全文获取类型
收费全文 | 3196篇 |
免费 | 164篇 |
专业分类
公路运输 | 671篇 |
综合类 | 1275篇 |
水路运输 | 569篇 |
铁路运输 | 454篇 |
综合运输 | 391篇 |
出版年
2024年 | 10篇 |
2023年 | 17篇 |
2022年 | 46篇 |
2021年 | 65篇 |
2020年 | 84篇 |
2019年 | 73篇 |
2018年 | 94篇 |
2017年 | 100篇 |
2016年 | 153篇 |
2015年 | 153篇 |
2014年 | 243篇 |
2013年 | 197篇 |
2012年 | 244篇 |
2011年 | 268篇 |
2010年 | 192篇 |
2009年 | 208篇 |
2008年 | 198篇 |
2007年 | 242篇 |
2006年 | 223篇 |
2005年 | 141篇 |
2004年 | 79篇 |
2003年 | 58篇 |
2002年 | 44篇 |
2001年 | 74篇 |
2000年 | 21篇 |
1999年 | 33篇 |
1998年 | 10篇 |
1997年 | 18篇 |
1996年 | 10篇 |
1995年 | 3篇 |
1994年 | 13篇 |
1993年 | 9篇 |
1992年 | 7篇 |
1991年 | 4篇 |
1990年 | 9篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1986年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有3360条查询结果,搜索用时 31 毫秒
31.
新建水曹铁路(AC25kV)与既有卑水线(DC1650V)在木厂口站接轨,本文以"如何实现2种制式供电系统的安全可靠转换"为目的,借鉴国外经验,结合工程实际,研究在木厂口车站设计"交直流转换场"牵引供电系统技术方案及操作程序。 相似文献
32.
33.
喷锚支护的时间效应与空间效应 总被引:2,自引:0,他引:2
喷锚支护是新奥法构筑隧道的主要支护手段,为使喷锚支护与围岩形成共同承载结构,必须在适宜的时机及根据适当的围岩变位量来确定恰当的喷锚支护结构。 相似文献
34.
推导和证明了Haar小波连续小波变换时间和尺度的周期性,指出这种周期性可以提取出信号中的周期成分,并且使谐波和冲击信号在时间-尺度域中有不同的图形特征。因此根据这些特性可以识别齿轮裂纹产生的冲击和刚度变化,仿真和汽车变速器齿轮故障分析验证了Haar小波变换的有效性和实用性。 相似文献
35.
36.
This paper assumes that activities at the home and work location are important determinants of individuals' paths through time and space. Fixed activities at these locations determine to a large extent the duration and timing of time windows – blocks of time available for participation in travel and out-of-home non-work activities. Taking the time spent at home and at the workplace as a starting point, this paper classifies activity patterns on workdays into six groups with distinct home- and work-stay patterns. For this, data are used from the 1998 Netherlands National Travel Survey. The six clusters vary in terms of the duration and timing of time windows and some of the differences can be explained by commute characteristics, types of non-work activities performed, workers' sociodemographic attributes, and their spatiotemporal environment. However, the impact of sociodemographic and spatiotemporal variables on cluster membership is shown to be weak. 相似文献
37.
38.
一种新型城市交通信息服务系统,它采用GPS接收机、数码像机、有线/无线智能传感器、辅以人工等方式完成路况信息采集,经控制中心处理后按1~3次/min频率生成全面、综合反映路况信息的实时、动态交通图,通过无线传输为公众提供实时、动态路况信息,并用全新概念的车载显示器Skipper显示路况信息,实现道路车辆均衡化、提高道路利用率。论述了其开发背景、系统构成及工作原理、核心产品开发与运用等。 相似文献
39.
40.
The timing and duration of an activity episode are two important temporal aspects of activity-travel behavior. Understanding the causal relationship between these two variables would be useful in the development of activity-based travel demand modeling systems. This paper investigates the relationship between these two variables by considering two different causal structures – one structure in which time-of-day choice is determined first and influences duration and a second structure in which activity duration is determined first and affects time-of-day choice. These two structures are estimated within a discrete-continuous simultaneous equations framework employing a full-information maximum likelihood methodology that allows error covariance. The estimation is performed separately for commuter and non-commuter samples drawn from a 1996 household travel survey data set from the Tampa Bay area in Florida. The results of the model estimation effort show that the causal structure in which activity duration precedes or affects activity timing (time of day choice) performs better for the non-commuter sample. For the commuter sample, the findings were less conclusive with both causal structures offering equally good statistical measures of fit. In addition, for the commuter sample, all error correlations were found to be zero. These two findings suggest that time of day choice and activity episode duration are only loosely related for the commuter sample, possibly due to the relatively non-discretionary and inflexible work activity and travel. 相似文献