全文获取类型
收费全文 | 411篇 |
免费 | 17篇 |
国内免费 | 48篇 |
专业分类
电工技术 | 38篇 |
综合类 | 30篇 |
化学工业 | 101篇 |
金属工艺 | 77篇 |
机械仪表 | 1篇 |
建筑科学 | 7篇 |
能源动力 | 1篇 |
轻工业 | 2篇 |
石油天然气 | 5篇 |
武器工业 | 2篇 |
无线电 | 53篇 |
一般工业技术 | 105篇 |
冶金工业 | 46篇 |
原子能技术 | 3篇 |
自动化技术 | 5篇 |
出版年
2023年 | 11篇 |
2022年 | 12篇 |
2021年 | 5篇 |
2020年 | 10篇 |
2019年 | 18篇 |
2018年 | 13篇 |
2017年 | 13篇 |
2016年 | 9篇 |
2015年 | 7篇 |
2014年 | 17篇 |
2013年 | 28篇 |
2012年 | 20篇 |
2011年 | 25篇 |
2010年 | 18篇 |
2009年 | 26篇 |
2008年 | 22篇 |
2007年 | 23篇 |
2006年 | 27篇 |
2005年 | 26篇 |
2004年 | 23篇 |
2003年 | 14篇 |
2002年 | 17篇 |
2001年 | 9篇 |
2000年 | 8篇 |
1999年 | 9篇 |
1998年 | 11篇 |
1997年 | 5篇 |
1996年 | 8篇 |
1995年 | 1篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1978年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有476条查询结果,搜索用时 0 毫秒
1.
Grazing incidence reflection absorption Fourier transform infrared (GIRA-FTIR) spectroscopy was used to characterize the ferroelectric behavior of a thin poly(vinylidene fluoride–trifluoroethylene) P(VDF–TrFE) copolymer. The lab-built GIRA-FTIR apparatus allowed the heating and corona poling process to be carried out whilst collecting the GIRA spectra of the thin polymer film. The Curie transition from the ferroelectric to paraelectric phase was confirmed from the abrupt change in intensity of the 849 cm−1 band in the RA-FTIR spectrum. It was found that the Curie temperature dropped dramatically when the film thickness was lowered to below a certain critical value of approximately 100 nm. The switching of the CF2 dipoles in the ferroelectric crystals after applying the external electric field could be determined by monitoring the change in the 849 cm−1 band intensity. For the 600 nm thick P(VDF–TrFE) film, the switching of the dipoles appears to occur almost instantaneously, while the kinetics of dipole switching of the 75 nm thick film were significantly retarded. The repeated switchability of the CF2 dipoles upon the application of a bipolar cyclic electric field was also confirmed. The bistability of the film due to remnant polarization was also confirmed from the absorbance of the 849 cm−1 band after removing the applied voltage during corona poling. 相似文献
2.
通过加入添加剂,制备了晶相单一、结晶度完好、具有较好磁性能的锰锌铁氧体纳米晶,然后研究添加剂对铁氧体晶相、磁性能和居里温度的影响.研究结果表明:添加剂可以使晶体生长更完善,晶粒变大;同时可以改善样品的磁性能,降低居里温度. 相似文献
3.
Yongping PuAuthor VitaeHaidong WuAuthor Vitae Jifeng WeiAuthor Vitae 《Sensors and actuators. A, Physical》2012,173(1):158-162
Nb2O5-doped (1 − x)Ba0.96Ca0.04TiO3-xBiYO3 (where x = 0.01, 0.02, 0.03 and 0.04) lead-free PTC thermistor ceramics were prepared by a conventional solid state reaction method. X-ray diffraction, scanning electron microscope, Agilent E4980A and resistivity-temperature measurement instrument, were used to characteristic the lattice distortion, microstructure, temperature dependence of permittivity and resitivity-temperature dependence. It was revealed that the tetragonality c/a of the perovskite lattice, the microstructure and the Curie temperature changed with the BiYO3 content. In order to decrease the room temperature resistivity, the effect of Nb2O5 on the room temperature resistivity was also studied, and its optimal doping content was finally chosen as 0.2 mol%. The 0.97Ba0.96Ca0.04TiO3-0.03BiYO3-0.002Nb2O5 thermistor ceramic exhibited a low ρRT of 3.98 × 103 Ω cm, a typical PTCR effect of ρmax/ρmin > 103 and a Tc of 153 °C. 相似文献
4.
