首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2120篇
  免费   553篇
  国内免费   166篇
化学   342篇
晶体学   12篇
力学   34篇
综合类   20篇
数学   147篇
物理学   576篇
无线电   1708篇
  2024年   10篇
  2023年   36篇
  2022年   33篇
  2021年   37篇
  2020年   74篇
  2019年   65篇
  2018年   74篇
  2017年   80篇
  2016年   88篇
  2015年   111篇
  2014年   176篇
  2013年   207篇
  2012年   199篇
  2011年   232篇
  2010年   158篇
  2009年   163篇
  2008年   134篇
  2007年   148篇
  2006年   139篇
  2005年   103篇
  2004年   91篇
  2003年   86篇
  2002年   56篇
  2001年   51篇
  2000年   44篇
  1999年   41篇
  1998年   37篇
  1997年   30篇
  1996年   22篇
  1995年   19篇
  1994年   16篇
  1993年   14篇
  1992年   17篇
  1991年   6篇
  1990年   13篇
  1989年   4篇
  1988年   1篇
  1987年   3篇
  1986年   5篇
  1985年   3篇
  1984年   3篇
  1983年   3篇
  1982年   5篇
  1981年   1篇
  1979年   1篇
排序方式: 共有2839条查询结果,搜索用时 15 毫秒
131.
研究了一种基于BCB材料的牺牲层接触平坦化技术,用于红外焦平面阵列Post CMOS工艺之前对读出电路表面的平坦化,以利于微测辐射热计微桥阵列与读出电路的集成。利用该方法成功将2μm的电路表面突起,平坦化为表面起伏56 nm的平面,可替代会给器件带来颗粒和损伤的化学机械抛光(CMP)技术。并在该平坦层上方成功进行了非晶硅敏感薄膜的沉积、微桥结构的图形化以及同时作为牺牲层的BCB的释放。通过实验研究了BCB膜层的厚度与转速、固化温度的关系,实验发现BCB的收缩率随温度小范围变化,约为30%。研究了BCB的等离子刻蚀特性,表明该材料适合用等离子刻蚀的方法进行接触孔的刻蚀和牺牲层释放。最后,利用BCB牺牲层接触平坦化技术成功地在读出电路(ROIC)芯片上制作了160×120面阵的非制冷红外焦平面阵列。  相似文献   
132.
李洵  胡兵  应花山  郭飞 《激光杂志》2007,28(2):33-34
本文介绍了传输线理论和微带线的设计方法和微带线在射频激光器中的具体应用--阻抗匹配网络、微带电容,并给出了有关的实验结果.  相似文献   
133.
134.
We present a self-organised approach for the synthesis of one-dimensional (1D) arrays of supported nanoclusters. By oxidising NiAl surfaces vicinal to the (1 0 0) plane tilted along the crystallographic direction [0 1 0], we produced ordered thin films of θ-Al2O3 that exhibit uniform protrusion stripes propagating uniquely along direction [0 0 1] of the NiAl. These protrusions are preferential centres for nucleation of metal deposited from a vapour; the nanoclusters grown from such metal are aligned and form massive 1D cluster arrays along direction [0 0 1]. The arrays of Co nanoclusters exhibit a diameter as small as 3 nm and length exceeding a micrometer. The results imply prospective applications for which a patterned assembly of nanoclusters is desired.  相似文献   
135.
The organic light‐emitting diode (OLED)‐based sensing platform is gaining momentum due to unique attributes of the compact OLEDs that are used as excitation sources. This paper, however, points to issues related to this sensing platform that will affect many (bio)chemical sensing applications, in particular in photoluminescence (PL)‐based sensors operated in the advantageous time domain, where pulsed OLEDs are utilized. The issues are related to the post‐pulse electroluminescence (EL) profile, i.e., transient EL, which depends on the OLED materials and structure, and to the long‐wavelength tail of the typically broad‐band EL spectrum. Depending on materials and device structure, the transient EL may exhibit spikes peaking at ~100–200 ns and μs‐long tails. As shown, these interfere with the determination of PL decay times (that are related to analyte concentrations) of sensing elements. The results also indicate that the long‐wavelength tail of the EL spectrum contributes to the interfering post‐pulse μs‐long EL tail. Hence, it is shown that the choice of OLED materials, the use of microcavity (μC) OLEDs with tunable, narrower EL bands, and the use of UV OLEDs alleviate these issues, resulting in more reliable data analysis. Furthermore, a 2‐D uniform 2 μm‐pitch microlens array that was previously used for improving light extraction from the OLEDs (J.‐M. Park et al., Optics Express 2011 , 19, A786) is used for directional PL scattering toward the photodetector, which leads to a ~2.1–3.8 fold enhancement of the PL signal. This behavior is shown for oxygen sensing, which is the basis for sensing of bioanalytes such as glucose, lactate, ethanol, cholesterol, and uric acid.  相似文献   
136.
