全文获取类型
收费全文 | 97589篇 |
免费 | 12454篇 |
国内免费 | 4521篇 |
专业分类
电工技术 | 49448篇 |
技术理论 | 3篇 |
综合类 | 7567篇 |
化学工业 | 4651篇 |
金属工艺 | 2099篇 |
机械仪表 | 3800篇 |
建筑科学 | 3097篇 |
矿业工程 | 2005篇 |
能源动力 | 7883篇 |
轻工业 | 2206篇 |
水利工程 | 2526篇 |
石油天然气 | 858篇 |
武器工业 | 666篇 |
无线电 | 12648篇 |
一般工业技术 | 3570篇 |
冶金工业 | 1742篇 |
原子能技术 | 2151篇 |
自动化技术 | 7644篇 |
出版年
2024年 | 187篇 |
2023年 | 1249篇 |
2022年 | 2344篇 |
2021年 | 2878篇 |
2020年 | 3207篇 |
2019年 | 2640篇 |
2018年 | 2368篇 |
2017年 | 3425篇 |
2016年 | 3681篇 |
2015年 | 4184篇 |
2014年 | 7028篇 |
2013年 | 5803篇 |
2012年 | 8011篇 |
2011年 | 8620篇 |
2010年 | 6260篇 |
2009年 | 6352篇 |
2008年 | 6223篇 |
2007年 | 7426篇 |
2006年 | 6610篇 |
2005年 | 5346篇 |
2004年 | 4352篇 |
2003年 | 3484篇 |
2002年 | 2654篇 |
2001年 | 2312篇 |
2000年 | 1844篇 |
1999年 | 1326篇 |
1998年 | 869篇 |
1997年 | 668篇 |
1996年 | 683篇 |
1995年 | 542篇 |
1994年 | 486篇 |
1993年 | 301篇 |
1992年 | 264篇 |
1991年 | 165篇 |
1990年 | 136篇 |
1989年 | 111篇 |
1988年 | 83篇 |
1987年 | 62篇 |
1986年 | 40篇 |
1985年 | 39篇 |
1984年 | 63篇 |
1983年 | 51篇 |
1982年 | 54篇 |
1981年 | 23篇 |
1980年 | 14篇 |
1979年 | 12篇 |
1978年 | 15篇 |
1977年 | 8篇 |
1959年 | 15篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
《全球能源互联网(英文)》2020,3(4):313-323
Recently, power electronic transformers (PETs) have received widespread attention owing to their flexible networking, diverse operating modes, and abundant control objects. In this study, we established a steady-state model of PETs and applied it to the power flow calculation of AC–DC hybrid systems with PETs, considering the topology, power balance, loss, and control characteristics of multi-port PETs. To address new problems caused by the introduction of the PET port and control equations to the power flow calculation, this study proposes an iterative method of AC–DC mixed power flow decoupling based on step optimization, which can achieve AC–DC decoupling and effectively improve convergence. The results show that the proposed algorithm improves the iterative method and overcomes the overcorrection and initial value sensitivity problems of conventional iterative algorithms. 相似文献
92.
93.
《International Journal of Hydrogen Energy》2020,45(53):29110-29122
This paper presents an experimental study of a standalone hybrid microgrid system. The latter is dedicated to remote area applications. The system is a compound that utilizes renewable sources that are Wind Generator (WG), Solar Array (SA), Fuel Cell (FC) and Energy Storage System (ESS) using a battery. The power electronic converters play a very important role in the system; they optimize the control and energy management techniques of the various sources. For wind and solar subsystem, the speed and Single Input Fuzzy Logic (SIFL) controllers are used respectively to harvest the maximum power point tracking (MPPT). To maintain a balance of energy in the hybrid system, an energy management strategy based on the battery state of charge (SOC) has been developed and implemented experimentally. The AC output voltage regulation was achieved using a Proportional Integral (PI) controller to supply a resistive load with constant amplitude and frequency. According to the obtained performances, it was concluded that the proposed system is very promising for potential applications in hybrid renewable energy management systems. 相似文献
94.
95.
针对三相整流负载产生的6k±1次谐波,提出静止坐标系下的改进型6k±1重复控制策略。同时将比例控制与改进型重复控制相结合,设计改进重复控制并联比例的复合控制结构。为减小改进重复控制中延时环节不为整数的影响,采用基于Lagrange插值近似的FIR滤波器逼近分数延时特性。最后对系统进行稳定性分析和详细设计方法进行推导。通过Matlab仿真验证改进重复控制策略能有效跟踪6k±1次谐波且具有良好的补偿效果,动态响应较快。 相似文献
96.
