全文获取类型
收费全文 | 131834篇 |
免费 | 13386篇 |
国内免费 | 7571篇 |
专业分类
电工技术 | 9262篇 |
技术理论 | 11篇 |
综合类 | 9848篇 |
化学工业 | 20233篇 |
金属工艺 | 7979篇 |
机械仪表 | 8719篇 |
建筑科学 | 10726篇 |
矿业工程 | 4708篇 |
能源动力 | 4063篇 |
轻工业 | 8766篇 |
水利工程 | 2840篇 |
石油天然气 | 7836篇 |
武器工业 | 1369篇 |
无线电 | 15551篇 |
一般工业技术 | 14197篇 |
冶金工业 | 5995篇 |
原子能技术 | 1710篇 |
自动化技术 | 18978篇 |
出版年
2024年 | 689篇 |
2023年 | 2338篇 |
2022年 | 4518篇 |
2021年 | 6342篇 |
2020年 | 4789篇 |
2019年 | 3824篇 |
2018年 | 4257篇 |
2017年 | 4760篇 |
2016年 | 4175篇 |
2015年 | 6003篇 |
2014年 | 7559篇 |
2013年 | 8729篇 |
2012年 | 9917篇 |
2011年 | 10425篇 |
2010年 | 9410篇 |
2009年 | 8574篇 |
2008年 | 8259篇 |
2007年 | 7663篇 |
2006年 | 6977篇 |
2005年 | 5793篇 |
2004年 | 4005篇 |
2003年 | 3441篇 |
2002年 | 3637篇 |
2001年 | 2952篇 |
2000年 | 2358篇 |
1999年 | 2357篇 |
1998年 | 1664篇 |
1997年 | 1421篇 |
1996年 | 1418篇 |
1995年 | 1108篇 |
1994年 | 842篇 |
1993年 | 610篇 |
1992年 | 466篇 |
1991年 | 366篇 |
1990年 | 267篇 |
1989年 | 212篇 |
1988年 | 200篇 |
1987年 | 113篇 |
1986年 | 90篇 |
1985年 | 46篇 |
1984年 | 38篇 |
1983年 | 26篇 |
1982年 | 34篇 |
1981年 | 23篇 |
1980年 | 40篇 |
1979年 | 20篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1959年 | 14篇 |
1951年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
81.
Global decrease in crude oil resources and frequent crude oil leaks cause the energy crisis and ecological pollution. The absorption and release of leaked crude oil through absorption materials are a necessary process for environmental protection and recycling. In this article, a CO2-responsive olefin copolymer was obtained by copolymerization of styrene and an amine-containing olefin monomer. The structure of resultant copolymer was characterized by FTIR; thermal properties and CO2-responsive morphology changes were determined by DSC/TGA and SEM, respectively. Copolymers had certain absorption capacity for toluene with absorption rate up to 180.0%. The absorbed toluene could be released upon CO2 stimulation with desorption rate up to 84.6%. The CO2-responsive copolymer could be regenerated through a simple heating process and showed stable absorption–desorption performance even after being recycled for 4 times. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47439. 相似文献
82.
Thermal barrier coatings (TBCs) produced by electron beam physical vapor deposition (EB-PVD) or plasma spray (PS) usually suffer from molten calcium-magnesium-alumino-silicate (CMAS) attack. In this study, columnar structured YSZ coatings were fabricated by plasma spray physical vapor deposition (PS-PVD). The coatings were CMAS-infiltrated at 1250?°C for short terms (1, 5, 30?min). The wetting and spreading dynamics of CMAS melt on the coating surface was in-situ investigated using a heating microscope. The results indicate that the spreading evolution of CMAS melt can be described in terms of two stages with varied time intervals and spreading velocities. Besides, the PS-PVD columnar coating (~100?μm thick) was fully penetrated by CMAS melt within 1?min. After the CMAS attack for 30?min, the original feathered-YSZ grains (tetragonal phase) in both PS-PVD and EB-PVD coatings were replaced by globular shaped monoclinic ZrO2 grains in the interaction regions. 相似文献
83.
84.
