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761.
杨文莉 《武汉船舶职业技术学院学报》2014,(2):137-139
本研究以问卷调查和访谈相结合的方法,对高职学生的英语课堂交流意愿和学习动机之间的关系进行了调查研究。问卷结果表明:高职学生的课堂英语交流意愿与学习动机存在显著的正相关关系。同时,通过访谈,进一步了解高职学生的课堂英语交流意愿与学习动机。最后,本研究提出建议来提高学生的英语课堂交流意愿。 相似文献
762.
借鉴国际海事组织利用船舶能效营运指数及船舶能效管理计划推动国际航行船舶减少温室气体排放的思想,提出了码头生产能效指数的设想,码头生产能效指数能够有效衡量港口经营人节能工作开展水平,为深入开展码头生产能效指数的研究和未来实施港口能效管理计划奠定了基础。 相似文献
763.
阐述了TRIBON M3船体高级建模中两个最实用的功能,即拓扑点和Free Position建肘板。详细介绍了这两个功能的具体操作过程,对其中的参数作了相应的解释说明,以便同业者更好地应用这些方法,提高生产设计效率。 相似文献
764.
陆大全 《华东交通大学学报》2009,26(1):101-104
基于傅里叶变换的方法,得到了超短脉冲椭圆高斯光束在自由空间中的解析表达式.并通过例子研究了超短脉冲椭圆高斯光束的传输性质.结果表明:在传输过程中,由于横向衍射效应和时空耦合效应,导致了光束边沿的脉冲延迟、椭圆长短轴的交换,及脉冲不同位置处的图样差异等效应. 相似文献
765.
基于完全信息条件下的港口竞争合作静态博弈分析 总被引:2,自引:0,他引:2
在激烈的竞争中,港口采取不同的策略不仅关系到自身的利润获得,同时也对其他港口的利润产生一定程度上的影响.在完全信息条件下构建了港口竞争合作静态博弈模型,寻求该博弈模型的Nash均衡,并且分析了不同参数的变化对该模型结果的影响.研究表明,港口服务替代率是影响港口竞争合作决策的主要因素. 相似文献
766.
Temporal key integrity protocol (TKIP) is a sub-protocol of IEEE 802.11i. TKIP remedies some security flaws in wired equivalent privacy (WEP) protocol. TKIP adds four new algorithms to WEP: a message integrity code (MIC) called Michael, an initialization vector (IV) sequencing discipline, a key mixing function and a re-keying mechanism. The key mixing function, also called temporal key hash, de-correlates the IVs from weak keys. Some cryptographic properties of the substitution box (S-box) used in the key mixing function are investigated in this paper, such as regularity, avalanche effect, differ uniform and linear structure. Moen et al pointed out that there existed a temporal key recovery attack in TKIP key mixing function. In this paper a method is proposed to defend against the attack, and the resulting effect on performance is discussed. 相似文献
767.
In this paper, we study an area localization problem in large scale underwater wireless sensor networks (UWSNs). The limited
bandwidth, the severely impaired channel and the cost of underwater equipment all make the underwater localization problem
very challenging. Exact localization is very difficult for UWSNs in deep underwater environment. We propose a range free method
based on mobile detachable elevator transceiver (DET) and 3D multi-power area localization scheme (3D-MALS) to address the
challenging problem. In the proposed scheme, the ideas of 2D multi-power area localization scheme (2D-ALS) and utilizing DET
are used to achieve the simplicity, location accuracy, scalability and low cost performances. The DET can rise and get down
to broadcast its position. And it is assumed that all the underwater nodes underwater have pressure sensors and know their
z coordinates. We evaluate the performances of 2D-ALS and our proposed 3D-MALS schemes under both ideal and non-ideal channel
propagation conditions, in terms of localization error and localization ratio. The simulation results show that our proposed
scheme is much more efficient than the 2D-ALS. 相似文献
768.
Most existing media access control (MAC) protocols in power line communication (PLC) networks just discard the colliding data
packets when collision occurs. The collision deteriorates throughput and delay performance of system under high traffic conditions.
This article presents a novel media access scheme with fast collision resolution for in-home power line networks. It works
by first recognizing the colliding stations through detecting the inserted unique ID sequence ahead of data packets, then
the source nodes retransmitting their packets immediately after the collision slot. The proposed protocol maintains the benefits
of ALOHA systems. It needs no scheduling overhead and is suitable for bursty sources, such as multimedia data packets. Computer
simulations have demonstrated that this approach can achieve high throughput due to its ability of resolving collisions. 相似文献
769.
Mobile ad hoc networks are often deployed in environments where the nodes of the networks are unattended and have little or
no physical protection against tampering. The nodes of mobile ad hoc networks are thus susceptible to compromise. The networks
are particularly vulnerable to denial of service (DoS) attacks launched through compromised nodes or intruders. In this paper,
we investigated the effects of flooding attacks in network simulation 2 (NS-2) and measured the packet delivery ratio and
packet delay under different flooding frequencies and different numbers of attack nodes. Simulation results show that with
the increase the flooding frequencies and the numbers of attack nodes, network performance drops. But when the frequency of
flooding attacks is greater than a value, the performance decrease gets smooth. Meanwhile the packet delay firstly increases
and then declines to a value of stability at the end. 相似文献
770.