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   463681篇
  免费   6620篇
  国内免费   2074篇
电工技术   8016篇
综合类   1256篇
化学工业   68433篇
金属工艺   18248篇
机械仪表   13448篇
建筑科学   11227篇
矿业工程   2660篇
能源动力   11390篇
轻工业   38791篇
水利工程   4908篇
石油天然气   8386篇
武器工业   49篇
无线电   51271篇
一般工业技术   87395篇
冶金工业   95258篇
原子能技术   10928篇
自动化技术   40711篇
  2021年   3382篇
  2019年   3221篇
  2018年   5806篇
  2017年   6091篇
  2016年   6788篇
  2015年   4653篇
  2014年   7070篇
  2013年   19121篇
  2012年   12806篇
  2011年   17296篇
  2010年   12459篇
  2009年   14487篇
  2008年   14559篇
  2007年   14543篇
  2006年   12515篇
  2005年   14221篇
  2004年   13431篇
  2003年   12410篇
  2002年   11015篇
  2001年   10965篇
  2000年   9959篇
  1999年   10567篇
  1998年   29317篇
  1997年   20451篇
  1996年   15488篇
  1995年   11503篇
  1994年   9822篇
  1993年   9915篇
  1992年   6758篇
  1991年   6580篇
  1990年   6339篇
  1989年   6329篇
  1988年   5987篇
  1987年   5346篇
  1986年   5296篇
  1985年   5911篇
  1984年   5358篇
  1983年   4999篇
  1982年   4701篇
  1981年   4877篇
  1980年   4758篇
  1979年   4436篇
  1978年   4463篇
  1977年   5459篇
  1976年   7639篇
  1975年   3830篇
  1974年   3734篇
  1973年   3822篇
  1972年   3221篇
  1971年   2886篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Wireless Personal Communications - Chronic kidney disease (CKD) is a gradual loss of kidney function over the period of time and it is irrevocable once functionality reaches the critical state....  相似文献   
2.
3.
Food Science and Biotechnology - A rich source of nutrients, figs have a number of clinically validated benefits. This study aimed to evaluate the in vitro simulated gastrointestinal digestion, and...  相似文献   
4.
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   
5.
Multimedia Tools and Applications - In this work, a new fuzzy logic-based algorithm is proposed for the enhancement of low light color images. A generalization of a fuzzy set known as an...  相似文献   
6.
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   
7.

We discuss the temperature dependence of a common low temperature local thermometer, a tunnel junction between a superconductor and a normal metal (NIS junction). Towards the lowest temperatures its characteristics tend to saturate, which is usually attributed to selfheating effects. In this technical note, we reanalyze this saturation and show that the temperature independent subgap current of the junction alone explains in some cases the low temperature behavior quantitatively.

  相似文献   
8.
Journal of Chemical Ecology - Biocontrol agents such as parasitic wasps use long-range volatiles and host-associated cues from lower trophic levels to find their hosts. However, this chemical...  相似文献   
9.
To investigate the evolution of the structural and enhanced magnetic properties of GdMnO3 systems induced by the substitution of Mn with Cr, polycrystalline GdMn1-xCrxO3 samples were synthesized via solid-state reactions. XRD characterization shows that all GdMn1-xCrxO3 compounds with single-phase structures crystallize well and that Cr3+ ions entering the lattice sites of GdMnO3 induce structural distortion. SEM results indicate that the grain size of the synthesized samples (a few microns) decreases as the Cr substitution concentration increases. Positron annihilation lifetime spectroscopy reveals that vacancy-type defects occur in GdMn1-xCrxO3 ceramics and that the vacancy size and concentration clearly change with the Cr content. The temperature and field dependence of the magnetization curves show that Cr substitution significantly influences the magnetic ordering of the gadolinium sublattice, improving the weak ferromagnetic transition temperature and magnetization of GdMn1-xCrxO3. The enhanced magnetization of GdMn1-xCrxO3 is closely related to the vacancy defect concentration.  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