全文获取类型
收费全文 | 4278篇 |
免费 | 40篇 |
国内免费 | 38篇 |
专业分类
电工技术 | 36篇 |
综合类 | 149篇 |
化学工业 | 468篇 |
金属工艺 | 225篇 |
机械仪表 | 45篇 |
建筑科学 | 1501篇 |
矿业工程 | 121篇 |
能源动力 | 42篇 |
轻工业 | 17篇 |
水利工程 | 250篇 |
石油天然气 | 28篇 |
武器工业 | 3篇 |
无线电 | 20篇 |
一般工业技术 | 606篇 |
冶金工业 | 734篇 |
原子能技术 | 25篇 |
自动化技术 | 86篇 |
出版年
2024年 | 2篇 |
2023年 | 20篇 |
2022年 | 56篇 |
2021年 | 38篇 |
2020年 | 49篇 |
2019年 | 14篇 |
2018年 | 35篇 |
2017年 | 62篇 |
2016年 | 84篇 |
2015年 | 97篇 |
2014年 | 142篇 |
2013年 | 139篇 |
2012年 | 167篇 |
2011年 | 347篇 |
2010年 | 301篇 |
2009年 | 298篇 |
2008年 | 322篇 |
2007年 | 300篇 |
2006年 | 284篇 |
2005年 | 273篇 |
2004年 | 249篇 |
2003年 | 236篇 |
2002年 | 215篇 |
2001年 | 122篇 |
2000年 | 118篇 |
1999年 | 119篇 |
1998年 | 50篇 |
1997年 | 44篇 |
1996年 | 36篇 |
1995年 | 23篇 |
1994年 | 34篇 |
1993年 | 22篇 |
1992年 | 17篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
排序方式: 共有4356条查询结果,搜索用时 31 毫秒
51.
The report of an investigation into the performance of concrete manufactured with recycled aggregate (RA) using durability indexes as indicators is presented in this paper. Durability indexes, such as chloride conductivity, oxygen permeability and water sorptivity, of three different concrete mixes containing 0%, 50% and 100% RA were monitored at ages 3, 7, 28 and 56 days. The results show that durability quality reduced with increase in the quantities of RA included in a mix; however, as expected, the quality improved with the age of curing. At the age of 56 days, increases in index value of a concrete mix made with 100% RA over that made with 100% natural aggregate were 86.5% and 28.8%, respectively, for chloride conductivity and water sorptivity. The corresponding value of oxygen permeability index (OPI) for the same concrete mixes was a reduction of 10.0%. For 50% RA concrete, the reductions in chloride conductivity and water sorptivity indexes at the curing age of 56 days compared to 3 days were 62.7% and 42.7%, respectively. The corresponding figure for OPI was an increase of 37.6%. The poor performance of the RA concrete is associated with the cracks and fissures, which were formed in RA during processing, thereby rendering the aggregate susceptible to permeation, diffusion and absorption of fluids. 相似文献
52.
Removal of phosphate from wastewaters 总被引:1,自引:0,他引:1
Gas concrete waste was used to remove phosphate from aqueous solutions in this study. The influence of suspension pH, temperature, mixing rate, and gas concrete dosage on phosphate removal was investigated by conducting a series of batch adsorption experiments. In addition, the yield and mechanisms of phosphate removal were explained on the basis of the results of X-ray spectroscopy, measurements of zeta potential of particles, both values of BET-N2 specific surface area, and images of scanning electron microscopy (SEM) of the particles before and after adsorption. In this study, phosphate removal in excess of 99% was obtained and it was concluded that wastes of gas concrete are an efficient adsorbent for the removal of phosphate. The removal of phosphate predominantly takes place by precipitation mechanism and the weak physical interactions between the surface of adsorbent and the metallic salts of phosphate. 相似文献
53.
