全文获取类型
收费全文 | 11847篇 |
免费 | 975篇 |
专业分类
公路运输 | 3185篇 |
综合类 | 4371篇 |
水路运输 | 3097篇 |
铁路运输 | 1407篇 |
综合运输 | 762篇 |
出版年
2024年 | 41篇 |
2023年 | 134篇 |
2022年 | 331篇 |
2021年 | 378篇 |
2020年 | 430篇 |
2019年 | 326篇 |
2018年 | 363篇 |
2017年 | 389篇 |
2016年 | 378篇 |
2015年 | 558篇 |
2014年 | 1016篇 |
2013年 | 710篇 |
2012年 | 1091篇 |
2011年 | 1003篇 |
2010年 | 918篇 |
2009年 | 874篇 |
2008年 | 711篇 |
2007年 | 856篇 |
2006年 | 709篇 |
2005年 | 431篇 |
2004年 | 289篇 |
2003年 | 202篇 |
2002年 | 117篇 |
2001年 | 149篇 |
2000年 | 81篇 |
1999年 | 60篇 |
1998年 | 48篇 |
1997年 | 40篇 |
1996年 | 48篇 |
1995年 | 32篇 |
1994年 | 17篇 |
1993年 | 22篇 |
1992年 | 14篇 |
1991年 | 14篇 |
1990年 | 10篇 |
1989年 | 14篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 7篇 |
1985年 | 2篇 |
1984年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
951.
高速公路交通管理系统用户满意度的测评研究对交通运输项目社会经济影响评价具有重要意义。利用计量经济学方法建立了基于交通运输信息的高速公路交通管理系统用户满意度指数模型,并对测评方法进行了研究。该方法为交通运输部门实时了解本系统运营质量水平提供了有效的参考依据。 相似文献
952.
通过建立矿石堆场地基的二维有限元模型,对矿石堆场下软弱地基的应力变形进行模拟计算,计算中采用了土体的线弹性模型和剑桥模型进行对比分析。重点研究了各种工况下堆场地基的水平、竖向变形问题,对荷载作用下斗轮机基础的长桩基、短桩基以及片筏基础设计方案进行计算,并与无基础方案进行对比分析,得出各种工况下不同基础的变位情况。计算研究成果直接为工程地基处理方案的确定及斗轮机基础的详细设计提供了依据。 相似文献
953.
单件小批量生产企业的P—M生产模型研究 总被引:2,自引:0,他引:2
根据单件小批量生产企业复杂产品生产的特点,综合PERT和MRP-Ⅱ两者的优点,提出P-M计划方法。这种方法既可以对产品上层部件进行优化排程,又可以对下层零部件进行有效管理,可以较好地解决这类企业当前管理模式中PERT太粗与MRP-Ⅱ太死的矛盾。 相似文献
954.
955.
建立整数型轨道状态最优综合维修计划模型 总被引:3,自引:0,他引:3
为实现高效的轨道不平顺养护维修,建立最优养护维修计划模型和采用大型养路机械进行作业是十分重要的。本文以养护维修时间为决策变量,以年度轨道不平顺平均值最小为目标函数,在考虑了一系列约束函数的情况下,建立了整数型轨道状态最优综合维修计划模型。该模型能有效利用现场的养护资源,从安全和舒适的角度出发来制定养护计划,该模型的建立从理论上解决了轨道不平顺状态计算机辅助决策系统的关键问题。 相似文献
956.
介绍了一个运用于摆式车辆的动力学性能仿真的数值计算模型,特别考虑了曲线通过工况。在此模型中,把实车上使用的控制软件和车辆数值计算机械结构模型结合起来,再现了倾摆主动控制装置的动力学。为了验证数值计算仿真模型,把数值计算结果与试验台试验及室外线路试验结果进行了比较。 相似文献
957.
Kunihiro Hamada Yukio Fujimoto Eiji Shintaku 《Journal of Marine Science and Technology》2002,6(4):205-215
Recently, the significance of ship inspections has been increasingly recognized because sea pollution and safety problems
are occurring more and more frequently. However, current ship inspections rely on the experience of the workers. Therefore,
it is difficult to understand, and hence to improve, the state of ship inspections. In this paper, ship inspection is directed
into three stages (plan, do, and check), and the configurations of a total system to support ship inspections are discussed.
