全文获取类型
收费全文 | 191164篇 |
免费 | 20047篇 |
国内免费 | 12250篇 |
专业分类
电工技术 | 15837篇 |
技术理论 | 4篇 |
综合类 | 16497篇 |
化学工业 | 26622篇 |
金属工艺 | 11789篇 |
机械仪表 | 12865篇 |
建筑科学 | 16360篇 |
矿业工程 | 6298篇 |
能源动力 | 5965篇 |
轻工业 | 14389篇 |
水利工程 | 4706篇 |
石油天然气 | 9220篇 |
武器工业 | 2215篇 |
无线电 | 23203篇 |
一般工业技术 | 19191篇 |
冶金工业 | 7613篇 |
原子能技术 | 2320篇 |
自动化技术 | 28367篇 |
出版年
2024年 | 964篇 |
2023年 | 3070篇 |
2022年 | 6144篇 |
2021年 | 8454篇 |
2020年 | 6356篇 |
2019年 | 4936篇 |
2018年 | 5503篇 |
2017年 | 6489篇 |
2016年 | 5612篇 |
2015年 | 8437篇 |
2014年 | 10658篇 |
2013年 | 12531篇 |
2012年 | 14643篇 |
2011年 | 15196篇 |
2010年 | 14228篇 |
2009年 | 13328篇 |
2008年 | 13149篇 |
2007年 | 12465篇 |
2006年 | 11272篇 |
2005年 | 8844篇 |
2004年 | 6581篇 |
2003年 | 6168篇 |
2002年 | 6500篇 |
2001年 | 5680篇 |
2000年 | 3959篇 |
1999年 | 2961篇 |
1998年 | 1780篇 |
1997年 | 1440篇 |
1996年 | 1364篇 |
1995年 | 1146篇 |
1994年 | 917篇 |
1993年 | 574篇 |
1992年 | 480篇 |
1991年 | 338篇 |
1990年 | 276篇 |
1989年 | 229篇 |
1988年 | 164篇 |
1987年 | 108篇 |
1986年 | 96篇 |
1985年 | 49篇 |
1984年 | 43篇 |
1983年 | 28篇 |
1982年 | 38篇 |
1981年 | 43篇 |
1980年 | 48篇 |
1979年 | 29篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1959年 | 18篇 |
1951年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
122.
Jianxin Wei Mark R Pickering Michael R Frater John F Arnold John A Boman Wenjun Zeng 《IEEE transactions on image processing》2005,14(8):1033-1042
It is well known that tile-boundary artifacts occur in wavelet-based lossy image coding. However, until now, their cause has not been understood well. In this paper, we show that boundary artifacts are an inescapable consequence of the usual methods used to choose tile size and the type of symmetric extension employed in a wavelet-based image decomposition system. This paper presents a novel method for reducing these tile-boundary artifacts. The method employs odd tile sizes (2N + 1 samples) rather than the conventional even tile sizes (2N samples). It is shown that, for the same bit rate, an image compressed using an odd tile length low-pass first (OTLPF) convention has significantly less boundary artifacts than an image compressed using even tile sizes. The OTLPF convention can also be incorporated into the JPEG 2000 image compression algorithm using extensions defined in Part 2 of this standard. 相似文献
123.
124.
Kameyama H. Miyajima T. Zhi Ding 《IEEE transactions on circuits and systems. I, Regular papers》2008,55(3):851-860
In multicarrier systems, when the order of a channel impulse response is larger than the length of the cyclic prefix (CP), there is a significant performance degradation due to interblock interference (IBI). This paper proposes a blind-channel shortening method in which the equalizer parameter vector is formed by the noise subspace of the received signal correlation matrix so that the output power is maximized. The proposed method can not only shorten the effective channel impulse response to within the CP length but also maximize the output signal-to-interference-and-noise ratio while eliminating the IBI. We point out that the performance depends on the choice of a decision delay and propose a simple method for determining the appropriate delay. We propose both a batch algorithm and an adaptive algorithm and show by simulation that they are superior to the conventional algorithms. 相似文献
125.
Shi Wei Zhao Xuefeng Ma Conghui Management of the National Development Reform Commission 《中国通信》2008,(3)
After the new round of restructuring of Chinese telecom sector,it's pressing to formulate and implement asymmetric regulation policies so as to shape an effectively competitive market structure in a relatively short term.This paper reviewed the asymmetric regulation policies and practices carried out in foreign telecom market,and then according to the specific situations of Chinese telecom market,proposed the principles and corresponding policies for establishing an asymmetric regulation system fit for Chin... 相似文献
126.
127.
憎水性栀子蓝色素制备的研究 总被引:1,自引:0,他引:1
以浓盐酸为催化剂,采用乙酸酐酯化处理水溶性栀子蓝色素,制备了憎水性栀子蓝色素.探讨了栀子蓝色素与乙酸酐料液比、反应时间和反应温度等因素对憎水性栀子蓝色素色价的影响.结果表明:采用料液比1:20,在常温下反应4 h,为制备憎水性栀子蓝色素的最优条件.同时,通过红外光谱、可见吸收光谱及溶解性对栀子蓝色素的酯化改性进行了初步的探讨. 相似文献
128.
随着人们对建筑安全的日益重视 ,对建筑抗震要求的提高 ,国内外有关规范都对箍筋末端的设置作了明确规定 ,要求做成 135度弯钩。而在工程实践中 ,由于施工上的技术困难 ,很多工程都只设置成 90度弯钩。笔者提出的箍筋末端 135度弯钩二次就位法在基本不增加 90度弯钩施工难度与费用的基础上实现了 135度弯钩的施工 ,其法是可行的 相似文献
129.
提出了基于压电技术的微操作系统的自动标定方法,采用混合式步进电机直接驱动的宏动平台,实现系统大行程宏动定位,安装在宏动平台上的压电陶瓷驱动的微动平台和精密光栅,实现亚微米级的分辨率和定位精度,通过以上两部分实现定位机构的全闭环反馈控制,采用显微视觉反馈获取微动台操作器在图像中的位置信息进行标定。实验结果表明:系统的动态和稳定性能良好,自动标定运算速度快,运行速度达到11 frame/s,实现了对系统的精确标定,标定精度达到0.1μm。 相似文献
130.
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