全文获取类型
收费全文 | 2874篇 |
免费 | 215篇 |
国内免费 | 14篇 |
专业分类
电工技术 | 58篇 |
综合类 | 17篇 |
化学工业 | 711篇 |
金属工艺 | 69篇 |
机械仪表 | 44篇 |
建筑科学 | 139篇 |
矿业工程 | 6篇 |
能源动力 | 133篇 |
轻工业 | 110篇 |
水利工程 | 12篇 |
石油天然气 | 10篇 |
无线电 | 282篇 |
一般工业技术 | 597篇 |
冶金工业 | 250篇 |
原子能技术 | 8篇 |
自动化技术 | 657篇 |
出版年
2024年 | 6篇 |
2023年 | 61篇 |
2022年 | 124篇 |
2021年 | 163篇 |
2020年 | 113篇 |
2019年 | 106篇 |
2018年 | 114篇 |
2017年 | 126篇 |
2016年 | 133篇 |
2015年 | 103篇 |
2014年 | 161篇 |
2013年 | 196篇 |
2012年 | 215篇 |
2011年 | 230篇 |
2010年 | 142篇 |
2009年 | 149篇 |
2008年 | 133篇 |
2007年 | 101篇 |
2006年 | 90篇 |
2005年 | 46篇 |
2004年 | 54篇 |
2003年 | 48篇 |
2002年 | 34篇 |
2001年 | 38篇 |
2000年 | 29篇 |
1999年 | 35篇 |
1998年 | 73篇 |
1997年 | 42篇 |
1996年 | 19篇 |
1995年 | 25篇 |
1994年 | 17篇 |
1993年 | 12篇 |
1992年 | 13篇 |
1991年 | 15篇 |
1990年 | 20篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 14篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1975年 | 5篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1971年 | 4篇 |
排序方式: 共有3103条查询结果,搜索用时 15 毫秒
991.
Natalia Vorontsova Evgenii Vorontsov Dmitrii Antonov Zoya Starikova Kim Butin Stefan Brse Sebastian Hfener Valeria Rozenberg 《Advanced Synthesis \u0026amp; Catalysis》2005,347(1):129-135
Bis‐bifunctional cis‐4,7‐diarylsubstituted‐4,7‐dihydroxy‐4,7‐dihydro[2.2]paracyclophanes 3–6 were synthesized by a highly diastereoselective reaction of ortho‐substituted aryllithium reagents with [2.2]paracyclophane‐4,7‐quinone ( 1 ). Enantiomerically pure diols 3–5 were tested as chiral inductors in the enantioselective addition of diethylzinc to benzaldehyde (up to 93.5% ee). Acid dehydration of cis‐4,7‐di(2‐methoxyphenyl)‐4,7‐dihydroxy‐4,7‐dihydro[2.2]paracyclophane ( 3 ) results in 4,7‐dihydro‐7,8‐di(2‐methoxyphenyl)[2.2]paracyclophane‐4‐one ( 8 ) – a planar chiral cyclohexadienone of the [2.2]paracyclophane series with a para‐semiquinoid substructure. X‐Ray investigations of compounds 3, 4 and 8 were performed. 相似文献
992.
F. Bugge A. Knauer S. Gramlich I. Rechenberg G. Beister J. Sebastian H. Wenzel G. Erbert M. Weyers 《Journal of Electronic Materials》2000,29(1):57-61
GaAs-based diode lasers for emission wavelengths between 800 nm and 1060 nm with AlGaAs-cladding and GaInP-waveguide layers
were grown by MOVPE. For wavelengths above 940 nm broad area devices with InGaAs QWs show state-of-the-art threshold current
densities. Ridge-waveguide lasers fabricated by selective etching achieve 200 mW CW monomode output powers. (In)GaAsP QW-based
diode lasers with an emitting wavelengths around 800 nm suffer from problems at the upper GaInP/AlGaAs interface. Asymmetric
structures with a lower AlGaAs/GaInP and an upper AlGaAs/AlGaAs waveguide not only avoid this interface but also offer better
carrier confinement. Such structures show very high slope efficiencies and a high T0. Maximum output powers of 7 W CW are obtained from 4 mm long devices. 相似文献
993.