A prototype system for the “plan” and “do” stages is developed. This is realized by organizing the information that relates
to inspection, and defining data models for damage and inspection states. Then the proposed system is integrated with a shipbuilding
computer integrated manufacturing (CIM) system so that the ship's structural information can be used effectively. In addition,
functions to calculate the damage-finding probability, and functions to generate information about damage and the inspection
state are introduced. Therefore, in the planning stage, as inspector can execute a virtual ship inspection, and then the damage-finding
probability of each hull part and oversight areas are calculated automatically. Further, by carrying this system into an inspection,
an inspector can generate damage information and inspection information simply and easily. Some examples of the proposed system
are shown at the end of the paper.
Received: November 12, 2001 / Accepted: January 30, 2002 相似文献
958.
变态河工模型垂线流速分布是不相似的。以此为基础对悬移质泥沙变态模型的沉降相似问题进行了探讨。结果表明 ,变态模型的泥沙沉降是不相似的 相似文献
959.
On the basis of analysis of the principle of delay restoration in a disturbed schedule, a heuristic algorithm for rescheduling trains is developed by restoring the total delay of the disturbed schedule. A discrete event topologic model is derived from the original undisturbed train diagram and a back propagation analysis method is used to label the maximum buffer time of each point in the model. In order to analyze the principle of delay restoration, the concept of critical delay is developed from the labeled maximum buffer time. The critical delay is the critical point of successful delay restoration. All the disturbed trains are classified into the strong-delayed trains and the weak-delayed trains by the criterion of the critical delay. Only the latter, in which actual delay is less than its critical delay, can be adjusted to a normal running state during time horizon considered. The heuristic algorithm is used to restore all the disturbed trains according to their critical details. The cores of the algorithm are the iterative repair technique and two repair methods for the two kinds of trains. The algorithm searches iteratively the space of possible conflicts caused by disturbed trains using an earfiest-delay-first heuristics and always attempts to repair the earliest constraint violation. The algorithm adjusts the weak-delayed trains directly back to the normal running state using the buffer time of the original train diagram. For the strong-delayed trains,the algorithm uses an utility function with some weighted attributes to determine the dynamic priority of the trains, and resolves the conflict according to the calculated dynamic priority. In the end, the experimental results show that the algorithm produces "good enough" schedules effectively and efficiently in disturbed situations. 相似文献
960.
The Arabian Sea exhibits a complex pattern of biogeochemical and ecological dynamics, which vary both seasonally and spatially. These dynamics have been studied using a one-dimensional vertical hydrodynamic model coupled to a complex ecosystem model, simulating the annual cycle at three contrasting stations. These stations are characterised by seasonally upwelling, mixed-layer-deepening and a-seasonal oligotrophic conditions, respectively, and coincide with extensively measured stations on the two JGOFS ARABESQUE cruises in 1994. The model reproduces many spatial and temporal trends in production, biomass, physical and chemical properties, both qualitatively and quantitatively and so gives insight into the main mechanisms responsible for the biogeochemical and ecological complexity. Monsoonal systems are typified by classical food web dynamics, whilst intermonsoonal and oligotrophic systems are dominated by the microbial loop. The ecosystem model (ERSEM), developed for temperate regions, is found to be applicable to the Arabian Sea system with little reparameterisation. Differences in in-situ physical forcing are sufficient to recreate contrasting eutrophic and oligotrophic systems, although the lack of lateral terms are probably the greatest source of error in the model. Physics, nutrients, light and grazing are all shown to play a role in controlling production and community structure. Small-celled phytoplanktons are predicted to be dominant and sub-surface chlorophyll maxima are robust centers of production during intermonsoon periods. Analysis of carbon fluxes indicate that physically driven outgassing of CO2 predominates in monsoonal upwelling systems but ecological activity may significantly moderate CO2 outgassing in the Arabian Sea interior. 相似文献