全文获取类型
收费全文 | 47507篇 |
免费 | 5195篇 |
国内免费 | 2583篇 |
专业分类
电工技术 | 3689篇 |
技术理论 | 2篇 |
综合类 | 3732篇 |
化学工业 | 7490篇 |
金属工艺 | 2735篇 |
机械仪表 | 3013篇 |
建筑科学 | 3843篇 |
矿业工程 | 1448篇 |
能源动力 | 1296篇 |
轻工业 | 4014篇 |
水利工程 | 969篇 |
石油天然气 | 2536篇 |
武器工业 | 535篇 |
无线电 | 5742篇 |
一般工业技术 | 5011篇 |
冶金工业 | 1931篇 |
原子能技术 | 811篇 |
自动化技术 | 6488篇 |
出版年
2024年 | 325篇 |
2023年 | 1038篇 |
2022年 | 2160篇 |
2021年 | 2765篇 |
2020年 | 2073篇 |
2019年 | 1626篇 |
2018年 | 1744篇 |
2017年 | 1858篇 |
2016年 | 1640篇 |
2015年 | 2169篇 |
2014年 | 2641篇 |
2013年 | 2881篇 |
2012年 | 3238篇 |
2011年 | 3333篇 |
2010年 | 2958篇 |
2009年 | 2796篇 |
2008年 | 2767篇 |
2007年 | 2548篇 |
2006年 | 2489篇 |
2005年 | 2130篇 |
2004年 | 1413篇 |
2003年 | 1300篇 |
2002年 | 1370篇 |
2001年 | 1240篇 |
2000年 | 989篇 |
1999年 | 827篇 |
1998年 | 499篇 |
1997年 | 495篇 |
1996年 | 446篇 |
1995年 | 306篇 |
1994年 | 291篇 |
1993年 | 214篇 |
1992年 | 196篇 |
1991年 | 114篇 |
1990年 | 82篇 |
1989年 | 81篇 |
1988年 | 68篇 |
1987年 | 44篇 |
1986年 | 30篇 |
1985年 | 17篇 |
1984年 | 18篇 |
1983年 | 15篇 |
1982年 | 14篇 |
1981年 | 9篇 |
1980年 | 12篇 |
1979年 | 5篇 |
1959年 | 8篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
This paper shows that the mechanical and thermal properties of EPR cable dielectrics are very stable with temperature. Commercially available EPR and TRXLPE cable dielectrics typically have about the same thermal conductivity, although the thermal conductivity of TRXLPE above the melting point of the crystallites drops below that of the EPR dielectrics. The mechanical properties of EPR cable dielectrics are much more stable with temperature than those of the TRXLPE, as EPR polymer is essentially amorphous so that EPR cable dielectrics do not suffer from the very large thermal expansion of TRXLPE as its crystallites melt. 相似文献
3.
精选了一系列有机和无机化合物为成核剂,使用砂浴法和热台法制备了一系列不同β晶含量的等规聚丙烯,发现最有效的β成核剂是溶靛素灰 IBL 和溶蒽素金黄 IGK,首次表明β成核剂具有排列紧密的稠球结构特征,且含有硫原子。 相似文献
4.
5.
Numerous power utilities have installed advanced distributed temperature sensing (DTS) systems to measure the temperature of underground cables. This paper presents a general procedure for real-time assessment of underground cable ratings based on DTS. After the identification and location of hot spots on a cable, the cable installation data, load, and DTS-recorded temperature over a period of time are used to estimate soil thermal parameters and assess cable ratings under normal and overloading conditions. In order to accurately estimate soil thermal parameters, a combined technique of the finite-element method and gradient-based optimization is used. The technique was validated in the laboratory and applied to a rating assessment of a 230-kV/500-MVA cable circuit. The assessed continuous and emergency ratings are helpful in improving the operation of this circuit. 相似文献
6.
二次型时频分析技术的开发与应用 总被引:1,自引:1,他引:0
基于二次型的时频分析是高分辨率时频分析技术的有效方法之一,该项技术能够有效反映时变信号的频谱特性,具有分辨率高、能量集中和跟踪瞬时频率的特点。从时变信号的特点出发,阐述了二次型时频分析技术的基本方法原理,采用正演模型分析验证了该方法的有效性,并在实际地震资料中应用于识别物源方向、划分沉积相带、预测储层结构以及相对厚度等诸多方面,均取得了较好的效果。 相似文献
7.
The stability of five major phenolics, namely (−)-epicatechin (EC), procyanidin B2 (PC-B2), chlorogenic acid (ChA), hyperoside (HP) and isoquercitrin (IQ), in hawthorn fruits and a canned hawthorn drink were evaluated during 6 months of storage in the dark at three different temperatures (4, 23 and 40 °C). HPLC with a diode-array detector was used to determine the contents of the individual compounds. The results showed that the studied phenolics in the hawthorn fruits and the drink were both stable at 4 °C and relatively unstable at 23 and 40 °C with varied extents of degradation. At room temperature (23 °C), marked degradations of EC and PC-B2 were observed in both the fruits and the drink with around 50% and 30% decrease after a 6-month storage, respectively. A more significant decrease of the phenolics was observed at 40 °C, especially for EC and PC-B2, which were almost completely degraded after a 6-month storage. HP, IQ and ChA were relatively stable at 23 °C, but unstable at 40 °C. Therefore, low-temperature storage is recommended for maintaining the quality and efficacy of hawthorn fruits and its preparations. 相似文献
8.
主要介绍了热电厂近几年来在技术管理方面取得的主要工作经验,以及围绕生产经营开展科技创新所取得的成绩,并且针对当前形势,进一步提出了热电厂今后一个时期科技工作的指导思想、任务目标和措施。 相似文献
9.
10.
The Uniform Geometrical Theory of Diffraction (UTD) has been successfully used in pattern analysis of airborne dipole antenna on the A-5 fighter in high-frequency region. In the analysis, several canonical problems are investigated first, then the complicated problem is calculated with compiling these canonical problems. The numerical results are compared with the experimental data, and good agreement has been seen. The effectiveness and practicality of the present analysis are thus verified. 相似文献