全文获取类型
收费全文 | 84386篇 |
免费 | 9708篇 |
国内免费 | 3498篇 |
专业分类
电工技术 | 1112篇 |
技术理论 | 1篇 |
综合类 | 3907篇 |
化学工业 | 34508篇 |
金属工艺 | 10554篇 |
机械仪表 | 1430篇 |
建筑科学 | 2327篇 |
矿业工程 | 1833篇 |
能源动力 | 1872篇 |
轻工业 | 11008篇 |
水利工程 | 483篇 |
石油天然气 | 2297篇 |
武器工业 | 347篇 |
无线电 | 2835篇 |
一般工业技术 | 17782篇 |
冶金工业 | 3690篇 |
原子能技术 | 592篇 |
自动化技术 | 1014篇 |
出版年
2024年 | 581篇 |
2023年 | 1955篇 |
2022年 | 2882篇 |
2021年 | 3801篇 |
2020年 | 3710篇 |
2019年 | 3166篇 |
2018年 | 3512篇 |
2017年 | 3900篇 |
2016年 | 3986篇 |
2015年 | 4036篇 |
2014年 | 4832篇 |
2013年 | 6144篇 |
2012年 | 5876篇 |
2011年 | 6507篇 |
2010年 | 4467篇 |
2009年 | 4826篇 |
2008年 | 3911篇 |
2007年 | 4418篇 |
2006年 | 4231篇 |
2005年 | 3236篇 |
2004年 | 3126篇 |
2003年 | 2656篇 |
2002年 | 2178篇 |
2001年 | 1529篇 |
2000年 | 1423篇 |
1999年 | 1084篇 |
1998年 | 968篇 |
1997年 | 820篇 |
1996年 | 641篇 |
1995年 | 550篇 |
1994年 | 463篇 |
1993年 | 340篇 |
1992年 | 328篇 |
1991年 | 246篇 |
1990年 | 276篇 |
1989年 | 262篇 |
1988年 | 117篇 |
1987年 | 98篇 |
1986年 | 80篇 |
1985年 | 95篇 |
1984年 | 90篇 |
1983年 | 47篇 |
1982年 | 64篇 |
1981年 | 13篇 |
1980年 | 43篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1976年 | 7篇 |
1974年 | 7篇 |
1951年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
981.
Zinc oxide (ZnO) thin films were prepared onto glass substrates at moderately low growth temperature by two-stage spray pyrolysis technique. The effects of growth temperature on structural, optical and acetone detection properties were investigated with X-ray diffractometry, a UV-visible spectrophotometer, photoluminescence (PL) spectroscopy and a homemade gas sensor testing unit, respectively. All the films are polycrystalline with a hexagonal wurtzite phase and exhibit a preferential orientation along [002] direction. The film crystallinity is gradually enhanced with an increase in growth temperature. The optical measurements show that all the films are physically highly transparent with a transmittance greater than 82% in the visible range. The band gap of the film is observed to exhibit a slight red shift with an increasing growth temperature. The PL studies on the films show UV/violet PL band at ~ 395 nm. Among all the films investigated, the film deposited at 250 ℃ demonstrates a maximum sensitivity of 13% towards 20 ppm of acetone vapors at 300 ℃ operating temperature. 相似文献
982.
《Microelectronics Journal》2014,45(12):1726-1733
This paper elucidates the thermal behavior of an LED employing metal filled polymer matrix as thermal interface material (TIM) for an enhanced heat dissipation characteristic. Highly thermal conductive aluminum (Al) particles were incorporated in bisphenol A diglycidylether (DGEBA) epoxy matrix to study the effect of filler to polymer ratio on the thermal performance of high power LEDs. The curing behavior of DGEBA was studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The dispersion nature of the Al fillers in polymer matrix was verified with Field Emission Scanning Electron Microscope (FESEM). The thermal performance of synthesized Al filled polymer composite as TIM was tested with an LED employing thermal transient measurement technique. Comparing the filler to polymer ratio, the rise in junction temperature for 60 wt% Al filled composite was higher by 11.1 °C than 50 wt% Al filled composite at cured state. Observed also from the structure function analysis that the total thermal resistance was 10.96 K/W higher for 60 wt% Al filled composite compared to 50 wt% Al filled composite. On the other hand, a significant rise of 9.5 °C in the junction temperature between cured and uncured samples of 50 wt% Al filled polymer TIM was observed and hence the importance of curing process of metal filled polymer composite for effective heat dissipation is discussed extensively in this work. 相似文献
983.
