全文获取类型
收费全文 | 145790篇 |
免费 | 13617篇 |
国内免费 | 7622篇 |
专业分类
电工技术 | 9520篇 |
技术理论 | 12篇 |
综合类 | 12257篇 |
化学工业 | 23147篇 |
金属工艺 | 8136篇 |
机械仪表 | 9377篇 |
建筑科学 | 11497篇 |
矿业工程 | 3929篇 |
能源动力 | 4218篇 |
轻工业 | 12710篇 |
水利工程 | 2838篇 |
石油天然气 | 8091篇 |
武器工业 | 1359篇 |
无线电 | 15919篇 |
一般工业技术 | 15974篇 |
冶金工业 | 5715篇 |
原子能技术 | 1652篇 |
自动化技术 | 20678篇 |
出版年
2024年 | 515篇 |
2023年 | 2249篇 |
2022年 | 4344篇 |
2021年 | 5990篇 |
2020年 | 4495篇 |
2019年 | 3647篇 |
2018年 | 3998篇 |
2017年 | 4632篇 |
2016年 | 4090篇 |
2015年 | 5816篇 |
2014年 | 7546篇 |
2013年 | 8786篇 |
2012年 | 10065篇 |
2011年 | 11044篇 |
2010年 | 9844篇 |
2009年 | 9341篇 |
2008年 | 9349篇 |
2007年 | 8768篇 |
2006年 | 8600篇 |
2005年 | 6937篇 |
2004年 | 4952篇 |
2003年 | 4615篇 |
2002年 | 4902篇 |
2001年 | 4202篇 |
2000年 | 3432篇 |
1999年 | 3169篇 |
1998年 | 2298篇 |
1997年 | 1866篇 |
1996年 | 1754篇 |
1995年 | 1328篇 |
1994年 | 1120篇 |
1993年 | 814篇 |
1992年 | 625篇 |
1991年 | 464篇 |
1990年 | 334篇 |
1989年 | 296篇 |
1988年 | 239篇 |
1987年 | 159篇 |
1986年 | 105篇 |
1985年 | 57篇 |
1984年 | 38篇 |
1983年 | 37篇 |
1982年 | 43篇 |
1981年 | 36篇 |
1980年 | 42篇 |
1979年 | 19篇 |
1976年 | 3篇 |
1960年 | 2篇 |
1959年 | 8篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Dy3+, Eu3+: NaLa(WO4)2 phosphors are successfully synthesized through the solid-state reaction technique. The phase-structure and morphology are measured via X-ray diffraction and energy dispersive spectrometry. The concentrations of Dy3+, Eu3+, La3+, and W6+ are measured via ICP. The absorption and excited spectra are presented, which indicate that a blue band ranging from 430 to 480 nm is suitable for excitation. Using a commercial blue LED with a wavelength of 450 nm as the excitation light source, emission spectra for samples with varying dopant concentration ratios of Dy3+ to Eu3+ are obtained, which show good tunable yellow and red emission. For the purpose of investigating white LED performance, CIE spectra and a white light photo are also presented. The results reveal that varying the dopant concentration ratio of Dy3+ to Eu3+ plays a key role in the warm-white performance. With increasing concentration of Eu3+, the correlated color temperature decreases from 4069 to 3172 K, which indicates good warm-white performance. 相似文献
42.
Huizhu Cai Bingbing Chen Xiao Zhang Yuchen Deng Dequan Xiao Ding Ma Chuan Shi 《Nano Research》2021,14(1):122-130
Over recent years,catalytic materials of Fe-N-C species have been recognized being active for oxygen reduction reaction(ORR).However,the identification of active site remains challenging as it generally involves a pyrolysis process and mixed components being obtained.Herein Fe3C/C and Fe2N/C samples were synthesized by temperature programmed reduction of Fe precursors in 15%CH4/H2and pure NH3,respectively.By acid leaching of Fe2N/C sample,only single sites of FeN4species were presented,providing an ideal model for identification of catalytic functions of the single sites of FeN4in ORR.A correlation was conducted between the concentration of FeⅡN4in low spin state by Mossbauer spectra and the kinetic current density at 0.8 V in alkaline media,and such a structure-performance correlation assures the catalytic roles of low spin FeⅡN4 species as highly active sites for the ORR. 相似文献
43.
44.
Xiaohui Hu Li Cheng Yan Hong Zhaofeng Li Caiming Li Zhengbiao Gu 《International Journal of Food Science & Technology》2021,56(8):4149-4158
Incorporating high level of potato flour into wheat flour enhances nutritional values of bread but induces a series of problems that lead to the decline of the bread quality. To overcome the barrier, wheat gluten and carboxymethylcellulose (CMC) were added into potato–wheat composite flour to improve dough machinability and bread quality. The rheological properties, thermo-mechanical properties and microstructures of dough were investigated. The results showed that the interaction between gluten and CMC mitigated the discontinuity of gluten matrix and gluten protein aggregation caused by the addition of potato flour, which yielded a more branched and compact gluten network. The compact three-dimensional viscoelastic structure induced improvements of gas retention capacity and dough stability, making it mimic the machinability properties of wheat flour dough. Bread qualities were apparently improved with the combined use of 4% gluten and 6% CMC, of which specific volume increased by 42.86%, and simultaneously, hardness reduced by 75.93%. 相似文献
45.
46.
47.
48.
与传统比例-积分-微分(PID)控制方法相比,滑模控制(SMC)方法可以比较容易地将不确定性纳入控制器设计中,从而增强系统的鲁棒性。探索了SMC技术在运载器主动段姿态控制中的工程应用,首先通过分析基于趋近律的SMC系统,提出了降低不连续切换项系数的需求,然后研究了基于干扰上界的SMC方法。三通道小偏差仿真结果验证了两种方法的控制效果,表明第2种控制器的鲁棒性更好,稳态误差小,同时发动机喷管摆角需求较小。 相似文献
49.
50.
Yong Xu Yun Li Songlin Li Francis Balestra Gerard Ghibaudo Wenwu Li Yen‐Fu Lin Huabin Sun Jing Wan Xinran Wang Yufeng Guo Yi Shi Yong‐Young Noh 《Advanced functional materials》2020,30(20)
Unreliable mobility values, and particularly greatly overestimated values and severely distorted temperature dependences, have recently hampered the development of the organic transistor field. Given that organic field‐effect transistors (OFETs) have been routinely used to evaluate mobility, precise parameter extraction using the electrical properties of OFETs is thus of primary importance. This review examines the origins of the various mobilities that must be determined for OFET applications, the relevant extraction methods, and the data selection limitations, which help in avoiding conceptual errors during mobility extraction. For increased precision, the review also discusses device fabrication considerations, calibration of both the specific gate‐dielectric capacitance and the threshold voltage, the contact effects, and the bias and temperature dependences, which must actually be handled with great care but have mostly been overlooked to date. This review serves as a systematic overview of the OFET mobility extraction process to ensure high precision and will also aid in improving future research. 相似文献