全文获取类型
收费全文 | 347564篇 |
免费 | 18644篇 |
国内免费 | 1331篇 |
学科分类
工业技术 | 367539篇 |
出版年
2021年 | 3445篇 |
2020年 | 3782篇 |
2019年 | 5813篇 |
2018年 | 7726篇 |
2017年 | 8021篇 |
2016年 | 8775篇 |
2015年 | 7039篇 |
2014年 | 9168篇 |
2013年 | 19063篇 |
2012年 | 11718篇 |
2011年 | 14051篇 |
2010年 | 11642篇 |
2009年 | 12572篇 |
2008年 | 12749篇 |
2007年 | 12360篇 |
2006年 | 10506篇 |
2005年 | 9493篇 |
2004年 | 9368篇 |
2003年 | 8997篇 |
2002年 | 8567篇 |
2001年 | 8227篇 |
2000年 | 7888篇 |
1999年 | 7711篇 |
1998年 | 18684篇 |
1997年 | 13072篇 |
1996年 | 9908篇 |
1995年 | 7396篇 |
1994年 | 6474篇 |
1993年 | 6517篇 |
1992年 | 4558篇 |
1991年 | 4354篇 |
1990年 | 4260篇 |
1989年 | 4186篇 |
1988年 | 3898篇 |
1987年 | 3512篇 |
1986年 | 3517篇 |
1985年 | 3874篇 |
1984年 | 3589篇 |
1983年 | 3301篇 |
1982年 | 3146篇 |
1981年 | 3174篇 |
1980年 | 3129篇 |
1979年 | 2909篇 |
1978年 | 2946篇 |
1977年 | 3286篇 |
1976年 | 4414篇 |
1975年 | 2481篇 |
1974年 | 2428篇 |
1973年 | 2444篇 |
1972年 | 2054篇 |
排序方式: 共有10000条查询结果,搜索用时 894 毫秒
101.
102.
103.
104.
In this work was investigated the effect of the addition of barium titanate (BaTiO3) on electrical properties of two chemically recyclable thermosets, polyhemiaminal (PHA) and polyhexahydro‐s‐triazine (PHT), both fabricated from 4,4′‐oxydianiline (ODA), an ether derivative of aniline and paraformaldehyde. Thermal and mechanical properties as well as chemical recyclability of the two polymers and their nanocomposites/nanodielectrics were also investigated. In addition, a quantitative analysis was conducted of the nanoparticle dispersion in the PHA‐/PHT‐based BaTiO3‐containing nanocomposites using transmission electron microscopy imaging and the nearest‐neighbor distance index and this index was used to analyze the investigated properties in connection with the proper mechanisms. Regarding the electrical properties for both neat polymers, conductivity values of the order of 10?8 S m?1 at 100 Hz were observed and dielectric constant values close to 2.80 for both polymers at 1 kHz. The addition of 0.5 wt% of BaTiO3 ferroelectric nanoparticles increased by about 44% the dielectric constant (1 kHz) and conductivity (102 Hz) of the PHA‐based nanocomposite. PHA and PHT exhibited glass transition temperature (Tg) values in the range 125–180 °C. An increase of 7 °C in Tg was observed after the incorporation of 0.5 wt% of BaTiO3 into PHA. Concerning the mechanical properties, values in the range 4.00–4.45 GPa for reduced modulus and 0.30–0.43 GPa for nanohardness for PHA and PHT polymers were observed. Independently of filler content or polymer matrix, both mechanical properties were enhanced after the addition of BaTiO3. The chemical recycling of PHA/PHT and all nanocomposites in the initial ODA reagent after sulfuric acid treatment was successfully characterized using the NMR and Fourier transform infrared spectroscopic techniques. © 2018 Society of Chemical Industry 相似文献
105.
Giorgio Benedek Joseph R. Manson Salvador Miret-Artés 《Advanced materials (Deerfield Beach, Fla.)》2020,32(25):2002072
Atom scattering is becoming recognized as a sensitive probe of the electron–phonon interaction parameter λ at metal and metal-overlayer surfaces. Here, the theory is developed, linking λ to the thermal attenuation of atom scattering spectra (in particular, the Debye–Waller factor), to conducting materials of different dimensions, from quasi-1D systems such as W(110):H(1 × 1) and Bi(114), to quasi-2D layered chalcogenides, and high-dimensional surfaces such as quasicrystalline 2ML-Ba(0001)/Cu(001) and d-AlNiCo(00001). Values of λ obtained using He atoms compare favorably with known values for the bulk materials. The corresponding analysis indicates in addition, the number of layers contributing to the electron–phonon interaction, which is measured in an atom surface collision. 相似文献
106.
Akopdzhanyan T. G. Chemagina E. A. Borovinskaya I. P. 《Russian Journal of Non-Ferrous Metals》2020,61(6):686-690
Russian Journal of Non-Ferrous Metals - The synthesis and sintering of the (AlN)x(SiC)1 – x solid solution have been studied under conditions of self-propagating high-temperature synthesis... 相似文献
107.
Madhu H. C. Edachery Vimal Lijesh K. P. Perugu Chandra Shekhar Kailas Satish V. 《Metallurgical and Materials Transactions A》2020,51(8):4086-4099
Metallurgical and Materials Transactions A - Hybrid nanocomposites have potential as wear-resistant materials. However, synthesizing these nanocomposites by conventional molten state methods result... 相似文献
108.
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
109.
Zavadiuk S.V. Loboda P.I. Soloviova T.O. Trosnikova I.Iu. Karasevska O.P. 《Powder Metallurgy and Metal Ceramics》2020,59(1-2):22-28
Powder Metallurgy and Metal Ceramics - The properties of sintered and heat-treated steels produced from the Catamold 8740 material by powder injection molding were examined. Parts made of the... 相似文献
110.
Correction to: Double Vision Model Using Space-Time Function Control within Silicon Microring System
Silicon - The original version of this article unfortunately contained a mistake in the “Acknowledgments” section. 相似文献