全文获取类型
收费全文 | 6790篇 |
免费 | 91篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 37篇 |
综合类 | 1篇 |
化学工业 | 613篇 |
金属工艺 | 124篇 |
机械仪表 | 100篇 |
建筑科学 | 118篇 |
矿业工程 | 5篇 |
能源动力 | 72篇 |
轻工业 | 292篇 |
水利工程 | 19篇 |
石油天然气 | 9篇 |
无线电 | 544篇 |
一般工业技术 | 698篇 |
冶金工业 | 3913篇 |
原子能技术 | 33篇 |
自动化技术 | 311篇 |
出版年
2021年 | 32篇 |
2019年 | 27篇 |
2018年 | 38篇 |
2017年 | 29篇 |
2016年 | 37篇 |
2015年 | 30篇 |
2014年 | 52篇 |
2013年 | 147篇 |
2012年 | 90篇 |
2011年 | 96篇 |
2010年 | 99篇 |
2009年 | 116篇 |
2008年 | 123篇 |
2007年 | 115篇 |
2006年 | 104篇 |
2005年 | 101篇 |
2004年 | 87篇 |
2003年 | 102篇 |
2002年 | 75篇 |
2001年 | 91篇 |
2000年 | 114篇 |
1999年 | 186篇 |
1998年 | 1148篇 |
1997年 | 704篇 |
1996年 | 453篇 |
1995年 | 287篇 |
1994年 | 240篇 |
1993年 | 284篇 |
1992年 | 75篇 |
1991年 | 95篇 |
1990年 | 123篇 |
1989年 | 118篇 |
1988年 | 92篇 |
1987年 | 92篇 |
1986年 | 66篇 |
1985年 | 81篇 |
1984年 | 69篇 |
1983年 | 65篇 |
1982年 | 51篇 |
1981年 | 75篇 |
1980年 | 76篇 |
1979年 | 45篇 |
1978年 | 30篇 |
1977年 | 137篇 |
1976年 | 252篇 |
1975年 | 40篇 |
1974年 | 36篇 |
1973年 | 45篇 |
1972年 | 23篇 |
1970年 | 24篇 |
排序方式: 共有6889条查询结果,搜索用时 15 毫秒
71.
The beam divergence in the vertical direction from a graded index separate confinement heterostructure (GRINSCH) multiquantum-well (MQW) laser has been studied. It is demonstrated both theoretically and experimentally that a circular beam MQW laser can be produced by choosing appropriate thicknesses for the GRINSCH layers, while maintaining other desired laser characteristics. The beam divergence is found to be more affected by the index change induced by injected carriers than by strain in the MQW active layer. Theoretical results are in good agreement with the measurements for 1.3-μm InGaAsP strained MQW lasers 相似文献
72.
JB Kornfeld 《Canadian Metallurgical Quarterly》1997,32(6):45-6, 51-2
73.
74.
75.
Mann-Fu Rau David Rieck James W. Evans 《Metallurgical and Materials Transactions B》1987,18(1):257-278
An “environmental cell” located in a high voltage transmission electron microscope has been used to study the reduction of
single crystal iron oxides by hydrogen and hydrogen-argon mixtures. The cell enables a direct observation of the solid during
reaction, thus permitting the nucleation and growth of solid reaction products to be observed. Hematite was reduced at temperatures
in the range 387 to 610°C with gas pressures up to 5.3 kP. Reduction with pure hydrogen was considerably faster than when
argon was present. Lath magnetite which rapidly transforms to porous magnetite and thence (more slowly) to porous iron was
observed. The reduction of magnetite and of wustite single crystals was observed in the temperature range 300 to 514°C using
both hydrogen and hydrogen-argon mixtures at gas pressures up to 6.6 kP. Incubation periods were found for magnetite reduction;
during these periods faceted pits formed in the oxide. Iron formed in the early stages was epitaxial with the host magnetite;
at later stages the epitaxy was lost and fissures frequently formed in the metal. The morphology of the iron differed between
the gas mixtures. Disproportionation accompanied the reduction of wustite, producing intermediate polycrystalline magnetite
despite reducing conditions. The disproportionation appeared to be promoted by the reduction reaction. For both oxides, reduction
in the hydrogen-argon mixture was slower than in pure hydrogen. 相似文献
76.
77.
In Situ Formation of a Novel Nanocomposite Structure Based on MCM-41 and Polyethylene 总被引:1,自引:0,他引:1
M41S materials are prepared by in situ assembly of inorganic precursors and organic template and can be viewed as nanocomposites of the siliceous phase and organic surfactant. Calcination of these precursors gives the M41S materials that have been used to prepare novel nanocomposite structures, in which the organic phase inside the nano-sized pores is isolated by the nano-sized inorganic pore walls. The nanocomposite structures can be formed by in situ polymerization of monomers inside the channels. Polymerization of ethylene takes place inside the nano-sized pores, producing the desired nanocomposite structure. The resulting polyethylene was found to be a mixture of crystalline and amorphous phases. 相似文献
78.
79.