全文获取类型
收费全文 | 2477篇 |
免费 | 402篇 |
国内免费 | 272篇 |
专业分类
电工技术 | 543篇 |
综合类 | 246篇 |
化学工业 | 256篇 |
金属工艺 | 137篇 |
机械仪表 | 266篇 |
建筑科学 | 204篇 |
矿业工程 | 33篇 |
能源动力 | 68篇 |
轻工业 | 37篇 |
水利工程 | 38篇 |
石油天然气 | 23篇 |
武器工业 | 12篇 |
无线电 | 550篇 |
一般工业技术 | 402篇 |
冶金工业 | 40篇 |
原子能技术 | 22篇 |
自动化技术 | 274篇 |
出版年
2024年 | 9篇 |
2023年 | 41篇 |
2022年 | 67篇 |
2021年 | 96篇 |
2020年 | 90篇 |
2019年 | 82篇 |
2018年 | 85篇 |
2017年 | 113篇 |
2016年 | 118篇 |
2015年 | 135篇 |
2014年 | 182篇 |
2013年 | 209篇 |
2012年 | 199篇 |
2011年 | 207篇 |
2010年 | 149篇 |
2009年 | 164篇 |
2008年 | 147篇 |
2007年 | 167篇 |
2006年 | 147篇 |
2005年 | 114篇 |
2004年 | 92篇 |
2003年 | 79篇 |
2002年 | 69篇 |
2001年 | 63篇 |
2000年 | 54篇 |
1999年 | 33篇 |
1998年 | 37篇 |
1997年 | 35篇 |
1996年 | 29篇 |
1995年 | 12篇 |
1994年 | 22篇 |
1993年 | 17篇 |
1992年 | 21篇 |
1991年 | 24篇 |
1990年 | 8篇 |
1989年 | 12篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有3151条查询结果,搜索用时 15 毫秒
1.
《Ceramics International》2020,46(7):8675-8681
The dielectric properties and bipolar polarization-electric field (P-E) and strain-electric field (S-E) dynamic hysteresis of a relaxor [001]c 0.73Pb(Mg1/3Nb2/3)O3-0.27PbTiO3 (PMN-0.27PT) single crystal were investigated to reveal more details of the temperature-induced phase transitions. Different linear scaling relations for ferroelectric hysteresis area <A>, coercive field Ec, saturation polarization Ps and remnant polarization Pr versus temperature τ were measured in different temperature regions. For each measurement frequency f, all hysteresis parameters were found to decrease linearly with temperature in the temperature range of the single rhombohedral (R) phase or tetragonal (T) phase, and the rate of decrease in the T phase was observed to be much larger than the corresponding rate in the R phase. In the temperature range near the R-T phase transition, the exponent α in the power law <A>∝f α for the R phase was found to be smaller than that for the T phase, and the magnitude of α depended strongly on temperature when the crystal was in the R-T coexisting phase state. Our experimental and theoretical results indicate that the difference in the activation energy and dipole moment in the R and T phases may lead to the observed discrepancy for the P-E and S-E hysteresis behaviour in different temperature regions. 相似文献
2.
压电驱动器迟滞特性的Preisach模型研究 总被引:15,自引:2,他引:13
压电驱动器的迟滞特性是影响其位移输出精度的主要因素。该文采用改进的Preisach模型对压电驱动器的迟滞特性进行建模,并进行了相应的实验研究。实验结果表明该模型可以很好地预测压电驱动器在经过一定的控制电压序列以后的位移输出值.能够有效地降低迟滞特性对压电驱动器位移输出精度的影响。 相似文献
3.
4.
The magnetic properties of polyethersulfone-matrix composites with 3-19 vol.% polycrystalline nickel filaments (0.4 (im diam)
were investigated. These filaments were found to exhibit hysteresis energy loss 10800 J/m3 of nickel and coercive force 16.9 kA/m, compared to corresponding values of 4930 J/m3 and 4.7 kA/m for 2 μ.m diam polycrystalline nickel fibers, 1020 J/m3 and 0.5 kA/m for 20 μm diam polycrystalline nickel fibers, and 1280 J/m3 and 2.3 kA/m for solid polycrystalline nickel. 相似文献
5.
ADT14是一种可编程温度监控器电路,可广泛应用于各种控制系统中进行温度检测和控制。用ADT14设计的新型电子温控器具有结构简单,安装方便,温控准确等优点。 相似文献
6.
7.
本文叙述了作者设计并制作的具有多种告警和保护功能的380V交流自动调压器的控制装置。它可使调压精度提高到工作电压的士1%以内,并在自动调压器输出电压过高或过低时、或出现故障时进行告警。当出现故障或误动作时自动切断调压电动机的电源。 相似文献
8.
基于变轴力和定轴力试验对比的钢筋混凝土柱恢复力滞回特性研究 总被引:6,自引:1,他引:5
在讨论了框架柱在地震作用下轴力变化规律的基础上,通过由变轴力柱和定轴力柱的低周交变加载试验获得的恢复力滞回曲线对比,给出了用各个“轴力变化半周”的“等效滞回轴力”修正恢复力骨架曲线,和用“等效累积滞回轴力”随时间步长调整累积强度退化系数从而修正恢复力滞回曲线的再加载刚度的建议。该建议能更有效、更方便地反映轴力变化的整个历程对变轴力柱恢复特征的影响,有利于提高钢筋混凝土杆系结构非弹性地震反应分析的有效性。 相似文献
9.
Investigation into the magnets with different squareness of hysteresis loop (SHL) reveals that the microstructure of sintered NdFeB magnets has great effects on the SHL of the magnets. The abnormal grain growth deteriorates the SHL seriously. The shape of the grain and the grain boundary affect the intensity of demagnetization field, and consequently on the SHL. The added elements have effects on the phase structures and distributions in the magnets, which influences the uniform of demagnetization field. 相似文献
10.
Magnetization measurements were carried out on bulk Tl2Ba2CaCu2O8 (referred to as Tl-2212) and on various site-selective substituted Tl-2212 samples. At 5K between 0 and 4.5 T, the 5 at.
% Mg-doped Tl-2212 (Tl,Mg-2212) samples displayed enhanced pinning as demonstrated by a field dependent increase of the magnetic
critical-current density Jc by 18 to 25 percent over that of pristine Tl-2212. Excess Mg (10–15 at. %), however, is deleterious. Rietveld refinement
of the x-ray diffraction pattern showed Mg on the Tl sites. Auger electron spectroscopy analysis showed part of the Mg on
grain boundaries. The flux-creep activation energies are higher for flux expulsion than for flux penetration in both Tl-2212
and Tl,Mg-2212 samples; the latter displays higher individual values. Our results demonstrate an increase in the number density
of flux lines as a result of increased density of atomic-size-structural, defects by Mg (5 at. %) doping. In the Tl2−yBa2(Ca1−zYz)Cu2O8−x(z=0–0.3; single phase; x and y represent oxygen and thallium vacancies) system also studied, the Tc decreases as z increases. At z=0.3, the sample becomes an antiferromagnetic semiconductor. 相似文献