全文获取类型
收费全文 | 33421篇 |
免费 | 4771篇 |
国内免费 | 2224篇 |
专业分类
电工技术 | 17969篇 |
技术理论 | 1篇 |
综合类 | 2441篇 |
化学工业 | 2033篇 |
金属工艺 | 890篇 |
机械仪表 | 1501篇 |
建筑科学 | 860篇 |
矿业工程 | 742篇 |
能源动力 | 1244篇 |
轻工业 | 491篇 |
水利工程 | 362篇 |
石油天然气 | 488篇 |
武器工业 | 187篇 |
无线电 | 5575篇 |
一般工业技术 | 1924篇 |
冶金工业 | 1054篇 |
原子能技术 | 478篇 |
自动化技术 | 2176篇 |
出版年
2024年 | 79篇 |
2023年 | 484篇 |
2022年 | 843篇 |
2021年 | 1027篇 |
2020年 | 1191篇 |
2019年 | 928篇 |
2018年 | 952篇 |
2017年 | 1396篇 |
2016年 | 1449篇 |
2015年 | 1708篇 |
2014年 | 2328篇 |
2013年 | 2095篇 |
2012年 | 2846篇 |
2011年 | 3062篇 |
2010年 | 2085篇 |
2009年 | 2166篇 |
2008年 | 2083篇 |
2007年 | 2353篇 |
2006年 | 2189篇 |
2005年 | 1647篇 |
2004年 | 1289篇 |
2003年 | 1158篇 |
2002年 | 915篇 |
2001年 | 867篇 |
2000年 | 678篇 |
1999年 | 486篇 |
1998年 | 347篇 |
1997年 | 248篇 |
1996年 | 290篇 |
1995年 | 250篇 |
1994年 | 211篇 |
1993年 | 179篇 |
1992年 | 130篇 |
1991年 | 97篇 |
1990年 | 73篇 |
1989年 | 63篇 |
1988年 | 56篇 |
1987年 | 37篇 |
1986年 | 24篇 |
1985年 | 27篇 |
1984年 | 20篇 |
1983年 | 12篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
优质电力园区以最低成本满足用户对电能质量的特殊需求,成为解决电压暂降问题的新途径,已在国内外开展了广泛的试点应用。针对中国优质电力园区规划缺少经济高效的优化配置方法的实际情况,提出了一种基于过程免疫力的动态电压恢复器优化配置方法。基于工业过程电压暂降免疫力,以满足用户用电需求为目标,以治理设备购置费用最低为约束,采用遗传算法对园区供电质量分级制定动态电压恢复器的优化配置方案,实现工业园区电压暂降治理的经济性。对大型精密温控系统的电压暂降治理装置的优化配置方法进行仿真计算,验证了所提方法的有效性与经济性。 相似文献
32.
针对阳煤五矿广场变电站的高压开关老化问题,为了保证安全性,采用了GIS气体的高压绝缘开关进行了改造。在改造后,变电站的安全性得到了显著提高,设备运行可以节省成本200多万元。 相似文献
33.
研究了脉冲辐解过程中氨基羟基脲与水辐解活性粒子(e-aq、·OH和·H)及单电子氧化剂·CO3-的反应动力学过程。反应近似为准一级反应,反应速率常数分别为k(e-aq)=1.41×108 L/(mol·s)、k(·OH)=1.05×1010 L/(mol·s)、k(·H)=2.68×105 L/(mol·s)、k(·CO-3)=4.25×108 L/(mol·s)。其中氨基羟基脲与·OH的反应速率常数最大,故在辐解过程中其为主要反应。 相似文献
34.
