全文获取类型
收费全文 | 7019篇 |
免费 | 407篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 99篇 |
综合类 | 28篇 |
化学工业 | 1962篇 |
金属工艺 | 184篇 |
机械仪表 | 153篇 |
建筑科学 | 416篇 |
矿业工程 | 39篇 |
能源动力 | 248篇 |
轻工业 | 480篇 |
水利工程 | 42篇 |
石油天然气 | 5篇 |
无线电 | 609篇 |
一般工业技术 | 1485篇 |
冶金工业 | 322篇 |
原子能技术 | 44篇 |
自动化技术 | 1316篇 |
出版年
2024年 | 14篇 |
2023年 | 102篇 |
2022年 | 152篇 |
2021年 | 270篇 |
2020年 | 187篇 |
2019年 | 192篇 |
2018年 | 191篇 |
2017年 | 186篇 |
2016年 | 283篇 |
2015年 | 299篇 |
2014年 | 353篇 |
2013年 | 506篇 |
2012年 | 476篇 |
2011年 | 629篇 |
2010年 | 414篇 |
2009年 | 421篇 |
2008年 | 405篇 |
2007年 | 356篇 |
2006年 | 279篇 |
2005年 | 251篇 |
2004年 | 192篇 |
2003年 | 152篇 |
2002年 | 151篇 |
2001年 | 74篇 |
2000年 | 100篇 |
1999年 | 92篇 |
1998年 | 87篇 |
1997年 | 82篇 |
1996年 | 95篇 |
1995年 | 60篇 |
1994年 | 53篇 |
1993年 | 49篇 |
1992年 | 49篇 |
1991年 | 36篇 |
1990年 | 22篇 |
1989年 | 20篇 |
1988年 | 18篇 |
1987年 | 21篇 |
1986年 | 14篇 |
1985年 | 18篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1972年 | 5篇 |
1967年 | 3篇 |
1954年 | 3篇 |
排序方式: 共有7432条查询结果,搜索用时 0 毫秒
991.
Amir Sammak Diego Sabbagh Nico W. Hendrickx Mario Lodari Brian Paquelet Wuetz Alberto Tosato LaReine Yeoh Monica Bollani Michele Virgilio Markus Andreas Schubert Peter Zaumseil Giovanni Capellini Menno Veldhorst Giordano Scappucci 《Advanced functional materials》2019,29(14)
Buried‐channel semiconductor heterostructures are an archetype material platform for the fabrication of gated semiconductor quantum devices. Sharp confinement potential is obtained by positioning the channel near the surface; however, nearby surface states degrade the electrical properties of the starting material. Here, a 2D hole gas of high mobility (5 × 105 cm2 V?1 s?1) is demonstrated in a very shallow strained germanium (Ge) channel, which is located only 22 nm below the surface. The top‐gate of a dopant‐less field effect transistor controls the channel carrier density confined in an undoped Ge/SiGe heterostructure with reduced background contamination, sharp interfaces, and high uniformity. The high mobility leads to mean free paths ≈ 6 µm, setting new benchmarks for holes in shallow field effect transistors. The high mobility, along with a percolation density of 1.2 × 1011cm?2, light effective mass (0.09me), and high effective g‐factor (up to 9.2) highlight the potential of undoped Ge/SiGe as a low‐disorder material platform for hybrid quantum technologies. 相似文献
992.
Kolleboyina Jayaramulu Deepak P. Dubal Andreas Schneemann Vclav Ranc Cecilia Perez‐Reyes Jana Strsk tpn Kment Michal Otyepka Roland A. Fischer Radek Zboil 《Advanced functional materials》2019,29(38)
Herein, a novel polymer‐templated strategy is described to obtain 2D nickel‐based MOF nanosheets using Ni(OH)2, squaric acid, and polyvinylpyrrolidone (PVP), where PVP has a dual role as a structure‐directing agent, as well as preventing agglomeration of the MOF nanosheets. Furthermore, a scalable method is developed to transform the 2D MOF sheets to Ni7S6/graphene nanosheet (GNS) heterobilayers by in situ sulfidation using thiourea as a sulfur source. The Ni7S6/GNS composite shows an excellent reversible capacity of 1010 mAh g?1 at 0.12 A g?1 with a Coulombic efficiency of 98% capacity retention. The electrochemical performance of the Ni7S6/GNS composite is superior not only to nickel sulfide/graphene‐based composites but also to other metal disulfide–based composite electrodes. Moreover, the Ni7S6/GNS anode exhibits excellent cycle stability (≈95% capacity retention after 2000 cycles). This outstanding electrochemical performance can be attributed to the synergistic effects of Ni7S6 and GNS, where GNS serves as a conducting matrix to support Ni7S6 nanosheets while Ni7S6 prevents restacking of GNS. This work opens up new opportunities in the design of novel functional heterostructures by hybridizing 2D MOF nanosheets with other 2D nanomaterials for electrochemical energy storage/conversion applications. 相似文献
993.
