全文获取类型
收费全文 | 872篇 |
免费 | 0篇 |
专业分类
化学工业 | 25篇 |
金属工艺 | 3篇 |
机械仪表 | 1篇 |
建筑科学 | 4篇 |
能源动力 | 15篇 |
轻工业 | 11篇 |
石油天然气 | 2篇 |
无线电 | 19篇 |
一般工业技术 | 46篇 |
冶金工业 | 734篇 |
原子能技术 | 1篇 |
自动化技术 | 11篇 |
出版年
2021年 | 2篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2016年 | 5篇 |
2015年 | 1篇 |
2014年 | 5篇 |
2012年 | 4篇 |
2011年 | 2篇 |
2010年 | 4篇 |
2009年 | 2篇 |
2008年 | 9篇 |
2007年 | 4篇 |
2006年 | 2篇 |
2005年 | 2篇 |
2004年 | 6篇 |
2003年 | 5篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 30篇 |
1998年 | 224篇 |
1997年 | 151篇 |
1996年 | 74篇 |
1995年 | 49篇 |
1994年 | 42篇 |
1993年 | 47篇 |
1992年 | 6篇 |
1991年 | 16篇 |
1990年 | 13篇 |
1989年 | 8篇 |
1988年 | 13篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 10篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 9篇 |
1981年 | 10篇 |
1980年 | 12篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 19篇 |
1976年 | 39篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1969年 | 1篇 |
1968年 | 3篇 |
1965年 | 1篇 |
排序方式: 共有872条查询结果,搜索用时 265 毫秒
1.
2.
Enzymic catalysts of thiol:disulfide oxidoreduction contain two cysteine residues in their active sites. Another common residue is an aspartate (or glutamate), the role of which has been unclear. Escherichia coli thioredoxin (Trx) is the best characterized thiol:disulfide oxidoreductase, and in Trx these three active-site residues are Cys32, Cys35, and Asp26. Structural analyses had indicated that the carboxylate of Asp26 is positioned properly for the deprotonation of the thiol of Cys35, which would facilitate its attack on Cys32 in enzyme-substrate mixed disulfides. Here, Asp26 of Trx was replaced with isologous asparagine and leucine residues. D26N Trx and D26L Trx are reduced and oxidized more slowly than is wild-type Trx during catalysis by E.coli thioredoxin reductase. Stopped-flow spectroscopy demonstrated that the cleavage of the mixed disulfide between Trx and a substrate is slower in the D26N and D26L enzymes. Buffers increase the rate of mixed disulfide cleavage in these variants but not in wild-type Trx. These results indicate that Asp26 serves as an acid/base in the oxidation/reduction reactions catalyzed by Trx. Specifically, Asp26 protonates (during substrate oxidation) or deprotonates (during substrate reduction) the thiol of Cys35. A similar role is likely filled by the analogous aspartate (or glutamate) residue in protein disulfide isomerase, DsbA, and other thiol:disulfide oxidoreductases. Moreover, these results provide the first evidence for general acid/base catalysis in a thiol:disulfide interchange reaction. 相似文献
3.
4.
5.
Expression of a human homeobox-containing gene is regulated by 1,25(OH)2D3 in bone cells 总被引:1,自引:0,他引:1
JE Hodgkinson CL Davidson J Beresford PT Sharpe 《Canadian Metallurgical Quarterly》1993,1174(1):11-16
The seasonal variation in the nutrient composition of Enhydra fluctuans and Marsilea quadrifolia, two edible semi-aquatic plants, was studied in order to promote their consumption as green leafy vegetables. Both plants had a high crude protein content throughout all harvesting seasons. Enhydra fluctuans had a low ash content and was a good source of beta-carotene (3.7 to 4.2 mg/100 g on a fresh weight basis). Marsilea quadrifolia exhibited wide fluctuations between seasons and was not very promising in nutrient composition when compared to other commonly used green leafy vegetables. 相似文献
6.
Gaidis M.C. Friedrich S. Segall K. Prober D.E. Szymkowiak A.E. Moseley S.H. 《Applied Superconductivity, IEEE Transactions on》1996,6(1):1-4
We report the development of Nb-Ta-Al-Al2O3-Al superconducting tunnel junction structures for high energy resolution and high efficiency X-ray detection. These devices utilize a Ta X-ray absorber with superconductor “bandgap engineered” quasiparticle trapping to improve charge collection. Experimental results at 0.3 K are presented, showing energy resolution of 102 eV full-width-half-maximum for 6 keV X-rays. Collected charge is in excess of 5×106 electrons. The absorption efficiency is better than 35%. Devices thermally cycle with no change in characteristics 相似文献
7.
8.
9.
10.