全文获取类型
收费全文 | 44863篇 |
免费 | 4427篇 |
国内免费 | 2470篇 |
专业分类
电工技术 | 4509篇 |
综合类 | 3613篇 |
化学工业 | 9327篇 |
金属工艺 | 6760篇 |
机械仪表 | 1993篇 |
建筑科学 | 4127篇 |
矿业工程 | 1324篇 |
能源动力 | 1513篇 |
轻工业 | 2526篇 |
水利工程 | 1102篇 |
石油天然气 | 1502篇 |
武器工业 | 344篇 |
无线电 | 2785篇 |
一般工业技术 | 4784篇 |
冶金工业 | 1904篇 |
原子能技术 | 302篇 |
自动化技术 | 3345篇 |
出版年
2024年 | 188篇 |
2023年 | 802篇 |
2022年 | 1484篇 |
2021年 | 1870篇 |
2020年 | 1613篇 |
2019年 | 1375篇 |
2018年 | 1270篇 |
2017年 | 1740篇 |
2016年 | 1672篇 |
2015年 | 1750篇 |
2014年 | 2440篇 |
2013年 | 2470篇 |
2012年 | 3065篇 |
2011年 | 3436篇 |
2010年 | 2387篇 |
2009年 | 2751篇 |
2008年 | 2329篇 |
2007年 | 2758篇 |
2006年 | 2598篇 |
2005年 | 2166篇 |
2004年 | 1819篇 |
2003年 | 1550篇 |
2002年 | 1299篇 |
2001年 | 1123篇 |
2000年 | 958篇 |
1999年 | 902篇 |
1998年 | 721篇 |
1997年 | 604篇 |
1996年 | 466篇 |
1995年 | 469篇 |
1994年 | 372篇 |
1993年 | 278篇 |
1992年 | 213篇 |
1991年 | 181篇 |
1990年 | 121篇 |
1989年 | 128篇 |
1988年 | 84篇 |
1987年 | 68篇 |
1986年 | 44篇 |
1985年 | 21篇 |
1984年 | 28篇 |
1983年 | 28篇 |
1982年 | 28篇 |
1981年 | 14篇 |
1980年 | 22篇 |
1979年 | 10篇 |
1963年 | 4篇 |
1962年 | 4篇 |
1959年 | 6篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
This paper considers the equalisation problem in Quadrature Phase-Shift Keying (QPSK) modulated signals which have been distorted by the passage through a transmission channel. The channel is modelled as a Rician fading channel to simulate the behaviour of the transmission channel in the mobile satellite context. The equalisation is treated as the generalisation of the channel behaviour, and some algorithms with the structure of an artificial neural network using the Multilayer Perceptron, Volterra Series and Radial Basis Function are described. Results for the BER performance of typical transversal equalisers, with Square-Root Kalman adaptation algorithm, and algorithms with artificial neural network structure are also reported and evaluated. Improved performance is exhibited by the artificial neural network approaches. 相似文献
92.
A serious problem in motion control is the occurrence of torque ripple. Since a direct drive (DD) motor with a magnet rotor uses a rare-earth magnet, the torque ripple is more serious than that of conventional servomotors. This paper presents an auto-compensation of torque ripple using a software-implemented torque observer. The frequency and amplitude of torque ripple can be obtained in the controller by using the estimated torque from an observer, and the autonomous generation of a compensating current component for a torque ripple is possible. The proposed algorithm has been verified by experiments. 相似文献
93.
金属清净剂的性能研究 总被引:2,自引:0,他引:2
为了改进金属清净剂的抗氧性和极压抗磨性能,用一种含硫磷的羧酸衍生物部分中和清净剂中过碱性组分,得到两种改进的金属清净剂,并用四球机和热重分析仪评价其极压抗磨和抗氧化性能。结果表明功能化处理提高了金属清净剂抗氧化和极压性能,但未对分散和抗磨性能产生显著影响。 相似文献
94.
分析了 TJ10—74规范受弯构件正截面诸修订因素(砼强度“双改方案”、设计表达式、正截面计算方法……).在此基础上推演出 TJ10—74与GBJ10—89两规范关于受弯构件抗力转换系数.可供结构设计使用. 相似文献
95.
用电化学方法测定砂浆试件中钢筋的极化电阻,并测定了砂浆的孔隙率,结果发现:砂浆的孔隙率、孔径分布与钢筋极化电阻大小有良好的对应关系。电化学方法能可靠、快速测定砂浆配合比、添加剂对钢筋腐蚀速度的影响。 相似文献
96.
离子注入对Cr12MoV钢表面组织结构和力学性能的影响 总被引:1,自引:0,他引:1
研究了Cr12MoV钢离子注入层的显微组织特征及其对表面性能的影响。结果表明,离子注入使Cr12MoV钢的表面硬度和耐磨性能得到显著改善,且存在着一个最佳的注入剂量,约为3×10^1^7N^+/cm^2左右。离了注入在Cr12MoV钢表面层中形成了大量细小弥散的第二相粒子,并使α-Fe晶格发生严重畸变,从而引起材料表面强化。 相似文献
97.
Trends in Hydrological Parameters of a Southern Brazilian Watershed and its Relation to Human Induced Changes 总被引:5,自引:1,他引:4
Moraes Jorge M. Pellegrino Giampaolo Q. Ballester Maria V. Martinelli Luiz A. Victoria Reynaldo L. Krusche Alex V. 《Water Resources Management》1998,12(4):295-311
The Piracicaba river basin is a subtropical watershed located in the southeastern region of Brazil. With an area of 12 400 km2, the basin is a typical example of new landscape resulting from development in tropical and sub-tropical regions: establishment of intensive industrial and agricultural processes were followed by significant population growth and water management. This scenario has led to significant increase in water demand and decrease in water quality. The main objective of this study is the detection of changes in the patterns of flow and precipitation in the basin, and its possible relation to man-induced changes. Statistical analyses were performed on records of precipitation, evapotranspiration and streamflow, from 1947 to 1991. Precipitation and evapotranspiration totals showed significant increasing trends for the entire basin. From eight streamflow gauge stations, half showed significant decreasing trend. The most probable cause of such trends is the export of water from the basin to the metropolitan region of São Paulo city. 相似文献
98.
99.
介绍了用有限元方法计算半导体方块电阻四探针测试中二维点电流势场的模型并且证明了其正确性。由于有限元方法对边界没有限制,该方法为方块电阻测试中精确确定边界修正系数,更重要的是为微样品测试结构确定提供直接明了的理论依据。 相似文献
100.
Yoshiyuki Uno Akira Okada Kensuke Uemura Purwadi Raharjo Toshihiko Furukawa Kosaku Karato 《Precision Engineering》2005,29(4):171-455
A new finishing process for metal molds by large-area electron beam (EB) irradiation is proposed in this study. In the large-area EB irradiation equipment used here, an EB with high-energy density is irradiated without focusing the beam, and so the EB with a maximum diameter of 60 mm can be used for melting or evaporating metal surface instantly. Experimental results show that the surface roughness decreases from 6 μmRz to less than 1 μmRz in just a few minutes under proper machining conditions. The corrosion resistance of metal mold surface also could be greatly improved by large-area EB irradiation. Furthermore, the surface roughness of tilting surface close to 90° could be well improved. Therefore, large-area EB irradiation method has a possibility to become a high-efficiency finishing process for metal molds. 相似文献