全文获取类型
收费全文 | 663157篇 |
免费 | 118462篇 |
国内免费 | 82448篇 |
专业分类
电工技术 | 68820篇 |
综合类 | 76425篇 |
化学工业 | 80283篇 |
金属工艺 | 57826篇 |
机械仪表 | 42654篇 |
建筑科学 | 49146篇 |
矿业工程 | 34062篇 |
能源动力 | 19803篇 |
轻工业 | 72932篇 |
水利工程 | 23636篇 |
石油天然气 | 29190篇 |
武器工业 | 11170篇 |
无线电 | 77965篇 |
一般工业技术 | 64840篇 |
冶金工业 | 26523篇 |
原子能技术 | 9625篇 |
自动化技术 | 119167篇 |
出版年
2024年 | 5438篇 |
2023年 | 11916篇 |
2022年 | 24279篇 |
2021年 | 30334篇 |
2020年 | 25625篇 |
2019年 | 26380篇 |
2018年 | 28475篇 |
2017年 | 32481篇 |
2016年 | 30224篇 |
2015年 | 38206篇 |
2014年 | 43331篇 |
2013年 | 47518篇 |
2012年 | 56793篇 |
2011年 | 55650篇 |
2010年 | 53203篇 |
2009年 | 48794篇 |
2008年 | 48594篇 |
2007年 | 47401篇 |
2006年 | 40000篇 |
2005年 | 33157篇 |
2004年 | 27477篇 |
2003年 | 18906篇 |
2002年 | 17713篇 |
2001年 | 16042篇 |
2000年 | 13285篇 |
1999年 | 7281篇 |
1998年 | 4551篇 |
1997年 | 3982篇 |
1996年 | 3732篇 |
1995年 | 3767篇 |
1994年 | 3054篇 |
1993年 | 2887篇 |
1992年 | 2778篇 |
1991年 | 2005篇 |
1990年 | 1606篇 |
1989年 | 1555篇 |
1988年 | 1148篇 |
1987年 | 393篇 |
1986年 | 352篇 |
1985年 | 234篇 |
1984年 | 198篇 |
1983年 | 153篇 |
1982年 | 186篇 |
1981年 | 233篇 |
1980年 | 267篇 |
1979年 | 168篇 |
1976年 | 230篇 |
1975年 | 212篇 |
1972年 | 237篇 |
1960年 | 206篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
High-T
c
Bi(Pb)-Sr-Ca-Cu-O thin films have been made on single-crystal MgO substrates using high-pressure dc sputtering technique. X-ray studies confirm the crystallinity and highly oriented structure withc-axis perpendicular to the substrate. By optimizing the annealing schedule the formation of the high-T
c
phase is stabilized. The best film exhibited superconducting transition temperature with zero-resistance temperature,T
c(0), as high as 101 K. Temperature dependence ofJ
c
indicates the presence of Josephson-type weak links. 相似文献
992.
The temperature dependence of a marginal Fermi liquid has been calculated. We showed that the expectedT lnT correction is characteristic for the low-temperature domain. The high-temperature domain has a supplementary correction. The results are in agreement with the non-Fermi behavior of some metallic systems the in low-temperature domain. 相似文献
993.
994.
Ben J. A. Kr se Kai M. Compagner Franciscus C. A. Groen 《Robotics and Autonomous Systems》1993,11(3-4):221-230
This paper describes a robust and accurate ultrasonic sensing system for a mobile robot. The system continuously updates a local map of the environment in which obstacles are represented by straight lines or points in a robot centered coordinate frame. The presented algorithms use a Kalman filter for the reduction of the noise in the ultrasonic data and use a systematical error correction (‘bundle correction’) to reduce the uncertainty in obstacle direction. Experiments are carried out in simulation and with a real mobile robot system. Results show that the accuracy with which line parameters can be estimated is in the order of 1 degree for the orientation and about 2 cm for the position. The effect of the bundle correction is significant and maximal when the robot approaches walls under a small angle. 相似文献
995.
996.
含淀粉聚乙烯膜的时控光降解研究 总被引:2,自引:0,他引:2
使用复合光降解剂,得到了可光降解的生物降解膜。对膜的光降解进行了考察,并对影响光降解的因素进行了讨论,结果表明,我们所制得的膜是一种较好的时控光降解膜。 相似文献
997.
A novel hierarchical intelligent controller configuration is proposed using an artificial neural network as a control-mode classifier in the supervisory level and a set of pre-designed controllers in the lower level. Controller outputs are modified nonlinearly by the classifying signals in a structure resembling one artificial neuron with adaptively changed weights. The lower-level local controllers are implemented using neural networks. An illustrative example of this approach is based on the transient stabilization of a single-machine infinite-bus system studied in Flexible AC Transmission Systems (FACTS) research. 相似文献
998.
本文介绍了一个用Turbo C语言在AST-286机器上实现的计算机辅助数据库设计系统CAD^2B。该系统提供了人机交互的环境,供设计者进行概念模型设计,并自动完成从概念模型逻辑模型的映射,创建满足规范化要求的关系表。该系统采用的概念模型是引入了事件和时间的扩展了的实体关系模型。该模型既能充分反映应用环境的静态和动态语义,又是向关系模式转化的基础。 相似文献
999.
1000.
Nitrogen addition to iron powder by mechanical alloying 总被引:3,自引:0,他引:3
Nitrogen was alloyed into iron (a) by mechanical processing in a nitrogen gas environment, and (b) by mechanically alloying with iron-nitride powders to characterize resulting nano-structure and nitrogen distribution. Although the infused nitrogen concentration was significantly greater than the thermodynamic equilibrium solubility of iron, no nitrides formed, even for nitrogen concentrations as high as 4.1 wt.% However, a bctFe phase did form. Lattice expansion calculations indicate that the sum of the interstitial bcc-Fe and bctFe nitrogen concentrations was significantly less than the total measured nitrogen concentration. A considerable portion of the mechanically infused nitrogen was determined to be associated with nanograin boundaries. 相似文献