全文获取类型
收费全文 | 68396篇 |
免费 | 4937篇 |
国内免费 | 3652篇 |
专业分类
电工技术 | 1226篇 |
技术理论 | 5篇 |
综合类 | 5234篇 |
化学工业 | 3421篇 |
金属工艺 | 18803篇 |
机械仪表 | 3448篇 |
建筑科学 | 15896篇 |
矿业工程 | 1276篇 |
能源动力 | 1056篇 |
轻工业 | 1162篇 |
水利工程 | 832篇 |
石油天然气 | 2045篇 |
武器工业 | 403篇 |
无线电 | 538篇 |
一般工业技术 | 7124篇 |
冶金工业 | 13587篇 |
原子能技术 | 466篇 |
自动化技术 | 463篇 |
出版年
2024年 | 124篇 |
2023年 | 651篇 |
2022年 | 1677篇 |
2021年 | 1924篇 |
2020年 | 2024篇 |
2019年 | 1543篇 |
2018年 | 1252篇 |
2017年 | 1987篇 |
2016年 | 2098篇 |
2015年 | 2442篇 |
2014年 | 4278篇 |
2013年 | 3745篇 |
2012年 | 4946篇 |
2011年 | 5746篇 |
2010年 | 4359篇 |
2009年 | 4494篇 |
2008年 | 3622篇 |
2007年 | 4602篇 |
2006年 | 4158篇 |
2005年 | 3454篇 |
2004年 | 2900篇 |
2003年 | 2507篇 |
2002年 | 2176篇 |
2001年 | 1793篇 |
2000年 | 1551篇 |
1999年 | 1289篇 |
1998年 | 1031篇 |
1997年 | 986篇 |
1996年 | 827篇 |
1995年 | 617篇 |
1994年 | 542篇 |
1993年 | 363篇 |
1992年 | 323篇 |
1991年 | 228篇 |
1990年 | 191篇 |
1989年 | 165篇 |
1988年 | 117篇 |
1987年 | 48篇 |
1986年 | 32篇 |
1985年 | 29篇 |
1984年 | 21篇 |
1983年 | 21篇 |
1982年 | 21篇 |
1981年 | 17篇 |
1980年 | 40篇 |
1979年 | 4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 15 毫秒
31.
Based on the phase transformation theories, especially the T0 concept of bainite transformation, alloy optimisation of bainitic steel with carbides has been carried out aiming at the produce of plastic mould with large cross-section. The effect of manganese and silicon on proeutectoid ferrite and bainite transformation is explored by dilatometric analysis, XRD and different microscopy techniques. The results show that after the alloy optimisation, the transformation of proeutectoid ferrite is suppressed and when the cooling rate is lower than 0·1°C?s??1, the new lower bainite transformation appears by decreasing carbon capacity of austenite and promoting carbide precipitation. Industrial production proves that the optimised alloy SDP1 can meet the demand for the plastic mould with the thickness of 1050?mm. 相似文献
32.
33.
《Oil and Energy Trends》2019,44(8):58-60
Currency exchanges rates – updated monthly. Economic indicators of industrial production. Countries included: France, Germany, Italy, the United Kingdom, the United States, Canada, Japan (Total G-7), Eurozone and Total EU-28 (Total OECD). Updated monthly. Economic indicators of car registration in the United States, Canada, France, Germany, Italy, Poland, Spain, Turkey, the United Kingdom, Japan, Republic of Korea and Other OECD (Total OECD-30). Updated monthly. Monthly averages of crude steel production in thousand metric tons for the United States, Canada, Brazil, Mexico, Austria, Belgium, Czech Republic, France, Germany, Italy, Netherlands, Poland, Spain, Sweden, Turkey, the United Kingdom, Russia, Ukraine, South Africa, Iran, China, India, Japan, Republic of Korea, Taiwan and Australia. 相似文献
34.
