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   542303篇
  免费   6750篇
  国内免费   1653篇
电工技术   9266篇
综合类   2749篇
化学工业   81444篇
金属工艺   22178篇
机械仪表   16909篇
建筑科学   13037篇
矿业工程   2710篇
能源动力   12856篇
轻工业   45726篇
水利工程   5599篇
石油天然气   8063篇
武器工业   47篇
无线电   64087篇
一般工业技术   103516篇
冶金工业   91500篇
原子能技术   10341篇
自动化技术   60678篇
  2021年   3951篇
  2019年   3672篇
  2018年   19984篇
  2017年   18878篇
  2016年   16083篇
  2015年   4748篇
  2014年   7510篇
  2013年   20745篇
  2012年   14456篇
  2011年   24707篇
  2010年   20427篇
  2009年   19432篇
  2008年   21359篇
  2007年   22287篇
  2006年   13461篇
  2005年   12830篇
  2004年   12363篇
  2003年   12453篇
  2002年   11502篇
  2001年   11388篇
  2000年   10758篇
  1999年   10978篇
  1998年   27433篇
  1997年   19227篇
  1996年   14826篇
  1995年   11291篇
  1994年   10052篇
  1993年   9940篇
  1992年   7327篇
  1991年   6979篇
  1990年   7011篇
  1989年   6694篇
  1988年   6407篇
  1987年   5588篇
  1986年   5553篇
  1985年   6211篇
  1984年   5809篇
  1983年   5431篇
  1982年   5104篇
  1981年   5078篇
  1980年   4913篇
  1979年   4694篇
  1978年   4500篇
  1977年   5247篇
  1976年   7026篇
  1975年   3870篇
  1974年   3748篇
  1973年   3807篇
  1972年   3244篇
  1971年   2885篇
排序方式: 共有10000条查询结果,搜索用时 593 毫秒
1.
2.
3.
4.
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   
5.
The effect of microwave roasting parameters (300, 450 and 600 W; 5, 10 and 15 min) on acrylamide content in sorghum grain was determined using High Pressure Liquid Chromatography (HPLC)-photo diode array (PDA) detector coupled with C-18 column. Samples roasted at 300 and 450 W did not possess acrylamide, whereas 600 W (15 min) favoured formation of 2740.19 µg/kg of acrylamide, levels far exceeding the defined European Union (EU) limits. The chronic daily intake (CDI) for acrylamide through consumption of such grain flour was 3.25–9.5-fold higher to Joint FAO/WHO Expert Committee on Food Additives (JECFA) defined high exposure limits. The margin of exposure (MOE) values ranged from 4.3 to 12.76 and from 11.07 to 32.27 for neoplastic and neurological effects, respectively, demonstrating high exposure and serious health concerns associated with dietary intake of this toxicant. This study assesses the risk for the Indian population and highlights the importance of optimising process parameters for food product to minimise such exposure risks.  相似文献   
6.
In this study, dilute chemical bath deposition technique has been used to deposit CdZnS thin films on soda-lime glass substrates. The structural, morphological, optoelectronic properties of as-grown films have been investigated as a function of different Zn2+ precursor concentrations. The X-ray diffractogram of CdS thin-film reveals a peak corresponding to (002) plane with wurtzite structure, and the peak shift has been observed with the increase of the Zn2+ concentration upon formation of CdZnS thin film. From morphological studies, it has been revealed that the diluted chemical bath deposition technique provides homogeneous distribution of film on the substrate even at a lower concentration of Zn2+. Optical characterization has shown that the transparency of the film is influenced by Zn2+ concentration and when the Zn2+ concentration is varied from 0 M to 0.0256 M, bandgap values of resulting films range from 2.42 eV to 3.90 eV while. Furthermore, electrical properties have shown that with increasing zinc concentration the resistivity of the film increases. Finally, numerical simulation validates and suggests that CdZnS buffer layer with composition of 0.0032 M Zn2+ concentration would be a promising candidate in CIGS solar cell.  相似文献   
7.
This study presents the development and characterization of PVDF-conjugated polymer nanofiber-based systems. Five different conducting polymers (CPs) were synthesized successfully and used to create the nanofiber systems. The CPs used are polyaniline (PANI), polypyrrole (PPY), polyindole (PIN), polyanthranilic acid (PANA), and polycarbazole (PCZ). Nanofiber systems were produced utilizing the Forcespinning® technique. The nanofiber systems were developed by mechanical stretching. No electrical field or post-process poling was used in the nanofiber systems. The morphology, structure, electrochemical and piezoelectric performance was characterized. All of the nanofiber PVDF/CP systems displayed higher piezoelectric performance than the fine fiber PVDF systems. The PVDF/PPY nanofiber system displays the highest piezoelectric performance of 15.56 V. The piezoelectric performance of the PVDF/CP nanofiber systems favors potential for an attractive source of energy where highly flexible membranes could be used in power actuators, sensors and portable, and wireless devices to mention some.  相似文献   
8.
Wireless Personal Communications - Despite its various benefits, the Mobile Ad-hoc Network (MANET) has a number of obstacles due to its mobility, unstable topology, energy efficiency, and other...  相似文献   
9.
Semiconductors - Abstract—In our work, we carry out a structural-spectroscopic study of AlGaN/GaN epitaxial layers grown by molecular-beam epitaxy with nitrogen-plasma activation on a hybrid...  相似文献   
10.
Journal of Communications Technology and Electronics - A statistical study of the effectiveness of the non-threshold search procedure for a noise-like phase-shift keyed signal by the delay time is...  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