全文获取类型
收费全文 | 45190篇 |
免费 | 4971篇 |
国内免费 | 2659篇 |
专业分类
电工技术 | 4119篇 |
综合类 | 3099篇 |
化学工业 | 12233篇 |
金属工艺 | 3833篇 |
机械仪表 | 1960篇 |
建筑科学 | 3992篇 |
矿业工程 | 653篇 |
能源动力 | 4030篇 |
轻工业 | 2325篇 |
水利工程 | 536篇 |
石油天然气 | 1912篇 |
武器工业 | 740篇 |
无线电 | 3517篇 |
一般工业技术 | 6556篇 |
冶金工业 | 1715篇 |
原子能技术 | 727篇 |
自动化技术 | 873篇 |
出版年
2024年 | 263篇 |
2023年 | 879篇 |
2022年 | 1306篇 |
2021年 | 1673篇 |
2020年 | 1833篇 |
2019年 | 1620篇 |
2018年 | 1504篇 |
2017年 | 1835篇 |
2016年 | 1799篇 |
2015年 | 1838篇 |
2014年 | 2616篇 |
2013年 | 3031篇 |
2012年 | 3066篇 |
2011年 | 3188篇 |
2010年 | 2367篇 |
2009年 | 2473篇 |
2008年 | 2143篇 |
2007年 | 2795篇 |
2006年 | 2698篇 |
2005年 | 2089篇 |
2004年 | 1832篇 |
2003年 | 1474篇 |
2002年 | 1355篇 |
2001年 | 1185篇 |
2000年 | 1015篇 |
1999年 | 810篇 |
1998年 | 703篇 |
1997年 | 621篇 |
1996年 | 509篇 |
1995年 | 385篇 |
1994年 | 307篇 |
1993年 | 256篇 |
1992年 | 252篇 |
1991年 | 224篇 |
1990年 | 190篇 |
1989年 | 151篇 |
1988年 | 115篇 |
1987年 | 67篇 |
1986年 | 63篇 |
1985年 | 65篇 |
1984年 | 58篇 |
1983年 | 44篇 |
1982年 | 45篇 |
1981年 | 25篇 |
1980年 | 17篇 |
1979年 | 5篇 |
1975年 | 4篇 |
1973年 | 2篇 |
1959年 | 7篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
大型水轮发电机组励磁变压器参数及绝缘方式的选择--由三峡机组励磁系统投运引起的思考 总被引:1,自引:0,他引:1
结合三峡机组励磁系统的调试及投运经验,对大型水电机组静止自励系统选型中存在的一些关键性技术课题进行分析与论证,期望得出的结论有助于在大型水轮发电机组励磁系统参数选择和在提高机组运行安全、可靠性方面提供有益的借鉴。文中提出的励磁系统设计新理念仅代表个人的观点。 相似文献
32.
基于高抗热震性能的陶瓷刀具材料的微观结构设计 总被引:1,自引:0,他引:1
本文以现有的抗热震断裂和抗热震损伤的评价理论为基础,通过对材料中微裂纹的长度进行预测,从而实现了对陶瓷刀具材料的抗热震性能的微观结构设计。根据此理论对现有材料的抗热震性能的进行预测,预测结果与实际的测量结果相符,验证了该理论的正确性。 相似文献
33.
34.
A. J. Slifka T. Hall E. S. Boltz 《Journal of research of the National Institute of Standards and Technology》2003,108(2):151-156
A simple measurement system is described for evaluating damage to graphite-epoxy panels, such as those used in high-performance aircraft. The system uses a heating laser and infrared imaging system to measure thermal performance. Thermal conductivity or diffusivity is a sensitive indicator of damage in materials, allowing this thermal measurement to show various degrees of damage in graphite-epoxy composites. Our measurements track well with heat-flux damage to graphite epoxy panels. This measurement system, including analysis software, could easily be used in the field, such as on the deck of an aircraft carrier or at remote air strips. 相似文献
35.
采用先加入絮凝剂脱灰,再经减压蒸馏切割420~500℃馏分的方法,将辽河催化裂化澄清油预处理,考察了澄清油、加入絮凝剂脱灰后的澄清油以及脱灰后再减压蒸馏所得的中间馏分这3种原料在热转化过程中中间相的转化历程,并采用偏光显微镜观察热转化产物。结果表明,澄清油预处理效果明显,所得中间馏分具有较低的H/C原子比(nH/nC)和适宜的组成分布,是生产针状焦的理想原料。热转化产物的光学组织结构属于各向异性发达的广域-流线型结构。 相似文献
36.
This paper presents the current understanding of the flame retardant mechanism of Casico?. The study includes the flame retardant effect of each individual component: ethylene–acrylate copolymer, chalk and silicone elastomer, as well as the formation of an intumescent structure during heating. The flame retardant properties were investigated by cone calorimetry and oxygen index tests. To obtain insight into the flame retardant mechanism, heat treatment under different conditions has also been performed. The results indicate that the flame retardant mechanism of Casico is complex and is related to a number of reactions, e.g. ester pyrolysis of acrylate groups, formation of carbon dioxide by reaction between carboxylic acid and chalk, ionomer formation and formation of an intumescent structure stabilized by a protecting char. Special emphasis is given to the formation of the intumescent structure and its molecular structure as evaluated from 13C MAS‐NMR and 29Si MAS‐NMR, ESCA and XRD analysis. After treatment at 500°C the intumescent structure consists mainly of silicon oxides and calcium carbonate and after treatment at 1000°C the intumescent structure consists of calcium silicate, calcium oxide and calcium hydroxide. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
37.
38.
N‐p‐Bromophenylmaleimide (BrPMI) does not polymerize in solution by conventional free radical mechanism. However, it readily polymerized in bulk when mixed with a free radical initiator and heated in a microwave oven for 7–8 min. Copolymerization of ethyl methacrylate or butyl methacrylate with BrPMI was conducted in dioxane. The copolymers were characterized by IR and 1H NMR spectroscopy and gel permeation chromatography. The monomer reactivity ratios were calculated by a non‐linear least‐square analysis. Thermal analysis indicated a great improvement in thermal stability of the copolymers compared with the methacrylate homopolymers. BrPMI was also polymerized in bulk in the DSC pan, which allowed the calculation of the activation energy of its polymerization. Copyright © 2003 Society of Chemical Industry 相似文献
39.
40.
Hydrothermal Synthesis and Low-Temperature Sintering of Zinc Gallate Spinel Fine Particles 总被引:1,自引:0,他引:1
Nanosized powders of single-phase zinc gallate (ZnGa2 O4 ) spinel were hydrothermally synthesized from solutions in the presence of NaOH over the pH range of 1.9 to 7.0 and from solutions above pH 7.0, i.e., the very basic medium (pH of 13.85), by removing the residual ZnO phase by washing with aqueous H2 SO4 from the precipitate mixtures of zinc gallate spinel particles and ZnO. A very wide compositional range (Zn/2Ga = 0.705–1.157) of zinc gallate spinel solid solutions could be hydrothermally synthesized in the form of nanosized particles from acid and very basic mediums (pH of 2.4–13.85) in the presence of NaOH. These hydrothermally synthesized spinel powders showed good sinterability and almost full densification at 1100°C for 1 h. Dense sintered bodies consisting of single-phase zinc gallate spinel were fabricated at 1100°C using zinc gallate spinel powders having almost stoichiometric composition formed from the solution at pH 9.95 in the presence of aqueous ammonia. 相似文献