全文获取类型
收费全文 | 2065篇 |
免费 | 144篇 |
专业分类
公路运输 | 670篇 |
综合类 | 810篇 |
水路运输 | 269篇 |
铁路运输 | 227篇 |
综合运输 | 233篇 |
出版年
2024年 | 3篇 |
2023年 | 14篇 |
2022年 | 67篇 |
2021年 | 98篇 |
2020年 | 88篇 |
2019年 | 68篇 |
2018年 | 66篇 |
2017年 | 67篇 |
2016年 | 70篇 |
2015年 | 97篇 |
2014年 | 166篇 |
2013年 | 111篇 |
2012年 | 164篇 |
2011年 | 170篇 |
2010年 | 120篇 |
2009年 | 123篇 |
2008年 | 118篇 |
2007年 | 172篇 |
2006年 | 155篇 |
2005年 | 77篇 |
2004年 | 36篇 |
2003年 | 34篇 |
2002年 | 29篇 |
2001年 | 33篇 |
2000年 | 9篇 |
1999年 | 7篇 |
1998年 | 8篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 6篇 |
1994年 | 8篇 |
1993年 | 8篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
排序方式: 共有2209条查询结果,搜索用时 515 毫秒
711.
水下爆炸载荷下舰船设备抗冲击生命力模糊综合评判方法研究 总被引:2,自引:0,他引:2
舰船设备抗冲击性能是舰船生命力设计的重要内容。基于模糊数学的基本理论,引入炸药当量、爆距、炸药方位、设备相对位置和抗冲击能力等因素作为基本评判参数,构建舰船设备抗冲击生命力评估的数学模型,按层次分析法确立各参数的权重系数,确定各参数隶属度函数,实现对水下爆炸载荷作用下舰船设备生命力的模糊综合评判,提出舰船设备生命力的评判方法。 相似文献
712.
通过人工海水挂片、氯化钠盐雾腐蚀试验和电化学腐蚀试验,研究了CuNiAlBe合金材料的腐蚀行为。利用X射线衍射仪和能谱仪,确定了腐蚀产物的基本组成,初步讨论了合金的腐蚀机理。结果表明:CuNiAlBe合金有着良好的耐蚀性能,由于钝化膜形成和腐蚀产物的堆集,腐蚀速度随着时间的延长而降低。合金腐蚀均匀,没有局部腐蚀的发生。腐蚀产物的主要组成为CuCl2。 相似文献
713.
柱上开关式分区所及接触网故障判别方案的研究 总被引:4,自引:3,他引:1
常规电气化铁道分区所设置断路器及保护装置 ,在接触网发生故障后 ,可以通过断路器跳闸 ,实现上、下行接触网的分开 ,隔离故障区段。结合秦沈客运专线的特点 ,提出柱上开关式分区所的主接线型式 ,并较为详细地探讨了与牵引变电所配合实现接触网故障的判别与切除的方法 相似文献
714.
实船设备结构振动和水声声强测试分析及噪声源的判别 总被引:4,自引:0,他引:4
通过对船上设备和船体的振动、近远场水噪声声压以及主机舱左舷外水声声强分布的测量和对振动与声的相干分析,判断主、辅机激振的耦合对产生声的影响。通过近场声强分布,分析结构和声场耦合、能量交换和有效辐射。提出用声强分布计算频带内噪声辐射声功率占总声功率的比例,结合主、辅机振动谱综合分析方法,实现噪声主要激振源的判断。 相似文献
715.
716.
非道路用柴油机瞬态行为分析和试验循环开发 总被引:1,自引:1,他引:0
针对车辆在水泥路、石块路、起伏路、沼泽路行驶采集的柴油机道路载荷数据,对齿杆位移与扭矩进行转换,设计了表征原始载荷数据总体瞬态特征的7个参数,包括转速变化率、扭矩变化率、功率、功率变化率、转速和扭矩、转速和扭矩变化率、扭矩和转速变化率,划分区间计算相对发生率确定了总体特征.采用x2校验和移动筛选的方法,从原始数据中选取了代表每种路面形式瞬态特征的微历程,进一步工程调整微历程中的部分数据段,确定了表征总体瞬态特征的最佳微历程.最后对微历程按任务比例组合形成了适合柴油机的瞬态加载试验循环. 相似文献
717.
This study explores the relationships between adoption and consideration of three travel-related strategy bundles (travel
maintaining/increasing, travel reducing, and major location/lifestyle change), linking them to a variety of explanatory variables.
