全文获取类型
收费全文 | 532篇 |
免费 | 21篇 |
专业分类
公路运输 | 213篇 |
综合类 | 111篇 |
水路运输 | 112篇 |
铁路运输 | 91篇 |
综合运输 | 26篇 |
出版年
2024年 | 4篇 |
2023年 | 27篇 |
2022年 | 13篇 |
2021年 | 16篇 |
2020年 | 15篇 |
2019年 | 26篇 |
2018年 | 30篇 |
2017年 | 9篇 |
2016年 | 15篇 |
2015年 | 11篇 |
2014年 | 41篇 |
2013年 | 37篇 |
2012年 | 34篇 |
2011年 | 26篇 |
2010年 | 33篇 |
2009年 | 29篇 |
2008年 | 30篇 |
2007年 | 33篇 |
2006年 | 26篇 |
2005年 | 14篇 |
2004年 | 18篇 |
2003年 | 12篇 |
2002年 | 14篇 |
2001年 | 8篇 |
2000年 | 8篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有553条查询结果,搜索用时 15 毫秒
201.
基于有限元软件,采用D-P材料模拟路基填土,加载汶川地震波,对公路路基路面结构进行弹塑性瞬态动力学分析。分析了不同路基填土高度、路基边坡坡率及路基宽度等参数影响下的路基顶面动力响应。在给定参数的情况下,相比于位移响应而言,路基顶部加速度响应由路基截面尺寸的变化引起的变化幅度较小。 相似文献
202.
鉴于路面微观构造对抗滑性能有着重要的影响,选取4种不同材质的石料分别成型试样,借助散射法-激光纹理仪测量各试样在不同磨损状况下的微观构造,运用分形理论的盒子计数法,通过MATLAB编程实现对试样在不同磨损状况下分维数的计算.试验结果表明:花岗岩的分维数水平和耐磨光性能均较优,石灰岩的耐磨光性能差,该评价方法可以准确评价路面的微观纹理复杂程度,并能有效预测路面的长期抗滑性能. 相似文献
203.
204.
基于STAR-CCM+的高速列车空气动力学性能数值分析 总被引:1,自引:0,他引:1
应用STAR-CCM+软件对某高速列车外流场CFD计算过程与结果做了通用性的描述,并从阻力系数、速度场和压力场几个方面对列车在明线运行工况下的空气动力性能进行了研究.通过仿真分析表明,列车的总阻力主要来源于列车受到的压差阻力,且鼻端处压力值最大并沿着过渡区域逐渐降低.对列车CFD分析应用流程做了初步的归纳与总结,并对列车头型设计提出参考性的建议. 相似文献
205.
206.
The horizontal vibration of towed seismic streamers is a main reason for efficiency reduction of the seismic survey and tail
tangling. A vibration suppression scheme of towed seismic streamers is investigated in this paper. The towed seismic streamer
is divided into two spans, a controlled span, i.e., the low tension span, and an uncontrolled span, i.e., the high tension
span, by a bird. The system model includes a hyperbolic partial differential equation with variable coefficient describing
the towed seismic streamers, and an ordinary differential equation describing the dynamic of bird. Robust based-model knowledge
and adaptive controllers, based on the Lyapunov method, are designed to isolate the vibration of towed seismic streamers caused
by the course deviations of towing vessel, the variations of towing vessel velocity and the variations of towed seismic streamer
density. The robust based-model knowledge and adaptive controllers exponentially and asymptotically drive the span-towed seismic
streamer displacement to zero, respectively. A finite difference scheme is used to validate the efficiency of the control
law. The proposed controller can isolate effectively the disturbance originated from the towed vessel, and can provide the
improved damping but not sacrifice the isolation performance. The adaptive scheme can tolerate the lack of knowledge of some
uncertain parameters and can directly execute the online adjustment of the parameters. Meanwhile, the proposed control law
is robust and can resist the model uncertainty due to parameter incertitude, model error and unknown disturbance and so on.
The control law only includes velocity and slope, while it does not need the displacement which is difficult to measure in
the practical operations. Thus it is easy to implement. 相似文献
207.
High functionality given to steel products results in incremental environment loads at the steelmaking stage. However, at the stage of utilization, high-functional steel products prove more environment friendly than their conventional counterparts in many cases. Therefore, evaluation on contribution of steel products to environmental improvement requires an integrated approach that considers the product over its entire life cycle — life cycle assessment (LCA). This paper discusses the relationship between the improvement of steel products performance and environmental impact from the entire life cycle perspectives. The LCA method to calculate and assess contribution of high-functional steel products during the life cycle to environmental improvement is explained. Two case studies of Baoshan Iron &; Steel Co., Ltd. (Baosteel for short) are given to show that LCA is a scientific and systematic method for eco-materials evaluation or eco-design: ? in a power transformer, using silicon steel B30P110 to replace B30G130 can reduce carbon dioxide emissions in the region of 15.1% over the life cycle of the power transformer; ? tinplate steel of Baosteel for two-piece steel cans experienced six times thickness reduction from 0.280 to 0.225mm, which results in 14.5% emission reduction over the life cycle of two-piece steel cans. It is a systematic and scientific method for evaluating on products environmental performance from life cycle perspective. 相似文献
208.
209.
通过对K26古滑坡的工程地质特征及稳定性的分析,提出以预应力锚索与抗滑桩结合为主要措施的防治方案。该治理方案已通过施工和运营检验,效果较好,值得借鉴。 相似文献
210.
基于荷载传递法的锚杆锚固段荷载变形分析 总被引:1,自引:0,他引:1
基于荷载传递法,推导了锚固段的荷载传递基本微分方程;结合Kelvin问题的位移解,得到锚固段的应力分布的解析表达式,认为锚杆体的直径、外荷载及锚杆体弹性模量与岩体剪切模量的比值等因素影响着锚固段的应力水平。计算结果表明:锚杆体直径增加到一定程度会使锚杆所受的最大剪应力快速增加;在较高的初始力条件下,锚固段前端应力集中现象明显;较小的锚杆体弹性模量与岩体剪切模量比值有利于锚固段应力的均匀分布。 相似文献