全文获取类型
收费全文 | 282092篇 |
免费 | 22835篇 |
国内免费 | 12882篇 |
专业分类
电工技术 | 16881篇 |
技术理论 | 18篇 |
综合类 | 18238篇 |
化学工业 | 47042篇 |
金属工艺 | 14648篇 |
机械仪表 | 16434篇 |
建筑科学 | 23405篇 |
矿业工程 | 7279篇 |
能源动力 | 8141篇 |
轻工业 | 19232篇 |
水利工程 | 4972篇 |
石油天然气 | 14574篇 |
武器工业 | 2026篇 |
无线电 | 33886篇 |
一般工业技术 | 34407篇 |
冶金工业 | 14244篇 |
原子能技术 | 3065篇 |
自动化技术 | 39317篇 |
出版年
2024年 | 1258篇 |
2023年 | 4492篇 |
2022年 | 8105篇 |
2021年 | 11042篇 |
2020年 | 8281篇 |
2019年 | 7140篇 |
2018年 | 7665篇 |
2017年 | 8750篇 |
2016年 | 7800篇 |
2015年 | 10451篇 |
2014年 | 13438篇 |
2013年 | 16704篇 |
2012年 | 17076篇 |
2011年 | 19010篇 |
2010年 | 16461篇 |
2009年 | 15900篇 |
2008年 | 15539篇 |
2007年 | 14834篇 |
2006年 | 14995篇 |
2005年 | 12907篇 |
2004年 | 9466篇 |
2003年 | 9143篇 |
2002年 | 9748篇 |
2001年 | 8550篇 |
2000年 | 7018篇 |
1999年 | 7193篇 |
1998年 | 6178篇 |
1997年 | 5159篇 |
1996年 | 4701篇 |
1995年 | 3908篇 |
1994年 | 3234篇 |
1993年 | 2478篇 |
1992年 | 1971篇 |
1991年 | 1452篇 |
1990年 | 1154篇 |
1989年 | 986篇 |
1988年 | 773篇 |
1987年 | 542篇 |
1986年 | 443篇 |
1985年 | 364篇 |
1984年 | 236篇 |
1983年 | 212篇 |
1982年 | 174篇 |
1981年 | 161篇 |
1980年 | 165篇 |
1979年 | 107篇 |
1978年 | 63篇 |
1977年 | 63篇 |
1976年 | 77篇 |
1975年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Lind M.G.J. Weidong Xiao Dunford W.G. 《IEEE transactions on circuits and systems. I, Regular papers》2006,53(2):409-418
This paper presents a comprehensive nonlinear model of the controlled constant voltage transformer also known as the ferroresonant transformer. Saturation is a normal mode of operation for this device. This paper derives an equivalent electrical circuit that relates to the physical structure of a typical design. The level of detail includes winding resistances, continuously nonlinear magnetizing inductances, tapped windings, and leakage inductances. The paper describes methods to extract the winding resistances, leakage inductances, and hysteresis loops of the transformer and how to fit the latter into single-valued nonlinear functions. The paper compares computer simulation results of the model with those obtained analytically and experimentally. The results show that the derived circuit will be very useful for designers of the ferroresonant transformer, which is used in uninterruptible power supplies. 相似文献
42.
43.
Chun-Yuan Chen Shiou-Ying Cheng Wen-Hui Chiou Hung-Ming Chuang Wen-Chau Liu 《Electron Device Letters, IEEE》2003,24(3):126-128
A novel InP/InGaAs tunneling emitter bipolar transistor (TEBT) is fabricated and demonstrated. The studied device exhibits a very small collector-emitter offset voltage of 40 mV and an extremely wide operation regime. The operation region is larger than 11 decades in magnitude of collector current (10/sup -12/ to 10/sup -1/A). A current gain of 3 is obtained even if the device is operated at an ultralow collector current of 3.9 /spl times/ 10/sup -12/A (1.56 /spl times/ 10/sup -7/A/cm/sup 2/). Furthermore, the common-emitter breakdown voltage of the studied device is higher than 2 V. Consequently, the studied device shows a promise for low supply voltage, and low-power consumption circuit applications. 相似文献
44.
45.
Hao Wang Ying Lin Biao Chen 《Signal Processing, IEEE Transactions on》2003,51(10):2613-2623
We investigate non data-aided channel estimation for cyclically prefixed orthogonal frequency division multiplexing (OFDM) systems. By exploiting channel diversity using only two receive antennas, a blind deterministic algorithm is proposed. Identifiability conditions are derived that guarantee the perfect channel retrieval in the absence of noise. In the presence of noise, the proposed method has the desired property of being data efficient-only a single OFDM block is needed to achieve good estimation performance for a wide range of SNR values. The algorithm is also robust to input symbols as it does not have any restriction on the input symbols with regard to their constellation or their statistical properties. In addition, this diversity-based algorithm is computationally efficient, and its performance compares favorably to most existing blind algorithms. 相似文献
46.
47.
Polyaryloxydiphenylsilanes were prepared from phosphorus‐containing diols and diphenydichlorolsilane through solution polymerization. With a stoichiometric imbalance in feed monomers, the resulting polymers exhibited moderate melting points and good processing properties. The polymers prepared showed initial decomposition temperatures above 340 °C, excellent thermal stability, high char yields at 850 °C and very high limited oxygen index values of 56–59. The polymers' char yields and their (P + Si) contents showed linear relationships. © 2003 Society of Chemical Industry 相似文献
48.
49.
50.
我们在上网时,经常遇到恶意攻击,如IE浏览器被修改、注册表被锁定等,本文主要介绍了遇到这些情况时,将其解决的几种方法. 相似文献