全文获取类型
收费全文 | 346篇 |
免费 | 17篇 |
国内免费 | 15篇 |
专业分类
化学 | 21篇 |
力学 | 25篇 |
综合类 | 2篇 |
数学 | 24篇 |
物理学 | 12篇 |
综合类 | 294篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 9篇 |
2021年 | 8篇 |
2020年 | 6篇 |
2019年 | 8篇 |
2018年 | 3篇 |
2017年 | 9篇 |
2016年 | 13篇 |
2015年 | 24篇 |
2014年 | 20篇 |
2013年 | 20篇 |
2012年 | 23篇 |
2011年 | 29篇 |
2010年 | 10篇 |
2009年 | 22篇 |
2008年 | 20篇 |
2007年 | 23篇 |
2006年 | 19篇 |
2005年 | 21篇 |
2004年 | 14篇 |
2003年 | 14篇 |
2002年 | 12篇 |
2001年 | 10篇 |
2000年 | 9篇 |
1999年 | 11篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1991年 | 1篇 |
排序方式: 共有378条查询结果,搜索用时 203 毫秒
1.
2.
缓凝砂浆螺旋输送理论研究 总被引:1,自引:0,他引:1
缓凝预应力筋包覆装置是将新型独特的缓凝材料应用于预应力混凝土体系的一种施工设备.通过对缓凝砂浆的流变性能分析,建立了螺旋输送物理模型,运用粘性流体力学的运动微分方程研究缓凝砂浆螺旋输送的速度场和流率,从而对其装置的设计和运行参数的合理选择提供了理论依据. 相似文献
3.
J. Lawry A. Ray D. Klimesch P. Thomas J.-P. Guerbois J. Harrison 《Journal of Thermal Analysis and Calorimetry》2005,80(3):637-641
Summary Due to growing environmental concerns and the need to use less energy-intensive building products, alternatives and improvements to Portland cement (PC) are being actively researched worldwide. Use of supplementary materials is now a common practice where PC is the predominant component of inorganic building products. This study aims to investigate the potential of magnesia (MgO), derived from a naturally occurring raw material magnesite, as a supplementary material. Results from mortar samples prepared with 10 and 20% replacements of ordinary Portland cement (OPC) by MgO are presented. DTA-TG was used to study and characterise the hydration behaviour of MgO in OPC environment after 3, 7, 14, 28, 56 and 90 days of moist curing. Microstructural and compressive strength determinations providing additional information on the influence of hydrated phases are also reported. 相似文献
4.
采用多质点层间剪切型模型,建立了基础摩擦隔震多层砌体结构在水平与竖向耦合地震作用下的运动微分方程及滑动与啮合状态判别准则·通过数值计算,分析了竖向地震作用对隔震结构的影响,研究表明,竖向地震作用的存在,使隔震结构下部各层,特别是首层的层间位移,层间剪力增加,隔震层加速度增加,且随地震烈度,竖向加速度峰值增大而增加,并使隔震层的滑动位移幅值有增大的可能·建议在高烈度震区考虑竖向地震作用对结构反应的影响· 相似文献
5.
胶砂质量比对钢纤维砂浆力学性能的影响 总被引:3,自引:0,他引:3
对胶砂质量比和纤维直径对钢纤维水泥浆体和砂浆的力学性能的影响进行了研究 .在水泥浆体中 ,微细钢纤维的增强和增韧作用显著高于较大直径的钢纤维 .在砂浆中 ,随着胶砂质量比的降低 ,较大直径的钢纤维的作用越来越强 ,而微细钢纤维的作用逐渐降低 .不同几何尺寸的钢纤维在水泥浆体和砂浆中具有不同的作用效果 ,尺寸效应显著 相似文献
6.
7.
沥青胶浆对沥青混合料高低温性能的影响 总被引:16,自引:3,他引:16
在沥青混合料设计中,对沥青胶浆在沥青混合料中的作用认识模糊,并且对沥青胶浆的作用重视不够。按照胶浆理论,将沥青胶浆作为沥青混合料构成中的重要部分,研究了粉胶比变化、纤维对沥青混合料高、低温性能的影响。研究表明,沥青混合料的性能不仅受沥青用量和填料量的影响,更重要的是受填料与沥青相对比例的影响;在沥青混合料设计时应注意结合工程实际作出相应的设计和控制;减少粉胶比,并加入适量纤维,可显著改善沥青混合料的低温柔性的低温松弛能力,同时也使沥青混合料的高温性能得到较大的提高。 相似文献
8.
Organobentonite (OBT)/sodium polyacrylate (PAAS) composite material was prepared. The OBT/PAAS humidity-control cement-based mortars were prepared by mixing OBT/PAAS in mortar. Its morphology and structure were characterized by environmental scanning electron microscope (ESEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and the Brunauer-Emmett-Teller (BET) method. The results showed that the morphology and humidity-control capacity of OBT/PAAS mortar are superior to those of the original mortar. The OBT/PAAS mortar had larger pore specific surface area and larger pore volume, corresponding to the most probable pore diameter, than that of mortar. There was no chemical reaction between mortar and OBT/PAAS and there was no new crystal structure generated. The prepared, solidified OBT-PAAS mortar can maintain humidity in a desiccator at 38~62 RH%. 相似文献
9.
The polymer-cement composite is an immiscible band having modified morphology. Polymer phase improves the toughness of brittle cement and has a reinforcing effect, and interactions between cement components and polymers provide stability. In this study, polymer latex [poly(methyl methacrylate), PMMA] – cement paste was prepared with different weight proportions of polymer content. The main scientific objective of this report has been the analysis and the prediction of high strength with the aim of understanding the interactions of PMMA polymer with Portland cement after hydration reaction of cement pastes and curing the specimens for 28 days. The samples were studied by Fourier transform infrared (FT-IR) spectroscopy. The results are critically examined. It is shown that bands support the interaction of PMMA with cement in the composite. 相似文献
10.
Yingyot Poo‐arporn Surachai Thachepan Rungtiva Palangsuntikul 《Journal of synchrotron radiation》2015,22(1):86-90
Evidence of internal sulfate attack in field exposure was demonstrated by the damaged interior wall of a three‐year‐old house situated in Nakhon Ratchasima Province, Thailand. Partial distension of the mortar was clearly observed together with an expansion of a black substance. Removal of the black substance revealed a dense black layer. This layer was only found in the vicinity of the damaged area, suggesting that this black material is possibly involved in the wall cracking. By employing synchrotron‐based X‐ray photoelectron spectroscopy (XPS) and X‐ray absorption near‐edge structure (XANES) techniques, the unknown sample was chemically identified. The S 2p and O 1s XPS results mutually indicated the existence of sulfate species in the materials collected from the damaged area. The XANES results indicated the presence of ferrous (II) sulfate, confirming sulfate‐induced expansion and cracking. The sulfate attack in the present case appeared to physically affect the structure whereas the chemical integrity at the molecular level of the calcium silicate hydrate phase was retained since there was a lack of spectroscopic evidence for calcium sulfate. It was speculated that internal sulfate probably originated from the contaminated aggregates used during the construction. The current findings would be beneficial for understanding the sulfate‐attack mechanism as well as for future prevention against sulfate attack during construction. 相似文献