全文获取类型
收费全文 | 287084篇 |
免费 | 35524篇 |
国内免费 | 15078篇 |
专业分类
电工技术 | 19770篇 |
技术理论 | 6篇 |
综合类 | 21912篇 |
化学工业 | 52005篇 |
金属工艺 | 15169篇 |
机械仪表 | 17366篇 |
建筑科学 | 21886篇 |
矿业工程 | 7763篇 |
能源动力 | 7994篇 |
轻工业 | 26610篇 |
水利工程 | 6179篇 |
石油天然气 | 11964篇 |
武器工业 | 2608篇 |
无线电 | 36122篇 |
一般工业技术 | 35512篇 |
冶金工业 | 10877篇 |
原子能技术 | 3125篇 |
自动化技术 | 40818篇 |
出版年
2024年 | 1127篇 |
2023年 | 3718篇 |
2022年 | 7299篇 |
2021年 | 10246篇 |
2020年 | 8883篇 |
2019年 | 8884篇 |
2018年 | 9436篇 |
2017年 | 10988篇 |
2016年 | 10496篇 |
2015年 | 14014篇 |
2014年 | 16906篇 |
2013年 | 20464篇 |
2012年 | 21083篇 |
2011年 | 21689篇 |
2010年 | 20626篇 |
2009年 | 19765篇 |
2008年 | 19157篇 |
2007年 | 18249篇 |
2006年 | 16928篇 |
2005年 | 13619篇 |
2004年 | 10329篇 |
2003年 | 9087篇 |
2002年 | 9438篇 |
2001年 | 8297篇 |
2000年 | 6520篇 |
1999年 | 4817篇 |
1998年 | 2876篇 |
1997年 | 2407篇 |
1996年 | 2237篇 |
1995年 | 1910篇 |
1994年 | 1551篇 |
1993年 | 1009篇 |
1992年 | 803篇 |
1991年 | 606篇 |
1990年 | 491篇 |
1989年 | 379篇 |
1988年 | 300篇 |
1987年 | 208篇 |
1986年 | 148篇 |
1985年 | 106篇 |
1984年 | 87篇 |
1983年 | 65篇 |
1982年 | 57篇 |
1981年 | 66篇 |
1980年 | 65篇 |
1979年 | 41篇 |
1978年 | 18篇 |
1977年 | 22篇 |
1976年 | 25篇 |
1951年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
Different qualities of concrete have been fire tested using different geometries of the specimens as well as different load levels and load configurations. The main objective with the study was to examine a test methodology consisting of a full‐scale test and different small scale‐tests for determining the probability of spalling and the amount of spalling of fire exposed concrete structures. A reference specimen was defined as a one‐sided fire exposed slab with the dimensions 1800 × 1200 mm2 giving an exposed area of 1500 × 1200 mm2. A number of concrete qualities with different probabilities for spalling, were tested using the reference specimen. These tests showed that the reference specimens worked well giving the expected test results. Small specimens were manufactured in different shapes with the same concrete as the one used in the reference tests. These small specimens were tested either at the same time as the reference specimens in the large furnace or afterwards on a small‐scale furnace where the fire exposed surface was 450 × 360 mm2. The test results clearly show the increased probability and the increased amount of spalling by using external compressive loading. The results also show that by using pre‐stress through bars or wires the load can be lost due to heating of the bars/wires which results in a decreased amount of spalling. The boundary of the specimen also affects the amount of spalling. The spalling around the edges was in all tests less than the spalling on the central parts of the exposed area. It could also be noted that the spalling did not pass completely through any of the specimens. The reason for this is probably that the water/vapour could migrate out from the unexposed surface of the specimen. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
83.
84.
85.
86.
G. Biallas Dr.‐Ing. C. Sick J. Schneider K.‐H. Trautmann 《Materialwissenschaft und Werkstofftechnik》2007,38(9):705-711
Biaxial fatigue of friction stir welded stiffened panels Within the framework of the European WelAir project, cruciform specimens made from stiffening FSW overlap joints were fatigued in the DLR biaxial test rig. To resemble the loading situation of pressurized fuselage structures, proportional loading without any phase shift, but with different load ratios λ between the loading components in both directions was applied.Natural crack initiation and subsequent crack growth were governed by the stiffness gradient caused by introducing the stringer. Cracks initiated and propagated at run‐in and run‐out locations in a direction perpendicular to the weld seam. The shortest fatigue life was observed for uniaxial loading in welding direction (λ = 0). An additional stress component perpendicular to the joint line (λ > 0) resulted in a higher number of cycles to failure. Similar to single stringer panels, increasing the load ratio also increased the number of cycles to failure for FSW clip‐stringer structural members, but additionally gives a different location of the fatal crack. 相似文献
87.
88.
介绍了阳泉市煤矿采空区对公路建设所造成的危害,对其上覆岩层变形破坏的地质因素及其破坏机理作了分析,指出应该采取各种措施减少对公路的破坏。 相似文献
89.
90.
This paper presents the current understanding of the flame retardant mechanism of Casico?. The study includes the flame retardant effect of each individual component: ethylene–acrylate copolymer, chalk and silicone elastomer, as well as the formation of an intumescent structure during heating. The flame retardant properties were investigated by cone calorimetry and oxygen index tests. To obtain insight into the flame retardant mechanism, heat treatment under different conditions has also been performed. The results indicate that the flame retardant mechanism of Casico is complex and is related to a number of reactions, e.g. ester pyrolysis of acrylate groups, formation of carbon dioxide by reaction between carboxylic acid and chalk, ionomer formation and formation of an intumescent structure stabilized by a protecting char. Special emphasis is given to the formation of the intumescent structure and its molecular structure as evaluated from 13C MAS‐NMR and 29Si MAS‐NMR, ESCA and XRD analysis. After treatment at 500°C the intumescent structure consists mainly of silicon oxides and calcium carbonate and after treatment at 1000°C the intumescent structure consists of calcium silicate, calcium oxide and calcium hydroxide. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献