全文获取类型
收费全文 | 101718篇 |
免费 | 10933篇 |
国内免费 | 6510篇 |
专业分类
电工技术 | 8422篇 |
技术理论 | 2篇 |
综合类 | 8759篇 |
化学工业 | 14086篇 |
金属工艺 | 6036篇 |
机械仪表 | 7211篇 |
建筑科学 | 8947篇 |
矿业工程 | 3190篇 |
能源动力 | 3161篇 |
轻工业 | 8268篇 |
水利工程 | 2542篇 |
石油天然气 | 4723篇 |
武器工业 | 1187篇 |
无线电 | 12050篇 |
一般工业技术 | 10154篇 |
冶金工业 | 3820篇 |
原子能技术 | 1313篇 |
自动化技术 | 15290篇 |
出版年
2024年 | 425篇 |
2023年 | 1619篇 |
2022年 | 3305篇 |
2021年 | 4543篇 |
2020年 | 3475篇 |
2019年 | 2747篇 |
2018年 | 3071篇 |
2017年 | 3334篇 |
2016年 | 3052篇 |
2015年 | 4498篇 |
2014年 | 5711篇 |
2013年 | 6369篇 |
2012年 | 7428篇 |
2011年 | 7590篇 |
2010年 | 6992篇 |
2009年 | 6830篇 |
2008年 | 6907篇 |
2007年 | 6282篇 |
2006年 | 6094篇 |
2005年 | 4929篇 |
2004年 | 3864篇 |
2003年 | 3501篇 |
2002年 | 4181篇 |
2001年 | 3477篇 |
2000年 | 2247篇 |
1999年 | 1659篇 |
1998年 | 1002篇 |
1997年 | 821篇 |
1996年 | 713篇 |
1995年 | 591篇 |
1994年 | 502篇 |
1993年 | 308篇 |
1992年 | 246篇 |
1991年 | 207篇 |
1990年 | 143篇 |
1989年 | 127篇 |
1988年 | 72篇 |
1987年 | 69篇 |
1986年 | 60篇 |
1985年 | 13篇 |
1984年 | 18篇 |
1983年 | 10篇 |
1982年 | 20篇 |
1981年 | 27篇 |
1980年 | 18篇 |
1979年 | 14篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1959年 | 20篇 |
1951年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
41.
在现有的时间银行系统中,时间币的发行功能和结算功能完全集中到一个中心节点上。这种极度中心化的功能结构,不仅存在容易发生中心节点单点失效、数据容易被篡改等信息安全问题,还存在着时间币的发行和流通缺乏透明度以及时间币的结算依赖中心化的结算机构等问题。针对这些问题,提出了一种基于区块链技术的解决方法。首先,将时间币的发行功能和结算功能从中心节点上分离出来;然后,利用具有分布式去中心化、集体维护和不可篡改等特性的区块链技术,将分离出来的发行功能逐步去中心化,将分离出来的结算功能去中心化,形成公益时间链(PWTB);最终,PWTB利用区块链技术以去中心化的方式将时间银行系统由单个节点维护账本变成由集体维护一个分布式的共享账本,使时间币的发行和流通公开透明,时间币的结算不依赖某个中心化的节点。安全分析表明所设计的PWTB能够实现安全的信息传输与存储,以及数据的共享。 相似文献
42.
Basins with various mineral resources coexisting and enriching often occupy an important strategic position. The exploration of various mineral resources is repetitive at present due to unshared data and imperfect management mechanism. This situation greatly increases the cost of energy exploitation in the country. Traditional data-sharing mode has several disadvantages, such as high cost, difficulty in confirming the right of data, and lack of incentive mechanism, which make achieving real data sharing difficult. In this paper, we propose a data-sharing mechanism based on blockchain and provide implementation suggestions and technical key points. Compared with traditional data-sharing methods, the proposed data-sharing mechanism can realize data sharing, ensure data quality, and protect intellectual property. Moreover, key points in the construction are stated in the case study section to verify the feasibility of the data-sharing system based on blockchain proposed in this paper. 相似文献
43.
