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   4922篇
  免费   6篇
电工技术   13篇
化学工业   104篇
金属工艺   17篇
机械仪表   8篇
建筑科学   22篇
能源动力   6篇
轻工业   41篇
水利工程   1篇
无线电   144篇
一般工业技术   88篇
冶金工业   4401篇
原子能技术   10篇
自动化技术   73篇
  2022年   3篇
  2021年   4篇
  2020年   8篇
  2019年   6篇
  2018年   6篇
  2017年   7篇
  2016年   7篇
  2014年   3篇
  2013年   19篇
  2012年   12篇
  2011年   13篇
  2010年   19篇
  2009年   11篇
  2008年   18篇
  2007年   13篇
  2006年   24篇
  2005年   26篇
  2004年   15篇
  2003年   13篇
  2002年   11篇
  2001年   12篇
  2000年   6篇
  1999年   153篇
  1998年   1465篇
  1997年   826篇
  1996年   540篇
  1995年   281篇
  1994年   259篇
  1993年   276篇
  1992年   44篇
  1991年   51篇
  1990年   54篇
  1989年   65篇
  1988年   58篇
  1987年   44篇
  1986年   33篇
  1985年   34篇
  1984年   13篇
  1983年   15篇
  1982年   18篇
  1981年   23篇
  1980年   47篇
  1979年   9篇
  1978年   9篇
  1977年   97篇
  1976年   208篇
  1975年   11篇
  1974年   6篇
  1973年   8篇
  1970年   3篇
排序方式: 共有4928条查询结果,搜索用时 15 毫秒
71.
72.
Both poverty and other factors associated with race are related to child health. However, the mechanisms of these relationships have not been adequately specified. The purpose of this study was to explore the relationship of the social environment to child health status in black and white children and further, to explore whether the patterns of the effects of social class were different by race. This study provides further evidence that the social environment is strongly associated with child health status. Several risk factors are similar for both white and black children: mothers who view their own health as fair or poor are much more likely to rate their children in poor health. The presence of childhood chronic medical conditions is independently associated with poor health status regardless of race. However, the relative importance of several social risks for poor health status differs between white and black children. Specifically, while low family income is a consistent risk factor for poor health among white children, low income alone is not a risk factor for black children. Among black children, other social risks that are associated with poverty, such as low maternal education and a mother's perception of her own health as poor, increased the risk of poorer health in the child.  相似文献   
73.
Immersive electronic books (IEBooks) for surgical training will let surgeons explore previous surgical procedures in 3D. The authors describe the techniques and tools for creating a preliminary IEBook, embodying some of the basic concepts.  相似文献   
74.
75.
76.
77.
Molecular electrostatic potential (MEP) maps of certain 3-methoxy flavone derivatives having different anti-picornavirus activities have been studied. Geometries of the molecules were optimised and charge distributions computed using the AM1 molecular orbital method. Hybridization displacement charges (HDC) were combined with the L?wdin charge distributions to compute the MEP maps. Reliability of the method of computing MEP maps was tested by studying certain other molecules for which ab initio MEP results are available. The anti-picornavirus activities of the flavones have been shown to be related with negative MEP values in two regions, one near the 3-methoxy group and another in a diagonally opposite region near the substituent attached to the C7 atom of the molecules.  相似文献   
78.
79.
The weak acid sorbic acid transiently inhibited the growth of Saccharomyces cerevisiae in media at low pH. During a lag period, the length of which depended on the severity of this weak-acid stress, yeast cells appeared to adapt to this stress, eventually recovering and growing normally. This adaptation to weak-acid stress was not due to metabolism and removal of the sorbic acid. A pma1-205 mutant, with about half the normal membrane H+-ATPase activity, was shown to be more sensitive to sorbic acid than its parent. Sorbic acid appeared to stimulate plasma membrane H+-ATPase activity in both PMA1 and pma1-205. Consistent with this, cellular ATP levels showed drastic reductions, the extent of which depended on the severity of weak-acid stress. The weak acid did not appear to affect the synthesis of ATP because CO2 production and O2 consumption were not affected significantly in PMA1 and pma1-205 cells. However, a glycolytic mutant, with about one-third the normal pyruvate kinase and phosphofructokinase activity and hence a reduced capacity to generate ATP, was more sensitive to sorbic acid than its isogenic parent. These data are consistent with the idea that adaptation by yeast cells to sorbic acid is dependent on (i) the restoration of internal pH via the export of protons by the membrane H+-ATPase in an energy-demanding process and (ii) the generation of sufficient ATP to drive this process and still allow growth.  相似文献   
80.
AIM: To assess cell proliferation in early prostate cancer and associated pathological lesions. METHODS: Using the Ki-67 antibody, the cell proliferation index was measured in early stage prostatic carcinoma in 37 incidental tumours diagnosed at transurethral prostatectomy (TURP) and in 20 low volume cancers treated by radical prostatectomy. Proliferation indexes have also been measured in areas of normal peripheral zone, transition zone hyperplasia, atrophic appearing lobules, and high grade prostatic intraepithelial neoplasia in the radical prostatectomy cases. RESULTS: In the TURP series the proliferation index correlated with grade and stage. Logistic regression analysis, however, showed that Gleason grade was the most reliable predictor of biopsy proven residual disease and clinical progression. In the radical series transition zone carcinoma the proliferation index was half that of peripheral zone carcinoma. The atrophic lobules also showed a high proliferation index of the same order as seen in the peripheral zone carcinoma. Normal peripheral zone showed the lowest proliferation index and in hyperplastic transition zone it was also less than the other areas. CONCLUSIONS: There is only limited support for the correlation of proliferation index with grade in early stage prostatic carcinoma. The findings do not suggest that proliferation index adds to the prognostic information given by grade and stage in pT1 disease. The significant difference in proliferation index in transition zone and peripheral zone carcinomas supports the morphological distinction of these tumour types and is consistent with differences in biological behaviour. The high proliferation index in lobules considered morphologically atrophic is reminiscent of previous observations in which carcinoma was spatially associated with atrophy.  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