全文获取类型
收费全文 | 2857篇 |
免费 | 177篇 |
国内免费 | 124篇 |
专业分类
电工技术 | 296篇 |
综合类 | 203篇 |
化学工业 | 441篇 |
金属工艺 | 114篇 |
机械仪表 | 411篇 |
建筑科学 | 198篇 |
矿业工程 | 89篇 |
能源动力 | 268篇 |
轻工业 | 103篇 |
水利工程 | 123篇 |
石油天然气 | 218篇 |
武器工业 | 107篇 |
无线电 | 110篇 |
一般工业技术 | 222篇 |
冶金工业 | 49篇 |
原子能技术 | 53篇 |
自动化技术 | 153篇 |
出版年
2024年 | 11篇 |
2023年 | 47篇 |
2022年 | 86篇 |
2021年 | 83篇 |
2020年 | 91篇 |
2019年 | 77篇 |
2018年 | 77篇 |
2017年 | 96篇 |
2016年 | 78篇 |
2015年 | 77篇 |
2014年 | 146篇 |
2013年 | 162篇 |
2012年 | 150篇 |
2011年 | 204篇 |
2010年 | 166篇 |
2009年 | 181篇 |
2008年 | 135篇 |
2007年 | 187篇 |
2006年 | 169篇 |
2005年 | 138篇 |
2004年 | 118篇 |
2003年 | 95篇 |
2002年 | 73篇 |
2001年 | 63篇 |
2000年 | 77篇 |
1999年 | 60篇 |
1998年 | 58篇 |
1997年 | 39篇 |
1996年 | 43篇 |
1995年 | 32篇 |
1994年 | 29篇 |
1993年 | 24篇 |
1992年 | 15篇 |
1991年 | 19篇 |
1990年 | 16篇 |
1989年 | 7篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有3158条查询结果,搜索用时 3 毫秒
91.
《Ceramics International》2022,48(22):33306-33314
Herein, a hydrothermal method was used for the synthesis of V2O5 nanowires (NWs) and Ag-doped V2O5. The prepared doped material was intercalated in MXene for the preparation of an Ag-doped V2O5/MXene nanocomposite using a facile ultrasonication method. For structural and morphological confirmation, X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Fourier transform infrared (FT-IR) spectroscopy were used. Additionally, for electrochemical measurements, cyclic voltammetry (CV), cyclic-charge discharge (CCD), and electrochemical impedance spectroscopy (EIS) were performed. To avoid the restacking of Al-etched layers of MXene, Ag–V2O5 nanowires were intercalated. This strategy ultimately increases the conductive channels, which helps in boosting the electrochemical properties of Ag–V2O5 nanowires. To fabricate electrodes, indium tin oxide (ITO) was used as a substrate. As prepared, the Ag-doped V2O5/MXene@ITO electrode showed a significant increase in the specific capacity. For the Ag-doped V2O5/MXene@ITO electrode, the calculated specific capacitance was 875 F/g (at 1 A/g) using galvanostatic charge-discharge (GCD) data. Also, it lost 6.1% of capacitance after the 3000th cycle. Results suggest that as-synthesized Ag–V2O5/MXene nanocomposite is a potential electrode material for energy storage. 相似文献
92.
《核技术(英文版)》2016,(5):98-105
For simulating more accurately neutron or proton production from photonuclear reactions,a data-based photonuclear reaction simulation algorithm has been developed.Reliable photonuclear cross sections from evaluated or experimental database are chosen as input data.For checking the validity of the use of the data-based photonuclear algorithm,benchmarking simulations are presented in detail.We calculate photonuclear cross sections or reaction yield for ~9Be,~(48)Ti,~(133)Cs,and ~(197)Au and compare them with experimental data in the region of incident photon energy below ~30 MeV.While Geant4 can hardly reproduce photonuclear experimental data,results obtained from the data-based photonuclear algorithm are found in good agreement with experimental measurements.Potential application in estimation of specific activity of radioisotopes is further discussed.We conclude that the developed data-based photonuclear algorithm is suitable for an accurate prediction of photoninduced neutron or proton productions. 相似文献
93.
Vivian Maria Carminato Blanco Lucas Tadeu Fuess Marcelo Zaiat 《International Journal of Hydrogen Energy》2017,42(17):12181-12196
Biohydrogen (bioH2) production via dark fermentation is an attractive approach to overcome the drawbacks of conventional hydrogen production methods and represents a preliminary alternative for the management of organic wastes. Fundamental studies are still required to enhance the performance of bioH2 production systems, with emphasis on the development of novel reactor configurations. The anaerobic structured-bed reactor (ASTBR) is a recently developed configuration with great potential for bioH2 production, although operating strategies are still required to minimize biomass washout in such systems. In this context, calcium dosing has been investigated as a strategy to enhance both biomass retention and bioH2 production rates in the ASTBR. The present study employed varying COD/calcium ratios (4423, 2079, 1357, 1012, 884, and 632) in continuous experiments under mesophilic conditions (25 °C). Calcium dosing effectively enhanced biomass retention within the ASTBR, directly increasing the availability of metabolic energy for different metabolic pathways rather than cell synthesis. An optimal COD/calcium ratio of 1360 was mathematically estimated for bioH2 production, which is consistent with the results obtained experimentally. The specific organic loading rate (SOLR) was better controlled at this ratio, indicating the establishment of balanced conditions in terms of substrate availability and biomass concentration. Conversely, bioH2 production was severely impaired at COD/calcium values below and above the optimal range, most likely due to enhancement of the homoacetogenic pathway as a result of unbalanced conditions in the SOLR. Furthermore, biomass accumulation did not strongly affect the mean residence time of the ASTBR, facilitating its robust and enhanced solid retention. 相似文献
94.
