全文获取类型
收费全文 | 6704篇 |
免费 | 237篇 |
国内免费 | 148篇 |
专业分类
电工技术 | 155篇 |
综合类 | 378篇 |
化学工业 | 489篇 |
金属工艺 | 141篇 |
机械仪表 | 557篇 |
建筑科学 | 661篇 |
矿业工程 | 274篇 |
能源动力 | 725篇 |
轻工业 | 259篇 |
水利工程 | 79篇 |
石油天然气 | 574篇 |
武器工业 | 104篇 |
无线电 | 378篇 |
一般工业技术 | 414篇 |
冶金工业 | 169篇 |
原子能技术 | 163篇 |
自动化技术 | 1569篇 |
出版年
2024年 | 2篇 |
2023年 | 53篇 |
2022年 | 83篇 |
2021年 | 126篇 |
2020年 | 126篇 |
2019年 | 92篇 |
2018年 | 102篇 |
2017年 | 123篇 |
2016年 | 161篇 |
2015年 | 199篇 |
2014年 | 383篇 |
2013年 | 363篇 |
2012年 | 408篇 |
2011年 | 546篇 |
2010年 | 405篇 |
2009年 | 408篇 |
2008年 | 368篇 |
2007年 | 421篇 |
2006年 | 364篇 |
2005年 | 325篇 |
2004年 | 273篇 |
2003年 | 253篇 |
2002年 | 195篇 |
2001年 | 172篇 |
2000年 | 138篇 |
1999年 | 178篇 |
1998年 | 161篇 |
1997年 | 105篇 |
1996年 | 111篇 |
1995年 | 76篇 |
1994年 | 67篇 |
1993年 | 58篇 |
1992年 | 58篇 |
1991年 | 34篇 |
1990年 | 28篇 |
1989年 | 25篇 |
1988年 | 10篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 15篇 |
1984年 | 11篇 |
1983年 | 10篇 |
1982年 | 7篇 |
1981年 | 9篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有7089条查询结果,搜索用时 359 毫秒
1.
2.
《International Journal of Hydrogen Energy》2022,47(8):5638-5649
The sustainable reduction of greenhouse gas emissions from road transport requires solutions to achieve net-zero carbon dioxide emissions. Therefore, in addition to vehicles with electrified powertrains, such as those implemented in battery electric of fuel cell vehicles, internal combustion engines fueled with e-fuels or biofuels are also under discussion. An e-fuel that has come into focus recently, is hydrogen due to its potential to achieve zero tank-to-wheel and well-to-wheel carbon dioxide emissions when the electrolysis is powered by electricity from renewable sources. Due to the high laminar burning velocity, hydrogen has the potential for engine operation with high cylinder charge dilution by e.g. external exhaust gas recirculation or enleanment, resulting in increased efficiency. On the other hand, the high burning velocity and high adiabatic flame temperatures pose a challenge for engine cooling due to increased heat losses compared to conventional fuels. To further evaluate the use of hydrogen for small passenger car engines, a series production 1 L 3 cylinder gasoline engine provided by Ford Werke GmbH was modified for hydrogen direct injection. The engine was equipped with a high pressure external exhaust gas recirculation system to investigate charge dilution at stoichiometric operation. Due to limitations of the turbocharging system, very lean operation, which can achieve nitrogen oxides raw emissions below 10 ppm, was limited to part load operation below BMEP = 8 bar. Thus, a reduction of the nitrogen oxides emission level at high loads compared to stoichiometric operation was not possible. At stoichiometric operation with external exhaust gas recirculation engine efficiency can be increased significantly. The comparison of stoichiometric hydrogen and gasoline operation shows a reduced indicated efficiency with hydrogen with significant faster combustion of hydrogen at comparable centers of combustion. However, higher boost pressures would allow to achieve even higher indicated efficiencies by charge dilution compared to gasoline engine operation. 相似文献
3.
《Journal of the European Ceramic Society》2020,40(1):56-62
In this work, 0.2 wt.% Mn-doped (1-x)AgNbO3-xBi0.5Na0.5TiO3 (x = 0.00–0.04) ceramics were synthesized via solid state reaction method in flowing oxygen. The evolution of microstructure, phase transition and energy storage properties were investigated to evaluate the potential as high energy storage capacitors. Relaxor ferroelectric Bi0.5Na0.5TiO3 was introduced to stabilize the antiferroelectric state through modulating the M1-M2 phase transition. Enhanced energy storage performance was achieved for the 3 mol% Bi0.5Na0.5TiO3 doped AgNbO3 ceramic with high recoverable energy density of 3.4 J/cm3 and energy efficiency of 62% under an applied field of 220 kV/cm. The improved energy storage performance can be attributed to the stabilized antiferroelectricity and decreased electrical hysteresis ΔE. In addition, the ceramics also displayed excellent thermal stability with low energy density variation (<6%) over a wide temperature range of 20−80 °C. These results indicate that Mn-doped (1-x)AgNbO3-xBi0.5Na0.5TiO3 ceramics are highly efficient lead-free antiferroelectric materials for potential application in high energy storage capacitors. 相似文献
4.
5.
7.
Clustering is a solution for classifying enormous data when there is not any early knowledge about classes. With emerging new concepts like cloud computing and big data and their vast applications in recent years, research works have been increased on unsupervised solutions like clustering algorithms to extract knowledge from this avalanche of data. Clustering time-series data has been used in diverse scientific areas to discover patterns which empower data analysts to extract valuable information from complex and massive datasets. In case of huge datasets, using supervised classification solutions is almost impossible, while clustering can solve this problem using un-supervised approaches. In this research work, the focus is on time-series data, which is one of the popular data types in clustering problems and is broadly used from gene expression data in biology to stock market analysis in finance. This review will expose four main components of time-series clustering and is aimed to represent an updated investigation on the trend of improvements in efficiency, quality and complexity of clustering time-series approaches during the last decade and enlighten new paths for future works. 相似文献
8.
9.
10.
Detector physics and simulation of resistive plate chambers 总被引:1,自引:0,他引:1
Werner Riegler Christian Lippmann Rob Veenhof 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2003,500(1-3):144-162
We present a simulation model suited to study efficiency, timing and pulse-height spectra of Resistive Plate Chambers. After discussing the details of primary ionisation, avalanche multiplication, signal induction and frontend electronics, we apply the model to timing RPCs with time resolution down to 50 ps and trigger RPCs with time resolution of about 1 ns. 相似文献