全文获取类型
收费全文 | 20609篇 |
免费 | 2293篇 |
国内免费 | 1531篇 |
专业分类
电工技术 | 3831篇 |
综合类 | 1537篇 |
化学工业 | 4047篇 |
金属工艺 | 1026篇 |
机械仪表 | 868篇 |
建筑科学 | 468篇 |
矿业工程 | 509篇 |
能源动力 | 570篇 |
轻工业 | 2594篇 |
水利工程 | 1373篇 |
石油天然气 | 446篇 |
武器工业 | 133篇 |
无线电 | 2747篇 |
一般工业技术 | 1998篇 |
冶金工业 | 870篇 |
原子能技术 | 688篇 |
自动化技术 | 728篇 |
出版年
2024年 | 48篇 |
2023年 | 294篇 |
2022年 | 505篇 |
2021年 | 574篇 |
2020年 | 697篇 |
2019年 | 620篇 |
2018年 | 556篇 |
2017年 | 775篇 |
2016年 | 786篇 |
2015年 | 837篇 |
2014年 | 1272篇 |
2013年 | 1238篇 |
2012年 | 1669篇 |
2011年 | 1727篇 |
2010年 | 1237篇 |
2009年 | 1286篇 |
2008年 | 1261篇 |
2007年 | 1527篇 |
2006年 | 1402篇 |
2005年 | 1114篇 |
2004年 | 946篇 |
2003年 | 815篇 |
2002年 | 594篇 |
2001年 | 513篇 |
2000年 | 414篇 |
1999年 | 354篇 |
1998年 | 258篇 |
1997年 | 214篇 |
1996年 | 169篇 |
1995年 | 170篇 |
1994年 | 125篇 |
1993年 | 94篇 |
1992年 | 92篇 |
1991年 | 80篇 |
1990年 | 42篇 |
1989年 | 26篇 |
1988年 | 21篇 |
1987年 | 14篇 |
1986年 | 12篇 |
1985年 | 11篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 12篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1964年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
91.
Qi LIU 《等离子体科学和技术》2019,21(7):74005-49
Plasma in the discharge channel of a pulsed plasma thruster (PPT) with flared electrodes is simulated by a self-developed two-dimensional code. The fully particle-in-cell method with Monte Carlo collision is employed to model the particle movement and collisions and investigate the plasma properties and acceleration process. Temporal and spatial variations of the electron density distribution and the ion velocity between electrodes are calculated and analyzed in detail. The computational results of the electron number density, which is in the order of 1023 m−3, show good agreements with experimental results of a PPT named ADD SIMP-LEX. The ion velocity distributions along the center line of the channel lead to a comprehensive understanding of ions accelerated by electromagnetic field. The electron distributions of PPT with discharge voltages varying from 1300 to 2000 V are compared. The diffusion of electrons presents strong dependency on discharge voltage and implies higher degree of ionization for higher voltage. 相似文献
92.
《Advanced Powder Technology》2020,31(9):4119-4128
Arc discharge synthesis has industrial relevance due to its low cost and scale-up potential. The production of titanium nitride nanoparticles was achieved by direct current arc discharge in an atmospheric-pressured ambient composed of N2 and Ar. We systematically investigated the effect of the synthesis parameters, including quench gas velocity, quench gas composition, and applied arc current, on the particle quality, yield, and size. It is found that increasing quench gas velocity enables to produce particles with a primary size of 10–15 nm, while titanium nitride particles of 20–50 nm are produced at low quench gas velocity based on scanning electron microscope (SEM) analysis. X-ray diffraction (XRD) results indicated that titanium nitride particles produced at various nitrogen compositions are almost stoichiometric, while the crystallite size increases almost 20 nm when increasing nitrogen contents in the quench gas. Quench gas composition also has a significant impact on the arc voltage as well as particle production rate. When increasing the nitrogen concentration from 20% to 100%, the production rate can be enhanced by a factor of three. Besides, raising the applied arc current from 12 A to 50 A leads to a yield enhancement of factor 10. According to the Brunauer-Emmett-Teller (BET) measurement, the increase of applied arc current has a limited impact on primary particle size. The enhancement in particle production rate is mainly reflected by the larger agglomerate sizes and agglomerate number concentration. Additionally, based on experimental observations and previous studies, a mechanism is presented to explain the growth of deposits on the cathode tip. 相似文献
93.
M.A. Abbas M.A. Lajis D.R. Abbas O.M. Merzah M.H. Kadhim A.A. Shamran 《Materialwissenschaft und Werkstofftechnik》2020,51(6):719-724
The quality of the machined surface resulted from the electrical discharge machining (EDM) environment is not efficient according to the previous studies. One of the significant problems is the impedance of dielectric fluid, where it is contributing to focusing the plasma channel in a limited area. Hence, this behavior leads to appearing deep craters on the machined zone. The researchers have attempted to enhance the average of surface roughness by employing powder particles or surfactant as the additive materials in the dielectric fluid. Unfortunately, these studies did not present a comparison between these additive materials in this environment. Therefore, the present study aims to compare the performance of the average of surface roughness (Ra) for AISI D2 steel by utilizing Nano chromium powder (NCP) and Span-20. The present work has proved that the behavior of the average of surface roughness for this steel is dropping at the maximum level of Nano chromium powder concentration and pulse duration as compared to the behavior with the Span-20. Moreover, the best roughness was produced by this steel with Nano chromium powder at 2 g/L and 20 μs for this powder and the pulse duration. 相似文献
94.
