全文获取类型
收费全文 | 22971篇 |
免费 | 3589篇 |
国内免费 | 1612篇 |
专业分类
电工技术 | 15848篇 |
综合类 | 1405篇 |
化学工业 | 616篇 |
金属工艺 | 440篇 |
机械仪表 | 817篇 |
建筑科学 | 362篇 |
矿业工程 | 402篇 |
能源动力 | 853篇 |
轻工业 | 166篇 |
水利工程 | 265篇 |
石油天然气 | 111篇 |
武器工业 | 57篇 |
无线电 | 4094篇 |
一般工业技术 | 789篇 |
冶金工业 | 448篇 |
原子能技术 | 247篇 |
自动化技术 | 1252篇 |
出版年
2024年 | 46篇 |
2023年 | 327篇 |
2022年 | 557篇 |
2021年 | 710篇 |
2020年 | 820篇 |
2019年 | 649篇 |
2018年 | 648篇 |
2017年 | 983篇 |
2016年 | 1022篇 |
2015年 | 1263篇 |
2014年 | 1710篇 |
2013年 | 1407篇 |
2012年 | 2047篇 |
2011年 | 2163篇 |
2010年 | 1524篇 |
2009年 | 1612篇 |
2008年 | 1576篇 |
2007年 | 1753篇 |
2006年 | 1586篇 |
2005年 | 1165篇 |
2004年 | 872篇 |
2003年 | 766篇 |
2002年 | 604篇 |
2001年 | 578篇 |
2000年 | 428篇 |
1999年 | 308篇 |
1998年 | 193篇 |
1997年 | 140篇 |
1996年 | 151篇 |
1995年 | 116篇 |
1994年 | 102篇 |
1993年 | 100篇 |
1992年 | 64篇 |
1991年 | 44篇 |
1990年 | 36篇 |
1989年 | 25篇 |
1988年 | 23篇 |
1987年 | 14篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
《International Journal of Hydrogen Energy》2020,45(19):11167-11175
A new titanium (III) phosphite Ti2(HPO3)3, has been synthesized under hydrothermal conditions. The solid-state structure of this material was solved using single-crystal X-ray diffraction. The anionic inorganic skeleton has a three-dimensional structure, which is built up by TiO6 octahedral units linked together via bridging HPO3 pseudo pyramids, giving rise to tunnels along the three crystallographic axes. This new compound displays a high thermal stability limit of 625 °C. IR and Raman spectroscopies show the vibrational modes of the (HPO3)2−oxoanions. Electrochemical activity of this phase toward reversible insertion of Li ion was studied for the first time by galvanostatic charge-discharge measurements, an insertion host for reversible accommodation of Li+ was observed. 相似文献
22.
Yue Wang Jingyi Qiu Zhongbao Yu Hai Ming Meng Li Songtong Zhang Yusheng Yang 《Ceramics International》2018,44(2):1312-1320
Surface-interface reaction between the electrode and electrolyte plays a key role in lithium-ion storage properties, especially for high voltage cathode such as LiCoPO4 and Ni-riched cathode. Generally, surface modification is an effective method to improve the electrochemical performance of electrode materials. Herein, in order to revise the LiCoPO4 cathode with desirable properties, uniform AlF3-modified LiCoPO4 (LiCoPO4@AlF3) cathode materials in nano-sized distribution are synthesized. XRD result indicates that there is no structural transformation observed after AlF3 coating. TEM characterization and XPS analysis reveal that the surface of LiCoPO4 particle is coated by a nano-sized uniform AlF3 layer. Further, the electrochemical results indicate that AlF3 layer significantly improves the cycling and rate performances of LiCoPO4 cathode within the voltage range of 3.0–5.0 V. After a series of optimization, 4 mol% AlF3-coated LiCoPO4 material exhibits the best properties including an initial discharge capacity of 159 mA h g?1 at 0.1 C with 91% capacity retention after 50 cycles, especially a discharge capacity of 90 mA h g?1 can be obtained at 1 C rate. CV curves indicate that the polarization of cathode is reduced by AlF3 layer and EIS curves reveal that AlF3 layer relieves the increase of resistance to facilitate Li-ion transfer at the interface between electrode and electrolyte during the cycling process. The enhanced electrochemical performances are attributed to that the AlF3 layer can stabilize the interface between the cathode and electrolyte, form steady SEI film and suppress the electrolyte continuous decomposition at 5 V high voltages. This feasible strategy and novel characteristics of LiCoPO4@AlF3 could promise the prospective applications in the stat-art of special lithium-ion battery with high energy and/or power density. 相似文献
23.
ABSTRACTThe novel model of the coupled beam-type electrodes with elastic roots, subjected to the AC and DC voltages is constructed. The exact critical pull-in voltage of the two coupled elastically restrained beams with size effect is presented. The analytical method of the general system subjected to the AC and DC voltages simultaneously is presented. The characteristic mechanism of coupled vibration is investigated. 相似文献
24.
