全文获取类型
收费全文 | 2033篇 |
免费 | 39篇 |
专业分类
公路运输 | 773篇 |
综合类 | 187篇 |
水路运输 | 524篇 |
铁路运输 | 123篇 |
综合运输 | 465篇 |
出版年
2023年 | 6篇 |
2022年 | 34篇 |
2021年 | 23篇 |
2020年 | 24篇 |
2019年 | 13篇 |
2018年 | 64篇 |
2017年 | 96篇 |
2016年 | 169篇 |
2015年 | 22篇 |
2014年 | 52篇 |
2013年 | 138篇 |
2012年 | 103篇 |
2011年 | 192篇 |
2010年 | 197篇 |
2009年 | 82篇 |
2008年 | 174篇 |
2007年 | 88篇 |
2006年 | 72篇 |
2005年 | 59篇 |
2004年 | 36篇 |
2003年 | 47篇 |
2002年 | 32篇 |
2001年 | 26篇 |
2000年 | 22篇 |
1999年 | 29篇 |
1998年 | 33篇 |
1997年 | 24篇 |
1996年 | 18篇 |
1995年 | 11篇 |
1994年 | 9篇 |
1993年 | 13篇 |
1992年 | 15篇 |
1991年 | 15篇 |
1990年 | 7篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 8篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 10篇 |
1972年 | 5篇 |
排序方式: 共有2072条查询结果,搜索用时 15 毫秒
111.
V. Alkan S. M. Karamihas G. Anlas 《International Journal of Automotive Technology》2011,12(4):529-535
To investigate static tire enveloping characteristics, a three dimensional (3-D) finite element model is proposed. The vertical
stiffness of the tire is studied on a flat surface with and without cleat. Tire rubber materials and cord layers are represented
independently using “rebar” elements available in MSC Marc Mentat. Comparisons of numerical and experimental results are given
to show the validity of the proposed model. It is shown that after a certain displacement, the results of the proposed model
agree well with experimental results. In addition, the model results show that regardless of the type of the cleat placed
under the rim center (hub center), all vertical force curves intersect after a certain displacement, which indicates typical
static enveloping characteristics. Moreover, another typical characteristic of the radial tires that is unlike those of bias-ply
constructions confirms that the contact patch does not expand laterally after a level vertical load is applied to the tire,
which is directly related to fuel consumption and tire tread life. 相似文献
112.
Contemporary transport planning requires a flexible modelling approach which can be used to monitor the implementation of a long term plan checking regularly its short term performance with easily available data; the original model is periodically updated using low cost information and this allows the evaluation of the changes to the plan which may be required. Such an approach requires models suited to regular updating and to the use of data from different sources. Models to update trip matrices from traffic counts have been available for some time; however, the estimation and/or updating of other model stages with low cost data has escaped analytical treatment. The paper discusses this idea and formulates the updating problem for an example involving a joint destination/mode choice model under various assumptions about the nature of the available data. Analytical solutions are proposed as well as some general conclusions.requests for offprints 相似文献
113.
Development of hot stamped center pillar using form die with channel type indirect blank holder 总被引:1,自引:0,他引:1
H. S. Choi B. M. Kim K. J. Nam S. Y. Ha S. H. Cha C. G. Kang 《International Journal of Automotive Technology》2011,12(6):887-894
The hot stamping process has been used in the automotive industry to reduce the weight of the body-in-white and to increase
passenger safety via improved crashworthiness. However, defects such as fracture and wrinkle occur when hot stamping is performed
using a conventional drawing or forming method. In this study, a channel-type indirect blank holder (CIBH) is proposed to
develop a high-strength center pillar in form-type hot stamping, so that the aforementioned drawbacks are overcome. This type
of blank holder plays an important role in reducing severe wrinkling at the flange; such wrinkling leads to folding after
the completion of form-type hot-stamping. First, we investigated the effect of the channel shape on the indirect blank holding
force by using a simplified two-dimensional plane-strain stamping process. Second, we selected the slope angle and corner
radius of the channel as the main shape parameters by finite element analysis and artificial neural network (ANN). It is known
that fracture at the hot formed wall and wrinkle at the flange are significantly affected by the slope angle of the channel,
and the appropriate value for eliminating fracture and wrinkle is determined to be 99°. By performing hot stamping using a
form die with the selected channel, we can manufacture a high-strength center pillar without wrinkle and fracture. 相似文献
114.
M. Ticã G. Dobre V. Mateescu G. Virzi-Mariotti 《International Journal of Automotive Technology》2014,15(6):885-891
The research is carried out to improve passenger’s comfort to increase the vehicles stability in dynamic conditions. The literature available in the automotive engineering considers different topics for studying suspensions. An example represents mechanisms structure and analysis (synthesis, kinematics, and dynamics) under various operating conditions. These aspects have been approached before analytically, numerical. The current paper studies the influence of the lateral force on the contact patch of the wheel and the corresponding variations of vehicle stability parameters, such as camber angle and wheel rear track. The study is performed for a newer innovative rear suspensions mechanism which does not have a wheel track and camber angle variation, relative to the chassis, when the suspension components was considered rigid. A numerical solution is obtained through a virtual model on several commercial codes: MSC Adams, Patran, Nastran. Concerning the analysed parametes, their variation increases as the applied force is increased. Moreover, the largest variation corresponds to the case were elastic bushings and deformable links are considered. 相似文献
115.
