首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   129875篇
  免费   2541篇
  国内免费   911篇
电工技术   2267篇
综合类   744篇
化学工业   18821篇
金属工艺   4374篇
机械仪表   4178篇
建筑科学   2871篇
矿业工程   978篇
能源动力   2718篇
轻工业   10330篇
水利工程   1561篇
石油天然气   2435篇
武器工业   45篇
无线电   9822篇
一般工业技术   22484篇
冶金工业   33750篇
原子能技术   2886篇
自动化技术   13063篇
  2022年   980篇
  2021年   1508篇
  2020年   1076篇
  2019年   1246篇
  2018年   2920篇
  2017年   3157篇
  2016年   3466篇
  2015年   2162篇
  2014年   2486篇
  2013年   4779篇
  2012年   5140篇
  2011年   6092篇
  2010年   3584篇
  2009年   3961篇
  2008年   3680篇
  2007年   3606篇
  2006年   3109篇
  2005年   6529篇
  2004年   5227篇
  2003年   4482篇
  2002年   2840篇
  2001年   2613篇
  2000年   2096篇
  1999年   2267篇
  1998年   9655篇
  1997年   6372篇
  1996年   4440篇
  1995年   2970篇
  1994年   2383篇
  1993年   2465篇
  1992年   1268篇
  1991年   1368篇
  1990年   1386篇
  1989年   1334篇
  1988年   1253篇
  1987年   1102篇
  1986年   1093篇
  1985年   1115篇
  1984年   859篇
  1983年   857篇
  1982年   812篇
  1981年   869篇
  1980年   854篇
  1979年   712篇
  1978年   725篇
  1977年   1375篇
  1976年   2231篇
  1975年   687篇
  1974年   596篇
  1973年   595篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
Multimedia Tools and Applications - Mammograms are the images used by radiologists to diagnose breast cancer. Breast cancer is one of the most common cancers in women. The early detection of breast...  相似文献   
4.
Combustion, Explosion, and Shock Waves - Results of a numerical study of mixing, ignition, and combustion of a cold hydrogen jet propagating along the lower wall of a channel parallel to a...  相似文献   
5.
Journal of Communications Technology and Electronics - In recent years, there has been a rapid improvement in photonics products due to the use of multilayer heterostructures grown on the basis of...  相似文献   
6.
Theoretical Foundations of Chemical Engineering - Calcium formate is widely used in construction, tanning, and textile manufacture and as an E238 biological additive in cosmetology and the food...  相似文献   
7.
Analog Integrated Circuits and Signal Processing - This paper presents the complete design of a phase locked loop-based clock synthesizer for reconfigurable analog-to-digital converters. The...  相似文献   
8.
Glass and Ceramics - An analysis of the specific mechanisms of the influence of the state of the grain structure on the thermoelectric properties (electrical resistivity and total thermal...  相似文献   
9.
This work presents the dielectric properties of YNbO4 (YNO)–TiO2 composites in the microwave range. X-ray diffraction analysis demonstrates that the addition of TiO2 to YNO results in the formation of a Y(Nb0.5Ti0.5)2O6 phase. In the microwave range, the values of permittivity and dielectric loss did not present major changes with the increment of TiO2. Moreover, the addition of TiO2 results in an improvement in the thermal stability of YNO, with YNO63 demonstrating a resonant frequency of ?8.96 ppm.°C?1. We utilised numerical simulations to evaluate the behaviour of these materials as dielectric resonator antennae and it is found that they exhibit a reflection coefficient below ?10 dB at the resonant frequency, with a realised gain of 4.94 – 5.76 dBi, a bandwidth of 665–1050 MHz and a radiation efficiency above 84%. Our results indicate that YNO–TiO2 composites are interesting candidates for microwave operating devices.  相似文献   
10.

Both water balance (WB) and rating curve (RC) are methods for estimating streamflow. The first is mostly used to estimate reservoir outflows, while the second is usually adopted in hydrometeorological network streamflow gauges. While WB uses hourly collected data, the RC estimates streamflow using current water level and extrapolation techniques. The objective of this study was to analyze variations in the reservoir’s hourly outflow at Queimado Hydroelectric Power Plant (HPP Queimado) and to propose a method to evaluate whether the estimate of the daily outflows, obtained by the WB method, is similar to the flow values obtained at a conventional station. The logistic regression (LR) model was used because it is a method that adopts binary, categorically dependent variables to identify the event of interest. The results showed that the values of streamflow, obtained from an average of two daily readings, were a good representation of the flows in the region. The LR was able to identify atypical data, especially in the rainy season. This means that data consistency analysis can be faster and safer, when adequately employed and considering the proposed conditions, contributing to both management policies and the management of water resources.

  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号