Hajime Tomita 《Electrical Engineering in Japan》2015,190(3):1-8
In this investigation, the nature of the electrostatic discharge (ESD) that occurs when a charged object moves toward a stationary grounded object is experimentally clarified. The spark lengths, discharge currents, and induced voltages in a magnetic probe were measured when a charged metallic spherical electrode connected to a 422 pF capacitor approached a stationary grounded object, which was the current target, for different moving speeds of the charged metallic spherical electrode in a range of 1 mm/s to 100 mm/s. The charge voltages of the capacitor were +6.5 kV and +10 kV. Based on the results, the average gap length shortened with the speed of the spherical electrode. The average peak values of the discharge current and the induced voltage were likely to increase with the speed of the spherical electrode. The average rise times of the discharge current and the induced voltage were likely to drop with the speed of the spherical electrode. The relation between the spark length and the discharge current due to the ESD can be explained qualitatively by using an equation derived from the spark resistance formula proposed by Rompe and Weizel. 相似文献
25.
26.
《Microelectronics Journal》2015,46(11):1012-1019
This paper presents a voltage reference generator architecture and two different realizations of it that have been fabricated within a standard 0.18 μm CMOS technology. The architecture takes the advantage of utilizing a sampled-data amplifier (SDA) to optimize the power consumption. The circuits achieve output voltages on the order of 190 mV with temperature coefficients of 43 ppm/°C and 52.5 ppm/°C over the temperature range of 0 to 120°C without any trimming with a 0.8 V single supply. The power consumptions of the circuits are less then 500 nW while occupying an area of 0.2 mm2 and 0.08 mm2, respectively. 相似文献
27.
Capacitance–voltage (C–V) characteristics of organic molecular semiconductors attracted much research interest recently, but no convincing physical mechanism has been established so far. In this work, the C–V characteristics of pentacene-based devices have been systematically investigated at various frequencies. Only one peak occurs when the measuring frequency is less than 3 kHz or greater than 8 kHz. While within the frequency range between the two, two C–V peaks are observed with quite different dependence on temperature, which suggests that the origins of these two C–V peaks are respectively mobile holes and trapped carriers. This conclusion is also experimentally validated with the C–V characteristics of intentionally doped devices. 相似文献
28.
低压配电系统对建筑电气工程是非常重要的,本文对其安装做论述,针对各种建筑物对配电的要求,对系统做合理的调试,最终实现建筑实体安全用电,同时也确保低压配电系统的稳定性。 相似文献
29.
The spin-transfer nano-oscillator(STNO) has recently acquired a huge amount of research interest, due to its promising easy tunability along with the miniature size. The output frequency control of an STNO through magnetic field and current has been examined almost to its full extent; however, there are issues that still need to be addressed. Here, we propose a novel way of voltage control of the output frequency of an STNO, and alongside reducing its power requirement. 相似文献
30.
Ning An Yunhao Cai Hongbo Wu Ailing Tang Kangning Zhang Xiaotao Hao Zaifei Ma Qiang Guo Hwa Sook Ryu Han Young Woo Yanming Sun Erjun Zhou 《Advanced materials (Deerfield Beach, Fla.)》2020,32(39):2002122
Compared with inorganic or perovskite solar cells, the relatively large non-radiative recombination voltage losses (ΔVnon-rad) in organic solar cells (OSCs) limit the improvement of the open-circuit voltage (Voc). Herein, OSCs are fabricated by adopting two pairs of D–π–A polymers (PBT1-C/PBT1-C-2Cl and PBDB-T/PBDB-T-2Cl) as electron donors and a wide-bandgap molecule BTA3 as the electron acceptor. In these blends, a charge-transfer state energy (ECT) as high as 1.70–1.76 eV is achieved, leading to small energetic differences between the singlet excited states and charge-transfer states (ΔECT ≈ 0.1 eV). In addition, after introducing chlorine atoms into the π-bridge or the side chain of benzodithiophene (BDT) unit, electroluminescence external quantum efficiencies as high as 1.9 × 10−3 and 1.0 × 10−3 are realized in OSCs based on PBTI-C-2Cl and PBDB-T-2Cl, respectively. Their corresponding ΔVnon-rad are 0.16 and 0.17 V, which are lower than those of OSCs based on the analog polymers without a chlorine atom (0.21 and 0.24 V for PBT1-C and PBDB-T, respectively), resulting in high Voc of 1.3 V. The ΔVnon-rad of 0.16 V and Voc of 1.3 V achieved in PBT1-C-2Cl:BTA3 OSCs are thought to represent the best values for solution-processed OSCs reported in the literature so far. 相似文献