全文获取类型
收费全文 | 321篇 |
免费 | 74篇 |
国内免费 | 17篇 |
专业分类
电工技术 | 11篇 |
综合类 | 19篇 |
化学工业 | 3篇 |
金属工艺 | 4篇 |
机械仪表 | 17篇 |
建筑科学 | 2篇 |
能源动力 | 3篇 |
武器工业 | 4篇 |
无线电 | 171篇 |
一般工业技术 | 106篇 |
原子能技术 | 1篇 |
自动化技术 | 71篇 |
出版年
2024年 | 9篇 |
2023年 | 22篇 |
2022年 | 19篇 |
2021年 | 22篇 |
2020年 | 31篇 |
2019年 | 58篇 |
2018年 | 23篇 |
2017年 | 29篇 |
2016年 | 23篇 |
2015年 | 23篇 |
2014年 | 24篇 |
2013年 | 55篇 |
2012年 | 12篇 |
2011年 | 22篇 |
2010年 | 11篇 |
2009年 | 11篇 |
2008年 | 7篇 |
2007年 | 6篇 |
2005年 | 4篇 |
2004年 | 1篇 |
排序方式: 共有412条查询结果,搜索用时 187 毫秒
151.
The paper introduces a new alternative towards fabrication of auxetic metamaterials (materials with negative Poisson’s ratio) controlled by geometric transformations. These transformations are derived from the theory of small (infinitesimal) elastic deformation superimposed on finite elastic deformations. By using this theory, a cylindrical region filled with initial deformed foam is transformed through deformation into a cylindrical shell region filled with auxetic metamaterial. As an example, the realization of the seismic cloak device becomes a practical possibility. 相似文献
152.
153.
Ultrathin cells have gained increasing attention due to their potential for reduced weight, reduced cost and increased flexibility. However, the light absorption in ultrathin cells is usually very weak compared to the corresponding bulk cells. To achieve enhanced photon absorption in ultrathin thermophotovoltaic (TPV) cells, this work proposed a film-coupled metamaterial structure made of nanometer-thick gallium antimonide (GaSb) layer sandwiched by a top one-dimensional (1D) metallic grating and a bottom metal film. The spectral normal absorptance of the proposed structure was calculated using the rigorous coupled-wave algorithm (RCWA) and the absorption enhancement was elucidated to be attributed to the excitations of magnetic polariton (MP), surface plasmon polariton (SPP), and Fabry-Perot (FP) resonance. The mechanisms of MP, SPP, and FP were further confirmed by an inductor-capacitor circuit model, dispersion relation, and phase shift, respectively. Effects of grating period, width, spacer thickness, as well as incidence angle were discussed. Moreover, short-circuit current density, open-circuit voltage, output electric power, and conversion efficiency were evaluated for the ultrathin GaSb TPV cell with a film-coupled metamaterial structure. This work will facilitate the development of next-generation low-cost ultrathin infrared TPV cells. 相似文献
154.
Aobo Li Xiaoguang Zhao Guangwu Duan Stephan Anderson Xin Zhang 《Advanced functional materials》2019,29(22)
Diatoms are photosynthetic algae that exist ubiquitously throughout the planet in water environments. Over the preceding decades, the diatom exoskeletons, termed frustules, featuring abundant micro‐ and nanopores, have served as the source material and inspiration for myriad research efforts. In this work, it is demonstrated that frustule‐inspired hierarchical nanostructure designs may be utilized in the fabrication of metamaterial absorbers, thereby realizing a broadband infrared (IR) absorber with excellent performance in terms of absorption. In an effort to investigate the origin of this absorption characteristic, numerical models are developed to study these structures, revealing that the hierarchical organization of the constituent nanoparticulate metamaterial unit cells introduce an additional resonance mode to the device, broadening the absorption spectrum. It is further demonstrated that the resonant peaks shift linearly as a function of inter‐unit‐cell spacing in the metamaterial, which is attributed to the induced collective dipole mode by the nanoparticles. Ultimately, the work herein represents an innovative perspective in terms of the design and fabrication of IR absorbers inspired by naturally occurring biomaterials, offering the potential to lead to advances in metamaterial absorber technology. 相似文献
155.
超材料指的是一些具有人工设计的结构,并呈现出自然材料所不具备的超常物理性质,它能够以一种新奇的方式实现对电磁波的调控。文中理论研究了单缝双环结构超材料太赫兹调制器的调制机理,运用等效电路法及微分方程法求解出调制器的共振频率与调制器本身几何参数的一般数学表达式,并用Matlab 对不同调制频率情况下的几何参数进行了计算。运用CST(microwave studio)对调制器进行了理论模拟,数值模拟结果显示,该调制器频率在0.775 THz,0.95 THz 和1.65 THz 处共振吸收强度分别为70%,65%和68%,该结构调制器可以作为太赫兹波的调制器。 相似文献
156.
157.
158.
超材料是将不同性质的材料按照某种规律组合在一起形成的一种周期材料.由于其对弹性波的传递会产生带隙效应,因此在噪声控制、减振隔振等领域得到重视.本文设计了一种压电超材料,通过压电材料元胞的周期性排列,产生频率带隙,以获得减振效果.结构尺寸及厚度小,可以粘贴在主结构上.首先分析了设计的压电超材料色散特性;其次,利用压电超材料对悬臂梁结构进行了减振研究,分析了若干个元胞组成的压电超材料对梁振动能量的调控,并结合压电片上的电压曲线;最后,研究了分流电路中的电阻值和电感值对压电超材料梁减振特性的影响.提出此类压电超材料的进一步改进方向. 相似文献
159.
除草剂不恰当的处理会导致土壤、水和空气的污染,并且会通过环境进入食物链,影响人体健康。莠去津作为常见的除草剂,在世界范围内的水环境中经常被检测到。目前常用的检测方法主要依赖于大型仪器,一般需要复杂的预处理,并且对操作人员的技能要求较高,难以普及。随着光学材料的发展,太赫兹超材料技术如今已扩展到越来越多的领域,常用于识别物质的细微变化。采用太赫兹光谱技术结合超材料检测低质量浓度莠去津溶液(0,1,10,100,1 000和2 000μg/L),测得的透射谱经过归一化处理以及拟合分析。实验结果表明,利用太赫兹光谱技术结合超材料能够精确检测到1~2 124μg/L的莠去津质量浓度变化,有效提高农药检测的灵敏度。 相似文献
160.
各向异性特异材料界面的反常折射与反射性质 总被引:1,自引:0,他引:1
根据电磁场边界条件和色散关系,理论研究了电磁波从各向同性右手材料向各向异性特异材料入射时的反常折射与反射性质,结果表明,从各向同性右手材料向never cutoff型特异材料入射时,透射波的波矢和坡印廷矢量的反射角具有相反的符号,折射角的幅度随着入射角的增大而增大并趋于一定值;研究了磁导率张量参数对折射角的影响,对于anti-cutoff型特异材料界面,当入射角小于临界角θc时可以发生反常的全反射,而对于always cutoff型特异材料界面总会发生全向全反射。这些电磁性质将在部分聚焦与全向反射镜方面具有潜在的应用价值。 相似文献