全文获取类型
收费全文 | 401篇 |
免费 | 30篇 |
专业分类
公路运输 | 92篇 |
综合类 | 107篇 |
水路运输 | 147篇 |
铁路运输 | 63篇 |
综合运输 | 22篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 20篇 |
2021年 | 13篇 |
2020年 | 21篇 |
2019年 | 12篇 |
2018年 | 6篇 |
2017年 | 6篇 |
2016年 | 13篇 |
2015年 | 19篇 |
2014年 | 29篇 |
2013年 | 32篇 |
2012年 | 34篇 |
2011年 | 30篇 |
2010年 | 31篇 |
2009年 | 18篇 |
2008年 | 33篇 |
2007年 | 34篇 |
2006年 | 22篇 |
2005年 | 14篇 |
2004年 | 5篇 |
2003年 | 2篇 |
2001年 | 9篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1985年 | 1篇 |
1983年 | 2篇 |
排序方式: 共有431条查询结果,搜索用时 15 毫秒
91.
The response of the Black Sea mean level to atmospheric pressure (AP) and wind forcing is investigated using 5 years of TOPEX/POSEIDON (T/P hereafter) data. A coherence analysis is first applied to mean sea level and pressure to examine the validity of the inverse barometer (IB) approximation over this area. As expected, it reveals very significant deviations from an IB response attributed to the narrowness of the Bosphorus Strait and its limiting role in water exchanges. A comparison is drawn with the Mediterranean Sea case. A single basin version of the Candela analytical model [Candela, J., 1991. The Gibraltar Strait and its role in the dynamics of the Mediterranean Sea. Dyn. Atmos. Oceans 15, 267–300], which takes linear friction at the strait into account, is then used. The model explains a significant part of the T/P mean sea level variance (about 30%, while the IB correction only explains 5% of its variance) and provides a means to correct the altimeter data for the pressure effect much better than the standard IB effect. The response of the mean sea level to wind forcing is then analysed. Coherence analysis between sea level and along-strait wind stress (WS) reveals a significant coherence at periods ranging from 40 to 100 days, with an almost steady phase of 270°. This result is confirmed with a multiple coherence analysis (mean sea level vs. WS and AP). A plausible mechanism is a piling-up of water at the northern or southern end of the strait due to along-strait wind forcing. The associated along-strait pressure gradient would modify the barotropic flow in the strait and then the mean sea level. Using an extension of the Candela model, we show that this mechanism is consistent with T/P mean sea level observations. 相似文献
92.
The buckling problem of a circular cylindrical shell has long been widely investigated due to its great importance in the design of aerospace and marine structures. Geometric imperfections and residual stresses are inevitable in practice and have been so far frequently considered in analytical and numerical predictions. But little attention has been paid until now on the combined influence of such initial defects on the critical and often unstable response of such elastoplastic structures. In this paper, a shell finite element is designed within the total Lagrangian formulation framework to deal with the elastoplastic buckling and post-buckling of thin cylindrical tubes under external pressure and axial compression. A specific experimental process will be introduced in order to measure residual stresses in the shell very accurately, so as to include them in the numerical calculations. The present formulation will enable us to describe the complete non-linear solutions, namely the critical pressures (bifurcation and limit (collapse) loads), the bifurcation modes and the bifurcated equilibrium branches up to advanced post-critical states. Comparisons will be made between numerical results and the experimental critical value and deformation patterns of a new generation profiler. Furthermore, the combined effects of geometric imperfections, residual stresses and plasticity will be analyzed. 相似文献
93.
Yann Ourmières Pierre Brasseur Marina Lévy Jean-Michel Brankart Jacques Verron 《Journal of Marine Systems》2009,75(1-2):100-115
A sequential assimilative system has been implemented into a coupled physical–biogeochemical model (CPBM) of the North Atlantic basin at eddy-permitting resolution (1/4°), with the long-term goal of estimating the basin scale patterns of the oceanic primary production and their seasonal variability. The assimilation system, which is based on the SEEK filter [Brasseur, P., Verron, J., 2006. The SEEK filter method for data assimilation in oceanography: a synthesis. Ocean Dynamics. doi: 10.1007/s10236-006-0080-3], has been adapted to this CPBM in order to control the physical and biogeochemical components of the coupled model separately or in combination. The assimilated data are the satellite Topex/Poseidon and ERS altimetric data, the AVHRR Sea Surface Temperature observations, and the Levitus climatology for salinity, temperature and nitrate.In the present study, different assimilation experiments are conducted to assess the relative usefulness of the assimilated data to improve the representation of the primary production by the CPBM. Consistently with the results obtained by Berline et al. [Berline, L., Brankart, J-M., Brasseur, P., Ourmières, Y., Verron, J., 2007. Improving the physics of a coupled physical–biogeochemical model of the North Atlantic through data assimilation: impact on the ecosystem. J. Mar. Syst. 64 (1–4), 153–172] with a comparable assimilative model, it is shown that the assimilation of physical data alone can improve the representation of the mixed layer depth, but the impact on the ecosystem is rather weak. In some situations, the physical data assimilation can even worsen the ecosystem response for areas where the prior nutrient distribution is significantly incorrect. However, these experiments also show that the combined assimilation of physical and nutrient data has a positive impact on the phytoplankton patterns by comparison with SeaWiFS ocean colour data, demonstrating the good complementarity between SST, altimetry and in situ nutrient data. These results suggest that more intensive in situ measurements of biogeochemical nutrients are urgently needed at basin scale to initiate a permanent monitoring of oceanic ecosystems. 相似文献
94.
