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   4219篇
  免费   968篇
  国内免费   232篇
化学   666篇
晶体学   103篇
力学   163篇
综合类   34篇
数学   353篇
物理学   4100篇
  2024年   7篇
  2023年   35篇
  2022年   69篇
  2021年   70篇
  2020年   86篇
  2019年   76篇
  2018年   109篇
  2017年   165篇
  2016年   177篇
  2015年   133篇
  2014年   302篇
  2013年   344篇
  2012年   292篇
  2011年   354篇
  2010年   236篇
  2009年   284篇
  2008年   342篇
  2007年   314篇
  2006年   257篇
  2005年   218篇
  2004年   244篇
  2003年   204篇
  2002年   187篇
  2001年   156篇
  2000年   140篇
  1999年   109篇
  1998年   103篇
  1997年   76篇
  1996年   66篇
  1995年   44篇
  1994年   37篇
  1993年   32篇
  1992年   24篇
  1991年   27篇
  1990年   30篇
  1989年   14篇
  1988年   17篇
  1987年   12篇
  1986年   6篇
  1985年   4篇
  1984年   4篇
  1983年   2篇
  1982年   6篇
  1981年   1篇
  1980年   1篇
  1979年   1篇
  1978年   1篇
  1977年   1篇
排序方式: 共有5419条查询结果,搜索用时 9 毫秒
81.
研制了一种在衍射光变图像器件上进行信息存储的新型数字化激光光刻系统。采用空间光调制器作图形自动输入,双远心投影成像系统在光刻记录面上缩微图形。通过光栅干涉光学头对记录面上的微图形进行干涉调制,使微图形上产生干涉条纹,条纹空间频率范围为500-1200lp/mm。在光刻胶干版上的存储实验表明,在衍射光变图像上的单角度存储信息密度大于3.7Mbit/cm^2。改变干涉条纹取向、条纹间隔和需要存储的图形,光刻系统可实现信息的旋转复用存储。上述光刻系统将会在防伪和衍射光变图像器件制造领域有良好应用。  相似文献   
82.
级联长周期光栅光谱特性   总被引:5,自引:0,他引:5  
崔丽萍  吴亚明 《光学学报》2005,25(8):019-1024
利用传输矩阵法分析了级联长周期光栅的光谱特性,讨论了级联处光纤的长度、位置以及包层模损耗系数对级联长周期光栅光谱的影响,并对级联长周期光栅和相移长周期光栅的光谱进行了比较。结果表明两者光谱存级联光纤长度较小或级联位置靠近光栅两端时具有较强的一致性,而在级联处光纤较长并且级联位置在中间时,两者表现出截然不同的光谱特性;在不考虑其他损耗的情况下,如果只改变级联处光纤长度,级联长周期光栅总量守恒;此外,当级联长周期光栅在级联处光纤包层模损耗系数较大时,级联长周期光栅的光谱等效于两个长周期光栅光谱的非相干叠加,从而为长周期光栅增益均衡器的优化设计和制作提供了一个简便有效的方法。  相似文献   
83.
吕丁成  张晓萍 《光学学报》2005,25(8):025-1029
提出了以单轴晶体材料为包层,光轴平行于光栅主轴(z轴)的新型啁啾光纤光栅模型,应用耦合模理论和传输矩阵方法在理论上分析了该类光纤光栅中的电光效应和弹光效应,理论研究发现在包层施加沿光栅轴向的电场和应变场可以改变布拉格波长和反射谱。得到了3种不同单轴晶体为包层时布拉格波长λB和反射光谱随外加电场和应变场变化的曲线。研究结果表明当轴向外加电场从1×107V/m变化到8×107V/m时λB减小0.12nm,当外加应变场从0变化到0.04时,λB减小0.45nm。  相似文献   
84.
用真空镀膜方法制备了含有单个CdS缺陷层的具有不同周期和结构参量的TiO2/SiO2一维光子晶体。用抽运一探测技术研究了CdS缺陷层的双光子吸收(TPA)现象。实验结果表明:一维光子晶体中CdS缺陷层的双光子吸收显著增强。不同周期和结构参量的一维光子晶体中CdS缺陷层的双光子吸收系数不同。双光子吸收的增强来源于由光局域化导致的缺陷层的电场强度的增加。缺陷层电场强度与一维光子晶体的结构有关,如周期,光子带隙的位置与宽度及缺陷模式等因素都会影响缺陷层电场强度。采用四分之一波长的高低折射率介质层和与入射波长匹配的缺陷模可以得到最大的缺陷层电场强度。  相似文献   
85.