Bin Zhang Meng Zhang Yu Li Huansheng Cheng Jianming Zheng 《Ceramics International》2019,45(3):3081-3087
Proton induced X-ray emission (PIXE) technique and factor analysis were used to study the recovery of making-technology of Chinese Longquan celadon made in the late Southern Song Dynasty (1127–1279 CE). Based on factor analysis, for the raw material for body and the recipe for glaze, there is a close but slightly different relationship between these Longquan celadons unearthed from the core area of Dayao and the non-core area, despite all the Longquan celadons belong to the high-calcium-glaze system. The chemical compositions of most of the tentative body and glaze samples are very close to those of Longquan celadons unearthed from the core area of Dayao and the non-core area. This study can provide a guidance for recovery of making-technology of Longquan celandon. 相似文献
44.
A novel bio‐based phthalonitrile resin derived from catechin: synthesis and comparison of curing behavior with petroleum‐based counterpart
下载免费PDF全文
![点击此处可从《Polymer International》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Yu Qi Zhihuan Weng Jinyan Wang Shouhai Zhang Lishuai Zong Cheng Liu Xigao Jian 《Polymer International》2018,67(3):322-329
The development of bio‐based thermosetting resins with good thermal stability can potentially afford sustainable polymers as replacements for petroleum‐based polymers. We report a practical route to a novel catechin‐based phthalonitrile resin precursor (CA‐Ph), which contains free phenolic hydroxyl groups that result in ‘self‐curing’ at elevated temperatures to afford a thermostable polymer. Comparison of the performance of this CA‐Ph resin with that of a conventional petroleum‐based bisphenol A phthalonitrile resin (BPA‐Ph; containing 5 wt% of the curing agent 4,4′‐diaminodiphenylsulfone) revealed that CA‐Ph exhibits a lower melting point and curing temperature. Cured CA‐Ph resin retains 95% of its weight at 520 °C under a nitrogen atmosphere, which compares favorably with results obtained for BPA‐Ph resin that retains 95% of its weight at a lower temperature of 484 °C. Kinetic results indicated that the curing reactions of both CA‐Ph and BPA‐Ph systems follow an autocatalytic mechanism. These results suggest that catechin is a useful bio‐based feedstock for the preparation of self‐curing and thermally stable phthalonitrile resins for advanced technological applications. © 2017 Society of Chemical Industry 相似文献
45.
Thermal comfort is an important factor for the design of buildings. Although it has been well recognized that many physiological parameters are linked to the state of thermal comfort or discomfort of humans, how to use physiological signal to judge the state of thermal comfort has not been well studied. In this paper, the feasibility of continuously determining feelings of personal thermal comfort was discussed by using electroencephalogram (EEG) signals in private space. In the study, 22 subjects were exposed to thermally comfortable and uncomfortably hot environments, and their EEG signals were recorded. Spectral power features of the EEG signals were extracted, and an ensemble learning method using linear discriminant analysis or support vector machine as a sub-classifier was used to build the discriminant model. The results show that an average discriminate accuracy of 87.9% can be obtained within a detection window of 60 seconds. This study indicates that it is feasible to distinguish whether a person feels comfortable or too hot in their private space by multi-channel EEG signals without interruption and suggests possibility for further applications in neuroergonomics. 相似文献
46.
47.
Functional expression and synergistic cooperation of xylan‐degrading enzymes from Hypocrea orientalis and Aspergillus niger
下载免费PDF全文
![点击此处可从《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
48.
49.
Zhen Wu Jing Yao Pengfei Zhu Fusheng Yang Xiangyu Meng Sandra Kurko Zaoxiao Zhang 《International Journal of Hydrogen Energy》2021,46(19):11183-11198
Advanced biogas power generation technology has been attracting attentions, which contributes to the waste disposal and the mitigation of greenhouse gas emissions. This work proposes and models a novel biogas-fed hybrid power generation system consisting of solid oxide fuel cell, water gas shift reaction, thermal swing adsorption and proton exchange membrane fuel cell (SOFC-WGS-TSA-PEMFC). The thermodynamic, exergetic, and thermo-economic analyses of this hybrid system for power generation were conducted to comprehensively evaluate its performance. It was found that the novel biogas-fed hybrid system has a gross energy conversion efficiency of 68.63% and exergy efficiency of 65.36%, indicating high efficiency for this kind of hybrid power technology. The market sensitivity analysis showed that the hybrid system also has a low sensitivity to market price fluctuation. Under the current subsidy level for the distributed biogas power plant, the levelized cost of energy can be lowered to 0.02942 $/kWh for a 1 MW scale system. Accordingly, the payback period and annual return on investment can reach 1.4 year and about 20%, respectively. These results reveal that the proposed hybrid system is promising and economically feasible as a distributed power plant, especially for the small power scale (no more than 2 MW). 相似文献
50.