全文获取类型
收费全文 | 29641篇 |
免费 | 2771篇 |
国内免费 | 1329篇 |
专业分类
电工技术 | 1894篇 |
技术理论 | 2篇 |
综合类 | 1926篇 |
化学工业 | 4685篇 |
金属工艺 | 1760篇 |
机械仪表 | 1944篇 |
建筑科学 | 2610篇 |
矿业工程 | 1085篇 |
能源动力 | 823篇 |
轻工业 | 1911篇 |
水利工程 | 592篇 |
石油天然气 | 1857篇 |
武器工业 | 259篇 |
无线电 | 3193篇 |
一般工业技术 | 3506篇 |
冶金工业 | 1401篇 |
原子能技术 | 303篇 |
自动化技术 | 3990篇 |
出版年
2024年 | 145篇 |
2023年 | 547篇 |
2022年 | 985篇 |
2021年 | 1343篇 |
2020年 | 977篇 |
2019年 | 710篇 |
2018年 | 896篇 |
2017年 | 933篇 |
2016年 | 866篇 |
2015年 | 1176篇 |
2014年 | 1384篇 |
2013年 | 1689篇 |
2012年 | 1807篇 |
2011年 | 2017篇 |
2010年 | 1749篇 |
2009年 | 1590篇 |
2008年 | 1648篇 |
2007年 | 1462篇 |
2006年 | 1619篇 |
2005年 | 1468篇 |
2004年 | 946篇 |
2003年 | 887篇 |
2002年 | 870篇 |
2001年 | 741篇 |
2000年 | 724篇 |
1999年 | 936篇 |
1998年 | 640篇 |
1997年 | 625篇 |
1996年 | 501篇 |
1995年 | 419篇 |
1994年 | 359篇 |
1993年 | 231篇 |
1992年 | 214篇 |
1991年 | 157篇 |
1990年 | 129篇 |
1989年 | 105篇 |
1988年 | 87篇 |
1987年 | 40篇 |
1986年 | 28篇 |
1985年 | 29篇 |
1984年 | 18篇 |
1983年 | 7篇 |
1982年 | 11篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1959年 | 3篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
该文基于掺钪AlN薄膜制备了高次谐波体声波谐振器(HBAR),研究了钪(Sc)掺杂浓度对AlN压电薄膜材料特性及器件性能的影响。研究表明,当掺入Sc的摩尔分数从0增加到25%时,压电应力系数e33增加、刚度 下降,导致Al1-xScxN压电薄膜的机电耦合系数 从5.6%提升至15.8%,从而使HBAR器件的有效机电耦合系数 提升了3倍。同时,当Sc掺杂摩尔分数达25%时,Al1-xScxN(x为Sc掺杂摩尔分数)压电薄膜的声速下降13%,声学损耗提高,导致HBAR器件的谐振频率和品质因数降低。 相似文献
3.
4.
Huizhu Cai Bingbing Chen Xiao Zhang Yuchen Deng Dequan Xiao Ding Ma Chuan Shi 《Nano Research》2021,14(1):122-130
Over recent years,catalytic materials of Fe-N-C species have been recognized being active for oxygen reduction reaction(ORR).However,the identification of active site remains challenging as it generally involves a pyrolysis process and mixed components being obtained.Herein Fe3C/C and Fe2N/C samples were synthesized by temperature programmed reduction of Fe precursors in 15%CH4/H2and pure NH3,respectively.By acid leaching of Fe2N/C sample,only single sites of FeN4species were presented,providing an ideal model for identification of catalytic functions of the single sites of FeN4in ORR.A correlation was conducted between the concentration of FeⅡN4in low spin state by Mossbauer spectra and the kinetic current density at 0.8 V in alkaline media,and such a structure-performance correlation assures the catalytic roles of low spin FeⅡN4 species as highly active sites for the ORR. 相似文献
5.
Nitrile rubber (NBR) blends with excellent performance have always been a hot research topic in petroleum field. Due to the excellent performance and compatibility of polyamide 6 (PA6), it provides an opportunity for the preparation of high-performance NBR/PA6 blends. In this article, NBR/PA6 blends were prepared by the three-step molding process. Experimentally, it was found that PA6 has a prominent reinforcement effect in NBR matrix. The variation of this mechanical property was investigated from different aspects of the crystal structure, crystallinities, phase morphology, and so on. It can be cleared that the formation of fibrous structure of PA6 phase is the main factor for reinforcement of the polymer blends. Meanwhile, the formation mechanism of the special phase structure induced by the three-step process is deeply expounded and its structural evolution schematic is established. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47472. 相似文献
6.
7.
8.
9.
Chuangang Yao Jixing Yang Haixia Zhang Sigeng Chen Jian Meng Kedi Cai 《Ceramics International》2021,47(17):24589-24596
Bismuth doped La2-xBixNiO4+δ (x = 0, 0.02 and 0.04) oxides are investigated as SOFC cathodes. The effects of Bi doping on the phase structure, thermal expansion, electrical conduction behavior as well as electrochemical performance are studied. All the samples exist as a tetragonal Ruddlesden-Popper structure. Bi-doped LBNO-0.02 and LBNO-0.04 have good chemical and thermal compatibility with LSGM electrolyte. The average TEC over 20–900°С was 13.4 × 10?6 and 14.2 × 10?6 K?1 for LBNO-0.02 and LBNO-0.04, respectively. The electrical conductivity was decreasing with the rise of Bi doping content. EIS measurement indicates Bi doping can decrease the ASR values. At 750 °C, the obtained ASR for LBNO-0.04 is 0.18 Ωcm2, which is 56% lower than that of the sample without Bi doping, suggesting Bi doping is beneficial to the electrochemical catalytic activity of LBNO cathodes. 相似文献
10.
Jiajia Ye Xuting Li Guang Xia Guanghao Gong Zhiqiang Zheng Chuanzhong Chen Cheng Hu 《材料科学技术学报》2021,77(18):100-107
We report for the first time a Na-ion battery anode material composed of P-doped CoSe2 nanoparticles(P-CoSe2)with the size of 5-20 nm that are uniformly embed in a 3D porous honeycomb-like carbon network.High rate capability and cycling stability are achieved simultaneously.The honeycomb-like carbon network is rationally designed to support high electrical conductivity,rapid Na-ion diffusion as well as the accommodation of the volume expansion from the active P-CoSe2 nanoparticles.In particular,heteroatom P-doping within CoSe2 introduces stronger P-Co bonds and additional P-Se bonds that signif-icantly improve the structure stability of P-CoSe2 for highly stable sodiation/desodiation over long-term cycling.P-doping also improves the electrical conductivity of the CoSe2 nanoparticles,leading to highly elevated electrochemical kinetics to deliver high specific capacities at high current densities.Benefiting from the unique nanostructure and atomic-level P-doping,the P-CoSe2(2∶1)/C anode delivers an excel-lent cycle stability with a specific capacity of 206.9 mA h g-1 achieved at 2000 mA g-1 after 1000 cycles.In addition,this material can be synthesized using a facile pyrolysis and selenization/phosphorization approach.This study provides new opportunities of heteroatom doping as an effective method to improve the cycling stability of Na-ion anode materials. 相似文献