全文获取类型
收费全文 | 55891篇 |
免费 | 2919篇 |
国内免费 | 204篇 |
专业分类
电工技术 | 733篇 |
综合类 | 320篇 |
化学工业 | 11090篇 |
金属工艺 | 1321篇 |
机械仪表 | 1204篇 |
建筑科学 | 1752篇 |
矿业工程 | 216篇 |
能源动力 | 1671篇 |
轻工业 | 8990篇 |
水利工程 | 446篇 |
石油天然气 | 336篇 |
武器工业 | 24篇 |
无线电 | 2688篇 |
一般工业技术 | 9055篇 |
冶金工业 | 11522篇 |
原子能技术 | 371篇 |
自动化技术 | 7275篇 |
出版年
2023年 | 484篇 |
2022年 | 618篇 |
2021年 | 1490篇 |
2020年 | 1032篇 |
2019年 | 1088篇 |
2018年 | 1660篇 |
2017年 | 1573篇 |
2016年 | 1743篇 |
2015年 | 1536篇 |
2014年 | 1943篇 |
2013年 | 3669篇 |
2012年 | 2806篇 |
2011年 | 3222篇 |
2010年 | 2576篇 |
2009年 | 2517篇 |
2008年 | 2475篇 |
2007年 | 2262篇 |
2006年 | 1746篇 |
2005年 | 1451篇 |
2004年 | 1262篇 |
2003年 | 1160篇 |
2002年 | 1088篇 |
2001年 | 795篇 |
2000年 | 748篇 |
1999年 | 899篇 |
1998年 | 3765篇 |
1997年 | 2332篇 |
1996年 | 1648篇 |
1995年 | 976篇 |
1994年 | 843篇 |
1993年 | 775篇 |
1992年 | 306篇 |
1991年 | 301篇 |
1990年 | 251篇 |
1989年 | 282篇 |
1988年 | 247篇 |
1987年 | 243篇 |
1986年 | 213篇 |
1985年 | 337篇 |
1984年 | 264篇 |
1983年 | 225篇 |
1982年 | 194篇 |
1981年 | 245篇 |
1980年 | 239篇 |
1979年 | 155篇 |
1978年 | 135篇 |
1977年 | 318篇 |
1976年 | 677篇 |
1975年 | 122篇 |
1973年 | 146篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Discontinuous mass-change measurements and corrosion-product analyses were made for Fe-20Cr and Ni-20Cr alloys after exposing them to Ar-H
2
O-HBr gas mixtures at 1000 K for 24 hours. Predominantly chromia scales formed on both alloys. Upon cooling, the scales remained adherent to the Fe-20Cr alloy but spalled extensively from Ni-20Cr samples. After tests in HBr-rich gas mixtures, bromine-rich corrosion products were found underneath chromia scales on both alloys while nickel evaporation was observed from Ni-20Cr samples. Preoxidation of the Ni-20Cr alloy prior to exposure to Ar-H
2
O-HBr gas mixtures increased chromia scale adherence but did not prevent nickel loss from the alloy. Chromia scales formed on the Fe-20Cr alloy were more protective due to the absence of iron oxides in the scale. Large NiO crystals formed over the Ni-20Cr alloy decreased chromia-scale adherence and increased nickel loss from the alloy due to the low stability of NiO in HBr-containing gas mixtures. 相似文献
992.
GasSourceMolecularBeamEpitaxyGrowthofSi1-xGex/SiAloysLiuXuefeng,LiJianpingandSunDianzhao(刘学锋)(李建平)(孙殿照)MaterialScienceCenter... 相似文献
993.
AISI 5140 low alloy steel was ion nitrided under different process parameters including time (1, 4, 8 and 12 h), temperature (400, 450, 500 and 550 °C) and gas mixture ratio (0.05, 0.33, 1 and 3 N2/H2). By determining the fatigue strength, surface hardness, compound layer thickness and case depth, the optimum working conditions were determined by using a Taguchi design of experiment. After ion nitriding process, it is aimed to maximize fatigue strength, surface hardness and case depth as well as to minimize compound layer thickness. While the optimum conditions were determined, due to the goals (above aims) more than one being, the trade-off among goals was considered. First of all, each goal was optimised, separately. Then, all the goals were optimised together, considering the priority of the goals, and the optimum results were obtained at 0.05 N2/H2 gas mixture ratio, at the temperature of 450 °C and for 12 h process time. 相似文献
994.
There exist many ideas and assumptions about the development and meaning of modularity in biological and technical neural systems. We empirically study the evolution of connectionist models in the context of modular problems. For this purpose, we define quantitative measures for the degree of modularity and monitor them during evolutionary processes under different constraints. It turns out that the modularity of the problem is reflected by the architecture of adapted systems, although learning can counterbalance some imperfection of the architecture. The demand for fast learning systems increases the selective pressure towards modularity. 相似文献
995.
采用Gleeble-1500热模拟试验机测试了2种微合金钢(Al、Al V)经1150℃加热、20%压缩变形条件下的显微组织状态,结果表明,Al、V复合强化的试验钢以2℃/s速度冷却时,钢中出现针状铁素体。冷却速度为5℃/s时出现贝氏体,而Al强化钢中出现针状铁素体的冷速要达到5℃/s,因此建议生产含V钢时冷速控制在1~5℃/s。 相似文献
996.
997.
Although the prominent concept of the last decade – user experience – maintains its significance in diverse disciplines, especially design, its focus has changed to eliciting positive user experiences by pursuing new possibilities for consumer products rather than by solely seeking solutions to existing problems. Designers continue to aim for rich user experiences with a variety of products, but have neglected self-service (interactive) kiosks. Hence, this paper, after giving a brief overview of the positive psychology literature, demonstrates the dimensions of positive user experiences with self-service kiosks through an empirical study conducted on coffee vending machines and automated tellers. 相似文献
998.
999.
1000.