全文获取类型
收费全文 | 124551篇 |
免费 | 10830篇 |
国内免费 | 8140篇 |
专业分类
电工技术 | 12128篇 |
技术理论 | 2篇 |
综合类 | 10193篇 |
化学工业 | 21460篇 |
金属工艺 | 7248篇 |
机械仪表 | 9730篇 |
建筑科学 | 6103篇 |
矿业工程 | 2523篇 |
能源动力 | 4760篇 |
轻工业 | 7733篇 |
水利工程 | 1519篇 |
石油天然气 | 5798篇 |
武器工业 | 1388篇 |
无线电 | 14988篇 |
一般工业技术 | 12235篇 |
冶金工业 | 3214篇 |
原子能技术 | 1459篇 |
自动化技术 | 21040篇 |
出版年
2024年 | 212篇 |
2023年 | 1627篇 |
2022年 | 2255篇 |
2021年 | 3422篇 |
2020年 | 3157篇 |
2019年 | 3160篇 |
2018年 | 2939篇 |
2017年 | 3877篇 |
2016年 | 4188篇 |
2015年 | 4327篇 |
2014年 | 6135篇 |
2013年 | 7046篇 |
2012年 | 7688篇 |
2011年 | 8990篇 |
2010年 | 7278篇 |
2009年 | 8196篇 |
2008年 | 7948篇 |
2007年 | 8965篇 |
2006年 | 8437篇 |
2005年 | 6889篇 |
2004年 | 5973篇 |
2003年 | 5600篇 |
2002年 | 4568篇 |
2001年 | 3727篇 |
2000年 | 3267篇 |
1999年 | 2539篇 |
1998年 | 1872篇 |
1997年 | 1563篇 |
1996年 | 1320篇 |
1995年 | 1327篇 |
1994年 | 1137篇 |
1993年 | 956篇 |
1992年 | 781篇 |
1991年 | 489篇 |
1990年 | 301篇 |
1989年 | 299篇 |
1988年 | 209篇 |
1987年 | 134篇 |
1986年 | 126篇 |
1985年 | 92篇 |
1984年 | 88篇 |
1983年 | 52篇 |
1982年 | 57篇 |
1981年 | 62篇 |
1980年 | 35篇 |
1979年 | 35篇 |
1978年 | 24篇 |
1977年 | 22篇 |
1976年 | 28篇 |
1975年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
针对氧化铝行业中常用的Cr28和Cr20高铬铸铁伞帽在相同工况条件下的磨损机理进行分析,并对比研究了实际生产中两种失效材料的成分、组织及性能。结果表明,伞帽部件在高温强碱腐蚀条件下受到外界冲刷时,磨损量由微切削磨损与变形磨损这两种机制共同决定。含铬量较高的Cr28高铬铸铁,其冲刷和抗腐蚀磨损性能均优于Cr20高铬铸铁。伞帽服役寿命主要受浆料和表层的铸铁材料两大因素影响。两种试验材料经淬火+回火处理后,基体组织中主要为回火马氏体+M7C3型碳化物+少量残留奥氏体,其中含铬量较高的Cr28高铬铸铁中共晶碳化物含量更高,且分布更加弥散,其平均硬度值为64.0 HRC,高于Cr20高铬铸铁的60.2 HRC。最终确定Cr28高铬铸铁作为伞帽材质更能满足氧化铝生产及设备检修周期的需要。 相似文献
92.
Shengyue Gu Shouyang Zhang Fei Liu Wei Li 《Journal of the European Ceramic Society》2018,38(15):5082-5091
Y2Hf2O7 possesses low thermal conductivity and high melting point, which make it promising for a new anti-ablation material. For evaluating the thermal stability and the potential applications of Y2Hf2O7 on anti-ablation protection of C/C composites, Y2Hf2O7 ceramic powder was synthesized by solution combustion method and Y2Hf2O7 coating was prepared on the surface of SiC coated C/C composites using SAPS. Results shown that the coating exhibits good ablation resistance under the heat flux of 2.4?MW/m2 with the linear and mass ablation rates are 0.16?μm?s?1 and ?0.028?mg?s?1, respectively, after ablation for 40?s. With the prolonging of the ablation time, the increasing thermal stress causes the increase of cracks. Moreover, the chemical erosion from SiO2 and the physical volatilization of low temperature molten products aggravate failure of the Y2Hf2O7 coating. 相似文献
93.