Yang-huan ZHANG Ya-qin LI Hong-wei SHANG Zhong-hui HOU Yan QI Dong-liang ZHAO 《中国有色金属学会会刊》2018,28(4):711-721
The La-Mg-Ni-Co-Al-based AB2-type La0.8–xCe0.2YxMgNi3.4Co0.4Al0.1 (x=0, 0.05, 0.1, 0.15, 0.2) alloys were prepared via melt spinning. The analyses of the X-ray diffraction (XRD) and scanning electron microscopy (SEM) proved that the experimental alloys contain the main phase LaMgNi4 and the second phase LaNi5. Increasing Y content and spinning rate lead to grain refinement and obvious change of the phase abundance without changing phase composition. Y substitution for La and melt spinning make the life-span of the alloys improved remarkably, which is attributed to the improvement of anti-oxidation, anti-pulverization and anti-corrosion abilities. In addition, the discharge capacity visibly decreases with increasing the Y content, while it firstly increases and then decreases with increasing spinning rate. The electrochemical kinetics increases to the optimum performance and then reduces with increasing spinning rate. Moreover, all the alloys achieve to the highest discharge capacities just at the initial cycle without activation. 相似文献
95.
96.
根据高拱坝泄流结构自身的工作特点,为准确辨识环境激励下的结构模态参数特征,提出了一种基于改进的HHT-RDT算法的高拱坝泄流结构工作模态识别方法。以某高拱坝原型振动响应测试资料为基础,利用改进的小波阈值-EMD算法对原始信号进行降噪预处理,滤除干扰噪声的同时保留有效特征信息;采用HHT-RDT算法识别高拱坝泄流结构的工作模态参数,运用带通滤波对振动响应信号的EMD过程进行控制得到结构的各阶模态分量,利用RDT法提取各阶模态分量的自由衰减信息,识别出高拱坝泄流结构系统的固有频率及阻尼比。工程实例表明,该方法避免了复杂系统定阶过程,有效提高结构振动响应工作模态识别精度,为辨识高拱坝泄流结构的工作模态参数提供捷径。 相似文献
97.
98.
Non-thermal plasma(NTP)is regarded as a potential application for environmental pollution control due to its ability to remove pollutants.As a major precursor of dioxins,the influence of the parameters of 1,2,4-trichlorobenzene(TCB)decomposition using NTP technology was investigated through a series of experiments,including voltage,frequency,water content,initial concentration,flow rate,and oxygen content.The experimental results show that the energy injected into the NTP system has a positive correlation to voltage and frequency.Oxygen has the greatest influence on TCB decomposition.The optimal reaction condition was at 15 kV,1000 Hz,an initial concentration of 20 mg m^?3,a flow rate of 2 l min^?1,H2O at 4%,and O2 at 0%.Under this condition,the TCB removal efficiency could reach 92%.According to the generated product backstepping,the hydroxyl radical(·OH)plays an important role in TCB decomposition due to its strong oxidation,which participates in the dechlorination and oxidation reactions as free radicals,and the possible decomposition pathway of TCB by NTP is inferred from the identified byproducts.It is of great significance to investigate the influence of the parameters of TCB decomposition using NTP technology in order to provide references for industrial application. 相似文献
99.
入江水道是淮河下游最大的泄洪河道,承担着淮河上中游70%以上的洪水泄入长江。根据1961—2018年大洪水期间的实测资料,利用水位流量法计算分析入江水道的泄洪能力和防洪能力。结果表明:因历史客观条件限制以及4个梯级控制河段整治的难度与复杂性,在不同时期各控制河段的行洪能力呈现各自不同的特点;经过多年持续有效治理,河道行洪能力整体得到提高;由近年来实测资料推算,各控制河段的行洪能力基本达到设计要求。对入江水道行洪能力的分析为淮河下游区的防汛抗洪和降低特大洪水威胁提供借鉴和参考,对区域经济社会又好又快发展具有现实意义。 相似文献
100.
The microstructure and electrochemical behavior of Mg–6Al–1Zn, Mg–6Al–1Zn–1Ga, Mg–6Al–1Zn–1Sn, and Mg–6Al–1Zn–0.5Sn–0.5Ga as anode materials in a 3.5 wt% NaCl solution are compared systematically. The results show that Sn alloying refines the second-phases of Mg–6Zn–1Al by promoting tiny granular Mg17Al12 phases containing Sn, and inspires their disperse distribution. However, the Ga results in the formation of semicontinuous reticular Ga containing Mg17Al12 phases. The comparison of discharge tests indicates that Mg–6Al–1Zn–1Sn has the highest discharge activity, and Mg–6Al–1Zn–1Ga displays the largest hydrogen evolution corrosion resistance in 3.5 wt% NaCl solution at 298 K. The synergy of Ga and Sn can shorten discharge activation time and promote low discharge potential. In addition, the utilization efficiencies of the alloys decrease as follows: Mg–6Al–1Zn–1Ga > Mg–6Al–1Zn–0.5Sn–0.5Ga > Mg–6Al–1Zn–1Sn > Mg–6Zn–1Al. This study illustrates that the Mg–6Al–1Zn–0.5Sn–0.5Ga alloy has acceptable utilization efficiency and desirable electrochemical activity, which implies that doping Ga and Sn obtains a balance between discharge activity and utilization efficiencies. 相似文献