全文获取类型
收费全文 | 3139篇 |
免费 | 191篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 46篇 |
综合类 | 11篇 |
化学工业 | 660篇 |
金属工艺 | 75篇 |
机械仪表 | 51篇 |
建筑科学 | 153篇 |
矿业工程 | 8篇 |
能源动力 | 64篇 |
轻工业 | 260篇 |
水利工程 | 18篇 |
石油天然气 | 3篇 |
无线电 | 239篇 |
一般工业技术 | 620篇 |
冶金工业 | 577篇 |
原子能技术 | 8篇 |
自动化技术 | 538篇 |
出版年
2024年 | 7篇 |
2023年 | 46篇 |
2022年 | 29篇 |
2021年 | 75篇 |
2020年 | 76篇 |
2019年 | 62篇 |
2018年 | 92篇 |
2017年 | 78篇 |
2016年 | 119篇 |
2015年 | 84篇 |
2014年 | 114篇 |
2013年 | 172篇 |
2012年 | 165篇 |
2011年 | 200篇 |
2010年 | 143篇 |
2009年 | 158篇 |
2008年 | 148篇 |
2007年 | 145篇 |
2006年 | 121篇 |
2005年 | 79篇 |
2004年 | 89篇 |
2003年 | 66篇 |
2002年 | 50篇 |
2001年 | 58篇 |
2000年 | 35篇 |
1999年 | 61篇 |
1998年 | 171篇 |
1997年 | 122篇 |
1996年 | 79篇 |
1995年 | 49篇 |
1994年 | 43篇 |
1993年 | 43篇 |
1992年 | 19篇 |
1991年 | 24篇 |
1990年 | 18篇 |
1989年 | 22篇 |
1988年 | 20篇 |
1987年 | 20篇 |
1986年 | 8篇 |
1985年 | 28篇 |
1984年 | 15篇 |
1983年 | 10篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 12篇 |
1978年 | 10篇 |
1977年 | 12篇 |
1976年 | 35篇 |
1974年 | 6篇 |
1973年 | 8篇 |
排序方式: 共有3331条查询结果,搜索用时 15 毫秒
1.
Knaust Thiemo Felnhofer Anna Kothgassner Oswald D. Hllmer Helge Gorzka Robert-Jacek Schulz Holger 《Virtual Reality》2022,26(3):925-938
Virtual Reality - It is generally accepted that natural environments reduce stress and improve mood. Since access to natural environments is sometimes limited, virtual natural environments,... 相似文献
2.
Jiajia Suo Bowen Yang Edoardo Mosconi Hyeon-Seo Choi YeonJu Kim Shaik M. Zakeeruddin Filippo De Angelis Michael Grätzel Hui-Seon Kim Anders Hagfeldt 《Advanced functional materials》2021,31(34):2102902
Surface passivation treatment is a widely used strategy to resolve trap-mediated nonradiative recombination toward high-efficiency metal-halide perovskite photovoltaics. However, a lack of passivation with mixture treatment has been investigated, as well as an in-depth understanding of its passivation mechanism. Here, a systematic study on a mixed-salt passivation strategy of formamidinium bromide (FABr) coupled with different F-substituted alkyl lengths of ammonium iodide is demonstrated. It is obtained better device performance with decreasing chain length of the F-substituted alkyl ammonium iodide in the presence of FABr. Moreover, they unraveled a synergistic passivation mechanism of the mixed-salt treatment through surface reconstruction engineering, where FABr dominates the reformation of the perovskite surface via reacting with the excess PbI2. Meanwhile, ammonium iodide passivates the perovskite grain boundaries both on the surface and top perovskite bulk through penetration. This synergistic passivation engineer results in a high-quality perovskite surface with fewer defects and suppressed ion migration, leading to a champion efficiency of 23.5% with mixed-salt treatment. In addition, the introduction of the moisture resisted F-substituted groups presents a more hydrophobic perovskite surface, thus enabling the decorated devices with excellent long-term stability under a high humid atmosphere as well as operational conditions. 相似文献
3.
Bilal Alashkar Alhamwe Daniel P. Potaczek Sarah Miethe Fahd Alhamdan Lukas Hintz Arslan Magomedov Holger Garn 《International journal of molecular sciences》2021,22(9)
Extracellular vesicles (EVs) are membranous structures, which are secreted by almost every cell type analyzed so far. In addition to their importance for cell-cell communication under physiological conditions, EVs are also released during pathogenesis and mechanistically contribute to this process. Here we summarize their functional relevance in asthma, one of the most common chronic non-communicable diseases. Asthma is a complex persistent inflammatory disorder of the airways characterized by reversible airflow obstruction and, from a long-term perspective, airway remodeling. Overall, mechanistic studies summarized here indicate the importance of different subtypes of EVs and their variable cargoes in the functioning of the pathways underlying asthma, and show some interesting potential for the development of future therapeutic interventions. Association studies in turn demonstrate a good diagnostic potential of EVs in asthma. 相似文献
4.
