全文获取类型
收费全文 | 3155篇 |
免费 | 92篇 |
国内免费 | 114篇 |
专业分类
电工技术 | 44篇 |
综合类 | 132篇 |
化学工业 | 700篇 |
金属工艺 | 257篇 |
机械仪表 | 319篇 |
建筑科学 | 399篇 |
矿业工程 | 141篇 |
能源动力 | 57篇 |
轻工业 | 231篇 |
水利工程 | 20篇 |
石油天然气 | 85篇 |
武器工业 | 12篇 |
无线电 | 42篇 |
一般工业技术 | 548篇 |
冶金工业 | 190篇 |
原子能技术 | 16篇 |
自动化技术 | 168篇 |
出版年
2024年 | 1篇 |
2023年 | 30篇 |
2022年 | 63篇 |
2021年 | 70篇 |
2020年 | 66篇 |
2019年 | 48篇 |
2018年 | 72篇 |
2017年 | 73篇 |
2016年 | 97篇 |
2015年 | 155篇 |
2014年 | 173篇 |
2013年 | 189篇 |
2012年 | 228篇 |
2011年 | 231篇 |
2010年 | 135篇 |
2009年 | 178篇 |
2008年 | 125篇 |
2007年 | 163篇 |
2006年 | 161篇 |
2005年 | 169篇 |
2004年 | 133篇 |
2003年 | 125篇 |
2002年 | 102篇 |
2001年 | 77篇 |
2000年 | 73篇 |
1999年 | 89篇 |
1998年 | 69篇 |
1997年 | 57篇 |
1996年 | 41篇 |
1995年 | 42篇 |
1994年 | 43篇 |
1993年 | 23篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 13篇 |
1988年 | 8篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1979年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有3361条查询结果,搜索用时 281 毫秒
31.
聚四氟乙烯烧结成型的制备工艺 总被引:6,自引:0,他引:6
对聚四氟乙烯(PTFE)进行了压制试验和烧结试验,讨论了成型压力与试件的致密度、压缩强度以及压缩模量之间的关系,且对不同烧结工艺下试件的压缩强度进行了分析,得到较合适的成型压力和烧结工艺。结果表明:咖材料的压缩强度随压制压力的升高而减小,压缩模量随压制压力的升高而增加;闻的成型压力为27.5MPa,烧结温度380℃,保温时间4h。 相似文献
32.
33.
34.
The strength of adhesion of elastomers to rigid substrates generally increases with time of contact. This effect has been studied for samples of butyl and chlorobutyl rubber adhering to some rigid substrates. The peel strength increased continuously over long periods of contact until in some cases failure became cohesive within the elastomer layer. At higher temperatures the strength increased more rapidly, consistent with the WLF relation governing molecular motions. It is postulated that slow molecular rearrangements occur at the interface and increase the bond strength. A criterion for the observed transition from interfacial to cohesive failure is suggested. 相似文献
35.
F. Vodák 《Cement and Concrete Research》2005,35(7):1447-1451
Concrete applied for construction of nuclear power plant (NPP) Temelín (Czech Republic) has been exposed to γ-irradiation up to dose 6×105 Gy. Depending on the level of irradiation, changes in strength, porous structure and phase composition of the concrete have been studied. It is found that irradiation lowers both the strength of concrete (about 10%) and volume (resp. surface) of porous space. On the other hand, γ-irradiation increases the ratio of calcite, CaCO3, in the concrete. Observed effects are discussed with respect to safety of NPPs. 相似文献
36.
37.
Pozzolanic properties of reject fly ash in blended cement pastes 总被引:2,自引:0,他引:2
Low-grade fly ash (reject fly ash, r-FA), a significant portion of the pulverized fuel ash (PFA) produced from coal-fired power plants and rejected from the ash classifying process, has remained unused due to its high carbon content and large particle size. But it may be used in certain areas, such as in solidification and stabilization processes of hazardous waste and materials for road base or subbase construction, which require relatively lower strength and reactivity. It is therefore necessary to extend research on the properties of r-FA and explore its possible applications. This paper presents experimental results of a study on the mechanical and hydration properties of cementitious materials prepared by blending r-FA with ordinary Portland cement (OPC). Parallel mixes were also prepared with the good ash [i.e., classified fine fly ash (f-FA)] for comparison. Selective chemical activators were added to the mix to study the effects of the activators on the properties of the blend system. The results show that r-FA generally has a lower rate of hydration than f-FA particularly at the early stage of hydration. Adding Ca(OH)2 alone almost had no effect on accelerating the hydration of r-FA. But adding a small quantity of Na2SO4 or K2SO4 together with Ca(OH)2 significantly accelerated the hydration reaction. The results of the compressive strength measurement correlated nicely with the degree of hydration results. It was also found that water-to-binder ratio (w/b) was an important factor in affecting the strength development and the hydration degree of r-FA pastes. 相似文献
38.
39.
介绍了粉煤灰对掺有M17塑化剂的混凝土拌合物泵送性能和混凝土强度的影响,通过扫描电镜对粉煤灰颗粒形貌进行了观察,初步探讨了粉煤灰的作用机理。试验说明在接有M17塑化剂的泵送混凝土中加入粉煤灰,可增加坍落度,降低泌水率,泵逆性能可得到改善。 相似文献
40.
?akir Erdo?du 《Cement and Concrete Research》2005,35(5):907-912
To have concrete possesses the specified engineering properties, its slump loss has to be compensated somehow at construction site so that concrete could be placed and compacted properly. Several attempts have been tried so far to render concrete workable at construction site including starting with a high initial slump at the stationary plant, or retempering with water and/or with chemical admixtures at construction site. In this investigation, ASTM C 494 Type F superplasticizer was used for retempering concrete to restore its initial slump. Concrete mixes having an initial slump of about 19 cm were prepared and subjected to prolonged mixing with different mixing duration such as 30, 60, 90, 120, and 150 min following an initial mixing of 5 min to ensure homogeneity. At the end of each mixing period, cube specimens of 15 cm were cast from concrete retempered to its initial slump level and tested at the age of 28 days for compressive strength. Results revealed that compared to the concrete retempered with water, those retempered with a superplasticizer admixture have yielded significantly higher strength regardless of the mixing duration. 相似文献