全文获取类型
收费全文 | 167048篇 |
免费 | 15314篇 |
国内免费 | 7983篇 |
专业分类
电工技术 | 10433篇 |
技术理论 | 14篇 |
综合类 | 11619篇 |
化学工业 | 27188篇 |
金属工艺 | 9040篇 |
机械仪表 | 10297篇 |
建筑科学 | 13247篇 |
矿业工程 | 4914篇 |
能源动力 | 4763篇 |
轻工业 | 12471篇 |
水利工程 | 3092篇 |
石油天然气 | 8646篇 |
武器工业 | 1389篇 |
无线电 | 20602篇 |
一般工业技术 | 19488篇 |
冶金工业 | 7844篇 |
原子能技术 | 1754篇 |
自动化技术 | 23544篇 |
出版年
2024年 | 854篇 |
2023年 | 3109篇 |
2022年 | 5614篇 |
2021年 | 7395篇 |
2020年 | 5463篇 |
2019年 | 4413篇 |
2018年 | 4960篇 |
2017年 | 5453篇 |
2016年 | 4762篇 |
2015年 | 6650篇 |
2014年 | 8211篇 |
2013年 | 9799篇 |
2012年 | 10956篇 |
2011年 | 11686篇 |
2010年 | 10131篇 |
2009年 | 9910篇 |
2008年 | 9716篇 |
2007年 | 9011篇 |
2006年 | 8907篇 |
2005年 | 7736篇 |
2004年 | 5442篇 |
2003年 | 4802篇 |
2002年 | 4627篇 |
2001年 | 4217篇 |
2000年 | 3806篇 |
1999年 | 4019篇 |
1998年 | 3262篇 |
1997年 | 2843篇 |
1996年 | 2519篇 |
1995年 | 2131篇 |
1994年 | 1719篇 |
1993年 | 1353篇 |
1992年 | 1060篇 |
1991年 | 807篇 |
1990年 | 652篇 |
1989年 | 534篇 |
1988年 | 424篇 |
1987年 | 318篇 |
1986年 | 231篇 |
1985年 | 184篇 |
1984年 | 114篇 |
1983年 | 86篇 |
1982年 | 105篇 |
1981年 | 63篇 |
1980年 | 66篇 |
1979年 | 41篇 |
1978年 | 26篇 |
1977年 | 25篇 |
1976年 | 40篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Thermally conductive polymers offer new possibilities for the heat dissipation in electric and electronic components, for example, by a three‐dimensional shaping of the heat sinks. To face safety regulations, improved fire performance of those components is required. In contrast to unfilled polymers, those materials exhibit an entirely different thermal behavior. To investigate the flammability, a phosphorus flame retardant was incorporated into thermally conductive composites of polyamide 6 and hexagonal boron nitride. The flame retardant decreased the thermal conductivity only slightly. However, the burning behavior changed significantly, due to a different heat propagation, which was investigated using a thermographic camera. An optimum content of hexagonal boron nitride for a sufficient thermal conductivity and fire performance was found between 20 and 30 vol%. The improvement of the fire performance was due to a faster heat release out of the pyrolysis zone and an earlier decomposition of the flame retardant. For higher contents of hexagonal boron nitride, the heat was spread faster within the part, promoting an earlier ignition and increasing the decomposition rate of the flame retardant. 相似文献
62.
63.
Adaptive backstepping repetitive learning control design for nonlinear discrete‐time systems with periodic uncertainties 下载免费PDF全文
Qiao Zhu Jian‐Xin Xu Shiping Yang Guang‐Da Hu 《International Journal of Adaptive Control and Signal Processing》2015,29(4):524-535
This paper addresses a tracking problem for uncertain nonlinear discrete‐time systems in which the uncertainties, including parametric uncertainty and external disturbance, are periodic with known periodicity. Repetitive learning control (RLC) is an effective tool to deal with periodic unknown components. By using the backstepping procedures, an adaptive RLC law with periodic parameter estimation is designed. The overparameterization problem is overcome by postponing the parameter estimation to the last backstepping step, which could not be easily solved in robust adaptive control. It is shown that the proposed adaptive RLC law without overparameterization can guarantee the perfect tracking and boundedness of the states of the whole closed‐loop systems in presence of periodic uncertainties. In addition, the effectiveness of the developed controller is demonstrated by an implementation example on a single‐link flexible‐joint robot. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
64.
