全文获取类型
收费全文 | 1566篇 |
免费 | 8篇 |
专业分类
公路运输 | 663篇 |
综合类 | 57篇 |
水路运输 | 410篇 |
铁路运输 | 45篇 |
综合运输 | 399篇 |
出版年
2023年 | 12篇 |
2022年 | 21篇 |
2021年 | 8篇 |
2020年 | 8篇 |
2019年 | 7篇 |
2018年 | 68篇 |
2017年 | 70篇 |
2016年 | 156篇 |
2015年 | 12篇 |
2014年 | 33篇 |
2013年 | 139篇 |
2012年 | 77篇 |
2011年 | 172篇 |
2010年 | 151篇 |
2009年 | 67篇 |
2008年 | 120篇 |
2007年 | 53篇 |
2006年 | 10篇 |
2005年 | 21篇 |
2004年 | 29篇 |
2003年 | 11篇 |
2002年 | 18篇 |
2001年 | 8篇 |
2000年 | 16篇 |
1999年 | 15篇 |
1998年 | 25篇 |
1997年 | 14篇 |
1996年 | 19篇 |
1995年 | 16篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 12篇 |
1991年 | 8篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 12篇 |
1982年 | 7篇 |
1981年 | 12篇 |
1980年 | 8篇 |
1979年 | 15篇 |
1977年 | 15篇 |
1976年 | 11篇 |
1975年 | 10篇 |
1974年 | 8篇 |
1973年 | 6篇 |
排序方式: 共有1574条查询结果,搜索用时 250 毫秒
961.
Sergey Paltsev Y.-H. Henry Chen Valerie Karplus Paul Kishimoto John Reilly Andreas Löschel Kathrine von Graevenitz Simon Koesler 《Transportation》2018,45(2):573-595
The European Union (EU) recently adopted CO2 emissions mandates for new passenger cars, requiring steady reductions to 95 gCO2/km in 2021. We use a multi-sector computable general equilibrium (CGE) model, which includes a private transportation sector with an empirically-based parameterization of the relationship between income growth and demand for vehicle miles traveled. The model also includes representation of fleet turnover, and opportunities for fuel use and emissions abatement, including representation of electric vehicles. We analyze the impact of the mandates on oil demand, CO2 emissions, and economic welfare, and compare the results to an emission trading scenario that achieves identical emissions reductions. We find that vehicle emission standards reduce CO2 emissions from transportation by about 50 MtCO2 and lower the oil expenditures by about €6 billion, but at a net added cost of €12 billion in 2020. Tightening CO2 standards further after 2021 would cost the EU economy an additional €24–63 billion in 2025, compared with an emission trading system that achieves the same economy-wide CO2 reduction. We offer a discussion of the design features for incorporating transport into the emission trading system. 相似文献
962.
In the present paper a vibrational differential equation governing on a rigid beam on viscoelastic foundation has been investigated. The nonlinear differential equation governing on this vibrating syst... 相似文献
963.
在隧道施工中通过对水平岩层围岩压力进行实测,总结水平岩层隧道的围岩压力特点。依据水平岩层隧道围岩力学特性和初期支护作用原理,有针对性地调整初期支护参数,现场实施后通过监控量测对围岩和支护稳定性进行检验。依据地下水和破碎带对水平岩层的影响,总结破碎带地段水平岩层隧道施工技术措施,达到了快速、安全、经济施工,对类似工程有一定的借鉴和参考价值。 相似文献
964.
D. K. Fleming 《Maritime Policy and Management》2013,40(4):253-267
The United States meets the world shipping crisis of the 1970s with a high-cost merchant fleet and a national maritime policy which needs clearer articulation. This paper examines the objectives, rationale and methods of implementation of the Us maritime programme with attention, finally, to the question of governmental reorganization. 相似文献
965.
K. D. Cocks 《Coastal management》2013,41(4):359-383
Abstract This paper is an abridged version of a report on the application of a land‐use planning method developed by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) to the task of providing a zoning scheme for a portion of the Great Barrier Reef Marine Park. The approach involves the development of guidelines for making zoning decisions, the development of methods for measuring whether a scheme satisfies these guidelines, and the use of a computer‐aided technique to create successive schemes for evaluation against these guidelines. 相似文献
966.
