全文获取类型
收费全文 | 1084篇 |
免费 | 64篇 |
专业分类
公路运输 | 263篇 |
综合类 | 464篇 |
水路运输 | 192篇 |
铁路运输 | 115篇 |
综合运输 | 114篇 |
出版年
2023年 | 4篇 |
2022年 | 30篇 |
2021年 | 43篇 |
2020年 | 31篇 |
2019年 | 27篇 |
2018年 | 22篇 |
2017年 | 27篇 |
2016年 | 39篇 |
2015年 | 55篇 |
2014年 | 95篇 |
2013年 | 59篇 |
2012年 | 90篇 |
2011年 | 71篇 |
2010年 | 65篇 |
2009年 | 60篇 |
2008年 | 85篇 |
2007年 | 100篇 |
2006年 | 75篇 |
2005年 | 39篇 |
2004年 | 32篇 |
2003年 | 23篇 |
2002年 | 5篇 |
2001年 | 15篇 |
2000年 | 5篇 |
1999年 | 4篇 |
1998年 | 10篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 2篇 |
排序方式: 共有1148条查询结果,搜索用时 31 毫秒
271.
在城市层面,影响基础设施PPP(公私合营模式)项目融资额的因素具有多样性。本文基于
2015—2017年我国地级市面板数据,采用空间回归模型对地级市基础设施PPP项目融资额的影
响因素进行实证分析,并验证了PPP项目融资额在空间层面具有溢出效应。研究结果表明:空间
误差模型相比混合OLS回归模型,对于分析PPP项目融资额影响因素的拟合效果更好;PPP项目
融资额在城市层面上具有显著的正向空间溢出效应,即一个城市PPP项目融资额更容易受到相
邻城市PPP项目融资额的影响。地方政府财政缺口、地区生产总值、固定资产投资额、人口密度
对PPP项目融资额虽然都具有显著相关关系,但在不同地区间影响的差异性较大。地方政府财
政缺口在中东部城市与PPP项目融资额呈现显著正相关,即地方政府财政缺口越大,城市越倾向
于采用PPP模式进行基础设施投融资;而在西部城市,两者间这种相关关系则不显著。 相似文献
272.
Daniel Ainalis Vincent Rouillard Michael Sek 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2016,54(6):765-783
This paper describes the application of a practical analytical technique based on the random decrement method to estimate the rigid sprung mass dynamic characteristics (frequency response function) of road vehicles using only vibration response data during constant-speed operation. A brief history and development of the random decrement technique is presented, along with a summary of work undertaken on optimal parameter selection to establish the random decrement signature. Two approaches to estimate the dynamic characteristics from the random decrement signature are described and evaluated. A custom, single-wheeled vehicle (physical quarter car) was commissioned to undertake a series of on-the-road experiments at various nominally constant operating speeds. The vehicle, also instrumented as an inertial profilometer, simultaneously measured the longitudinal pavement profile to establish the vehicle's actual dynamic characteristics during operation. The main outcome of the paper is that the random decrement technique can be used to provide accurate estimates of the sprung mass mode of the vehicle's dynamic characteristics for both linear and nonlinear suspension systems of an idealised vehicle. 相似文献
273.
