全文获取类型
收费全文 | 1837篇 |
免费 | 93篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 23篇 |
综合类 | 1篇 |
化学工业 | 388篇 |
金属工艺 | 45篇 |
机械仪表 | 30篇 |
建筑科学 | 52篇 |
矿业工程 | 2篇 |
能源动力 | 76篇 |
轻工业 | 160篇 |
水利工程 | 10篇 |
石油天然气 | 2篇 |
无线电 | 180篇 |
一般工业技术 | 363篇 |
冶金工业 | 272篇 |
原子能技术 | 18篇 |
自动化技术 | 310篇 |
出版年
2023年 | 15篇 |
2022年 | 15篇 |
2021年 | 54篇 |
2020年 | 35篇 |
2019年 | 57篇 |
2018年 | 52篇 |
2017年 | 43篇 |
2016年 | 57篇 |
2015年 | 53篇 |
2014年 | 75篇 |
2013年 | 117篇 |
2012年 | 108篇 |
2011年 | 163篇 |
2010年 | 116篇 |
2009年 | 103篇 |
2008年 | 104篇 |
2007年 | 85篇 |
2006年 | 81篇 |
2005年 | 58篇 |
2004年 | 34篇 |
2003年 | 39篇 |
2002年 | 32篇 |
2001年 | 17篇 |
2000年 | 20篇 |
1999年 | 23篇 |
1998年 | 59篇 |
1997年 | 50篇 |
1996年 | 38篇 |
1995年 | 27篇 |
1994年 | 25篇 |
1993年 | 23篇 |
1992年 | 7篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 11篇 |
1976年 | 14篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 4篇 |
排序方式: 共有1932条查询结果,搜索用时 15 毫秒
991.
Volume Bragg gratings (VBGs) in photothermorefractive (PTR) glass are widely used for laser beam control including high-power laser systems. Among them, spectral beam combining based on VBGs is one of the most promising. Achieving 100+ kW of combined laser beams requires the development of PTR glass and VBGs with an extremely low absorption coefficient and therefore methods of its measurement. This paper describes the calorimetric method that was developed for measuring a low absorption coefficient in PTR glass and VBGs. It is based on transmission monitoring of the intrinsic Fabry-Perot interferometer produced by the plane-parallel surfaces of the measured optical elements when heated by high-power laser radiation. An absorption coefficient at 1085 nm as low as 5×10(-5) cm(-1) is demonstrated in pristine PTR glass while an absorption coefficient as low as 1×10(-4) cm(-1) is measured in high-efficiency reflecting Bragg gratings with highest purity. The actual level of absorption in PTR glass allows laser beam control at the 10 kW level, while the 100 kW level would require active cooling and/or decreasing the absorption in PTR Bragg gratings to a value similar to that in virgin PTR glass. 相似文献
992.
Obadia L Julien M Quillard S Rouillon T Pilet P Guicheux J Bujoli B Bouler JM 《Journal of materials science. Materials in medicine》2011,22(3):593-600
Synthetic calcium phosphate ceramics as β-tricalcium phosphate (Ca3(PO4)2; β-TCP) are currently successfully used in human bone surgery. The aim of this work was to evaluate the influence of the
presence of sodium ion in β-TCP on its mechanical and biological properties. Five Na-doped-β-TCP [Ca10.5−x/2Na
x
(PO4)7, 0 ≤ x ≤ 1] microporous pellets were prepared via solid phase synthesis, and their physico-chemical data (lattice compacity, density,
porosity, compressive strength, infrared spectra) denote an increase of the mechanical properties and a decrease of the solubility
when the sodium content is raised. On the other hand, the in vitro study of MC3T3-E1 cell activity (morphology, MTS assay
and ALP activity) shows that the incorporation of sodium does not modify the bioactivity of the β-TCP. These results strongly
suggest that Na-doped-β-TCP appear to be good candidates for their use as bone substitutes. 相似文献
993.
994.
Strachan JP Strukov DB Borghetti J Yang JJ Medeiros-Ribeiro G Williams RS 《Nanotechnology》2011,22(25):254015
Memristors are memory resistors promising a rapid integration into future memory technologies. However, progress is still critically limited by a lack of understanding of the physical processes occurring at the nanoscale. Here we correlate device electrical characteristics with local atomic structure, chemistry and temperature. We resolved a single conducting channel that is made up of a reduced phase of the as-deposited titanium oxide. Moreover, we observed sufficient Joule heating to induce a crystallization of the oxide surrounding the channel, with a peculiar pattern that finite element simulations correlated with the existence of a hot spot close to the bottom electrode, thus identifying the switching location. This work reports direct observations in all three dimensions of the internal structure of titanium oxide memristors. 相似文献
995.
