全文获取类型
收费全文 | 219篇 |
免费 | 77篇 |
国内免费 | 77篇 |
专业分类
化学 | 158篇 |
晶体学 | 4篇 |
力学 | 6篇 |
综合类 | 9篇 |
数学 | 16篇 |
物理学 | 180篇 |
出版年
2023年 | 3篇 |
2022年 | 3篇 |
2021年 | 8篇 |
2020年 | 13篇 |
2019年 | 5篇 |
2018年 | 7篇 |
2017年 | 16篇 |
2016年 | 15篇 |
2015年 | 12篇 |
2014年 | 24篇 |
2013年 | 28篇 |
2012年 | 30篇 |
2011年 | 28篇 |
2010年 | 20篇 |
2009年 | 18篇 |
2008年 | 16篇 |
2007年 | 19篇 |
2006年 | 20篇 |
2005年 | 12篇 |
2004年 | 18篇 |
2003年 | 18篇 |
2002年 | 5篇 |
2001年 | 11篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1998年 | 4篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
排序方式: 共有373条查询结果,搜索用时 218 毫秒
351.
352.
353.
The electrical characteristics of a 4H-silicon carbide metal-insulator-semiconductor structure with Al2O3 as the gate dielectric 下载免费PDF全文
A 4H-silicon carbide metal-insulator-semiconductor structure with ultra-thin Al2O3 as the gate dielectric, deposited by atomic layer deposition on the epitaxial layer of a 4H-SiC (0001) 80N-/N+ substrate, has been fabricated. The experimental results indicate that the prepared ultra-thin Al2O3 gate dielectric exhibits good physical and electrical characteristics, including a high breakdown electrical field of 25 MV/cm, excellent interface properties (1×1014 cm-2) and low gate-leakage current (IG = 1 × 10-3 A/cm-2@Eox = 8 MV/cm). Analysis of the current conduction mechanism on the deposited Al2O3 gate dielectric was also systematically performed. The confirmed conduction mechanisms consisted of Fowler-Nordheim (FN) tunneling, the Frenkel-Poole mechanism, direct tunneling and Schottky emission, and the dominant current conduction mechanism depends on the applied electrical field. When the gate leakage current mechanism is dominated by FN tunneling, the barrier height of SiC/Al2O3 is 1.4 eV, which can meet the requirements of silicon carbide metal-insulator-semiconductor transistor devices. 相似文献
354.
MU WeiBing GONG Min & CAO Qun School of Physical Science Technology Sichuan University Chengdu China 《中国科学:物理学 力学 天文学(英文版)》2011,(1)
N-type and p-type 6H-SiC metal oxide semiconductor (MOS) capacitor samples are fabricated with a typical method,and the high frequency capacitor voltage (C-V) curves of these samples are measured at temperatures ranging from 293 to 533 K.There exists huge difference between the n-type and p-type samples.Flat-band voltage shift of the n-type sample becomes larger with temperature rising,but that of the p-type sample have very little change.This may be caused by the residual Al in the p-type oxide.Both types ... 相似文献
355.
M.Y. Ho P.S. Khiew D. Isa T.K. Tan W.S. Chiu C.H. Chia 《Current Applied Physics》2014,14(11):1564-1575
In this study, a symmetric electrochemical capacitor was fabricated by adopting a lithium iron phosphate (LiFePO4)-activated carbon (AC) composite as the core electrode material in 1.0 M Na2SO3 and 1.0 M Li2SO4 aqueous electrolyte solutions. The composite electrodes were prepared via a facile mechanical mixing process. The structural properties of the nanocomposite electrodes were characterised by scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) analysis. The electrochemical performances of the prepared composite electrode were studied using cyclic voltammetry (CV), galvanostatic charge–discharge (CD) and electrochemical impedance spectroscopy (EIS). The experimental results reveal that a maximum specific capacitance of 112.41 F/g was obtained a 40 wt% LiFePO4 loading on an AC electrode compared with that of a pure AC electrode (76.24 F/g) in 1 M Na2SO3. The improvement in the capacitive performance of the 40 wt% LiFePO4–AC composite electrode is believed to be attributed to the contribution of the synergistic effect of the electric double layer capacitance (EDLC) of the AC electrode and pseudocapacitance via the intercalation/extraction of H+, OH−, Na+ and SO32− and Li+ ions in LiFePO4 lattices. In contrast, it appears that the incorporation of LiFePO4 into AC electrodes does not increase the charge storage capability when Li2SO4 is used as the electrolyte. This behaviour can be explained by the fact that the electrolyte system containing SO42− only exhibits EDLC in the Fe-based electrodes. Additionally, Li+ ions that have lower conductivity and mobility may lead to poorer charge storage capability compared to Na+ ions. Overall, the results reveal that the AC composite electrodes with 40 wt% LiFePO4 loading on a Na2SO3 neutral electrolyte exhibit high cycling stability and reversibility and thus display great potential for electrochemical capacitor applications. 相似文献
356.
以r_{sl}, r_{f}以及x_{c}为分岔参数,对具有串补电容的单
机无穷大电力系统的失稳振荡问题,运用动态分岔理论进行了研究. 对系统同时出现有3对
纯虚根特征值的一类多参数高余维分岔情况,运用中心流行方法降维后得到约化方程,对此
强非线性约化方程的求解难点,运用多参数稳定性理论、谐波平衡法、归一化技术和Normal
Form方法,得到了系统的解析解. 由分析得知,系统会出现3种Hopf分岔情况、二维环面
情况,以及三维环面分岔解,甚至会出现四维环面,或者更高维的环面分岔. 详细讨论
了系统各种分岔解的稳定性条件和稳定区域,并作了详细的数值分析加以验证. 相似文献
357.
358.
介绍了用电磁波谐振法测量液体相对电容率的方法,解决了可变电容器的准确取值问题,液体相对电容率的实验测量结果与实际标准值符合较好。 相似文献
359.
化学氧化法制备聚苯胺/多壁碳纳米管复合材料(PANI/MWCNT),扫描电镜(SEM)、XRD及IR表征样品结构及形貌,电化学方法测定复合电极循环伏安曲线、恒流充放电曲线及电极交流阻抗.结果表明,PANI/MWCNT电极在1mol/L的Li2SO4溶液中具有较好电容性能,在电流密度为5mA/cm2时,比电容为412F/g.PANI/MWCNT电极较PANI电极有更好的大电流放电能力,50mA/cm2下复合电极的比电容仍达318F/g,为5mA/cm2时该电极比电容的77.2%,而PANI电极的比电容仅为其5mA/cm2时的56.2%.交流阻抗证明碳纳米管降低复合电极的电阻,显著提高大电流放电能力. 相似文献
360.
将MAX相陶瓷通过液相刻蚀等方法移除A原子层可得到与石墨烯(Graphene)类似二维结构的过渡金属碳或氮化物(MXene),是近年来二维材料领域出现的新成员。独特的二维结构与丰富可调的组分使得MXene具有优异的导电与机械性能、高亲水表面与离子传输性能,受到越来越广泛的关注。目前已成功制备出的MXene材料有20余种,研究发现MXene应用于锂离子、非锂离子(如Na+、K+、Mg2+、Ca2+和Al3+)二次电池和电化学超级电容器均表现出优异的性能,是一种很有潜力的电极材料。本文总结对比了MXene材料制备方法,简要概述了MXene材料的电子、电磁与机械性能,重点介绍了MXene在电化学电池与超级电容器储能方面的应用,最后对MXene材料目前存在的主要问题及未来研究与应用前景进行了展望。 相似文献