全文获取类型
收费全文 | 77112篇 |
免费 | 8149篇 |
国内免费 | 4542篇 |
专业分类
电工技术 | 5869篇 |
技术理论 | 2篇 |
综合类 | 6526篇 |
化学工业 | 11717篇 |
金属工艺 | 4404篇 |
机械仪表 | 5159篇 |
建筑科学 | 6047篇 |
矿业工程 | 2331篇 |
能源动力 | 2078篇 |
轻工业 | 7115篇 |
水利工程 | 1867篇 |
石油天然气 | 3279篇 |
武器工业 | 853篇 |
无线电 | 8967篇 |
一般工业技术 | 8019篇 |
冶金工业 | 3080篇 |
原子能技术 | 1052篇 |
自动化技术 | 11438篇 |
出版年
2024年 | 379篇 |
2023年 | 1391篇 |
2022年 | 2858篇 |
2021年 | 3754篇 |
2020年 | 2761篇 |
2019年 | 2115篇 |
2018年 | 2368篇 |
2017年 | 2648篇 |
2016年 | 2317篇 |
2015年 | 3434篇 |
2014年 | 4570篇 |
2013年 | 5318篇 |
2012年 | 6037篇 |
2011年 | 6307篇 |
2010年 | 5860篇 |
2009年 | 5354篇 |
2008年 | 5276篇 |
2007年 | 5046篇 |
2006年 | 4459篇 |
2005年 | 3667篇 |
2004年 | 2567篇 |
2003年 | 1881篇 |
2002年 | 1705篇 |
2001年 | 1404篇 |
2000年 | 1309篇 |
1999年 | 1157篇 |
1998年 | 741篇 |
1997年 | 626篇 |
1996年 | 580篇 |
1995年 | 439篇 |
1994年 | 360篇 |
1993年 | 259篇 |
1992年 | 205篇 |
1991年 | 152篇 |
1990年 | 109篇 |
1989年 | 92篇 |
1988年 | 72篇 |
1987年 | 26篇 |
1986年 | 37篇 |
1985年 | 10篇 |
1984年 | 24篇 |
1983年 | 10篇 |
1982年 | 21篇 |
1981年 | 21篇 |
1980年 | 27篇 |
1979年 | 13篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1959年 | 8篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
微型步进马达线圈组卷线上下料基本靠手动作业,效率低下,同时因工人技术水平的不同造成产品品质不稳定的问题多发.为此专门设计了微型步进马达线圈组自动卷线及上下料设备.通过结合现阶段的先进工业技术,采用振动盘分离区分进料,多机构并联三菱PLC及威纶人机界面触摸屏研发了此微型步进马达线圈组自动上下料及卷线设备.通过该设备实现了微型步进马达因工人不足导致产能减少和品质多发问题,减少企业成本,提升产品品质. 相似文献
22.
In this article, the silver-plated polyamide fabrics (SPPAFs) with high electroconductibility and shielding effectiveness were fabricated by using in situ reduction of polydopamine and chemical silvering. The effects of SPPAFs dopamine (C8H11O2N) and silver nitrate (AgNO3) concentration on surface resistivity and electromagnetic interference shielding effectiveness were studied. The results showed that the surface resistivity of SPPAFs can reach a minimum value of 0.06 ± 0.014 Ω cm−1, when C8H11O2N concentration is 4 g L−1 and the AgNO3 concentration is 120 g L−1. The shielding effectiveness of SPPAFs in the wide frequency range of 10–3000 MHz increases with the increase in the concentration of AgNO3, and increases first and stabilizes afterward with increasing C8H11O2N concentration. When the concentration of C8H11O2N and AgNO3 is 3 and 120 g L−1, respectively, mean shielding effectiveness values in the low-, medium-, and high-frequency bands are 71.3, 73.8, and 76.1 dB, respectively. Moreover, the mean shielding effectiveness values is 83.79 dB in the frequency range of 1.2–2.3 GHz. The dominant shielding mechanism of SPPAFs is the reflected electromagnetic waves and the absorption shielding effectiveness is less than 2 dB. The average electromagnetic shielding values of SPPAFs are above 67 dB after 16 weeks of storage, when C8H11O2N concentration is 4 g L−1 and the AgNO3 concentration is 80 and 100 g L−1. The prepared SPPAFs show promising applications in military textiles and smart wearable clothing. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48227. 相似文献
23.
介绍了尿素装置中3起液位仪表失真案例,分析了故障现象和设备工况,确定失真原因,采取了相应的处理措施,解决了仪表故障。 相似文献
24.
In this study, the crystal structure, thermal, oxygen transport, electrical conductivity and electrochemical properties of the perovskite NdBa0.5Sr0.5Co2O5+δ (NBSC55) are investigated. In the temperature range of 250 °C–350 °C, the weight loss upon heating was due to a partial loss of lattice oxygen and along with a reduction of Co4+ to Co3+. The tend of weight-loss slows down as temperature increased above 350 °C indicating a reduction of Co3+ to Co2+ during this stage. The oxygen migration is dominated by surface exchange process at high temperature range (650-800 °C); however, the bulk diffusion process prevails at low temperature range (500–600 °C). For long-term testing, the polarization resistance of NBSC55 increases gradually form 3.13 Ω cm2 for 2 h to 3.34 Ω cm2 for 96 h at 600 °C and an increasing-rate for polarization resistance is around 0.22% h?1. The power density of the single cell with NBSC55 cathode reached 341 mW cm?2 at 800 °C. 相似文献
25.
26.
27.
The effect of Li2O on the crystallization properties of CaO-Al2O3-SiO2-Li2O-Ce2O3 slags was investigated. With increasing the Li2O content, LiAlO2 and CaCeAlO4 were the main crystalline phases. LiAlO2 formed for the charge compensating of Li+ ions to [AlO45?]-tetrahedrons, and CaCeAlO4 formed as a result of the charge balance of Ce3+ ions, Ca2+ ions, and [AlO69?]-octahedrons. Increasing the content of Li2O to 10%, the crystallization temperature was the highest, and the incubation time was the shortest. The crystallization ability was strong due to the three factors of strengthening the interaction between ions and ion groups, decreasing the polymerization degree, and increasing the melting temperature. Further increasing the content of Li2O, the crystallization performance was obviously suppressed, because the melting temperature and the force between the cations and the anion groups decreased. 相似文献
29.
Scientometrics - Due to the development of academic, more and more attentions are paid to citation recommendation. To solve the citation recommendation problem, researchers begin to focus on the... 相似文献
30.