全文获取类型
收费全文 | 243304篇 |
免费 | 3149篇 |
国内免费 | 1241篇 |
专业分类
电工技术 | 4829篇 |
综合类 | 264篇 |
化学工业 | 35421篇 |
金属工艺 | 10861篇 |
机械仪表 | 7066篇 |
建筑科学 | 6238篇 |
矿业工程 | 481篇 |
能源动力 | 6273篇 |
轻工业 | 24150篇 |
水利工程 | 1837篇 |
石油天然气 | 1335篇 |
武器工业 | 3篇 |
无线电 | 31037篇 |
一般工业技术 | 44880篇 |
冶金工业 | 50120篇 |
原子能技术 | 3860篇 |
自动化技术 | 19039篇 |
出版年
2021年 | 1563篇 |
2019年 | 1424篇 |
2018年 | 2321篇 |
2017年 | 2223篇 |
2016年 | 2444篇 |
2015年 | 1907篇 |
2014年 | 3159篇 |
2013年 | 10793篇 |
2012年 | 5449篇 |
2011年 | 7786篇 |
2010年 | 6284篇 |
2009年 | 6963篇 |
2008年 | 7559篇 |
2007年 | 7659篇 |
2006年 | 7032篇 |
2005年 | 6519篇 |
2004年 | 6245篇 |
2003年 | 6261篇 |
2002年 | 6240篇 |
2001年 | 6372篇 |
2000年 | 5801篇 |
1999年 | 6418篇 |
1998年 | 16562篇 |
1997年 | 11597篇 |
1996年 | 8949篇 |
1995年 | 6690篇 |
1994年 | 5910篇 |
1993年 | 5728篇 |
1992年 | 4052篇 |
1991年 | 3995篇 |
1990年 | 3583篇 |
1989年 | 3504篇 |
1988年 | 3440篇 |
1987年 | 2907篇 |
1986年 | 2842篇 |
1985年 | 3413篇 |
1984年 | 3050篇 |
1983年 | 2745篇 |
1982年 | 2547篇 |
1981年 | 2570篇 |
1980年 | 2431篇 |
1979年 | 2271篇 |
1978年 | 2235篇 |
1977年 | 2808篇 |
1976年 | 4173篇 |
1975年 | 1901篇 |
1974年 | 1795篇 |
1973年 | 1783篇 |
1972年 | 1461篇 |
1971年 | 1318篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Dr. Jiayao Y. Wang Dr. Jiaqi Q. Li Prof. Dr. Yumei M. Xiao Prof. Dr. Bin Fu Prof. Dr. Zhaohai H. Qin 《ChemMedChem》2020,15(5):404-410
Mitochondrial oxidative damage and dysfunction contribute to a wide range of human diseases. Considering the limitation of conventional antioxidants and that mitochondria are the main source of reactive oxygen species (ROS) which induce oxidative damage, mitochondria-targeted antioxidants which can selectively block mitochondrial oxidative damage and prevent various types of cell death have been widely developed. As a lipophilic cation, triphenylphosphonium (TPP) has been commonly used in designing mitochondria-targeted antioxidants. Conjugated with the TPP moiety, antioxidants can achieve more than 1000-fold higher mitochondrial concentration depending on cell membrane potentials and mitochondrial membrane potentials. Herein we discuss the deficiencies of conventional antioxidants and the advantages of mitochondrial targeting, and review various types of TPP-based mitochondria-targeted antioxidants. These provide theoretical and background support for the design of new anti-oxidant. 相似文献
32.
Potential mGAT4 inhibitors derived from the lead substance (S)-SNAP-5114 have been synthesized and characterized for their inhibitory potency. Variations from the parent compound included the substitution of one of its aromatic 4-methoxy and 4-methoxyphenyl groups, respectively, with a more polar moiety, including a carboxylic acid, alcohol, nitrile, carboxamide, sulfonamide, aldehyde or ketone function, or amino acid partial structures. Furthermore, it was investigated how the substitution of more than one of the aromatic 4-methoxy groups affects the potency and selectivity of the resulting compounds. Among the synthesized test substances (S)-1-{2-[(4-formylphenyl)bis(4-methoxyphenyl)-methoxy]ethyl}piperidine-3-carboxylic acid, that features a carbaldehyde function in place of one of the aromatic 4-methoxy moieties of (S)-SNAP-5114, was found to have a pIC50 value of 5.89±0.07, hence constituting a slightly more potent mGAT4 inhibitor than the parent substance while showing comparable subtype selectivity. 相似文献
33.
34.
ABSTRACT The concept of digital game-based learning (DGBL) evolves rapidly together with technological enhancements of virtual reality (VR) and smart phones. However, the mental workload (MWL) that VR-training applications demand and motivational qualities originating from user experience (UX) should be identified in order to create effective and enjoyable training/learning challenges that fit with individual users’ capabilities. This study examined the effects of reality-based interaction (RBI) and VR on measures of student motivation and MWL, in a mental arithmetic game for secondary school pupils. In a randomised controlled trial with sixty school children, a mental arithmetic game was tested with three different interaction and two different presentation methods – VR RBI, VR head-mounted-display tapping and tablet flick-gesture. Results found a significant effect of RBI on MWL but no differences in enjoyment of training were found between VR-experience and tablet training-experience. In fact, adding the gaming-context to the mental arithmetic task created an enjoyable, motivating experience regardless of presentation or interaction-style. 相似文献
35.
36.
37.
38.
Strength of Materials - A metallographic method, dilatometry, and X-ray diffraction were applied to investigate the effects of undercooling and holding time on bainitic transformation,... 相似文献
39.
Wireless Personal Communications - Current mobile communications technology relies heavily on efficient design of antennas, where the operational characteristics of the wireless communication... 相似文献
40.
D. Kherifi H. Belhouchet S. Ramesh K.Y. Sara Lee A. Kenzour S. Djoualah M.K.G. Abbas Y.H. Wong S. Ramesh 《Ceramics International》2021,47(12):16483-16490
In this work, the sintering behaviour of fluorapatite (FAp)–silicate composites prepared by mixing variable amounts of natural quartz (2.5 wt% to 20 wt%) and FAp was studied. The composites were pressureless sintered in air at temperatures from 1000 °C to 1350 °C. The effects of temperatures on the densification, phase formation, chemical bonding and Vickers hardness of the composites were evaluated. All the samples exhibited mixed phase, comprising FAp and francolite as the major constituents along with some minor phases of cristobalite, wollastonite, dicalcium silicate and/or whitlockite dependent on the quartz content and sintering temperature. The composite containing 2.5 wt% quartz exhibited the best sintering properties. The highest bulk density of 3 g/cm3 and a Vickers hardness of >4.2 GPa were obtained for the 2.5 wt% quartz–FAp composite when sintered at 1100 °C. The addition of quartz was found to alter the microstructure of the composites, where it exhibited a rod-like morphology when sintered at 1000 °C and a regular rounded grain structure when sintered at 1350 °C. A wetted grain surface was observed for composites containing high quartz content and was believed to be associated with a transient liquid phase sintering. 相似文献