全文获取类型
收费全文 | 44279篇 |
免费 | 3273篇 |
国内免费 | 1188篇 |
专业分类
电工技术 | 555篇 |
综合类 | 6398篇 |
化学工业 | 2787篇 |
金属工艺 | 578篇 |
机械仪表 | 482篇 |
建筑科学 | 26364篇 |
矿业工程 | 928篇 |
能源动力 | 506篇 |
轻工业 | 160篇 |
水利工程 | 4918篇 |
石油天然气 | 223篇 |
武器工业 | 170篇 |
无线电 | 282篇 |
一般工业技术 | 2799篇 |
冶金工业 | 675篇 |
原子能技术 | 74篇 |
自动化技术 | 841篇 |
出版年
2024年 | 49篇 |
2023年 | 402篇 |
2022年 | 967篇 |
2021年 | 1013篇 |
2020年 | 1034篇 |
2019年 | 676篇 |
2018年 | 799篇 |
2017年 | 1014篇 |
2016年 | 1137篇 |
2015年 | 1484篇 |
2014年 | 2946篇 |
2013年 | 1901篇 |
2012年 | 3072篇 |
2011年 | 3327篇 |
2010年 | 2635篇 |
2009年 | 3279篇 |
2008年 | 3152篇 |
2007年 | 3749篇 |
2006年 | 3036篇 |
2005年 | 2637篇 |
2004年 | 2016篇 |
2003年 | 1764篇 |
2002年 | 1532篇 |
2001年 | 1201篇 |
2000年 | 994篇 |
1999年 | 724篇 |
1998年 | 496篇 |
1997年 | 402篇 |
1996年 | 314篇 |
1995年 | 230篇 |
1994年 | 202篇 |
1993年 | 139篇 |
1992年 | 113篇 |
1991年 | 71篇 |
1990年 | 47篇 |
1989年 | 46篇 |
1988年 | 32篇 |
1987年 | 31篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 11篇 |
1982年 | 17篇 |
1980年 | 24篇 |
1979年 | 2篇 |
1975年 | 2篇 |
1967年 | 1篇 |
1964年 | 1篇 |
1962年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
41.
42.
本文采用有限元分析软件ANSYS模拟了不同围压(0,25.5,51.2 MPa)条件下素混凝土圆柱试样压缩响应特征。首先,综合对比分析了Druck-Prager模型及多线性强化(MISO)模型的模拟效果。此外,进一步基于MISO模型分析了混凝土试件端部约束条件对模拟结果的影响。最终得到的主要结论包括:(1)单轴压缩条件下,有限元模拟结果与试验结果一致性较好,且Druck-Prager模型更适宜模拟混凝土体应变特征;(2)施加围压时,MISO模型所得抗压强度较保守,而Druck-Prager模型高估了混凝土抗压强度;(3)就MISO模型而言,端部摩擦约束对混凝土应力—应变曲线无显著影响,但会加剧混凝土体积膨胀(剪胀)。 相似文献
43.
44.
Construction and demolition waste (CDW) recycling is generally limited to the use of the coarser fraction as aggregate for new concrete. The recovery of fine aggregates requires a cleaning by removing the hydrated cement waste (HCW). In this paper, the possibility to use HCW extracted from CDW as alternative component for the production of new clinker is explored.A pure HCW sample was prepared and used in partial replacement of natural materials in raw admixtures for new clinker production. At a replacement degree of 30%, a new Portland clinker containing almost 50% of C3S could be produced with a huge spare in the release of CO2 (about 1/3 less). At higher HCW dosage a non-Portland clinker containing almost 80% of C2S has been obtained: its use as supplementary cementing material in blended cements revealed satisfying long term performances. 相似文献
45.
46.
针对红岭铅锌矿分级充填骨料来源不足、地表废石堆积污染环境的情况,提出将该矿选厂产生的全尾砂和地表废石作为充填骨料的联合胶结充填方案。分别测试了全尾砂和地表废石的物理化学性质,验证了碎石和全尾砂作为联合充填骨料的可行性。通过充填配比试验,分析了不同配比全尾砂废石充填体强度特性,得出了最佳充填配比。结果表明,充填试块的强度随灰砂比减小而减小,随养护龄期增加呈增大趋势,随充填料浆质量浓度增大而增大,最佳配比为: 胶结充填灰砂比1∶8、普通充填灰砂比1∶12,全尾砂∶废石配比4∶6,质量浓度78%。根据研究结果,在红岭铅锌矿进行了全尾砂废石充填技术工业应用,证实该技术可行。 相似文献
47.
48.
This paper presents the fresh, mechanical, and durability performance, of a structural concrete mix classified as C-1, by the Canadian Standards Association (CSA) made with controlled quality Recycled Concrete Aggregate (RCA). Five mixes with water-to-cementing material (w/cm) ratio of 0.40 were produced with various RCA contents and tested against two 0% RCA control mixes made with General Use (GU) cement, and General Use Limestone cement (GUL). The RCA contents in the mixes were 10%, 20%, and 30% by coarse aggregate volume replacement, as well as 10% and 20% fine and coarse (granular) aggregate volume replacement. All evaluated mixes met the specifications from the CSA for fresh, mechanical, and durability properties. The coarse RCA mixes performed better than the granular RCA mixes in terms of flexural and splitting tensile strengths, linear drying shrinkage, water sorptivity, and rapid chloride-ion permeability, where the test results were significantly affected by the ultra fines present in the granular RCA. 相似文献
49.
Concrete spalling due to fire exposure is often defined as the sudden detachment of fragments from a concrete surface. It can be quantified by various parameters of which weight loss and spalling depth are the most common ones. The risk of spalling is influenced by many factors such as concrete composition, heating rate and applied testing methods. A reduced scale testing method should be developed to analyse the spalling behaviour and to understand its effectiveness in more detail. As a subsection of this development, this study aimed to analyse the effect of different‐sized, circular heated areas in semi full‐scale fire tests. Therefore, vermiculite slabs with varying cut‐outs in their centre were placed between a specimen made of a spalling‐sensitive concrete and the combustion chamber. The combustion chamber was heated following a standard fire curve. Our experimental results show that the thermal expansion inside of equal‐sized specimens is strongly dependent on the size of the heated area. In addition, this area also affects thermal stresses. They decrease as a result of lower temperature gradients for tests with smaller unheated boundary areas. Apart from this, the analysis of fragments shows no correlation between their relative volume distribution and the heated area. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
50.
The objective of this research was to analyse the differences in the dissipated energy under uniaxial tension and biaxial tension–compression load of fibre reinforced concretes using the Wedge Splitting Test. Under biaxial load the specimens were subjected to compressive stress ratios from 10% to 50% of the concrete compressive strength perpendicular to the direction of the tensile load.Under biaxial tension–compression load the energy dissipation capacity of the specimens decreases compared to the uniaxial tension load case on average 20–30%. It is believed that the decrease is a result of the damage mechanism of the concrete matrix and deterioration of the fibre–matrix and/or aggregate–cement paste interfaces in case the section is additionally loaded with compression stresses. This indicates that dimensioning of concrete elements under biaxial stress states using material parameters obtained from tests conducted on specimens under uniaxial tensile load is unsafe and could potentially lead to a non-conservative design.In the second part of this paper the extent of the fracture process zone under uniaxial tension and biaxial tension–compression load will be examined with the Acoustic Emission technique and the reasons for decrease of the energy dissipation capacity under biaxial load will be further discussed. 相似文献