收费全文 | 454664篇 |
免费 | 7128篇 |
国内免费 | 2160篇 |
电工技术 | 9003篇 |
技术理论 | 5篇 |
综合类 | 1394篇 |
化学工业 | 70996篇 |
金属工艺 | 18627篇 |
机械仪表 | 13794篇 |
建筑科学 | 10972篇 |
矿业工程 | 2884篇 |
能源动力 | 9985篇 |
轻工业 | 44586篇 |
水利工程 | 4939篇 |
石油天然气 | 9815篇 |
武器工业 | 274篇 |
无线电 | 48137篇 |
一般工业技术 | 85334篇 |
冶金工业 | 86185篇 |
原子能技术 | 10353篇 |
自动化技术 | 36669篇 |
2021年 | 4023篇 |
2019年 | 3754篇 |
2018年 | 6248篇 |
2017年 | 6164篇 |
2016年 | 6645篇 |
2015年 | 4684篇 |
2014年 | 7760篇 |
2013年 | 20064篇 |
2012年 | 12646篇 |
2011年 | 17082篇 |
2010年 | 13539篇 |
2009年 | 14638篇 |
2008年 | 15698篇 |
2007年 | 15903篇 |
2006年 | 14133篇 |
2005年 | 12355篇 |
2004年 | 11399篇 |
2003年 | 10731篇 |
2002年 | 10479篇 |
2001年 | 10342篇 |
2000年 | 9651篇 |
1999年 | 9817篇 |
1998年 | 23077篇 |
1997年 | 16639篇 |
1996年 | 12595篇 |
1995年 | 9953篇 |
1994年 | 9003篇 |
1993年 | 8786篇 |
1992年 | 6870篇 |
1991年 | 6433篇 |
1990年 | 6716篇 |
1989年 | 6509篇 |
1988年 | 6157篇 |
1987年 | 5385篇 |
1986年 | 5401篇 |
1985年 | 6155篇 |
1984年 | 5962篇 |
1983年 | 5399篇 |
1982年 | 4954篇 |
1981年 | 5187篇 |
1980年 | 4874篇 |
1979年 | 4982篇 |
1978年 | 4920篇 |
1977年 | 5316篇 |
1976年 | 6930篇 |
1975年 | 4412篇 |
1974年 | 4148篇 |
1973年 | 4249篇 |
1972年 | 3602篇 |
1971年 | 3298篇 |
The non-centrosymmetric space group organic nonlinear optical single crystal of 4-chloro-2-nitroaniline (4Cl2NA) was developed by slow evaporation method at 40 °C. Grown 4Cl2NA was monoclinic structure with Pc space group which was recognized by single-crystal XRD analysis. An intermolecular contact of 4Cl2NA was visually analysed by Hirshfeld surface analysis. Active functional groups and their respective vibrations were identified by FTIR and FT-Raman spectral analysis. Optical properties were evaluated by UV–Visible spectral analysis. Thermal TG/DTA thermogram analysis and mechanical Vickers hardness analysis revealed that the synthesis material was thermally stable up to 115 °C and mechanical work hardness coefficient (n?=?2.98) confirmed the grown crystal was soft material. Laser beam-irradiated LDT analysis expressed the laser utility limitation of the 4Cl2NA crystal. The NLO second harmonic generation efficiency was tested by Kurtz Perry powder method.
相似文献During homogenisation of the AA3104 cast ingot, a phase transformation of intermetallic particles from β-Al6(Fe,Mn) orthorhombic phase to harder α-Alx(Fe,Mn)3Si2 cubic phase occurs. The large constituent intermetallic particles, regardless of phase, assist in the recrystallisation nucleation process through particle stimulated nucleation (PSN). Ultimately, this helps to refine grain size. The sub-micron dispersoids act to impede grain boundary migration through a Zener drag mechanism. For this reason, the dispersoids that form during homogenisation are critical in the recrystallisation kinetics during subsequent rolling, with smaller dispersoids being better suited to reverse rolling mills. This work simulates an industrial two-step homogenisation practice with variations in the peak temperature of the first step between 560 °C and 580 °C. The effect of this temperature variation on the intermetallic particle-phase evolution is investigated. The aim is to identify the ideal intermetallic phase balance and the dispersoid structure that are best suited for hot rolling on a single stand reversing mill, in order to minimise recrystallisation during rolling through maximising Zener drag and maintaining galling resistance. The results indicate a trend where an increase in homogenisation temperature from 560 °C to 580 °C yields, firstly, an increase in the volume fraction of the α-phase particles to greater than 50% of the total volume fraction at both the edge and the center of the ingot and, secondly, it yields an increased dispersoid size. Thus, in the context of a reverse rolling operation, a lower temperature homogenisation practice produces a near-ideal combination of intermetallic particle-phase distribution, as well as dispersoid size, which is critical for Zener drag and the minimization of recrystallisation during the hot rolling processes.
Graphical abstractSEM BEI images and corresponding EDS maps, highlighting the variation in intermetallic particle phase balance, size and morphology after homogenisation at different temperatures. With a focus on the exaggerated differences seen between material the center of and at the edge of a DC cast ingot of AA3104 Aluminum alloy.
相似文献