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   271470篇
  免费   4677篇
  国内免费   871篇
电工技术   5194篇
综合类   252篇
化学工业   39653篇
金属工艺   10090篇
机械仪表   7965篇
建筑科学   6988篇
矿业工程   1005篇
能源动力   7584篇
轻工业   23524篇
水利工程   2352篇
石油天然气   3247篇
武器工业   15篇
无线电   35705篇
一般工业技术   55690篇
冶金工业   49158篇
原子能技术   5274篇
自动化技术   23322篇
  2021年   2583篇
  2020年   1953篇
  2019年   2285篇
  2018年   4055篇
  2017年   4081篇
  2016年   4276篇
  2015年   2937篇
  2014年   4837篇
  2013年   13196篇
  2012年   7294篇
  2011年   9825篇
  2010年   7996篇
  2009年   8891篇
  2008年   9532篇
  2007年   9351篇
  2006年   8143篇
  2005年   7154篇
  2004年   6828篇
  2003年   7068篇
  2002年   6548篇
  2001年   6905篇
  2000年   6306篇
  1999年   6676篇
  1998年   16736篇
  1997年   11678篇
  1996年   9011篇
  1995年   6739篇
  1994年   6027篇
  1993年   5932篇
  1992年   4201篇
  1991年   4088篇
  1990年   3913篇
  1989年   3670篇
  1988年   3578篇
  1987年   3034篇
  1986年   2970篇
  1985年   3350篇
  1984年   3064篇
  1983年   2894篇
  1982年   2705篇
  1981年   2613篇
  1980年   2527篇
  1979年   2358篇
  1978年   2176篇
  1977年   2634篇
  1976年   3580篇
  1975年   1809篇
  1974年   1760篇
  1973年   1702篇
  1972年   1472篇
排序方式: 共有10000条查询结果,搜索用时 46 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.
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   
5.
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   
6.
Multimedia Tools and Applications - Endometriosis is a common gynecologic condition typically treated via laparoscopic surgery. Its visual versatility makes it hard to identify for non-specialized...  相似文献   
7.
Forschung im Ingenieurwesen - Das Arbeitsmittel in Wärmepumpen unterliegt einer Vielzahl von Anforderungen, welche für einen effizienten und sicheren Betrieb eingehalten werden...  相似文献   
8.
A set of novel hydrazone derivatives were synthesized and analyzed for their biological activities. The compounds were tested for their inhibitory effect on the phosphorylating activity of the protein kinase CK2, and their antioxidant activity was also determined in three commonly used assays. The hydrazones were evaluated for their radical scavenging against the DPPH, ABTS and peroxyl radicals. Several compounds have been identified as good antioxidants as well as potent protein kinase CK2 inhibitors. Most hydrazones containing a 4-N(CH3)2 residue or perfluorinated phenyl rings showed high activity in the radical-scavenging assays and possess nanomolar IC50 values in the kinase assays.  相似文献   
9.
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   
10.
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   
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