Jungyong Wang Ayhan Akinturk Neil Bose Stephen J. Jones Yun Young Song Ho Hwan Chun Moon Chan Kim 《Journal of Marine Science and Technology》2008,13(3):244-255
The objective of this study was to investigate the performance of a model azimuthing podded propulsor in ice-covered water.
Model tests were carried out with two different depths of cut into the ice (15 and 35 mm), two different ice conditions (presawn
and pack ice conditions), and four different azimuthing angles. The depth of cut is the maximum penetration depth of the propeller
blade into the ice block. The 0.3-m-diameter model propeller was operated in a continuous ice milling condition. Ice loads
were measured by several sensors which were installed in various positions on the model. Six one-axis pancake-style load cells
on the top of the model measured the global loads and two six-component dynamometers were installed on the shaft to measure
the shaft loads. One six-component dynamometer was attached to the one of the propeller blades inside the hub to measure the
blade loads. The pod unit and propeller performance in ice are presented. Ice-related loads, which were obtained when the
blade was inside the ice block, are introduced and discussed. During the propeller–ice interaction, a blade can experience
the path generated by the previous blade, which is called the shadowing effect. The effects of shadowing, depth of cut, azimuthing
angle, and advance coefficient on propulsor performance are presented and discussed. 相似文献
116.
J. Benajes S. Molina R. Novella M. Riesco 《International Journal of Automotive Technology》2008,9(3):257-265
A combined theoretical and experimental study has been carried out to determine the real potential of reducing pollutant emissions
in a HD diesel engine by means of retarding the intake valve closing. The effects produced by this alteration of the basic
operation cycle have been examined by a preliminary modelling study, and from the obtained results, a modified camshaft was
manufactured with a delayed intake valve closing of 60 crank angle degrees. Single-cylinder engine tests were carried out
with this modified camshaft, and the emissions and fuel consumption were recorded. The results showed that the retarded intake
valve closing can enhance the premixed combustion phase, and thus simultaneously reduce soot and NOx emissions. Moreover,
the combustion process attained is extremely tolerant to exhaust gas recirculation, and by adoption of this measure, Euro-5
emissions limits can be achieved at the tested conditions without after-treatment. 相似文献
117.
Seasonal changes in the abundance and biomass of cyanobacteria (Synechococcus and Prochlorococcus) and picoeukaryotes were studied by flow cytometry in the upper layers of the central Cantabrian Sea continental shelf, from April 2002 to April 2006. The study area displayed the typical hydrographic conditions of temperate coastal zones. A marked seasonality of the relative contribution of prokaryotes and eukaryotes was found. While cyanobacteria were generally more abundant for most of the year (up to 2.4 105 cells mL− 1), picoeukaryotes dominated the community (up to 104 cells mL− 1) from February to May. The disappearance of Prochlorococcus from spring through summer is likely related to shifts in the prevailing current regime. The maximum total abundance of picophytoplankton was consistently found in late summer–early autumn. Mean photic-layer picoplanktonic chlorophyll a ranged from 0.06 to 0.53 µg L− 1 with a relatively high mean contribution to total values (33 ± 2% SE), showing maxima around autumn and minima in spring. Biomass (range 0.58–40.16 mg C m− 3) was generally dominated by picoeukaryotes (mean ± SE, 4.28 ± 0.27 mg C m− 3) with an average contribution of cyanobacteria of 30 ± 2%. Different seasonality of pigment and biomass values resulted in a clear temporal pattern of picophytoplanktonic carbon to chlorophyll a ratio, which ranged from 10 (winter) to 140 (summer). This study highlights the important contribution of picoplanktonic chlorophyll a and carbon biomass in this coastal ecosystem. 相似文献
118.
介绍海上平台生活楼HVAC系统通风管线下送风气流组织设计,其中,海上平台生活楼HVAC系统通风管线设计引用某平台生活楼详细设计及加工设计,下送风气流组织设计是在建造结束并在海上调试后,对每个房间内部通风效果和舒适性的思考及总结. 相似文献
119.
120.
测定了30例二尖瓣脱垂综合征伴室性心律失常患者的QTd。结果发现,二尖瓣脱垂组QTd、QTcd、JTd显著延长,说明心室肌复极有局部的不均一性和电不稳定性,离散度与室性心律失常的发生密切相关,可能是室性心律失常发生的机理之一。QTd不仅能预测室性心律失常及猝死,而且能指导临床用药,是一很好的临床观察指标。 相似文献