全文获取类型
收费全文 | 2029篇 |
免费 | 11篇 |
专业分类
公路运输 | 688篇 |
综合类 | 62篇 |
水路运输 | 631篇 |
铁路运输 | 61篇 |
综合运输 | 598篇 |
出版年
2023年 | 12篇 |
2022年 | 37篇 |
2021年 | 17篇 |
2020年 | 13篇 |
2019年 | 21篇 |
2018年 | 64篇 |
2017年 | 51篇 |
2016年 | 80篇 |
2015年 | 17篇 |
2014年 | 84篇 |
2013年 | 310篇 |
2012年 | 102篇 |
2011年 | 103篇 |
2010年 | 96篇 |
2009年 | 94篇 |
2008年 | 102篇 |
2007年 | 49篇 |
2006年 | 41篇 |
2005年 | 41篇 |
2004年 | 32篇 |
2003年 | 31篇 |
2002年 | 25篇 |
2001年 | 26篇 |
2000年 | 36篇 |
1999年 | 24篇 |
1998年 | 35篇 |
1997年 | 38篇 |
1996年 | 33篇 |
1995年 | 45篇 |
1994年 | 22篇 |
1993年 | 20篇 |
1992年 | 15篇 |
1991年 | 12篇 |
1990年 | 18篇 |
1989年 | 13篇 |
1988年 | 16篇 |
1987年 | 16篇 |
1986年 | 14篇 |
1985年 | 20篇 |
1984年 | 21篇 |
1983年 | 18篇 |
1982年 | 25篇 |
1981年 | 29篇 |
1980年 | 20篇 |
1979年 | 33篇 |
1978年 | 12篇 |
1977年 | 21篇 |
1976年 | 8篇 |
1975年 | 10篇 |
1974年 | 8篇 |
排序方式: 共有2040条查询结果,搜索用时 46 毫秒
11.
HE Tseng J. Asgari D. Hrovat P. van der Jagt A. Cherry S. Neads 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2005,43(3):199-216
In the pursuit of an objective rating on vehicle stability performance, it is always desirable to reduce disturbances and inconsistencies during experimental evaluations, especially the ones introduced by human drivers. This paper presents the development of a steering robot designed for closed-loop steering tasks during evasive manoeuvres. It describes the controller structure and discusses experimental results, in addition to simulation/vehicle model verifications and theoretical control analysis. 相似文献
12.
以FRP正弦波形夹心桥面板作为研究对象,得到等效正交各项异性实心板,通过理论分析和数值对比,证明了方法的可行性;采用该法对一实际的FRP正弦波形夹心板桥进行了模态分析。 相似文献
13.
Organic carbon budget for the Gulf of Bothnia 总被引:1,自引:0,他引:1
Grete Algesten Lars Brydsten Per Jonsson Pirkko Kortelainen Stefan Lfgren Lars Rahm Antti Rike Sebastian Sobek Lars Tranvik Johan Wikner Mats Jansson 《Journal of Marine Systems》2006,63(3-4):155-161
We calculated input of organic carbon to the unproductive, brackish water basin of the Gulf of Bothnia from rivers, point sources and the atmosphere. We also calculated the net exchange of organic carbon between the Gulf of Bothnia and the adjacent marine system, the Baltic Proper. We compared the input with sinks for organic carbon; permanent incorporation in sediments and mineralization and subsequent evasion of CO2 to the atmosphere. The major fluxes were riverine input (1500 Gg C year− 1), exchange with the Baltic Proper (depending on which of several possible DOC concentration differences between the basins that was used in the calculation, the flux varied between an outflow of 466 and an input of 950 Gg C year− 1), sediment burial (1100 Gg C year− 1) and evasion to the atmosphere (3610 Gg C year− 1). The largest single net flux was the emission of CO2 to the atmosphere, mainly caused by bacterial mineralization of organic carbon. Input and output did not match in our budget which we ascribe uncertainties in the calculation of the exchange of organic carbon between the Gulf of Bothnia and the Baltic Proper, and the fact that CO2 emission, which in our calculation represented 1 year (2002) may have been overestimated in comparison with long-term means. We conclude that net heterotrophy of the Gulf of Bothnia was due to input of organic carbon from both the catchment and from the Baltic Proper and that the future degree of net heterotrophy will be sensible to both catchment export of organic carbon and to the ongoing eutrophication of the Baltic Proper. 相似文献
14.
