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1.
    
《Fire Safety Journal》1999,33(1):45-56
Real explosions in domestic structures (Rasbash and Stretch, Struct. Eng 1969;47;403–11) and industrial plants (Howard, Loss Prevention 1972;6;68–73) have been analyzed. Deflagration dynamics are solved for enclosures of volumes of 130–8000 m3 for vent release overpressures in the range of 0–0.21 bar, and for different inertia of covers over the venting spaces in the range 0–15 kg/m2. From comparisons of the real explosion data with the modeling of pressure-time behavior during vented gaseous deflagrations according to an earlier lumped parameter theory values of the main parameter, a turbulence factor, χ, are obtained. The results suggest the combustion is highly turbulent for real conditions in domestic structures (turbulence factor χ⩾8 with discharge coefficient μ=0.6) and especially in large-scale enclosures such as a plant, with internal obstacles (turbulence factor χ⩾17). On the basis of the devised effective turbulence factors (the ratio χ/μ) the design procedures for avoiding the development of excessive overpressures during deflagrations, in both domestic and industrial plant, can be improved.  相似文献   
2.
运用LS-DYNA程序将表征钢筋的梁单元和表征混凝土的实体单元通过节点耦合进行钢筋混凝土分离建模,数值模拟Hanchak等关于钢筋混凝土靶的穿甲实验,进一步修正HJC模型的参数,在讨论单元失效删除准则的静水压和主应变2种参数对混凝土拉伸破坏影响的基础上,重点对HJC模型关键字参数中的失效类型参数(FS)进行分析,并研究其对混凝土压实破坏的影响。通过改变弹丸侵彻钢筋混凝土靶时的着靶位置,加深了对钢筋在侵彻过程中作用的认识,同时验证该数值模拟方法可行性。所确定的建模方法及参数进一步用于某大质量卵形弹侵彻钢筋混凝土试验的研究工作。  相似文献   
3.
文中通过试验观察与数值模拟相结合,尝试分析界面波的形成与结构特征.对2024铝开展系列准对称爆炸焊接,获得了界面波结构特征随装药比变化样品,并基于Autodyn软件中的光滑粒子法对铝-铝爆炸焊接斜碰撞过程进行了模拟,获得与试验现象吻合良好的计算结果.结果表明,装药比的提高使得再入射流厚度和界面波长波幅增加,且界面更加连续;装药比的提高对再入射流速度的影响不大;再入射流量的逐渐增多使得基板承受的剪切应力增大,进而导致界面出现平直到波状的渐变.分析得到的铝-铝爆炸焊接界面波特征随装药比的变化规律以及所使用的数值方法为相关分析提供了有用的参考.  相似文献   
4.
    
Passive acoustic wave manipulations are severely constrained by the narrow frequency bandwidth of acoustic metastructures. In this research, an unprecedented type of reconfigurable acoustic metascreen is proposed for broadband manipulations of transmitted acoustic waves. The conceived structure is composed of uniquely designed unit cells producing the modulation of the transmitted phase shift within the full 2π range with an excellent impedance matching with the background medium. By rationally arranging the reconfigurable elements within the metascreen based on the corresponding parameter profile, different phenomena and functionalities can be easily realized. As examples, acoustic focusing and acoustic bending are presented to showcase the performance of the proposed metascreen. We indeed numerically and experimentally demonstrate the ultra-broadband and reconfigurable features of our concept over an astonishing frequency range extending from 3 to 17 kHz, which covers the majority spectrum of the audible range of human hearing. Our work provides a unique and remarkable conceptual design of acoustic metascreen opening a promising and pragmatic route to conceive compact broadband acoustic devices, where wavefront manipulations on broadband sound signals or pulsed signals are required.  相似文献   
5.
    
