全文获取类型
收费全文 | 1947篇 |
免费 | 20篇 |
专业分类
公路运输 | 714篇 |
综合类 | 74篇 |
水路运输 | 581篇 |
铁路运输 | 57篇 |
综合运输 | 541篇 |
出版年
2023年 | 11篇 |
2022年 | 26篇 |
2021年 | 13篇 |
2020年 | 8篇 |
2019年 | 20篇 |
2018年 | 42篇 |
2017年 | 56篇 |
2016年 | 94篇 |
2015年 | 28篇 |
2014年 | 77篇 |
2013年 | 303篇 |
2012年 | 93篇 |
2011年 | 112篇 |
2010年 | 98篇 |
2009年 | 90篇 |
2008年 | 107篇 |
2007年 | 59篇 |
2006年 | 40篇 |
2005年 | 42篇 |
2004年 | 32篇 |
2003年 | 30篇 |
2002年 | 21篇 |
2001年 | 28篇 |
2000年 | 46篇 |
1999年 | 21篇 |
1998年 | 24篇 |
1997年 | 30篇 |
1996年 | 38篇 |
1995年 | 42篇 |
1994年 | 13篇 |
1993年 | 24篇 |
1992年 | 27篇 |
1991年 | 18篇 |
1990年 | 15篇 |
1988年 | 23篇 |
1987年 | 13篇 |
1986年 | 17篇 |
1985年 | 19篇 |
1984年 | 11篇 |
1983年 | 19篇 |
1982年 | 17篇 |
1981年 | 20篇 |
1980年 | 12篇 |
1979年 | 14篇 |
1978年 | 12篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1975年 | 16篇 |
1974年 | 8篇 |
1973年 | 10篇 |
排序方式: 共有1967条查询结果,搜索用时 328 毫秒
141.
Using current meters and systematically repeated vessel mounted ADCP data legs, we describe the role of the semidiurnal and diurnal constituents in the tidal currents and investigate the mesoscale variability of the M2 tidal currents field along three cross-shelf legs over the Galician shelf. We found that the estimated values of the semi-major axes of the main semidiurnal tidal constituents are closely related to those obtained in previous research and that the tidal currents are predominantly semidiurnal. Amplitudes of the M2 and S2 semi-major axes constituents are comparable, and important fortnightly variability should thus be expected in the amplitude of the semidiurnal tidal currents. Vertical profiles of the semi-major axes of the main tidal constituents reveal that, in the absence of stratification, and far from the bottom frictional effects, the tidal currents are mostly barotropic. Over the slope, the tidal ellipses tilt from a north–south orientation toward the northeast–southwest direction and, as we go further into the shelf, their amplitude is increased, a feature that is reasonably explained by the transition from the dynamics of a Poincaré wave offshore to the dynamics of a northward alongshore propagating Kelvin wave over the shelf. The Ría de Vigo exerts a notable influence over the tidal currents, acting as an extension of the shelf and introducing a meridional variation in the orientation of the ellipses from the alongshore direction in the southern straight coast toward the northeast–southwest direction at the latitude of the Rías. Finally, the spatial fitting methods we tried have proved to be successful in VMADCP data detiding in this region. 相似文献
142.
Environmental improvement and energy issues are increasingly becoming more important as worldwide concerns. Natural gas is
a good alternative fuel that can help to improve these issues because of its large quantity and clean burning characteristics.
This paper provides the experimental performance results of a Bi-Fuel engine that uses Compressed Natural Gas as its Primary
fuel and gasoline as its secondary fuel. This engine is a modification of the basic 1.4-liter gasoline engine. Generally,
on the unmodified base engine, torque and power for CNG fuel are considerably lower than gasoline fuel. In this paper, the
influence of fuels on wall temperature, performance and emissions are investigated. 相似文献
143.
144.
S. Lee 《International Journal of Automotive Technology》2008,9(4):429-436
This paper addresses the application of the perturbation/correlation method to optimizing the torque output of internal combustion
engines. This application was inspired by observations of the limitations in current techniques of the automotive performance
tuning industry. Performance issues such as errors from true optimum spark timing and fuel injector pulse width values as
well as convergence were considered for optimal tuning. The ability of the system to deal with engine cycle-to-cycle variations
and their effect on input parameters is also analyzed. 相似文献
145.
146.
Hai Yang Cowina W.Y. Leung S.C. Wong Michael G.H. Bell 《Transportation Research Part B: Methodological》2010,44(8-9):1067-1083
This paper proposes an equilibrium model to characterize the bilateral searching and meeting between customers and taxis on road networks. A taxi driver searches or waits for a customer by considering both the expected searching or waiting time cost and ride revenue, and a customer seeks a taxi ride to minimize full trip price. We suppose that the bilateral taxi–customer searching and meeting occurs anywhere in residential and commercial zones or at prescribed taxi stands, such as an airport or a railway station. We propose a meeting function to spell out the search and meeting frictions that arise endogenously as a result of the distinct spatial feature of the area and the taxi–customer moving decisions. With the proposed meeting function and the assumptions underlying taxi–customer search behaviors, the stationary competitive equilibrium achieved at fixed fare prices is determined when the demand of the customers matches the supply of taxis or there is market clearing at the prevailing searching and waiting times in every meeting location. We establish the existence of such an equilibrium by virtue of Brouwer’s fixed-point theorem and demonstrate its principal operational characteristics with a numerical example. 相似文献
147.
148.
149.
The new Dutch shipping policy has given rise to high expectation and curiosity in the world of shipping. This, together with the obvious difficulties of an ex-post study of the effectiveness of such innovative policy, has prompted the authors to take an interest in attempting to investigate changes in ownership of the Dutch fleet 2 years after the new policy has been introduced. To do this, a rather new concept of ‘flagging out’ has been adopted, which is interpreted as a process leading to different degrees of ‘foreignness’ in a shipping operation. In this paper, a method to structure is presented, and ownership information, and changes in it are presented, that are essentially based on the theory of stochastic processes. The data used is the Dutch fleet data, which includes information on the nationality of the flag, parent ownership and management over the period 1994–1998. The results yield interesting insights in the shifts in the ownership and operational structure of shipping companies induced by the new policy. In particular, they allow one to establish the origin of new vessels, in which stage of ownership/operation it is most likely that shifts occur, and to determine the relationship between the different stages of the ‘flagging out’ process. These results, thus, enable an evaluation of the areas in which the policy can be expected to yield results. 相似文献
150.