94.
Ying Chen HuiLi Zhang YuNing Liang YanHua Gao Yongchao Li 《Petroleum Science and Technology》2019,37(7):787-795
In this study, a simple hydrothermal synthesis method was adapted for the preparation of Co-doping Co2+/F-/TiO2 nanotubes photocatalyst, and the micro-nano structure of catalysts prepared by biomimetic technology which makes the catalyst have super-oleophilicity property. Co2+/F-/TiO2 revealed improved photocatalytic performance for denitrification of light oil compared to single TiO2 photocatalysts. The enhance of photocatalytic activity can be attributed to narrowing the band gap, increasing the light response wavelength and exposing more highly active crystal surfaces due to synergistic effects of Co2+ and F? in the photocatalyst. 相似文献
95.
Artificial bee colony (ABC) algorithm has several characteristics that make it more attractive than other bio-inspired methods. Particularly, it is simple, it uses fewer control parameters and its convergence is independent of the initial conditions. In this paper, a novel artificial bee colony based maximum power point tracking algorithm (MPPT) is proposed. The developed algorithm, does not allow only overcoming the common drawback of the conventional MPPT methods, but it gives a simple and a robust MPPT scheme. A co-simulation methodology, combining Matlab/Simulink™ and Cadence/Pspice™, is used to verify the effectiveness of the proposed method and compare its performance, under dynamic weather conditions, with that of the Particle Swarm Optimization (PSO) based MPPT algorithm. Moreover, a laboratory setup has been realized and used to experimentally validate the proposed ABC-based MPPT algorithm. Simulation and experimental results have shown the satisfactory performance of the proposed approach. 相似文献
96.
97.
Catalytic Hydrocracking of a Bitumen‐Derived Asphaltene over NiMo/γ‐Al2O3 at Various Temperatures 下载免费PDF全文
Hydrocracking of a bitumen‐derived asphaltene over NiMo/γ‐Al2O3 was investigated in a microbatch reactor at varying temperatures. The molar kinetics of asphaltene cracking reaction was examined by fitting the experimental data. Below a defined temperature, the molar reaction showed the first‐order kinetic feature while at higher temperatures secondary reactions such as coke formation became significant, causing deviation of the reaction behavior from the proposed first‐order kinetic model. Selectivity analysis proved that dominant products varied from gases to liquids to gases with increasing temperature, shifting the dominant reaction from C–S bonds cleavage to C–C bonds cleavage. 相似文献
98.
The eutectic 80Au/20Sn solder alloy is widely used in high power electronics and optoelectronics packaging. In this study, low cycle fatigue behavior of a eutectic 80Au/20Sn solder alloy is reported. The 80Au/20Sn solder shows a quasi-static fracture characteristic at high strain rates, and then gradually transforms from a transgranular fracture (dominated by fatigue damage) to intergranular fracture (dominated by creep damage) at low strain rates with increasing temperature. Coffin-Manson and Morrow models are proposed to evaluate the low cycle fatigue behavior of the 80Au/20Sn solder. Besides, the 80Au/20Sn solder has enhanced fatigue resistance compared to the 63Sn/37Pb solder. 相似文献
99.
张居晓 《计算机技术与发展》2015,(1)
计算机录入编辑盲文是信息处理的特殊应用领域,是特殊教育中的重要研究课题。文中将盲文制作为特殊符号,通过制作字库,编写个性化码表,然后嵌入到主流输入法,从而实现盲文与汉字混排以及实现单手盲文输入。该系统具有易学易记性、盲文编码多样性、嵌入性强等优点,并通过实验证明输入盲文效率能提高5~6倍,在盲文出版、盲文印刷、盲文教学等领域有重要的应用价值。但盲文字符在不同平台(如智能手机)与不同操作系统兼容性问题还有待进一步研究开发。 相似文献