Landraces are used in breeding programs as a source of resistance and compose a small group of genetic materials accepted under organic seed production. The goal of this study was to evaluate the susceptibility of Brazilian landraces grains to the attack of Sitophilus zeamais. Ten different landraces were subjected to the attack of S. zeamais in choice and no-choice experiments. We evaluated the number of emerged insects and the weight reduction of the damaged grains. The Presidente Amarelo landrace received 4.4 and 5.4 times less insects than Colorado and Cateto in the choice experiment. Also, the Ligeirinho and Presidente Amarelo landrace provided the emergence of 4.2 times less adults than Cateto. The landraces presented different results when submitted to choice and no-choice experiments. However, Cateto grains presented the highest susceptibility to attack in both experiments. Presidente Amarelo, on the other hand, presented the highest resistance to the attack of S. zeamais and so might be considered to be used as a source of resistance in breeding programs.  相似文献   
6.
测量了轻型柴油车在高怠速和低怠速运转的条件下,其尾气烟羽中粒径范围在15nm到30μm的颗粒数量和粒径的分布。利用SMPS和APS测量装置测量尾气烟羽中心线和环境背景条件下的颗粒排放。测量结果表明,测试的柴油车在高怠速运转的条件下会排放出更多的颗粒。然而,在两种怠速条件下,总的颗粒数量浓度由于沉降的作用会随着远离排气管的距离而减少。测量结果还表明,柴油车排放的颗粒主要是粒径小于700nm的颗粒,这些细颗粒比粗颗粒更易长期悬浮于大气中,从而引发局部的颗粒物污染问题。  相似文献   
7.
This paper presents an analysis method, based on MacCormack's technique, for the evaluation of the time domain sensitivity of distributed parameter elements in high-speed circuit networks. Sensitivities can be calculated from electrical and physical parameters of the distributed parameter elements. The proposed method is a direct numerical method of time-space discretization and does not require complicated mathematical deductive process. Therefore, it is very convenient to program this method. It can be applied to sensitivity analysis of general transmission lines in linear or nonlinear circuit networks. The proposed method is second-order-accurate. Numerical experiment is presented to demonstrate its accuracy and efficiency.  相似文献   
8.
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This paper presents an analysis method, based on MacCormack'stechnique, for the evaluation of the time domain sensitivity ofdistributed parameter elements in high-speed circuit networks.Sensitivities can be calculated from electrical and physicalparameters of the distributed parameter elements. The proposedmethod is a direct numerical method of time-space discretization anddoes not require complicated mathematical deductive process.Therefore, it is very convenient to program this method. It can beapplied to sensitivity analysis of general transmission lines inlinear or nonlinear circuit networks. The proposed method issecond-order-accurate. Numerical experiment is presented todemonstrate its accuracy and efficiency.  相似文献   
9.
电磁轨道炮被动式炮口消弧装置的理论分析与优化设计   总被引:1,自引:0,他引:1  
为了研究电磁轨道炮消除炮口电弧的方法,提出了一种新型结构的被动式炮口消弧装置,建立了含有消弧装置的内弹道计算模型。分析了被动式消弧器的两个作用原理,第一个是磁通压缩原理,能够在电枢中产生反向电流,以减小炮口剩余电流; 第二个是续流原理,使系统中残余能量可以从消弧器中释放,而不是经过电弧,从而大大减小炮口弧光。发现消弧器的电气参数必须与发射器的电气参数相匹配才能达到最佳效果,过大或过小的感抗和阻抗都会导致不良消弧状态,最优参数应为较小的电感与稍大的电阻组合。进一步研究了炮口消弧器的工程化设计方法,所提出的结构最适合使用不锈钢材料,能显著降低炮口残余电流和电弧,而初速基本没有减小,该理论分析和设计思路可以为轨道炮消弧器的研究提供参考。  相似文献   
10.
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Active boundary layer flow control and boundary layer manipulation in the channel flow that was based on low temperature plasma were studied by means of a lattice Boltzmann method.Two plasma actuators were placed in a row to obtain the influence rule of their separation distance on the velocity profile at three locations and maximum velocity in the flow field.Two plasma actuators were placed symmetrically inside a channel to examine the effect of channel height and voltage on the velocity profile and flow rate.It was found that the channel height controls the distribution of flow velocity,which affected the flow rate and its direction.Increasing plasma voltage had a negative effect on the flow rate due to the generation of a larger and stronger flow vortex.  相似文献   
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