全文获取类型
收费全文 | 5553篇 |
免费 | 395篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 57篇 |
综合类 | 5篇 |
化学工业 | 1474篇 |
金属工艺 | 77篇 |
机械仪表 | 159篇 |
建筑科学 | 219篇 |
矿业工程 | 13篇 |
能源动力 | 199篇 |
轻工业 | 1065篇 |
水利工程 | 66篇 |
石油天然气 | 27篇 |
无线电 | 375篇 |
一般工业技术 | 740篇 |
冶金工业 | 276篇 |
原子能技术 | 24篇 |
自动化技术 | 1177篇 |
出版年
2024年 | 15篇 |
2023年 | 64篇 |
2022年 | 196篇 |
2021年 | 278篇 |
2020年 | 188篇 |
2019年 | 205篇 |
2018年 | 234篇 |
2017年 | 201篇 |
2016年 | 248篇 |
2015年 | 201篇 |
2014年 | 249篇 |
2013年 | 579篇 |
2012年 | 385篇 |
2011年 | 509篇 |
2010年 | 340篇 |
2009年 | 308篇 |
2008年 | 285篇 |
2007年 | 226篇 |
2006年 | 184篇 |
2005年 | 123篇 |
2004年 | 132篇 |
2003年 | 104篇 |
2002年 | 105篇 |
2001年 | 52篇 |
2000年 | 54篇 |
1999年 | 60篇 |
1998年 | 83篇 |
1997年 | 57篇 |
1996年 | 45篇 |
1995年 | 40篇 |
1994年 | 28篇 |
1993年 | 22篇 |
1992年 | 11篇 |
1991年 | 14篇 |
1990年 | 15篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 11篇 |
1986年 | 7篇 |
1985年 | 13篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1975年 | 3篇 |
1967年 | 3篇 |
排序方式: 共有5953条查询结果,搜索用时 15 毫秒
201.
Carmen Coya Constanza Ruiz Ángel Luis Álvarez Susana Álvarez-García Eva M. García-Frutos Berta Gómez-Lor Alicia de Andrés 《Organic Electronics》2012,13(10):2138-2148
We present a series of differently substituted star-shaped hexaaryltriindoles with tunable light-emitting properties. The deep blue emission is unchanged by donor peripheral substituents while an increasing acceptor character produces a reduction of the optical gap, an increased Stokes shift and eventually leads to the appearance of a new electronic level and to the simultaneous deep blue (413 nm) and green (552 nm) emission in solution. Quenching by concentration increases with the acceptor character but is lower as the tendency of these compounds to aggregate is stronger. Solution processed thin films present optical and morphological qualities adequate for device fabrication and similar electronic structure compared to solutions with an emission range from 423 nm up to 657 nm (red), demonstrating the possibility of tuning the energy levels by chemical functionalization. We have fabricated and characterized single-layer solution processed organic light emitting diodes (OLED) to investigate the influence on transport and emission properties of the substituting species. We analyzed the I–V response using a single-carrier numerical model that includes injection barriers and non-uniform electric-field across the layer. As a result, we obtained the electric field dependence of the mobility for each device. Best results are obtained on the most electron rich derivative functionalized with six donor methoxy groups. This material shows the highest emission efficiency in solid state, due to aggregation-induced enhancement, and better transport properties with the highest mobility and a very low turn-on voltage of 2.8 V. The solution processed OLED devices produce stable deep blue (CIE coordinates (0.16, 0.16)) to white (CIE coordinates (0.33, 0.3)) emission with similar luminous efficiencies. 相似文献
202.
Asteria Luzardo‐Álvarez Álvaro Antelo‐Queijo Victor H. Soto José Blanco‐Méndez 《应用聚合物科学杂志》2012,123(6):3595-3604
Hydrophobically modified chitosan containing β‐cyclodextrin (CD) units was synthesized by using tosylated β‐CD. The final product was characterized by Fourier transform infrared (FTIR) spectroscopy, elemental analysis and TGA, and rheometry. The polymer bearing β‐CD moieties was used to obtain crosslinked microparticles by spray‐drying which could then be used in a controlled release system for drugs. FTIR confirmed the formation of an amide linkage between cyclodextrin and chitosan. As fluorescence spectroscopy demonstrated, hydrophobic microenvironments were formed by chitosan bearing cyclodextrin in solution at lower concentrations than for chitosan. Rheometry and FTIR showed the crosslinking of the new polymer using genipin, a molecule of natural origin. Microspheres (MS) obtained by spray‐drying showed narrow size distribution when β‐CD was grafted onto chitosan and ξ‐potential of MS was slightly lower although it remained positive. In conclusion, β‐CD linked chitosan polymer can be considered as a very promising controlled drug delivery system for drugs. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
203.
