全文获取类型
收费全文 | 83499篇 |
免费 | 6354篇 |
国内免费 | 3262篇 |
专业分类
电工技术 | 4393篇 |
技术理论 | 6篇 |
综合类 | 5158篇 |
化学工业 | 14366篇 |
金属工艺 | 4534篇 |
机械仪表 | 5448篇 |
建筑科学 | 5967篇 |
矿业工程 | 2724篇 |
能源动力 | 2550篇 |
轻工业 | 5641篇 |
水利工程 | 1209篇 |
石油天然气 | 5817篇 |
武器工业 | 584篇 |
无线电 | 8695篇 |
一般工业技术 | 10550篇 |
冶金工业 | 4520篇 |
原子能技术 | 849篇 |
自动化技术 | 10104篇 |
出版年
2024年 | 362篇 |
2023年 | 1427篇 |
2022年 | 2443篇 |
2021年 | 3404篇 |
2020年 | 2542篇 |
2019年 | 2236篇 |
2018年 | 2630篇 |
2017年 | 2807篇 |
2016年 | 2418篇 |
2015年 | 3129篇 |
2014年 | 3999篇 |
2013年 | 4812篇 |
2012年 | 5083篇 |
2011年 | 5582篇 |
2010年 | 4859篇 |
2009年 | 4584篇 |
2008年 | 4403篇 |
2007年 | 4234篇 |
2006年 | 4348篇 |
2005年 | 3869篇 |
2004年 | 2630篇 |
2003年 | 2347篇 |
2002年 | 2112篇 |
2001年 | 1867篇 |
2000年 | 2023篇 |
1999年 | 2232篇 |
1998年 | 1919篇 |
1997年 | 1570篇 |
1996年 | 1503篇 |
1995年 | 1281篇 |
1994年 | 1041篇 |
1993年 | 775篇 |
1992年 | 602篇 |
1991年 | 452篇 |
1990年 | 355篇 |
1989年 | 279篇 |
1988年 | 243篇 |
1987年 | 153篇 |
1986年 | 132篇 |
1985年 | 103篇 |
1984年 | 73篇 |
1983年 | 41篇 |
1982年 | 51篇 |
1981年 | 38篇 |
1980年 | 30篇 |
1979年 | 17篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1976年 | 13篇 |
1975年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
ESCA (electron spectroscopy for chemical analysis) studies of β-C2S in the early stages of hydration have yielded valuable information on the chemical changes on the hydrating surface. These changes are less pronounced than, but very similar to, those noted for C3S. The data indicate that, although β-C2S hydrates more slowly than C3S, the same hydration mechanism applies to both. The studies also suggest surface hydroxylation as a first step in the hydration process. 相似文献
102.
Jinpeng Zhang Hongfeng Gao Nini Yuan Qiang Wang Yuhua Wu Yanli Sun Hongcun Bai 《中国化学工程学报》1982,28(11):2771-2777
Understanding and modulating the interaction between various reactive molecules and oxygen carriers are the key issue to achieve process intensification of chemical looping technology. C1 chemical molecules play an important role in many reactions involved with chemical looping processes. However, up to now, there is still a lack of systematic and in-depth understanding of the adsorption mechanism of C1 molecules on the surface of oxygen carriers (OCs). In this work, the intrinsic interaction between a series of C1 molecules composed of CH4, CO, CO2, CH3OH, HCHO and HCOOH and surface of NiO OCs in the chemical looping process have been studied using density functional theory calculations. Various adsorption configurations of C1 molecules and also different adsorption sites of NiO have been considered. The structural features of stable configuration of C1 molecules on the surface of NiO OCs have been obtained. Further, the interacted sites, types and strengths of C1 molecules on the surface of NiO have been directly pictured by the independent gradient model methods. Also, the nature of the interaction between C1 molecule and NiO surface has been investigated with the aid of energy decomposition analysis from a quantitative view. 相似文献
103.
