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   3151篇
  免费   3篇
电工技术   3篇
综合类   3篇
化学工业   35篇
金属工艺   4篇
机械仪表   2篇
建筑科学   9篇
能源动力   3篇
轻工业   7篇
水利工程   7篇
石油天然气   2篇
无线电   11篇
一般工业技术   17篇
冶金工业   3022篇
原子能技术   8篇
自动化技术   21篇
  2021年   2篇
  2018年   2篇
  2017年   1篇
  2016年   1篇
  2015年   1篇
  2014年   2篇
  2013年   10篇
  2012年   5篇
  2011年   6篇
  2010年   7篇
  2009年   6篇
  2008年   3篇
  2007年   4篇
  2006年   7篇
  2005年   4篇
  2004年   3篇
  2003年   8篇
  2002年   3篇
  2001年   3篇
  2000年   5篇
  1999年   94篇
  1998年   895篇
  1997年   499篇
  1996年   321篇
  1995年   173篇
  1994年   152篇
  1993年   175篇
  1992年   25篇
  1991年   37篇
  1990年   38篇
  1989年   47篇
  1988年   55篇
  1987年   54篇
  1986年   39篇
  1985年   34篇
  1984年   3篇
  1983年   12篇
  1982年   14篇
  1981年   20篇
  1980年   41篇
  1979年   4篇
  1978年   12篇
  1977年   93篇
  1976年   218篇
  1975年   8篇
  1974年   2篇
  1971年   1篇
  1970年   1篇
  1967年   1篇
  1955年   1篇
排序方式: 共有3154条查询结果,搜索用时 15 毫秒
61.
In the present study, we evaluated changes in brain-derived neurotrophic factor (BDNF) immunoreactivity in the rat lumbar (L) 5 dorsal root ganglion (DRG) and areas where afferents from the DRG terminate, the L5 spinal cord and gracile nuclei, following unilateral sciatic nerve transection or crush. From 3 days to 4 weeks following cut or crush injury, the percentage of medium and large BDNF-immunoreactive neurons in the ipsilateral DRG increased significantly compared with those on the contralateral side. Following cut injury, there was no significant change in the percentage of small BDNF-immunoreactive neurons in the ipsilateral DRG; however, the intensity of immunoreactivity of these cells decreased. Following crush injury, however, both the percentage and intensity of small BDNF-immunoreactive neurons in the ipsilateral DRG significantly increased. Following cut injury, the expression of BDNF-immunoreactive axonal fibers decreased markedly in the ipsilateral superficial laminae of the L5 spinal cord and increased significantly in the ipsilateral deeper laminae of the spinal cord and gracile nuclei. Crush injury induced a marked increase in the expression of BDNF-immunoreactive axonal fibers in the superficial laminae of the spinal cord and gracile nuclei. These differences in BDNF response in the DRG and spinal cord after cut or crush injuries may reflect differences in trophic support to the injured DRG neurons and altered neuronal activity in the spinal cord and gracile nuclei following different types of peripheral nerve injury.  相似文献   
62.
The presence of octoxynol from dried bear-bile was examined. Octoxynol was coextracted when glycolipids by Folch-Suzuki partition method. Octoxynol formed mixed-micelles with glycosphingolipids. The glycolipids were purified by DEAE-Sephadex A-25 column chromatography. The fractions containing mixed micelles were obtained from linear gradient solvent of 0.05M-0.5M ammonium acetate in methanol. HPLC ( Bondapak-NH(2) - linked to a Bondapak-C(18) column) chromatogram showed five peaks. Two possible structures for the fourth peak fraction were proposed as (CH(3))(3)C-CH(2)-C(CH(3))(2)-C(6)H(4)-OR and (CH(3))(3)C-C(CH(3))(2)-CH(2)-C(6)H(4)-OR by NMR spectroscopy. The structure was further confirmed by electrospray tandem mass spectrometry (ESI MS/MS). The spectrum showed a protonated molecule at m/z 559 and three different series of ions with mass difference of 44 were detected in the MS/MS spectrum. Therefore, the structure of the fourth peak fraction from HPLC was confirmed as octoxynol, (CH(3))(3)C-CH(2)-C(CH(3))(2)-C(6)H(4)-(OCH(2)-CH(2))n-OH, based on mass spectrometry and NMR spectroscopy.  相似文献   
63.
64.
65.
66.
67.
BACKGROUND: Recent reports suggest that gamma-glutamyl transferase (GGT) decreases with coffee intake. The aim of this study was to examine the joint influence of alcohol, tobacco, cotinine, coffee, and caffeine on biological markers of heavy drinking in an alcoholic population. METHODS: Subjects were 160 alcohol-dependent inpatients. Biological assessments, performed at admission, were plasma levels of GGT, apolipoprotein AI, aspartate aminotransferase, and mean corpuscular volume (MCV), and urine cotinine and caffeine indexes. Years of alcohol abuse and of smoking, alcohol and coffee intake, and smoking rate were estimated in a semistructured interview, and Fagerstr?m Tolerance Questionnaire was completed by inpatients. RESULTS: Coffee intake, but not caffeine, correlated negatively with biological markers of heavy drinking, after controlling for alcohol and tobacco intake. Years of smoking correlated positively to MCV, after controlling for alcohol and coffee intake. CONCLUSIONS: Concerning the effect of coffee, the most likely hypothesis is that noncaffeine coffee fractions have a protective effect on liver cells. Concerning the effect of smoking, one can propose that the increase of MCV with smoking could be a consequence of carbon monoxide inhalation, leading to hypoxemia, or of folate deficiency.  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