全文获取类型
收费全文 | 13749篇 |
免费 | 1185篇 |
国内免费 | 849篇 |
专业分类
电工技术 | 713篇 |
综合类 | 1181篇 |
化学工业 | 1981篇 |
金属工艺 | 2076篇 |
机械仪表 | 288篇 |
建筑科学 | 1371篇 |
矿业工程 | 732篇 |
能源动力 | 274篇 |
轻工业 | 312篇 |
水利工程 | 595篇 |
石油天然气 | 419篇 |
武器工业 | 61篇 |
无线电 | 583篇 |
一般工业技术 | 1268篇 |
冶金工业 | 3472篇 |
原子能技术 | 138篇 |
自动化技术 | 319篇 |
出版年
2024年 | 23篇 |
2023年 | 339篇 |
2022年 | 474篇 |
2021年 | 533篇 |
2020年 | 524篇 |
2019年 | 417篇 |
2018年 | 442篇 |
2017年 | 315篇 |
2016年 | 360篇 |
2015年 | 354篇 |
2014年 | 565篇 |
2013年 | 581篇 |
2012年 | 754篇 |
2011年 | 860篇 |
2010年 | 676篇 |
2009年 | 701篇 |
2008年 | 657篇 |
2007年 | 784篇 |
2006年 | 808篇 |
2005年 | 727篇 |
2004年 | 615篇 |
2003年 | 640篇 |
2002年 | 512篇 |
2001年 | 503篇 |
2000年 | 423篇 |
1999年 | 467篇 |
1998年 | 340篇 |
1997年 | 281篇 |
1996年 | 232篇 |
1995年 | 202篇 |
1994年 | 164篇 |
1993年 | 133篇 |
1992年 | 109篇 |
1991年 | 77篇 |
1990年 | 59篇 |
1989年 | 36篇 |
1988年 | 19篇 |
1987年 | 24篇 |
1986年 | 15篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1975年 | 1篇 |
1959年 | 1篇 |
1957年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
91.
《中国有色金属学会会刊》2020,30(4):1124-1134
To solve the problems of high energy consumption, low efficiency and short service life of conventional rare earth reduction cells, a 20 kA new rare earth reduction cell (NRERC) was presented. The effects of the anode-cathode distance (ACD) and electrolyte height (EH) on the thermo-electrical behavior of the NRERC were studied by ANSYS. The results illustrate that the cell voltage drop (CVD) and the temperature will rise with a similar tendency when the ACD increases. Also, the temperature rises gradually with EH, but the CVD decreases. Ultimately, when the ACD is 115 mm and the EH is 380 mm, the CVD is 4.61 V and the temperature is 1109.8 °C. Under these conditions, the thermal field distribution is more reasonable and the CVD is lower, which is beneficial to the long service life and low energy consumption of the NRERC. 相似文献
92.
《Journal of the European Ceramic Society》2020,40(15):5067-5075
The influence of Y2O3 addition on the microstructure, thermo-mechanical properties and oxidation resistance of carbon fibre reinforced ZrB2/SiC composites was investigated. Y2O3 reacted with oxide impurities present on the surface of ZrB2 and SiC grains and formed a liquid phase, effectively lowering the sintering temperature and allowing to reach full density at 1900 °C. The presence of a carbon source (fibres) led to additional reactions which resulted in the formation of new secondary phases such as yttrium boro-carbides. Mechanical properties were significantly enhanced compared to the un-doped composite. Further tests at high temperatures resulted in strength increase up to 700 MPa at 1500 °C which was attributed to stress relaxation. Oxidation tests carried out at 1500 °C and 1650 °C in air showed that the presence of the Y-based secondary phases enhanced the growth of ZrO2 grains, but offered limited protection to oxygen due to the lower availability of surficial SiO2 formed from SiC. 相似文献
93.
《中国有色金属学会会刊》2020,30(6):1647-1661
The two-dimensional infiltration experiment was carried out by means of digital image technology. The evolution process of the wetting body was described. The wetted front distance and the time show a very significant power function relationship. The horizontal wetted distance is larger than the vertical wetted distance in the initial stage. Then, the vertical distance of the wetted body gradually approaches to the horizontal distance. The infiltration distance decreases as the content of fine particles increases. The wetted front migration rate curve shows a three-stage change law, and it increases with the increase of coarse particle content. The directional velocity ratio is defined. The initial value of horizontal infiltration rate is larger than that of vertical one, and then the vertical infiltration rate is gradually close to the horizontal value. The empirical relationship between the characteristic particle size and the stable infiltration rate is established, which provides a theoretical basis for the prediction of the stable infiltration rate in in-situ leaching. 相似文献
94.
95.
随着战略性新兴产业的兴起发展,稀土作为战略资源的重要地位不断凸显,作为公共产品供给,稀土出口问题备受国内外关注。文章运用CiteSpace软件并基于文献计量与知识图谱分析方法,以CNKI文献资料为数据源,对1993~2019年稀土出口研究相关文献从发文量、作者群体、发文机构、关键词、突现词及时间线方面进行分析,以探讨国内稀土出口领域研究的演进趋势与发展热点。结果表明:近年来稀土出口领域文献整体呈增长趋势,但是文献发表具有明显的波动性和政策关联性。作者群体和发文机构主要集中在具有科研优势或资源优势地区的高校,研究团队之间合作程度较低。稀土产业、出口管制、出口配额、出口定价、出口政策等成为文献关键词和高频词。未来的稀土出口领域的研究方向主要集中在出口定价、可持续发展、本土稀土产业链发展和稀土产业资本出口四个方面。 相似文献
96.
