全文获取类型
收费全文 | 2650篇 |
免费 | 171篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 37篇 |
综合类 | 2篇 |
化学工业 | 697篇 |
金属工艺 | 45篇 |
机械仪表 | 67篇 |
建筑科学 | 109篇 |
矿业工程 | 1篇 |
能源动力 | 91篇 |
轻工业 | 272篇 |
水利工程 | 18篇 |
石油天然气 | 3篇 |
无线电 | 231篇 |
一般工业技术 | 406篇 |
冶金工业 | 150篇 |
原子能技术 | 20篇 |
自动化技术 | 676篇 |
出版年
2024年 | 4篇 |
2023年 | 42篇 |
2022年 | 101篇 |
2021年 | 177篇 |
2020年 | 79篇 |
2019年 | 76篇 |
2018年 | 117篇 |
2017年 | 69篇 |
2016年 | 134篇 |
2015年 | 88篇 |
2014年 | 128篇 |
2013年 | 205篇 |
2012年 | 180篇 |
2011年 | 234篇 |
2010年 | 145篇 |
2009年 | 150篇 |
2008年 | 150篇 |
2007年 | 125篇 |
2006年 | 106篇 |
2005年 | 81篇 |
2004年 | 62篇 |
2003年 | 55篇 |
2002年 | 42篇 |
2001年 | 23篇 |
2000年 | 26篇 |
1999年 | 29篇 |
1998年 | 41篇 |
1997年 | 33篇 |
1996年 | 34篇 |
1995年 | 15篇 |
1994年 | 18篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1990年 | 1篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1969年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有2825条查询结果,搜索用时 15 毫秒
161.
Subir Parui Luca Pietrobon David Ciudad Saül Vélez Xiangnan Sun Fèlix Casanova Pablo Stoliar Luis E. Hueso 《Advanced functional materials》2015,25(20):2972-2979
The formation of an energy‐barrier at a metal/molecular semiconductor junction is a universal phenomenon which limits the performance of many molecular semiconductor‐based electronic devices, from field‐effect transistors to light‐emitting diodes. In general, a specific metal/molecular semiconductor combination of materials leads to a fixed energy‐barrier. However, in this work, a graphene/C60 vertical field‐effect transistor is presented in which control of the interfacial energy‐barrier is demonstrated, such that the junction switches from a highly rectifying diode at negative gate voltages to a highly conductive nonrectifying behavior at positive gate voltages and at room temperature. From the experimental data, an energy‐barrier modulation of up to 660 meV, a transconductance of up to five orders of magnitude, and a gate‐modulated photocurrent are extracted. The ability to tune the graphene/molecular semiconductor energy‐barrier provides a promising route toward novel, high performance molecular devices. 相似文献
162.
D. A. De Luca E. Destefanis M. G. Forno M. Lasagna L. Masciocco 《Bulletin of Engineering Geology and the Environment》2014,73(2):409-427
The fontanili are typical lowland springs that occur in Northern Italy along the transition zone from high to low plain (the “fontanili line”), due to changes in both the slope surface and the sediment grain size. These resurgences of phreatic water were investigated in the western sector of the Po Plain in the Turin Province. Although the available bibliographic data through 2005 reveal the occurrence of 111 fontanili in the study area, only 51 preserved fontanili have been identified in field surveys. The main morphological and geological features of these resurgences were recorded and entered into a database. In addition, the small-scale hydrogeologic framework of these fontanili was clarified by means of lithostratigraphic cross-sections. Taking into account the drastic decrease in the number of these particular springs, ten fontanili were selected for detailed investigation based on their state of preservation and accessibility. A geological map of each emergence was constructed to explain its origin. The main hydrochemical and physical variables and parameters were measured every month for a period of one year. Only three sources provided water throughout the entire year, and their flow rates reached 60–80 l/S during the summer due to recharge from irrigation channels. All other fontanili remained dry during different periods of the year. The hydrochemical data revealed a Ca–Mg bicarbonate composition. The electrical conductivity increased from the north (100–300 μS/cm) to the south (300–600 μS/cm), and nitrate concentrations were below the limits imposed by Italian law (50 mg/l). This study should be considered as the basis of a proposal to the local government for the protection of a subset of these springs as sites of special geological interest (geo-sites). 相似文献
163.