目的 提高以水作为润滑介质的织构型非金属推力轴承的润滑性能,为水润滑推力轴承的优化设计提供参考.方法 基于计算流体力学方法建立织构型水润滑推力轴承的流体动压润滑模型,采用双向流固耦合方法计算润滑流场与材料变形之间的相互作用.随后,以承载力最高和摩擦力最低为目标,采用响应曲面与非支配排序遗传算法相结合的多目标协同优化方法,对4种非金属材料的织构型推力轴承进行优化.结果 随着轴承材料弹性模量的降低,轴承内最高压力值逐渐降低,最大变形逐渐增加,且最优织构覆盖率值逐渐减小.当织构覆盖率为20%时,轴承材料对最优织构深度值无明显影响;当织构覆盖率增至40%及以上时,随着轴承材料弹性模量的降低,最优织构深度值逐渐增加.在同一轴承材料下,最优织构参数之间相互影响,随着织构覆盖率的增加,最优织构深度值逐渐增大.对于碳化硅陶瓷和尼龙等弹性模量较大的轴承材料,优化后,轴承内流体最高压力明显提升;对于超高分子量聚乙烯和赛龙等弹性模量较小的轴承材料,优化后,高压区面积明显增大.结论 轴承材料对轴承润滑性能及最优织构参数均有明显影响,且最优织构参数间相互影响.经过对织构型水润滑推力轴承的多目标协同优化,轴承润滑性能明显改善. 相似文献
95.
直线电机边端效应是由定子铁心、次级开断所致的固有效应,该效应会引起电机电磁推力的不同频率的脉动。本文首先基于电磁推力公式对边端效应所致的推力脉动频率进行了理论分析。然后利用一维磁路法对动态纵向边端效应引起的次级感应涡流沿轴向的分布规律进行了理论分析和解析计算,根据次级感应涡流进而计算得到了动态纵向边端效应引起的转差频率两倍频推力脉动幅值的解析表达式,并得到了推力脉动幅值和不考虑边端效应时的电磁推力值的比例关系,最后通过峰值功率20 MW,最大出力900 k N的大功率直线感应电动机实验系统对分析结论进行了试验验证。理论分析和试验结果表明:计及边端效应时直线电机电磁推力存在供电频率两倍频和转差频率两倍频的脉动,其中转差频率两倍频的脉动由动态纵向边端效应导致,主要和次级极数以及转差频率有关。 相似文献
96.
97.
98.
The thermal elastic hydro dynamic(TEHD) lubrication analysis for the thrust bearing is usually conducted by combining Reynolds equation with finite element analysis(FEA). But it is still a problem to conduct the computation by combining computational fluid dynamics(CFD) and FEA which can simulate the TEHD more accurately. In this paper, by using both direct and separate coupled solutions together, steady TEHD lubrication considering the viscosity-temperature effect for a bidirectional thrust bearing in a pump-turbine unit is simulated combining a 3D CFD model for the oil film with a 3D FEA model for the pad and mirror plate. Cyclic symmetry condition is used in the oil film flow as more reasonable boundary conditions which avoids the oil temperature assumption at the leading and trailing edge. Deformations of the pad and mirror plate are predicted and discussed as well as the distributions of oil film thickness, pressure, temperature. The predicted temperature shows good agreement with measurements, while the pressure shows a reasonable distribution comparing with previous studies. Further analysis of the three-coupled-field reveals the reason of the high pressure and high temperature generated in the film. Finally, the influence of rotational speed of the mirror plate on the lubrication characteristics is illustrated which shows the thrust load should be balanced against the oil film temperature and pressure in optimized designs. This research proposes a thrust bearing computation method by combining CFD and FEA which can do the TEHD analysis more accurately. 相似文献
99.
100.
Dong-Xu Qiao Hui Jiang Wen-Na Jiao Yi-Ping Lu Zhi-Qiang Cao Ting-Ju Li 《金属学报(英文版)》2019,32(8):925-931
A series of Ti_2ZrHf_(0.5)VNb_x( x = 0, 0.25, 0.5, 0.75 and 1.0) refractory high-entropy alloys were prepared to investigate the alloying effect of Nb on the microstructures and mechanical properties.All the alloys displayed a simple BCC structure.The microstructures of the alloys changed from the initial single-phase columnar structure( x = 0) to dendrite microstructure( x 0).At room temperature, all the alloys exhibited high ductility(with the compressive strains of more than 50%).With the increase in Nb content, the yield strength slightly decreased from 1160 to 980 MPa and the hardness dropped from 338 to 310 HV.Moreover, the alloys exhibited low density from 6.47 to 6.84 g/cm~3 and high specific yield strength(SYS) from 143 to 179 kPa m~3/kg.The comprehensive performance of ductility and SYS was superior to most of the reported highentropy alloys.The yield strength of the alloys increased from 405 to 859 MPa and from 85 to 195 MPa with the addition of Nb element at 873 K and 1073 K, respectively. 相似文献