全文获取类型
收费全文 | 251篇 |
免费 | 23篇 |
国内免费 | 5篇 |
专业分类
综合类 | 11篇 |
化学工业 | 179篇 |
机械仪表 | 9篇 |
建筑科学 | 8篇 |
水利工程 | 1篇 |
石油天然气 | 15篇 |
无线电 | 2篇 |
一般工业技术 | 36篇 |
冶金工业 | 13篇 |
原子能技术 | 5篇 |
出版年
2023年 | 4篇 |
2022年 | 6篇 |
2021年 | 4篇 |
2020年 | 8篇 |
2019年 | 10篇 |
2018年 | 15篇 |
2017年 | 11篇 |
2016年 | 14篇 |
2015年 | 5篇 |
2014年 | 7篇 |
2013年 | 22篇 |
2012年 | 8篇 |
2011年 | 15篇 |
2010年 | 7篇 |
2009年 | 5篇 |
2008年 | 6篇 |
2007年 | 7篇 |
2006年 | 7篇 |
2005年 | 10篇 |
2004年 | 4篇 |
2003年 | 12篇 |
2002年 | 15篇 |
2001年 | 10篇 |
2000年 | 10篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 5篇 |
1991年 | 10篇 |
1990年 | 12篇 |
1989年 | 11篇 |
1985年 | 1篇 |
排序方式: 共有279条查询结果,搜索用时 15 毫秒
1.
R. Talero 《Cement and Concrete Research》2002,32(5):707-717
In this research, former XRD experiments have been verified by Le Chatelier-Ansttet (L-A) test. For this purpose, 28 cements consisting of 7 Portland cements and 21 blended cements containing 20%, 30% and 40% metakaolin have been submitted to the Le Chatelier-Anstett (L-A) test for 2 years. With all these cements, L-A specimens were manufactured and a direct parameter was measured for these specimens: increase in diameter, Δ∅, or diameter growth. Other complementary determinations were chemical analysis, XDA patterns and SEM of ettringites and specific properties of some cements tested. The experimental results have borne out that the formation rate of the ettringite formed from the reactive alumina, Al2O3r−, present in pozzolans must be considerably higher than the formation rate of the ettringite from C3A and much higher than the ettringite from C4AF, both present in OPC. Owing to this, these ettringites were proposed being named “rapid formation” (ett-rf), “slow formation” (ett-lf) and “very slow formation” (ett-vlf) ettringites, respectively. On the other hand, these experimental results have also shown that the ett-rf has a much smaller size than the ett-lf (this is a direct consequence of the aforementioned conclusion); that almost all the alumina, Al2O3, present in M pozzolan must be regarded as being “reactive,” Al2O3r−, or at least, the greatest part; that the detrimental effects derived from gypsum attack are shown much earlier in these POZC than in their plain OPC and, to such an extent, that this aggressive action can be described as rapid gypsum attack; and that none of the 21 POZC tested can be described as high nor moderate sulphate resistant cements according to L-A test. 相似文献
2.
Geometry-Dependent R-Curve for Quasi-Brittle Materials 总被引:4,自引:0,他引:4
Fracture of quasi-brittle materials such as ceramics and cement-based materials can be described by an R -curve, defined as fracture resistance. The R -curve can be constructed as the envelope of the strain energy release rates ( G ). In this study, R -curve is defined as an envelope of G -curves obtained by varying the dimensions of identical specimens, while keeping the geometry and the initial flaw size constant. By approximating the G -curve with a second-order function of the crack length, a simple formulation of the R -curve is derived by solving a differential equation. Three parameters are needed for the proposed R -curve. These parameters can be obtained by testing a notched-beam specimen and using linear elastic fracture mechanics. The proposed R -curve simulates well the geometry dependency as well as other characteristics of the fracture response of quasi-brittle materials. 相似文献
3.
A study of radiation effects on various types of glasses, dielectric optical coatings, cemented optics and fiber was undertaken with a view to select them for extreme radiation environments. Samples were exposed to different radiation doses in the Pakistan Research Reactor-I (PARR-I) for neutron and Cobalt 60 source for gamma irradiation. Transmissions were measured before and after irradiation. The dielectric coatings were subjected to additional tests (adhesion, abrasion and humidity, etc.) as per MIL-M-13508C and MIL-C-675C. All 15 glasses studied showed varying amounts of transmission loss as expected, with negligible degradation for three types. Recovery of transmissions with time/ageing was also studied, with more or less complete recovery with temperature annealing. A faster bleaching of darkened/brown glasses was achieved by using UV lamps or UV laser. The dielectric coatings (HR, AR) and one of the two commercial optical cements showed excellent resistance to neutrons and gamma radiations, and could be good candidates for the fabrication and utilization of optical components in extreme radiation environments. The data allowed several Chinese glasses to be studied for the first time. 相似文献
4.