Kai Wei Yinling Dou Feng Wang Pengbo Niu Ping Wang 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2018,56(12):1838-1863
A hybrid Spectral Element Method (SEM)–Symplectic Method(SM) method for high-efficiency computation of the high-frequency random vibrations of a high-speed vehicle–track system with the frequency-dependent dynamic properties of rail pads is presented. First, the Williams-Landel-Ferry (WLF) formula and Fractional Derivative Zener (FDZ) model were, respectively, applied for prediction and representation of the frequency-dependent dynamic properties of Vossloh 300 rail pads frequently used in China's high-speed railway. Then, the proposed hybrid SEM–SM method was used to investigate the influence of the frequency-dependent dynamic performance of Vossloh 300 rail pads on the high-frequency random vibrations of high-speed vehicle–track systems at various train speeds or different levels of rail surface roughness. The experimental results indicate that the storage stiffness and loss factors of Vossloh 300 rail pad increase with the decrease in dynamic loads or the increase in preloads within 0.1–10,000?Hz at 20°C, and basically linearly increase with frequency in a logarithmic coordinate system. The results computed by the hybrid SEM–SM method demonstrate that the frequency-dependent viscous damping of Vossloh 300 rail pads, compared with its constant viscous damping and frequency-dependent stiffness, has a much more conspicuous influence on the medium-frequency (i.e. 20–63?Hz) random vibrations of car bodies and rail fasteners, and on the mid- (i.e. 20–63?Hz) and high-frequency (i.e. 630–1250?Hz) random vibrations of bogies, wheels and rails, especially with the increase in train speeds or the deterioration of rail surface roughness. The two sensitive frequency bands can also be validated by frequency response function (FRF) analysis of the proposed infinite rail–fastener model. The mid and high frequencies influenced by the frequency-dependent viscous damping of rail pads are exactly the dominant frequencies of ground vibration acceleration and wheel rolling noise caused by high-speed railways, respectively. Even though the existing time-domain (or frequency-domain) finite track models associated with the time-domain (or frequency-domain) fractional derivative viscoelastic (FDV) models of rail pads can also be used to reach the same conclusions, the hybrid SEM–SM method in which only one element is required to compute the high-order vibration modes of infinite rail is more appropriate for high-efficiency analysis of the high-frequency random vibrations of high-speed vehicle–track systems. 相似文献
274.
275.
采用黑箱模型理论建立了船舶多功能舱室动态负荷数学模型,经分析求解,获得了某典型欧亚远洋航线上的船舶动态负荷变化规律.结果表明:船舶空调负荷随航区、航行时刻发生显著变化,通风负荷占总负荷的51.92%,而舱壁导热、辐射负荷仅分别占总负荷的7.47%,6.68%;同一航区同一时刻,各功能舱室负荷最大值是最小值的2.684倍;此外,运用回归分析知,可变舱室负荷的91.72%受室外温度变化的影响. 相似文献
276.
In this article, we assume that the product in the burn-in procedure only experiences continuous smooth degradation process, while in the field operation period the product experiences both continuous smooth degradation process and shock process. The shock process can cause the product not only traumatic failure,but also additional abrupt degradation damage. After the system reliability model and maintenance model have been proposed, the optimal burn-in setting and age replacement duration are obtained under the considering of minimizing the long run average cost rate. A numerical example with the real data is analyzed to illustrate the application of the model. 相似文献
277.
城市隧道出口公交车换道行为对交通流的影响 总被引:1,自引:0,他引:1
为了研究城市隧道出口处公交车的换道行为对交通流的影响,以城市隧道出口公交车的换道特性为研究对象,阐述并分析了公交车在城市隧道出口换道过程中的3种影响状态.然后采用摄像法采集相关数据并分析,借助SPSS软件构建了关于公交换道频率、公交换道持续时间、最大公交换道长度及其存在时间、隧道交通流量与车头时距关系的多元线性模型,并进行了相关性检验,得出了公交车换道对城市隧道出口交通流影响的主要因素. 相似文献
278.
以chou等人提出的伪氨酸组成方法为基础,从蛋白质序列的氨基酸组成信息和顺序信息着手,提出一种新的伪氨酸组成方法,即利用新伪氨酸序列的自相关函数、氨基酸的平均中程接触和氨基酸频率构造了23维向量来描述蛋白质序列,进而建立多元线性回归函数对蛋白质折叠速率进行预测,经jackknife检验相关系数达到了0.84.并与其他两种方法进行比较使本文的结论得到较好的验证.同时验证了本文提取的特征参数对蛋白质折叠速率有一定的影响. 相似文献
279.
通过三角级数叠加法模拟桥面不平顺激励,运用大型有限元通用分析软件ANSYS的耦合技术对车-桥耦合振动进行了分析.提出了5个自由度的车辆模型模拟重车,160个梁单元模型模拟简支梁桥,把车辆和桥梁结构视为2个系统,利用Newmark-β法求解车-桥耦合振动方程组,进行了桥梁结构振动的位移、弯矩的响应研究.得到了桥梁跨中最大位移和弯矩都不是发生在桥梁跨中位置;随着桥面不平顺有明显的变化,随着桥面状况的变差,其响应越来越大. 相似文献
280.