《AEUE-International Journal of Electronics and Communications》2014,68(6):550-560
In this paper, an in-depth comparative analysis of the most accepted and approved Rayleigh fading channel simulators is presented. Our study addresses the three common methods for generating time-correlated Rayleigh fading processes: the inverse discrete Fourier transform (IDFT) method, the filtering white Gaussian noise (FWGN) method and the sum-of-sinusoids (SOS) method. Totally seven models, including the recently proposed models, are analyzed and compared with Clarke's reference model. We use four quantitative measures for judicious assessment of the quality of generated processes in terms of both first-order and second-order statistics. Additionally, these measures cover analysis in time domain as well as in frequency domain. An evaluation of the computational effort is also depicted. The simulation results suggest that the recently published Wang's model is very attractive and it outperforms all SOS-based models. We conclude that Zheng and Xiao's first model remains the best choice among Zheng and Xiao's family models. Several other important remarks and conclusions about the accuracy and the capability of the different Rayleigh fading simulators are driven from this study. 相似文献
984.
Benjamin W. Riblett Nicola L. Francis Margaret A. Wheatley Ulrike G. K. Wegst 《Advanced functional materials》2012,22(23):4920-4923
Successful spinal cord repair is thought to be promoted with hierarchically structured scaffolds. These should combine aligned porosity with additional linear features on the micrometer scale to guide axons across multiple length scales. Such scaffolds are generated through the carefully controlled directional solidification of an aqueous biopolymer solution, followed by lyophilization. Under specific freezing conditions this yields a highly regular and aligned lamellar architecture. This architecture exhibits uniform ridges of controlled height and width on the lamellar surface. These ridges run parallel to the pore axis, serving as secondary guidance features. The ridges are capable of linearly aligning 62.4% of chick dorsal root ganglia neurites to within ±10° of the ridge direction. Notably, neurites sprouting perpendicular to the ridge are guided into alignment with these microridged features. 相似文献
985.
李阳 《兵器材料科学与工程》2010,33(4):4-7
多晶硅薄膜晶体管(poly-Si TFT)因较非晶硅薄膜晶体管(a-Si TFT)相比具有更高的场效应迁移率而成为目前显示界研究的热点。在制备多晶硅薄膜及其TFT器件的过程中,发现不同厚度的多晶硅薄膜具有不同的电学特性。经分析,不同厚度的多晶硅薄膜有源层TFT器件也势必表现出不同的器件电学特性。为此,制备3种多晶硅薄膜有源层厚度的TFT器件,比较且优化器件的各种电学特性—场迁移率、阈值电压、亚阈值幅摆、电流开关比等,最后确定TFT器件有源层的最佳厚度。 相似文献
986.
以羰基铁粉作为颜填料,聚氨酯作为树脂基体,制备雷达/红外兼容隐身单涂层,分析羰基铁粉的形态、含量以及球磨时间对涂层红外低发射率以及雷达吸波性能的影响。结果表明:未球磨时,颜填料质量分数为60%,涂层厚为2 mm,在18 GHz处其涂层反射率的最小值达-9.3 dB,其涂层的红外发射率为0.85;球磨16 h,羰基铁粉由球状变为片状,质量分数为60%,其涂层的红外发射率降低至0.69,雷达吸波性能略有降低。羰基铁粉有望成为红外/雷达兼容隐身材料。 相似文献
987.
为实现功能结构一体化,提高泡沫铝复合材料的力学性能和吸能性能,制备硅橡胶改性环氧树脂的高分子材料填充泡沫铝的复合材料。静态压缩试验表明,填充改性环氧树脂的泡沫铝的平台屈服阶段明显抬升,改善泡沫铝的力学性能,提高泡沫铝的吸能能力。 相似文献
988.
989.
液晶分子的初始排列在液晶显示器中起着关键的作用。纳米粒子掺杂到液晶体系可扰乱液晶分子的排列,从而改变液晶的自组装特性,进而影响液晶的各项性能。将制备的Au八面体纳米颗粒掺杂到向列相液晶4-氰基-4′-正戊基联苯(5CB)中,灌入液晶盒后,通过使用偏光显微镜对液晶盒的观察发现,掺杂的八面体Au纳米颗粒诱导5CB液晶分子发生了垂直取向,而球形Au纳米颗粒不能诱导液晶分子垂直取向。这归因于八面体Au纳米颗粒的表面能比较小,液晶分子间的作用力比较大,使液晶分子易于垂直取向。随着O-Au NPs的浓度增大,液晶分子的取向效果先变好又逐渐变差。这是因为O-Au NPs的浓度越高,可诱导越多的液晶分子垂直取向排列,但随着纳米粒子浓度的增加,纳米粒子团聚,减少了与液晶分子的作用,使取向效果变差。动态过程实验显示,0.1%的八面体金纳米颗粒可诱导向列相液晶5CB在2 min内快速完成垂直取向,表明O-Au NPs具有优异的诱导5CB取向的动态效果。 相似文献
990.