全文获取类型
收费全文 | 10456篇 |
免费 | 437篇 |
国内免费 | 632篇 |
专业分类
电工技术 | 98篇 |
综合类 | 440篇 |
化学工业 | 667篇 |
金属工艺 | 4849篇 |
机械仪表 | 316篇 |
建筑科学 | 30篇 |
矿业工程 | 108篇 |
能源动力 | 405篇 |
轻工业 | 7篇 |
水利工程 | 1篇 |
石油天然气 | 9篇 |
武器工业 | 75篇 |
无线电 | 279篇 |
一般工业技术 | 3218篇 |
冶金工业 | 780篇 |
原子能技术 | 99篇 |
自动化技术 | 144篇 |
出版年
2024年 | 13篇 |
2023年 | 211篇 |
2022年 | 171篇 |
2021年 | 349篇 |
2020年 | 328篇 |
2019年 | 325篇 |
2018年 | 273篇 |
2017年 | 299篇 |
2016年 | 231篇 |
2015年 | 260篇 |
2014年 | 411篇 |
2013年 | 734篇 |
2012年 | 460篇 |
2011年 | 917篇 |
2010年 | 511篇 |
2009年 | 646篇 |
2008年 | 579篇 |
2007年 | 586篇 |
2006年 | 597篇 |
2005年 | 482篇 |
2004年 | 485篇 |
2003年 | 430篇 |
2002年 | 309篇 |
2001年 | 249篇 |
2000年 | 241篇 |
1999年 | 216篇 |
1998年 | 161篇 |
1997年 | 192篇 |
1996年 | 120篇 |
1995年 | 122篇 |
1994年 | 106篇 |
1993年 | 79篇 |
1992年 | 71篇 |
1991年 | 50篇 |
1990年 | 48篇 |
1989年 | 40篇 |
1988年 | 21篇 |
1987年 | 27篇 |
1986年 | 27篇 |
1985年 | 15篇 |
1984年 | 22篇 |
1983年 | 17篇 |
1982年 | 21篇 |
1981年 | 15篇 |
1980年 | 14篇 |
1979年 | 9篇 |
1978年 | 14篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1975年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
21.
《International Journal of Hydrogen Energy》2020,45(33):16698-16707
It is of key importance to develop membrane assembly electrodes (MEAs) offering high conductivity, thermal stability and suitable performance in the fuel cell. The mesoporous materials functionalized with acid groups are appropriate candidates to improve membrane's properties. The goal of this work was to assess the addition of functionalized porous silica, bearing different acid groups, on the MEA performance in a PEM type single fuel cell. Ni59Nb40Pt0.6Fe0.4 -based amorphous alloys were applied as anode electrocatalysts. The synthesis of functionalized mesoporous silica (UGM-fx) with different acid groups, namely [SO3H], [COOH] and [PO(OH)2], was carried out following a nonaqueous sol gel method. The results showed that the MEA containing silica with PO(OH)2 groups leads to an outstanding fuel cell performance compared to that of the other organic groups-based MEAs and that it outperformed a commercial Pt-based sample. This might be due to the higher proton conductivity exhibited by the phosphonic groups. 相似文献
22.
Guangyao Chen Juyun Kang Baobao Lan Pengyue Gao Xionggang Lu Chonghe Li 《Ceramics International》2018,44(11):12627-12633
In this study, a new Ca-doped BaZrO3 refractory was designed by using thermodynamics approaches and tested for its applicability for vacuum induction melting (VIM) of TiAl alloys. The influence of CaO on the BaZrO3 phase constitution and microstructure, as well as the key features of the TiAl melt interaction with the Ca-doped BaZrO3 crucibles were investigated by X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM). Results revealed that the Ca-doped BaZrO3 refractory consisted of Ba1-xCaxZrO3 and CaO phases. An obvious interaction occurred during the melting of the TiAl alloy in the Ca-doped BaZrO3 crucible along with the generation of BaAl2O4 as a reaction product, with formation of a reaction layer up to 5?µm thick. Dissolution of Ca-doped BaZrO3 refractory in the TiAl melt was the main reason for the alloy-crucible reaction. Moreover, the Ca-doped BaZrO3 crucible was found to substantially reduce the contamination of the TiAl alloy, with lower oxygen concentration as compared with other conventional oxide crucibles. Overall results confirmed that vacuum induction melting using the Ca-doped BaZrO3 refractory can be considered as an appropriate method for the fabrication of TiAl alloys. 相似文献
23.
24.
25.
ABSTRACT The circular-patch welding test was used to study the liquation and liquation cracking of AZ-series Mg alloys. A heat treatment was carried out on the as-received AZ91 alloy to dissolve the γ(Mg17Al12) particles before welding. The circular-patch welding test was then conducted on the heat-treated, as-received AZ91 alloy using AZ61 and AZ91 filler wires. The results showed that the susceptibility of AZ91 alloy to liquation and liquation cracking was significantly reduced by the dissolution of massive γ(Mg17Al12) particles via a heat treatment before welding as the liquation mechanism was changed. Both constitutional liquation and incipient melting occurred in the partially melted zone of the as-received AZ91 welds, while only incipient melting occurred in the heat-treated AZ91 welds. 相似文献
26.
Junyuan Bai Xueyong Pang Xiangying Meng Hongbo Xie Hucheng Pan Yuping Ren Min Jiang Gaowu Qin 《材料科学技术学报》2020,(1):167-175
The crystal structure of the single-unit-cell thickness γ " phase,as a key strengthening phase in Mg-REZn(Ag) series alloys,has been extensively studied,and several structural models have been proposed in the past two decades.However,these reported models,and even the lattice constants at the same proposed structure,are scattered severely,which has led to considerable confusion and not available for further mechanical property simulation and prediction of Mg alloys containing this phase.In this study,by using first-principles calculations,the crystal structure of y" phase is clarified,resolving the discrepancies among different experiments,and its intrinsic mechanical properties have also been studied for the first time.It is verified that the γ " phase contains quasi-five atomic layers,instead of the previously reported tri-layer,and surprisingly,its crystal structure has many variants,which would change with the alloy composition.Besides,with the help of the simulated selected area electron diffraction(SAED) patterns,it is found that the atoms in the central layer remain partially ordered distribution,and this ordered extent primarily depends on the atomic ratio of RE:Zn(Ag) and the solute content in an alloy.That is,the ordered extent increases with decreasing the atomic ratio of RE:Zn(Ag) and/or increasing solute content of alloy,and vice versa.Ag and Zn dissolved in the γ" phase would produce almost opposed mechanical anisotropy for the γ " phase under the identical crystal structure,and the addition of Ag shows more efficient on increasing the shear modulus of γ" phase. 相似文献
27.
28.
29.
30.