全文获取类型
收费全文 | 6759篇 |
免费 | 820篇 |
国内免费 | 449篇 |
专业分类
电工技术 | 1395篇 |
综合类 | 663篇 |
化学工业 | 793篇 |
金属工艺 | 282篇 |
机械仪表 | 581篇 |
建筑科学 | 360篇 |
矿业工程 | 221篇 |
能源动力 | 242篇 |
轻工业 | 149篇 |
水利工程 | 141篇 |
石油天然气 | 137篇 |
武器工业 | 76篇 |
无线电 | 1197篇 |
一般工业技术 | 659篇 |
冶金工业 | 147篇 |
原子能技术 | 61篇 |
自动化技术 | 924篇 |
出版年
2024年 | 21篇 |
2023年 | 71篇 |
2022年 | 140篇 |
2021年 | 177篇 |
2020年 | 192篇 |
2019年 | 188篇 |
2018年 | 168篇 |
2017年 | 226篇 |
2016年 | 239篇 |
2015年 | 293篇 |
2014年 | 363篇 |
2013年 | 370篇 |
2012年 | 516篇 |
2011年 | 549篇 |
2010年 | 421篇 |
2009年 | 407篇 |
2008年 | 455篇 |
2007年 | 531篇 |
2006年 | 414篇 |
2005年 | 367篇 |
2004年 | 337篇 |
2003年 | 273篇 |
2002年 | 239篇 |
2001年 | 195篇 |
2000年 | 179篇 |
1999年 | 137篇 |
1998年 | 111篇 |
1997年 | 84篇 |
1996年 | 69篇 |
1995年 | 68篇 |
1994年 | 68篇 |
1993年 | 38篇 |
1992年 | 30篇 |
1991年 | 19篇 |
1990年 | 15篇 |
1989年 | 15篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1969年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有8028条查询结果,搜索用时 359 毫秒
1.
Pengfei Liang Jie Zhu Di Wu Hui Peng Xiaolian Chao Zupei Yang 《Journal of the American Ceramic Society》2021,104(6):2702-2710
Due to the demand of miniaturization and integration for ceramic capacitors in electronic components market, TiO2-based ceramics with colossal permittivity has become a research hotspot in recent years. In this work, we report that Ag+/Nb5+ co-doped (Ag1/4Nb3/4)xTi1−xO2 (ANTOx) ceramics with colossal permittivity over a wide frequency and temperature range were successfully prepared by a traditional solid–state method. Notably, compositions of ANTO0.005 and ANTO0.01 respectively exhibit both low dielectric loss (0.040 and 0.050 at 1 kHz), high dielectric permittivity (9.2 × 103 and 1.6 × 104 at 1 kHz), and good thermal stability, which satisfy the requirements for the temperature range of application of X9R and X8R ceramic capacitors, respectively. The origin of the dielectric behavior was attributed to five dielectric relaxation phenomena, i.e., localized carriers' hopping, electron–pinned defect–dipoles, interfacial polarization, and oxygen vacancies ionization and diffusion, as suggested by dielectric temperature spectra and valence state analysis via XPS; wherein, electron-pinned defect–dipoles and internal barrier layer capacitance are believed to be the main causes for the giant dielectric permittivity in ANTOx ceramics. 相似文献
2.
《International Journal of Hydrogen Energy》2022,47(26):12829-12840
In the present work, nitrogen doped hierarchically activated porous carbon (APC) samples have been synthesized via single step scalable method using ethylene di-amine tetra acetic acid (EDTA) as precursor and KOH as activating agent. Activated porous carbons with different pore sizes have been developed by varying the activation temperature. SEM, TEM and SAXS analysis suggest that with variation of activation temperature, a hierarchical porous structure with interconnected meso-pore and micro pores has been achieved. The sufficiently high surface area of the synthesized materials provides active sites to enhance the diffusion of ions between the electrolyte and the carbon electrodes. The electrode prepared at 800 °C activated sample exhibited highest specific capacitance of 274 Fg-1 in two electrode setup, at a current density of 0.1 Ag-1 in 1 M aqueous H2SO4. Along with this, it showed maximum energy density of 9.5 Whkg?1 at a power density of 64.5 Wkg-1. The remarkable electrochemical performance reveals that the synthesized nitrogen doped activated carbon electrodes derived from EDTA can be tuned to have optimum pore structure and pore size distribution for better electrochemical performance, so it can be considered as a potential electrode material for applications in electrochemical energy storage. 相似文献
3.
Numerical simulation, using SILVACO-TCAD, is carried out to explain experimentally observed effects of different types of deep levels on the capacitance–voltage characteristics of p-type Si-doped GaAs Schottky diodes grown on high index GaAs substrates. Two diodes were grown on (311)A and (211)A oriented GaAs substrates using Molecular Beam Epitaxy (MBE). Although, deep levels were observed in both structures, the measured capacitance–voltage characteristics show a negative differential capacitance (NDC) for the (311)A diodes, while the (211)A devices display a usual behaviour. The NDC is related to the nature and spatial distribution of the deep levels, which are characterized by the Deep Level Transient Spectroscopy (DLTS) technique. In the (311)A structure only majority deep levels (hole traps) were observed while both majority and minority deep levels were present in the (211)A diodes. The simulation, which calculates the capacitance–voltage characteristics in the absence and presence of different types of deep levels, agrees well with the experimentally observed behaviour. 相似文献
4.
5.
结合国内外对碳钢CO2腐蚀影响因素的研究成果,采用模糊层次分析法对影响输油管道 CO2腐蚀的因素进行定量分析,明确界定出这些因素对二氧化碳腐蚀影响的相对重要性(权重),为后续制定经济有效的管道内腐蚀防护措施提供了客观依据。 相似文献
6.
7.
醇镁还原法一步制取对氯苯胺是一种新的方法 ,研究发现最佳反应温度为 80℃~ 85℃ ,反应时间为4h ,对氯硝基苯与镁粉的用量 (物质的量比 )为 1∶3,产率为 80 %。 相似文献
8.
基于充放电原理实现的微电容测量电路 总被引:1,自引:0,他引:1
具有抗分布电容以及简单实用等特性的充放电电路是目前微电容测量中广泛采用的一种测量电路。本文对基于充放电原理的微电容测量电路进行了深入研究,并介绍一种基于充放电原理的实用电路。 相似文献
9.
10.
On the basis of the experimental data, we show that the difference between the macroscopic and microscopic fatigue crack growth rates in the second section of the kinetic diagram of fatigue fracture is caused by the effect of crack closure within the limits of its existence. We establish the relationships between the macroscopic and microscopic fatigue crack growth rates and the structure of the material in the second section of the diagram for various values of the load ratio with regard for the effect of crack closure and propose a procedure of examination of the fracture processes in structural materials based on the analysis of microscopic and macroscopic fatigue crack growth rates. 相似文献