204.
205.
206.
Natalia Veizaga José Fernandez Mariano Bruno Osvaldo Scelza Sergio de Miguel 《International Journal of Hydrogen Energy》2012,37(23):17910-17920
The objective of this study is to evaluate different methods to obtain Pt (20 wt%)/carbon electrocatalysts, in order to identify the conditions that lead to electrocatalysts with the best electrochemical performance. This paper involves the study of different methods for the deposition and reduction of H2PtCl6 on three carbon supports: Vulcan carbon, Multiwall carbon nanotubes and mesoporous carbons. The deposition–reduction methods in liquid phase were carried out with HCOOH or NaBH4 as reducing agents. Besides, the conventional impregnation was carried out by deposition of H2PtCl6 on carbon followed by a reduction with H2 at high temperature. The electrochemical performance of supported Pt catalysts prepared by reduction in liquid phase is strongly dependent on the metallic dispersion, the particle size distribution and the nature of the carbonaceous material used as a support. Results show that the deposition–reduction method using HCOOH 0.3 M at 50–60 °C and a mesoporous carbon leads to the most efficient electrocatalyst. 相似文献
207.
208.
Pablo H. Ibargüengoytia Miguel Angel Delgadillo Uriel A. García Alberto Reyes 《Engineering Applications of Artificial Intelligence》2013,26(9):2153-2163
Thermo-electrical power plants utilize fossil fuel oil to transform the calorific power of fuel into electric power. An optimal combustion in the boiler requires the fuel oil to be in its best conditions. One of fuel's most important properties to consider is viscosity. Viscosity has influence on the optimal combustion between fuel and air. Hardware viscosity meters for fuel oils are expensive and unreliable to operate in power plant conditions. Chemical laboratory measures viscosity accurately with special apparatus, but they cannot be used in a real time process. This paper describes the development of a virtual sensor that estimates fuel oil viscosity in the combustion process of a power plant. A virtual sensor or soft sensor is a computer program that estimates the value of a certain variable based on related measurements and a model of the process where the variable participates. In this project, a probabilistic model is constructed using automatic learning algorithms with historical data and experts' advice. The learning and validation experiments are described and discussed. The virtual sensor is installed in the Tuxpan Power Plant in Veracruz, Mexico. 相似文献
209.
Quoc Ahn Tran Bastien Chevalier Miguel Angel Benz-Navarrete Pierre Breul Roland Gourvès 《Soils and Foundations》2019,59(6):2348-2355
This paper presents a calculation method for obtaining the continuous variation in stress between the tip and the soil during dynamic penetration tests, particularly in the case of using the Panda 3® penetration testing device. The originality of the method is that the tip stress can be computed continuously throughout the driving process. For each impact of the hammer on the penetrometer, data are recorded by sensors located at the top of the apparatus. Then, the stress at the tip and the displacement of the apparatus are calculated with a method based on the propagation of waves in the device. A three-dimensional numerical model of the penetration test, based on the Panda 3® specifications and using the discrete element method (DEM), is proposed in this paper. The purpose of the simulations is to validate the calculation method by comparing the curves of the tip stress versus the penetration distance obtained in two different ways, the first being the distance directly observed at the tip and the second being the distance calculated from the data recorded at the top of the penetrometer, as with the experimental device. The entire apparatus is represented, including the hammer, the rod, and the tip, and is driven into the model soil. The calculation method is applied, and the results are compared to the actual response of the soil to the driving of the penetrometer directly at the tip, which can be obtained with the numerical model. The responses are found to be very similar, confirming the theoretical framework and its underlying assumptions. This method is applied to dynamic penetration tests and provides the opportunity to obtain mechanical parameters other than the tip resistance from the tests. 相似文献
210.