全文获取类型
收费全文 | 17390篇 |
免费 | 2155篇 |
国内免费 | 1515篇 |
专业分类
电工技术 | 1738篇 |
综合类 | 1809篇 |
化学工业 | 1988篇 |
金属工艺 | 1241篇 |
机械仪表 | 1135篇 |
建筑科学 | 1276篇 |
矿业工程 | 586篇 |
能源动力 | 503篇 |
轻工业 | 1743篇 |
水利工程 | 729篇 |
石油天然气 | 634篇 |
武器工业 | 199篇 |
无线电 | 1949篇 |
一般工业技术 | 1609篇 |
冶金工业 | 692篇 |
原子能技术 | 294篇 |
自动化技术 | 2935篇 |
出版年
2024年 | 94篇 |
2023年 | 304篇 |
2022年 | 777篇 |
2021年 | 967篇 |
2020年 | 663篇 |
2019年 | 464篇 |
2018年 | 485篇 |
2017年 | 602篇 |
2016年 | 471篇 |
2015年 | 804篇 |
2014年 | 961篇 |
2013年 | 1164篇 |
2012年 | 1420篇 |
2011年 | 1420篇 |
2010年 | 1361篇 |
2009年 | 1270篇 |
2008年 | 1413篇 |
2007年 | 1321篇 |
2006年 | 1141篇 |
2005年 | 964篇 |
2004年 | 769篇 |
2003年 | 479篇 |
2002年 | 489篇 |
2001年 | 378篇 |
2000年 | 365篇 |
1999年 | 150篇 |
1998年 | 86篇 |
1997年 | 58篇 |
1996年 | 50篇 |
1995年 | 30篇 |
1994年 | 30篇 |
1993年 | 18篇 |
1992年 | 11篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1976年 | 1篇 |
1959年 | 10篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
2.
Sheng Mingming Yang Rongkun Gong Hongyu Zhang Yujun Lin Xiao Jing Jie 《Journal of Materials Science》2022,57(10):5805-5824
Journal of Materials Science - With the extensive use of high-power electronic appliances, polymer-based thermal insulation composites with excellent thermal properties are utilized in the field of... 相似文献
3.
The Fe/C/SiCN composite ceramics were synthesized by polymer-derived method to obtain the integration of structure and functions. The electromagnetic waves (EMW) absorption properties at X and Ku bands were investigated. The addition of nano-sized Fe particles improved the magnetic loss and impedance matching, and the carbon nanotubes generated by the iron in-situ catalysis increased the internal relaxation polarization and interfacial polarization, which together improved the EMW absorption properties significantly. In particular, the Fe/C/SiCN-9 showed the optimum reflection loss (RL) of ?31.06 dB at 10.03 GHz with an effective absorption bandwidth (EAB, RL < ?10 dB) of 3.03 GHz at 2.51 mm, indicating the excellent EMW absorption properties of Fe/C/SiCN composite ceramics. 相似文献
4.
5.
The mammalian cell cycle is important in controlling normal cell proliferation and the development of various diseases. Cell cycle checkpoints are well regulated by both activators and inhibitors to avoid cell growth disorder and cancerogenesis. Cyclin dependent kinase 20 (CDK20) and p21Cip1/Waf1 are widely recognized as key regulators of cell cycle checkpoints controlling cell proliferation/growth and involving in developing multiple cancers. Emerging evidence demonstrates that these two cell cycle regulators also play an essential role in promoting cell survival independent of the cell cycle, particularly in those cells with a limited capability of proliferation, such as cardiomyocytes. These findings bring new insights into understanding cytoprotection in these tissues. Here, we summarize the new progress of the studies on these two molecules in regulating cell cycle/growth, and their new roles in cell survival by inhibiting various cell death mechanisms. We also outline their potential implications in cancerogenesis and protection in heart diseases. This information renews the knowledge in molecular natures and cellular functions of these regulators, leading to a better understanding of the pathogenesis of the associated diseases and the discovery of new therapeutic strategies. 相似文献
6.
为了研究荷电细水雾对瓦斯爆炸超压的影响规律和机理,采用小尺寸管道模拟瓦斯爆炸,研究不同荷电电压作用下的瓦斯爆炸超压和平均压升速率,以及不同雾通量作用下的瓦斯爆炸超压.结果表明:随着荷电电压的升高,瓦斯爆炸超压和平均压升速率受到明显的抑制;随着雾通量的增加,瓦斯爆炸超压明显降低.在实验条件下,和普通细水雾相比,当雾通量为4L、荷电电压为8kV时,瓦斯爆炸超压峰值降低10.798kPa,降幅达49.78%;平均压升速率峰值降低180.468kPa/s,降幅达49.90%. 相似文献
7.
通过文献计量方法从样本选取、研究动态分析、主题分布三方面对健康人力资本发展现状及热点问题进行总结.研究结果表明,自2004年开始该领域所属学科种类和期刊源日益丰富,并形成合著度较高的核心作者群体,健康人力资本研究成为人力资本领域的研究热点,健康人力资本与经济增长或收入的关系、健康人力资本指标体系的构建和居民健康人力资本收入效应的测算等问题都成为当前和未来的研究重点. 相似文献
8.
Hao Li Pengcheng Zhang Shengquan Yu Hongyu Yang Bin Tang Fuhai Li Shuren Zhang 《Ceramics International》2019,45(9):11639-11647
Mg2(Ti1-xSnx)O4 (x?=?0–1) ceramics were prepared through conventional solid-state method. This paper focused on the dependence of microwave dielectric properties on crystal structural characteristics via crystal structure refinement, Raman spectra study and complex chemical bond theory. XRD spectrums delineated the phase information of a spinel structure, and structural characteristic of these compositions were achieved with the help of Rietveld refinements. Raman spectrums were used to depict the correlations between vibrational phonon modes and dielectric properties. The variation of permittivity is ascribed to the Mg2(Ti1-xSnx)O4 average bond covalency. The relationship among the B-site octahedral bond energy, tetrahedral bond energy and temperature coefficient are discussed by defining on the change rate of bond energy and the contribution rate of octahedral bond energy. The quality factor is affected by systematic total lattice energy, and the research of XPS patterns illustrated that oxygen vacancies can be effectively restrained in rich oxygen sintering process. Obviously, the microwave dielectric properties of Mg2(Ti1-xSnx)O4 compounds were obtained (= 12.18, ?=?170,130?GHz, ?=??53.1?ppm/°C, x?=?0.2). 相似文献
9.
10.
BDI模型能够很好地解决在特定环境下的Agent的推理和决策问题,但在动态和不确定环境下缺少决策和学习的能力。强化学习解决了Agent在未知环境下的决策问题,却缺少BDI模型中的规则描述和逻辑推理。针对BDI在未知和动态环境下的策略规划问题,提出基于强化学习Q-learning算法来实现BDI Agent学习和规划的方法,并针对BDI的实现模型ASL的决策机制做出了改进,最后在ASL的仿真平台Jason上建立了迷宫的仿真,仿真实验表明,在加入Q-learning学习机制后的新的ASL系统中,Agent在不确定环境下依然可以完成任务。 相似文献