全文获取类型
收费全文 | 390篇 |
免费 | 120篇 |
国内免费 | 43篇 |
专业分类
化学 | 118篇 |
晶体学 | 1篇 |
力学 | 14篇 |
综合类 | 3篇 |
数学 | 9篇 |
物理学 | 184篇 |
无线电 | 224篇 |
出版年
2024年 | 3篇 |
2023年 | 6篇 |
2022年 | 13篇 |
2021年 | 17篇 |
2020年 | 30篇 |
2019年 | 10篇 |
2018年 | 19篇 |
2017年 | 16篇 |
2016年 | 27篇 |
2015年 | 20篇 |
2014年 | 36篇 |
2013年 | 27篇 |
2012年 | 34篇 |
2011年 | 34篇 |
2010年 | 28篇 |
2009年 | 17篇 |
2008年 | 34篇 |
2007年 | 28篇 |
2006年 | 34篇 |
2005年 | 19篇 |
2004年 | 17篇 |
2003年 | 7篇 |
2002年 | 16篇 |
2001年 | 17篇 |
2000年 | 9篇 |
1999年 | 3篇 |
1998年 | 8篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1992年 | 4篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有553条查询结果,搜索用时 171 毫秒
141.
Ki-Change Lee Mitchell A. Winnik Tze-Chi Jao 《Journal of polymer science. Part A, Polymer chemistry》1994,32(12):2333-2344
Submicron and micron sized particles containing a crosslinked core and a polar shell were prepared by 3-stage nonaqueous dispersion [NAD] polymerization in an aliphatic hydrocarbon medium. When a poly (12-hydroxystearic acid) [PHS] comb stabilizer was used in all three stages, the particles produced were spherical, submicron in size, and had a relatively broad size distribution. If the monomer mixture in the third stage contained relatively large amounts of butyl acrylate, stable dispersions of sponge-like aggregates, 3–5 μm in size, were obtained. When butyl rubber was employed as a stabilizer precursor in the seed formation step, the shape of the final particles depended upon whether a crosslinker was employed in the second stage polymerization. When a crosslinker was present, the second-stage particles and the subsequent third-stage particles had a shrunken, raisin-like appearance. When no crosslinker was present, spherical particles were obtained. In both cases, the resulting third-stage particles were easily dispersed in water containing a small amount of amine base, indicating that ? COOH and ? OH groups are located at the surface (or in a shell at the surface) in these NAD particles. © 1994 John Wiley & Sons, Inc. 相似文献
142.
不对称半桥的一种改进电路 总被引:1,自引:0,他引:1
为了实现软开关,设计者经常要在不对称半桥上加一个谐振电感,这就在整流管上产生了很高的谐振电压。文章对该谐振电压的产生进行了理论分析,并给出了消除的方法。 相似文献
143.
提出一种新的抑制离散效应的方法——非对称脉冲对法,并对采用该方法和采用非同步耦合法在基于脉冲对交叉相位调制对脉冲进行压缩过程中,对离散效应影响的抑制效果进行了研究.数值模拟的结果显示:对于峰值功率为10mW、半极大全宽度为5ps的高斯入射脉冲,采用非对称脉冲对法,可以获得压缩比为137、基座能量比为0122、峰值功率为116mW的压缩脉冲.
关键词:
交叉相位调制
离散效应
非同步耦合法
非对称脉冲对法 相似文献
144.
145.
146.
Changjun Peng Jiankang Li Honglai Liu Ying Hu 《Macromolecular theory and simulations》2005,14(3):172-180
Summary: We have performed Monte Carlo simulations to study the bridging of symmetrical or asymmetrical triblock copolymers confined between two similar or different solid surfaces based on a simple lattice model. The influence of the molecular structure, surface separation, adsorption energy, chain composition, and the chain concentration on the fractions of chains with bridge, loop and dangling configurations are reported in detail. The results show that the largest bridging fraction is given only when symmetrical triblock copolymers are confined between two parallel surfaces with the same adsorption energy. The bridge fraction is decreased so long as the asymmetry of the copolymers or the difference between the two surfaces is enhanced. It was found also that the bridging fraction increases as the adsorption energy increases. The bridging fraction Ωbridge under different separations, Lz, can be expressed as in various situations. On the other hand, by introducing a symmetry index ν, the influence of molecular structure of copolymers on the bridges can be illustrated approximately by a relation when the two surfaces are similar and the adsorption energy is not too high. Combining the two expressions, data of the bridge fractions for copolymers of different symmetries confined between surfaces with different separations can be described with a single equation, which, in some occasion, can be used for prediction.
147.
148.
By using the transfer matrix method, within the framework
of the dielectric continuum approximation, uniform forms for the
interface optical (IO) phonon modes as well as the corresponding electron-IO
phonon interaction Hamiltonians in n-layer coupling low-dimensional systems
(including the coupling quantum well (CQW), coupling quantum-well wire
(CQWW), and coupling quantum dot (CQD)) have been presented. Numerical
calculations on the three-layer asymmetrical AlGaAs/GaAs systems are
performed, and the analogous characteristics for limited frequencies of IO phonon in the three types of systems (CQW, CQWW, and CQD) when the
wave-vector and the quantum number approach zero or infinity are analyzed
and specified. 相似文献
149.
本文详细介绍了一种利用微电子加工工艺制作的硅微型两自由度振动轮式陀螺仪的新结构 ,分析了该种陀螺仪的工作原理 ,推导了陀螺仪动力学方程 ,并讨论了梳状谐振器的工作机理和陀螺仪模拟力反馈的闭环控制方案 ;目前已制作完成了该型陀螺仪的原理样机 相似文献
150.
提出一种新型GaAs/GaAlAs子带间光吸收的红外光电导探测机理,利用MOCVD系统进行器件材料的生长,研制了200μm×200μm的台面形式单管,测到了明显的红外光电流信号及阱间共振遂穿效应造成的负阻震荡现象,对器件的性能测试结果表明,器件的光电流响应和信噪比随着阱数增加而增加,器件噪声比常规GaAs/GaAlAs量子阱红外探测器低一个数量级. 相似文献