Cu and Zn modified 13X zeolites prepared by ion exchange or impregnation and activated carbons (ACs) treated with KOH, NaOH or Na2CO3 solutions were studied as H2S sorbents for biogas purification for fuelling molten carbonate fuel cells. H2S sorption was studied in a new experimental set-up equipped with a high sensitivity potentiometric system for the analysis of H2S. Breakthrough curves were obtained at 40 °C with a fixed bed of 20 mg of the samples under a stream (6 L h−1) of 8 ppm H2S/He mixture. The adsorption properties of 13X zeolite improved with addition of Cu or Zn:Cu exchanged zeolite showed the best performances with a breakthrough time of 580 min at 0.5 ppm H2S, that is 12 times longer than the parent zeolite. In general, unmodified and modified ACs were more effective H2S sorbents than zeolites. Treating ACs with NaOH, KOH, or Na2CO3 solutions improved the H2S adsorption properties: AC treated with Na2CO3 was the most effective sorbent, showing a breakthrough time of 1222 min at 0.5 ppm, that is twice the time of the parent AC. 相似文献
164.
Nowadays two main approaches are being pursued to reduce energy consumption of networks: the use of sleep modes in which devices enter a low-power state during inactivity periods, and the adoption of energy proportional mechanisms where the device architecture is designed to make energy consumption proportional to the actual load. Common to all the proposals is the evaluation of energy saving performance by means of simulation or experimental evidence, which typically consider a limited set of benchmarking scenarios. 相似文献
165.
Luca Consolini Oscar Gerelli Corrado Guarino Lo Bianco Aurelio Piazzi 《Mechatronics》2009,19(3):348-356
The paper proposes a linear programming approach to the feed-forward minimum-time control of flexible joints. Taking into account both input and output constraints, the optimal bang–bang control is computed by discretizing a continuous-time joint model and by solving a sequence of linear programming feasibility problems. The resulting joint motion is a smooth rest-to-rest motion without oscillations. Theoretical analysis is presented and proof of convergence is given. Experimental results illustrate the proposed open-loop technique. Comparisons are made with inversion-based techniques. 相似文献
166.
Massimiliano Ferronato Luca Bergamaschi Giuseppe Gambolati 《International journal for numerical methods in engineering》2010,81(3):381-402
Block constraint preconditioners are a most recent development for the iterative solution to large‐scale, often ill‐conditioned, coupled consolidation problems. A major limitation to their practical use, however, is the somewhat difficult selection of a number of user‐defined parameters (at least 4) in a more or less optimal way. The present paper investigates the robustness of three variants of the block constraint preconditioning in relation to the above parameters. A theoretical analysis of the eigenspectrum of the preconditioned matrix provides relatively simple bounds of the eigenvalues as a function of these parameters. A number of test problems used to validate the theoretical results show that both the mixed constraint preconditioner (MCP) combined with the symmetric quasi‐minimal residual (SQMR) solver and the MCP triangular variant (T‐MCP) combined with the bi‐conjugate gradient stabilized (Bi‐CGSTAB) are efficient and robust tools for the solution to difficult Finite Element‐discretized coupled consolidation problems. Moreover, the practical selection of the user‐defined parameters is relatively easy as a stable behavior is observed for a wide range of fill‐in degree values. The theoretical bounds on the eigenspectrum of the preconditioned matrix may help to suggest the most appropriate parameter combination. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
167.
168.
169.
170.
项目地点:沙特阿拉伯利雅得项目类型:建筑(住宅)开工日期:未知该项目获2005年豪瑞可持续建筑大奖赛非洲中东地区提名奖 相似文献