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1.
温雅  彭滟  张冬生  陈宏彦  陈麟  朱亦鸣 《中国激光》2012,39(4):406001-133
介绍了在SF6气体环境下由不同脉冲能量的飞秒激光在硅表面蚀刻出的尖峰结构的变化。其中,硅表面形成的尖峰高度先是随脉冲能量的升高而增加,然而当脉冲能量增加到一定程度时,脉冲能量的继续升高却会导致尖峰高度的降低。尖峰高度在开始阶段的增加是由于激光的消融作用;而过高的能量在前几百个脉冲入射后无法穿透到硅材料深处,聚集在硅表面的能量除了引发最外层的硅材料的飞溅,还使次外层的硅一直处于熔融状态,这种状态阻碍了尖峰结构的形成,即使后继能量顺利导入内部,但由于前一部分脉冲对尖峰结构的形成并无贡献,因此表面的尖峰高度反而有所降低。  相似文献   
2.
海上目标随海面颠簸导致姿态变化,引起回波功率调制效应,导致回波多普勒体现时变和非平稳特性.为此,本文将微多普勒理论应用于海杂波中弱目标检测,提出一种基于高斯短时分数阶Fourier变换(GSTFRFT)的海面微动目标检测方法.首先,建立海面目标的平动和三维转动回波模型;然后,基于海尖峰判别方法对回波信号进行数据筛选,改善信杂比,并采用GSTFRFT对微动信号进行增强处理,利用海面目标与海杂波的微动特征差异设计恒虚警检测方法;最后,通过GSTFRFT域滤波,提取信号的微动特征并得到瞬时频率.实测雷达数据仿真结果验证了算法的有效性,具有在强海杂波中检测微弱目标的能力.  相似文献   
3.
详细分析了ZVS移相全桥变换器中电压电流尖峰的产生机理和抑制方法。在此基础上分别设计了电压、电流尖峰抑制电路,给出了详细的参数计算过程,并在一台3 kW(15 V/200 A)ZVS移相全桥变换器上得到验证,电压、电流尖峰和EMI抑制效果明显。最后,给出了改进前后的对比波形。  相似文献   
4.
利用自行研制的磁性液体进行艺术字字模、展示台、磁铁升降系统、电动机传动装置、电气控制部分等的设计和加工,并且利用磁性液体场致界面不稳定性,研制出磁性液体艺术字展示装置。将该装置接通电源后,在磁场作用下4个艺术汉字将依次瞬间动态呈现。在呈现过程中,磁性液体逐渐突起的尖峰个数、高度、间距均与永磁场之间存在规律性的变化,这种变化规律将启示观察者进一步研究神奇液体材料的结构组成,为深入研究场致磁性液体界面不稳定性奠定基础。  相似文献   
5.
The dependence of the sputtering yield on the incident angle, Θ, is determined using molecular dynamics (MD) simulations for a cylindrical track produced by a fast ion. For a ‘small' spike radius and for the mean energy in the track, Eexc, smaller than the binding energy, U, a (cosΘ)−1.7 dependence is found, close to the linear collision cascade (LCC) result and to some thermal spike models. On the other hand, when Eexc>U, the incident angle dependence is (cosΘ)−1. For a larger spike radius we obtain a (cosΘ)−1.6 dependence for both high and low energy densities. Analytic spike models based on diffusive transport are shown not to give satisfactory results. In addition, at low energy densities we see correlated atom ejection ignored in analytic models. Applying the MD results to the experimental data for electronic sputtering of solid O2 at large excitation densities suggests that the effective spike radius is larger than the initial Bohr adiabatic radius indicating that energy is rapidly transported from the initially narrow track.  相似文献   
6.
热峰效应发生在离子束注入及激光表面材料处理过程中.引进了δ函数来描述热峰在离子溅射中的效应,从经典的热传导方程出发,对球形热峰效应及圆柱形热峰效应作了特别讨论,发现不同形状的热峰在材料处理过程中会引起不同程度的非线性效应  相似文献   
7.