以2,6-二甲基苯胺为原料,通过重氮化反应制备2,6-二甲基苯腈,经水蒸汽蒸馏法提纯后,采用75%硫酸酸化,再经酸碱法对产物进行脱色和纯化得产物2,6-二甲基苯甲酸,总收率68.4%。工艺简单、操作安全、适合工业化生产。 相似文献
85.
Qun Ren Haijun Su Jun Zhang Haifang Liu Weidan Ma Guangrao Fan Di Zhao Min Guo Lin Liu Hengzhi Fu 《Ceramics International》2019,45(6):6632-6638
Directionally solidified microstructures of Al2O3-Er3Al5O12 eutectic and off-eutectic in situ composite ceramics were explored under abrupt-change pulling rate conditions. Corresponding temperature distributions and interface locations were studied. In eutectic composition, fluctuation of eutectic spacing occurred when the pulling rate increased abruptly. A gradually increase or abrupt increase in eutectic spacing was observed when the pulling rate decreased abruptly. In hypoeutectic and hypereutectic compositions, formation of the primary phases were suppressed when the pulling rate increased abruptly from 10?µm/s to 100?µm/s, while primary phases precipitated when the pulling rate decreased abruptly from 100?µm/s to 10?µm/s. The interface altitude decreased after the pulling rate increased abruptly, but increased after the pulling rate decreased abruptly. The liquid composition restriction (around the eutectic composition) at the eutectic interface plays an important role in the suppression of the primary dendrite and coupled eutectic oxides can be obtained in off-eutectic compositions even under higher solidification rate conditions. 相似文献
86.
测向误差的减小一直以来都是无线电测向精度提高的一个难点,对于不同的测向体制所采用的减小测向误差的方法都不尽相同。本文主要介绍的是相关干涉仪测向体制的基本原理以及通过内插法的应用来减小测向误差的方法。 相似文献
87.
Sumeng Wei Yuling Yang Xiao Feng Shanshan Li Lei Zhou Jingyu Wang Xiaozhi Tang 《International Journal of Food Science & Technology》2020,55(7):2691-2699
Structures and properties of myofibrillar protein gel prepared at different power (300–800 W) were evaluated. Amino acid analysis demonstrated that changes in microwave power did not alter primary structure of gel. However, an increase in microwave power could change higher structures of gel. As microwave power increased, α-helix content decreased and β-sheet content increased. Increased microwave power probably facilitated protein to unfold and expose the internal groups, causing surface hydrophobicity and the formation of disulphide bonds were enhanced, which indicated changes in tertiary and quaternary structures of protein. At 500 W, gel had the best ultrastructure where surface morphology, springiness and water holding capacity reached the optimum. Our findings suggested that microwave at an appropriate power (500 W) could change higher structures of myofibrillar protein gel to achieve desired processing and quality protein gel characteristics. 相似文献
88.
89.
Li Lei Limin Li Shasha Wang Gaoyang Zhao Yoshifumi Oshima Yang Ren Lei Zhao Lihua Jin Yao Wang Chengshan Li Pingxiang Zhang 《Journal of the European Ceramic Society》2018,38(14):4694-4700
Highly (100)-oriented Ce1-x(Y0.2Zr0.8)xOδ (CYZO) films were prepared on biaxially textured NiW substrates by a chemical solution deposition approach using metal inorganic salts as starting materials. It has been found that both the preferential orientation and surface roughness of CYZO films decrease gradually with increasing of the doping percentage of Y3+ and Zr4+ ions. The epitaxial growth relationship of (220)CYZO//(200)NiW and [00?l]CYZO//[001]NiW was demonstrated by XRD texture measurement as well as atomic resolution STEM observation. XRD, Raman and XPS spectra results indicate that Y3+ and Zr4+ ions were indeed introduced into CeO2 lattice to substitute Ce4+ ions and form cubic fluorite CYZO solid solution. Moreover, CeO2 buffer layer can be endowed a strong enough capability to prevent element diffusion through co-doping of yttrium and zirconium, provided that an optimal doping ratio of them is adopted. This will provide a new approach to fabricating strong-barrier single buffer layer for coated conductor. 相似文献