全文获取类型
收费全文 | 1905篇 |
免费 | 85篇 |
专业分类
公路运输 | 268篇 |
综合类 | 343篇 |
水路运输 | 727篇 |
铁路运输 | 503篇 |
综合运输 | 149篇 |
出版年
2024年 | 2篇 |
2023年 | 14篇 |
2022年 | 38篇 |
2021年 | 43篇 |
2020年 | 56篇 |
2019年 | 30篇 |
2018年 | 15篇 |
2017年 | 46篇 |
2016年 | 41篇 |
2015年 | 50篇 |
2014年 | 169篇 |
2013年 | 89篇 |
2012年 | 165篇 |
2011年 | 159篇 |
2010年 | 138篇 |
2009年 | 139篇 |
2008年 | 121篇 |
2007年 | 167篇 |
2006年 | 166篇 |
2005年 | 98篇 |
2004年 | 56篇 |
2003年 | 29篇 |
2002年 | 30篇 |
2001年 | 30篇 |
2000年 | 13篇 |
1999年 | 6篇 |
1998年 | 11篇 |
1997年 | 9篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 4篇 |
排序方式: 共有1990条查询结果,搜索用时 203 毫秒
991.
992.
本文对九相感应电机接成三相运行时的定子电流进行了理论分析,并利用a n s o f t软件进行了仿真分析。仿真结果验证了理论分析的正确性。 相似文献
993.
为了确保舰船电场防护装置的正常工作,必须对装置中阳极、大轴隔断以及各种异种金属连接处进行防腐绝缘检测。针对这种需要,设计了一种新型绝缘检测设备来进行绝缘检测。设备采用电压测量和电阻测量两种方式进行双重检测,确定被检对象的绝缘程度。经实船检测,测试结果良好。 相似文献
994.
采用传统控制策略对低脉冲逆变装置的交流电流控制器进行设计时,控制器系统带宽通常会接近系统的基波频率,导致系统动态响应变差。提出了一种改进的电流控制策略,通过状态反馈控制的极点配置方法克服了这一难题,从而大大提高线性控制器的增益。电流控制器的设计以离散条件下的线性状态空间设计为原则,可使控制系统的动态响应和稳定性能更加优越,且系统具有更强的鲁棒性。最后,对设计结果进行了仿真。结果表明,基于状态反馈控制规律的极点配置法所设计的电流控制器比传统的PR设计方案具有更好的动态性能。 相似文献
995.
996.
章雨晨 《广东交通职业技术学院学报》2014,(3):86-88
财务分析是一门集理论性与实践性于一体的综合性学科。目前高职院校财务分析课程的教学模式并不利于学生综合素质和创新精神的培养,有必要对其进行改革。因此,如何加强财务分析课程的改革与建设,以培养学生的实际财务分析能力成为目前教学中急需解决的问题。 相似文献
997.
从整车鼓风机电流表现,利用台架标定得到空调系统风量和流道阻力的关系,进而得到整车空调系统鼓风机工作点,为系统的优化和改进提供帮助和借鉴。 相似文献
998.
The galvanic corrosion behaviour of alumiuium 3004 - ∝ brass with different area ratios was studied in the tropical marine atmosphere at Tuticorin harbour over a period of 426 days. The area ratios, viz. AAluminiurn:A∝ brass, studied were 0.125, 0.25, 0.5, 1, 2, 4 and 8. The galvanic corrosion behaviour of the metals was studied in terms of the relative increase in the corrosion rate of aluminium due to galvanic coupling with oc brass, the relative decrease in the corrosion rate of ∝ brass due to galvanic coupling with aluminium, and the susceptibility of aluminium to pitting owing to galvanic coupling with ∝ brass. The galvanic potential and galvanic current of the system were monitored. Pits of different dimensions ranging from mild etchings to perforations were experienced on the borders arid the surfaces of the interface of aluminium in contact with ∝ brass. The corrosion products resulting from galvanic corrosion were analysed using XRD and the pitting on aluminium as a result of galvanic corrosion was highlighted in terms of pit depth, size and density of pit, using a high resolution microscope. The most favourable area ratio of aluminium - ∝ brass in marine atmosphere in terms of gravimetric corrosion rate is 8:1 and the most unfavourable area ratio of aluminium - ∝ brass is 1:4. 相似文献
999.
In the present study an attempt has been made toinvestigate the relationship between the variations in the foulingassemblage and corrosion behaviour of HSLA steel at three coastallocations in the Gulf of Marmar, India, over a period of 24 months.Oyster fouling was dominant in the Tuticorin open sea, whilebarnacles were the major foulants in the Tuticorin harbour andMandapam. The fouling load in the Tuticorin waters was higherwhen compared to the Mandapam waters. The corrosion ratesdecreased progressively with the immersion time at all three testlocations. In the Tuticorin open sea, the corrosion rates were higherwhen compared to the other two locations throughout the studyperiod. The surface of the coupons was characterized by crevicesbeneath the hard foulers in the Tuticorin harbour and Mandapam,whereas in the Tuticorin open sea, the coupons experiencedcrevices of a tunneling nature. The percentage of the loss of thetensile strength increased with time at all the test locations. 相似文献
1000.
This paper proposed a new concept of an adaptable multi-legged skid design for retro-fitting to a remotely-operated vehicle(ROV) during high tidal current underwater pipeline inspection. The sole reliance on propeller-driven propulsion for ROV is replaced with a proposed low cost biomimetic solution in the form of an attachable hexapod walking skid. The advantage of this adaptable walking skid is the high stability in positioning and endurances to strong current on the seabed environment. The computer simulation flow studies using Solidworks Flow Simulation shown that the skid attachment in different compensation postures caused at least four times increase in overall drag, and negative lift forces on the seabed ROV to achieve a better maneuvering and station keeping under the high current condition(from 0.5 m/s to 5.0 m/s). A graphical user interface is designed to interact with the user during robot-in-the-loop testing and kinematics simulation in the pool. 相似文献