的效果却不亚于新设备,是一个值得推广的方式。 相似文献
76.
Jonathon Tanks Stephen Sharp Devin Harris Celik Ozyildirim 《Advanced Composite Materials》2017,26(3):245-258
One of the main causes of structural deficiency in concrete bridges is the deterioration of the constituent materials. Some transportation agencies have started exploring the use of carbon fiber reinforced polymers (CFRP) as a corrosion-resistant alternative to steel prestressing materials for longer lasting concrete bridge structures. To implement CFRP in prestressed concrete bridge structures with more confidence, an understanding of the challenges pertaining to durability under in-service environmental conditions is essential. This paper explores the effects of temperature with alkaline and alkaline/chloride solutions on material properties over time, in the context of reinforced and prestressed concrete structures for transportation applications. The durability testing yielded several key findings: (1) higher temperatures accelerate degradation, (2) moisture sorption was the primary process responsible for the observed degradation, with plasticization and microcracking as the controlling mechanisms leading to fiber–matrix interfacial debonding, and (3) a relaxation-based analytical model was implemented to predict residual properties after environmental exposure, showing promising agreement with experimental data. 相似文献
77.
Conducting carbon/polymer composites as a catalyst support for proton exchange membrane fuel cells
下载免费PDF全文
![点击此处可从《国际能源研究杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Carbon/poly(3,4‐ethylene dioxythiophene) (C/PEDOT) composites are synthesized by in situ chemical oxidative polymerization of EDOT monomer on carbon black in order to decrease carbon corrosion that occurred in carbon‐supported catalysts used in proton exchange membrane fuel cell. The effects of different dopants including polystyrene sulfonic acid, p‐toluenesulfonic acid and camphorsulfonic acid with the addition of ethylene glycol or dimethyl sulfoxide on the properties of the composites are investigated. The synthesized composites are characterized by X‐ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, surface area analysis and scanning electron microscope. Electrical conductivity is determined by using the four‐point probe technique. Electrochemical oxidation characteristics of the synthesized C/PEDOT composites are investigated by cyclic voltammetry by applying 1.2 V for 24 h. The composite prepared at 25 °C with p‐toluenesulfonic acid and ethylene glycol shows the best carbon corrosion resistance. Platinum‐supported catalyst by using this composite was prepared using microwave irradiation technique, and it was seen that the prepared catalyst did not significantly lose its hydrogen oxidation and oxygen reduction reaction activities after electrochemical oxidation. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
78.
Minh Truong Xuan Nguyen Minh-Kha Nguyen Phuong Thi Thuy Pham Ha Ky Phuong Huynh Son Truong Nguyen 《International Journal of Hydrogen Energy》2021,46(5):3909-3921
One-dimensional (1D) metal-coated Pd structures are efficient catalysts for the ethanol electro-oxidation and promising strategy for minimizing the Pd-loading toward commercialization of direct ethanol fuel cells (DEFCs). Herein, the decorated and core-shell architectures of a novel Pd coating on Ag nanowires (PdAg-NWs) are controllable by a two-step polyol method based on the galvanic replacement reaction. The integration of uniform shell with a low Pd concentration and partial hollow structure onto 1D PdAg-NWs exhibits the highest efficiency for ethanol oxidation reaction (EOR) in alkaline solution. In comparison with Pd nanoparticles (PdNPs/C), the PdAgNWs/C performes 11 times superior EOR activity, and the onset potential shifts 80 mV negatively. The presence of Ag in PdAg-NWs enhances the absorption capacity of ethanol molecules and hydroxyl ions on the active sites, and improves the catalyst tolerance to CO-like intermediates, making them a potential anodic catalyst for DEFCs. 相似文献
79.
This study presents a methodology for making bricks, in a cost-effective and environmentally friendly manner, using the tailings produced from iron ore mines in Western Australia (WA). The study was based on the geopolymerisation process, which is known to conserve energy by reducing the emission of greenhouse gases. The reduction is accomplished by avoiding the processes of high temperature kiln firing, traditionally utilised when making bricks from sandy soils with high clay content. In this study, the sodium silicate was added to the mine tailings in powder form, as an activator for the formulation of the geopolymer bricks. The effects of the initial setting time, curing temperature, curing time and activator content on the unconfined compressive strength (UCS), water absorption and other durability properties of the bricks were investigated. X-ray diffraction analysis was performed to investigate the phase composition of the geopolymer bricks. The bricks achieved an UCS as high as 50.53 MPa for the optimum values of the parameters. Technically, the geopolymer bricks that were produced met both the American Society of Testing and Materials and the Australian Standards (AS) requirements for bricks. A cost analysis of the geopolymer bricks is also presented, and this shows that the cost of geopolymer bricks is lower than that of the commercial, fired clay bricks. 相似文献
80.
Latent heat energy storage characteristics of building composites of bentonite clay and pumice sand with different organic PCMs
下载免费PDF全文
![点击此处可从《国际能源研究杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In the present work, six new kinds of building composite PCMs (BCPCMs), PS/octadecane, BC/octadecane, PS/CA–MA, BC/CA–MA, PS/PEG1000, and BC/PEG1000 composites, were prepared by using vacuum impregnation method. The maximum percent of PCM in the composites was assigned to be 12, 13, 18, 23, 30, and 42 wt%, respectively. The form‐stable BCPCMs were characterized using SEM, FT‐IR, DSC, and TG analysis techniques. The characterization results showed the existence of homogenous dispersion of the PCM into the PBM matrixes. The DSC measurements indicated that the melting temperatures of the form‐stable BCPCMs are in the range of 20–33°C while they have latent heats of melting in the range of about 28–55 J/g. These results make them promising BCPCMs for low temperature‐passive TES applications in buildings. Thermal cycling test indicated that the prepared BCPCMs have good thermal reliability and chemical stability. TG analysis proved that the prepared BCPCMs have good thermal durability. In addition, the thermal conductivity of BCPCMs was enhanced considerably by addition of expanded graphite (EG). The improvement in thermal conductivity of the BCPCMs caused appreciably reduction in their melting times. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献