全文获取类型
收费全文 | 3326篇 |
免费 | 162篇 |
专业分类
公路运输 | 544篇 |
综合类 | 1204篇 |
水路运输 | 779篇 |
铁路运输 | 822篇 |
综合运输 | 139篇 |
出版年
2024年 | 4篇 |
2023年 | 17篇 |
2022年 | 45篇 |
2021年 | 90篇 |
2020年 | 80篇 |
2019年 | 56篇 |
2018年 | 61篇 |
2017年 | 59篇 |
2016年 | 73篇 |
2015年 | 110篇 |
2014年 | 210篇 |
2013年 | 170篇 |
2012年 | 278篇 |
2011年 | 305篇 |
2010年 | 231篇 |
2009年 | 208篇 |
2008年 | 198篇 |
2007年 | 291篇 |
2006年 | 316篇 |
2005年 | 213篇 |
2004年 | 136篇 |
2003年 | 87篇 |
2002年 | 72篇 |
2001年 | 63篇 |
2000年 | 32篇 |
1999年 | 10篇 |
1998年 | 14篇 |
1997年 | 11篇 |
1996年 | 4篇 |
1995年 | 8篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有3488条查询结果,搜索用时 218 毫秒
971.
移动闭塞列控系统集成列车定位技术 总被引:1,自引:0,他引:1
在分析单一的列车定位技术优缺点和不同闭塞方式列控系统列车定位要求的基础上,指出应该采用列车集成定位技术。重点介绍一个实用移动闭塞列控系统集成列车定位技术的组成、定位流程及其应用效果,说明如何应用集成技术手段,综合各单一的列车定位技术的优点,实现互补、冗余和多信息,从而使在定位精度、实时性、安全性和可靠性等方面满足移动闭塞列控系统的列车定位要求。 相似文献
972.
CAD与CAPP信息共享研究 总被引:5,自引:0,他引:5
如何实现CAPP与CAD之间的信息共享,无缝连接,一直是CAPP系统开发过程中的一个难点,对该问题进行了研究与探索,介绍了一种如何获取CAD图纸界面上零件总体信息及将CAPP系统处理后的数据库信息写到CAD图纸界面上的方法。 相似文献
973.
从铁路局角度出发,针对机车质量信息管理系统的研究开发,提出系统的建设思路和原则,并围绕系统的构成、现场流程控制及基础技术数据处理,对系统的先进性、安全性、易用性、可扩展性,以及可维护性原则等方面加以论述。机车质量信息管理系统的建立,可以提高机务段检修管理水平,为机车检修从计划修向状态修转变创造条件。 相似文献
974.
搜索引擎相关技术研究概述 总被引:1,自引:0,他引:1
主要介绍了搜索引擎的概念、分类和主要工作原理,并详细介绍了目前该领域所涉及的关键技术及相应的主要研究方向,最后指出了目前的搜索引擎存在的问题,并提出了一种改进的研究方向. 相似文献
975.
ABSTRACTConventional travel time reliability assessment has evolved from road segments to the route level. However, a connection between origin and destination usually consists of multiple routes, thereby providing the option to choose. Having alternatives can compensate for the deterioration of a single route; therefore, this study assesses the reliability and quality of the aggregate of the route set of an origin-destination (OD) pair. This paper proposes two aggregation methods for analyzing the reliability of travel times on the OD level: 1) an adapted Logsum method and 2) a route choice model. The first method analyzes reliability from a network perspective and the second method is based on the reliability as perceived by a traveler choosing his route from the available alternatives. A case study using detailed data on actual travel times illustrates both methods and shows the impact of having variable departure times and the impact of information strategies on travel time reliability. 相似文献
976.
Rosaline Canessa Michael Butler Claudette Leblanc Christian Stewart Don Howes 《Coastal management》2013,41(1):105-142
Access to current, comprehensive, and reliable spatial information is necessary for informed decision making in integrated coastal and ocean management. This need is being met through development of a marine spatial information infrastructure that encompasses both technological and institutional responses. This article traces Canada's experience in developing a marine spatial information infrastructure over the last 30 years starting with the compilation of coastal atlases, through the development of geographic information systems, to remote data acquisition instruments and Web mapping portals. Because of the plethora of initiatives, it has been essential to be selected and limit the number and choice of examples. The institutional response has lagged behind that of technological innovation and hinges on understanding users’ needs and decision support drivers, sustainability of institutional and individual champions, and, above all, cooperation and collaboration among the broad community of practice. 相似文献
977.
978.
This paper reports the results of a 1998 survey carried out among a small sample of people who had called the TravInfo Travel Advisory Telephone System (TATS) in April 1997 looking for current information about traffic conditions in the San Francisco Bay Area. The survey employed a series of tradeoff questions designed to identify the specific attributes of the information that the respondents felt to be most important, and to estimate the relative values that these users had for various possible information improvements. Despite the small size of the sample, it proved feasible to investigate how the implicit valuations placed on each attribute of the service (update frequency, extent of road coverage, and level of customization) varied among different user segments. For the most part, respondents appeared to value basic enhancements – those that establish an initial quality differential above the baseline set by free broadcast traffic information – more than they value further subsequent improvements. Overall, more frequent information updates are the highest priority among the range of possible enhancements explored in the survey, followed by an extension of coverage to include major arterials in addition to freeways. However, the evidence suggests relatively little value in door-to-door coverage – that is, coverage of streets beyond the freeway and major arterial networks. This research produced some estimates of the average monetary values ("willingness to pay") that the sample of current users attached to information improvements of various kinds. While these values varied among subgroups in ways that fit a priori expectations, it is not clear whether they provide an unbiased picture of the users' absolute levels of willingness to pay, such that they could be used reliably to inform (for example) information pricing decisions. The value of this research lies more clearly in the light it sheds on the relative structure of user preferences, and on the variations in preferences between information attributes and market segments. Overall, the authors conclude that the prospects for self-sustaining ATIS services are unclear. In response to a direct question, a majority of users (perhaps influenced by a strategic bias) indicated that they were unwilling to pay for ATIS services; some of these same people, however, indicated later that they might indeed be willing to buy a particular enhanced ATIS package, in direct competition with free broadcast services. 相似文献
979.
980.