全文获取类型
收费全文 | 212569篇 |
免费 | 19046篇 |
国内免费 | 10870篇 |
专业分类
电工技术 | 60233篇 |
技术理论 | 9篇 |
综合类 | 19168篇 |
化学工业 | 17596篇 |
金属工艺 | 8893篇 |
机械仪表 | 9365篇 |
建筑科学 | 9313篇 |
矿业工程 | 4493篇 |
能源动力 | 11643篇 |
轻工业 | 8430篇 |
水利工程 | 5312篇 |
石油天然气 | 6183篇 |
武器工业 | 1739篇 |
无线电 | 21570篇 |
一般工业技术 | 19361篇 |
冶金工业 | 5642篇 |
原子能技术 | 4538篇 |
自动化技术 | 28997篇 |
出版年
2024年 | 512篇 |
2023年 | 2044篇 |
2022年 | 3522篇 |
2021年 | 4405篇 |
2020年 | 5214篇 |
2019年 | 4333篇 |
2018年 | 4080篇 |
2017年 | 5174篇 |
2016年 | 5989篇 |
2015年 | 7241篇 |
2014年 | 12546篇 |
2013年 | 11706篇 |
2012年 | 13818篇 |
2011年 | 15095篇 |
2010年 | 11548篇 |
2009年 | 13072篇 |
2008年 | 12930篇 |
2007年 | 14797篇 |
2006年 | 13348篇 |
2005年 | 11060篇 |
2004年 | 9340篇 |
2003年 | 8351篇 |
2002年 | 7304篇 |
2001年 | 5951篇 |
2000年 | 5743篇 |
1999年 | 4871篇 |
1998年 | 3799篇 |
1997年 | 3375篇 |
1996年 | 3518篇 |
1995年 | 3379篇 |
1994年 | 3063篇 |
1993年 | 1875篇 |
1992年 | 1834篇 |
1991年 | 1232篇 |
1990年 | 944篇 |
1989年 | 838篇 |
1988年 | 760篇 |
1987年 | 455篇 |
1986年 | 283篇 |
1985年 | 421篇 |
1984年 | 485篇 |
1983年 | 493篇 |
1982年 | 385篇 |
1981年 | 432篇 |
1980年 | 289篇 |
1979年 | 129篇 |
1978年 | 127篇 |
1977年 | 80篇 |
1976年 | 44篇 |
1975年 | 61篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
《International Journal of Hydrogen Energy》2022,47(12):7600-7623
In this paper, a salinity gradient solar pond (SGSP) is used to harness the solar energy for hydrogen production through two cycles. The first cycle includes an absorption power cycle (APC), a proton exchange membrane (PEM) electrolyzer, and a thermoelectric generator (TEG) unit; in the second one, an organic Rankine cycle (ORC) with the zeotropic mixture is used instead of APC. The cycles are analyzed through the thermoeconomic vantage point to discover the effect of key decision variables on the cycles’ performance. Finally, NSGA-II is used to optimize both cycles. The results indicate that employing ORC with zeotropic mixture leads to a better performance in comparison to utilizing APC. For the base mode, unit cost product (UCP), exergy, and energy efficiency when APC is employed are 59.9 $/GJ, 23.73%, and 3.84%, respectively. These amounts are 47.27 $/GJ, 29.48%, and 5.86% if ORC with the zeotropic mixture is utilized. The APC and ORC generators have the highest exergy destruction rate which is equal to 6.18 and 10.91 kW. In both cycles, the highest investment cost is related to the turbine and is 0.8275 $/h and 0.976 $/h for the first and second cycles, respectively. In the optimum state the energy efficiency, exergy efficiency, UCP, and H2 production rate of the system enhances 42.44%, 27.54%,15.95%, and 38.24% when ORC with the zeotropic mixture is used. The maximum H2 production is 0.47 kg/h, and is obtained when the mass fraction of R142b, LCZ temperature, pumps pressure ratio, generator bubble point temperature are 0.603, 364.35 K, 2.12, 337.67 K, respectively. 相似文献
13.
