全文获取类型
收费全文 | 2532篇 |
免费 | 35篇 |
专业分类
公路运输 | 998篇 |
综合类 | 82篇 |
水路运输 | 692篇 |
铁路运输 | 74篇 |
综合运输 | 721篇 |
出版年
2023年 | 17篇 |
2022年 | 56篇 |
2021年 | 19篇 |
2020年 | 13篇 |
2019年 | 20篇 |
2018年 | 104篇 |
2017年 | 100篇 |
2016年 | 181篇 |
2015年 | 22篇 |
2014年 | 100篇 |
2013年 | 295篇 |
2012年 | 143篇 |
2011年 | 207篇 |
2010年 | 180篇 |
2009年 | 134篇 |
2008年 | 142篇 |
2007年 | 78篇 |
2006年 | 42篇 |
2005年 | 53篇 |
2004年 | 36篇 |
2003年 | 41篇 |
2002年 | 38篇 |
2001年 | 35篇 |
2000年 | 30篇 |
1999年 | 31篇 |
1998年 | 27篇 |
1997年 | 30篇 |
1996年 | 35篇 |
1995年 | 31篇 |
1994年 | 17篇 |
1993年 | 22篇 |
1992年 | 20篇 |
1991年 | 16篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 14篇 |
1984年 | 16篇 |
1983年 | 14篇 |
1982年 | 10篇 |
1981年 | 20篇 |
1980年 | 19篇 |
1979年 | 16篇 |
1978年 | 11篇 |
1977年 | 16篇 |
1976年 | 17篇 |
1975年 | 24篇 |
1974年 | 8篇 |
1973年 | 8篇 |
排序方式: 共有2567条查询结果,搜索用时 15 毫秒
991.
992.
993.
Development of engine control using the in-cylinder pressure signal in a high speed direct injection diesel engine 总被引:1,自引:0,他引:1
S. Yu H. Choi S. Cho K. Han K. Min 《International Journal of Automotive Technology》2013,14(2):175-182
Emission regulations are becoming more stringent and remain a principal issue for vehicle manufacturers. Many engine subsystems and control technologies have been introduced to meet the demands of these regulations. For diesel engines, combustion control is one of the most effective approaches for reducing not only engine exhaust emissions but also cylinder-by-cylinder variation. However, the high cost of pressure sensors and the complex engine head design for additional equipment present difficulties for manufacturers. In this paper, cylinder pressure-based engine control logic is introduced for a multi-cylinder high speed direct injection (HSDI) diesel engine. The time for 50% of the mass fraction to be burned (MFB50) and the IMEP are valuable for determining the combustion status. These two in-cylinder quantities are measured and applied to the engine control logic. Fuel injection timing is controlled to adjust the operating MFB50 to the target MFB50 using PID control logic, and the fuel injection quantity is controlled to adjust the measured IMEP to the desired IMEP. The control logic is demonstrated at steady state and during transient conditions and is applied to an NEDC mode test. 相似文献
994.
995.
996.
In this paper, an indirect feedback active noise control (ANC) scheme, based on the fundamental frequency-estimation method, is proposed for systems with multiple tonal noises. The engine noise consists of the harmonic components of the rotation of the crankshaft in the engine. When it is difficult to obtain reference signals, which are necessary for a feedforward ANC, conventional ANC algorithms do not work. In this paper, a new method is proposed to generate reference signals with estimated frequencies. The proposed algorithm consists of two parts: the frequency-estimation (FE) algorithm for the estimation of the fundamental frequency of the rotating machinery and then the conventional filtered-x LMS (FX-LMS) algorithm. In the second algorithm, the reference signal is generated using the fundamental frequency as estimated in the first algorithm. The FE algorithm uses a second-order adaptive notch filter, which is insensitive to impulse noise. In addition, the FE algorithm has good tracking capability and a lower variance of frequency-estimation error for a constant sinusoid signal and chirp signal. The performance of the proposed ANC method is verified through simulations and an experiment using a DSP board (DS-1104) inside a short duct. 相似文献
997.