5.
A series of calcium substituted polycrystalline ferrite ceramics with magnetoplumbite structures were synthesized using perfect
stoichiometric mixtures of oxides with chemical composition, CaAlxCoxFe12−2xO19 (x = 2−5), by standard ceramic technique. The variation in the values ofH
candM
s,which depends on the additive content and the temperature, was studied by means of a vibration magnetometer. The strong variation
observed in coercivity, saturation magnetization and Curie temperature with chemical composition give rise to the possibility
of controlling these properties and hence applying these compounds in the millimeter— microwave range. 相似文献
6.
7.
Hongwei QIN Jifan HU Juan CHEN Hongdong NIU Luming ZHU Zhuo WANG Department of Physics Shandong University Jinan China State Key Laboratory for Crystal Materials Shandong University Jinan China 《材料科学技术学报》2004,(3)
With substitution of La by Tb in (La_(1-x)Tb_x)_(0.67)Sr_(0.33)MnO_3, the room temperature magnetoresistance △R/R_0drops at first, then undergoes an increase near x≈0.1, and finally drops again. The value of room temperaturemagnetoresistance at a field H=12 kOe for (La_(0.9)Tb_(0.1))_(0.67)Sr_(0.33)MnO_3 is -3.56%. The enhancement of the roomtemperature magnetoresistance induced by an appropriate Tb substitution in (La_(1-x)Tb_x)_(0.67)Sr_(0.33)MnO_3 is correlatedwith the shifts of the Curie temperature and metal-insulator temperature to near room temperature. The drop ofthe room temperature magnetoresistance at large Tb doping-contents may be due to its lower T_C and T_(MI) far fromthe room temperature. 相似文献
8.
研究了用稳定元素Mn、Mo、Al和V代替非磁性的Si和Ge对Gd5Ge2Si2化合物的居里温度的影响;并且研究了Gd5(Ge2-xSi2-xM2x)(M=Mn、Mo、Al和V)样品退火处理对居里温度的影响.结果表明少量的合金化元素替代会提高Gd5Ge2Si2化合物的居里温度;退火后居里温度随替代元素的含量变化比退火前更敏感.X射线粉末衍射分析表明少量的合金化元素(Mn、Mo、Al和V)替代不会影响母体Gd5Ge2Si2化合物的晶体结构.对样品的晶态显微组织和表面微结构研究发现退火后组织分布比退火前更均匀。 相似文献
9.
衬底同步加热溅射BST薄膜的研究 总被引:1,自引:0,他引:1
介绍了一种衬底同步加热射频磁控溅射制备BST(BaxSr1-xTiO3)薄膜的新方法,讨论了BST薄膜的晶化效果对介电常数的影响,分析了薄膜的居里温度和εr-V铁电性能.XRD测试结果表明制备的BST薄膜具有完整的钙钛矿晶体结构,相对介电常数超过150,介质击穿强度大于1.3 MV/cm.使用这种方法不需要专门的退火工艺,就可以制备晶体结构完整的高介电常数BST薄膜. 相似文献
10.
采用固相工艺制备BaTiO3-R2O3-MgO-MnO2(R=La,Ce,Pr,Nd,Sm,Gd,Dy,Ho,Y,Er,Yb)系陶瓷,全面研究了稀土掺杂对还原烧结钛酸钡(BaTiO3)陶瓷微结构和电性能的影响.扫描电镜分析结果显示:小离子半径稀土比大离子半径稀土更有效地改善微观结构,并且随着稀土离子半径的减小,其晶粒抑制作用更加显著.实验发现:大半径稀土掺杂可生成化学均匀性晶粒,得到介电常数-温度(ε-T)单峰曲线,并导致Curie点下降;小半径稀土掺杂可生成壳-芯结构晶粒,获得ε-T双峰曲线,晶粒壳的体积相对膨胀,对晶粒芯产生的张应力作用促使Curie点上升,其平坦的电容变化率-温度(△C/C-T)特性满足X8R.随着稀土离子半径的增大,该体系的绝缘电阻率总体呈降低趋势,归因于稀土元素在BaTiO3中取代位及补偿方式的不同. 相似文献