Matthieu Waeles Ricardo D. Riso Jean-Franois Maguer Jean-Franois Guillaud Pierre Le Corre 《Journal of Marine Systems》2008,72(1-4):358
The dissolved lead was studied in the whole salinity gradient of the system composed of the Loire estuary and the North Biscay continental shelf. About 130 samples were collected in winter 2001 and spring 2002 during Nutrigas and Gasprod campaigns (Programme PNEC-Golfe de Gascogne, RV Thalassa) and metal measurements were conducted on board by Potentiometric Stripping Analysis. In the Loire estuary, levels of dissolved lead ranged from 0.15 to 0.24 nM and from 0.04 to 0.26 nM in winter and spring, respectively. Compared to the concentrations reported in 1987 and 1990 (0.4–1.7 nM; Boutier, B., Chiffoleau, J.F., Auger, D., Truquet, I., 1993. Influence of the Loire river on dissolved lead and cadmium concentrations in coastal waters of Brittany. Estuar. Coast. Shelf S., 36:133–143, Estuarine, Coastal and Shelf Science 36, 133–143) our study indicated much lower values. The fall in concentration in the estuary could be attributed to the stopping of activity of Octel, a big manufacturer of tetra alkyl lead. Discharge in dissolved metal to the continental shelf by the Loire river was assessed as 7.5 and 1.9 kg day− 1 for winter and spring, respectively. On the continental shelf, levels of dissolved lead varied within 0.06 and 0.27 nM in winter (0.15 ± 0.06 nM, sd = 1.96, n = 49), whereas concentrations measured in spring were in the range 0.06–0.17 nM (0.09 ± 0.03 nM, sd = 1.96, n = 60). This difference in metal concentration was related to the amounts of rainfall that have fallen over the continental shelf: estimations of inputs by this way (74 and 32 kg day− 1 in winter and spring, respectively) appeared to be significantly higher than inputs from the Loire river (7.5 and 1.9 kg day− 1 in winter and spring, respectively). The distributions of dissolved metal in the surface waters highlighted the role of suspended particular matter (SPM) for a rapid “trapping” of lead near the mouth of the estuary. The vertical distributions showed, in the stratified area, a biological transfer of lead between winter and spring from surface waters to the halocline. 相似文献
967.
新型快餐盒生物降解性能试验方法研究 总被引:1,自引:0,他引:1
通过固体培养微生物侵蚀试验、液体培养微生物侵蚀试验、降解过程中纤维素酶活性测定、纤维素酶侵蚀试验和降解过程中 C O2 生成体积分数的测定等试验结果分析,认为固体培养微生物侵蚀试验、纤维素酶侵蚀试验及 C O2 生成量测定试验可用于评价新型快餐盒生物降解性能。 相似文献
968.
变频技术是近年来应用范围广泛的一门技术,尤其在节约电能、自动控制等方面更为突出。变频技术应用在锅炉的燃烧控制中,既节约了电能,又使燃烧充分而节约了燃煤。由于改变了传统控制模式的运行方式,使锅炉自动燃烧控制系统运行更稳定,安全可靠。该系统应用于青岛四方机车车辆厂、山海关桥梁厂、齐齐哈尔车辆厂、南口机务段等单位,经测试效果明显,推广价值很大。 相似文献
969.
T. Shamim 《International Journal of Automotive Technology》2011,12(4):475-487
This paper presents a computational investigation of the effect of engine exhaust gas modulations on the performance of an
automotive catalytic converter during cold starts. The objective is to assess if the modulations can result in faster catalyst
light-off conditions and thus reduce cold-start emissions. The study employs a single-channel based, one-dimensional, non-adiabatic
model. The modulations are generated by forcing the variations in exhaust gases air-fuel ratio and gas compositions. The results
show that the imposed modulations cause a significant departure in the catalyst behavior from its steady behavior, and modulations
have both favorable and harmful effects on pollutant conversion during the cold-starts. The operating conditions and the modulating
parameters have substantial influence on catalyst behavior. 相似文献
970.
ABSTRACTA shift from private motorised transport to more active transportation can, among other things, deliver significant health benefits. The main disadvantage of active transport (in particular walking) for most people compared to private motorised transport is the limited range. Public transport (PT) can complement the use of active modes and extend their range. Therefore, there might be potential to increase physical activity through an increase in PT use. This article takes a closer look at how walking relates to the use of PT by examining existing literature on the topic. It aims to study how far people walk to and from PT and what key factors influence this. Scopus, Transport Research International Documentation and Web of Science have been searched systematically for relevant articles, conference papers and books. After screening of titles and abstracts, 41 relevant publications were identified. Studies were included if they quantified the amount of walking (measured as either distance or time) that is directly related to the use of PT. Studies that quantified walking using general measures of daily physical activity or daily walking or that used stated preference designs were excluded. The PT systems considered in this paper are mass transport systems in urban areas, either road- or rail-based, with fixed schedules and stops. Demand responsive transport services, which can offer door-to-door travel, are not considered, as these systems can to a large extent eliminate the need to walk. In the identified publications, a large variety of walking distances and times have been reported, and these seem to be highly context-specific. The paper establishes the evidence for the wide range of factors that influence walking related to PT, which have been categorised as personal, PT-related, environmental, and journey-related. The different methods that have been used are discussed by critically analysing their advantages and limitations. Only a limited number of these methods used allow for an accurate assessment of the walking distances to and from PT. The paper concludes with suggestions for future research, such as a need for more accurate measurement of walking and research in different geographical areas to shed light on underlying influences of culture and climate. 相似文献