全文获取类型
收费全文 | 190084篇 |
免费 | 29739篇 |
国内免费 | 9362篇 |
专业分类
电工技术 | 12189篇 |
技术理论 | 11篇 |
综合类 | 13213篇 |
化学工业 | 39144篇 |
金属工艺 | 9670篇 |
机械仪表 | 10897篇 |
建筑科学 | 13998篇 |
矿业工程 | 4706篇 |
能源动力 | 4875篇 |
轻工业 | 22052篇 |
水利工程 | 4023篇 |
石油天然气 | 7173篇 |
武器工业 | 1703篇 |
无线电 | 23654篇 |
一般工业技术 | 26530篇 |
冶金工业 | 6919篇 |
原子能技术 | 2053篇 |
自动化技术 | 26375篇 |
出版年
2024年 | 766篇 |
2023年 | 2644篇 |
2022年 | 5361篇 |
2021年 | 7196篇 |
2020年 | 6639篇 |
2019年 | 7005篇 |
2018年 | 7554篇 |
2017年 | 8479篇 |
2016年 | 8379篇 |
2015年 | 10592篇 |
2014年 | 12368篇 |
2013年 | 14983篇 |
2012年 | 14360篇 |
2011年 | 14788篇 |
2010年 | 14103篇 |
2009年 | 13242篇 |
2008年 | 12700篇 |
2007年 | 11850篇 |
2006年 | 10489篇 |
2005年 | 8620篇 |
2004年 | 6587篇 |
2003年 | 5584篇 |
2002年 | 5407篇 |
2001年 | 4667篇 |
2000年 | 3872篇 |
1999年 | 2784篇 |
1998年 | 1595篇 |
1997年 | 1342篇 |
1996年 | 1135篇 |
1995年 | 930篇 |
1994年 | 735篇 |
1993年 | 550篇 |
1992年 | 408篇 |
1991年 | 342篇 |
1990年 | 248篇 |
1989年 | 199篇 |
1988年 | 140篇 |
1987年 | 85篇 |
1986年 | 90篇 |
1985年 | 39篇 |
1984年 | 51篇 |
1983年 | 34篇 |
1982年 | 27篇 |
1981年 | 38篇 |
1980年 | 49篇 |
1979年 | 23篇 |
1977年 | 9篇 |
1976年 | 18篇 |
1959年 | 16篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
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
82.
Initialization speed is one of the most important factors in network real time kinematic (NRTK) performance. Owing to the low correlation among the error s 相似文献
83.
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
84.
85.
86.
87.
在高压耐压实验中,由于施加耐压较大(可达额定电压的3倍),因此常遇到实验线路对设备或对地距离不够导致实验中发生放电或实验数据测试异常的情况.为了保证实验线路对设备或对地有足够的距离,常用绝缘操作杆将高压实验线路挑起或用绝缘带拉紧高压实验线使其悬空,既费时费力又不安全,尤其在刮风天气极易造成绝缘杆滑落、塑料带摆动等,导致实验数据不准确,影响判断.这种情况下,就必须进行多次实验,降低了工作效率.为此研制一款功能完善、能有效解决现场实验困难的实验线支撑工具,以达到提高工作效率和安全性的目的. 相似文献
88.
Yafei Liu Zhilong Fu Xingyu Chen Yaxin Wei Bo Zhang Aimin Chang 《Journal of the American Ceramic Society》2021,104(5):2134-2142
Rare-earth ions doped Ca0.9R0.1CeNbMoO8 (R = Y, Sm, Nd, La) ceramics have been successfully prepared by solid-state method, and their modifications to the microstructure and electrical properties are also investigated. The rare-earth ions doped ceramics exhibit the scheelite structure. With the increase in the radius of rare-earth ions, the lattice distortion and bond interaction will be enhanced, and the consistency of grain size will be reduced. The ceramics exhibit negative temperature coefficient (NTC) thermistor characteristics in the temperature range of 473 K-1273 K, and the activation energy decreases with the increase of the radius of rare-earth ions. Rare-earth ions doping can increase the content of Ce3+ ions and promote the conductivity of ceramics. Except for Sm3+-doped ceramics, the high-temperature aging rate of other ceramics is less than 2%. The existence of some metastable Sm2+ ions in Sm3+-doped ceramics not only increases the activation energy, but also reduces the high-temperature stability of the ceramics. 相似文献
89.
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