全文获取类型
收费全文 | 203457篇 |
免费 | 3889篇 |
国内免费 | 829篇 |
专业分类
电工技术 | 3747篇 |
综合类 | 337篇 |
化学工业 | 32455篇 |
金属工艺 | 8513篇 |
机械仪表 | 5717篇 |
建筑科学 | 5154篇 |
矿业工程 | 1016篇 |
能源动力 | 5132篇 |
轻工业 | 20061篇 |
水利工程 | 1886篇 |
石油天然气 | 3261篇 |
武器工业 | 12篇 |
无线电 | 21315篇 |
一般工业技术 | 38229篇 |
冶金工业 | 39673篇 |
原子能技术 | 4440篇 |
自动化技术 | 17227篇 |
出版年
2021年 | 1916篇 |
2020年 | 1410篇 |
2019年 | 1653篇 |
2018年 | 2944篇 |
2017年 | 2847篇 |
2016年 | 3066篇 |
2015年 | 2340篇 |
2014年 | 3596篇 |
2013年 | 9458篇 |
2012年 | 5791篇 |
2011年 | 7633篇 |
2010年 | 6113篇 |
2009年 | 6903篇 |
2008年 | 7011篇 |
2007年 | 6909篇 |
2006年 | 5795篇 |
2005年 | 5294篇 |
2004年 | 4936篇 |
2003年 | 4573篇 |
2002年 | 4485篇 |
2001年 | 4448篇 |
2000年 | 4200篇 |
1999年 | 4469篇 |
1998年 | 12382篇 |
1997年 | 8590篇 |
1996年 | 6516篇 |
1995年 | 4813篇 |
1994年 | 4047篇 |
1993年 | 3964篇 |
1992年 | 2760篇 |
1991年 | 2701篇 |
1990年 | 2554篇 |
1989年 | 2580篇 |
1988年 | 2506篇 |
1987年 | 2265篇 |
1986年 | 2190篇 |
1985年 | 2570篇 |
1984年 | 2348篇 |
1983年 | 2163篇 |
1982年 | 1997篇 |
1981年 | 2107篇 |
1980年 | 1962篇 |
1979年 | 1921篇 |
1978年 | 1869篇 |
1977年 | 2303篇 |
1976年 | 3124篇 |
1975年 | 1633篇 |
1974年 | 1625篇 |
1973年 | 1710篇 |
1972年 | 1387篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
Mechanical durability of extruded fish feed must be optimized to lower economic losses as well as emission of organic matter to aquatic environments. The glass transition hypothesis for viscoelastic biopolymers is demonstrated and confirmed experimentally to be valid for extruded fish feed pellets. It is proposed and demonstrated that it is important to avoid early glass transition onset, to optimize the obtained mechanical durability. From the proposed glass transition hypothesis, immediate process relevance to the pre-drying transport mechanism is demonstrated. Furthermore, measured mechanical durability is found to range from 1.5 to 5.0% loss, for different combinations of drying parameters. 相似文献
53.
54.
Metallurgist - We consider domestic and foreign standards for rolled metals used in bridge building. Domestic standards contain elevated requirements to the reliability of rolled metals in terms of... 相似文献
55.
Sebastian Roth Peter Stockinger Jakob Steff Simon Steimle Dr. Viktor Sautner Prof. Dr. Kai Tittmann Prof. Dr. Jürgen Pleiss Prof. Dr. Michael Müller 《Chembiochem : a European journal of chemical biology》2020,21(18):2615-2619
The family of NAD(P)H-dependent short-chain dehydrogenases/reductases (SDRs) comprises numerous biocatalysts capable of C=O or C=C reduction. The highly homologous noroxomaritidine reductase (NR) from Narcissus sp. aff. pseudonarcissus and Zt_SDR from Zephyranthes treatiae, however, are SDRs with an extended imine substrate scope. Comparison with a similar SDR from Asparagus officinalis (Ao_SDR) exhibiting keto-reducing activity, yet negligible imine-reducing capability, and mining the Short-Chain Dehydrogenase/Reductase Engineering Database indicated that NR and Zt_SDR possess a unique active-site composition among SDRs. Adapting the active site of Ao_SDR accordingly improved its imine-reducing capability. By applying the same strategy, an unrelated SDR from Methylobacterium sp. 77 (M77_SDR) with distinct keto-reducing activity was engineered into a promiscuous enzyme with imine-reducing activity, thereby confirming that the ability to reduce imines can be rationally introduced into members of the “classical” SDR enzyme family. Thus, members of the SDR family could be a promising starting point for protein approaches to generate new imine-reducing enzymes. 相似文献
56.
Refractories and Industrial Ceramics - The article is devoted to the preparation of ecologically clean composites by powder metallurgy and the study of tribological properties. Tribological tests... 相似文献
57.
58.
59.
60.