Carrier depletion and transport in a single ZnO nanowire Schottky device have been investigated at 5?K, using cathodoluminescence measurements. An exciton diffusion length of 200?nm has been determined along the nanowire axis. The depletion width is found to increase linearly with the reverse bias. The origin of this unusual dependence in semiconductor material is discussed in terms of charge location and dimensional effects on the screening of the junction electric field. 相似文献
996.
Adrian J Postal V Moessinger M Rascle N Charles A 《Accident; analysis and prevention》2011,(5):1652-1659
The present study investigated how executive functions and personality traits are related with driving performance among older drivers. Forty-two participants aged 60 and over were recruited to complete a battery of cognitive tests, measures of personality traits and an on-road driving test. Significant correlations were found between poor driving performances and low scores on tests assessing shifting and updating functions. In addition, extraversion had a negative relation with driving performance and made the only contribution, among the psychological factors, to the prediction of driving performance. Finally, gender and age emerged as the best predictors of on-road driving performance. Gender, personality traits and executive functions should be taken into account when studying safety among older drivers. 相似文献
997.
In this work, the analytical potential of cyclical electrical field flow fractionation (CyElFFF) for nanomaterial and colloidal particle characterization has been experimentally demonstrated. Different operating parameters were investigated in order to evaluate their effect on the mechanisms of retention and fractionation power of CyElFFF. The voltage and frequency of the oscillating electrical field appeared to be the most influential parameters controlling the separation mode. Mobile phase flow rate was also found to be a key parameter controlling the fractionation efficiency. This work allowed the definition of operating conditions such that a reliable CyElFFF analysis could be performed on different nanoparticles on the basis of the direct comparison of their theoretical and experimental behavior. The results show that this technique in optimized conditions is a powerful tool for electrophoretic mobility based separation and characterization of various nanoparticles. 相似文献
998.
Size exclusion chromatography (SEC) on a semipreparative scale (10 mg and more) was used to size-select ultrasmall gold nanoclusters (<2 nm) from polydisperse mixtures. In particular, the ubiquitous byproducts of the etching process toward Au(38)(SR)(24) (SR, thiolate) clusters were separated and gained in high monodispersity (based on mass spectrometry). The isolated fractions were characterized by UV-vis spectroscopy, MALDI mass spectrometry, HPLC, and electron microscopy. Most notably, the separation of Au(38)(SR)(24) and Au(40)(SR)(24) clusters is demonstrated. 相似文献
999.
Robert Zierold Zhenyu Wu Johannes Biskupek Ute Kaiser Julien Bachmann Carl E. Krill III Kornelius Nielsch 《Advanced functional materials》2011,21(2):226-232
This work presents a synthesis route for low‐aspect‐ratio nanotubes consisting of a layer of magnetite (Fe3O4) sandwiched between SiO2 layers. In this template‐based strategy, self‐ordered porous alumina membranes are combined with the atomic layer deposition of SiO2 and Fe2O3. An optimized electrochemical setup yields nanoporous Al2O3 membranes on 4‐inch Al substrates, which serve as templates for the large‐scale fabrication of nanotubes. A selective chemical etching step releases the magnetic tubes for suspension in a carrier fluid and permits recycling of the underlying aluminum foils for the fabrication of subsequent nanotube batches. The nanotubes consisting of an iron oxide layer protected by a silica shell are magnetically characterized in suspensions as well as in dried form on a substrate. High‐resolution transmission electron imaging reveals a polycrystalline, magnetite spinel structure of iron oxide, with the proper stoichiometry proven by the presence of the Verwey transition. Furthermore, field‐dependent viscosity measurements show an enhancement of the magnetoviscosity, thus demonstrating the technological potential of nanotube suspensions as a new class of ferrofluidic solutions. Owing to the tubular shape being closed at one end, these nanoparticles might additionally function as magnetic containers for targeted drug‐delivery or as chemical nanoreactors. 相似文献
1000.
The objective of this study is to estimate the technical and economic feasibilities of hydrogen applied to automotive traction. The problems of mass storage and transportation of hydrogen, capillary distribution, storage aboard vehicles and those concerning hydrogen thermal engines and hydrogen fuel cells are investigated. The different ways of using hydrogen, either compressed or liquefied or combined in hydrides, are taken into account.Energy and economic balance sheets lead to the conclusion that hydrogen internal combustion engines cannot compete with gasoline engines with regard to primary energy consumption and fuel cost. To the contrary, a hydrogen fuel cell, thanks to its high efficiency, provides for appreciable energy saving and leads to a fuel expense of the same order of magnitude as premium gasoline in an urban vehicle. 相似文献