Simon Neumann Pin Hu Felix Bretschneider Holger Schmalz Andreas Greiner 《大分子材料与工程》2021,306(7):2100090
In this study, blends of the bio-based poly(limonene carbonate) (PLimC) with different commodity polymers are investigated in order to explore the potential of PLimC toward generating more sustainable polymer materials by reducing the amount of petro- or food-based polymers. PLimC is employed as minority component in the blends. Next to the morphology and thermal properties of the blends the impact of PLimC on the mechanical properties of the matrix polymers is studied. The interplay of incompatibility and zero-shear melt viscosity contrast determines the blend morphology, leading for all blends to a dispersed droplet morphology for PLimC. Blends with polymers of similar structure to PLimC (i.e., aliphatic/aromatic polyester) show the best performance with respect to mechanical properties, whereas blends with polystyrene or poly(methyl methacrylate) are too brittle and polyamide 12 blends show very low elongations at break. In blends with Ecoflex (poly(butylene adipate-co-terephthalate)) and Arnitel EM400 (copoly(ether ester)) with poly(butylene terephthalate) hard and polytetrahydrofuran soft segments) a threefold increase in E-modulus can be achieved, while keeping the elongation at break at reasonable high values of ≈200%, making these blends highly interesting for applications. 相似文献
5.
6.
Dr. Alexander Fries Dr. Laura S. Mazzaferro Dr. Björn Grüning Dr. Philippe Bisel Karin Stibal Patrick C. F. Buchholz Prof. Dr. Jürgen Pleiss Prof. Dr. Georg A. Sprenger Prof. Dr. Michael Müller 《Chembiochem : a European journal of chemical biology》2019,20(13):1672-1677
Chorismate and isochorismate constitute branch-point intermediates in the biosynthesis of many aromatic metabolites in microorganisms and plants. To obtain unnatural compounds, we modified the route to menaquinone in Escherichia coli. We propose a model for the binding of isochorismate to the active site of MenD ((1R,2S, 5S,6S)-2-succinyl-5-enolpyruvyl-6-hydroxycyclohex-3-ene-1-carboxylate (SEPHCHC) synthase) that explains the outcome of the native reaction with α-ketoglutarate. We have rationally designed variants of MenD for the conversion of several isochorismate analogues. The double-variant Asn117Arg–Leu478Thr preferentially converts (5S,6S)-5,6-dihydroxycyclohexa-1,3-diene-1-carboxylate (2,3-trans-CHD), the hydrolysis product of isochorismate, with a >70-fold higher ratio than that for the wild type. The single-variant Arg107Ile uses (5S,6S)-6-amino-5-hydroxycyclohexa-1,3-diene-1-carboxylate (2,3-trans-CHA) as substrate with >6-fold conversion compared to wild-type MenD. The novel compounds have been made accessible in vivo (up to 5.3 g L−1). Unexpectedly, as the identified residues such as Arg107 are highly conserved (>94 %), some of the designed variations can be found in wild-type SEPHCHC synthases from other bacteria (Arg107Lys, 0.3 %). This raises the question for the possible natural occurrence of as yet unexplored branches of the shikimate pathway. 相似文献
7.
8.
9.
Overproduction of proteinase A by recombinant Saccharomyces cerevisiae was investigated by cultivations in a cell-recycling bioreactor. Membrane filtration was used to separate cells from the broth. Recycling ratios and dilution rates were varied and the effect on enzyme production was studied both experimentally and by computer simulations. Experiments and simulations showed that cell mass and product concentration were enhanced by high ratios of recycling. Additional simulations showed that the proteinase A concentration decreased drastically at high dilution rates and the optimal volumetric productivities were at high dilution rates just below washout and at high ratios of recycling. Cell-recycling fermentation gave much higher volumetric productivities and stable product concentrations in contrast to simple continuous fermentation. 相似文献
10.
Dr.-Ing. Holger Boche 《Forschung im Ingenieurwesen》1996,62(10):291-299
Zusammenfassung Bei der praktischen Anwendung der analytischen Signale ist es erforderlich, die Ermittlung der Hilbert-Transformation numerisch
durchzuführen. Dazu wurden u.a. Verfahren von H.W. Schü?ler, R. Unbehauen und G. Wunsch vorgeschlagen. In der Arbeit werden
allgemeine Ergebnisse zur numerischen Umsetzung der Hilbert-Transformation dargestellt. Es wird gezeigt, da? alle praktisch
realisierbaren Verfahren für bestimmte Signale divergieren. Damit ist es m?glich, die in der Experimentalphysik schon l?nger
bekannten Schwierigkeiten bei der Umsetzung der Hilbert-Transformation zu erkl?ren. 相似文献