Design and fabrication of thermoelectric waste heat reutilization system—possible industrial application 下载免费PDF全文
Souvik Biswas Ayan Roynaskar Chetan Kumar Hirwani Subrata Kumar Panda 《国际能源研究杂志》2018,42(12):3977-3986
The current article discussed the detail design and development of an experimental test rig to derive usable energy by utilizing the waste heat energy through a heat exchanger made of Bi2Te3 material. The accuracy including the efficiency of the fabricated device is demonstrated further by verifying the associated parameter through a simulation model (commercial finite element package, ANSYS 15.0). To imitate the waste hot air from the industry is achieved via a heat gun and fed to the test rig for the generation of thermoelectric power. The simulation model accuracy has been demonstrated by juxtaposing the associated experimental data and computational readings. Subsequently, the feasibility and optimum range of design parameters are established by comparing the experimental and the simulation data (triggered temperature difference, voltage output, and heat flux) generated at the interface of the thermoelectric power generators. In addition, the coefficient of determination (R2) value has been evaluated statistically and verified with the current experimental results for the demonstration of the relevancy. The statistical study shows the existence of the correlation between the current experimental and the simulation model. Also, the experimental result indicates the possible implementation of the newly developed system for the recovery from the waste heat either the automobile exhaust or any other kind of dissipated heat from the industries. 相似文献
35.
In this work, a series of fluorine‐functionalized polysulfone (F‐PSU) copolymers with intrinsic low dielectric constants (low ε) are reported, which are derived from the polycondensation reaction of 4,4′‐dichlorophenyl sulfone with bisphenol A and bisphenol F (BPF) compounds. The resulting F‐PSU copolymers show high glass transition temperatures (Tg) varying from 187 to 201 °C and are thermally stable up to 500 °C under an N2 atmosphere. The introduction of BPF units into the PSU copolymers imparts enhanced hydrophobic properties to the F‐PSU films with increased water contact angle values from 66.2° to 93.7°. Moreover, the dielectric constant and dielectric loss of the F‐PSU (sample V) film are as low as 2.2 and 0.003 at 1 kHz, respectively. Interestingly, the dielectric properties are relatively stable to near the glass transition temperature, which is because of the existence of BPF structures in the molecular backbone. Furthermore, the F‐PSU copolymers are soluble in common solvents and can be readily fabricated into flexible transparent films by the spin casting method. © 2020 Society of Chemical Industry 相似文献
36.
David Bernhard Thomas Kadyk Ulrike Krewer Sebastian Kirsch 《International Journal of Hydrogen Energy》2021,46(26):13791-13805
In this work, proton exchange membrane fuel cell cathodes are degraded with accelerated-stress-tests.These PtCo containing cathodes are analyzed at begin-of-life and end-of-test with a dedicated diagnostic procedure. For every individual load point, the oxygen transport resistance and voltage losses due to the formation of platinum oxides were obtained in addition to commonly measured electrochemical surface area, high frequency resistance, as well as cathode ionomer resistance. These data were used to break down the voltage losses into six different contributors. With this break down, performance gains and performance losses were determined at end-of-test. At low current densities, it was found that voltage losses due to degradation are dominated by the loss of specific activity and catalyst surface area - in line with the state-of-the-art knowledge. But by quantifying the losses from platinum oxide formation explicitly, we show that end-of-test an unassigned voltage loss is not only present at highest current densities, but already at low current density. More precisely, the unassigned voltage loss shows a linear increase with decreasing half cell voltage and is independent from the chosen accelerated stress test. As this unassigned loss depends on half cell voltage, it might arise from ionomer adsorption. 相似文献
37.
Bo PENG 《等离子体科学和技术》2020,22(8):85603
Voltage sags in power system may lead to serious problems such as the off-grid of distributed
generation and electrical equipment failures. As a novel type of power electronic equipment, a
flexible multi-state switch (FMSS) is capable to support the voltage during the grid faults. In this
paper, a voltage control strategy to support the voltage in a distribution network is proposed by
introducing three-port FMSS. The positive–negative-sequence compensation (PNSC) scheme is
adopted to control the active and reactive current. This control scheme eliminates active power
oscillations at the port of voltage sags and reduces coupling oscillations of other ports. Based on
the characteristics of the voltage support under PNSC scheme, two voltage support strategies are
proposed. A proportional-integral controller is introduced to provide the reactive power
references, which eliminates the errors when estimating the grid voltage and impedance. A
current limiting scheme is adopted to keep the port current in a safe range by adjusting the active
and reactive power references. The voltage support strategies in two different voltage sags are
simulated, and results show the feasibility and effectiveness of the proposed control strategies. 相似文献
38.
