全文获取类型
收费全文 | 434239篇 |
免费 | 48536篇 |
国内免费 | 33169篇 |
专业分类
电工技术 | 37560篇 |
技术理论 | 2篇 |
综合类 | 44639篇 |
化学工业 | 55181篇 |
金属工艺 | 29862篇 |
机械仪表 | 30039篇 |
建筑科学 | 32665篇 |
矿业工程 | 17452篇 |
能源动力 | 11474篇 |
轻工业 | 45932篇 |
水利工程 | 13836篇 |
石油天然气 | 15795篇 |
武器工业 | 6110篇 |
无线电 | 47020篇 |
一般工业技术 | 38311篇 |
冶金工业 | 19014篇 |
原子能技术 | 7144篇 |
自动化技术 | 63908篇 |
出版年
2024年 | 1381篇 |
2023年 | 6823篇 |
2022年 | 16095篇 |
2021年 | 21274篇 |
2020年 | 14838篇 |
2019年 | 10624篇 |
2018年 | 11412篇 |
2017年 | 13176篇 |
2016年 | 11628篇 |
2015年 | 18683篇 |
2014年 | 23896篇 |
2013年 | 28754篇 |
2012年 | 35520篇 |
2011年 | 37640篇 |
2010年 | 35043篇 |
2009年 | 33367篇 |
2008年 | 34636篇 |
2007年 | 33517篇 |
2006年 | 29307篇 |
2005年 | 24039篇 |
2004年 | 16950篇 |
2003年 | 11446篇 |
2002年 | 10679篇 |
2001年 | 9492篇 |
2000年 | 7887篇 |
1999年 | 4046篇 |
1998年 | 2318篇 |
1997年 | 1946篇 |
1996年 | 1703篇 |
1995年 | 1407篇 |
1994年 | 1092篇 |
1993年 | 949篇 |
1992年 | 779篇 |
1991年 | 590篇 |
1990年 | 519篇 |
1989年 | 427篇 |
1988年 | 328篇 |
1987年 | 244篇 |
1986年 | 201篇 |
1985年 | 169篇 |
1984年 | 126篇 |
1983年 | 105篇 |
1982年 | 105篇 |
1981年 | 118篇 |
1980年 | 150篇 |
1979年 | 102篇 |
1978年 | 34篇 |
1976年 | 55篇 |
1959年 | 74篇 |
1951年 | 79篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Da-Wang Tan Zhen-Yong Lao Zhan Zhang Wei-Ming Guo Shi-Kuan Sun Hua-Tay Lin 《Journal of the American Ceramic Society》2021,104(6):2860-2867
B4C-TiB2 ceramics (TiB2 ranging 5~70 vol%) with Mo-Co-WC as the sintering additive were prepared by spark plasma sintering. In comparison with B4C-TiB2 without additive, the enhanced densification was evident in the sintered specimen with Mo-Co-WC additive. Core-rim structured grain was observed around TiB2 grains. The interface of the rim between TiB2 and B4C phases demonstrated different feature: the inner borderline of the rim exhibited a smooth feature, whereas a sharp curved grain boundary was observed between the rim and the B4C grain. The formation mechanism is discussed: the epitaxial growth of (Ti,Mo,W)B2 rim around the TiB2 core may occur as a result of the solid solution and dissolution-precipitation between TiB2 phase and the sintering additive. It was revealed that the fracture toughness increased as the content of TiB2 content increased, alongside the decreased hardness. B4C-30 vol% TiB2 specimen demonstrated the optimal combination of mechanical properties, reaching Vickers hardness of 24.3 GPa and fracture toughness of 3.33 MPa·m1/2. 相似文献
22.
本文结合慕课堂线上学习数据与线下考试成绩,研究学生在线学习的行为表现与学习效果之间的关联性,所获得的信息能够体现出不同学生群体的特点以及不同学习维度的作用,从而提醒教师适时调整教学策略,持续改进,有助于教师改进教学方法,提高教学质量. 相似文献
23.
本文通过对巡检仪进行示值稳定性、重复性的试验,探讨热电偶的选择与巡检仪示值之间的关系,以确定校准方法,指导使其有效溯源. 相似文献
24.
25.
Shilin Du Yichen Dong Feiqiang Guo Beile Tian Songbo Mao Lin Qian Chengyun Xin 《International Journal of Hydrogen Energy》2021,46(27):14138-14147
The potential of using high metals containing coal gangue and lignite to prepare high-activity coal char-based catalysts is investigated for effective biomass tar decomposition. Loose structure and rough surface are formed for these char-based catalysts with heterogeneous distribution of a large number of inorganic particles. In the biomass tar decomposition, the performance of the coal char-based catalysts is significantly influenced by the content of the metals in the raw materials and coal gangue char (GC) with the ash content as high as 50.80% exhibits the highest activity in this work. A high biomass tar conversion efficiency of 93.5% is achieved at 800 °C along with a significant increase in the fuel gas product. During the five-time consecutive tests, the catalytic performance of GC increases a little at the second or third times reuse and remains relatively stable, showing the remarkable stability of the catalyst in biomass tar decomposition applications. 相似文献
26.
27.
28.
29.
Shuhai Liu Ming Han Xiaolong Feng Qiuhong Yu Long Gu Longfei Wang Yong Qin Zhong Lin Wang 《Advanced functional materials》2021,31(17):2010339
Utilizing inner-crystal piezoelectric polarization charges to control carrier transport across a metal-semiconductor or semiconductor–semiconductor interface, piezotronic effect has great potential applications in smart micro/nano-electromechanical system (MEMS/NEMS), human-machine interfacing, and nanorobotics. However, current research on piezotronics has mainly focused on systems with only one or rather limited interfaces. Here, the statistical piezotronic effect is reported in ZnO bulk composited of nanoplatelets, of which the strain/stress-induced piezo-potential at the crystals’ interfaces can effectively gate the electrical transport of ZnO bulk. It is a statistical phenomenon of piezotronic modification of large numbers of interfaces, and the crystal orientation of inner ZnO nanoplatelets strongly influence the transport property of ZnO bulk. With optimum preferred orientation of ZnO nanoplatelets, the bulk exhibits an increased conductivity with decreasing stress at a high pressure range of 200–400 MPa, which has not been observed previously in bulk. A maximum sensitivity of 1.149 µS m−1 MPa−1 and a corresponding gauge factor of 467–589 have been achieved. As a statistical phenomenon of many piezotronic interfaces modulation, the proposed statistical piezotronic effect extends the connotation of piezotronics and promotes its practical applications in intelligent sensing. 相似文献
30.
凌庄子水厂蓄水池进水口处有一保水堰,为非标准薄壁堰,不能使用已有堰流公式对其过流量进行准确计算。为了得出较为精确的过流流量,按照重力相似准则制作几何比尺为1∶5的模型进行试验研究。在已有自由出流公式的基础上,对自由出流流量系数进行修正并对淹没情况下流量变化过程进行研究。对该非标准堰自由出流流量系数的实测值与经验值进行分析比较,发现堰板槽降低了实际自由出流过流能力。淹没出流的流量系数主要与下游尾水位有关,试验中形成的淹没式堰流受实际堰型尺寸影响,下游尾水位和堰上水位近似相等,不完全适用已有淹没出流流量公式,通过试验给出了修正淹没系数随h/p的变化关系。结果表明利用堰前、堰后水位初步计算过流流量是可行的,可为该工程提供参考,也可为实际工程中非标准矩形堰的流量计算提供思路。 相似文献