全文获取类型
收费全文 | 5212篇 |
免费 | 1322篇 |
国内免费 | 576篇 |
专业分类
化学 | 1586篇 |
晶体学 | 186篇 |
力学 | 73篇 |
综合类 | 41篇 |
数学 | 45篇 |
物理学 | 1989篇 |
无线电 | 3190篇 |
出版年
2024年 | 19篇 |
2023年 | 76篇 |
2022年 | 110篇 |
2021年 | 130篇 |
2020年 | 164篇 |
2019年 | 133篇 |
2018年 | 131篇 |
2017年 | 230篇 |
2016年 | 265篇 |
2015年 | 244篇 |
2014年 | 294篇 |
2013年 | 623篇 |
2012年 | 420篇 |
2011年 | 424篇 |
2010年 | 344篇 |
2009年 | 332篇 |
2008年 | 392篇 |
2007年 | 306篇 |
2006年 | 378篇 |
2005年 | 267篇 |
2004年 | 246篇 |
2003年 | 234篇 |
2002年 | 225篇 |
2001年 | 172篇 |
2000年 | 140篇 |
1999年 | 128篇 |
1998年 | 107篇 |
1997年 | 73篇 |
1996年 | 77篇 |
1995年 | 71篇 |
1994年 | 51篇 |
1993年 | 43篇 |
1992年 | 40篇 |
1991年 | 36篇 |
1990年 | 20篇 |
1989年 | 30篇 |
1988年 | 16篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 20篇 |
1984年 | 18篇 |
1982年 | 15篇 |
1981年 | 11篇 |
1980年 | 4篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 3篇 |
1973年 | 4篇 |
1972年 | 2篇 |
排序方式: 共有7110条查询结果,搜索用时 713 毫秒
1.
Saqib Kamal Arif I. Inamdar Kuan-Ru Chiou Batjargal Sainbileg Muhammad Usman Jenq-Wei Chen Tzuoo-Tsair Luo Michitoshi Hayashi Chen-Hsiung Hung Wen-Feng Liaw Kuang-Lieh Lu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(30):e202103905
The dielectric properties of coordination polymers has been a topic of recent interest, but the role of different functional groups on the dielectric properties of these polymers has not yet been fully addressed. Herein, the effects of electron-donating (R=NH2) and electron-withdrawing (R=NO2) groups on the dielectric behavior of such materials were investigated for two thermally stable and guest-free Zn-based coordination polymers, [Zn(L1)(L2)]n ( 1 ) and [Zn(L1)(L3)]n ( 2 ) [L1=2-(2-pyridyl) benzimidazole (Pbim), L2=5-aminoisophthalate (Aip), and L3=5-nitroisophthalate (Nip)]. The results of dielectric studies of 1 revealed that it possesses a high dielectric constant (κ=65.5 at 1 kHz), while compound 2 displayed an even higher dielectric constant (κ=110.3 at 1 kHz). The electron donating and withdrawing effects of the NH2 and NO2 substituents induce changes in the polarity of the polymers, which is due to the inductive effect from the aryl ring for both NO2 and NH2. Theoretical results from density functional theory (DFT) calculations, which also support the experimental findings, show that both compounds have a distinct electronic behavior with diverse wide bandgaps. The significance of the current work is to provide information about the structure-dielectric property relationships. So, this study promises to pave the way for further research on the effects of different functional groups on coordination polymers on their dielectric properties. 相似文献
2.
Sha Xia Dan Wang Nian-Ke Chen Dong Han Xian-Bin Li Hong-Bo Sun 《Annalen der Physik》2020,532(3):1900318
Defects play a central role in controlling the electronic properties of two-dimensional (2D) materials and realizing the industrialization of 2D electronics. However, the evaluation of charged defects in 2D materials within first-principles calculation is very challenging and has triggered a recent development of the WLZ (Wang, Li, Zhang) extrapolation method. This method lays the foundation of the theoretical evaluation of energies of charged defects in 2D materials within the first-principles framework. Herein, the vital role of defects for advancing 2D electronics is discussed, followed by an introduction of the fundamentals of the WLZ extrapolation method. The ionization energies (IEs) obtained by this method for defects in various 2D semiconductors are then reviewed and summarized. Finally, the unique defect physics in 2D dimensions including the dielectric environment effects, defect ionization process, and carrier transport mechanism captured with the WLZ extrapolation method are presented. As an efficient and reasonable evaluation of charged defects in 2D materials for nanoelectronics and other emerging applications, this work can be of benefit to the community. 相似文献
3.
4.
应用二维器件仿真程序 PISCES- ,对槽栅结构和平面结构器件的特性进行了模拟比较 ,讨论了槽栅结构 MOSFET的沟道电场特征及其对热载流子效应的影响。槽栅结构对抑制短沟道效应和抗热载流子效应是十分有利的 ,而此种结构对热载流子的敏感 ,使器件的亚阈值特性、输出特性变化较大 相似文献
5.
6.
本文回顾了PCB制造常用的环氧树脂及其增强材料的性能和用途。同时,还介绍了代用树脂材料和代用增强材料的最新进展,如改性环氧树脂、无卤树脂、Thermount、PTFE、氰酸酯等,并就其性能进行了探讨。 相似文献
7.
8.
9.
贝克曼Allegra^TM 21R型超高速离心机开机后,操作面板上出现错误代码“28”,离心机不旋转。离心机的电机采用无刷感应驱动,由电机驱动电源模块BSMl0GD60DN2驱动离心机的电机。故障是由于电源模块BSMl0GD60DN2损坏引起的。采用东芝三相桥式IGBT电源模块MG25Q6ES42代替BSMl0GD60DN2,并更换已烧毁的栅极电阻后。开机试验,仪器恢复正常。 相似文献
10.
In this paper the performances of inhomogeneous dielectric slabs as solar light collectors for both illumination and solar energy applications are analysed. 相似文献