全文获取类型
收费全文 | 117709篇 |
免费 | 9951篇 |
国内免费 | 5460篇 |
专业分类
电工技术 | 7400篇 |
技术理论 | 3篇 |
综合类 | 7717篇 |
化学工业 | 18476篇 |
金属工艺 | 6328篇 |
机械仪表 | 6952篇 |
建筑科学 | 8835篇 |
矿业工程 | 2750篇 |
能源动力 | 3396篇 |
轻工业 | 9455篇 |
水利工程 | 2335篇 |
石油天然气 | 5586篇 |
武器工业 | 879篇 |
无线电 | 14713篇 |
一般工业技术 | 14463篇 |
冶金工业 | 5869篇 |
原子能技术 | 1344篇 |
自动化技术 | 16619篇 |
出版年
2024年 | 508篇 |
2023年 | 1850篇 |
2022年 | 3422篇 |
2021年 | 4711篇 |
2020年 | 3331篇 |
2019年 | 2797篇 |
2018年 | 3157篇 |
2017年 | 3699篇 |
2016年 | 3245篇 |
2015年 | 4477篇 |
2014年 | 5864篇 |
2013年 | 7397篇 |
2012年 | 7845篇 |
2011年 | 8831篇 |
2010年 | 7645篇 |
2009年 | 7367篇 |
2008年 | 7317篇 |
2007年 | 6915篇 |
2006年 | 6613篇 |
2005年 | 5509篇 |
2004年 | 3722篇 |
2003年 | 3088篇 |
2002年 | 3065篇 |
2001年 | 2632篇 |
2000年 | 2514篇 |
1999年 | 2504篇 |
1998年 | 2266篇 |
1997年 | 1973篇 |
1996年 | 1749篇 |
1995年 | 1459篇 |
1994年 | 1171篇 |
1993年 | 922篇 |
1992年 | 748篇 |
1991年 | 538篇 |
1990年 | 450篇 |
1989年 | 334篇 |
1988年 | 297篇 |
1987年 | 210篇 |
1986年 | 167篇 |
1985年 | 145篇 |
1984年 | 112篇 |
1983年 | 82篇 |
1982年 | 74篇 |
1981年 | 65篇 |
1980年 | 57篇 |
1979年 | 37篇 |
1978年 | 32篇 |
1977年 | 32篇 |
1976年 | 54篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Enhanced light output in nitride-based light-emitting diodes by roughening the mesa sidewall 总被引:1,自引:0,他引:1
Chia-Feng Lin Zhong-Jie Yang Jing-Hui Zheng Jing-Jie Dai 《Photonics Technology Letters, IEEE》2005,17(10):2038-2040
In this letter, we will report on a nitride-based light emitting diode with a mesa sidewall roughening process that increases light output power. The fabricated GaN-based light-emitting diode (LED) wafers were first treated through a photoelectrochemical (PEC) process. The Ga/sub 2/O/sub 3/ layers then formed around the GaN : Si n-type mesa sidewalls and the bottoms mesa etching regions. Selective wet oxidation occurred at the mesa sidewall between the p- and the n-type GaN interface. The light output power of the PEC treated LED was seen to increase by about 82% which was caused by a reduced index reflectance of GaN-Ga/sub 2/O/sub 3/-air layers, by a rough Ga/sub 2/O/sub 3/ surface, by a microroughening of the GaN sidewall surface, and by a selective oxidation step profile of the mesa sidewall that increases the light-extraction efficiency from the mesa sidewall direction. Consequently, this wet PEC treated process is suitable for high powered nitride-based LEDs lighting applications. 相似文献
72.
Tsang T.K.K. Kuan-Yu Lin El-Gamal M.N. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2008,55(3):214-218
This paper presents design techniques of CMOS ultra-wide-band (UWB) amplifiers for multistandard communications. The goal of this paper is to propose a compact, simple, and robust topology for UWB low-noise amplifiers, which yet consumes a relatively low power. To achieve this goal, a common-gate amplifier topology with a local feedback is employed. The first amplifier uses a simple inductive peaking technique for bandwidth extension, while the second design utilizes a two-stage approach with an added gain control feature. Both amplifiers achieve a flat bandwidth of more than 6 GHz and a gain of higher than 10 dB with supply voltages of 1.8-2.5 V. Designs with different metal thicknesses are compared. The advantage of using thick-metal inductors in UWB applications depends on the chosen topology. 相似文献
73.
Lei Liu Ying Kong Hong Xu Jin P. Li Jin X. Dong Zhi Lin 《Microporous and mesoporous materials》2008,115(3):624-628
A three-dimensional zinc phosphate compound with DFT topology, designated as ZnPO4-EU1, has been synthesized by an ionothermal approach from the system HF-ZnO–P2O5-choline chloride-imidazolidone. Ethylenediamine, derived from decomposition of the imidazolidone component of the deep-eutectic solvent (DES) itself, is delivered to the synthesis and serves as an appropriate template for ZnPO4-EU1. Experiments in which the synthesis conditions were varied showed that ZnPO4-EU1 may be prepared over a wide molar ratio of P/Zn = 0.55–13.0. Powder X-ray diffraction patterns have been obtained at intervals to track the crystallization process of this material. The experimental data show that Zn3(PO4)2 · 4H2O (a dense phase) was first isolated from the DES after reaction for 1 h. Subsequently, the pure phase of ZnPO4-EU1 was obtained with increasing crystallization time from 12 h to 72 h. The experimental results show that the nucleation and crystallization take place with relatively low levels of solvent degradation, demonstrating that zinc phosphate with a three-dimensional framework can be synthesized by in situ generation of an appropriate template using an unstable DES at high temperatures (150–200 °C). 相似文献
74.
75.
Haijun Fang Zongli Lin 《Automatic Control, IEEE Transactions on》2006,51(7):1177-1184
In this note, we revisit the problem of global practical stabilization for planar linear systems subject to actuator saturation and input additive disturbances. A parameterized linear state feedback law is designed such that, by tuning the value of the parameter, all trajectories of the closed-loop system converge to an arbitrarily small neighborhood of the origin in a finite time and remain in there. 相似文献
76.
火焰图像特征在火灾数字图像识别中的运用 总被引:1,自引:0,他引:1
火焰尖角数目和圆形度是早期火灾火焰的主要特征,本文主要论述了如何在数学形态学基础上,利用火灾火焰的两个特点判断和识别早期火情。实验中,对火焰的二值图像进行开运算,即先腐蚀,再膨胀,目的是为了对火焰图像进行形态学滤波,去噪。从实验结果可以看出,该算法可以很好的识别火焰和干扰源。 相似文献
77.
Zhiping Lin Xu L. Bose N.K. 《IEEE transactions on circuits and systems. I, Regular papers》2008,55(1):445-461
78.
79.
80.
介绍液态软起动技术在济钢 15000 m3/h制氧机配套的 6000 kW同步电动机上的应用情况,阐述了系统的原理、特点、仿真计算及实际应用后达到的效果. 相似文献