全文获取类型
收费全文 | 3594篇 |
免费 | 1814篇 |
国内免费 | 376篇 |
专业分类
化学 | 291篇 |
晶体学 | 40篇 |
力学 | 470篇 |
综合类 | 96篇 |
数学 | 199篇 |
物理学 | 4688篇 |
出版年
2024年 | 54篇 |
2023年 | 121篇 |
2022年 | 119篇 |
2021年 | 142篇 |
2020年 | 93篇 |
2019年 | 137篇 |
2018年 | 85篇 |
2017年 | 135篇 |
2016年 | 160篇 |
2015年 | 160篇 |
2014年 | 415篇 |
2013年 | 279篇 |
2012年 | 294篇 |
2011年 | 307篇 |
2010年 | 313篇 |
2009年 | 324篇 |
2008年 | 343篇 |
2007年 | 275篇 |
2006年 | 263篇 |
2005年 | 239篇 |
2004年 | 246篇 |
2003年 | 195篇 |
2002年 | 137篇 |
2001年 | 133篇 |
2000年 | 109篇 |
1999年 | 92篇 |
1998年 | 85篇 |
1997年 | 90篇 |
1996年 | 71篇 |
1995年 | 52篇 |
1994年 | 51篇 |
1993年 | 38篇 |
1992年 | 48篇 |
1991年 | 43篇 |
1990年 | 39篇 |
1989年 | 29篇 |
1988年 | 18篇 |
1987年 | 14篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1979年 | 1篇 |
排序方式: 共有5784条查询结果,搜索用时 15 毫秒
931.
采用超精密车削技术加工微尺度正弦波调制曲面微结构,解决了尖刃金刚石刀具刃磨和刀具对中等关键技术,研究了进给量、背吃刀量和主轴转速等主要切削参数对铜模板表面粗糙度的影响规律。加工出波长为(20~150)m0.5 m﹑峰谷高度差为(0.2~20)m0.1 m的带正弦波调制曲面。采用原子力显微镜对模板表面轮廓扫描,在20 m20 m的范围内,其表面粗糙度均方根值小于10 nm。将正弦波调制曲面测量结果与理论轮廓进行比较,采用最小二乘寻优算法评定轮廓误差。完成了曲面轮廓的功率谱表征,利用加工的曲面微结构制备了平面调制靶,实现正弦波调制曲面轮廓的精确转移。 相似文献
932.
933.
基于交叉相位调制制备四光子偏振纠缠态及其在隐形传态上的运用 总被引:1,自引:1,他引:0
利用克尔介质、偏振分束器、半波片和对强相干探测场的零拍探测,呈现了一个关于制备四光子偏振Diche态、GHZ态和W态的方案,当前量子光学实验技术条件均能有效满足该方案的要求.强的探测模相继和多个信号模光子相互作用,每次对于探测模而言,都会产生一个相位旋转.接下来,对探测模利用零拍探测,信号模可以投影得到想要的光子偏振纠缠态.此外,为了展现所制备的纠缠态作为重要的量子信息资源的价值,基于交叉相位调制进一步提出了一个隐形传送三光子偏振纠缠态的实验方案. 相似文献
934.
935.
1.多普勒效应的概念多普勒效应是奥地利物理学家、数学家克里斯琴·约翰·多普勒于1842年首先提出的。由于波源和观察者之间有相对运动,使观察者感到频率变化的现象叫做多普勒效应.2.多普勒效应的基本原理根据声波的多普勒效应公式,当声源与接收器 相似文献
936.
A temperature independent 80-Gb/s 100-km transmission system is demonstrated with the use of spectral phase modulation-based tunable dispersion compensator (TDC). The principle of dispersion compensation based on spectral phase modulation as well as the relationship between spectral phase modulation function and group velocity dispersion (GVD) are theoretically studied. TDC based on spectral phase modulation is implemented. The performance of 80-Gb/s transmission system is experimentally evaluated. The nonlinear relationship between temperature and temperature-induced dispersion fluctuations is demonstrated through the asymmetric temperature-induced power penalty without dispersion compensation. With respect to the low temperature area, the temperature-induced dispersion fluctuations are smaller than those in the high temperature area. By using the proposed TDC, temperature independent 80-Gb/s transmission is successfully demonstrated under a temperature range of -20 - 60 ?C with a power penalty of less than 0.8 dB. 相似文献
937.
We propose a power spectrum analysis method to directly identify the time delay of a chaotic semiconductorlaser with optical feedback. By measuring the radio frequency (RF) power spectrum of the chaotic laserand performing an inverse Fourier transform, we can easily unveil all the time delay signatures, regardless ofwhether the chaotic output is induced by single or multiple feedback. This method successfully retrieves thetwo time delay signatures from the power spectrum of a semiconductor laser with double-cavity feedback. 相似文献
938.
In order to avoid stimulated Brillouin scattering and smooth the final focal spot that reaches the D-T capsule, spectral broadening is essential. However, the modulation of spectral structure might result in frequency-to-amplitude modulation (FM-to-AM) conversion. The spatial filter pinhole is used to cut off the high-frequency transmission laser, and to ensure the desired pass. Improper parameter of pinhole would lead a negative impact. Using the spatial filter pinhole, we analyze the characteristic of intensity modulation using several pinholes of improper parameters. We then compare these results with the intensity modulation obtained from an experiment. Experimental diagnosis and design of an appropriate pinhole parameter would be highly beneficial to the field of high-power lasers. 相似文献
939.
A 1 064-nm pulsed coherent Doppler lidar (CDL) prototype is developed to measure short range wind speed in the lower altitude troposphere layer. The CDL system adopts an injection-seeded Nd:YAG laser with the pulse duration of 80 ns, single pulse energy of 0.5 mJ, and pulse repetition rate of 200 Hz. Speed calibration experiments are implemented to obtain a speed accuracy of 0.3 m/s using a hard target. Data analysis results show that the CDL system can obtain a line-of-sight wind velocity at a range of 30 to 500 m with the range resolution of 40 m and 38 pulses accumulation. 相似文献
940.
Lock-in phenomenon in ring laser gyroscopes is directly related to effective backscattering,which includes both backscattering and nonuniform loss.Effective backscattering often differs in different states and can only be reflected in a working state via online estimation in the working state.Moreover,effective backscattering can result in the intensity modulation of beams in the opposite directions.The effective backscattering parameters can be obtained by measuring the weak modulations in the intensity signals under different rotation rates and by using the curve-fitting method.This letter demonstrates the online estimation of backscattering. 相似文献