65.
Wan‐Xia Wu 《Polymer International》2019,68(11):1848-1855
A series of novel aliphatic poly(β‐thioether ester)s with various methylene group contents were prepared by direct lipase‐catalyzed polycondensation of the monomer with an acid‐labile β‐thiopropionate group. The polycondensation reaction using immobilized lipase B from Candida antarctica was carried out in diphenyl ether at 90 °C. Poly(β‐thioether ester)s with high molecular weights of 20 500–57 000 Da and narrow polydispersities in the range 1.40–1.48 were obtained. Thermogravimetric analysis, differential scanning calorimetry and wide‐angle X‐ray diffraction were used to investigate the thermal properties and crystal structures of these polyesters. All the poly(β‐thioether ester)s were semicrystalline polymers and thermally stable up to at least 200 °C. In vitro degradation studies showed that they can rapidly degrade under acidic conditions by the hydrolysis of the β‐thiopropionate groups, suggesting their potential as acid‐degradable polymeric materials. © 2019 Society of Chemical Industry 相似文献
66.
使用气-质联用仪测定餐饮废油生物柴油(WCME)和-10号柴油(-10PD)的组成,使用冷滤点试验器和运动黏度试验器测定WCME的低温流动性,同时使用调合、添加低温流动性改进剂的方法改进WCME的低温流动性。实验结果表明,WCME主要由饱和脂肪酸甲酯和不饱和脂肪酸甲酯组成,质量分数分别为27.63%和71.81%;WCME冷滤点为0℃,运动黏度(40℃)为4.41mm2/s;WCME与-10PD调合后,冷滤点降低,其中B20的冷滤点最低,为-13℃,运动黏度随着WCME的体积分数的减少,逐渐接近-10PD的运动黏度。通过添加低温流动性改进剂,WCME,B10,B20的冷滤点分别从0,-8,-13℃降至-4,-26,-25℃。 相似文献
67.
应急避难场所广播体系由应急广播、场所广播室、接收端、网络接收、广播管理群、监测系统等6部分组成.针对电台在市区建立应急避难场所广播作出设计,在学校、社区、广场上安装广播系统,做到市区全方面覆盖. 相似文献
68.
Wai-Ching Liu Huey-Yuan Wang Lung-Chien Chen Shih-Wei Huang Chengtie Wu Ren-Jei Chung 《Ceramics International》2019,45(5):5668-5679
Tricalcium silicate (C3S) and hydroxyapatite (HAp) composites were fabricated through the sol-gel process. The aim of this research is to improve the biocompatibility of C3S through HAp addition and study the potential of using this as coating materials. The composites (HAp/C3S) were characterised by Fourier transform infrared spectrometry, thermal gravity-differential thermal analysis and X-ray diffraction. The working and setting times of cement pastes were tested using Gillmore needle. Mechanical properties were examined by nanoindentation and material testing system. In vitro biocompatibility of the materials were studied by cell attachment and viability of L929 and MG-63 cells. HAp/C3S as a coating material on gelatin film were measured with the surface roughness and imaged by scanning electron microscope. With the addition of HAp, no undesirable free CaO was detected with the synthesis by the sol-gel preparation. The pH values of HAp added groups were between 7.54 and 8.76, which were much lower than pure C3S group (pH?=?11.75). For in vitro studies, the presence of HAp could effectively enhance the cell attachment and viability of both L929 and MG-63 cells grown in the extract or directly on the composites. However, the mechanical properties of the composites were impaired as compared to pure C3S. Lastly, HAp/C3S cement could be evenly coated on gelatin film. HAp is successfully demonstrated to improve C3S biocompatibility with this new composites HAp/C3S. C-75 (75% C3S and 25% HAp), in particular, has good biocompatibility, relatively high compressive strength and can be uniformly coated onto gelatin film. Thus, C-75 is a promising material for further investigation as a coating on other biopolymers. 相似文献
69.
70.