Ashish Verma H.S. Sudhira Sujaya Rathi Robin King Nibedita Dash 《Research in Transportation Economics》2013
Considering the present trends of urbanization and motorization in India, there is an urgent need for integration, revitalization and renewal of the smaller towns and cities to make urban areas in India more sustainable. Unless our regional space is reorganized to upgrade development of towns and cities and integrate them with each other and the larger cities, the urbanization process in India will become unsustainable. It is argued that High Speed Rail (HSR) can play a role in achieving this more balanced and sustainable development of towns and cities, opening up opportunities for growth across a wider, inter-connected, region, with the benefit of taking the pressure of the larger cities to absorb additional burgeoning populations. This paper will make the case that in the current Indian context, current patterns of mega-city growth are unsustainable, and that HSR can play an important role in providing opportunities for medium and smaller size cities through their interconnections. It begins by highlighting the role that railways have played in India and other countries, noting that merely economic analysis of their costs and benefits generally underestimated their contributions to development. It then provides an introduction to HSR and its potential impact in general, before applying this to the example of the State of Karnataka in South India. 相似文献
998.
Iván Cáceres Rabionet Vicente Gracia García Montserrat Rubio Galindo 《Coastal management》2013,41(3):254-273
Artificial islands have been constructed next to large cities due to the need for extra space in highly populated areas. These emerged structures have been used by many countries as platforms for developing infrastructure (airports, harbors, highways, etc.), rebuilding ecological areas, and creating new spaces for tourism or residential areas. In this study, two state-of-the-art numerical models for wave propagation and nearshore circulation are used to simulate the effects of an emerged artificial island on the Barcelona coast. Several sea indicators (wave height, intensity and direction of currents, and mean water level) are analyzed to assess the changes likely to be induced by an artificial island. Three different situations are studied and the indicators are compared across the different tests to obtain information that can be used in the planning process of these structures. In two-meter wave conditions, the tests show that wave height is generally reduced in the sheltered area, which leads to improved safety for beach users (bathing is prohibited when wave height exceeds the two-meter threshold). However, the numerical models also reveal that velocities in the sheltered area usually decrease, which must be controlled to prevent stagnation in the bathing area. 相似文献
999.
J.-D. Caprace C. Petcu M. G. Velarde P. Rigo 《Journal of Marine Science and Technology》2013,18(3):404-417
In this article we describe the development of a tool that allows planners to efficiently and effectively plan space within valuable areas of a shipyard. Traditionally, space is considered as resource; however, it is difficult to accurately account for and plan its consumption with the currently available planning software’s. The spatial scheduling tool described in this article can be used by planners to manually or automatically reserve space within the shipyard for construction of large blocks over the entire erection period of the ship. The software is coupled with a heuristic optimization solver inspired by an algorithm used for "3D bin-packing problems." The result is the ability to efficiently generate and compare multiple space allocation alternatives in a reduced time with the ultimate goal of maintaining the critical ship erection schedule. A better solution than manual or semi-automatic allocation of blocks can be obtained through the optimization module. 相似文献
1000.
César Ducruet 《Maritime Policy and Management》2013,40(4):377-394
While the geographical and economic factors concerning the development of hub ports are widely described by a variety of scholars and professionals, there is no recognized methodology measuring the hub dependence of a given port, region, or country. Based on a 20-year database of vessel movements, this paper proposes a methodology measuring hub dependence. North Korea offers a good case of a constrained economy facing dramatic internal and external pressures. Notably, the weight and geographical extent of its maritime connections are worth analysing because of its contrasted evolution from Soviet influence, geopolitical isolation, and growing trade due to economic reforms and increased foreign investments. The main results of this study show the spatial shift from long-distance calls to feeder calls: global foreland contraction, regionalization within Northeast Asia, and traffic concentration upon closest hubs of which South Korean ports. We conclude that hub dependence is a combination of local constraints and trade growth. The political implications of this phenomenon are explored, and a spatial model of hub dependence is proposed. 相似文献