全文获取类型
收费全文 | 189209篇 |
免费 | 8382篇 |
国内免费 | 4560篇 |
专业分类
电工技术 | 6817篇 |
技术理论 | 5篇 |
综合类 | 5809篇 |
化学工业 | 25798篇 |
金属工艺 | 10584篇 |
机械仪表 | 8588篇 |
建筑科学 | 9743篇 |
矿业工程 | 2699篇 |
能源动力 | 5279篇 |
轻工业 | 11335篇 |
水利工程 | 2249篇 |
石油天然气 | 5806篇 |
武器工业 | 698篇 |
无线电 | 25024篇 |
一般工业技术 | 31669篇 |
冶金工业 | 29340篇 |
原子能技术 | 2430篇 |
自动化技术 | 18278篇 |
出版年
2024年 | 331篇 |
2023年 | 1609篇 |
2022年 | 2630篇 |
2021年 | 3966篇 |
2020年 | 3060篇 |
2019年 | 2774篇 |
2018年 | 3570篇 |
2017年 | 3873篇 |
2016年 | 3524篇 |
2015年 | 4116篇 |
2014年 | 5526篇 |
2013年 | 9585篇 |
2012年 | 8013篇 |
2011年 | 9650篇 |
2010年 | 8021篇 |
2009年 | 8560篇 |
2008年 | 8552篇 |
2007年 | 8582篇 |
2006年 | 8488篇 |
2005年 | 7592篇 |
2004年 | 6001篇 |
2003年 | 5455篇 |
2002年 | 4906篇 |
2001年 | 4950篇 |
2000年 | 4958篇 |
1999年 | 5697篇 |
1998年 | 11524篇 |
1997年 | 7864篇 |
1996年 | 6515篇 |
1995年 | 4590篇 |
1994年 | 3946篇 |
1993年 | 3547篇 |
1992年 | 2308篇 |
1991年 | 2122篇 |
1990年 | 1900篇 |
1989年 | 1636篇 |
1988年 | 1428篇 |
1987年 | 1035篇 |
1986年 | 993篇 |
1985年 | 994篇 |
1984年 | 852篇 |
1983年 | 727篇 |
1982年 | 738篇 |
1981年 | 709篇 |
1980年 | 589篇 |
1979年 | 482篇 |
1978年 | 416篇 |
1977年 | 533篇 |
1976年 | 958篇 |
1975年 | 299篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
61.
62.
63.
Chaoxin Li Yi Zhou Yuming Tian Yuanyuan Zhao Kaiyue Wang Guomin Li Yuesheng Chai 《Ceramics International》2019,45(5):5613-5616
Ceramics with mullite whiskers were prepared from coal fly ash and Al2O3 raw materials, with AlF3 used as an additive. The phase structures and microstructures of the ceramics were identified via X-ray diffraction and scanning electron microscopy, respectively. The results show that pickling of coal fly ash is an effective method for enhancing the flexural strength of ceramics. Sintering temperature and AlF3 addition were also key factors influencing the creation of ideal ceramics. The ceramic made from pickled coal fly ash, 6?wt% AlF3, and sintered at 1200?°C, exhibited the highest flexural strength of 59.1?MPa, and had a bulk density of 1.32?g/cm3 and porosity of 26.8%. The results show that ceramic materials made under these conditions are ideal candidates for manufacturing ceramic proppants for the exploitation of unconventional oil and gas resources. 相似文献
64.
65.
