全文获取类型
收费全文 | 795篇 |
免费 | 46篇 |
国内免费 | 23篇 |
专业分类
电工技术 | 29篇 |
技术理论 | 2篇 |
综合类 | 32篇 |
化学工业 | 7篇 |
金属工艺 | 33篇 |
机械仪表 | 77篇 |
建筑科学 | 274篇 |
矿业工程 | 27篇 |
能源动力 | 28篇 |
轻工业 | 1篇 |
水利工程 | 15篇 |
石油天然气 | 1篇 |
武器工业 | 1篇 |
无线电 | 44篇 |
一般工业技术 | 134篇 |
冶金工业 | 19篇 |
自动化技术 | 140篇 |
出版年
2024年 | 2篇 |
2023年 | 3篇 |
2022年 | 16篇 |
2021年 | 17篇 |
2020年 | 21篇 |
2019年 | 9篇 |
2018年 | 9篇 |
2017年 | 16篇 |
2016年 | 23篇 |
2015年 | 31篇 |
2014年 | 58篇 |
2013年 | 45篇 |
2012年 | 64篇 |
2011年 | 90篇 |
2010年 | 61篇 |
2009年 | 57篇 |
2008年 | 40篇 |
2007年 | 51篇 |
2006年 | 43篇 |
2005年 | 37篇 |
2004年 | 38篇 |
2003年 | 31篇 |
2002年 | 17篇 |
2001年 | 18篇 |
2000年 | 16篇 |
1999年 | 20篇 |
1998年 | 10篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1988年 | 1篇 |
排序方式: 共有864条查询结果,搜索用时 15 毫秒
1.
Based on the investigation reports for two major railway accidents in China and the USA, as well as the analysis of related systems, this paper compares the differences between Chinese and American railway accident investigation modes along different dimensions. The four aspects attended to are the investigation purpose, institutional basis, scope and process, and type of conclusion. The results reveal the role of social factors in shaping the investigation pattern of engineering accidents, and show engineering accidents can serve as a window to understanding a society and the ways that learning from engineering accidents is a socially institutionalized process. A final discussion considers possible improvements that might be introduced into the Chinese mode of engineering accident investigation. 相似文献
2.
The limited research on the geopolymer concrete mix design for targeting a specific strength is identified an obstacle for their effective design and wide use. In this paper, a mix design procedure has been proposed for fly-ash based geopolymer concrete and its use as infill hybrid composite beam is investigated. Then, the structural performance of geopolymer concrete filled hybrid composite beam is investigated to determine their possible application in civil infrastructure. Firstly, a detailed procedure of mix design for fly-ash based geopolymer concrete is presented. Secondly, three hybrid beams filled with geopolymer concrete were prepared and tested in a four-point bending setup to evaluate their flexural modulus and modulus of rupture. Numerical and analytical evaluation of the behaviour of hybrid beam were performed and results showed a good agreement with the experimental investigation. Thirdly, the suitability of the beam for a composite railway sleeper is evaluated and compared with existing timber and composite sleepers. Finally, the beams’ performance in a ballast railway track is analysed using Strand7 finite element simulation software and the results showed that the new concept of using geopolymer concrete as infill to pultruded composite section satisfied the stiffness and strength requirements for a railway sleeper. 相似文献
3.
铁路扣件系统是将钢轨固定在轨枕上,阻止钢轨相对于轨枕发生横纵向移动,保持轨距,在高速铁路运行过程中起到缓冲减震作用的系统。经过长期使用及列车的运行,有些尼龙产品扣件存在不同程度的损坏,产生松动现象,进而影响铁路运行安全。以扣件系统中的绝缘轨距块为研究对象,从环境及气候等多种因素研究其对轨距块性能的影响,找寻较为关键的影响因素。研究结果发现,室外环境放置的轨距块极限剪切性能下降更明显,耐冲击性更差。经过研究不同恶劣环境下轨距块性能的变化,发现高温高湿及高温环境下产品性能下降幅度较大,其中高温高湿影响最大。 相似文献
4.
5.
6.
Mehdi Koohmishi 《Soils and Foundations》2019,59(6):2265-2278
The aggregate in the ballast layer of the railway track structure degrades due to the splitting of single particles and the abrasion of the angular corners, resulting in a ballast course comprised of degraded aggregate with a lower drainage potential. In the present study, the hydraulic conductivity of clean, degraded and clay-fouled degraded ballast specimens was evaluated considering the initial particle size distribution of aggregate and the degradation mechanism to investigate the permeability of ballast fouled by both internal and external factors. First, degraded ballast aggregate was generated by using a large-scale impact loading testing apparatus. Then, a large-scale constant head permeability test was performed to estimate the hydraulic conductivity of degraded ballast aggregate contaminated with clay. Based on the obtained results, the flow regime through extremely degraded ballast remained between a completely turbulent regime (observed in the case of clean ballast) and a laminar flow regime. Darcy’s law was shown to be valid for degraded aggregate samples contaminated with clay. While the degradation of the aggregate had the expected effect of reducing hydraulic conductivity, the abrasion of asperities was shown to have an even greater impact on hydraulic conductivity. Also, the further degradation of aggregate under impact loading was shown to accelerate the reduction in the permeability of clay-fouled degraded ballast to an unacceptable extent. 相似文献
7.
8.
青藏铁路站场路基比一般铁路路基宽度大,为此,在清水河高温细粒土地段进行了专门的现场试验研究。通过采用不同深度处地温场变化、上限变化、阴阳坡温度变化以及积温等分析方法,对该试验段3个冻融循环过程中监测到的温度场分析,并与普通路基的温度场数据进行对比。通过分析可以看出,站场路基下人为上限的上升幅度比普通路堤要大,路基表面以下同样深度处的地温,站场路基下的地温要低于普通路堤下的地温,因此路堤宽度较大的站场路基对多年冻土的保温效果比普通宽度的路堤好。由变形观测数据看出,冻胀量较小,变形主要为沉降变形,路堤阳坡冻胀板的变形量要大于路堤阴坡相应位置的冻胀板变形量。阳坡上层冻胀板最大沉降量是0.241 m;下层冻胀板最大沉降量0.237 m,且随着时间推移,变形趋于稳定。 相似文献
9.
10.
介绍大吨位轨道梁在复杂环境条件下的运输与架设技术。轨道梁重达190吨,选用法国威廉姆TG300机车和法国NICOLAS挂车运梁,运输线路要通过繁忙运河,采用开启式升降栈桥解决上面通过运梁车,下面继续通航的矛盾。架梁时,一般地段采用专门设计制作的门式架梁机;特殊地段采用门式架梁机和膺架相结合的办法,通过纵横向移动达到架设目的。 相似文献