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   218468篇
  免费   2496篇
  国内免费   601篇
电工技术   3688篇
综合类   158篇
化学工业   33637篇
金属工艺   10527篇
机械仪表   7298篇
建筑科学   4456篇
矿业工程   2183篇
能源动力   4864篇
轻工业   14393篇
水利工程   3019篇
石油天然气   7753篇
武器工业   22篇
无线电   22789篇
一般工业技术   46921篇
冶金工业   37383篇
原子能技术   6774篇
自动化技术   15700篇
  2021年   2231篇
  2019年   2159篇
  2018年   3878篇
  2017年   3909篇
  2016年   4232篇
  2015年   2375篇
  2014年   4042篇
  2013年   9316篇
  2012年   6118篇
  2011年   7763篇
  2010年   6289篇
  2009年   6911篇
  2008年   7084篇
  2007年   6959篇
  2006年   5945篇
  2005年   5496篇
  2004年   4936篇
  2003年   4854篇
  2002年   4632篇
  2001年   4750篇
  2000年   4454篇
  1999年   4497篇
  1998年   11129篇
  1997年   7781篇
  1996年   5950篇
  1995年   4473篇
  1994年   3872篇
  1993年   4121篇
  1992年   3138篇
  1991年   3135篇
  1990年   3034篇
  1989年   2991篇
  1988年   2997篇
  1987年   2615篇
  1986年   2676篇
  1985年   3009篇
  1984年   2790篇
  1983年   2646篇
  1982年   2370篇
  1981年   2363篇
  1980年   2437篇
  1979年   2449篇
  1978年   2430篇
  1977年   2596篇
  1976年   3027篇
  1975年   2240篇
  1974年   2110篇
  1973年   2224篇
  1972年   1974篇
  1971年   1781篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
The peroxisomes of the asporogenic yeast Candida tropicalis contain about 20 major polypeptides (PXPs). We have isolated a number of genes encoding them; 11 POX genes encoded independent PXPs and three POY genes were likely to encode three other PXPs. To locate these genes on the chromosomes, chromosomes of C. tropicalis were separated by pulsed-field gel electrophoresis. Eight chromosomal bands were observed over the range of 1.0 Mbp (band 1) to 2.8 Mbp (band VIII); the genome size was estimated to be about 20 Mbp. Southern blot analysis showed that ten genes were on band V, three genes were on band IV, and the other gene was on band VI. Three genes gave hybridization signals of nearly equal intensity on two different chromosomal bands: POX6A and POX8B, on bands V and VII; and POX8A, on bands IV and VI. Ribosomal RNA genes also hybridized to two bands, VI and VII. Most genes assigned to only one band hybridized to two restriction fragments produced by either NotI or SfiI endonuclease. The results suggested that C. tropicalis was diploid and that restriction sites were conserved little between homologues. The three POX genes that were found on two chromosomal bands hybridized to not more than two restriction fragments, implying that the allelic genes were present on different chromosomal bands.  相似文献   
992.
Development of accurate schemes is a technical issue related to calculation of electromagnetic fields. This study uses constrained interpolation profile (CIP) method to analyze electromagnetic fields created by line current. This is a novel method proposed by Yabe. Comparison of results obtained using finite difference time domain (FDTD) analysis and CIP analysis indicates that CIP analysis provides higher accuracy using identical discretization. In addition, given the same level of accuracy, CIP analysis requires less memory and less calculation time  相似文献   
993.
994.
995.
996.
Design for a high power-density Astron reactor   总被引:1,自引:0,他引:1  
A liquid lithium blanket surrounding the plasma volume is described. The liquid lithium flows along magnetic flux tubes at a high speed. There is no vacuum wall between the blanket and the plasma. The E-layer of relativistic particles within which the plasma is confined serves as a vacuum wall protecting the plasma from the lithium vapor, which is continuously produced at the surface of the blanket, by ionizing the lithium atoms and ejecting the same along open magnetic lines. The heat load at the surface of the blanket generated by 14 MeV neutrons can be several hundred MW per square meter.Work performed under the auspices of the U.S. Atomic Energy Commission.Deceased September 24, 1972.  相似文献   
997.
998.
999.
The device developed allows one to measure the dielectric characteristics of solid substances and their melts at frequencies of 20–20000 Hz and in a wide temperature range of 20–250°C. The measured temperature dependencies of the dielectric permittivities of several molecular and liquid crystals (stilbene, diphenyl, naphthalene, cholesterylpelargonate, and 8OCB) are presented.  相似文献   
1000.
Presented herein are the studies of laminar–turbulent transition in micropolar and power law fluids flowing in a circular pipe. For some parametric values of micropolar and power law fluids, both depict the drag reducing properties. The parametric values of these representations have been obtained from the experimental results of Mc-Comb. It has been observed that, in both the cases, as the drag-reducing property in the solution increases, the first transition point moves towards the walls of the pipe. It is also observed that the onset of early turbulence phenomenon occurs for the drag-reducing polymeric solutions.  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