全文获取类型
收费全文 | 5950篇 |
免费 | 131篇 |
专业分类
公路运输 | 1247篇 |
综合类 | 1885篇 |
水路运输 | 1618篇 |
铁路运输 | 851篇 |
综合运输 | 480篇 |
出版年
2024年 | 4篇 |
2023年 | 13篇 |
2022年 | 84篇 |
2021年 | 136篇 |
2020年 | 102篇 |
2019年 | 33篇 |
2018年 | 372篇 |
2017年 | 337篇 |
2016年 | 310篇 |
2015年 | 126篇 |
2014年 | 162篇 |
2013年 | 241篇 |
2012年 | 303篇 |
2011年 | 498篇 |
2010年 | 508篇 |
2009年 | 462篇 |
2008年 | 511篇 |
2007年 | 555篇 |
2006年 | 388篇 |
2005年 | 323篇 |
2004年 | 119篇 |
2003年 | 111篇 |
2002年 | 72篇 |
2001年 | 50篇 |
2000年 | 61篇 |
1999年 | 33篇 |
1998年 | 27篇 |
1997年 | 28篇 |
1996年 | 21篇 |
1995年 | 16篇 |
1994年 | 18篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1986年 | 8篇 |
1984年 | 4篇 |
排序方式: 共有6081条查询结果,搜索用时 265 毫秒
691.
京津高速公路天津东段跨北环铁路立交桥,主跨为78 m的钢桁梁。钢桁梁在引桥上拼装,然后顶推到位。文章介绍临时支架与滑道的构造、导梁的安装以及钢梁顶推、落梁等施工工艺。 相似文献
692.
693.
Hyung Seok Heo Suk Jung Bae Sung Mok Hong Seung Uk Park 《International Journal of Automotive Technology》2018,19(2):221-231
Although fuel cost has been the largest portion of annual operating costs of construction equipment, it is possible to save the energy and reduce cost using fuel economy enhancement technology. In this study, an organic Rankine cycle is applied to an excavator in order to recover waste heat, reproduce it into electrical energy, and consequently reduce the fuel consumption by 10 %. A design process was carried out to develop an exhaust gas superheater that recovers the waste heat from exhaust gas through a composite-dimensional thermal flow analysis. A one-dimensional code was developed to perform a size design for the exhaust gas superheater. The ranges for the major design parameters were determined to satisfy the target of the heat recovery, as well as the pressure drop at both fluid sides. Performance analysis was done through onedimensional design code results, which were compared with three-dimensional CFD analysis. By utilizing a 3D commercial code, the arrangement of the tubes was selected and the working fluid pressure drop was reduced through a detailed layout design. The design procedure was verified by a performance evaluation of the prototype, which yielded only a 7 % tolerance in heat recovery. 相似文献
694.
Research on the coefficient of sound absorption in turbid water 总被引:2,自引:0,他引:2
China’s coastal waters are turbid and the properties of the seabed are complex. This negatively impacts the performance of underwater detection equipment. The properties of sound absorption in turbid water are not well understood. In this paper, the coefficient of sound absorption in turbid water was measured by the reverberation technique. All work was done in a reverberation barrel made of seamless aluminum. First, pure water was poured into the reverberation barrel and its reverberation time measured. Next, various concentrations of turbid water were poured into the barrel and their reverberation time measured. After all data had been gathered, the coefficient of sound absorption in turbid water of different concentrations was calculated. From this we determined a law of sound absorption in turbid water as summarized in the paper. 相似文献
695.
696.
马绍辰 《铁路工程造价管理》2008,23(1):21-25
援外建设项目的概预算编制原理与方法与国内工程项目存在很大差别,此文从援外项目人工综合单价和机械台班单价如何确定2个基础性问题着笔,通过对计算原理的深入分析和举例对比计算,分析出对人工、机械台班单价影响较大的几个因素,进一步说明人工、机械台班单价的确定是以项目现场实地调查为基础的,而设计人员的经验、对项目的理解程度以及施工组织安排的合理性,都可对项目最终造价的控制产生影响。 相似文献
697.
高强度抽取地下水形成地下水漏斗是造成地面沉降的重要原因,地面沉降将严重影响客运专线的安全运行.对首山地下水漏斗区形成的过程,地下水开采的历史、现状和发展趋势进行了分析,评估了漏斗区对附近铁路工程的影响,并提出了治理的意见和措施. 相似文献
698.
699.
本文通过42例移植肾患者的B超检查,根据移植肾术后的体积大小、肾孟积水,肾周积液等,着重讨论了各自的图象特点。认为术后进行B超动态观察,可及时发现移植肾的排异反应及手术合并症的发生,对临床诊断和及时治疗具有重要价值。 相似文献
700.
“Today, the idea of allowing aircraft pilots to operate as they see fit, without any control from the land, is unthinkable. Will the same things apply to ships in twenty to thirty years’ time?”Current maritime pilotage regimes are clearly seen in some quarters as too restrictive and old fashioned. Change is “in the air” and VTS, pilotage, and the relationship between them cannot be immune to it. Subject to the attainment of the appropriate standards by both ships and their crews there is no practical reason why more flexible Vessel Traffic Management cannot be introduced. The required technology is largely available and, with the introduction of AIS, the required dynamic data can be available. Technical problems foreseen are believed capable of solution. The more significant obstacles to implementation are, therefore, largely political, commercial, organisational, and cultural. These issues are discussed in this paper taking into account the viewpoints of major stakeholders. 相似文献