全文获取类型
收费全文 | 450087篇 |
免费 | 15173篇 |
国内免费 | 6363篇 |
专业分类
电工技术 | 13882篇 |
技术理论 | 9篇 |
综合类 | 8990篇 |
化学工业 | 69030篇 |
金属工艺 | 23859篇 |
机械仪表 | 20857篇 |
建筑科学 | 15996篇 |
矿业工程 | 5727篇 |
能源动力 | 9235篇 |
轻工业 | 34376篇 |
水利工程 | 6364篇 |
石油天然气 | 14460篇 |
武器工业 | 1080篇 |
无线电 | 46679篇 |
一般工业技术 | 84199篇 |
冶金工业 | 59327篇 |
原子能技术 | 10582篇 |
自动化技术 | 46971篇 |
出版年
2022年 | 4655篇 |
2021年 | 7721篇 |
2020年 | 5878篇 |
2019年 | 5719篇 |
2018年 | 14876篇 |
2017年 | 15664篇 |
2016年 | 12225篇 |
2015年 | 7993篇 |
2014年 | 10829篇 |
2013年 | 18571篇 |
2012年 | 17379篇 |
2011年 | 24804篇 |
2010年 | 21432篇 |
2009年 | 20791篇 |
2008年 | 21103篇 |
2007年 | 22415篇 |
2006年 | 13954篇 |
2005年 | 14922篇 |
2004年 | 12024篇 |
2003年 | 11495篇 |
2002年 | 10553篇 |
2001年 | 9434篇 |
2000年 | 8621篇 |
1999年 | 8124篇 |
1998年 | 14733篇 |
1997年 | 10692篇 |
1996年 | 8443篇 |
1995年 | 6925篇 |
1994年 | 6059篇 |
1993年 | 5731篇 |
1992年 | 4696篇 |
1991年 | 4315篇 |
1990年 | 4491篇 |
1989年 | 4272篇 |
1988年 | 4012篇 |
1987年 | 3535篇 |
1986年 | 3517篇 |
1985年 | 3919篇 |
1984年 | 3764篇 |
1983年 | 3396篇 |
1982年 | 3241篇 |
1981年 | 3321篇 |
1980年 | 3188篇 |
1979年 | 3221篇 |
1978年 | 3290篇 |
1977年 | 3535篇 |
1976年 | 4406篇 |
1975年 | 2927篇 |
1974年 | 2794篇 |
1973年 | 2923篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
1.
L.J. Espinoza-Pérez S. Esquivel-Medina E. López-Honorato 《Ceramics International》2021,47(11):15527-15532
The influence of the microstructure on the corrosion rate of three monolithic SiC samples in FLiNaK salt at 900 °C for 250 h was studied. The SiC samples, labeled as SiC-1, SiC-2, and SiC-3, had corrosion rates of 0.137, 0.020, and 0.043 mg/cm2h, respectively. Compared with grain size and the presence of special grain boundaries (i.e., Σ3), the content of high-angle grain boundaries (HAGBs) appeared to have the strongest influence on the corrosion rate of SiC in FLiNaK salt, since the corrosion rate increased six times as the concentration of high-angle grain boundaries increased from 19 to 32% for SiC-2 and SiC-1, respectively. These results stress the importance of controlling the content of HAGBs during the production process of SiC. 相似文献
2.
Macintosh Katrina A. McDowell Richard W. Wright-Stow Aslan E. Depree Craig Robinson Guy M. 《Nutrient Cycling in Agroecosystems》2021,120(2):121-129
Nutrient Cycling in Agroecosystems - Reducing agriculturally derived diffuse contaminant losses (via non-point sources) from land to water has proven difficult for decades. Owing to the diversity... 相似文献
3.
Kedong Xia Shuoshuo Yu Yunling Li Huijuan Han Lingyao Duan Zhenyu Hou Xiao Liu 《Journal of the European Ceramic Society》2021,41(4):2375-2385
In this study, C/SiOC and C/SiO2 composites were prepared by using carbonaceous microspheres with different surface functional groups. Carbonaceous microspheres based on hydrothermal reaction of glucose contains hydroxyl group, while the surface carboxyl group increases after NaOH etching. The hydroxyl group increases the oxygen-enriched structural units of SiOC ceramics, and the C spheres are closely enwrapped in SiOC matrix after pyrolysis at 900 °C. However, the interfacial reaction of surface carboxyl with Si–OH results in the formation of cristobalite SiO2, and C spheres are not only encased inside the SiOC matrix, but also dispersed outside of SiOC ceramics. After removal of C via calcination at 500 °C for 5 h, C/SiOC and C/SiO2 composites are transformed into amorphous SiO2 and cristobalite SiO2, respectively. The thermogravimetric analysis indicates the oxidation resistance of SiOC is superior to that of C and SiO2. 相似文献
4.
