全文获取类型
收费全文 | 520篇 |
免费 | 42篇 |
国内免费 | 31篇 |
专业分类
电工技术 | 6篇 |
综合类 | 15篇 |
化学工业 | 192篇 |
金属工艺 | 13篇 |
机械仪表 | 3篇 |
建筑科学 | 11篇 |
矿业工程 | 2篇 |
能源动力 | 17篇 |
轻工业 | 25篇 |
水利工程 | 1篇 |
石油天然气 | 94篇 |
武器工业 | 1篇 |
无线电 | 104篇 |
一般工业技术 | 89篇 |
冶金工业 | 8篇 |
原子能技术 | 4篇 |
自动化技术 | 8篇 |
出版年
2024年 | 1篇 |
2023年 | 20篇 |
2022年 | 15篇 |
2021年 | 28篇 |
2020年 | 19篇 |
2019年 | 19篇 |
2018年 | 15篇 |
2017年 | 27篇 |
2016年 | 16篇 |
2015年 | 21篇 |
2014年 | 34篇 |
2013年 | 39篇 |
2012年 | 30篇 |
2011年 | 33篇 |
2010年 | 22篇 |
2009年 | 17篇 |
2008年 | 26篇 |
2007年 | 27篇 |
2006年 | 31篇 |
2005年 | 19篇 |
2004年 | 18篇 |
2003年 | 10篇 |
2002年 | 13篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 8篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 8篇 |
1995年 | 1篇 |
1994年 | 10篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1985年 | 7篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有593条查询结果,搜索用时 15 毫秒
51.
52.
53.
施主掺杂多晶(Sr,Ba)TiO3微观结构和介电性能的研究 总被引:2,自引:0,他引:2
系统地研究了施主掺杂对多晶SrTiO3(Sr,Ba)TiO3微观结构和介电性能的影响。SEM观察表明:掺杂不同施主,对多晶SrTiO3晶粒生长起着不同的作用。施主掺杂量影响多晶SrTiO3,(Sr,Ba)TiO3晶粒的半导化程度及试样介电特性。 相似文献
54.
Electrical activity and energy levels as well as diffusion properties of nickel in silicon have not yet been reliably established.
In this paper, we investigated the diffusion and the electrical properties of nickel in silicon to confirm that nickel is
electrically active and introduces one acceptor and one donor level by combined measurements of Hall coefficient and DLTS,
and measurements of the distribution of electrically active nickel in various silicon diodes by DLTS. The former experiments
show that bothn- andp- type silicon are compensated by nickel and that nickel introduces an acceptor level ofE
c-0.47 ± 0.04 eV and a donor level ofE
v +0.18 ± 0.02 eV. The concentrations of these two levels are almost identical over the diffusion temperatures from about 800
to 1100° C, indicating that these donor and acceptor levels are due to different charge states of the same nickel center.
In the distribution measurements of electrically active nickel in silicon diodes, we inspected how nickel can be observed
by DLTS. It was found that the nickel diffusion intop- n junction is rather complicated, the distribution profiles of nickel in the vicinity of thep- n junction being markedly influenced by an additional heating at elevated temperatures after the nickel diffusion. This gives
evidence that the difference in silicon devices used in various studies could give rise to different results. 相似文献
55.
56.
57.
采用第一性原理计算了Bi掺杂BaTiO3陶瓷3种不同的晶格缺陷结构,分别为单独的BiBa掺杂缺陷模式(BTB模型),1个BiBa掺杂缺陷与1个VBa钡空位同时存在(BTB1模型),符合化学计量比的BiBa掺杂缺陷与VBa钡空位缺陷模式(BTB2模型)。BTB模型显示缺陷结构是由施主掺杂机制控制的,Bi与周围的O原子形成典型的离子键,Ti 4+被还原成Ti 3+。在BTB1模型中钡空位的存在则影响了Bi在晶格中与O的相互作用,Bi偏离初始的中心位置,与邻近的3个氧原子形成了弱的共价键,而正是由于这些弱的共价键导致缺陷附近的[TiO6]八面体产生较大畸变,削弱了Ti 4+的极化能力,使缺陷附近的[TiO6]八面体极化能力减弱,此时缺陷结构是由Ba2+离子空位补偿机制控制的。而BTB2模型可以看成是BTB模型与BTB1模型的叠加,因此缺陷结构是由施主掺杂机制与Ba2+离子空位补偿机制共同控制的。 相似文献
58.
Takehiro Takahashi Katsuyuki Shizu Kazunori Togashi 《Science and Technology of Advanced Materials》2014,15(3)
A new series of luminescent 1,4-diazatriphenylene (ATP) derivatives with various peripheral donor units, including phenoxazine, 9,9-dimethylacridane and 3-(diphenylamino)carbazole, is synthesized and characterized as thermally activated delayed fluorescence (TADF) emitters. The influence of the donor substituents on the electronic and photophysical properties of the materials is investigated by theoretical calculations and experimental spectroscopic measurements. These ATP-based molecules with donor–acceptor–donor (D–A–D) structures can reduce the singlet–triplet energy gap (0.04–0.26 eV) upon chemical modification of the ATP core, and thus exhibit obvious TADF characteristics in solution and doped thin films. As a demonstration of the potential of these materials, organic light-emitting diodes containing the D–A–D-structured ATP derivatives as emitters are fabricated and tested. External electroluminescence quantum efficiencies above 12% and 8% for green- and sky-blue-emitting devices, respectively, are achieved. 相似文献
59.
Low-frequency and high-frequency Capacitance-Voltage(C-V) curves of Metal-Oxide-Semiconductor Capacitors(MOSC),including electron and hole trapping at the dopant donor and acceptor impurities,are presented to illustrate giant trapping capacitances,from>0.01Cox to>10Cox.Five device and materials parameters are varied for fundamental trapping parameter characterization,and electrical and optical signal processing applications.Parameters include spatially constant concentration of the dopant-donor-impurity electron trap,NDD,the ground state electron trapping energy level depth measured from the conduction band edge, EC—ED,the degeneracy of the trapped electron at the ground state,gD,the device temperature,T,and the gate oxide thickness,xOX. 相似文献
60.
Chlorine auto-doping phenomenon was found for the first time in InP epitaxial growth by using a PCl3/InP/H2 system. Chlorine atoms act as a donor in the epitaxial layer and the carrier concentration is dependent on the facet of InP
substrate. The carrier concentration of the InP layer on ( 111)B facet was over 103 times higher than that on (111)A substrate. 相似文献