全文获取类型
收费全文 | 5323篇 |
免费 | 447篇 |
国内免费 | 317篇 |
专业分类
电工技术 | 525篇 |
技术理论 | 1篇 |
综合类 | 461篇 |
化学工业 | 680篇 |
金属工艺 | 213篇 |
机械仪表 | 178篇 |
建筑科学 | 371篇 |
矿业工程 | 102篇 |
能源动力 | 193篇 |
轻工业 | 250篇 |
水利工程 | 93篇 |
石油天然气 | 248篇 |
武器工业 | 372篇 |
无线电 | 717篇 |
一般工业技术 | 604篇 |
冶金工业 | 379篇 |
原子能技术 | 260篇 |
自动化技术 | 440篇 |
出版年
2024年 | 35篇 |
2023年 | 104篇 |
2022年 | 144篇 |
2021年 | 189篇 |
2020年 | 167篇 |
2019年 | 168篇 |
2018年 | 113篇 |
2017年 | 142篇 |
2016年 | 180篇 |
2015年 | 164篇 |
2014年 | 323篇 |
2013年 | 376篇 |
2012年 | 359篇 |
2011年 | 452篇 |
2010年 | 348篇 |
2009年 | 315篇 |
2008年 | 283篇 |
2007年 | 382篇 |
2006年 | 348篇 |
2005年 | 255篇 |
2004年 | 177篇 |
2003年 | 164篇 |
2002年 | 140篇 |
2001年 | 110篇 |
2000年 | 96篇 |
1999年 | 81篇 |
1998年 | 66篇 |
1997年 | 44篇 |
1996年 | 59篇 |
1995年 | 54篇 |
1994年 | 36篇 |
1993年 | 27篇 |
1992年 | 32篇 |
1991年 | 23篇 |
1990年 | 24篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1966年 | 4篇 |
1965年 | 7篇 |
1964年 | 3篇 |
1963年 | 6篇 |
1960年 | 5篇 |
1959年 | 7篇 |
1958年 | 4篇 |
1955年 | 3篇 |
1954年 | 5篇 |
排序方式: 共有6087条查询结果,搜索用时 15 毫秒
1.
In this article, the silver-plated polyamide fabrics (SPPAFs) with high electroconductibility and shielding effectiveness were fabricated by using in situ reduction of polydopamine and chemical silvering. The effects of SPPAFs dopamine (C8H11O2N) and silver nitrate (AgNO3) concentration on surface resistivity and electromagnetic interference shielding effectiveness were studied. The results showed that the surface resistivity of SPPAFs can reach a minimum value of 0.06 ± 0.014 Ω cm−1, when C8H11O2N concentration is 4 g L−1 and the AgNO3 concentration is 120 g L−1. The shielding effectiveness of SPPAFs in the wide frequency range of 10–3000 MHz increases with the increase in the concentration of AgNO3, and increases first and stabilizes afterward with increasing C8H11O2N concentration. When the concentration of C8H11O2N and AgNO3 is 3 and 120 g L−1, respectively, mean shielding effectiveness values in the low-, medium-, and high-frequency bands are 71.3, 73.8, and 76.1 dB, respectively. Moreover, the mean shielding effectiveness values is 83.79 dB in the frequency range of 1.2–2.3 GHz. The dominant shielding mechanism of SPPAFs is the reflected electromagnetic waves and the absorption shielding effectiveness is less than 2 dB. The average electromagnetic shielding values of SPPAFs are above 67 dB after 16 weeks of storage, when C8H11O2N concentration is 4 g L−1 and the AgNO3 concentration is 80 and 100 g L−1. The prepared SPPAFs show promising applications in military textiles and smart wearable clothing. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48227. 相似文献
2.
3.
The present study was aimed to utilize low‐cost alumina (Al2O3) nanoparticles for improving the heat transfer behavior in an intercooler of two‐stage air compressor. Experimental investigation was carried out with three different volume concentrations of 0.5%, 0.75%, and 1.0% Al2O3/water nanofluids to assess the performance of the intercooler, that is, counterflow heat exchanger at different loads. Thermal properties such as thermal conductivity and overall heat transfer coefficient of nanofluid increased substantially with increasing concentration of Al2O3 nanoparticles. Specific heat capacity of nanofluids were lower than base water. The intercooler performance parameters such as effectiveness and efficiency improved appreciably with the employment of nanofluid. The efficiency increased by about 6.1% with maximum concentration of nanofluid, that is, 1% at 3‐bar compressor load. It is concluded from the study that high concentration of Al2O3 nanoparticles dispersion in water would offer better heat transfer performance of the intercooler. 相似文献
4.
5.
微波体声波延迟线的电磁屏蔽 总被引:1,自引:1,他引:0
本文分析了微波体声波延迟线多层介质的电磁屏蔽效应,结果表明,全屏蔽方式可以有效地解决微波延迟线研制中的直通抑制问题。实验结果证实了理论分析。 相似文献
6.
7.
屏蔽暂堵技术在青西地区的应用 总被引:3,自引:0,他引:3
对玉门油田青西地区裂缝性储层的保护方法 ,最有效的技术手段就是利用屏蔽暂堵技术。根据该地区储层岩性不同 ,分别选用聚磺、金属离子、阳离子钻井液体系 ,在原浆的基础上加入EP - 2、LF - 1和硅油消泡剂 ,配制成屏蔽暂堵钻井液体系。通过室内试验 :屏蔽暂堵钻井液体系API失水小于 5ml,HTHP失水小于 13ml,岩心渗透率恢复值大于 70 % ,起到了良好的屏蔽暂堵效果。经完井试油发现 ,储层污染明显减小 ,产量与邻井相比有大幅度提高 相似文献
8.
M. Polák M. Majoro F. Hanic J. Pitel M. Kedrová P. Kottman J. Talapa L. Vencel 《Journal of Superconductivity》1989,2(2):219-233
A method for contactless measurement of the shielding critical current density and its dependence on the external magnetic field is described and analyzed. The obtained values are compared with those measured resistively on two different samples. It is shown that the shielding critical current densityJ
cs
and the intergranular transport current densityJ
cr
are identical if the measurement conditions are similar. A degradation ofJ
cs
measured in the external field with AC ripple has been observed. 相似文献
9.
The authors report a meta-analysis of age differences in everyday problem-solving/decision-making effectiveness (EPSE). Effect sizes were calculated to reflect 3 age group comparisons: old versus young, young versus middle-aged, and middle-aged versus old. Findings from the meta-analysis of 28 separate studies with an aggregate of 4,482 participants do not support theories of preserved EPSE in late adulthood. Although significant age differences of moderate magnitude persisted across methodological and theoretical domains, rating criteria (experimenter vs. participant) emerged as a significant moderator of the effect magnitude and direction. In addition, EPSE in older adults was bolstered when problem content was interpersonal and when samples were highly educated. Finally, the current results support the conceptual integration of findings from the everyday problem-solving and everyday decision-making literatures. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
10.
激光武器对抗效能指标体系研究 总被引:1,自引:0,他引:1
武器系统的效能是规划、研制、配置和部署武器系统的基本依据,是评价武器系统优劣最重要的综合性指标,建立正确的效能指标体系是进行效能分析与评价的前提。在详细研究了激光武器对抗机理、效能指标选用原则的基础上,构建了相对完整的激光武器对抗效能指标体系结构,并提出了在不同作战任务下量度激光武器对抗能力的效能定义。 相似文献