N. De Belie J. Monteny A. Beeldens E. Vincke D. Van Gemert W. Verstraete 《Cement and Concrete Research》2004,34(12):2223-2236
New equipment and procedures for chemical and microbiological tests, simulating biogenic sulfuric acid corrosion in sewerage systems, are presented. Subsequent steps of immersion and drying, combined with mechanical abrasion, were applied to simulate events occurring in sewer systems. Both chemical and microbiological tests showed that the aggregate type had the largest effect on degradation. Concrete with limestone aggregates showed a smaller degradation depth than did the concrete with inert aggregates. The limestone aggregates locally created a buffering environment, protecting the cement paste. This was confirmed by microscopic analysis of the eroded surfaces. The production method of concrete pipes influenced durability through its effect on W/C ratio and water absorption values. In the microbiological tests, HSR Portland cement concrete performed slightly better than did the slag cement concrete. A possible explanation can be a more rapid colonisation by microorganisms of the surface of slag cement samples. A new method for degradation prediction was suggested based on the parameters alkalinity and water absorption (as a measure for concrete porosity). 相似文献
54.
Arezki Tagnit-Hamou Mladenka Saric-Coric Patrice Rivard 《Cement and Concrete Research》2005,35(1):99-107
This paper presents research results on the causes of a severe concrete deterioration, which occurred in many building foundations approximately 2 years after construction. Concrete samples were investigated with X-ray diffraction (XRD) analysis, a scanning electron microscope (SEM) and a petrographic examination performed with a stereomicroscope. It was found that the early cracking of concrete stemmed from the oxidation of the pyrrhotite found in the anorthosite aggregates used to produce the concrete. The oxidation process led to the precipitation of iron hydroxides having a higher volume than the original pyrrhotite does. The presence of micas (biotite) close to the pyrrhotite seemed to promote and accelerate the oxidation process. 相似文献
55.
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
56.
A comparison of bending strength between adhesive and steel reinforced concrete with steel only reinforced concrete 总被引:1,自引:0,他引:1
Cracking of brittle cementitious composites subjected to excessive loading causes a potential reduction in material performance. Steel bars or metal fibers typically act as tensile reinforcing in concrete composites to increase the material's structural capacity in bending and to delay or prevent matrix cracking.The goal of this research is to determine whether the performance in bending strength and material integrity of a typically reinforced cementitious composite may be improved through the release of “healing” chemicals, such as adhesives, from hollow fibers into cracks induced by loading in addition to the metal reinforcing. Adhesive-filled repair fibers are intended to break immediately upon cracking in the concrete thereby activating the healing process with the release of a sealing or adhering substance. This self-repair occurs whenever and wherever cracks are generated. 相似文献
57.
58.
The specific fracture energy GF was measured in six types of simple concrete: all from the same matrix. The aggregates were spheres of the same diameter (strong aggregates, that debonded during concrete fracture, and weak aggregates, able to break); three kinds of matrix-aggregate interface (weak, intermediate and strong) were used. All in all, 55 test results are reported. These results are intended to be used as an experimental benchmark for checking numerical models of concrete fracture.A meso-level analysis of these results showed a correlation between the measured GF values and the properties of the matrix, aggregates and interfaces, particularly with the actual area of the fracture surface. The strength of the matrix-aggregate interface correlates quite well with GF, and concrete ductility, measured by means of the characteristic length, correlates also with the strength of the matrix-aggregate interface. 相似文献
59.
Permeability characteristics of carbonated concrete considering capillary pore structure 总被引:3,自引:0,他引:3
During carbonation process, the calcium phases present in cement are attacked by CO2 and converted into CaCO3 and the permeability of concrete is changing due to the change in porosity. The rate of carbonation depends upon porosity and moisture content of the concrete. Especially in underground reinforced concrete structures, the interior portion of concrete surface may be exposed to carbonation and the exterior portion of concrete surface exposed to wet soil or underground water. As carbonation proceeds from outer surface into internal portion of concrete, microstructure is also changed continuously from outer surface into internal portion of concrete. Even the deteriorations in the structures due to the carbonation have been reported more, research on permeability characteristics of concrete considering carbonation and micro-structural information is very scarce.In this study, the permeability coefficient in carbonated concrete is derived by applying a capillary pore structure formation model in carbonated cement mortar and assuming that aggregates do not affect carbonation process in early-aged concrete as a function of porosity. The permeability obtained from the micro-level modeling for carbonated concrete is verified with the results of accelerated carbonation test and water penetration test in cement mortar. 相似文献
60.