全文获取类型
收费全文 | 23268篇 |
免费 | 2659篇 |
国内免费 | 1347篇 |
专业分类
电工技术 | 1771篇 |
技术理论 | 5篇 |
综合类 | 1850篇 |
化学工业 | 3725篇 |
金属工艺 | 1340篇 |
机械仪表 | 1449篇 |
建筑科学 | 1737篇 |
矿业工程 | 704篇 |
能源动力 | 695篇 |
轻工业 | 2358篇 |
水利工程 | 501篇 |
石油天然气 | 1069篇 |
武器工业 | 264篇 |
无线电 | 2717篇 |
一般工业技术 | 2671篇 |
冶金工业 | 788篇 |
原子能技术 | 242篇 |
自动化技术 | 3388篇 |
出版年
2024年 | 120篇 |
2023年 | 558篇 |
2022年 | 1026篇 |
2021年 | 1416篇 |
2020年 | 1021篇 |
2019年 | 826篇 |
2018年 | 900篇 |
2017年 | 951篇 |
2016年 | 892篇 |
2015年 | 1210篇 |
2014年 | 1456篇 |
2013年 | 1670篇 |
2012年 | 1868篇 |
2011年 | 1909篇 |
2010年 | 1661篇 |
2009年 | 1421篇 |
2008年 | 1373篇 |
2007年 | 1289篇 |
2006年 | 1110篇 |
2005年 | 806篇 |
2004年 | 616篇 |
2003年 | 449篇 |
2002年 | 430篇 |
2001年 | 396篇 |
2000年 | 375篇 |
1999年 | 322篇 |
1998年 | 222篇 |
1997年 | 178篇 |
1996年 | 160篇 |
1995年 | 133篇 |
1994年 | 127篇 |
1993年 | 95篇 |
1992年 | 79篇 |
1991年 | 39篇 |
1990年 | 33篇 |
1989年 | 35篇 |
1988年 | 22篇 |
1987年 | 15篇 |
1986年 | 14篇 |
1985年 | 6篇 |
1984年 | 12篇 |
1983年 | 3篇 |
1982年 | 10篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1959年 | 4篇 |
1958年 | 1篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
991.
992.
993.
994.
995.
996.
Yiguang Jiang Benxue Jiang Nan Jiang Dapeng Jiang Jiang Li Liangbi Su Long Zhang 《Journal of the American Ceramic Society》2020,103(10):5808-5812
Er3+-doped CaF2 transparent ceramics are promising mid-infrared gain materials because of their utra-low phonon energy as well as excellent physical, chemical, and optical properties. However, existing hot-pressed and hot-formed CaF2 ceramics are very difficult to be used in practical applications due to residual pores and weak polycrystallization, respectively. Here, we developed the high quality Er3+-doped CaF2 transparent polycrystalline ceramic by single crystal ceramization. The sample exhibits obvious polycrystalline structure, good mechanical properties, perfectly transmittance, and excellent mid-infrared performance, which provides significant and wide-ranging opportunities for advanced mid-infrared gain materials. 相似文献
997.
Yu Wang He Zhang Shuqiang Jiao Kuo-Chih Chou Guo-Hua Zhang 《Journal of the American Ceramic Society》2020,103(4):2399-2406
Molybdenum boride is an ideal hard and wear-resistant material. In this study, a new method is proposed for preparing molybdenum boride, by which Mo first reacts with B4C to generate the mixture of molybdenum boride and C, and then the product is decarburized by molten Ca to generate CaC2. Pure molybdenum boride could be obtained after acid leaching to remove the by-product CaC2. According to the experimental and thermodynamic calculation results, it is concluded that the single-phase MoB could be successfully prepared, while Mo2B, Mo2B5, and MoB4 could not be synthesized by this method. Moreover, it was found that the particle size of finally prepared MoB is determined by particle size of raw Mo powder. The residual carbon content of the product could be decreased to 0.10 wt% after first reaction at 1673 K for 6 hours and then decarburization reaction at 1673 K for 6 hours. 相似文献
998.
Mengting Guo Chongyun Shao Yang Zhang Jingbo Yu Yan Jiao Malgorzata Guzik Georges Boulon Jinjun Ren Lili Hu 《Journal of the American Ceramic Society》2020,103(8):4275-4285
The homogeneous Yb3+/Al3+/B3+-co-doped silica glasses were prepared via a sol-gel method. The impact of B2O3 addition on the physical and optical properties and network structure was systematically studied. The network structure was investigated by the Fourier Transform Infrared (FT-IR), Raman spectra, and Solid State Nuclear Magnetic Resonance (SSNMR). Herein, B2O3 addition can continuously decrease the refractive index and density. When B2O3 is lower than 2 mol%, B2O3 addition can obviously decrease the scalar crystal field parameters, Yb3+ asymmetry degree, Yb3+ cross-sections, due to the generation of Yb–O–B bonds at the cost of partial Yb–O–Al/Si ones. When B2O3 is more than 2 mol%, FT-IR, Raman spectra, and SSNMR results indicate that further increased B atoms prefer to connect with Si and Al rather than Yb. Consequently, the above parameters are basically unchanged. Based on the results, an intuitive model of structure and properties evolution during the substitution of SiO2 by B2O3 has been established. 相似文献
999.
1000.