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   692941篇
  免费   8320篇
  国内免费   1913篇
电工技术   13387篇
综合类   915篇
化学工业   102417篇
金属工艺   28749篇
机械仪表   23669篇
建筑科学   15902篇
矿业工程   3356篇
能源动力   18337篇
轻工业   53587篇
水利工程   6959篇
石油天然气   11216篇
武器工业   24篇
无线电   83224篇
一般工业技术   139024篇
冶金工业   124815篇
原子能技术   13679篇
自动化技术   63914篇
  2021年   5521篇
  2020年   4176篇
  2019年   5302篇
  2018年   14518篇
  2017年   14719篇
  2016年   12695篇
  2015年   6522篇
  2014年   10334篇
  2013年   30962篇
  2012年   18452篇
  2011年   28274篇
  2010年   23493篇
  2009年   25033篇
  2008年   25684篇
  2007年   26865篇
  2006年   18683篇
  2005年   19435篇
  2004年   17602篇
  2003年   17167篇
  2002年   15776篇
  2001年   15383篇
  2000年   14652篇
  1999年   15246篇
  1998年   37984篇
  1997年   26760篇
  1996年   20779篇
  1995年   15715篇
  1994年   14076篇
  1993年   13836篇
  1992年   10183篇
  1991年   9642篇
  1990年   9535篇
  1989年   9177篇
  1988年   8777篇
  1987年   7616篇
  1986年   7579篇
  1985年   8724篇
  1984年   7932篇
  1983年   7300篇
  1982年   6655篇
  1981年   6855篇
  1980年   6324篇
  1979年   6180篇
  1978年   6006篇
  1977年   7039篇
  1976年   9101篇
  1975年   5238篇
  1974年   4968篇
  1973年   5014篇
  1972年   4201篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Objective

To develop a 3D multi-contrast IVW protocol with 0.5-mm isotropic resolution and a scan time of 5 min per sequence.

Materials and methods

Pre-contrast T1w VISTA, DANTE prepared PDw VISTA, SNAP, and post-contrast T1w VISTA were accelerated using cartesian undersampling with target ordering method (CUSTOM) and self-supporting tailored k-space estimation for parallel imaging reconstruction (STEP). CUSTOM + STEP IVW was compared to full-sample IVW, SENSE-accelerated IVW, and CUSTOM + zero-filled Fourier reconstruction in normal volunteers and subjects with intracranial atherosclerotic disease (ICAD). Image quality, vessel delineation, CSF suppression, and blood suppression were compared.

Results

CUSTOM + STEP vessel wall delineation was comparable to full-sample IVW and better than SENSE IVW for vessel wall delineation on T1w VISTA and luminal contrast on SNAP. Average image quality and wall depiction were significantly improved using STEP reconstruction compared with zero-filled Fourier reconstruction, with no significant difference in CSF or blood suppression.

Conclusions

CUSTOM + STEP allowed multi-contrast 3D 0.5-mm isotropic IVW within 30 min. Although some quantitative and qualitative scores for CUSTOM − STEP were lower than fully sampled IVW, CUSTOM + STEP provided comparable vessel wall delineation as full-sample IVW and was superior to SENSE. CUSTOM + STEP IVW was well tolerated by patients and showed good delineation of ICAD plaque.

  相似文献   
62.
Measurement Techniques - A comparative analysis of the results of estimation of measurement uncertainty is conducted. The results are obtained by a method described in the Handbook on the...  相似文献   
63.
64.
Journal of Communications Technology and Electronics - Microstrip band-pass filters (BPFs) containing quarter-wavelength resonators and a Π-shaped half-wavelength resonator placed next to each...  相似文献   
65.
Wireless Personal Communications - The majority of security systems for wireless sensor networks are based on symmetric encryption. The main open issue for these approaches concerns the...  相似文献   
66.
Strength of Materials - The paper addresses the investigation of high-strain rate compressive behavior of Al foams subjected to impact at the intermediate striking velocity ranged from 40 to...  相似文献   
67.
The separation of iron oxide from banded hematite jasper(BHJ) assaying 47.8% Fe, 25.6% Si O2 and 2.30%Al2O3 using selective magnetic coating was studied. Characterization studies of the low grade ore indicate that besides hematite and goethite,jasper, a microcrystalline form of quartzite, is the major impurity associated with this ore. Beneficiation by conventional magnetic separation technique could yield a magnetic concentrate containing 60.8% Fe with 51% Fe recovery. In order to enhance the recovery of the iron oxide minerals, fine magnetite, colloidal magnetite and oleate colloidal magnetite were used as the coating material. When subjected to magnetic separation, the coated ore produces an iron concentrate containing 60.2% Fe with an enhanced recovery of56%. The AFM studies indicate that the coagulation of hematite particles with the oleate colloidal magnetite facilitates the higher recovery of iron particles from the low grade BHJ iron ore under appropriate conditions.  相似文献   
68.
69.
70.
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