以商用Y2O3、MgO纳米粉体为原料,通过球磨混合方法制备了不同Y2O3/MgO配比的Y2O3-MgO纳米复合粉体,使用X射线衍射、扫描电镜、能量色散谱等表征手段对制备粉体的晶体结构、形貌、成分以及均匀性进行了表征。然后采用热压烧结方法制备Y2O3-MgO复相红外透明陶瓷,使用红外光谱仪、维氏硬度计等测试设备对复相透明陶瓷的光学和力学性能进行了分析。重点研究了粉体配比、热压温度、保温和保压时间等关键制备参数对Y2O3-MgO复相红外透明陶瓷晶粒尺度、致密化程度、光学及力学性能的影响。并通过调控粉体制备工艺和热压烧结工艺,制备出了红外透过率达到~80%的Y2O3-MgO复相红外透明陶瓷。同时在Y2O3:Mg0=1:1时,该复相陶瓷的硬度达到了12.3 GPa。 相似文献
97.
介绍了稀土晶体的科学内涵,包括稀土晶体的概念、学科特色和分类。阐述了稀土晶体材料的研发现状,包括稀土磁学材料、光学材料、电学材料、催化材料、能源材料、合金材料以及稀土原料。指出中国已建成从稀土矿产勘探开采、选矿、萃取、分离、冶炼等稀土原材料生产技术到下游稀土结构与功能材料研发和工业生产体系,形成了全球门类最齐全、规模第一的稀土新材料产业体系,但是仍未系统掌握稀土高技术材料和器件领域的核心技术。针对创新引领能力不足、稀土资源高端利用能力不强等系列问题,中国还需要在基础科学研究、应用基础研究、产业发展、资源回收等方面进一步加强战略规划。 相似文献
98.
《中国稀土学报(英文版)》2020,38(5):506-513
Energy transfer among the co-doped activators is an efficient route to achieve color-tunable emission in inorganic phosphors.Herein,photoluminescence tuning from blue to cyan has been achieved in the Lu_2MgAl_4 SiO_(12);Eu~(2+),Ce~(3+)phosphors by varying the Ce~(3+) concentration with a fixed Eu~(2+)content.With the further introduction of a Mn~(2+)-Si4+couple into the host lattice,the emission color can be tuned to red through the energy transfer of Eu~(2+)and Mn~(2+).The luminescence properties and the energy transfer mechanism were studied in detail.The energy transfer from Eu~(2+)to Ce~(3+)is certified as a dipolequadrupole interaction with the energy transfer efficiency of 41.4% and Eu~(2+)to Mn~(2+)belongs to a dipole-dipole interaction with the energy transfer efficiency of 94.3%.The results imply that this singlephased Lu_2MgAl4 SiO_(12):Eu~(2+),Ce~(3+),Mn~(2+)phosphor has a potential prospect for application in near-UV chip pumped white light emitting diodes. 相似文献
99.
Microalloying is thought to improve the performance of Al–Mg alloys commonly used in transport applications. The effect of Y addition (0–0.4%) on the microstructure, mechanical properties, and corrosion resistance of Al–9.2Mg–0.7Mn alloy is investigated for potential use in engineering applications. The generation of the β-Al3Mg2 phase along the grain boundaries is suppressed in the as-cast alloy due to the formation of the AlMgY ternary phase. The average intergranular corrosion mass loss of the alloy with 0.1% Y addition decreases about 53.1% almost at no expense of mechanical performance in the as-rolled alloy after annealing. Moreover, the alloy with 0.1% Y addition shows the corrosion mass loss about 30.2% lower than the Y-free alloy in the sensitized state. The enhanced corrosion resistance of the alloy can be ascribed to the reduced β-Al3Mg2 precipitation along the grain boundaries associated with Y addition. 相似文献
100.
采用溶胶-凝胶法制备了经稀土元素Ce掺杂改性的Ti/RuO_2-SnO_2-Ce电极,利用SEM、XRD、EDS等分析方法对电极表面的形貌、物相和涂层成分进行了表征,利用CV曲线、LSV曲线等检测手段对电极的电化学性能进行了测试。以Ti/RuO_2-SnO_2-Ce电极为阳极,钛板为阴极,构建电化学氧化反应装置,并采用其对焦化废水进行电解处理。结果表明,Ti/RuO_2-SnO_2电极经稀土Ce改性后极板表面活性位点数量明显增大,金属涂层的结晶化程度明显增强,电极的催化氧化活性显著提高。室温条件下,保持pH值为7.83,在电流密度为30mA/cm~2,电解时间为30min时,焦化废水经电解处理后COD去除率可达91.63%,TOC去除率可达66.22%,UV254值下降到0.921。 相似文献