The pad pitch of modern radio frequency integrated circuits is in the order of few tens of micrometers. Connecting a large number of high‐speed I/Os to the outside world with good signal fidelity at low cost is an extremely challenging task. To cope with this requirement, we need reflection‐free transmission lines from an on‐chip pad to on‐board SMA connectors. Such a transmission line is very hard to design due to the difference in on‐chip and on‐board feature size and the requirement for extremely large bandwidth. In this paper, we propose the use of narrow tracks close to chip and wide tracks away from the chip. This narrow‐to‐wide transition in width results in impedance discontinuity. A step change in substrate thickness is utilized to cancel the effect of the width discontinuity, thus achieving a reflection‐free microstrip. To verify the concept, several microstrips were designed on multilayer FR4 PCB without any additional manufacturing steps. The TDR measurements reveal that the impedance variation is less than 3 Ω for a 50 Ω microstrip and S11 better than –9 dB for the frequency range 1 GHz to 6 GHz when the width changes from 165 µm to 940 µm, and substrate thickness changes from 100 µm to 500 µm.  相似文献   
137.
Using the Born expansion of the Green tensor, we consider the spontaneous decay rate of an excited atom placed in the vicinity of a rectangular plate. We discuss the limitations of the commonly used simplifying assumption that the plate extends to infinity in the lateral directions and examine the effects of the atomic dipole moment orientation, atomic position, and plate boundary and thickness on the atomic decay rate. In particular, it is shown that due to the plate finite size, the spontaneous decay may be inhibited even when the atom is situated very close to the surface, and that in the boundary region, the spontaneous decay rate can be strongly modified.  相似文献   
138.
Zhou  Pingheng  Xue  Desheng  Luo  Haiqing  Shi  Huigang 《Hyperfine Interactions》2002,142(3-4):601-606
Highly ordered Prussian blue nanowires with diameter of about 50 nm and length up to 4 m have been fabricated by an electrodepositing technology with two-step anodizing anodic aluminum oxide films. The Mössbauer spectra taken between 15 and 300 K indicate that the hyperfine parameters decrease as the temperature increases. The temperature dependence of the quadrupole splitting, the isomer shift and the spectra area are discussed. A decrease of Debye temperature for Prussian blue nanowires was found with respect to that of Prussian blue bulk.  相似文献   
139.
平面交叉型微透镜阵列的制作及成像特性研究   总被引:6,自引:0,他引:6  
介绍了采用光刻离子交换工艺制作平面交叉型微透镜阵列的方法。利用积分形式的光线方程式讨论了平面交叉型微透镜的近轴光学特性,研究了微透镜的光线轨迹方程式和一些重要的近轴成像特性,利用ABCD定理得到了平面交叉型微透镜像距、焦距、像高、横向放大率和主平面位置的数学表达式,焦距的理论计算结果和实验数据吻合得很好。  相似文献   
140.
Many useful DSP algorithms have high dimensions and complex logic. Consequently, an efficient implementation of these algorithms on parallel processor arrays must involve a structured design methodology. Full-search block-matching motion estimation is one of those algorithms that can be developed using parallel processor arrays. In this paper, we present a hierarchical design methodology for the full-search block matching motion estimation. Our proposed methodology reduces the complexity of the algorithm into simpler steps and then explores the different possible design options at each step. Input data timing restrictions are taken into consideration as well as buffering requirements. A designer is able to modify system performance by selecting some of the algorithm variables for pipelining or broadcasting. Our proposed design strategy also allows the designer to study time and hardware complexities of computations at each level of the hierarchy. The resultant architecture allows easy modifications to the organization of data buffers and processing elements-their number, datapath pipelining, and complexity-to produce a system whose performance matches the video data sample rate requirements.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号