全文获取类型
收费全文 | 2642篇 |
免费 | 0篇 |
专业分类
公路运输 | 422篇 |
综合类 | 685篇 |
水路运输 | 924篇 |
铁路运输 | 27篇 |
综合运输 | 584篇 |
出版年
2022年 | 13篇 |
2021年 | 4篇 |
2020年 | 8篇 |
2019年 | 14篇 |
2018年 | 350篇 |
2017年 | 302篇 |
2016年 | 270篇 |
2015年 | 11篇 |
2014年 | 29篇 |
2013年 | 145篇 |
2012年 | 85篇 |
2011年 | 241篇 |
2010年 | 248篇 |
2009年 | 81篇 |
2008年 | 203篇 |
2007年 | 139篇 |
2006年 | 18篇 |
2005年 | 62篇 |
2004年 | 54篇 |
2003年 | 63篇 |
2002年 | 34篇 |
2001年 | 10篇 |
2000年 | 14篇 |
1999年 | 8篇 |
1998年 | 15篇 |
1997年 | 8篇 |
1996年 | 17篇 |
1995年 | 11篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 10篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 12篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 5篇 |
1981年 | 16篇 |
1980年 | 8篇 |
1979年 | 17篇 |
1978年 | 6篇 |
1977年 | 10篇 |
1976年 | 9篇 |
1975年 | 5篇 |
1974年 | 8篇 |
1973年 | 10篇 |
排序方式: 共有2642条查询结果,搜索用时 15 毫秒
1.
The Straits of Malacca and Singapore are an important trade route linking the Indian Ocean to the South China Sea and Pacific Ocean. They are also rich in resources and support a range of activities that benefit the economies of the littoral states (Indonesia, Malaysia and Singapore). This important shipping route is a very congested waterway and the authorities are keen to improve navigation facilities to promote ship safety and reduce the risk of groundings, collisions and accidents. This will also help to protect the marine environment from the effects of pollution and hence reduce its damaging impact on activities related to the Straits, e.g. fisheries and tourism. The Marine Electronic Highway (MEH) is an attempt to bring together maritime safety technologies and environmental management systems. The paper examines the costs of providing such a highway and considers some of the benefits which could accrue from its implementation. The analysis, conducted in the form of a cost-benefit study, clearly shows the economic viability of the scheme. 相似文献
2.
The shipping industry in Nigeria since the early 1990s has been experiencing a continuous disastrous downturn. Nigerian shipping companies' participation in international shipping has continued to be very limited. Their presence and impact is hardly felt in the world's shipping industry. Both the national carriers (that is shipping companies with national carrier status) and other indigenous private shipping companies have vessel as well as management problems. These problems have led to the poor performance of the Nigerian shipping industry for over a decade now. The carriers in the industry are not attaining for the country the gains that are supposed to emanate from shipping. This paper points out the importance of shipping to a nation, identifies the problems the country's shipping companies are facing and proffers solutions that include merging of the companies to have strong financial standing and a competitive edge. 相似文献
3.
The rate equations and the power evolution equations based on excited state absorption (ESA) and cooperative upconversion (CUC) of high concentration erbium-doped yttrium aluminum garnet (YAG) transparent ceramic waveguide amplifier are set up to analyze the effects of the pump power, active ion concentration and waveguide length on the amplifier gain and noise figure (NF). The numerical analysis predicts that with a pump power of 100mW, an active ion concentration of 1.0×1026 ion/m3 and a waveguide length of 3 cm, a small-signal gain of 30 dB and an NF of 5 dB can be achieved in the micro-chip amplifier. 相似文献
4.
Robert Warren 《Coastal management》2013,41(1-2):119-125
This article reviews the history of esthetics and its role in the development of outdoor recreation policy. Current research is also reviewed, demonstrating the broad scope and complexity of esthetics as a focus for research. Finally, in the absence of sufficient research for formulating coastal recreation planning and management decisions, the ethics of coastal recreation “development”; is considered. 相似文献
5.
