全文获取类型
收费全文 | 17815篇 |
免费 | 1157篇 |
专业分类
公路运输 | 4959篇 |
综合类 | 5485篇 |
水路运输 | 3622篇 |
铁路运输 | 3970篇 |
综合运输 | 936篇 |
出版年
2024年 | 108篇 |
2023年 | 149篇 |
2022年 | 404篇 |
2021年 | 678篇 |
2020年 | 699篇 |
2019年 | 412篇 |
2018年 | 339篇 |
2017年 | 423篇 |
2016年 | 395篇 |
2015年 | 567篇 |
2014年 | 1430篇 |
2013年 | 1066篇 |
2012年 | 1566篇 |
2011年 | 1561篇 |
2010年 | 1310篇 |
2009年 | 1140篇 |
2008年 | 1220篇 |
2007年 | 1565篇 |
2006年 | 1402篇 |
2005年 | 818篇 |
2004年 | 502篇 |
2003年 | 329篇 |
2002年 | 225篇 |
2001年 | 192篇 |
2000年 | 120篇 |
1999年 | 72篇 |
1998年 | 43篇 |
1997年 | 32篇 |
1996年 | 35篇 |
1995年 | 34篇 |
1994年 | 28篇 |
1993年 | 20篇 |
1992年 | 18篇 |
1991年 | 18篇 |
1990年 | 5篇 |
1989年 | 12篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
691.
主要介绍了我国首艘浅海锆钛砂矿采选一体船的设计背景、主要技术参数和功能,并进一步重点论述了本船总体设计、采矿系统、选矿系统、总纵强度计算和高压岸电系统的设计思路和成果,以供今后开发类似船型的行业同仁借鉴。 相似文献
692.
为研究柴油机燃烧系统参数匹配对柴油机动力和排放性能的影响,首先分别利用AVL_BOOST和AVL_FIRE仿真软件建立4190ZLC-2型船用柴油机整机模型和缸内燃烧高压循环模型,然后基于已建模型应用正交试验设计方法安排柴油机进气系统、喷油系统和燃烧室结构尺寸参数匹配仿真计算。研究结果表明,通过极差分析可以得出燃烧系统参数对4190ZLC-2型柴油机性能的影响主次顺序。以柴油机指示功率为评价指标时,参数组合0.26 mm-28°CA-160°-0.9-145 mm-2.6 mm-22 mm(喷孔直径-喷油提前角-油束夹角-涡流比-喉口直径-凸台高度-凹坑半径)对应的指示功率为63.40 k W,比原机仿真值高15%;以NOX排放为评价指标时,参数组合0.30 mm-24°CA-140°-0.4-135 mm-6.6 mm-14 mm(喷孔直径-喷油提前角-油束夹角-涡流比-喉口直径-凸台高度-凹坑半径)对应的NOX排放质量分数为0.015 7%,比原机仿真值低30.2%。 相似文献
693.
694.
695.
696.
697.
698.
699.
Water bursts during tunnel construction endanger construction, and it is therefore necessary to reserve a waterproof dike with the required thickness to avoid water bursts and to take reinforcement of the dike and treatment of the structure liable to trigger a water burst. Using the water burst at K5+398 of the Mingyueshan tunnel of the Shanghai-Chengdu expressway as an example, and considering the type of tunnel section and the upright mudstone of the dike, the waterproof dike at the work face is simplified as a round thin plate. A formula for the calculation of a minimum safety thickness for the critical waterproof dike is deduced by analyzing the force applied on the water-proof dike, and the minimum safety thickness for the water burst section at K5+398 of the Mingyueshan tunnel is cal-culated. The numerical simulation analysis demonstrates the critical thickness of waterproof dike at K5+398 of the Mingyueshan tunnel is 1.4-1.55 m, and the calculated water inflow and water burst basically agree with the actual condition. © 2018, Editorial Office of "Modern Tunnelling Technology". All right reserved. 相似文献
700.
In the countries of the Global South such as India, rapid urbanization and the increase in individual motorization may lead to a predominance of unsustainable commuting patterns. However, urbanization also has important positive effects, including the empowerment of women. This paper examines newly released, spatially disaggregated data on home-to-work commuting by non-agricultural workers in the National Capital Region of India. It aims to understand and compare commuting patterns in urban and rural areas, including choice of travel modes, commuting distances, and gender differentials.The results reveal a tendency observable in urban residents to use individual motorized transport more often both for short and for long trips, although the proportion of individual motorization is far from what it is in the industrial world. Rural areas are characterized by the predominance of non-motorized travel modes and a large share of long trips. The mobility gap between men and women does not appear to increase with literacy. In urban areas, women often choose to commute by car rather than using green modes of transportation (especially in higher-income districts). The paper stresses the importance of the area and gender differentials that need to be taken into account when formulating regional transport policies. 相似文献