全文获取类型
收费全文 | 29291篇 |
免费 | 3135篇 |
国内免费 | 1696篇 |
专业分类
电工技术 | 4231篇 |
综合类 | 2667篇 |
化学工业 | 3446篇 |
金属工艺 | 2723篇 |
机械仪表 | 2359篇 |
建筑科学 | 2163篇 |
矿业工程 | 1812篇 |
能源动力 | 1076篇 |
轻工业 | 1381篇 |
水利工程 | 783篇 |
石油天然气 | 1049篇 |
武器工业 | 332篇 |
无线电 | 2707篇 |
一般工业技术 | 3524篇 |
冶金工业 | 1172篇 |
原子能技术 | 280篇 |
自动化技术 | 2417篇 |
出版年
2024年 | 61篇 |
2023年 | 430篇 |
2022年 | 753篇 |
2021年 | 926篇 |
2020年 | 966篇 |
2019年 | 797篇 |
2018年 | 794篇 |
2017年 | 1063篇 |
2016年 | 1130篇 |
2015年 | 1260篇 |
2014年 | 2122篇 |
2013年 | 1947篇 |
2012年 | 2296篇 |
2011年 | 2319篇 |
2010年 | 1771篇 |
2009年 | 1782篇 |
2008年 | 1506篇 |
2007年 | 2037篇 |
2006年 | 1748篇 |
2005年 | 1403篇 |
2004年 | 1193篇 |
2003年 | 984篇 |
2002年 | 850篇 |
2001年 | 752篇 |
2000年 | 602篇 |
1999年 | 481篇 |
1998年 | 309篇 |
1997年 | 299篇 |
1996年 | 261篇 |
1995年 | 224篇 |
1994年 | 206篇 |
1993年 | 126篇 |
1992年 | 123篇 |
1991年 | 90篇 |
1990年 | 131篇 |
1989年 | 80篇 |
1988年 | 51篇 |
1987年 | 32篇 |
1986年 | 40篇 |
1985年 | 29篇 |
1984年 | 32篇 |
1983年 | 23篇 |
1982年 | 29篇 |
1981年 | 8篇 |
1980年 | 14篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1977年 | 4篇 |
1975年 | 4篇 |
1974年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
J.P. Ramos T. Stora A.M.R. Senos P. Bowen 《Journal of the European Ceramic Society》2018,38(15):4882-4891
In the ISOL (Isotope Separator OnLine) method a target at high temperatures (up to 2300?°C), is bombarded with high energy protons in order to produce isotopes through nuclear reactions which are simultaneously extracted from the target, ionized and delivered to physics experiments. Due to the enhanced isotope release properties of nanosized porous materials, titanium carbide-carbon porous nanocomposites have been developed at CERN and tested up to 1500?°C. In the interest of the ISOL application, in this study we extended the range of temperatures up to 1800?°C, to test the sintering hindering capabilities of different carbon allotropes. Carbon black was the most effective with the smallest TiC crystallite size: <80?nm at 1800?°C. Additionally, using thermodynamic modelling, ex-situ X-ray powder diffraction and in-situ gas phase analysis, we show that there are interesting additional phase and lattice parameter changes due to the ZrO2 impurities from the attrition milling. 相似文献
73.
Hierarchical micro-nanostructured albite-based glass-ceramic for high dielectric strength insulators
V. Fuertes M.J. Cabrera J. Seores D. Muñoz J.F. Fernández E. Enríquez 《Journal of the European Ceramic Society》2018,38(7):2759-2766
A novel glass-ceramic material based on albite type Na-rich feldspar has been synthesized by conventional ceramic process. High crystallinity, >94%?Vol.% is obtained by fast sintering which allows energy saving processing. Albite is the main crystalline phase and tetragonal SiO2 is a secondary phase. Electrical properties were examined by complex impedance, DC measurements, and dielectric breakdown test. Dielectric characterization shows a non-Debye type dielectric behavior with low dielectric constant, 4.6 at 1?MHz, low dielectric losses, (~10?3 at 1?MHz, and a large dielectric strength, ~60?kV/mm), that it is the largest value reported in ceramic insulators. Those dielectric properties are attained by the low glassy phase content in the samples and their unique micro-nanostructure. All these properties make this novel material a very promising candidate in the market of ceramic electrical insulator, highlighting for high-voltage applications. 相似文献
74.