6.
Robert A. Kagan 《Coastal management》2013,41(3):313-341
Abstract Seaport expansion often generates tensions between the national interest in efficient transport and local interests in water quality and habitat preservation. The governing American permitting system, however, establishes an extraordinarily cumbersome, legalistic, and costly method for balancing environmental and economic considerations. A case study of the Port of Oakland illustrates the tendency. For four years, plans to find an environmentally acceptable site for dredged material have been stymied by a sequence of inconclusive regulatory and judicial proceedings. Meanwhile, large container ships can enter and leave Oakland harbor only at high tide, and not fully loaded. Despite the absence of any authoritative determination concerning environmental risks, the port was compelled to accede to progressively more expensive disposal methods. Such “adversarial legalism”; is not unique to the Oakland harbor case, but recurs in other policy spheres. It stems from a governmental structure that fragments decision‐making power among many agencies, that constrains regulatory discretion with legal demands for scientific certainty, and that by allowing agency decisions to be challenged readily in court, encourages legalistic defensiveness and extortion rather than compromise. The article concludes with a discussion of the conditions under which regional planning bodies might overcome these centrifugal tendencies. 相似文献
7.
CAI Cheng-tao ZHU Qi-dan YAN Yong-jie 《船舶与海洋工程学报》2005,4(4):43-46
Helicopter blade running elevation measurement is an important measure target in helicopter blade dynamic balance experimentation. The elevation influences the helicopter' s security and other performance capabilities. In testing, however, it has been difficult to measure the elevation when the rotor reaches high speeds. To get a simple, fast and highly accurate measurement system, photo electricity technology was applied to measuring the blade running elevation. Discussed is the measurement principle of blade running elevation, tire design of the measurement system and analysis of the measurement precision. 相似文献
8.
Traditional liner carriers, operating in the highly competitive commercial environment of the last few years, have attempted to lower the marginal cost of each box carried. Technological improvements in both construction and propulsion systems have led to a steady growth in carrying capacity. Ships of 600+ TEUs are now in service and, as a result of this trend, have displaced 'smaller' ships from the major east-west trades. The more competitive environment of these trades has in turn led to a redeployment of ships in the 2500+ TEU range to the north-south trades. The result has been a rapid increase in north-south capacity, including feeder services and falling freight rates. Despite the current excess supply in shipping and historically low freight rates, significant developments in technology have created opportunities for new fast containerships. The paper analyses the key economic factors in the differentiation of the new fast ship technology from the traditionally designed containerships and demonstrates the potential financial viability to owners of these new 'greyhounds'. 相似文献
9.
HANBing ZHAOGuo-liang 《船舶与海洋工程学报》2004,3(1):24-27
The course-keeping control of underactuated hovercraft with two aft propellers was considered. The control of the heading error and cross-track error was accomplished by the yaw torque merely in this case. The hovercraft dynamic model is nonlinear and underactuated. At first the Controllability of course-keeping control for hovercraft was proved, then a course-keeping control law was derived that keeps hovercraft heading constant as well as minimizes the lateral movement of hovercraft. The proposed law guarantees heading error and sway error all converge to zero exponentially. Simulation tests were carried out to illustrate the effectiveness of the proposed control law. For further research, the disturbance influence would be considered in the dynamic equations. 相似文献
10.
ZHANGJun-an XUEKai ZHANGJia-tai ZHANGQiang 《船舶与海洋工程学报》2004,3(1):87-90
At present ESG (Electrostatic Suspended Gyro) is the most precise inertia element in the world. The electrode bowl, which has direct effect on the precision of ESG, is a key part to ESG. Through the analysis of the function and characteristic of the electrode bowl in hollow rotor ESG and the present situation of new material development in the world, the alumina ceramic is regarded as the best material for the electrode bowl of hollow rotor ESG. By analyzing the present situation of alumina ceramic in the world, main technique requirements have been put forward for the alumina ceramic of ESG electrode bowl which is also fit for solid rotor ESG. 相似文献