全文获取类型
收费全文 | 12993篇 |
免费 | 1767篇 |
国内免费 | 1131篇 |
专业分类
电工技术 | 1328篇 |
综合类 | 534篇 |
化学工业 | 1184篇 |
金属工艺 | 1295篇 |
机械仪表 | 1318篇 |
建筑科学 | 675篇 |
矿业工程 | 51篇 |
能源动力 | 1390篇 |
轻工业 | 161篇 |
水利工程 | 163篇 |
石油天然气 | 126篇 |
武器工业 | 42篇 |
无线电 | 1992篇 |
一般工业技术 | 1812篇 |
冶金工业 | 222篇 |
原子能技术 | 196篇 |
自动化技术 | 3402篇 |
出版年
2024年 | 17篇 |
2023年 | 238篇 |
2022年 | 169篇 |
2021年 | 209篇 |
2020年 | 302篇 |
2019年 | 248篇 |
2018年 | 154篇 |
2017年 | 252篇 |
2016年 | 314篇 |
2015年 | 383篇 |
2014年 | 566篇 |
2013年 | 737篇 |
2012年 | 1213篇 |
2011年 | 1187篇 |
2010年 | 933篇 |
2009年 | 1276篇 |
2008年 | 1075篇 |
2007年 | 1573篇 |
2006年 | 1570篇 |
2005年 | 654篇 |
2004年 | 382篇 |
2003年 | 253篇 |
2002年 | 317篇 |
2001年 | 286篇 |
2000年 | 317篇 |
1999年 | 211篇 |
1998年 | 170篇 |
1997年 | 117篇 |
1996年 | 100篇 |
1995年 | 103篇 |
1994年 | 78篇 |
1993年 | 56篇 |
1992年 | 56篇 |
1991年 | 50篇 |
1990年 | 50篇 |
1989年 | 39篇 |
1988年 | 45篇 |
1987年 | 46篇 |
1986年 | 54篇 |
1985年 | 15篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 7篇 |
1981年 | 20篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1965年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
We report a simple processing method to simultaneously improve the efficiency and stability of organic solar cells (OSCs). Poly(4-styrene sulfonate)-doped poly(3,4-ethylenedioxy-thiophene (PEDOT:PSS), widely used as hole transport layer (HTL) in OSCs, tends to accelerate the degradation of devices because of its hygroscopic and acidic properties. In this regard, we have modified PEDOT:PSS to reduce its hygroscopic and acidic properties through a condensation reaction between PEDOT:PSS and poly(ethylene glycol) methyl ether (PEGME) in order to improve the efficiency and stability of OSCs. As a result, the power conversion efficiency (PCE) increased by 21%, from 2.57% up to 3.11%. A better energy level alignment by the reduced work function of the modified PEDOT:PSS with a highest occupied molecular orbital (HOMO) level of poly(3-hexylthiophene-2,5-diyl) (P3HT) is considered the origin of the improved the efficiency. The half-life of OSCs with PEDOT:PSS modified with PEGME buffer layer also increased up to 3.5 times compared to that of devices with pristine PEDOT:PSS buffer layer. 相似文献
2.
Waveguide configurations of hierarchical system are proposed as new microstructures for composites in absorbing enhancement. Supercritical fluid (SCF) one-pot exfoliation of layered graphite and manganese oxide mixing materials is developed to obtain a hierarchical system, containing graphene nanosheets (GNS) and exfoliated manganese oxides (EMO) in different sizes. Composites with GNS–EMO embedded in epoxy resin matrix are produced for a design of dielectric and magnetic loss integrated absorber. Volume fraction of GNS–EMO in composites is given for an optimal quantity of resin epoxy in fixation and formation. The effect of mixing ratios between electric and magnetic components is provided for the design of dielectric and magnetic loss integrated absorbers. Frequency shifting phenomena are revealed in the component adjusting course. Excluding the offsetting sizes, reflection loss of composites is enhanced as thickness increases. Synergistic effect of electric and magnetic coordinated materials demonstrates the superiority of micro-waveguide structures in GNS–EMO composite absorber. 相似文献
3.
Research funding has been seen as one of the most important resource in the reward system of science. And usage of publications denotes an interesting perspective of user behavior in scientific communication. This study aims to address the relationship between funding and Usage Count, which is a new metrics item established on the platform of Web of Science. Full records of 300,010 articles published in 2013 were downloaded in October 2015, and divided into six disciplines, including information science library science, education educational research, economics, computer science, materials science, and chemistry. Seven indicators were proposed to measure the impact, including Funding rate, Citation per paper, Usage rate, Usage per paper, Citation difference, Usage difference, and Conversion rate. It concluded funding has impact on usage and citation, and funded papers attract more usage, but varying in different disciplines. Usage Count can be used in the extension of citation metrics but with limits. This study originally engages with usage metrics and detected that there is positive correlation between usage and funding. 相似文献
4.
5.
《Journal of the European Ceramic Society》2020,40(8):3348-3353
Large transduction coefficient () is difficult to obtain in piezoelectric ceramics because these two parameters show opposite trends with compositional modifications. Herein, the Pb(Zr0.53Ti0.47)O3 ceramic powders were calcinated under different temperatures (A:830 °C, B:860 °C, and C:890 °C), and then mixed together according to different weight ratios (1A:1B:1C, 1A:2B:1C, 1A:2B:3C and 3A:2B:1C) for ceramics preparation. Both d33 and g33 are improved successfully, and the transduction coefficient with the weight ratio of 1A:2B:3C reaches up to 17,500 × 10−15 m2/N, which is 60 % higher than that with the powders calcinated under 830 °C, and at least twice those of commercial PZT-4, PZT-5A and PZT-8 ceramics. The improved transduction coefficient is owing to the enhanced piezoelectric constant and spontaneous polarization resulted from the increased grain size, relative density and the fraction of tetragonal phase. These results indicate that this is a simple but effective way to tailor the transduction coefficient in piezoelectric ceramics. 相似文献
6.
进入21世纪,随着集成电路的发展,SoC(System on Chip)片上系统应运而生。而作为SoC重要组成部分的嵌入式存储器,在SoC中所占的比重正逐步增加,并起着越来越重要的作用,那么嵌入式存储器与独立的存储器芯片在设计上存在着哪些差异?对此本文将以NOR型闪存为例在制造工艺的选取、衍生产品的设计、功耗与噪声、后端功能仿真、测试与修复等方面进行分析和研究。 相似文献
7.
8.
先说明市内接入网的单位用户和住家用户两大类使用通信和电视、交互型和分配型业务的要求不相同,相应地对光纤传输的应用须作不同的考虑,文中认为;光纤从市内交换局直连办公大楼是合乎现实需要的,而对于居民住家,宜选用光纤连至路边或光纤与同轴结合和适当利用无源光网络等方案,俟将来时机成熟才实行光纤连至每一家,文末有概括总结,说明接入网不同于长途网,接入网的光纤系统可以使用常规单模光纤,工作于波长1.3μm,而光放大器和波分多路系统不是普遍需要,但光电子集成在光端机中是必要的。 相似文献
9.
数模混合仿真中模拟信号的恢复及其误差对整个仿真过程具有重要影响。本文探讨了用零阶保持和一阶保持进行信号恢复的方法,比较了它们的误差及工作特点。特别指出了一阶保持中,由于存在积分器复原时间及数字机操作时间的影响而会带来附加的误差,因此一阶保持方法较难达到其理论的精度。 相似文献
10.