Single crystals of pure, Ca2+ and Sr2+ doped NH4Sb3F10 are grown by slow evaporation technique. The effect of dopants on the growth and physicochemical properties also have been investigated and reported for the first time. The grown crystals are characterized with the aid of single crystal X-ray diffractometry to confirm the crystal structure. EDAX studies are done to confirm the presence of dopants in the crystal lattice. The vibrational frequencies of various group ligands in the crystals have been derived from the Fourier transform infrared (FT-IR) spectrum. From the optical absorption spectrum the band gap energy was calculated and it was found to be 5.76, 6.29 and 6.35 eV for pure, Ca2+ and Sr2+ doped NH4Sb3F10 crystals respectively. Thermal stability of the sample has been analysed using TG-DTA analysis. The activation energy of pure, Ca2+ and Sr2+ doped NH4Sb3F10 crystals were calculated from the dc conductivity measurements and it is found to be 0.2728, 0.2816 and 0.3622 eV Experimental results shows improved physicochemical properties when the dopant is added to the pure material.  相似文献   
86.
A theoretical analysis of nano-deep corrugated long-period waveguide gratings on a SU-8 polymer-based channel waveguide with NOA61 optical epoxy coated upper- and lower cladding is presented. The transmission spectra of the gratings show strong rejection bands both at visible (at wavelength region of 450?460 nm) and infra-red (at wavelength region of 1530?1540 nm) regions when a grating period of ?68 μm with optimized grating tooth height is considered. Phase-matching graphs are studied to find the relationship between resonance wavelength and grating period. These results show that the grating parameters significantly affect the characteristics of transmission spectra as well as the resonance wavelength of the grating. Long-period waveguide grating-based band pass filter made by use of same polymer materials are also designed and analyzed. These types of waveguide grating-based filters can widely be used for visible and infra-red wavelength sensing applications.  相似文献   
87.
A new sensor for simultaneous measurement of humidity and temperature is proposed. The sensor consists of Fabry–Perot cavity formed by two identical uniform fiber Bragg gratings. To make the cavity serves as humidity sensor, moisture sensitive polymer, which is polyimide, is coated on the FBG and on the cavity with different thickness. When the sensor is exposed to the relative humidity change, the polyimide will expand and stretch the fiber and induces strain on the FBG and on the cavity. The induced strain alters the grating period, cavity length and effective refractive index of fiber. The simulation results show that the humidity sensitivity and thermal sensitivity are 1.92 pm/%RH and 8.87 pm/°C, respectively, for polyimide coating thickness of 10 μm on the FBG and 15 μm on the cavity.  相似文献   
88.
A fiber Bragg grating (FBG) pickup exploiting Intensity Modulation-Direct Detection (IM-DD) interrogation system was put forward in this paper. The feasibility of detecting the vibration of the guitar was revealed by FFT analysis. There was certain correlation between the FBG pickup and the magnetic pickup. A high signal-to-noise ratio (42.85 dB) was obtained. The FBG pickup has a frequency response range (0–3000 Hz) that is comparable to the reference pickup. The results indicated that the proposed pickup is effective to pick up the vibration. A simple structure design and low-cost interrogation system set-ups were proposed.  相似文献   
89.
An efficient broadband out-coupler on silicon-on-insulator (SOI) with high-index contrast grating (HCG) is proposed. The presence of a silicon-air (high-index contrast) grating on the top silicon layer in SOI allows a strong interaction between the guided mode and the grating. The broadband design of the out-coupler is presented by optimising the various grating parameters. The design analysis and simulation of such an out-coupler is performed with finite difference method. Coupling efficiency of 54% is achieved over an ultra-wide wavelength range from 1500 nm to 1650 nm.  相似文献   
90.
We investigate the roles of different qubit-environment decoherence models on the entanglement trapping of two qubits. By considering three environmental models (the single photonic band gap model, the common photonic band gap model, and the two independent photonic band gaps model), we note that the final values of entanglement trapping are determined by these different models. We also give the conditions of obtaining the larger entanglement trapping by comparing two-qubit entanglement dynamics in different decoherence models. Moreover, the comparison of entanglement trapping between two Bell-like states in the same decoherence model are also carried out.  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