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   2004篇
  免费   25篇
  国内免费   2篇
电工技术   3篇
化学工业   87篇
金属工艺   5篇
机械仪表   9篇
建筑科学   1篇
能源动力   17篇
轻工业   36篇
水利工程   1篇
石油天然气   2篇
无线电   20篇
一般工业技术   34篇
冶金工业   1771篇
原子能技术   3篇
自动化技术   42篇
  2023年   2篇
  2022年   2篇
  2021年   8篇
  2020年   4篇
  2019年   6篇
  2018年   13篇
  2017年   8篇
  2016年   9篇
  2015年   13篇
  2014年   5篇
  2013年   19篇
  2012年   19篇
  2011年   29篇
  2010年   14篇
  2009年   14篇
  2008年   11篇
  2007年   20篇
  2006年   6篇
  2005年   9篇
  2004年   7篇
  2003年   8篇
  2002年   5篇
  2001年   3篇
  2000年   3篇
  1999年   48篇
  1998年   512篇
  1997年   295篇
  1996年   199篇
  1995年   98篇
  1994年   96篇
  1993年   112篇
  1992年   20篇
  1991年   26篇
  1990年   28篇
  1989年   27篇
  1988年   42篇
  1987年   33篇
  1986年   27篇
  1985年   24篇
  1984年   1篇
  1983年   5篇
  1982年   13篇
  1981年   9篇
  1980年   11篇
  1979年   1篇
  1978年   1篇
  1977年   54篇
  1976年   108篇
  1975年   2篇
  1955年   1篇
排序方式: 共有2031条查询结果,搜索用时 484 毫秒
91.
Although cytotoxic T lymphocytes (CTLs) are thought to be involved in the control of human immunodeficiency virus-type 1 (HIV-1) infection, it has not been possible to demonstrate a direct relation between CTL activity and plasma RNA viral load. Human leukocyte antigen-peptide tetrameric complexes offer a specific means to directly quantitate circulating CTLs ex vivo. With the use of the tetrameric complexes, a significant inverse correlation was observed between HIV-specific CTL frequency and plasma RNA viral load. In contrast, no significant association was detected between the clearance rate of productively infected cells and frequency of HIV-specific CTLs. These data are consistent with a significant role for HIV-specific CTLs in the control of HIV infection and suggest a considerable cytopathic effect of the virus in vivo.  相似文献   
92.
93.
94.
95.
The aim of the present investigation was to determine spin lock (SL) relaxation parameters for the normal brain tissues and thus, to provide basis for optimizing the imaging contrast at 0.1 T. 68 healthy volunteers were included. On-resonance spin lock relaxation time (T1rho) and off-resonance spin lock relaxation parameters (T1rho(off), Me/Mo), MT parameters (T1sat, Ms/Mo), and T1, T2 were determined for the cortical gray matter, and for the frontal and parietal white matters. The T1rho for the frontal and parietal white matters ranged from 110 to 133 ms and from 122 to 155 ms with locking field strengths from 50 microT to 250 microT, respectively. Accordingly, the values for the gray matter ranged from 127 to 155 ms. With a locking field strength of 50 microT, T1rho(off) for the frontal and parietal white matters were from 114 to 217 ms and from 126 to 219 ms, and for the gray matter from 136 to 267 ms with the angle between the effective magnetic field (B(eff)) and the z-axis (theta) ranging from 60 degrees to 15 degrees, respectively. The T1rho of the white and gray matters increased significantly with increasing locking field amplitude (p < 0.001). The T1rho(off) decreased significantly with increasing theta (p < 0.001). T1rho and T1rho(off) with theta > or = 30 degrees were statistically significantly shorter in the frontal than in the parietal white matters (p < 0.05). The duration, amplitude and theta of the locking pulse provide additional parameters to optimize contrast in brain SL imaging.  相似文献   
96.
We evaluated the role of intravascular ultrasound (IVUS) in 16 patients with unprotected left main coronary artery (LMCA) stenting compared with 80 patients with other (non-LMCA) native coronary artery stenting and found that (1) additional high-pressure or larger size balloon dilations were more frequently performed in LMCA stenting than in non-LMCA stenting (p <0.05) and (2) after IVUS-guided stent implantation, minimum lumen area was > or = 9 mm2 in 88% of patients who underwent LMCA stenting and in 19% of those who underwent non-LMCA stenting (p <0.001). IVUS guidance may be a more important adjunctive imaging modality in the stenting of unprotected LMCA stenoses than in stenting of non-LMCA stenoses.  相似文献   
97.
98.
99.
To observe the expression of p16, pRb, cdk4 and cyclinD1 in non-small cell lung cancers, 104 cases of resected lung cancers were collected, which included squamous cell carcinomas, adenocarcinomas and large cell carcinomas. Immunohistochemistry assay was carried out. The results showed that 67% of squamous cell carcinomas and 46% of adenocarcinomas expressed p16, 64% of squamous cell carcinomas and 85% of adenocarcinomas expressed pRb and 66% of cancers expressed p16 or pRb. About 70% of the tumors expressed cyclinD1. More than 90% of the tumors expressed cdk4 and there was an increased trend with decreasing differentiation of both squamous cell carcinomas and adenocarcinomas. Sixty-seven percent of the highly differentiated and 100% of the poorly differentiated squamous cell carcinomas expressed cdk4. The aberrant p16 and pRb gene product expression played a significant role in the development and histological subtype of lung cancers by conditioning the biological behavior of NSCLC. cdk4 was an important factor in histological differentiation.  相似文献   
100.
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