摘要:为了研究退火温度对镀锌DP980+Z烘烤硬化值的影响,退火温度控制在760~820℃之间,系统分析退火温度对烘烤硬化值的影响。通过准静态拉伸试验机测量烘烤硬化值及抗拉强度,采用lepara试剂对组织中的马氏体进行着色,利用金相显微镜及图像处理软件测量马氏体的体积分数;采用扫描电镜观察DP980+Z的双相组织特点,并且将组织图片通过CAD转化成有限元图进行网格划分,建立代表性体积单元(RVE),通过有限元分析铁素体、马氏体强度对烘烤硬化值的影响。在同样的变形量情况下,DP980+Z的原始屈服强度越高,烘烤硬化值越高。 相似文献
35.
《International Journal of Hydrogen Energy》2020,45(7):4054-4064
The feasibility of microbial hydrogen consumption to mitigate the hydrogen embrittlement (HE) under different cathodic potentials was evaluated using the Devanathan-Stachurski electrochemical test and the hydrogen permeation efficiency η. The hydrogen permeation efficiency η in the presence of strain GA-1 was lower than that in sterile medium. The cathodic potential inhibited the adherence of strain GA-1 to AISI 4135 steel surface, thereby reducing the hydrogen consumption of strain GA-1. The adherent GA-1 cells were capable of consuming ‘cathodic hydrogen’ and reducing the proportions of absorbed hydrogen, indicating that it is theoretically possible to control HE by hydrogen-consuming microbes. 相似文献
36.
按照管道加工工艺的不同,管道可分为内径控制管和外径控制管。通过热轧工艺生产的外径控制无缝钢管,可满足火力发电厂汽水系统中绝大部分管道的使用要求。对于超(超)临界机组的主蒸汽和高温再热蒸汽管道采用的P91/P92材质的大口径厚壁无缝钢管,由于对材料性能和加工工艺有特殊要求,因此宜采用内径控制管。 相似文献
37.
The toughness of 31Mn2SiRE wear-resistance cast steel were increased by means of RE compound modification and high temperature austenitizing. The results show that the microstructures can be refined, needle and network ferrite are eliminated, the dislocation density and the quantity of dislocated martensite are increased remarkably, and the shape and distribution of inclusions are improved by the addition of RE. Therefore, the mechanical properties of the modified steel can be greatly increased, especially the toughness (αK) by 44%, yield strength (σs) by 10%, and elongation (δ5) by 42%. 相似文献
38.
The influence of network density on the strain hardening behaviour of amorphous polymers is studied. The network density of polystyrene is altered by blending with poly(2,6-dimethyl-1,4-phenylene-oxide) and by cross-linking during polymerisation. The network density is derived from the rubber-plateau modulus determined by dynamic mechanical thermal analysis. Subsequently uniaxial compression tests are performed to obtain the intrinsic deformation behaviour and, in particular, the strain hardening modulus. At room temperature, the strain hardening modulus proves to be proportional to the network density, irrespective of the nature of the network, i.e. physical entanglements or chemical cross-links. With increasing temperature, the strain hardening modulus is observed to decrease. This decrease appears to be related to the influence of thermal mobility of the chains, determined by the distance to the glass-transition temperature (T−Tg). 相似文献
39.
The analysis of 124 curves obtained in short-term tensile tests demonstrate that they can be described by varying strain hardening and softening characteristics. Different stress–strain curves can be produced at invariable yield strength and ultimate strength and interrelated proportional variations of the above characteristics. To determine some specific stress–strain curve, it is necessary to take account of yield strength and ultimate strength as well as strain corresponding to the latter. The relations between yield strength, ultimate strength and hardening and their practically complete absence between these parameters and softening were statistically established. 相似文献
40.
摘 要:主要介绍Sasol Agri公司硫酸四系统的技术改造,分两步进行,第一步更换转化器、热换热器及主省煤器,生产能力由1600t/d提高到1750 t/d,且鼓风机出口压力很低。第二步更换干燥塔、二吸塔及冷换热器,连续生产能力在1950 t/d以上。使用不锈钢材质及克瓦纳·凯密迪公司专有的换热器,使装置的改造相当成功,维护及操作费用较低,并具有较大的灵活性和可操作性。 相似文献