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71.
Lei Lu Qingli Hao Wu Lei Xifeng Xia Peng Liu Dongping Sun Xin Wang Xujie Yang 《Small (Weinheim an der Bergstrasse, Germany)》2015,11(43):5833-5843
Catalysts with low‐cost, high activity and stability toward oxygen reduction reaction (ORR) are extremely desirable, but its development still remains a great challenge. Here, a novel magnetically separable hybrid of multimetal oxide, cobalt ferrite (CoFe2O4), anchored on nitrogen‐doped reduced graphene oxide (CoFe2O4/NG) is prepared via a facile solvothermal method followed by calcination at 500 °C. The structure of CoFe2O4/NG and the interaction of both components are analyzed by several techniques. The possible formation of Co/Fe N interaction in the CoFe2O4/NG catalyst is found. As a result, the well‐combination of CoFe2O4 nanoparticles with NG and its improved crystallinity lead to a synergistic and efficient catalyst with high performance to ORR through a four‐electron‐transfer process in alkaline medium. The CoFe2O4/NG exhibits particularly comparable catalytic activity as commercial Pt/C catalyst, and superior stability against methanol oxidation and CO poisoning. Meanwhile, it has been proved that both nitrogen doping and the spinel structure of CoFe2O4 can have a significant contribution to the catalytic activity by contrast experiments. Multimetal oxide hybrid demonstrates better catalysis to ORR than a single metal oxide hybrid. All results make the low‐cost and magnetically separable CoFe2O4/NG a promising alternative for costly platinum‐based ORR catalyst in fuel cells and metal‐air batteries. 相似文献
72.
以堇青石(Mg2Al4Si5O18)、Fe2O3、MnO2、CuO和Co2O3为原料,通过微波加热合成堇青石-铁氧体基红外复合陶瓷材料,利用X射线衍射、红外光谱仪、热重-差热分析等手段分析该复合陶瓷的物相组成与结构、辐射率及热稳定性,研究名义成分对复合陶瓷材料结构与性能的影响。结果表明:该复合陶瓷中的铁氧体为混合型尖晶石结构。铁氧体含量(质量分数,下同)为10%时,随原料粉末中Fe2O3含量增加或MnO2含量减少(即Fe2O3与MnO2的质量比增大),Mn3+尖晶石相含量减少,但Fe2O3与MnO2的质量比对复合陶瓷辐射率的影响较小;w(Fe2O3):w(MnO2)的值为3:1时,随铁氧体含量增加,堇青石的衍射峰向小角度方向偏移,堇青石的晶面间距增大,陶瓷材料的辐射率相应增加;当铁氧体含量为30%时,300℃下复合陶瓷在8~14μm波段的红外辐射率达0.80~0.89。此外,微波加热合成的堇青石-铁氧体基红外陶瓷热稳定性较好,可在1300℃高温环境下使用。 相似文献
73.
X90管线钢管是目前正在研究开发的一种新型高强度管线钢管. 随着管材强度的提高,焊缝的组织与性能成为研究与控制的关键. 文中对焊缝、热影响区(HAZ)和母材微观组织、晶粒取向、大/小角度晶界占比及冲击断口形貌等进行了分析研究. 结果表明,焊缝试样近断口区组织为针状铁素体(AF)+准多边形铁素体(QPF),M-A组元呈楔形、块状和条带状,分布于相界处,尺寸较大,长1.8 μm,宽0.5 μm,组织有效平均晶粒尺寸为3.12 μm,大角度晶界比例为67.15%;而HAZ试样近断口区组织为粒状贝氏体(GB)+多形态M-A组元,晶粒粗大,M-A组元多以条带状、楔形分布于晶界和晶内,组织有效平均晶粒尺寸为4.52 μm,大角度晶界比例为85.95%. 母材试样近断口区组织是以细小AF+QPF+板条贝氏体(LB)+少量M-A组元为主的多相匹配的复相组织,M-A组元尺寸细小,组织有效平均晶粒尺寸为2.1 μm,大角度晶界比例为93.75%.密集分布的大尺寸M-A组元和大角晶界占比较小是导致焊缝冲击韧性低于母材的重要原因. 相似文献
74.
75.
76.
