全文获取类型
收费全文 | 18673篇 |
免费 | 1615篇 |
国内免费 | 677篇 |
专业分类
电工技术 | 146篇 |
综合类 | 1688篇 |
化学工业 | 5075篇 |
金属工艺 | 3565篇 |
机械仪表 | 353篇 |
建筑科学 | 3812篇 |
矿业工程 | 693篇 |
能源动力 | 166篇 |
轻工业 | 343篇 |
水利工程 | 407篇 |
石油天然气 | 1218篇 |
武器工业 | 106篇 |
无线电 | 158篇 |
一般工业技术 | 2095篇 |
冶金工业 | 989篇 |
原子能技术 | 64篇 |
自动化技术 | 87篇 |
出版年
2024年 | 72篇 |
2023年 | 271篇 |
2022年 | 442篇 |
2021年 | 545篇 |
2020年 | 492篇 |
2019年 | 401篇 |
2018年 | 478篇 |
2017年 | 674篇 |
2016年 | 595篇 |
2015年 | 679篇 |
2014年 | 1091篇 |
2013年 | 900篇 |
2012年 | 1265篇 |
2011年 | 1430篇 |
2010年 | 1146篇 |
2009年 | 1118篇 |
2008年 | 921篇 |
2007年 | 1445篇 |
2006年 | 1389篇 |
2005年 | 1037篇 |
2004年 | 925篇 |
2003年 | 707篇 |
2002年 | 612篇 |
2001年 | 464篇 |
2000年 | 393篇 |
1999年 | 296篇 |
1998年 | 225篇 |
1997年 | 188篇 |
1996年 | 153篇 |
1995年 | 114篇 |
1994年 | 116篇 |
1993年 | 90篇 |
1992年 | 66篇 |
1991年 | 54篇 |
1990年 | 56篇 |
1989年 | 31篇 |
1988年 | 19篇 |
1987年 | 14篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 10篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1976年 | 2篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Behavior of Magnesium‐Alloys for Automotive Applications under Mechanical and Environmental Loading: Influence of Passivating Films and Mechanisms of Local Breakdown To assure an efficient design of components under cyclic loading, all available data concerning fatigue have to be observed. Therefore the influences of manufacturing on the material condition, the mechanical loads and environmental effects have to be analysed. Magnesium‐alloys are of special interest for lightweight applications because of their excellent strength‐density ratio. The corrosion resistance of magnesium‐alloys depends on the same factors that are critical to other metals. The alloys have a good stability to atmospheric exposure and a good resistance to attack by alkali, chromic and hydrofluoric acids. However, because of the electrochemical activity of magnesium, the relative importance of some factors is greatly amplified. The nature and composition of passive films formed on magnesium‐alloys depend on the prevailing conditions, viz. alloy‐composition, passivation potential, pH, electrolyte composition and temperature. Passive films may be damaged by local breakdown. Because of this, magnesium‐alloys suffer a degradation of their properties when exposed to an aqueous environment. The main topic of the present investigations is the verification of mechanisms of the local breakdown of the protecting film. At least two mechanisms are possible for this localization: mechanical breakdown by slip steps and electrochemical breakdown (for e.g. by the effects of chloride ions). Corrosion and passivation of different high purity alloys have been studied in different solutions (neutral, alkaline with specific anions and cations) using electrochemical techniques. The diecasted alloys were tested as produced and machined. The results clarified that depending on alloy/material and surface condition/corrosion environment different mechanisms for electrochemical breakdown of the protecting films are possible. Hence fatigue life under environmental loading is influenced by surface and testing conditions. 相似文献
3.
4.
醇镁还原法一步制取对氯苯胺是一种新的方法 ,研究发现最佳反应温度为 80℃~ 85℃ ,反应时间为4h ,对氯硝基苯与镁粉的用量 (物质的量比 )为 1∶3,产率为 80 %。 相似文献
5.
John Bensted 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1985,35(4):181-184
Characterisation of raw materials for Portland cement manufacture by use of the methylene blue adsorption method is discussed. The method is shown to be a simple, convenient ‘rule of thumb’ procedure. It provides a guide to the quantity and type of argillaceous minerals present in a given raw material sample. 相似文献
6.
7.
Significant increases in the activity of vanadium(III) amidinate catalysts for ethylene polymerization have been obtained by immobilization on a MgCl2‐based support prepared by reaction of AlEt3 with a MgCl2/ethanol adduct. Catalyst immobilization and activation on this type of support prevents the rapid decay in activity observed under homogeneous polymerization conditions with unsupported catalysts. Stable polymerization activity is also observed with analogous titanium(III) complexes. Polyethylene with narrow molecular weight distribution and spherical particle morphology is obtained without reactor fouling. Copyright © 2005 Society of Chemical Industry 相似文献
8.
9.
10.
为了改善M2高速钢共晶碳化物的分布,本文利用小凝固试样变质的方法研究了Ti,N和Mg对M2高速钢凝固组织和硬度的影响。试验结果表明,加入Ti或Ti-N后,共晶碳化物形态和分布有很大改善,而加入Ti-N后对凝固组织有轻微的细化作用,但只添加Ti不补碳时,钢的淬火硬度和回火硬度均下降;加入适量的Mg可以使片状的M2C型共晶碳化物转为鱼骨状的M6C型共晶碳化物,使其分布有所改善,Ti和Mg复合加入可以明 相似文献