全文获取类型
收费全文 | 112319篇 |
免费 | 12035篇 |
国内免费 | 7302篇 |
专业分类
电工技术 | 8833篇 |
技术理论 | 7篇 |
综合类 | 9461篇 |
化学工业 | 16722篇 |
金属工艺 | 6469篇 |
机械仪表 | 7178篇 |
建筑科学 | 9679篇 |
矿业工程 | 3713篇 |
能源动力 | 3333篇 |
轻工业 | 8373篇 |
水利工程 | 2613篇 |
石油天然气 | 5598篇 |
武器工业 | 1334篇 |
无线电 | 13480篇 |
一般工业技术 | 11390篇 |
冶金工业 | 4584篇 |
原子能技术 | 1546篇 |
自动化技术 | 17343篇 |
出版年
2024年 | 468篇 |
2023年 | 1927篇 |
2022年 | 3720篇 |
2021年 | 5358篇 |
2020年 | 3937篇 |
2019年 | 3342篇 |
2018年 | 3565篇 |
2017年 | 3918篇 |
2016年 | 3431篇 |
2015年 | 5059篇 |
2014年 | 6103篇 |
2013年 | 7138篇 |
2012年 | 8213篇 |
2011年 | 8534篇 |
2010年 | 7833篇 |
2009年 | 7376篇 |
2008年 | 7199篇 |
2007年 | 6528篇 |
2006年 | 6218篇 |
2005年 | 5198篇 |
2004年 | 3879篇 |
2003年 | 3713篇 |
2002年 | 4470篇 |
2001年 | 3761篇 |
2000年 | 2448篇 |
1999年 | 1944篇 |
1998年 | 1139篇 |
1997年 | 1013篇 |
1996年 | 964篇 |
1995年 | 800篇 |
1994年 | 608篇 |
1993年 | 441篇 |
1992年 | 388篇 |
1991年 | 226篇 |
1990年 | 200篇 |
1989年 | 138篇 |
1988年 | 119篇 |
1987年 | 68篇 |
1986年 | 66篇 |
1985年 | 40篇 |
1984年 | 32篇 |
1983年 | 16篇 |
1982年 | 17篇 |
1981年 | 23篇 |
1980年 | 27篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1959年 | 14篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 209 毫秒
51.
Zhang Huawei Yang Zhi Wu Zhaoyu Hong Xiaoyu Li Zhong Xu Yulai Li Jun Ni Gaojin Xiao Xueshan 《Oxidation of Metals》2019,92(1-2):49-65
Oxidation of Metals - The isothermal oxidation behavior and oxide-scale evolution on a newly developed Ni–Fe-based superalloy were investigated. Three oxidation stages were generally... 相似文献
52.
In this research, the three‐dimensional structural and colorimetric modeling of three‐dimensional woven fabrics was conducted for accurate color predictions. One‐hundred forty single‐ and double‐layered woven samples in a wide range of colors were produced. With the consideration of their three‐dimensional structural parameters, three‐dimensional color prediction models, K/S‐, R‐, and L*a*b*‐based models, were developed through the optimization of previous two‐dimensional models which have been reported to be the three most accurate models for single‐layered woven structures. The accuracy of the new three‐dimensional models was evaluated by calculating the color differences ΔL*, ΔC*, Δh°, and ΔECMC(2:1) between the measured and the predicted colors of the samples, and then the error values were compared to those of the two‐dimensional models. As a result, there has been an overall improvement in color predictions of all models with a decrease in ΔECMC(2:1) from 10.30 to 5.25 units on average after the three‐dimensional modeling. 相似文献
53.
Zhuo Wang Haonan Chen Tian Wang Yujia Xiao Wenwen Nian Jiahao Fan 《Journal of the European Ceramic Society》2018,38(11):3847-3852
The appearance of colossal permittivity materials broadened the choice of materials for energy-storage applications. In this work, colossal permittivity in ceramics of TiO2 co-doped with niobium and europium ions ((Eu0.5Nb0.5)xTi1-xO2 ceramics) was reported. A large permittivity (εr ~ 2.01?×?105) and a low dielectric loss (tanδ ~ 0.095) were observed for (Eu0.5Nb0.5)xTi1-xO2 (x?=?1%) ceramics at 1?kHz. Moreover, two significant relaxations were observed in the temperature dependence of dielectric properties for (Eu, Nb) co-doped TiO2 ceramics, which originated from defect dipoles and electron hopping, respectively. The low dielectric loss and high relative permittivity were ascribed to the electron-pinned defect-dipoles and electrons hopping. The (Eu0.5Nb0.5)xTi1-xO2 ceramic with great colossal permittivity is one of the most promising candidates for high-energy density storage applications. 相似文献
54.
Tao Li Zehui Du Nobumichi Tamura Mao Ye Saikumar Inguva Wei Lu Xierong Zeng Shanming Ke Haitao Huang 《Journal of the European Ceramic Society》2018,38(4):1488-1497
(1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 ((1-x)PZN-xPT in short) is one of the most important piezoelectric materials. In this work, we extensively investigated (1-x)PZN-xPT (x = 0.07–0.11) ferroelectric single crystals using in-situ synchrotron μXRD, complemented by TEM and PFM, to correlate microstructures with phase transitions. The results reveal that (i) at 25 °C, the equilibrium state of (1-x)PZN-xPT is a metastable orthorhombic phase for x = 0.07 and 0.08, while it shows coexistence of orthorhombic and tetragonal phases for x = 0.09 and x = 0.11, with all ferroelectric phases accompanied by ferroelastic domains; (ii) upon heating, the phase transformation in x = 0.07 is Orthorhombic → Monoclinic → Tetragonal → Cubic. The coexistence of ferroelectric tetragonal and paraelectric cubic phases was in-situ observed in x = 0.08 above Curie temperature (TC), and (iii) phase transition can be explained by the evolution of the ferroelectric and ferroelastic domains. These results disclose that (1-x)PZN-xPT are in an unstable regime, which is possible factor for its anomalous dielectric response and high piezoelectric coefficient. 相似文献
55.
56.
57.
58.
Catalytic Hydrocracking of a Bitumen‐Derived Asphaltene over NiMo/γ‐Al2O3 at Various Temperatures
下载免费PDF全文
![点击此处可从《化学工程与技术》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Hydrocracking of a bitumen‐derived asphaltene over NiMo/γ‐Al2O3 was investigated in a microbatch reactor at varying temperatures. The molar kinetics of asphaltene cracking reaction was examined by fitting the experimental data. Below a defined temperature, the molar reaction showed the first‐order kinetic feature while at higher temperatures secondary reactions such as coke formation became significant, causing deviation of the reaction behavior from the proposed first‐order kinetic model. Selectivity analysis proved that dominant products varied from gases to liquids to gases with increasing temperature, shifting the dominant reaction from C–S bonds cleavage to C–C bonds cleavage. 相似文献
59.
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
60.
To improve the electrochemical properties of rare-earth–Mg–Ni-based hydrogen storage alloys, the effects of stoichiometry and Cu-substitution on the phase structure and thermodynamic properties of the ... 相似文献