Shan Feng Haigang Du Taiping Xie Longjun Xu Yajing Wang 《Ceramics International》2019,45(8):10468-10474
BiOI/MnxZn1-xFe2O4 magnetic photocatalysts were successfully prepared for the first time. With the degradation of simulated RhB wastewater as a pointer to the photocatalytic reaction and combined with Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible diffuse reflectance spectroscopy (UV–vis DRS), and vibrating sample magnetometer (VSM), the reasons influencing the photocatalytic performance of the magnetic photocatalysts were further explored. The excessive or insufficient Mn-Zn ferrite both leads to a relatively low photocatalytic activity. When the calcination temperature reaches to 200 and 400?°C, the photocatalytic activity is enhanced significantly, but the main active component in the photocatalysts has changed from BiOI to Bi5O7I at 400?°C. The nanocomposites prepared under alcohol water environment with hollow microspheres morphology possess a highly photocatalytic efficiency, and the RhB degradation rate within 4?h in the ethanol water environment is significantly higher than that in pure water (98% vs. 59%). 相似文献
77.
ABSTRACTMedium-Mn steels are energetically investigated as a candidate of the third generation advanced high strength steels (AHSSs). However, their phase transformation and microstructaure evolution during various heat treatments and thermomechanical processing are still unclear. The present study first confirmed the kinetics of static phase transformation behaviour in a 3Mn-0.1C medium-Mn steel. Hot compression tests were also carried out to investigate the influence of high-temperature deformation of austenite on subsequent microstructure evolution. It was found that static ferrite transformation was quite slow in this steel, but ferrite transformation was greatly accelerated by the hot deformation in austenite and ferrite two-phase regions. Characteristic dual-phase microstructures composed of martensite and fine-grained ferrite were obtained, which exhibited superior mechanical properties.This paper is part of a Thematic Issue on Medium Manganese Steels. 相似文献
78.
In the present work, the microstructural evolution and hardness of HSLA X70 joined by friction stir welding were investigated. The FSW was applied to HSLA X70 with and without the addition of titanium dioxide (TiO2) powders. To evaluate the microstructural features and hardness of different weld zones, optical microscopy and Vickers microhardness measurements were applied. The results show that the distribution of TiO2 powders is strongly dependent on the applied friction stir processing, which in turn changed significantly the microstructure and hardness profile. In this regard, the optimum stirring action resulted in a homogeneous and fine dispersion of particles leading to the domination of an acicular ferrite phase with a hardness of 370 HV. On the other hand, the lower stirring action resulted in coarse particles as well as the development of the polygonal ferrite structure with a hardness of ~185 HV. 相似文献
79.
摘要:为了深入了解铁素体基Ti-Mo高强钢在连续冷却相变过程中组织及硬度的变化及其原因,通过热膨胀法、金相及硬度等实验研究了Ti-Mo微合金钢在连续冷却条件下组织及性能的变化,探讨了冷却速率对组织、硬度及相变行为的影响机理,揭示了(Ti,Mo)C在奥氏体和铁素体中Ti/Mo原子比变化的原因。结果表明,随着冷却速率由0.06℃/s增加至17.9℃/s,组织依次为多边形铁素体+珠光体→多边形铁素体+粒状贝氏体→粒状贝氏体,硬度由144HV逐渐增大至228HV。当冷速由0.14℃/s增大至0.90℃/s时,组织中多边形铁素体比例不断增大,珠光体比例不断降低,硬度的提高主要来自于铁素体晶粒尺寸的细化及纳米级(Ti,Mo)C粒子的增多;当冷速由1.79℃/s增大至17.9℃/s时,组织中多边形铁素体比例不断降低,贝氏体比例不断提高,硬度的提高主要是由于贝氏体组织的细化及其比例的增加。(Ti,Mo)C粒子主要有2类:一类是奥氏体中析出的10~20nm的粒子,Ti原子数分数约为88%,另一类是铁素体中析出的小于10nm的粒子,Ti原子数分数约为68%,EDS测量结果与计算结果大致相当。 相似文献
80.
Yang Liu 《Materials Science & Technology》2019,35(5):536-543
The δ-ferrite to γ-austenite phase transformation in duplex stainless steels was observed using ultra high-temperature confocal laser scanning microscope, and the orientation relationship between the γ phase, and precipitate is discussed. Owing to mutual promotion action, the γ phase was observed at δ/δ grain boundary at the beginning of δ-ferrite→γ-austenite transformation, followed by two-dimensional γ-phase growth at the same speed (0.625?µm?s?1) along the grain boundary and into the δ grain matrix. The γ-phase growth rate decreases to 0.244?µm?s?1 when precipitate stops growing. In the process of grain growth at high temperature, the precipitated pinning grain boundary will slow the movement speed of the grain boundary.
The mutual promotion action leads to preferential nucleation of the γ phase, and the nucleation and growth of the austenite also promoting the growth of MnS the growth. 相似文献