全文获取类型
收费全文 | 224247篇 |
免费 | 23166篇 |
国内免费 | 13442篇 |
专业分类
电工技术 | 18169篇 |
技术理论 | 8篇 |
综合类 | 18199篇 |
化学工业 | 31986篇 |
金属工艺 | 13684篇 |
机械仪表 | 14767篇 |
建筑科学 | 19214篇 |
矿业工程 | 7095篇 |
能源动力 | 6743篇 |
轻工业 | 16487篇 |
水利工程 | 5245篇 |
石油天然气 | 11247篇 |
武器工业 | 2480篇 |
无线电 | 27355篇 |
一般工业技术 | 23579篇 |
冶金工业 | 9169篇 |
原子能技术 | 2638篇 |
自动化技术 | 32790篇 |
出版年
2024年 | 1139篇 |
2023年 | 3735篇 |
2022年 | 7197篇 |
2021年 | 9938篇 |
2020年 | 7403篇 |
2019年 | 5764篇 |
2018年 | 6485篇 |
2017年 | 7639篇 |
2016年 | 6625篇 |
2015年 | 9765篇 |
2014年 | 12195篇 |
2013年 | 14591篇 |
2012年 | 16746篇 |
2011年 | 17512篇 |
2010年 | 16157篇 |
2009年 | 15131篇 |
2008年 | 15147篇 |
2007年 | 14383篇 |
2006年 | 13344篇 |
2005年 | 10621篇 |
2004年 | 7447篇 |
2003年 | 6410篇 |
2002年 | 6316篇 |
2001年 | 5591篇 |
2000年 | 4566篇 |
1999年 | 4018篇 |
1998年 | 2708篇 |
1997年 | 2283篇 |
1996年 | 2167篇 |
1995年 | 1814篇 |
1994年 | 1487篇 |
1993年 | 990篇 |
1992年 | 844篇 |
1991年 | 625篇 |
1990年 | 460篇 |
1989年 | 390篇 |
1988年 | 302篇 |
1987年 | 198篇 |
1986年 | 152篇 |
1985年 | 95篇 |
1984年 | 70篇 |
1983年 | 47篇 |
1982年 | 63篇 |
1981年 | 59篇 |
1980年 | 59篇 |
1979年 | 33篇 |
1978年 | 11篇 |
1976年 | 10篇 |
1959年 | 12篇 |
1951年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
Nanoscale Hybrid Langmuir-Blodgett Films Based on Cerium-Substituted Heteropolymolybdate and Polyquinoline 总被引:2,自引:0,他引:2
Nanoscale hybrid organic/inorganic Langmuir-Blodgett films of cerium-substituted heteropolymolybdates (CeHPMo) and π-conjugated macromolecule poly(1,2-dihydro-2,2,4-trimethyl) quinoline (PQ) were obtained with auxiliary film-forming material stearic acid(SA) or octadecylamine(ODA). The surface pressure-area isotherms illuminate the formation of the hybrid LB films of PQ/ODA/Ce-HPMo and PQ/SA/Ce-HPMo. The different film-forming mechanism was discussed when the different auxiliary film-forming materials were used in the system. The absorption spectra indicate that the molecules of PQ and Ce-HPMo are incorporated into the LB films. Tapping-mode AFM image reveals a granular surface texture of nanosized Ce-substituted heteropolymolybdate. STM image shows that the conductivity is greatly improved after Ce-substituted heteropolymolybdates are incorporated in the films. 相似文献
994.
995.
996.
We show how a long string can be used to probe the incident field across the target zone of a radar cross section (RCS) test range. The string may be stretched horizontally from wall to wall, or vertically from floor to ceiling. One end of the string is fixed and the other end is moved by an actuator mounted in the wall or ceiling. The resulting motion changes the angle of the string with respect to the incident-field direction, during which time the coherent radar echo is recorded as a function of the string angle. The coherent signal-as-a-function-of-angle data are then transformed to the cross-range domain using the fast Fourier transform (FFT), whence we obtain a chart of the incident field amplitude as a function of cross-range distance. Numerical examples are presented that show how variations in the incident field influence the string echo. A sample of experimental data shows that the processed data are readily interpreted. 相似文献
997.
Bauwelinck J. Wei Chen Verhulst D. Martens Y. Ossieur P. Xing-Zhi Qiu Vandewege J. 《Solid-State Circuits, IEEE Journal of》2005,40(6):1322-1330
An innovative burst-mode laser transmitter (BM-TX) is presented for gigabit-capable passive optical network (GPON) upstream transmission at 1.25 Gb/s. The laser bias and modulation current each can reach 80 mA with a resolution of 0.1 mA providing a total drive current up to 160 mA. Both currents are generated by 10-bit current steering digital-to-analog converters (DACs), the architecture of which is specially adapted to yield a monotonic current setting at settling times below 12.8 ns. Tests show that fast automatic power control (APC) can stabilize and track the launched optical power with a tolerance of less than 1 dB over a wide temperature range for outdoor operation. The APC only requires a straightforward calibration of the "0" and the "1" level at room temperature. Optical level monitoring on strings of four consecutive "0" bytes and two consecutive "1" bytes at 1.25 Gb/s is demonstrated. APC based on such short strings of data has not been shown before. The circuits have been designed in a 0.35 /spl mu/m SiGe BiCMOS process. Experimental results show that this dc-coupled BM-TX meets the specifications of the recently approved ITU-T Recommendation G.984.2 supporting an intelligent power leveling mechanism (PLM). 相似文献
998.
999.
采用倒链葫芦、卷扬机或软牵引装置对斜拉索进行牵引安装 ,使牵引力达到 5 0 0余kN ,解决了斜拉索安装拉力大这一施工难题。 相似文献
1000.