在80 MHz~1 GHz频段,单个功率管输出功率能达到100 W以上,为研制输出功率400 W的功率放大器,文中设计了四路功率合成器。该合成器需要实现功率容量大、工作频带宽、体积小的设计目标。在功率容量方面,文中采用悬置带状线结构,其功率容量远远大于微带线结构;在工作频带方面,采用切比雪夫九节阻抗变换器,将工作带宽拓宽为80 MHz~1 GHz;在体积方面,文中合成器的功率合成部分采用Y型节级联实现四路功率合成,阻抗变换部分采用切比雪夫阻抗变换器进行阻抗变换,该结构相较于磁环巴伦功率合成器,不但具有损耗小、平坦度高的优点,而且通过将阻抗变换器设计成曲折的形状,进一步缩小了合成器体积。仿真与实测结果显示该合成器在80 MHz~1 GHz范围内还具有较高的平坦度,合成效率可达90%以上。 相似文献
14.
15.
16.
This paper proposes a method for the coordinated control of power factor by means of a multiagent approach. The proposed multiagent system consists of two types of agent: single feeder agent (F_AG) and bus agent (B_AG). In the proposed system, an F_AG plays as an important role, which decides the power factors of all distributed generators by executing the load flow calculations repeatedly. The voltage control strategies are implemented as the class definition of Java into the system. In order to verify the performance of the proposed method, it has been applied to a typical distribution model system. The simulation results show that the system is able to control very violent fluctuation of the demands and the photovoltaic (PV) generations. 相似文献
17.
Wassim Bahr 《国际自然能源杂志》2018,39(8):802-812
This paper assesses building integrated photovoltaic (BIPV) installation parameters based on the profit generated by a photovoltaic system. It takes into consideration a home building case study and it investigates its monthly energy demand based on a specific location and a typical occupancy. The capability of a photovoltaic (PV) system to generate more profit occurs when solar intensity is maximum while the electric energy price is at its highest rate. The paper traces a framework that encompasses different aspects such as energy demand, energy price, and solar intensity. This framework identifies profit alternatives according to different installation parameters. A tool that predicts a PV installation hourly electric energy production is developed. The profit generated is simulated for home buildings located in Beirut (Lebanon) and Xihua (China), both at 33.8° latitude north. The paper highlights a new approach for BIPV installations, taking into account weather conditions, energy demand, and electric energy utility rates. 相似文献
18.
19.
In this work, the longitudinal permeability of squarely packed dual-scale fiber preforms is studied theoretically. These fiber preforms are composed of aligned porous tows and the tows are tightly packed. The effective permeability is calculated as a parallel-like network of intra-tow permeability and inter-tow permeability, which are quantified by Darcy’s law and the inscribed radius between tows, respectively. The jump velocity at the interface between inter-tow fluids and porous tows is considered, as derived by substituting Beavers and Joseph’s correlation into Brinkman’s equation. We further examine the effects of intra-tow permeability on the effective permeability of the fibrous system with three interface conditions: (1) interface velocity = 0, (2) interface velocity = mean intra-tow velocity, and (3) interface velocity = jump velocity. The jump-velocity-based model is found to be closest to numerical data. The influence of the fiber volume fraction of tows on the effective permeability is also analyzed. 相似文献
20.
《Ceramics International》2020,46(4):4148-4153
The ferroelectric photovoltaic (FPV) effect obtained in inorganic perovskite ferroelectric materials has received much attention because of its large potential in preparing FPV devices with superior stability, high open-circuit voltage (Voc) and large short-circuit current density (Jsc). In order to obtain suitable thickness for the ferroelectric thin film as light absorption layer, in which, the sunlight can be fully absorbed and the photo-generated electrons and holes are recombined as few as possible, we prepare Pb0.93La0.07(Zr0.6Ti0.4)0.9825O3 (PLZT) ferroelectric thin films with different layer numbers by the sol-gel method and based on these thin films, obtain FPV devices with FTO/PLZT/Au structure. By measuring photovoltaic properties, it is found that the device with 4 layer-PLZT thin film (~300 nm thickness) exhibits the largest Voc and Jsc and the photovoltaic effect obviously depends on the value and direction of the poling electric field. When the device is applied a negative poling electric field, both the Voc and Jsc are significantly higher than those of the device applied the positive poling electric field, due to the depolarization field resulting from the remnant polarization in the same direction with the built-in electric field induced by the Schottky barrier, and the higher the negative poling electric field, the larger the Voc and Jsc. At a -333 kV/cm poling electric field, the FPV device exhibits the most superior photovoltaic properties with a Voc of as high as 0.73 V and Jsc of as large as 2.11 μA/cm2. This work opens a new way for developing ferroelectric photovoltaic devices with good properties. 相似文献