全文获取类型
收费全文 | 146228篇 |
免费 | 16373篇 |
国内免费 | 10477篇 |
专业分类
电工技术 | 12547篇 |
技术理论 | 3篇 |
综合类 | 13535篇 |
化学工业 | 19415篇 |
金属工艺 | 10080篇 |
机械仪表 | 10701篇 |
建筑科学 | 12008篇 |
矿业工程 | 5125篇 |
能源动力 | 4514篇 |
轻工业 | 11688篇 |
水利工程 | 4300篇 |
石油天然气 | 6289篇 |
武器工业 | 2095篇 |
无线电 | 16687篇 |
一般工业技术 | 14302篇 |
冶金工业 | 5568篇 |
原子能技术 | 2503篇 |
自动化技术 | 21718篇 |
出版年
2024年 | 328篇 |
2023年 | 2010篇 |
2022年 | 4441篇 |
2021年 | 6213篇 |
2020年 | 4547篇 |
2019年 | 3541篇 |
2018年 | 3737篇 |
2017年 | 4360篇 |
2016年 | 4091篇 |
2015年 | 6295篇 |
2014年 | 7930篇 |
2013年 | 9430篇 |
2012年 | 11577篇 |
2011年 | 12434篇 |
2010年 | 11785篇 |
2009年 | 11291篇 |
2008年 | 11491篇 |
2007年 | 11250篇 |
2006年 | 10058篇 |
2005年 | 8063篇 |
2004年 | 5976篇 |
2003年 | 4540篇 |
2002年 | 4302篇 |
2001年 | 3810篇 |
2000年 | 2966篇 |
1999年 | 1808篇 |
1998年 | 960篇 |
1997年 | 800篇 |
1996年 | 648篇 |
1995年 | 546篇 |
1994年 | 422篇 |
1993年 | 323篇 |
1992年 | 226篇 |
1991年 | 177篇 |
1990年 | 140篇 |
1989年 | 132篇 |
1988年 | 74篇 |
1987年 | 65篇 |
1986年 | 65篇 |
1985年 | 21篇 |
1984年 | 25篇 |
1983年 | 28篇 |
1982年 | 20篇 |
1981年 | 24篇 |
1980年 | 32篇 |
1979年 | 18篇 |
1978年 | 5篇 |
1977年 | 8篇 |
1959年 | 24篇 |
1951年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Yi Qin Tao Xiong Ting Zhao Jianfeng Zhu Jun Yang Yi Liu Xingang Kong Xiaohan Li 《Ceramics International》2021,47(9):12641-12650
The strengthening method of multi-element M-site solid solution is a common approach to improve mechanical properties of MAX phase ceramic. However, the research on capability of multi-element A-site solid solution to improve mechanical properties has rarely been reported. Thereupon, quasi-high-entropy MAX phase ceramic bulks of Ti2(Al1?xAx)C and Ti3(Al1?xAx)C2 (A = Ga, In, Sn, x = 0.2, 0.3, 0.4) were successfully synthesized by in situ vacuum hot pressing via multi-elements solid solution. The multi-elements solid solution in single-atom thick A layer was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy as well as by energy dispersive X-ray spectroscopy mappings. Effects of doped multi-elements contents on the phase, microstructure, mechanical properties, and high temperature tribological behaviors were studied. Results demonstrated that the Vickers hardness, anisotropic flexural strength, fracture toughness, and tribological properties of Ti–Al–C based MAX ceramics could be remarkably improved by constitution of quasi-high-entropy MAX phase in A layers. Moreover, the strengthening and wear mechanisms were also discussed in detail. This method of multi-element solid solution at A-site provides new way to enhance mechanical properties of other MAX phase ceramics. 相似文献
42.
43.
Effective distribution coefficients of 9 impurities in 1,2-diphenylethane have been calculated by directional crystallization under different ambient frozen temperature. The effect of varied zone size, temperature difference between the melt and ambient frozen environment, number of zone on purity of 1,2-diphenylethane have been also investigated during the process of zone refining. The results indicate that the product purity in the intermediate purified region with varied zone size is higher 0.04%-0.2% than that with constant zone size. The product purity increases with temperature difference between the melt and ambient frozen environment. The appropriate temperature difference is adopted 50℃. The product purity in the intermediate region of sample bar with 2 molten zones is higher 0.05%-0.43% than that with 1 molten zone. In addition, the change of enthalpy and entropy between impurities and 1,2-diphenylethane have been determined. 相似文献
44.
45.
以太阳纸业备料车间木片筛选碎料(筛余物)为原料,对其烧碱法半化学制浆的实验室工艺和生产试验进行了研究。结果表明,筛余物采用半化学法制浆可获得较高得率和环压强度的纸浆,且用碱量对纸浆性能有显著影响。相对8%NaOH (相对于绝干原料)化学预处理,采用14%NaOH化学预处理结合两段浆浓22%的高浓磨浆工艺,所制半化学浆抄造浆张的裂断长和环压指数分别达2.89 km和9.76 N·m/g,是前者的1.9倍和1.2倍,而且优于现用国内OCC废纸浆抄造浆张;生产试验得到的浆张性能指标与实验室相吻合,其中紧度和环压强度分别达到GB/T 13023—2008瓦楞芯(原)纸AA级和A级优等品要求。 相似文献
48.
Expanded graphite (EG) is introduced into poly(vinylidene fluoride) (PVDF) by melt mixing extrusion with water injection. The results demonstrate that the unfunctionalized EG in composite prepared with water injection exbibits better dispersion than that in the one prepared without water injection due to the promoting role of water during extrusion. Thus, the PVDF/EG composite with loading of 4 wt% prepared by water‐assisted mixing extrusion (WAME) exhibits electrical conductivity of about three orders of magnitude higher than the neat PVDF and one order of magnitude higher than the one prepared without water injection. Comparing to the neat PVDF, the thermal conductivity of the composites prepared with and without water injection is increased by 101.5% and 75.0%, respectively. The introduced EG leads to increased Young’s modulus and tensile strength especially for the composite prepared by WAME. The present work indicates that WAME can promote the dispersion of EG in PVDF matrix without any extra functionalization. 相似文献
49.
50.
建立车辆动力学模型,研究车辆在高速避让工况下的路径跟踪控制策略。基于自抗扰控制设计车辆横摆角速度以及道路曲率2种不同的路径跟踪控制器;设计基于车辆偏航位移和偏航角度加权的线性二次最优控制器;对3种控制器控制效果进行仿真验证,分析路径跟踪侧向位移误差、侧向加速度、前轮转向角以及偏航角度变化。越野车实车测试结果表明,路径跟踪控制策略正确。 相似文献