全文获取类型
收费全文 | 67068篇 |
免费 | 5219篇 |
国内免费 | 3443篇 |
专业分类
电工技术 | 1208篇 |
技术理论 | 5篇 |
综合类 | 5039篇 |
化学工业 | 3291篇 |
金属工艺 | 18082篇 |
机械仪表 | 3233篇 |
建筑科学 | 15719篇 |
矿业工程 | 1220篇 |
能源动力 | 1025篇 |
轻工业 | 1111篇 |
水利工程 | 808篇 |
石油天然气 | 2011篇 |
武器工业 | 371篇 |
无线电 | 407篇 |
一般工业技术 | 6998篇 |
冶金工业 | 14354篇 |
原子能技术 | 414篇 |
自动化技术 | 434篇 |
出版年
2024年 | 159篇 |
2023年 | 685篇 |
2022年 | 1663篇 |
2021年 | 1884篇 |
2020年 | 2037篇 |
2019年 | 1514篇 |
2018年 | 1277篇 |
2017年 | 2036篇 |
2016年 | 2142篇 |
2015年 | 2452篇 |
2014年 | 4280篇 |
2013年 | 3729篇 |
2012年 | 4879篇 |
2011年 | 5676篇 |
2010年 | 4291篇 |
2009年 | 4420篇 |
2008年 | 3524篇 |
2007年 | 4545篇 |
2006年 | 4051篇 |
2005年 | 3369篇 |
2004年 | 2804篇 |
2003年 | 2413篇 |
2002年 | 2064篇 |
2001年 | 1725篇 |
2000年 | 1500篇 |
1999年 | 1221篇 |
1998年 | 963篇 |
1997年 | 932篇 |
1996年 | 792篇 |
1995年 | 581篇 |
1994年 | 525篇 |
1993年 | 360篇 |
1992年 | 318篇 |
1991年 | 218篇 |
1990年 | 183篇 |
1989年 | 156篇 |
1988年 | 105篇 |
1987年 | 56篇 |
1986年 | 37篇 |
1985年 | 27篇 |
1984年 | 19篇 |
1983年 | 19篇 |
1982年 | 21篇 |
1981年 | 16篇 |
1980年 | 39篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1975年 | 3篇 |
1959年 | 10篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Thermography represents an important tool to study fatigue behaviour of materials.In this work, the fatigue limit of martensitic and precipitation hardening stainless steels has been determined with thermographic methods. Despite their use in corrosive and cryogenic environments, there is a data lack in literature concerning the study of fatigue behaviour.The peculiarity of these materials is the brittle behaviour: therefore, during fatigue tests the characteristic small deformations determine small changes of temperature. Thus, to properly determine the fatigue limit of aforementioned stainless steels, a more accurate setup is necessary in order to correctly detect surface temperature of specimens due to dissipation heat sources.In literature, different procedures have already been proposed to evaluate the fatigue limit from thermal data but very few works lead to an early detection of dissipation process which can obtain a further reduction of overall testing time. The aim of the paper is to propose a new robust thermal data analysis procedure for estimating fatigue limit of stainless steels in automatable way. 相似文献
12.
13.
There are many potential causes of corrosion in animal buildings. Animals exhale large quantities of moisture into the air creating high relative humidity in the building if the moisture is not properly vented. High humidity increases the potential for condensation. In addition, ammonia may be found in large quantities in animal buildings. Ammonia is released from manure and urine. In addition, ammonium chloride is used as a nitrogen source in fertilisers. In this study, the atmospheric corrosion of hot-dip-galvanised steel and zinc alloy-coated steel such as zinc–aluminium and zinc–aluminium–magnesium has been studied in atmospheres containing different levels of ammonia. Investigations have also been conducted at different levels of ammonium chloride. The results are discussed in view of the mechanisms of corrosion of zinc and zinc alloy-coated steel in ammonia and ammonium chloride-containing environments. 相似文献
14.
Abrasive water jet technology can be used for micro-milling using recently developed miniaturized nozzles. Abrasive water jet (AWJ) machining is often used with both the nozzle tip and workpiece submerged in water to reduce noise and contain debris. This paper compares the performance of submerged and unsubmerged abrasive water jet micro-milling of channels in 316L stainless steel and 6061-T6 aluminum at various nozzle angles and standoff distances. The effect of submergence on the diameter and effective footprint of AWJ erosion footprints was measured and compared. It was found that the centerline erosion rate decreased with channel depth due to the spreading of the jet as the effective standoff distance increased, and because of the growing effect of stagnation as the channel became deeper. The erosive jet spread over a larger effective footprint in air than in water, since particles on the jet periphery were slowed much more quickly in water due to increased drag. As a result, the width of a channel machined in air was wider than that in water. Moreover, it was observed that the instantaneous erosion rate decreased with channel depth, and that this decrease was a function only of the channel cross-sectional geometry, being independent of the type of metal, the jet angle, the standoff distance, and regardless of whether the jet was submerged or in air, in either the forward or backward directions. It is shown that submerged AWJM results in narrower features than those produced while machining in air, without a decrease in centerline etch rate. 相似文献
15.
16.
Electrochemical impedance spectroscopy (EIS), anodic polarization and scanning electron microscopy techniques were used to investigate the damage mechanism in the transpassive potential region of AISI ... 相似文献
17.
18.
19.
20.
热轧态中锰TRIP钢首先经650 ℃退火2 h,随后在550 ℃进行等温时效热处理,采用场发射扫描电镜(FE-SEM)研究该钢中P的偏聚和时效析出行为的变化情况。结果表明,中锰TRIP钢中P在晶界的偏聚是一种非平衡偏聚现象,临界时间约为50 h,与理论计算结果48 h较为吻合。在局部偏聚区域内,C与P存在共偏聚的关系,即P偏聚量高的地方,C含量也高。而合金元素Nb具有抑制P偏聚的效果,在20~70 h时效时间内,可以相对降低6.57%~19.5%的最大P偏聚量。根据电子背散射衍射(EBSD)菊池线分析,P偏聚量低于2.28at%时,P为固溶状态,高于2.28at.%时,P为析出状态。 相似文献