Baoqing Liu Yijun Zheng Ruijia Cheng Zilong Xu Manman Wang Zhijiang Jin 《中国化学工程学报》2018,26(9):1785-1791
The effects of impeller type, stirring power, gas flow rate, and liquid concentration on the gas–liquid mixing in a shear-thinning system with a coaxial mixer were investigated by experiment, and the overall gas holdup, relative power demand, and volumetric mass transfer coefficient under different conditions were compared. The results show that, the increasing stirring power or gas flow rate is beneficial in promoting the overall gas holdup and volumetric mass transfer coefficient, while the increasing system viscosity weakens the mass transfer in a shearing–thinning system. Among the three turbines, the six curved-blade disc turbine (BDT-6) exhibits the best gas pumping capacity; the six 45° pitched-blade disc turbine (PBDT-6) has the highest volumetric mass transfer coefficient at the same unit volume power. 相似文献
97.
Carolin Spatz Nico Langhof Jens Schmidt Walter Krenkel 《Journal of the European Ceramic Society》2018,38(8):2954-2960
Steel materials suffer extensive creep by the application at temperatures of about 700?°C and pressures about 350?bar in a power plant environment. The presented concept overwraps a steel pipe with a ceramic matrix composite (CMC) jacket in order to support the steel pipe and provide high temperature strength. Finite Element simulations show the influence of the wall thickness of CMC jacket and the coefficient of thermal expansion (CTE) on circumferential stresses within the hybrid metal ceramic pipe. Suitable fiber and matrix materials were studied, composites fabricated and mechanical properties determined. Finally, a prototype was designed in order to confirm the feasibility of the concept. The lifetime of a pure steel pipe was increased by more than four-fold by the additional CMC jacket. 相似文献
98.
Effect of the composition and degree of crosslinking on the properties of poly(l‐lactic acid)/crosslinked polyurethane blends 下载免费PDF全文
Meng Ma Kai Liu Haiming Zheng Si Chen Bozhen Wu Yanqin Shi Xu Wang 《Polymer International》2018,67(9):1221-1228
Poly(l ‐lactic acid)/crosslinked polyurethane (PLLA/CPU) blends which were prepared via reactive blending of PLLA with poly(?‐caprolactone) (PCL), glycerol and 4,4′‐methylenediphenyl diisocyanate showed excellent toughness. The effects of the composition of the mixture and degree of crosslinking of CPU on the toughness of the PLLA/CPU blends (80/20 w/w) were studied in detail. Dynamic mechanical analysis and rheological measurements were used to characterize the structure of the in situ formed CPU in the PLLA matrix. A novel netlike phase structure was observed when the average molecular weight of PCL and degree of crosslinking were 1 kDa and 10%, respectively. The impact strength of the blend was enhanced from 2.2 kJ m?2 for pure PLLA to 62.4 kJ m?2; meanwhile, the elongation at break was increased to 489.8%. Therefore, the mechanical properties of PLLA/CPU blends can be easily tailored by tuning the composition of the mixture and the degree of crosslinking of CPU. © 2018 Society of Chemical Industry 相似文献
99.
Thermal comfort is an important factor for the design of buildings. Although it has been well recognized that many physiological parameters are linked to the state of thermal comfort or discomfort of humans, how to use physiological signal to judge the state of thermal comfort has not been well studied. In this paper, the feasibility of continuously determining feelings of personal thermal comfort was discussed by using electroencephalogram (EEG) signals in private space. In the study, 22 subjects were exposed to thermally comfortable and uncomfortably hot environments, and their EEG signals were recorded. Spectral power features of the EEG signals were extracted, and an ensemble learning method using linear discriminant analysis or support vector machine as a sub-classifier was used to build the discriminant model. The results show that an average discriminate accuracy of 87.9% can be obtained within a detection window of 60 seconds. This study indicates that it is feasible to distinguish whether a person feels comfortable or too hot in their private space by multi-channel EEG signals without interruption and suggests possibility for further applications in neuroergonomics. 相似文献
100.
Alireza HEIDARI Ali ESMAEEL NEZHAD Ahmad TAVAKOLI Navid REZAEI Foad H. GANDOMAN Mohammad Reza MIVEH Abdollah AHMADI Majid MALEKPOUR 《Frontiers in Energy》2020,14(3):510
Recently, renewable energy resources and their impacts have sparked a heated debate to resolve the Australian energy crisis. There are many projects launched throughout the country to improve network security and reliability. This paper aims to review the current status of different renewable energy resources along with their impacts on society and the environment. Besides, it provides for the first time the statistics of the documents published in the field of renewable energy in Australia. The statistics include information such as the rate of papers published, possible journals for finding relative paper, types of documents published, top authors, and the most prevalent keywords in the field of renewable energy in Australia. It will focus on solar, wind, biomass, geothermal and hydropower technologies and will investigate the social and environmental impacts of these technologies. 相似文献