全文获取类型
收费全文 | 1611篇 |
免费 | 4篇 |
专业分类
电工技术 | 5篇 |
综合类 | 1篇 |
化学工业 | 38篇 |
金属工艺 | 6篇 |
机械仪表 | 6篇 |
建筑科学 | 29篇 |
能源动力 | 15篇 |
轻工业 | 48篇 |
水利工程 | 5篇 |
石油天然气 | 3篇 |
无线电 | 29篇 |
一般工业技术 | 71篇 |
冶金工业 | 1319篇 |
原子能技术 | 5篇 |
自动化技术 | 35篇 |
出版年
2021年 | 5篇 |
2020年 | 3篇 |
2017年 | 3篇 |
2015年 | 2篇 |
2014年 | 3篇 |
2013年 | 13篇 |
2012年 | 5篇 |
2011年 | 8篇 |
2010年 | 8篇 |
2009年 | 9篇 |
2008年 | 9篇 |
2007年 | 20篇 |
2006年 | 10篇 |
2005年 | 9篇 |
2004年 | 10篇 |
2003年 | 17篇 |
2002年 | 9篇 |
2001年 | 9篇 |
2000年 | 7篇 |
1999年 | 44篇 |
1998年 | 354篇 |
1997年 | 208篇 |
1996年 | 148篇 |
1995年 | 103篇 |
1994年 | 74篇 |
1993年 | 87篇 |
1992年 | 10篇 |
1991年 | 25篇 |
1990年 | 22篇 |
1989年 | 29篇 |
1988年 | 26篇 |
1987年 | 39篇 |
1986年 | 23篇 |
1985年 | 25篇 |
1984年 | 9篇 |
1983年 | 15篇 |
1982年 | 11篇 |
1981年 | 14篇 |
1980年 | 15篇 |
1979年 | 5篇 |
1978年 | 11篇 |
1977年 | 44篇 |
1976年 | 80篇 |
1975年 | 7篇 |
1973年 | 6篇 |
1972年 | 5篇 |
1971年 | 2篇 |
1970年 | 5篇 |
1947年 | 1篇 |
1946年 | 1篇 |
排序方式: 共有1615条查询结果,搜索用时 15 毫秒
1.
2.
3.
S Modi DE Gilham MJ Sutcliffe LY Lian WU Primrose CR Wolf GC Roberts 《Canadian Metallurgical Quarterly》1997,36(15):4461-4470
1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a neurotoxin that produces Parkinsonism symptoms in man, has been examined as a substrate of recombinant human cytochrome P450 2D6. When cumene hydroperoxide is used as an oxygen and electron donor, a single product is formed, identified as 4-phenyl-1,2,3,6-tetrahydropyridine. The K(m) for formation of this product (130 microM) is in agreement with the dissociation constants for MPTP binding to the enzyme determined by optical and nuclear magnetic resonance (NMR) spectroscopy. When the reaction is carried out with nicotinamide adenine dinucleotide phosphate (reduced) (NADPH) and recombinant human NADPH-cytochrome P450 reductase, a second product, identified as 1-methyl-4-(4'-hydroxyphenyl)-1,2,3,6-tetrahydropyridine, is formed in addition to 4-phenyl-1,2,3,6-tetrahydropyridine. The K(m) values for formation of these two products are 19 microM and 120 microM, respectively. Paramagnetic relaxation experiments have been used to measure distances between the protons of bound MPTP and the heme iron, and these have been used to construct models for the position and orientation of MPTP in the active site. For the cytochrome alone, a single mode of binding was observed, with the N-methyl close to the heme iron in a position appropriate for the observed N-demethylation reaction. In the presence of the reductase, the data were not consistent with a single mode of binding but could be explained by the existence of two alternative orientations of MPTP in the active site. One of these, characterized by a dissociation constant of 150 microM, is essentially identical to that observed in the absence of the reductase. In the second, which has a K(d) of 25 microM, the MPTP is oriented so that the aromatic ring is close to the heme iron, in a position appropriate for p-hydroxylation leading to the formation of the product seen only in the presence of the reductase. In the case of codeine, another substrate for cytochrome P450 2D6, the addition of reductase had no effect on the nature of the product formed, the dissociation constant, or the orientation in the binding site. These observations show that NADPH-cytochrome P450 reductase has an allosteric effect on the active site of cytochrome P450 2D6 that affects the binding of some substrates but not others. 相似文献
4.
5.
6.
The need for frequent injections and monitoring, the possibility of multiple gestations, and the higher cost compared to clomiphene citrate, prevents many clinicians from using human menopausal gonadotrophin (HMG) for ovulation induction. A sequential medication regimen, in which HMG is taken after clomiphene, overcomes these problems. We retrospectively compared per cycle fecundity and birth rates in 119 cycles of clomiphene-HMG, 524 cycles of clomiphene alone, 57 cycles of HMG alone, and 79 cycles of concurrent HMG and clomiphene in patients receiving intra-uterine insemination (IUI), who were free of endometriosis or tubal disease. Per cycle fecundity for clomiphene-HMG was 22% [95% confidence interval (CI) 12-34%], double that of clomiphene alone (11%) (95% CI 8-14%) (P < 0.01), and equal to HMG alone (18%) (95% CI 7-29%) or HMG and clomiphene together (19%) (95% CI 10-28%). The multiple birth rate for clomiphene-HMG (7/21) equalled that for HMG alone (3/12) and HMG and clomiphene together (3/8). The average number of ampoules of HMG required [follicle stimulating hormone (FSH) 75 mIU, luteinizing hormone (LH) 75 mIU] was decreased by 65% from 24.5 +/- 1.0 for HMG or HMG and clomiphene together to 8.6 +/- 0.3 for clomiphene-HMG (P < 0.001). Per cycle fecundity was identical when one, two or three ampoules of HMG per day were administered after clomiphene. We conclude that ovulation induction with sequential clomiphene-HMG results in fecundity double that of clomiphene alone and equal to HMG alone or concurrent with clomiphene, thereby reducing the requirement for HMG. 相似文献
7.
This report demonstrates how to calculate distances between points described in terms of latitude and longitude, using the Postal Code Conversion File (PCCF) and other files available from the Geography Division of Statistics Canada. Examples based on hospital data show how the results can be summarized in the form of tables, figures, or maps. Aerial distance to the nearest hospital is a crude but objective indicator of geographic accessibility to hospital services. Distances were calculated between enumeration area centroids for the population and blockface or enumeration area centroids for the hospitals. The median aerial distance to the nearest hospital facility in Canada was less than 3 km, while the mean distance was about 6 km. For teaching hospitals, the median aerial distance was a little less than 30 km, while the mean distance was a little more than 90 km. As most health files for administrative and research purposes contain postal codes, these techniques have potentially wide application. 相似文献
8.
9.
Two forms of glutathione synthetase deficiency have been described. While one form is mild, causing hemolytic anemia, the other more severe form causes 5-oxo-prolinuria with secondary neurological involvement. Despite the existence of two deficiency phenotypes, Southern blots hybridized with a glutathione synthetase cDNA suggest that there is a single glutathione synthetase gene in the human genome. Analysis of somatic cell hybrids showed the human glutathione synthetase gene (GSS) to be located on chromosome 20, and this assignment has been refined to subband 20q11.2 using in situ hybridization. 相似文献
10.