Nakshatra B. Singh Awadhesh K. Singh Shashi Prabha Singh 《Journal of the American Ceramic Society》1990,73(10):3063-3068
Hydration occurring in the system Ca3 Al2 O6 –CaSO4 · 2H2 O–Ca(OH)2 –H2 O has been studied at different temperatures and it was found that the reactions are diffusion controlled. The kinetic data obeyed Jander's equation and the rate of reaction increased with increasing temperature. X-ray diffraction studies and calorimetric measurements show that when gypsum is consumed, ettringite is converted into monosulfate. The rate of this conversion also increased with the increasing temperature and decreased in the presence of citric acid. Spectroscopic studies showed that there was some interaction between citric acid and the cement and that the product of hydration is of colloidal nature. Zeta potential measurements show that retardation of Ca3 Al2 O6 hydration in the presence of gypsum and Ca(OH)2 is not due to SO2− 4 adsorption. Electrical conductivity and thermoelectric potential measurements of solid Ca3 Al2 O6 show that Ca3 Al2 O6 is an n -type semiconductor and contains defects. The retardation of Ca3 Al2 O6 may be due to poisoning of reaction sites by gypsum and Ca(OH)2. 相似文献
5.
Zeolite Formation in Class F Fly Ash Blended Cement Pastes 总被引:5,自引:0,他引:5
Judith L. LaRosa Stephen Kwan Michael W. Grutzeck 《Journal of the American Ceramic Society》1992,75(6):1574-1580
Zeolite formation in Class F fly ash blended cement pastes is under investigation. A Na–P type zeolite and Zeolite Y were synthesized from Class F fly ash and NaOH solution after 2 days of aging at room temperature and 6 days of curing at 80°C. However, no zeolites formed when KOH was used. In additional experiments, a Na–P type zeolite, Zeolite Y, and chabazite developed in cement pastes blended with Class F fly ash and NaOH solution which had been aged 2 days at room temperature and then cured 6 days at temperatures ranging from room temperature to 90°C. Seeding the pastes with natural zeolites was also investigated. 相似文献
6.
7.
分析现有参加水成球开环控制系统存在的问题,提出一种基于计算机图象识别的技术的水泥预加水成球闭环控制方法。 相似文献
8.
Elisabetta Mangione 《Journal of Adhesion Science and Technology》2019,33(14):1572-1583
This study evaluated the adhesion of resin cements to zirconia after saliva contamination using resin cements with different chemistries. Zirconia discs (N?=?240, n?=?10 per group) were randomly divided into three groups: (a) C: No contamination (Control), (b) S: Contamination with saliva, (c) S?+?AA: Contamination with saliva followed by air-abrasion (CoJet). While half of the specimens were not conditioned, the other half were conditioned with 37.5% H3PO4 for 60?s. After rinsing, all specimen surfaces were silanized (Monobond Plus). Resin cements based on either methacrylate (Variolink II–VL) or MDP monomer (Panavia 21-PN) were polymerized on the substrates. The specimens were randomly divided into two further groups to be tested either after (a) 24?h dry storage at 37?°C or (b) thermocycling (×5000, 5–55?°C). Microshear bond (MSB) tests were conducted in a Universal Testing Machine and failure types were analyzed. Data were analyzed using Univariate analysis and Tukey’s tests (alpha = 0.05). While saliva contamination, 37.5% H3PO4 application (p?<?.001) and aging (p?<?.05) significantly affected the bond results, cement type did not show significant difference after aging (p?>?.05). Adhesive strength of PN (1.2–4.4?MPa) on saliva contaminated and etched zirconia was more stable than that of VL (0–2.8?MPa). After aging, bond strength results decreased the most with VL (3–100%) compared to PN (32–71%) but the decrease was less in the air-abraded groups after aging (VL: 3%; PN: 32%). Exclusively adhesive failures were experienced in all groups. 相似文献
9.
10.
Emmanuel Nonnet Nicolas Lequeux Philippe Boch Sally L. Colston Paul Barnes 《Journal of the American Ceramic Society》2001,84(3):583-587
In situ Young's modulus measurements and synchrotron radiation-energy dispersive diffraction have been used to study changes in high-alumina castables subjected to heat treatment from room temperature to 1600°C. Particular attention was paid to the hydrate "conversion" process and the effects of high temperature. 相似文献