全文获取类型
收费全文 | 464篇 |
免费 | 32篇 |
专业分类
公路运输 | 131篇 |
综合类 | 130篇 |
水路运输 | 109篇 |
铁路运输 | 121篇 |
综合运输 | 5篇 |
出版年
2024年 | 5篇 |
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 18篇 |
2020年 | 14篇 |
2019年 | 21篇 |
2018年 | 9篇 |
2017年 | 6篇 |
2016年 | 17篇 |
2015年 | 23篇 |
2014年 | 37篇 |
2013年 | 27篇 |
2012年 | 55篇 |
2011年 | 37篇 |
2010年 | 28篇 |
2009年 | 23篇 |
2008年 | 29篇 |
2007年 | 39篇 |
2006年 | 28篇 |
2005年 | 17篇 |
2004年 | 8篇 |
2003年 | 14篇 |
2002年 | 4篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有496条查询结果,搜索用时 15 毫秒
491.
492.
飓风引起的极端波浪是影响近海桥梁结构安全的重要灾种之一,曾在美国墨西哥湾沿岸造成了大量已建低矮跨海桥梁损毁。探究台风波浪对桥梁上部结构的作用机理,发展波浪作用力计算方法,对保证中国近海地区桥梁结构安全具有重要意义。为准确考虑台风极端波浪的频谱特征,使用连续聚焦波作为入射波,开展了不同波幅、峰值频率和净空的模型试验。试验基于Froude准则采用1∶25缩尺比进行设计,研究对象为T形肋梁桥,试验过程中观测了聚焦波作用下T形梁桥受到的水平和竖向波浪作用力。研究结果表明:采用连续聚焦波作为入射波,通过设置合适的聚焦波周期可以避免二次反射波对入射波的污染,确保试验结果的可信性;波浪作用力中包含了低频准静力和高频砰击力,砰击力峰值一般出现在波浪与结构接触的初始阶段;一般情况下波浪作用力随波幅增大而增大,但存在明显的非单调特征;T形梁桥波浪力随净空增大有明显的先减小后增大的趋势,但峰值频率为0.4 Hz的大波幅聚焦波在净空为2.0~3.0 cm时波浪作用力最大;基于试验结果拟合出的波浪力简便估算方法能够有效计算波浪作用力,可为T形梁桥抗波浪设计提供参考。 相似文献
493.
全尺寸汽车空气动力学风洞是汽车空气动力性能重要的研究平台与开发工具。但风洞间测试结果普遍存在差异,这对气动性能的研究与分析造成了一定的困难,因此有必要开展风洞间的横向相关性和修正研究,提高风洞测试结果的统一性和一致性。分别对德国和中国的两座全尺寸汽车风洞进行实车风洞测试,开展风洞相关性及修正研究。研究表明,对于同一工况,不同风洞间的测试结果存在一定差异,但不同工况与基础工况间差异变化趋势一致,大小相似,不同风洞间的测试结果能建立较好的相关关系,形成相关性线性函数。通过空气阻力系数C D 修正方法,可以减小风洞间由结构尺寸、流场参数导致的系统性误差,修正后的风洞间空气阻力系数C D 测试结果差异降低了近60%。 相似文献
494.
Sigma Energy has performed its foremost prototype tests of scaled wave energy converter in a real sea environment. The prototype was a point absorber with a cylindrical buoy, a mechanical power take-off system with a counterweight, moored to the seabed as a tension leg platform (TLP) with three equal tendons. In these extensive experiments, numerous device characteristics were measured and analysed. The present paper focuses on the dynamic forces in the mooring lines, and some unexpected and rare data obtained. It is well known that TLP tendons are prone to a brief loss of tension (the slacking) and that, after such events, high snapping forces of short duration can arise. Partly by intention, and partly due to underestimation of the dynamical forces, several such slacking-snapping incidents were recorded during the experiments. In some severe storms, the snapping forces were up to six times higher than the tendon pretension. The paper presents several recordings of dynamic forces and platform motion during these critical events. It analysis them, and gives a typical scenario under which they occur. It gives also some theoretical explanations, and numerical predictions of dynamical tendon forces, with their comparison to the experimental results. 相似文献
495.
496.
The effects of surface roughness as induced by marine fouling on the hydrodynamic forces on a submerged floating tunnel (SFT) are experimentally and numerically investigated in detail at Reynolds numbers Re = 8.125 × 103–5.25 × 104. A sensitivity analysis to different roughness parameters including roughness height, skewness, coverage ratio, and spatial arrangement is performed. In addition, an optimized parametric cross-section for an SFT is proposed, and the hydrodynamic performance of the parametric shape and circular SFT cross-section shape with roughness elements is compared. The pressure distribution along the SFT, flow separation and wake characteristics are analyzed to provide a systematic insight into the fundamental mechanism relating the roughness parameters and flow around an SFT. In order to better understand the nonlinear relationships among structural geometry, roughness parameters, flow states, and structural response, an artificial intelligence method using Random Forest (RF) for feature importance ranking is applied. The results show that with the parametric shape, the hydrodynamic forces on the fouled SFT can be effectively mitigated. The roughness height and coverage ratio affect the equivalent blockage and hence, change flow separation and recirculation length in the wake. Lower skewness of the roughness elements can increase the critical Re by changing the relative roughness parameter. Horizontal arrangement of the roughness elements on an SFT generally results in the largest hydrodynamic forces, compared to staggered and vertical distributions. Throughout the feature importance ranking, the flow regime is found to be the most important feature of the hydrodynamics of the SFT. In addition, the SFT cross-section shape and roughness coverage ratio play a dominant role. 相似文献