全文获取类型
收费全文 | 22463篇 |
免费 | 1767篇 |
国内免费 | 1149篇 |
专业分类
电工技术 | 424篇 |
技术理论 | 2篇 |
综合类 | 935篇 |
化学工业 | 5122篇 |
金属工艺 | 3143篇 |
机械仪表 | 1264篇 |
建筑科学 | 193篇 |
矿业工程 | 389篇 |
能源动力 | 660篇 |
轻工业 | 1412篇 |
水利工程 | 16篇 |
石油天然气 | 196篇 |
武器工业 | 102篇 |
无线电 | 3117篇 |
一般工业技术 | 7457篇 |
冶金工业 | 456篇 |
原子能技术 | 183篇 |
自动化技术 | 308篇 |
出版年
2024年 | 63篇 |
2023年 | 294篇 |
2022年 | 277篇 |
2021年 | 467篇 |
2020年 | 472篇 |
2019年 | 483篇 |
2018年 | 575篇 |
2017年 | 729篇 |
2016年 | 685篇 |
2015年 | 739篇 |
2014年 | 1027篇 |
2013年 | 1292篇 |
2012年 | 1378篇 |
2011年 | 1956篇 |
2010年 | 1421篇 |
2009年 | 1462篇 |
2008年 | 1315篇 |
2007年 | 1562篇 |
2006年 | 1441篇 |
2005年 | 1172篇 |
2004年 | 1108篇 |
2003年 | 971篇 |
2002年 | 900篇 |
2001年 | 710篇 |
2000年 | 552篇 |
1999年 | 405篇 |
1998年 | 371篇 |
1997年 | 334篇 |
1996年 | 216篇 |
1995年 | 200篇 |
1994年 | 144篇 |
1993年 | 133篇 |
1992年 | 122篇 |
1991年 | 110篇 |
1990年 | 70篇 |
1989年 | 40篇 |
1988年 | 31篇 |
1987年 | 26篇 |
1986年 | 22篇 |
1985年 | 24篇 |
1984年 | 13篇 |
1983年 | 10篇 |
1982年 | 12篇 |
1981年 | 5篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1974年 | 9篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
GaN buffer and main layers were grown by the conventional hydride vapor phase epitaxy technique using GaCl3 consecutively. The deposited buffer layers were investigated by atomic force microscopy and X-ray analysis. To examine the behavior of the buffer layers at main layer growth temperature, heat treatment was conducted at 900°C. Based on the results of the buffer layer study, GaN thick films were grown at 1050°C. Optimum deposition conditions of buffer layer from the buffer and main layer studies generally coincided. On the φ scanning pattern, the GaN films grown on (0001) Al2 O3 were single-crystalline. Band-edge emission dominated photoluminescence was observed at room temperature. 相似文献
92.
Abstract— We have developed a process to fabricate optical components, such as a lens, prism, or diffuser, directly on to a glass substrate. Processes include precision mastering by diamond cutting and multi‐layer photopolymer (2P) molding to realize flat surfaces and the integration of multiple components with an alignment within a few micrometers. 相似文献
93.
n-Al2O3/Ni复合镀层的组织与滑动磨损性能研究 总被引:24,自引:4,他引:20
用电刷镀技术制得了镍基n-Al2O3复合镀层,并对镀层的滑动磨损性能进行了试验研究。纳米复合镀层的表面形貌比较细腻,镀层中纳米粒子分布均匀,与基质金属结合紧密。镀层显微硬度达到HV700,比快速镍镀层提高约40%。滑动磨损试验结果表明,随着纳米粒子含量的增大,镀层的耐磨性提高,摩擦系数也呈增大趋势;但当镀层中n-Al2O3粒子的超过2.56%(质量分数)时,镀层的耐磨性显著下降。纳米复合镀层的磨损机制以疲劳磨损为主,而快速镍底层以粘着磨损为主。 相似文献
94.
The optical and thermal properties of prepared poly(ethylene oxide)/MnCl2 films were studied as a function of MnCl2 concentration at room temperature. The observed optical energy gap (Eopt) and energy gap tail (ΔE) were determined from the measured absorption spectra. It was found that the optical energy gap decreases with MnCl2 concentration, and the absorption coefficient reduces sharply at concentration of 5 wt% MnCl2 compared with the neat PEO. Differential scanning calorimetry (DSC) measurement shows that the heat of fusion increases with the MnCl2 concentration, while the melting point decreases. Correlation between the observed optical energy gap and heat of fusion is presented. 相似文献
95.
Sonny g. Sundaresan William R. Finkenstadt 《International Journal of Refrigeration》1991,14(6):317-320
Earlier studies conducted in the use of sealed tubes with polyalkylene glycol lubricants and polyethylene terephthalete (PET) films revealed that the PET films exhibited embrittlement and (visual) degradation. This led to an investigation of PET embrittlement mechanisms with the new lubricants used with HFC 134a. The lubricants studied were three polypropylene glycols (the monol, the diol and the completely end-capped glycols), pentaerythritol ester and a blend of monol and ester. The effects of moisture content, temperature and lubricant structure were studied. All lubricants in this study were of viscosity grade ISO-32 (150 SUS). The results were compared to PET film embrittlement in the presence of CFC 12 and mineral oil. This study reconfirmed the earlier findings that the PET films must be dried to lower than 0.1 wt.% moisture content for use in hermetic systems. This paper discusses the effect of the moisture content of the lubricant and the effect of the lubricant structure on PET films. The dependence of the various mechanisms on temperature is shown. Esters and end-capped polyalkylene glycols are recommended for use with HFC 134a. 相似文献
96.
97.
As part of a study of the possible application of polymerisable Langmuir-Blodgett (LB) films as ultra-fine-line e-beam resists, an investigation of the variation of film structure of 22-tricosenoic acid with differing deposition conditions has been made. Unexpected effects with significant implications for deposition speed and resist sensitivity have been observed, and the new techniques for film characterisation developed during the investigation have resulted in a revised model of deposition explaining the observed independence of the disorder causing optical scattering and the macroscopic features observed by polarised microscopy. 相似文献
98.
99.
非晶软磁合金的巨磁阻抗效应及应用 总被引:3,自引:2,他引:1
近来在FeCoSiB等Co基非晶体丝带中现了巨磁阻抗效应,由于在一小的直流纵向偏置场下该效应能使丝带两端的交流电压发生大而灵敏的变化,因而在磁记录头和传顺技术中具有巨大的应用科学潜能,受到各国学者的关注,本文简单介绍了巨磁阻抗效应的来源,并综述了近年来非晶体软磁合金材料的的巨磁阻抗效应及应用的研究进展,文章最后说明了尚待深入解决的问题。 相似文献
100.