Summary Three pairs of polyimide/polyimide blends (50/50 wt%) with different molecular structures were prepared by two ways, i.e. mixing of the polyamic acid precursors with subsequent imidization, and direct solution mixing of the polyimides. The blends were studied with DMA technique. The results obtained show that all the blends prepared with these two different ways are miscible, as there existed only one glass transition temperature (Tg) for all the blends. It is suggested that the miscibility of these polyimide/polyimide blends is a result of the strong inter-molecular charge-transfer interaction between the chains of their components. 相似文献
104.
5—烃基—2,3—二甲基吡嗪的合成 总被引:4,自引:1,他引:4
2,3-二基-5,6-二氢吡嗪与醛或酮在氢氧化钠的乙醇溶液中反应制得16种5-烃基-2,3-二甲基吡嗪。产率66%~90%。其中6种为新合成的化合物。产率17%~87.9%。 相似文献
105.
系统研究了苏州高岭土碳热还原氮化合成SiAlON过程在不同温度下的相变。对试样的XRD、SEM以及EDXA分析结果表明 ,1 30 0℃之前 ,试样中没有氮化物生成 ,物相为莫来石、石英和方石英 ;1 30 0℃时 ,高岭土开始发生氮化反应 ,生成过渡型SiAlON和β SiAlON。此时 ,石英和方石英相基本消失 ;1 4 0 0℃时 ,过渡型SiAlON、β SiAlON和X SiAlON三相共存 ,β SiAlON有所增多并有少量刚玉相生成 ;从 1 4 50℃到 1 550℃ ,Z值为 3的β SiAlON成为惟一的氮化产物 ,与少量SiC和刚玉相并存。莫来石在 1 50 0℃时完全消失 相似文献
106.
研究了钛酸酯类偶联剂和硅烷类偶联剂对钙矿、硅酸盐填充的PVC填允材料力学性能、相态结构、密度、热失重率及吸水伸长率和耐热阻燃性能的影响。结果表明,偶联剂可改善填充PVC的抗冲性能,降低其拉伸强度,扫描电镜分析表明,填料越细,分散越均匀,越易被PVC树脂所包覆,力学性能越好,研究得到了比重大、热失重率低、吸水伸长率小、阻燃耐烧灼性好的高填充PVC硬质塑料地板砖。 相似文献
107.
108.
动态硫化技术及其发展 总被引:3,自引:0,他引:3
结合动态硫化技术的发展史,重点评述了国外80年代该技术的发展及其特点,揭示了TPV性能及特征与制备条件的关系;简介我国开发研究TPV的概况,并提出了看法。 相似文献
109.
Fushe-Kruje水泥厂项目位于距阿尔巴尼亚首都地拉那市28公里处,是由黎巴嫩SEAMENT集团投资兴建的.是迄今阿尔巴尼亚最大的外商投资项目,设计能力为3300t/d新型干法水泥熟料生产线,是全套生产线由我公司设计、制造成套、施工、安装、调试及试生产的总承包项目。 相似文献
110.
This investigation focuses on slow, isothermal, two-phase flow of gas bubble suspensions in Separan solutions, prepared with the help of a sodium borohydride blowing agent at room temperature. The total residence time in these experiments is much smaller than characteristic times for growth or rise of bubbles. The variation of bubble volume fraction across a narrow gap between two planes, is recorded at two locations along the flow direction. This is done with a Cesium gamma-radiation source focused on a region of area.012 cm2 in the flow plane, and a Sodium iodide detector across the channel yielding a resolution of.01 over the range of void fractions investigated from.02 to.08. This measurement allows us to identify conditions under which the two-phase flow may be described by a two fluid model with a uniform bubbly core and a bubble free wall layer. With this two phase flow structure, a relative viscosity equation for the suspension is used to compute an apparent viscosity. Such calculations indicate that the observed reduction in apparent viscosity for the two phase flow may be attributed to a bubbly core which is more shear thinning than the medium. The additional shear thinning factor for the suspension is related to the elasticity of the medium. 相似文献