全文获取类型
收费全文 | 106620篇 |
免费 | 7983篇 |
国内免费 | 3210篇 |
专业分类
电工技术 | 4580篇 |
技术理论 | 4篇 |
综合类 | 4380篇 |
化学工业 | 19610篇 |
金属工艺 | 5435篇 |
机械仪表 | 7080篇 |
建筑科学 | 5617篇 |
矿业工程 | 1337篇 |
能源动力 | 3699篇 |
轻工业 | 8015篇 |
水利工程 | 1455篇 |
石油天然气 | 2730篇 |
武器工业 | 486篇 |
无线电 | 14991篇 |
一般工业技术 | 17674篇 |
冶金工业 | 6277篇 |
原子能技术 | 1398篇 |
自动化技术 | 13045篇 |
出版年
2024年 | 285篇 |
2023年 | 1381篇 |
2022年 | 2490篇 |
2021年 | 3711篇 |
2020年 | 2689篇 |
2019年 | 2584篇 |
2018年 | 2941篇 |
2017年 | 3107篇 |
2016年 | 3447篇 |
2015年 | 3614篇 |
2014年 | 4902篇 |
2013年 | 6456篇 |
2012年 | 6931篇 |
2011年 | 7971篇 |
2010年 | 6517篇 |
2009年 | 6326篇 |
2008年 | 6221篇 |
2007年 | 5390篇 |
2006年 | 5250篇 |
2005年 | 4509篇 |
2004年 | 3608篇 |
2003年 | 3463篇 |
2002年 | 3561篇 |
2001年 | 2979篇 |
2000年 | 2492篇 |
1999年 | 2217篇 |
1998年 | 2604篇 |
1997年 | 1857篇 |
1996年 | 1596篇 |
1995年 | 1246篇 |
1994年 | 1050篇 |
1993年 | 847篇 |
1992年 | 616篇 |
1991年 | 531篇 |
1990年 | 451篇 |
1989年 | 387篇 |
1988年 | 334篇 |
1987年 | 244篇 |
1986年 | 176篇 |
1985年 | 153篇 |
1984年 | 121篇 |
1983年 | 78篇 |
1982年 | 61篇 |
1981年 | 62篇 |
1980年 | 46篇 |
1979年 | 40篇 |
1978年 | 32篇 |
1977年 | 38篇 |
1976年 | 70篇 |
1975年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
Chenxu Liu Shuguang Zhang Ruonan Ji Peng Wang Jin Zhang Yu Tian Yonggang Meng Yedong He 《Ceramics International》2019,45(4):4747-4755
Semiconductor particles doped Al2O3 coatings were prepared by cathode plasma electrolytic deposition in Al(NO3)3 electrolyte dispersed with SiC micro- and nano-particles (average particle sizes of 0.5–1.7?µm and 40?nm respectively). The effects of the concentrations and particle sizes of the SiC on the microstructures and tribological performances of the composite coatings were studied. In comparison with the case of dispersing with SiC microparticles, the dispersion of SiC nanoparticles in the coatings was more uniform. When the concentration of SiC nanoparticles was 5?g/L, the surface roughness of the composite coating was reduced by 63%, compared with that of the unmodified coating. Friction results demonstrated that the addition of 5?g/L SiC nanoparticles reduced the friction coefficient from 0.60 to 0.38 and decreased the wear volume under dry friction. The current density and bath voltage were measured to analyze the effects of SiC particles on the deposition process. The results showed that the SiC particles could alter the electrical behavior of the coatings during the deposition process, weaken the bombardment of the plasma, and improve the structures of the coatings. 相似文献
32.