Matthias Diethelm Andreas Schiller Maciej Kawecki Andrius Deviis Balthasar Blülle Sandra Jenatsch Evelyne Knapp Quirin Grossmann Beat Ruhstaller Frank Nüesch Roland Hany 《Advanced functional materials》2020,30(33)
In light‐emitting electrochemical cells (LECs), the position of the emission zone (EZ) is not predefined via a multilayer architecture design, but governed by a complex motion of electrical and ionic charges. As a result of the evolution of doped charge transport layers that enclose a dynamic intrinsic region until steady state is reached, the EZ is often dynamic during turn‐on. For thick sandwich polymer LECs, a continuous change of the emission color provides a direct visual indication of a moving EZ. Results from an optical and electrical analysis indicate that the intrinsic zone is narrow at early times, but starts to widen during operation, notably well before the electrical device optimum is reached. Results from numerical simulations demonstrate that the only precondition for this event to occur is that the mobilities of anions (μa) and cations (μc) are not equal, and the direction of the EZ shift dictates μc > μa. Quantitative ion profiles reveal that the displacement of ions stops when the intrinsic zone stabilizes, confirming the relation between ion movement and EZ shift. Finally, simulations indicate that the experimental current peak for constant‐voltage operation is intrinsic and the subsequent decay does not result from degradation, as commonly stated. 相似文献
994.
Effect of alternating postures on cognitive performance for healthy people performing sedentary work
Bernhard Schwartz Jay M. Kapellusch Andreas Schrempf Kathrin Probst Michael Haller Arnold Baca 《Ergonomics》2018,61(6):778-795
Prolonged sitting is a risk factor for several diseases and the prevalence of worksite-based interventions such as sit-to-stand workstations is increasing. Although their impact on sedentary behaviour has been regularly investigated, the effect of working in alternating body postures on cognitive performance is unclear. To address this uncertainty, 45 students participated in a two-arm, randomised controlled cross-over trial under laboratory conditions. Subjects executed validated cognitive tests (working speed, reaction time, concentration performance) either in sitting or alternating working postures on two separate days (ClinicalTrials.gov Identifier: NCT02863731). MANOVA results showed no significant difference in cognitive performance between trials executed in alternating, standing or sitting postures. Perceived workload did not differ between sitting and alternating days. Repeated measures ANOVA revealed significant learning effects regarding concentration performance and working speed for both days. These results suggest that working posture did not affect cognitive performance in the short term.
Practitioner Summary: Prior reports indicated health-related benefits based on alternated (sit/stand) body postures. Nevertheless, their effect on cognitive performance is unknown. This randomised controlled trial showed that working in alternating body postures did not influence reaction time, concentration performance, working speed or workload perception in the short term. 相似文献
995.
996.
Historic masonry buildings under earthquakes – Load‐bearing behaviour in contradiction to the currently applied methods of analysis The stability of historic masonry buildings must be guaranteed not only under normal conditions, but also during natural disasters. The seismic assessment of the masonry buildings of the Gründerzeit (1840–1918) in Vienna is a central topic in the qualitative and constructive assessment. Although masonry construction has been used for many centuries, the realistic evaluation of the load‐bearing behaviour is still a complex challenge. The methods of analysis according to current regulations are only insufficiently able to reflect the real load‐bearing behaviour and the possible activation of global failure mechanisms. As a result, the simplified verification is often difficult to calculate for many historic buildings, and questionable reinforcement measures are taken to compensate, even though the buildings have already experienced several earthquakes and survived most of them without damage. The present work deals with the approaches of current methods of analysis and aims to identify problem points and to compare them with time history analysis, which is supported by a powerful material model based on test series. It is shown that the conventional analysis for the historic masonry buildings without consideration of the interaction and load transfer effects as well as the characteristic construction methods only partially reflect the real load‐bearing behaviour. The work is intended to be a contribution to the technical expert discussions on the seismic safety of historic buildings and to stimulate the discussion on the formulation of realistic methods of analysis. 相似文献
997.
998.
Herbert Canziani Salvatore Chiera Thomas Schuffenhauer Sebastian‐Paul Kopp Florian Metzger Andreas Bück Michael Schmidt Nicolas Vogel 《Small (Weinheim an der Bergstrasse, Germany)》2020,16(30)
Additive manufacturing promises high flexibility and customized product design. Powder bed fusion processes use a laser to melt a polymer powder at predefined locations and iterate the scheme to build 3D objects. The design of flowable powders is a critical parameter for a successful fabrication process that currently limits the choice of available materials. Here, a bottom‐up process is introduced to fabricate tailored polymer‐ and composite supraparticles for powder‐based additive manufacturing processes by controlled aggregation of colloidal primary particles. These supraparticles exhibit a near‐spherical shape and tailored composition, morphology, and surface roughness. These parameters can be precisely controlled by the mixing and size ratio of the primary particles. Polystyrene/silica composite particles are chosen as a model system to establish structure–property relations connecting shape, morphology, and surface roughness to the adhesion within the powder, which is accessed by tensile strength measurements. The adhesive properties are then connected to powder flowability and it is shown that the resulting powders allow the formation of dense powder films with uniform coverage. Finally, successful powder bed fusion is demonstrated by producing macroscopic single layer specimens with uniform distribution of nanoscale silica additives. 相似文献
999.
1000.