三元复合驱油体系中驱油剂的协同效应,会使油水间的界面张力大幅度下降,原油采收率大幅度提高;但三元复合驱油体系的色谱分离现象也会破坏其协同效应和完整性,揭示色谱分离现象及其影响因素对于改善三元复合驱油效果具有十分重要意义。以油藏工程和分析化学理论为指导,以化学分析和物理模拟为技术途径,并以大庆喇嘛甸油田典型区块地质特征和流体性质为研究对象,开展强碱三元复合驱色谱分离现象及其影响因素研究。结果表明,采用前置高浓度聚合物段塞后,可以有效扩大波及体积,但表面活性剂与碱和聚合物之间无因次等浓距增加,色谱分离现象加剧。大庆油区喇嘛甸油田不同区块油水性质差异对色谱分离现象存在影响,原因在于部分重烷基苯石油磺酸进入油相,影响水相中浓度检测值。强碱三元复合驱油体系中表面活性剂与碱和聚合物之间色谱分离程度比较严重,碱与聚合物之间较弱。 相似文献
66.
67.
Spinel LiSr0·1Cr0·1Mn1·8O4 was synthesised by high temperature solid state method in order to enhance the electrochemical performance. The LiSr0·1Cr0·1Mn1·8O4 (LSCMO) materials were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests. The XRD and SEM studies confirm that LSCMO had spinel crystal structure with a space group of Fd3m, and the particle of LSCMO shows irregular shape. The cyclic voltammetry data illustrated that the heavy current charge–discharge performance of LMO was improved by Sr2+ and Cr3+ doping. The galvanostatic charge–discharge of LSCMO cathode materials was measured at 1, 5, 10 and 20 C. The results indicated that LSCMO improved the capacity retention. 相似文献
68.
Strength of Materials - A metallographic method, dilatometry, and X-ray diffraction were applied to investigate the effects of undercooling and holding time on bainitic transformation,... 相似文献
69.
In this study, 30 subjects were exposed to different combinations of air temperature (Ta: 24, 27, and 30°C) and CO2 level (8000, 10 000, and 12 000 ppm) in a high-humidity (RH: 85%) underground climate chamber. Subjective assessments, physiological responses, and cognitive performance were investigated. The results showed that as compared with exposure to Ta = 24°C, exposure to 30°C at all CO2 levels caused subjects to feel uncomfortably warm and experience stronger odor intensity, while increased mental effort and greater intensity of acute health symptoms were reported. However, no significant effects of Ta on task performance or physiological responses were found. This indicated that subjects had to exert more effort to maintain their performance in an uncomfortably warm environment. Increasing CO2 from 8000 to 12 000 ppm at all Ta caused subjects to report higher rates of headache, fatigue, agitation, and feeling depressed, although the results were statistically significant only at 24 and 27°C. The text typing performance and systolic blood pressure (SBP) decreased significantly at this exposure, whereas diastolic blood pressure (DBP) and thermal discomfort increased significantly. These effects suggest higher arousal/stress. No significant interaction effect of Ta and CO2 concentration on human responses was identified. 相似文献
70.
D. Kherifi H. Belhouchet S. Ramesh K.Y. Sara Lee A. Kenzour S. Djoualah M.K.G. Abbas Y.H. Wong S. Ramesh 《Ceramics International》2021,47(12):16483-16490
In this work, the sintering behaviour of fluorapatite (FAp)–silicate composites prepared by mixing variable amounts of natural quartz (2.5 wt% to 20 wt%) and FAp was studied. The composites were pressureless sintered in air at temperatures from 1000 °C to 1350 °C. The effects of temperatures on the densification, phase formation, chemical bonding and Vickers hardness of the composites were evaluated. All the samples exhibited mixed phase, comprising FAp and francolite as the major constituents along with some minor phases of cristobalite, wollastonite, dicalcium silicate and/or whitlockite dependent on the quartz content and sintering temperature. The composite containing 2.5 wt% quartz exhibited the best sintering properties. The highest bulk density of 3 g/cm3 and a Vickers hardness of >4.2 GPa were obtained for the 2.5 wt% quartz–FAp composite when sintered at 1100 °C. The addition of quartz was found to alter the microstructure of the composites, where it exhibited a rod-like morphology when sintered at 1000 °C and a regular rounded grain structure when sintered at 1350 °C. A wetted grain surface was observed for composites containing high quartz content and was believed to be associated with a transient liquid phase sintering. 相似文献