Ustinov V. S. Volkov A. N. Samoilov O. B. Morozov O. A. Polyanskikh S. A. Alekseev V. I. Galitskikh V. Yu. 《Atomic Energy》2021,130(2):69-75
Atomic Energy - The physical aspects and main results of reactor tests of a two-stage core consisting of fresh fuel assemblies and a significant number of fuel assemblies from the previous core,... 相似文献
5.
Wireless Personal Communications - A GPS spoofing attack broadcasts counterfeit signals to resemble standard GPS satellite signals to take control of the correlation peaks of GPS signals to force... 相似文献
6.
7.
Avdeev Ya. G. Kuznetsov D. S. Kuznetsov Yu. I. 《Protection of Metals and Physical Chemistry of Surfaces》2021,57(7):1307-1312
Protection of Metals and Physical Chemistry of Surfaces - Impedance spectroscopy was used to study the adsorption of the IFKhAN-92 inhibitor, a triazole derivative, on cathodically polarized... 相似文献
8.
Shimei Fu Song Xue Jun Chen Shuai Shang Hui Xiao Yu Zang Xuexi Tang 《International journal of molecular sciences》2021,22(4)
The effects of ultraviolet (UV) radiation, particularly UV-B on algae, have become an important issue as human-caused depletion of the protecting ozone layer has been reported. In this study, the effects of different short-term UV-B radiation on the growth, physiology, and metabolism of Porphyra haitanensis were examined. The growth of P. haitanensis decreased, and the bleaching phenomenon occurred in the thalli. The contents of total amino acids, soluble sugar, total protein, and mycosporine-like amino acids (MAAs) increased under different UV-B radiation intensities. The metabolic profiles of P. haitanensis differed between the control and UV-B radiation-treated groups. Most of the differential metabolites in P. haitanensis were significantly upregulated under UV-B exposure. Short-term enhanced UV-B irradiation significantly affected amino acid metabolism, carbohydrate metabolism, glutathione metabolism, and phenylpropane biosynthesis. The contents of phenylalanine, tyrosine, threonine, and serine were increased, suggesting that amino acid metabolism can promote the synthesis of UV-absorbing substances (such as phenols and MAAs) by providing precursor substances. The contents of sucrose, D-glucose-6-phosphate, and beta-D-fructose-6-phosphate were increased, suggesting that carbohydrate metabolism contributes to maintain energy supply for metabolic activity in response to UV-B exposure. Meanwhile, dehydroascorbic acid (DHA) was also significantly upregulated, denoting effective activation of the antioxidant system. To some extent, these results provide metabolic insights into the adaptive response mechanism of P. haitanensis to short-term enhanced UV-B radiation. 相似文献
9.
Kyle L. Covington Alexander K. Goroncy Teresa E. Lehmann Zuhao Kou Heng Wang Vladimir Alvarado 《American Institute of Chemical Engineers》2021,67(2):e17074
Microtomography (μCT) and nuclear magnetic resonance (NMR) have been used to characterize porous media for decades. Magnetic resonance imaging (MRI) enables direct visualization of pore architecture and many pulse sequences exist. In this work, we tested the MRI pulse sequence Zero Echo Time (ZTE) to study sandstone and carbonate for its ability to address short relaxation times. We aimed at resolving two fluid conduit scales, that is, pores and fractures. In this research, we study tighter porous systems than those previously reported using ZTE. Additionally, pore cluster analysis (PCA), combined with ZTE, can be used to analyze pore-fracture connectivity of relatively large core plugs. We show that ZTE can resolve two-scale pore systems simultaneously, that is, fractures and pores. By combining time-domain NMR pore-size analysis and PCA, we show that careful selection of resolution is necessary to understand transport in porous media. 相似文献
10.
E.N. Lysenko V.A. Vlasov A.V. Malyshev E.A. Sheveleva A.P. Surzhikov 《Ceramics International》2021,47(17):23935-23941
The effect of dry and wet ball milling of LiFe5O8 ferrite powder on the microstructure and electromagnetic properties of ferrite ceramics was studied using XRD analysis, scanning electron microscopy, dilatometry, thermogravimetry, calorimetry, and measurement of specific magnetization and electrical resistance. The sintering temperature was 1050 °C; the sintering time was 2 h. It was found that ferrite fabricated from dry-milled powder exhibits an ordered α-LiFe5O8 phase with bulk density of 91%. Its saturation magnetization and Curie temperature are 55 emu/g and 628°С, respectively. Specific electrical resistance is 4?106 Ω cm. Wet milling in isopropyl alcohol causes formation of a disordered β-LiFe5O8 phase. Ceramics produced by this method shows higher bulk density (97%) and low porosity, and an order of magnitude lower resistivity. Its saturation magnetization and Curie temperature are 51 emu/g and 607°С, respectively. 相似文献