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   229497篇
  免费   4087篇
  国内免费   1300篇
电工技术   4249篇
综合类   198篇
化学工业   37214篇
金属工艺   10756篇
机械仪表   6717篇
建筑科学   5972篇
矿业工程   1128篇
能源动力   6168篇
轻工业   20593篇
水利工程   2143篇
石油天然气   4277篇
武器工业   2篇
无线电   24352篇
一般工业技术   46768篇
冶金工业   40106篇
原子能技术   5082篇
自动化技术   19159篇
  2021年   1973篇
  2019年   1870篇
  2018年   3246篇
  2017年   3252篇
  2016年   3501篇
  2015年   2589篇
  2014年   4098篇
  2013年   11230篇
  2012年   6521篇
  2011年   8882篇
  2010年   7134篇
  2009年   8151篇
  2008年   8080篇
  2007年   8157篇
  2006年   6790篇
  2005年   6159篇
  2004年   5855篇
  2003年   5454篇
  2002年   5436篇
  2001年   5429篇
  2000年   5029篇
  1999年   5131篇
  1998年   12456篇
  1997年   9076篇
  1996年   7134篇
  1995年   5330篇
  1994年   4417篇
  1993年   4380篇
  1992年   3222篇
  1991年   3132篇
  1990年   2971篇
  1989年   2942篇
  1988年   2756篇
  1987年   2534篇
  1986年   2437篇
  1985年   2827篇
  1984年   2603篇
  1983年   2382篇
  1982年   2237篇
  1981年   2333篇
  1980年   2197篇
  1979年   2181篇
  1978年   2118篇
  1977年   2548篇
  1976年   3330篇
  1975年   1912篇
  1974年   1870篇
  1973年   1932篇
  1972年   1610篇
  1971年   1508篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
3.
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 - 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   
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.
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   
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.
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.
Journal of Communications Technology and Electronics - A new design of wavelets based on the convolution of a compactly supported function with a rectangular pulse is proposed and theoretically...  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