全文获取类型
收费全文 | 12517篇 |
免费 | 555篇 |
专业分类
公路运输 | 3425篇 |
综合类 | 3550篇 |
水路运输 | 3331篇 |
铁路运输 | 2284篇 |
综合运输 | 482篇 |
出版年
2024年 | 31篇 |
2023年 | 56篇 |
2022年 | 346篇 |
2021年 | 546篇 |
2020年 | 370篇 |
2019年 | 164篇 |
2018年 | 192篇 |
2017年 | 178篇 |
2016年 | 251篇 |
2015年 | 418篇 |
2014年 | 599篇 |
2013年 | 770篇 |
2012年 | 856篇 |
2011年 | 981篇 |
2010年 | 1003篇 |
2009年 | 1061篇 |
2008年 | 957篇 |
2007年 | 1108篇 |
2006年 | 1088篇 |
2005年 | 704篇 |
2004年 | 244篇 |
2003年 | 186篇 |
2002年 | 129篇 |
2001年 | 196篇 |
2000年 | 165篇 |
1999年 | 83篇 |
1998年 | 69篇 |
1997年 | 48篇 |
1996年 | 64篇 |
1995年 | 52篇 |
1994年 | 45篇 |
1993年 | 23篇 |
1992年 | 22篇 |
1991年 | 22篇 |
1990年 | 15篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 8篇 |
1985年 | 4篇 |
1984年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 843 毫秒
541.
542.
543.
本文通过对国内典型高速动车组齿轮箱进行有限元仿真和试验测试,对比两种不同结构型式齿轮箱箱体的模态特征,研究分析了整体箱和分体箱对振型模态的影响,针对局部薄弱区域提出优化设计建议并进行验证. 相似文献
544.
545.
2010年12月17日,经济合作与发展组织(OECD)造船工作组宣布,新一轮的国际造船协定谈判,因各方始终缺乏统一立场,难以达成共识而再次终结。回首这起历经20余年的"跨世纪谈判",一幅各方利益博弈图跃然纸上。而这张博弈图,清晰地勾勒出了世界造船版图由西向东的变迁。 相似文献
546.
The effect of travel time variability (TTV) on route choice behavior is explored in this study. A stated preference survey is conducted to collect behavioral data on Shanghai drivers’ choice between a slow but stable route and a fast but unreliable route. Travel time and TTV are respectively measured by mean and standard deviation of random travel time. The generalized linear mixed model (GLMM) is applied to quantify trade-offs between travel time and TTV. The GLMM based route choice model effectively accounts for correlations among repeated observations from the same respondent, and captures heterogeneity in drivers’ values of TTV. Model estimation results show that, female drivers and drivers with rich driving experience are less likely to choose a route with high TTV; smaller expected travel time of a route increase the probability of its being chosen; all drivers have intrinsic preference for a route with smaller expected travel time, but the degree of preference may vary within the population; TTV on average has negative effects on route choice decision, but a small portion of drivers are risk-prone to choose a fast but unreliable route despite high TTV. 相似文献
547.
548.
A hierarchized container ports network, with several super hubs and many multilevel hub ports, will be established, mainly serving transshipment and carrying out most of its business in the hub-spoke mode. This paper sums up a programming model, in which the elementary statistic units, cost and expense of every phase of any shipment are the straight objects, and the minimum cost of the whole network is taken as the objective. This is established based on a dynamic system to make out the hierarchical structure of the container ports network, i.e. the trunk hub and feeder hubs can be planned in a economic zone, then the optimal scale vector can also be obtained for all container ports concerned with the network. The vector is a standard measurement to decide a port's position and their scale distribution in the whole network. 相似文献
549.
Over the past several decades, human activities have had significant impacts on coastal wetlands worldwide. Here, using a model of “Drivers-Pressures-State-Impacts-Responses (DPSIR)” and data collected from coastal wetlands in Xiamen, China, we have analyzed temporal changes in regional coastal wetland ecosystem structure and function from 1950 through 2005. The study period was divided into four parts for comparative analysis: pre-1980s, 1980s, 1990s, and 2000 to present. Our results show that anthropogenic drivers of coastal wetland degradation in this region have increased substantially since 1950, and that this is correlated with a decline in coastal wetland function over the same period. 相似文献
550.