The interaction of molten metal drop and coolant is numerically analyzed to investigate the mechanism of fragmentation in vapor explosion. The numerical study is carried out by using a developed simulation code based on multi-phase thermal hydraulic model, which includes physical phenomena required for the analysis: heat transfer, mass change, liquid evaporation and treatment of surface. Several computational techniques are also implemented to improve the efficiency and stability of the numerical scheme. The obtained numerical results show that the growth of spikes on the molten metal drop surface is similar to that observed in Ciccarelli's experiment. The numerical study suggests that quick growth of spikes is the essential mechanism of fragmentation, which is caused by Taylor instability.  相似文献   
8.
通过求解量子系统的密度矩阵方程 ,采用迭代法计算了在 TEA CO2 - 1 0 R(6)泵浦下 ,小型脉冲光泵 NH3分子远红外激光器中 ,NH3分子的 V2 :a→ s R(0 ,0 )跃迁和 a→s Q(5,4)跃迁的频谱特性。理论计算结果表明 ,对于 a→ s R(0 ,0 )跃迁 ,当工作气压比临界值 Pc高或泵功率密度比临界值 Ipoc低时 ,将出现 Raman频谱尖峰 ;对于 a→ s Q(5,4)跃迁 ,不出现频谱尖峰。频谱尖峰现象的根源是 AC Stark分裂的双光子相互作用的结果。  相似文献   
9.
Ion beam mixing has been studied since 1980, and since then a lot of experimental and theoretical work has been done and knowledge has been gathered. Nevertheless, there are still many fundamental aspects that need to be clarified and with that aim many experiments need to be performed. Copper and iron are miscible in the liquid state, while silver and iron are not. However, both systems are thermally immiscible in the solid state. In order to have an insight into the importance of mixing within thermal spikes during ion beam irradiation, we deposited Cu/Fe and Ag/Fe bilayers onto Si substrates and irradiated them at room temperature with 2 MeV Cu and 2.5 MeV Au ions. A combination of Rutherford backscattering spectrometry (RBS) and atomic force microscopy (AFM) was used to analyze the atomic transport at the interface and the morphology changes of the samples. From the element profiles at the interface we conclude a mixing efficiency, which is indeed larger than the prediction of the ballistic model in the Cu/Fe system and smaller in the Ag/Fe system. Since ballistic mixing is expected in any case, we argue that demixing and phase separation in the Ag/Fe system occur in the thermal spike phase of the cascade as a consequence of the positive heat of mixing. Further mixing does occur in the thermal spike in the Cu/Fe system and they remain mixed even at the solid state because of the high cooling rate. In addition, ion irradiation induces a large surface roughening of the Ag and Cu top layers as proven by AFM. This effect is important for the correct interpretation of the results. Furthermore, this recrystallization affects also the interface, producing a rough interface, that appears in the RBS spectra as an atomic ‘diffusion’ at the interface.  相似文献   
10.
The assembly modes of dragonfly wings are observed through FEG-ESEM. Different from airplane wings, dragonfly wings are found to be assembled through smooth transition mode and global package mode. First, at the vein/membrane conjunctive site, the membrane is divided into upper and lower portions from the center layer and transited smoothly to the vein. Then the two portions pack the vein around and form the outer surface of the vein. Second, at the vein/spike conjunctive site, the vein and spike are connected smoothly into a triplet. Last, at the vein/membrane/spike conjunctive site, the membrane (i.e., the outer layer of the vein) transits smoothly to the spike, packs it around, and forms its outer layer. In short, the membrane looks like a closed coat packing the wing as a whole. The smooth transition mode and the global package mode are universal assembly modes in dragonfly wings. They provide us the references for better understanding of the functions of dragonfly wings and the bionic manufactures of the wings of flights with mini sizes.  相似文献   
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