全文获取类型
收费全文 | 224311篇 |
免费 | 23928篇 |
国内免费 | 14322篇 |
专业分类
电工技术 | 18723篇 |
技术理论 | 7篇 |
综合类 | 19103篇 |
化学工业 | 31708篇 |
金属工艺 | 13586篇 |
机械仪表 | 15070篇 |
建筑科学 | 18851篇 |
矿业工程 | 7457篇 |
能源动力 | 6741篇 |
轻工业 | 18702篇 |
水利工程 | 5581篇 |
石油天然气 | 10679篇 |
武器工业 | 2687篇 |
无线电 | 27053篇 |
一般工业技术 | 22148篇 |
冶金工业 | 8641篇 |
原子能技术 | 2449篇 |
自动化技术 | 33375篇 |
出版年
2024年 | 1275篇 |
2023年 | 4095篇 |
2022年 | 8219篇 |
2021年 | 10997篇 |
2020年 | 8074篇 |
2019年 | 6233篇 |
2018年 | 6843篇 |
2017年 | 7959篇 |
2016年 | 6883篇 |
2015年 | 10369篇 |
2014年 | 12837篇 |
2013年 | 14844篇 |
2012年 | 17590篇 |
2011年 | 18240篇 |
2010年 | 16599篇 |
2009年 | 15755篇 |
2008年 | 15408篇 |
2007年 | 14436篇 |
2006年 | 12977篇 |
2005年 | 10261篇 |
2004年 | 7265篇 |
2003年 | 6273篇 |
2002年 | 6229篇 |
2001年 | 5386篇 |
2000年 | 4087篇 |
1999年 | 3159篇 |
1998年 | 1950篇 |
1997年 | 1615篇 |
1996年 | 1454篇 |
1995年 | 1254篇 |
1994年 | 1019篇 |
1993年 | 659篇 |
1992年 | 519篇 |
1991年 | 373篇 |
1990年 | 300篇 |
1989年 | 245篇 |
1988年 | 181篇 |
1987年 | 126篇 |
1986年 | 115篇 |
1985年 | 50篇 |
1984年 | 43篇 |
1983年 | 29篇 |
1982年 | 49篇 |
1981年 | 49篇 |
1980年 | 58篇 |
1979年 | 33篇 |
1978年 | 10篇 |
1976年 | 10篇 |
1959年 | 12篇 |
1951年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Yu‐Qing Cao Zhan Zhang Yan‐Xin Guo 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(10):1441-1444
A new efficient method for synthesising nitriles, important organic reagents, is reported in this paper. In an environmentally benign solvent‐free system, aryl carboxylic acids were converted into the corresponding nitriles via one‐pot reactions, by amidation with ethyl carbamate followed by dehydration with thionyl chloride, in excellent yields. The results showed that the method has the advantages of lower cost, higher yield, less pollution and greater ease of work‐up. Copyright © 2008 Society of Chemical Industry 相似文献
63.
Xiang‐Dan Li Zhen‐Xin Zhong Sang‐Hoon Han Seung Hee Lee Myong‐Hoon Lee 《Polymer International》2005,54(2):406-411
From chloromethylated polyimide, a useful starting material for modification of aromatic polyimides, a thermocurable transparent polyimide having acrylate side groups was prepared. In the presence of 1,8‐diazabicyclo[5,4,0]undec‐7‐ene, chloromethylated polyimide was esterified with acrylic acid to synthesize poly(imide methylene acrylate). The polymer was soluble in organic solvent, which makes it possible to prepare a planar film by spin coating. The polymer film became insoluble after thermal treatment at 230 °C for 30 min. Optical transparency of the film at 400 nm (for 1 µm thickness) was higher than 98 % and not affected by further heating at 230 °C for 250 min. Adhesion properties measured by the ASTM D3359‐B method ranged from 4B to 5B. Preliminary results of planarization testing showed a high degree of planarization (DOP) value (>0.53). These properties demonstrate that poly(imide methylene acrylate) could be utilized as a thermocurable transparent material in fabricating display devices such as TFT‐LCD. Copyright © 2004 Society of Chemical Industry 相似文献
64.
本文介绍了一个用户接口管理系统NUUIMS的设计和实现.重点叙述了该系统基于规范化目标用户接口模型的设计思想,系统组成及描述方法.文章也讨论了使用NUUIMS设计而成的用户接口的特点. 相似文献
65.
66.
中国铜冶炼企业的竞争趋势及对策建议 总被引:1,自引:0,他引:1
文章分析了我国大型及中小型铜冶炼企业所面临竞争环境,提出了我国铜冶炼企业应采取的对策建议,即:联合进口原料;走大型企业联合之路,组建中国铜业集团;开发利用海外资源;加大国内资源勘探;继续进行技改、挖潜,提高企业竞争力等。 相似文献
67.
A photochromic nanocomposite based on Keggin structure phosphomolybdic acid (PMoA) well dispersed in polyethyleneglycol (PEG) was fabricated. TEM image showed that PMoA nanoparticles with narrow size distribution were finely dispersed in polymer matrix. FT-IR results showed that the Keggin geometry of polyoxometalates was still preserved inside the composites and strong coulombic interaction was built between PMoA and polymer matrix. Under UV irradiation, the film was reduced photochemically to yield a blue species, which was in accordance with a charge-transfer mechanism. 相似文献
68.
69.
本文提出了强扩散准则,强雪崩效应以及扩散效应的逼近优势等相关概念,给出了差分均匀性与强k阶扩散准则之间的相互关系,利用给出的设计准则改进了Rijndael密码的S盒。 相似文献
70.
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