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通过TEM、HAADF-STEM和室温拉伸实验开展Al-2.8%Cu-1.35%Li-0.3%Mn-0.11%Zr合金在人工时效和蠕变时效状态下的析出相演化规律和力学性能研究。结果表明,160 ℃时效条件下,人工时效和160 MPa应力时效过程中合金中析出相数量均随时效时间的延长而增多,相同时效时间条件下应力时效状态合金T1相数量较多,但其平均直径减小了约5~15 nm。这主要是因为外加应力增加了合金中的位错密度从而促进析出相析出。T1相在时效析出过程中并未受外加应力的影响而沿某个方向择优析出,无明显的应力位向效应,这可能与T1相具有更大的惯习平面变体上的形核与临界应力值有关。相比于人工时效,应力时效后合金的室温屈服强度和抗拉强度均增加,且在时效初期对屈服强度效果更为显著。 相似文献
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隧道掘进机刀盘在掘进过程中承受高强度冲击载荷,振动十分剧烈,导致关键构件过早损伤失效,有必要在设计阶段研究刀盘系统的振动特性及其参数影响。为此,在已有TBM刀盘系统多自由度耦合动力学模型的基础上,通过求解各阶固有频率和振型,得到各构件的模态能量分布,进一步区分各阶模态振型,识别模态敏感参数,并分析了敏感参数对前10阶频率的影响。研究结果表明,刀盘系统模态振动主要集中在中间阶,且纯扭转振型对应的固有频率为57 Hz;模态能量能够区分各阶振型,且和常规的振型分析结论一致;第2~10阶固有频率主要受小齿轮转动惯量和输入端扭转刚度的影响,且这两个值分别取原始方案的1.1倍和1.3倍时,系统振动特性较稳定。 相似文献
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Xiaogang Wang Ming Yang Junzhou Luo 《Journal of Network and Computer Applications》2013,36(6):1660-1670
Network watermarking schemes have been proposed to trace secret network attack flows transferred through stepping stones as well as anonymous channels. However, most existing network flow watermark detection techniques focus on a fixed sample size of network data to achieve the required accuracy. Irrespective of the uncertainty or information content of successive observations, such detection techniques will result in low efficiency of watermark detection. We herein propose a novel sequential watermark detection model (SWDM) supporting three sequential detectors for efficient traceback of network attack flows. By exploiting the sequential probability ratio test approach, we first propose the intuitive paired-intervals-based optimum watermark detector (POWD) and the single-interval-based optimum watermark detector (SOWD) under the assumption of known parameters of the observed attack flow. We then propose the sequential sign watermark detector (SSWD) that operates on two-level quantized observations for nonparametric watermark detection. Based on our SWDM model, a statistical analysis of sequential detectors, with no assumptions or limitations concerning the distribution of the timing of packets, proves their effectiveness despite traffic timing perturbations. The experiments using a large number of synthetically-generated SSH traffic flows demonstrate that there is a significant advantage in using our sequential watermark detectors based on the proposed SWDM model over the existing fixed sample size watermark detector (FSWD). Compared to the FSWD detector, the POWD detector achieves almost 28% savings in the average number of packets. Especially, given the required probability of detection errors, the SOWD detector and the SSWD detector can achieve almost 47% and 29% savings, respectively, in the average number of required packets, thus resulting in not only guaranteed rates of detection errors but also high efficiency of flow traceback. 相似文献
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The quality of plane layout design of the disc cutters for the full-face rock tunnel boring machine (TBM) directly affects the balance of force distribution on the cutter head during the excavating. Various layout patterns have been adopted in practice during the layout design of the disc cutters. Considering the engineering technical requirements and the corresponding structure design requirements of the cutter head, this study formulates a nonlinear multi-objective mathematical model with multiple constraints for the disc cutters plane layout design, and analyses the characteristics of a multi-spiral layout pattern, a dynamic star layout pattern and a stochastic layout pattern. And then a genetic algorithm is employed to solve a disc cutters’ multi-spiral layout problem, and a cooperative co-evolutionary genetic algorithm (CCGA) is utilized to solve a disc cutters’ star or stochastic layout problems. The emphasis was put on the study of superiority of three different layout patterns. Finally, an instance of the disc cutters’ plane layout design was solved by the proposed methods using three different kinds of layout patterns. Experimental results showed the effectiveness of the method of combining the mathematical model with the algorithms, and the pros and cons of the three layout patterns. 相似文献
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A trust degree based access control in grid environments 总被引:1,自引:0,他引:1
The purpose of grid computing is to enable coordinated resource sharing and support cooperative work between different domains in dynamic grid environments. In order to protect each participant’s privilege and security, a secure and efficient access control is essential. This paper presents a new approach of access mechanism based on trust relationships across domains. A new calculation method of trust in grid is proposed and the difference between intro-domain trust and inter-domain trust is analyzed. In addition, a novel access control framework combined with trust degree is given from this proposal. It is shown to be adaptive for both intro-domain and inter-domain conditions. Hence, a prototype system based on the proposed model is introduced; furthermore, it has been shown as a dynamic and fine-granularity access control method through performance analyses and has also been demonstrated as a suitable system for grid environments. 相似文献
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一种交叉点小缓存CICQ交换机高性能调度算法 总被引:5,自引:1,他引:5
CICQ(combined input crosspoint queued/queuing)结构具有内部无需提速及输入和输出的分组调度可以分布并行执行的优点,使用RR(round robin)算法在高性能交换机设计中具有独特优势.然而,CICQ交换机使用RR算法在非均匀流量下不能达到100%的吞吐率. RR-RR算法在非均匀流量下性能有两个关键因素组成:中央缓存容量大小和输入端长队列未能及时服务导致的服务损失.基于理论分析,提出了一种小缓存高性能调度算法,仿真结果表明,即使在1个信元缓存的情况下新算法在均匀与非均匀流量下均能达到100%吞吐率.新算法仅具有O(1)的复杂度,保持了RR-RR算法简单有效特性,同时克服了RR-RR算法在非均匀流量下的不稳定性. 相似文献
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EPr/TN网可达性分析的冗余并发后继标识 总被引:2,自引:0,他引:2
文中针对EPr/TN网在可达性分析时出现的冗余发后继现象,从产生原因入手,给出一种解决算法,并由此深入这种扩展Petri网固有不完备性,最后提出了改进方法。 相似文献