全文获取类型
收费全文 | 2399篇 |
免费 | 29篇 |
专业分类
公路运输 | 766篇 |
综合类 | 338篇 |
水路运输 | 572篇 |
铁路运输 | 172篇 |
综合运输 | 580篇 |
出版年
2023年 | 19篇 |
2022年 | 54篇 |
2021年 | 33篇 |
2020年 | 17篇 |
2019年 | 23篇 |
2018年 | 68篇 |
2017年 | 58篇 |
2016年 | 113篇 |
2015年 | 42篇 |
2014年 | 91篇 |
2013年 | 299篇 |
2012年 | 136篇 |
2011年 | 179篇 |
2010年 | 151篇 |
2009年 | 148篇 |
2008年 | 140篇 |
2007年 | 110篇 |
2006年 | 107篇 |
2005年 | 89篇 |
2004年 | 35篇 |
2003年 | 15篇 |
2002年 | 21篇 |
2001年 | 34篇 |
2000年 | 48篇 |
1999年 | 24篇 |
1998年 | 31篇 |
1997年 | 23篇 |
1996年 | 31篇 |
1995年 | 36篇 |
1994年 | 13篇 |
1993年 | 20篇 |
1992年 | 14篇 |
1991年 | 19篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 14篇 |
1987年 | 9篇 |
1986年 | 15篇 |
1985年 | 21篇 |
1984年 | 12篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 11篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1975年 | 11篇 |
1973年 | 8篇 |
排序方式: 共有2428条查询结果,搜索用时 78 毫秒
961.
根据约束混凝土应力-应变关系,采用纤维单元模型与插值函数结合的方法,编制适用于计算不同截面的约束混凝土弯矩-曲率曲线的程序,经比较该程序具有良好的精度和适用性. 相似文献
962.
桩承式加筋路堤在软土地基道路工程中的应用越来越广泛,在对该复合体系中的水平土工加筋进行等效兜提作用的薄膜效应评价时,传统研究方法主要存在2点不足:一是在进行加筋体受力分析时对筋材的区段工作模式的区分还不够明确,这不利于定量刻画筋层的拉伸应变分布和大小及其受挠曲形态变化的影响;二是多数加筋拉应变分析方法以基于筋材净跨挠曲... 相似文献
963.
964.
965.
966.
L. D. K. Nguyen N. W. Sung S. S. Lee H. S. Kim 《International Journal of Automotive Technology》2011,12(3):339-350
The effects of split injection, oxygen enriched air, and heavy exhaust gas recirculation (EGR) on soot emissions in a direct
injection diesel engine were studied using the KIVA-3V code. When split injection is applied, the second injection of fuel
into a cylinder results in two separate stoichiometric zones, which helps soot oxidation. As a result, soot emissions are
decreased. When oxygen enriched air is applied together with split injection, a higher concentration of oxygen causes higher
temperatures in the cylinder. The increase in temperature promotes the growth reaction of acetylene with soot. However, it
does not improve acetylene formation during the second injection of fuel. As more acetylene is consumed in the growth reaction
with soot, the concentration of acetylene in the cylinder is decreased, which leads to a decrease in soot formation and thus
soot emissions. A combination of split injection, a high concentration of oxygen, and a high EGR ratio shows the best results
in terms of diesel emissions. In this paper, the split injection scheme of 75.8.25, in which 75% of total fuel is injected
in the first pulse, followed by 8°CA of dwell time, and 25% of fuel is injected in the second pulse, with an oxygen concentration
of 23% in volume and an EGR ratio of 30% shows a 45% reduction in soot emissions, with the same NOx emissions as in single
injection. 相似文献
967.
This paper introduces a methodology for the characterization of ports, employing specifically defined eco-efficiency indicators and combining typically available data (handled cargo, containers and passengers) with ship exhaust pollutants values (mainly NOx, SOx and PM) and anticipated external costs (ECs) due to emitted air pollutants to provide a collective overview of all port-related economic and environmental activities. The results from an applied case study allow a comparative evaluation of 16 selected ports based on 17 different evaluation criteria and denote that the employment of such an overall approach can allow port authorities to improve managerial aspects, potentially lower operational costs and promote reduced environmental effects. 相似文献
968.
Karl Sörenson 《WMU Journal of Maritime Affairs》2018,17(1):31-48
This article considers whether the Somali pirates were deterred by the naval task forces between the years 2009 and 2013. By disaggregating data and using previously unpublished records regarding the naval operations, two areas of operations are identified as potential periods of deterrence. The article uses a model of asymmetric deterrence to study the outcomes and equilibria of the navy-pirate interaction. It is found that the naval operations eventually did deter the Somali pirates in the Gulf of Aden, but that this objective was not met in the Somali Basin. It is concluded that the operational focus on the Gulf of Aden coupled with the fact that the area is relatively smaller than the Somali Basin enabled the naval credibility, thus effectively denying the pirates access to the sea. Conversely, limited attention by the naval units and the long Somali southern coast with its open waters impeded naval control in the Somali Basin. In connection to these findings some conclusions regarding naval deterrence are discussed. 相似文献
969.
The present study deals with the scattering of oblique surface water waves by small undulation on the bottom in the presence of a thin vertical barrier. Here, three different configurations of vertical barriers are investigated. Perturbation analysis is employed to determine the physical quantities, namely, the reflection and transmission coefficients. In this analysis, many different Boundary Value Problems (BVPs) are obtained out of which the first two bvps are considered. The zeroth order bvp is solved with the aid of eigenfunction expansion method. The first order reflection and transmission coefficients are derived in terms of the integrals by the method of the Green’s integral theorem. The variation of these coefficients is plotted and analyzed for different physical parameters. Furthermore, the energy balance relation, an important relation in the study of water wave scattering, is derived and checked for assuring the correctness of the numerical results for the present problem. 相似文献
970.
Despite decades of research, it is unclear under which circumstances travel is most onerous. While studies have found that some individuals derive positive utility from aspects of commuting, others have shown that traffic congestion can entail important time, monetary, and mental stress costs. Moreover, responses to traffic congestion-related stressors differs by individual characteristics. In response, this research captures how exposure to traffic congestion events, the duration of this exposure, and individual trait susceptibility to congestion affect the utility of commuting. Working through the lens of individual satisfaction with the duration of their commute, we show that not every minute of travel is valued the same by car commuters in Canadian cities. Results suggest a complex relationship between travel time, congestion, and individual predisposition to congestion-related stress. While improvements in travel time matter for increasing commute satisfaction, it is reductions in travel in congested conditions that matter most, particularly among those susceptible to congestion-related stressors. 相似文献