Gulf menhaden, Brevoortia patronus, which constitutes a major industrial reduction fishery in the USA, spawn across the northern Gulf of Mexico with a focus of spawning about the Mississippi Delta. This species is estuarine dependent; adults spawn over the continental shelf and their larvae are transported, by mechanisms that are presently not well understood, to estuarine nursery areas. Larval gulf menhaden, along with some other surface oriented larval fishes, appear to aggregate along the Mississippi River plume front, while evidence of the ecological consequences of this aggregation in terms of the feeding, growth, and survival of larvae is ambiguous. On an annual scale, Mississippi River discharge is negatively associated with numbers of half year old recruits. Discharge of the Mississippi River and the population recruitment of gulf menhaden may be plausibly linked through the action of the river's plume and its front on the shoreward transport of larvae. Greater river discharge results in an expansive plume that might project larvae farther offshore and prolong the shoreward transport of larvae. An indirect, decadal scale, positive response of recruitment and river discharge is possible, but not certain. Recruitment became elevated after 1975 when river discharge increased and became highly variable. This response might owe to enhanced primary and secondary production driven by nutrient influx from the Mississippi River. 相似文献
15.
Two-dimensional and three-dimensional Green-Naghdi (GN) models equipped with a numerical wave-absorbing beach have been developed to simulate nonlinear, regular, and irregular wave propagation. The numerical beach is introduced near the downstream boundary to absorb outgoing waves. An appropriate amount of numerical damping and an appropriate length of numerical beach are investigated using numerical experiments. The results show that the GN models with a numerical beach work very well in simulating wave propagation in water in a small computational domain. 相似文献
16.
Brian J. Thomas 《Maritime Policy and Management》1995,22(3):239-253
Overmanning and restrictive labour practices are major causes of low productivity in Indian ports. Proposals are put forward for a programme of reforms to support investment in modern cargo handling systems. 相似文献
17.
Basic Analytical Study of Pantograph-catenary System Dynamics 总被引:9,自引:0,他引:9
T.X. Wu M.J. Brennan 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1998,30(6):443-456
For a high speed electrical rail system, good dynamic performance of the pantograph-catenary system is vital for smooth and continuous current collection. It has been known for many years that to achieve this the head of the pantograph should be made as light as possible and the average stiffness of the catenary should be high. These conclusions, however, have been reached by numerical modelling and operational experience. In this paper the pantograph-catenary system is modelled as a time-varying, single degree-of-freedom system to facilitate an analytical investigation of the system dynamics. Although the model is very simple, it allows physical insight into the dynamic behaviour of the system, and because the excitation is parametric it also allows the stability of the system to be investigated. The finite element method is used to determine the catenary characteristics and Floquet theory is used to analyse the behaviour of the coupled system. 相似文献
18.
A linear theory for the physical fields in the water column under the action of large amplitude internal lee waves at the main sill of the Strait of Gibraltar is developed. The procedure is a combination of the perturbation and normal modes methods in order to study steady resonant conditions. The lowest order linear approach of the methodology resumes the Taylor–Goldstein equation, which can reconstruct the main features of the observed fields but the high order approach gives the finest structure and sometimes the largest contributions. The role of the non-linear terms is investigated up to the second order taking into account the non-linear interactions between modes, leading to an effective reconstruction of the whole water column for the velocity field. 相似文献
19.
This paper presents a procedure for the estimation of origin‐destination (O‐D) matrices for a multimodal public transit network. The system consists of a number of favored public transit modes that are obtained from a modal split process in a traditional four‐step transportation model. The demand of each favored mode is assigned to the multimodal network, which is comprised of a set of connected links of different public transit modes. An entropy maximization procedure is proposed to simultaneously estimate the O‐D demand matrices of all favored modes, which are consistent with target data sets such as the boarding counts and line segment flows that are observed directly in the network. A case study of the Hong Kong multimodal transit network is used to demonstrate the effectiveness of the proposed methodology. 相似文献
20.