Morphology,mechanical properties and electromagnetic shielding effectiveness of poly(styrene‐b‐ethylene‐ran‐butylene‐b‐styrene)/carbon nanotube nanocomposites: effects of maleic anhydride,carbon nanotube loading and processing method 下载免费PDF全文
Nanocomposites based on poly(styrene‐b‐ethylene‐ran‐butylene‐b‐styrene) (SEBS) and carbon nanotubes (CNTs) (SEBS/CNT) as well as SEBS grafted with maleic anhydride (SEBS‐MA)/CNT were successfully prepared for electromagnetic shielding applications. Both SEBS/CNT and SEBS‐MA/CNT nanocomposites were prepared by melt compounding and were post‐processed using two different techniques: tape extrusion and compression moulding. The different nanocomposites were characterized by Raman spectroscopy and rheological analysis. Their mechanical properties, electrical properties (10-2–105 Hz) and electromagnetic shielding effectiveness (8.2–12.4 GHz) were also evaluated. The results showed that the CNT loading amount, the presence of MA in the matrix and the shaping technique used strongly influence the final morphologies and properties of the nanocomposites. Whilst the nanocomposite containing 8 wt% CNTs prepared by compression moulding presented the highest electromagnetic shielding effectiveness (with a value of 56.73 dB, which corresponds to an attenuation of 99.9996% of the incident radiation), the nanocomposite containing 5 wt% CNTs prepared by tape extrusion presented the best balance between electromagnetic and mechanical properties and was a good candidate to be used as an efficient flexible electromagnetic interference shielding material. © 2018 Society of Chemical Industry 相似文献
75.
76.
Herein, electrically conductive natural and synthetic yarns through electrophoretic deposition (EPD) technique were fabricated. A parametric study on the conductivity enhancement of the yarns is carried out by Taguchi method. Using this method, the desirable conditions are determined by studying the effects of important parameters on the electrical conductivity of the yarns in the EPD coating process. Based on the L18 design of experiments table, the preferred combination of factors to obtain the highest electrical conductivity of the yarns is found by Taguchi analysis. In addition, the Pareto ANOVA analysis is conducted to identify the major contributing factors on the electrical conductivity of the yarns. Characterisation techniques, such as scanning electron microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR) in attenuated total reflectance (ATR) mode, and thermogravimetric analysis (TGA) are utilised for better understanding the microstructure and physical properties. When powered by only 3 V, the maximum temperature of a Joule heated conductive sample based on natural fibre yarns reached 102°C in less than 25 s. 相似文献
77.
78.
高压水射流割缝是一项能够有效提高煤层透气性的卸压增透技术,卸压增透效果与高压水射流割缝参数密切相关.为了研究适合长平矿的高压水射流割缝参数,本文设计并施工了水射流割缝压力、割缝间距、割缝时间的试验钻孔,通过现场试验数据分析,研究了割缝压力、时间、间距与割缝效率以及瓦斯抽采效果之间的关系.研究结果表明:适合于长平矿的割缝压力为70 MPa^80 MPa较为合理,割缝时间4 min左右,割缝间距为1 m^1.5 m为宜. 相似文献
79.
Because of the introduction of new processing parameters in water-assisted injection molding (WAIM), processes control has become more difficult. First, design of experiment (DOE) was carried out by using optimized Latin hypercubes (Opt LHS). On the basis of this, computational fluid dynamics (CFD) method was used to simulate and calculate hollowed core ratios and wall thickness differences of cooling water pipe at different positions. Then inverse radial basis function (RBF) neural network model reflecting the fitting relationship between processing parameters and molding quality was established, and accuracy of the model was detected by cross validation. Finally, expected molding quality was applied to predict processing parameters, and the obtained molding quality under the predicted processing parameters was verified by computer aided engineering (CAE) simulation and experimental methods. The results showed that mean relative precisions of processing parameters such as melt temperature, delay time, short shot size, water pressure, and mold temperature for inverse RBF model were 98.6%, 93.6%, 98.5%, 93.9%, and 97.9%, respectively, which met the accuracy requirements. Furthermore, compared with expected values of hollowed core ratios and wall thickness differences, the average errors of CAE and experiment were 2.3% and 4.9%, respectively. 相似文献
80.
针对光伏以低惯量、弱阻尼的特征大规模接入电网,给电网稳定性带来不利影响的问题,基于功频下垂控制的光伏并网发电系统,借鉴经典电气转矩分析法,从物理机制层面上分析影响系统惯量、阻尼以及同步能力的作用规律。研究结果表明对于控制参数的影响规律而言,惯量特性主要受功率环的比例系数Kp影响,且随Kp的增大而增强;阻尼特性受频率下垂系数Dp影响比较明显,且随Dp的增大而减弱;同步特性只受功率环的比例积分系数Ki影响,且随Ki的增大而增强。通过仿真验证了理论分析的正确性。 相似文献