Jagadeeswari Sivanadanam Ramesh Mukkamala Sudip Mandal Raman Vedarajan Noriyoshi Matsumi Indrapal Singh Aidhen Kothandaraman Ramanujam 《International Journal of Hydrogen Energy》2018,43(9):4691-4705
Six triphenylamine-based dyes were explored for their application in dye-sensitized solar cells (DSSCs). Dyes 1–3 and dyes 4–6 possess cyanoacrylic acid (C-acceptor) and rhodanine-3-acetic acid (R-acceptor), respectively. Stilbene (in dyes 2 and 5) and bis(styryl)benzene (in dyes 3 and 6) were used as π-spacers. There is no π-spacer in the dye 1 and 4. To elucidate the role of π-spacers, optical, electrochemical, and photovoltaic properties of the dyes were studied. Among C-acceptor dyes, dye 2 exhibits the highest light-to-electricity conversion efficiency of 4.45%, followed by dye 3 (4.16%). Similarly, among R-acceptor dyes, dye 5 is the best. These results indicate that stilbene is a better π-spacer over bis(styryl)benzene. Although bis(styryl)benzene could extend the light absorption range (in dye-adsorbed TiO2 film), its tendency to promote intermolecular π-π stacking is possibly the reason for its poor performance in DSSCs. Furthermore, the conjugation break in the R-acceptor moiety attached to the TiO2 surface limits the electron injection of R-acceptor dyes poorer than C-acceptor dyes. Density functional theory calculations were performed for the dye-(TiO2)8 cluster, assuming a bidentate chelation of a carboxylic acid group with Ti4+ of TiO2 anatase. The natural bond orbital (NBO) analysis indicated relatively more electron-accepting ability of cyanoacrylic acid over rhodanine-3-acetic acid. 相似文献
39.
This paper presents a direct model-based predictive control scheme for voltage source inverters (VSIs) with reduced common-mode voltages (CMVs). The developed method directly finds optimal vectors without using repetitive calculation of a cost function. To adjust output currents with the CMVs in the range of –Vdc/6 to +Vdc/6, the developed method uses voltage vectors, as finite control resources, excluding zero voltage vectors which produce the CMVs in the VSI within ±Vdc/2. In a model-based predictive control (MPC), not using zero voltage vectors increases the output current ripples and the current errors. To alleviate these problems, the developed method uses two non-zero voltage vectors in one sampling step. In addition, the voltage vectors scheduled to be used are directly selected at every sampling step once the developed method calculates the future reference voltage vector, saving the efforts of repeatedly calculating the cost function. And the two non-zero voltage vectors are optimally allocated to make the output current approach the reference current as close as possible. Thus, low CMV, rapid current-following capability and sufficient output current ripple performance are attained by the developed method. The results of a simulation and an experiment verify the effectiveness of the developed method. 相似文献
40.
ABSTRACTThis paper proposes a novel tracking method to deal with fast changes of solar irradiation and power limit change in order to increase tracking efficiency. This goal is achieved by estimating (i) next operating mode and (ii) next step point with the use of tangent rule in triangle. After every fast response to sudden changes, accurate response phase starts in order to track desired power in each operating mode by adaptive step size. Drift problem in defining next operating mode is eliminated in proposed method by estimating next operating mode, and settling time is decreased to about 25 percent of settling time of other methods by estimating next step point. Simulation and experimental results show the performance of proposed method. 相似文献