Sandra Arndt Geneviève Lacroix Nathalie Gypens Pierre Regnier Christiane Lancelot 《Journal of Marine Systems》2011,84(3-4):49-66
This study presents a first attempt to quantify the biogeochemical transformations and fluxes of carbon and nutrients along the entire mixing zone of the shallow, tidally-dominated estuary–coastal zone continuum of the Scheldt (Belgium/The Netherlands). A fully transient, two-dimensional, nested-grid hydrodynamic model of the continuum is coupled to the biogeochemical MIRO model for the coastal zone and the CONTRASTE model for the estuary. Transient model simulations are performed with a high spatial (80–750 m) and temporal (30 min) resolution over a period of one year (January–December 1995). The high temporal resolution allows including the short-term variability triggered by the tides, the freshwater discharge and the wind stress. System scale simulations provide time series of nutrient transformations and fluxes along the entire estuary–coastal zone continuum, as well as highly resolved nutrient inventories for the estuarine and the coastal zone sub-domains. Simulation results reveal that the balance between highly variable estuarine nutrient inputs and physical constrains set by the unsteady residual transport field exert an important control on the magnitude and succession of phytoplankton blooms and the ecosystem structure in the coastal zone. In addition, they suggest that the poorly surveyed estuarine–coastal zone interface plays a central role in the continuum. In this dynamic area, marked spatial concentration gradients develop and episodically lead to a reversal of material fluxes from the coast into the estuary. During distinct episodes of the productive period, euryhaline coastal diatoms intrude far upstream into the saline estuary. This intrusion reduces the estuarine nutrient concentrations and export fluxes, thereby reinforcing the nutrient limitation in the coastal area. As a consequence, the estuarine filter does not operate independently from the processes in the coastal zone. The dynamic interplay between the two ecosystems and the intense process rates operating at their transition, therefore, strongly supports our continuum approach. 相似文献
95.
在进行罐车检定和罐体安全检测时,准确判断罐体标记是否准确对罐车检定工作十分重要,同时还要对罐体进行外观检查,确定外表面是否有明显的腐蚀、损伤和变形。车辆型号和封头形式对罐体型号的判断有影响。企业名称、车型、车号、载重、自重、容积、容积表号和介质名称等所有罐体标记是否准确,影响着检定工作的准确和检定证书的可靠有效。举例说明在日常检定工作中遇到的情况及处理方法。 相似文献
96.
随着社会经济的发展和公路网的不断建设,我国长途客运业也得到了迅猛的发展,但是长途客运车辆交通事故屡屡发生,本文提设计了一种基于GPRS的长途客车监控系统,它是利用卫星定位技术,无线通讯技术,谷歌地图技术和图像压缩等相关技术,且在Visual Basic 6.0开发平台上而完成的,该系统将采集到的车辆GPS信息、车内图像信息以及报警等信息通过GPRS网络发送到监控中心,实现监控中心对运行中长途客车的监控,以确保长途客车安全运行。 相似文献
97.
98.
99.
通过建立城市道路交叉口交通流黄红灯前后边界条件与计算方法,利用LWR模型描述了交叉口周期性中断交通流.在数值差分模型中,应用仿真时步交叉口状态数组标识交叉口信号灯状态,并依时推进仿真计算.不同于连续交通流,城市道路交叉口交通流根据红绿灯的变换采用各路段分时、分段计算方法突出各子路段在不同信号灯下的不同路权特征,同时在差分计算和边界上考虑不同子路段的相互影响与衔接,整体刻画了交叉口及相关道路交通流的时空变化.算例表明,LWR模型与特殊边界条件结合,并配合基本图的灵活性,在城市道路交通流推算中结果合理可信,模型具有良好应用潜力. 相似文献
100.