Product selectivity and yield in chemical reactions can be limited by side product formation or low conversions due to equilibrium limitations. Extractive reaction systems (ERS) employ an in situ liquid‐liquid extraction that separates the product from the reaction phase to overcome these difficulties. The design of ERS requires a broad knowledge of the discipline of process intensification and extraction and reaction engineering. Furthermore, specific knowledge about the interplay of reaction and extraction phenomena is unique to ERS. This review gives an overview of the design of ERS and enables their application to any suitable reaction. 相似文献
994.
Muttashar Wisam R. Bryson L. Sebastian McGlue Michael Woolery Edward 《Bulletin of Engineering Geology and the Environment》2020,79(2):925-939
Bulletin of Engineering Geology and the Environment - Grain-size distribution (GSD) characteristics are often used to classify different types of sediment and to understand how variations in... 相似文献
995.
Sebastian O. Long Anthony V. Powell Stephen Hull Fabio Orlandi Chiu C. Tang Andrew R. Supka Marco Fornari Paz Vaqueiro 《Advanced functional materials》2020,30(12)
Tetrahedrite, Cu12Sb4S13, is an abundant mineral with excellent thermoelectric properties owing to its low thermal conductivity. The electronic and structural origin of the intriguing physical properties of tetrahedrite, including its metal‐to‐semiconductor transition (MST), remains largely unknown. This work presents the first determination of the low‐temperature structure of tetrahedrite that accounts for its unique properties. Contrary to prior conjectures, the results show that the trigonal–planar copper cations remain in planar coordination below the MST. The atomic displacement parameters of the trigonal–planar copper cations, which have been linked to low thermal conductivity, increase by 200% above the MST. The phase transition is a consequence of the orbital degeneracy of the highest occupied 3d cluster orbitals of the copper clusters found in the cubic phase. This study reveals that a Jahn–Teller electronic instability leads to the formation of “molecular‐like” Cu57+ clusters and suppresses copper rattling vibrations due to the strengthening of direct copper–copper interactions. First principles calculations demonstrate that the structural phase transition opens a small band gap in the electronic density of states and eliminates the unstable phonon modes. These results provide insights on the interplay between phonon transport, electronic properties, and crystal structure in mixed‐valence compounds. 相似文献
996.
997.
Due to the long history of the Südzucker Group in sugar production, the company owns key know-how in processing biomass. In the last decades, the product portfolio was extended from sugar to various products such as ethanol, starch, proteins, or glucose syrups. This article presents Zeitz as the largest production site of the Südzucker Group today. The historical development is described and the synergies between the different units from which the location benefits today as a highly integrated site. Recent R&D activities are presented, and existing technologies are discussed as future perspectives to further develop Zeitz. 相似文献
998.
Electricity generation is a major contributor to carbon dioxide emissions, and abatement in this sector is a key determinant of economy-wide regulation costs. The complexity of an integrated representation of economic and electricity systems makes simplifying assumptions appealing, but there is no evidence in the literature on how important the pitfalls may be. The aim of this paper is to provide such evidence, drawing on numerical simulations from a suite of partial and general equilibrium models that share common technological features and are calibrated to the same benchmark data. We report two basic findings. First, general equilibrium inter-sectoral effects of an economy-wide carbon policy are large. It follows that assessing abatement potentials and price changes in the electricity sector with a partial equilibrium Marshallian demand can only provide a crude approximation of the complex demand-side interactions. Second, we provide evidence that widely used top-down representations of electricity technologies produce fuel substitution patterns that are inconsistent with bottom-up cost data. This supports the view that the parametrization of substitution possibilities with highly aggregated production functions is difficult to validate empirically. The overall picture that emerges is one of large quantitative and even qualitative differences, highlighting the role of key structural assumptions in the interpretation of climate policy projections. 相似文献
999.
An integrated flow‐through fixed‐bed reactor concept for lignocellulose separation at 3 L scale is presented. Wheat straw is degraded using sequential liquid hot water treatment and enzymatic hydrolysis in a single‐pot reactor setup. System responses on process parameters are modeled and optimized using response surface methodology. Accurate empiric models and significant factor influences could be identified for both treatment steps. With optimal factor settings, 23.9 and 49.2 wt % hot‐water‐soluble lignin and C5 oligomers could be recovered, respectively. 70.0 wt % cellulose solubilization could be achieved in the fixed‐bed enzymatic hydrolysis after 72 hours. 相似文献
1000.
The Cluster Editing problem is defined as follows: Given an undirected, loopless graph, we want to find a set of edge modifications (insertions
and deletions) of minimum cardinality, such that the modified graph consists of disjoint cliques. 相似文献