Eui Dae Jung Amit Kumar Harit Do Hui Kim Chung Hyeon Jang Jong Hyun Park Shinuk Cho Myoung Hoon Song Han Young Woo 《Advanced materials (Deerfield Beach, Fla.)》2020,32(30):2002333
A series of anionic conjugated polyelectrolytes (CPEs) is synthesized based on poly(fluorene-co-phenylene) by varying the side-chain ionic density from two to six per repeat units (MPS2-TMA, MPS4-TMA, and MPS6-TMA). The effect of MPS2, 4, 6-TMA as interlayers on top of a hole-extraction layer of poly(bis(4-phenyl)-2,4,6-trimethylphenylamine (PTAA) is investigated in inverted perovskite solar cells (PeSCs). Owing to the improved wettability of perovskites on hydrophobic PTAA with the CPEs, the PeSCs with CPE interlayers demonstrate a significantly enhanced device performance, with negligible device-to-device dependence relative to the reference PeSC without CPEs. By increasing the ionic density in the MPS-TMA interlayers, the wetting, interfacial defect passivation, and crystal growth of the perovskites are significantly improved without increasing the series resistance of the PeSCs. In particular, the open-circuit voltage increases from 1.06 V for the PeSC with MPS2-TMA to 1.11 V for the PeSC with MPS6-TMA. The trap densities of the PeSCs with MPS2,4,6-TMA are further analyzed using frequency-dependent capacitance measurements. Finally, a large-area (1 cm2) PeSC is successfully fabricated with MPS6-TMA, showing a power conversion efficiency of 18.38% with negligible hysteresis and a stable power output under light soaking for 60 s. 相似文献
33.
34.
Su-Il Ri Song-Il Hong Jong-Chol Kim Ju-Hyok Wi 《International Journal of Hydrogen Energy》2021,46(5):3319-3328
We investigated some properties of the hydride Mg2FeH6 substituted with yttrium by a first principles calculation. Some experimental results showed that 4d transition metal, yttrium serves as a good catalyst for magnesium based hydrogen storage alloys, but there are a few theoretical studies about magnesium based hydrides substituted with it. Mg2FeH6 is regarded as a cheaper material than pure MgH2, while it is crystalized into Fm3m structure (space group 225). Although it has high hydrogen storage capacity, many investigations have not been devoted to it due to its extremely high thermodynamic stability. The yttrium substituted Mg2FeH6 exhibits very low energy of formation, and its desorption temperature, 75 °C is very suitable for practical hydrogen storage applications. Our results showed that Mg2FeH6 is destabilized effectively by yttrium substitution and introducing vacancy defects has additive effect to the improvement of dehydrogenation performance. 相似文献
35.
Jeongchan Lee Dr. Joonwon Kim Hyun Kim Eun-Jung Kim Prof. Dr. Hee-Jin Jeong Prof. Dr. Kwon-Young Choi Prof. Dr. Byung-Gee Kim 《Chembiochem : a European journal of chemical biology》2020,21(10):1446-1452
Tryptophan halogenases are found in diverse organisms and catalyze regiospecific halogenation. They play an important role in the biosynthesis of halogenated indole alkaloids, which are biologically active and of therapeutic importance. Here, a tryptophan 6-halogenase (SatH) from Streptomyces albus was characterized by using a whole-cell reaction system in Escherichia coli. SatH showed substrate specificity for chloride and bromide ions, leading to regiospecific halogenation at the C6-position of l -tryptophan. In addition, SatH exhibited higher performance in bromination than that of previously reported tryptophan halogenases in the whole-cell reaction system. Through structure-based protein mutagenesis, it has been revealed that two consecutive residues, A78/V79 in SatH and G77/I78 in PyrH, are key determinants in the regioselectivity difference between tryptophan 6- and 5-halogenases. Substituting the AV with GI residues switched the regioselectivity of SatH by moving the orientation of tryptophan. These data contribute to an understanding of the key residues that determine the regioselectivity of tryptophan halogenases. 相似文献
36.
37.
38.
39.
Choi Paul Santos Christian Ariane Kim Min-Kun Jung Hyunsook Hong Do-Young Koo Junemo 《Journal of Mechanical Science and Technology》2021,35(11):5007-5022
Journal of Mechanical Science and Technology - This study delivers equations useful for low-height pleated fibrous filter design: two pressure drop equations and one set of optimum design equations... 相似文献
40.