The data for this study are the responses to a fourteen-page survey returned by nearly 1,300 commuting workers living in three
distinct San Francisco Bay area neighborhoods in May 1998. We first identified patterns of adoption and consideration among
the bundles, using pairwise correlation tests. The test results indicate that those who have adopted coping strategies continue
to seek for improvements across the spectrum of generalized cost, but perhaps most often repeating the consideration of a
previously-adopted bundle. Furthermore, we developed a multivariate probit model for individuals’ simultaneous consideration
of the three bundles. It is found that in addition to the previous adoption of the bundles, qualitative and quantitative Mobility-related
variables, Travel Attitudes, Personality, Lifestyle, Travel Liking, and Sociodemographics significantly affect individual
consideration of the strategy bundles. Overall, the results of this study give policy makers and planners insight into understanding
the dynamic nature of individuals’ responses to travel-related strategies, as well as differences between the responses to
congestion that are assumed by policy makers and those that are actually adopted by individuals.
Sangho Choo is a Research Associate at The Korea Transport Institute. His research interests include travel demand modeling, travel survey methods with GPS, and travel behavior modeling. Patricia L. Mokhtarian is a professor of Civil and Environmental Engineering, chair of the interdisciplinary Transportation Technology and Policy MS/PhD program, and Associate Director for Education of the Institute of Transportation Studies at the University of California, Davis. She has been modeling travel behavior and attitudes for more than 30 years. 相似文献
Patricia L. Mokhtarian (Corresponding author)Email: |
Sangho Choo is a Research Associate at The Korea Transport Institute. His research interests include travel demand modeling, travel survey methods with GPS, and travel behavior modeling. Patricia L. Mokhtarian is a professor of Civil and Environmental Engineering, chair of the interdisciplinary Transportation Technology and Policy MS/PhD program, and Associate Director for Education of the Institute of Transportation Studies at the University of California, Davis. She has been modeling travel behavior and attitudes for more than 30 years. 相似文献
718.
This paper analyzes transportation mode choice for short home-based trips using a 1999 activity survey from the Puget Sound
region of Washington State, U.S.A. Short trips are defined as those within the 95th percentile walking distance in the data,
here 1.40 miles (2.25 km). The mean walking distance was 0.4 miles (0.6 km). The mode distribution was automobile (75%), walk
(23%), bicycle (1%), and bus (1%). Walk and bicycle are found less likely as the individual’s age increases. People are more
likely to drive if they can or are accustomed to. People in multi-person families are less likely to walk or use bus, especially
families with children. An environment that attracts people’s interest and provides activity opportunities encourages people
to walk on short trips. Influencing people’s choice of transport mode on short trips should be an important part of efforts
encouraging the use of non-automobile alternatives.
相似文献
Gudmundur F. UlfarssonEmail: |
719.
This study seeks to online calibrate the parameters of aggregate evacuee behavior models used in a behavior‐consistent information‐based control module for determining information strategies for real‐time evacuation operations. It enables the deployment of an operational framework for mass evacuation that integrates three aspects underlying an evacuation operation: demand (evacuee behavior), supply (network management), and disaster characteristics. To attain behavior‐consistency, the control module factors evacuees' likely responses to the disseminated information in determining information‐based control strategies. Hence, the ability of the behavior models to predict evacuees' likely responses is critical to the effectiveness of traffic routing by information strategies. The mixed logit structure is used for the aggregate behavior models to accommodate the behavioral heterogeneity across the population. An online calibration problem is proposed to calibrate the random parameters in the behavior models by using the least square estimator to minimize the gap between the predicted network flows and unfolding traffic dynamics. Background traffic, an important but rarely studied issue for modeling evacuation traffic, is also accounted for in the proposed problem. Numerical experiments are conducted to illustrate the importance of the calibration problem for addressing the system consistency issues and integrating the demand, supply, and disaster characteristics for more efficient evacuation operations. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
720.
高速公路标识站选址模型与算法研究 总被引:1,自引:0,他引:1
以路网拓扑结构为基础,采用图论中的支撑树理论来研究高速公路标识站数量及选址问题。基于支撑树任意两点之间恰有一条路径的性质,定义了余边集的概念,在此基础上提出了标识站确定理论,从根本上确立了标识站最优数量,并将破圈法与展开树法有机结合,提出了适合大型路网的标识站选址算法。标识站数量确定理论和展开树算法,从根本上解决了路网收费中二义性路径的标识问题,可以直接用于高速公路及城市轨道的标识站设计与建设中,能够确定所有标识站选址方案。给出了一个试验实例以证明该理论与算法的可行性。 相似文献