全文获取类型
收费全文 | 30755篇 |
免费 | 2617篇 |
国内免费 | 1249篇 |
专业分类
电工技术 | 1738篇 |
技术理论 | 6篇 |
综合类 | 1673篇 |
化学工业 | 5177篇 |
金属工艺 | 2211篇 |
机械仪表 | 1924篇 |
建筑科学 | 2272篇 |
矿业工程 | 919篇 |
能源动力 | 958篇 |
轻工业 | 2238篇 |
水利工程 | 487篇 |
石油天然气 | 2109篇 |
武器工业 | 232篇 |
无线电 | 3196篇 |
一般工业技术 | 3660篇 |
冶金工业 | 1719篇 |
原子能技术 | 349篇 |
自动化技术 | 3753篇 |
出版年
2024年 | 165篇 |
2023年 | 592篇 |
2022年 | 956篇 |
2021年 | 1379篇 |
2020年 | 1065篇 |
2019年 | 893篇 |
2018年 | 972篇 |
2017年 | 1047篇 |
2016年 | 892篇 |
2015年 | 1265篇 |
2014年 | 1454篇 |
2013年 | 1917篇 |
2012年 | 1967篇 |
2011年 | 2070篇 |
2010年 | 1816篇 |
2009年 | 1680篇 |
2008年 | 1643篇 |
2007年 | 1595篇 |
2006年 | 1625篇 |
2005年 | 1404篇 |
2004年 | 894篇 |
2003年 | 846篇 |
2002年 | 795篇 |
2001年 | 651篇 |
2000年 | 718篇 |
1999年 | 837篇 |
1998年 | 681篇 |
1997年 | 514篇 |
1996年 | 513篇 |
1995年 | 400篇 |
1994年 | 352篇 |
1993年 | 237篇 |
1992年 | 179篇 |
1991年 | 125篇 |
1990年 | 102篇 |
1989年 | 60篇 |
1988年 | 72篇 |
1987年 | 48篇 |
1986年 | 39篇 |
1985年 | 34篇 |
1984年 | 30篇 |
1983年 | 16篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 14篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1974年 | 3篇 |
1959年 | 4篇 |
1958年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
This study investigated the impact of weblog use on individual learning in the context of university senior-level business education. As an emergent form of personal communication, weblogs enable people to publish their thoughts as webpages, and to share information and knowledge. Recognizing the potential impact of weblogs on knowledge expression and sharing, this research sought to empirically examine whether the continuous use of weblogs as online learning logs would affect student learning performance. The assumption was that effective use of weblogs promoted the constructivist models of learning by supporting both cognitive and social knowledge construction, and by reinforcing individual accountability in learning. Results from an Information Systems undergraduate course with 31 participants indicated that the performance of students' weblogs was a significant predictor of the learning outcome (while traditional coursework was not). Moreover, individuals' cognitive construction effort to build their own mental models and social construction effort to further enrich/expand knowledge resources appeared to be two key aspects of the constructivist learning with weblogs. Our results imply the potential benefit of using weblogs as a knowledge construction tool and a social learning medium 相似文献
982.
Tao Jiang Weidong Xiang Richardson P.C. Daiming Qu Guangxi Zhu 《Wireless Communications, IEEE Transactions on》2007,6(6):2017-2021
In this paper, we provide the design criteria of the nonlinear companding transforms for reduction in peak-to-average power ratio (PAPR) of multi-carrier modulation (MCM) signals, which can enable the original MCM signals to be transformed into the desirable distribution. As examples, some novel nonlinear companding transforms have been proposed to transform the amplitude or power of the original MCM signals into uniform distribution, which can effectively reduce the PAPR for different modulation formats and subcarrier sizes without any complexity increase and bandwidth expansion. It has been shown by computer simulations that the proposed schemes can significantly improve the performance of MCM systems including bit-error-rate and PAPR reduction. 相似文献
983.
Weidong Cheng Zhenghui Wu Shanpeng Wen Bin Xu Hui Li Furong Zhu Wenjing Tian 《Organic Electronics》2013,14(9):2124-2131
Two new low band gap conjugated polymers containing a benzo[1,2-b:4,5-b′]dithiophene donor unit and a tetrazine acceptor unit were synthesized by Stille cross-coupling polymerization. The structural and thermal properties of copolymers were characterized using nuclear magnetic resonance, gel permeation chromatography and thermogravimetric analysis. The results show that the donor–acceptor copolymers thus developed have good thermal stability with decomposition temperature of 294 °C and 305 °C. Cyclic voltammetric study revealed that the copolymers possess a deep-lying highest occupied molecular orbital energy level, which is desired for high open circuit voltage polymer solar cells (PSCs) and is also favorable for stable device operation in air. Bulk-heterojunction PSCs based on blend of low band gap copolymers: [6,6]-phenyl-C71-butyric acid methyl ester on indium tin oxide/glass substrates were fabricated. This work yielded a promising power conversion efficiency of >5.0%, with a high open circuit voltage of ~1.0 V, measured under air mass 1.5 global irradiation of 100 mW/cm2. 相似文献
984.
阐述了3G核心网的体系结构及3G安全域的划分方式,3G核心网各安全域内该包含的主要设备,并在此基础上详细分析了各安全域所面临的安全威胁。 相似文献
985.
986.
987.
988.
989.
UV‐Triggered Polydopamine Secondary Modification: Fast Deposition and Removal of Metal Nanoparticles
Yi Zeng Xin Du Wei Hou Xiaojiang Liu Cun Zhu Bingbing Gao Liangdong Sun Qiwei Li Junlong Liao Pavel A. Levkin Zhongze Gu 《Advanced functional materials》2019,29(34)
Since the first report in 2007, polydopamine (PDA) coating has shown great potential as a general and versatile method to create functional nanocoatings on arbitrary substrates. Slow kinetics and poor controllability of the coating and secondary modification processes, however, have limited the further development of this attractive method. In this work, it is demonstrated that UV irradiation at 365 nm significantly accelerates the process of secondary modification of a PDA‐coated surface. The kinetics of both thiol and amine modifications of PDA are increased 12‐fold via UV irradiation, while the kinetics of metal ion reduction at the PDA interface is increased more than 550 times. Moreover, it is demonstrated that irradiating a PDA/metal nanoparticle composite surface with UV light at 254 nm leads to dissolution of the deposited metal nanoparticles (MNPs). Finally, grayscale metallic patterns, dynamic deposition, and removal of MNPs on PDA surface are realized with the proposed method. 相似文献
990.
本文描述了一个关于模式自动切换电荷泵的开关感应误差电压的精确表达式,此误差电压会在输出电容上产生一个冲击电压。这将会导致一些不希望得到的结果:大的输出电压纹波,有害的高频噪声和低的效率。通过这个表达式可以得到一些减小输出电容上冲击电压的方法。一个等效集总模型被用来推出此表达式。本文中的模式自动切换电荷泵使用SILTERRA0.18?m CMOS工艺实现。实验结果显示冲击电压的值与表达式的计算结果十分吻合。通过比较三个不同的经过改进的版本的测试结果,可以看到由开关感应产生的过冲电压明显的减小。 相似文献