全文获取类型
收费全文 | 229004篇 |
免费 | 17483篇 |
国内免费 | 9225篇 |
专业分类
电工技术 | 12454篇 |
技术理论 | 24篇 |
综合类 | 14152篇 |
化学工业 | 38797篇 |
金属工艺 | 13157篇 |
机械仪表 | 14527篇 |
建筑科学 | 17569篇 |
矿业工程 | 7500篇 |
能源动力 | 6426篇 |
轻工业 | 13498篇 |
水利工程 | 3586篇 |
石油天然气 | 16630篇 |
武器工业 | 1647篇 |
无线电 | 25148篇 |
一般工业技术 | 27374篇 |
冶金工业 | 12803篇 |
原子能技术 | 2247篇 |
自动化技术 | 28173篇 |
出版年
2024年 | 998篇 |
2023年 | 3809篇 |
2022年 | 6482篇 |
2021年 | 9112篇 |
2020年 | 7089篇 |
2019年 | 6021篇 |
2018年 | 6742篇 |
2017年 | 7546篇 |
2016年 | 6759篇 |
2015年 | 8869篇 |
2014年 | 11261篇 |
2013年 | 13294篇 |
2012年 | 14217篇 |
2011年 | 15473篇 |
2010年 | 13438篇 |
2009年 | 12693篇 |
2008年 | 12357篇 |
2007年 | 11859篇 |
2006年 | 12344篇 |
2005年 | 10766篇 |
2004年 | 7266篇 |
2003年 | 6231篇 |
2002年 | 5462篇 |
2001年 | 4885篇 |
2000年 | 5434篇 |
1999年 | 6438篇 |
1998年 | 5434篇 |
1997年 | 4453篇 |
1996年 | 4188篇 |
1995年 | 3498篇 |
1994年 | 2812篇 |
1993年 | 1965篇 |
1992年 | 1537篇 |
1991年 | 1226篇 |
1990年 | 933篇 |
1989年 | 740篇 |
1988年 | 537篇 |
1987年 | 336篇 |
1986年 | 278篇 |
1985年 | 196篇 |
1984年 | 139篇 |
1983年 | 114篇 |
1982年 | 125篇 |
1981年 | 98篇 |
1980年 | 70篇 |
1979年 | 36篇 |
1978年 | 26篇 |
1977年 | 20篇 |
1976年 | 35篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
81.
Voltage switching induced by long-wavelength infrared light from a CO2 laser was observed using a double-barrier resonant tunneling diode (RTD) biased in the bistable region and the intersubband transition (IT) between the quantum confined states. Possible optoelectronic and all-optical switching applications involving hysteresis are proposed and discussed 相似文献
82.
83.
Effect of magnesium content on the ageing behaviour of water-chilled Al-Si-Cu-Mg-Fe-Mn (380) alloy castings 总被引:1,自引:0,他引:1
A study of the effect of magnesium concentration on the ageing behaviour as measured by the hardness of 380 alloy was conducted
for three levels of magnesium, namely 0.06 (base alloy), 0.33 and 0.5 wt%, for water-chilled castings (dendrite arm spacing
∼ 10–15 μm). Differential scanning calorimetry analysis of as-cast samples was carried out to determine the changes in the
reactions of the phases obtained during alloy solidification, employing heating rates of 0.1 and 1.0°Cs−1, up to approximately 700°C. Two heat treatments were applied to the as-cast alloys: T5 comprising ageing at 25 (room temperature),
155, 180, 200 and 220°C, for times up to 200 h, and T6 comprising solution heat treatment at 480 °C or 515°C for 8 h, followed
by quenching in warm water at 60°C, followed by immediate artificial ageing at 155 or 180°C for varying times up to 100h.
The results show that the higher hardness values obtained with T6 treatment can be explained by the excess precipitation of
magnesium-containing phases in the as-solidified alloys. This precipitation could be eliminated under the high cooling-rate
conditions prevalent in die-casting operations so that T5 treatment may be used to replace T6 treatment to produce the same
hardness values. In addition, solution heat treatment in the low-temperature range (480–515°C) is adequate to produce the
required changes in silicon morphology and dissolution of magnesium in the matrix. No significant difference in hardness behaviour
was observed when the magnesium content was increased beyond 0.3 wt%. 相似文献
84.
85.
86.
87.
对选矿废水综合利用的探讨 总被引:4,自引:0,他引:4
通过对金堆城钼业公司选矿废水再用于选矿作业的选矿试验,证明选矿废水循环利用是可行的,既提高了选矿浓度,又减少了对环境的污染,经济和社会效益显著。 相似文献
88.
89.
Ramon R. Costa Liu Hsu 《International Journal of Adaptive Control and Signal Processing》1992,6(1):19-33
A variable structure model reference adaptive controller (VS-MRAC) using only input and output measurements was recently proposed and shown to be globally asymptotically stable with superior transient behaviour and disturbance rejection properties. In this paper a singular perturbation approach is used in order to establish the robustness of the controller in the presence of unmodelled dynamics (parasitics) and disturbances. We develop a new Lyapunov-based technique to analyse the overall system and show that for sufficiently small parasitics the system remains stable and the output error is small in some sense. 相似文献
90.
Guha A. Pavan A. Liu J. Rastogi A. Steeves T. 《Selected Areas in Communications, IEEE Journal on》1995,13(4):749-763
This paper describes the distributed system, network and software architecture, the application development environment, the performance, and the early lessons learned on the ATM LAN testbed Mercuri established at the Honeywell Technology Center, to develop distributed multimedia technologies for real-time control applications. We have developed a client-server-based software architecture on Sun Sparcstation-2s connected by a Fore Systems' ASX-100 ATM switch, with video processing handled by Parallax's X Video cards. The architecture enables network-transparent applications and provides simple primitives for multimedia capture, display, transmission, storage, and retrieval. A real-time multimedia-in-the-loop control application was developed as the vehicle for testing the capabilities and performance of the network. Our test measurements focus on the end-user-level performance metrics such as message throughput and round-trip delay as well as video-frame jitter under no-load and load conditions. Our results show that the maximum burst throughput that can be supported at the user level is 48 Mb/s using AAL 5, while round-trip delays for 4-kbyte messages are about 3 ms. Our experience reveals a number of performance bottlenecks and open issues in using commercial ATM switches for practical applications. Our conclusions are outlined 相似文献