全文获取类型
收费全文 | 993篇 |
免费 | 7篇 |
国内免费 | 3篇 |
专业分类
1003篇 |
出版年
2024年 | 8篇 |
2023年 | 39篇 |
2022年 | 23篇 |
2021年 | 33篇 |
2020年 | 82篇 |
2019年 | 68篇 |
2018年 | 51篇 |
2017年 | 81篇 |
2016年 | 79篇 |
2015年 | 68篇 |
2014年 | 55篇 |
2013年 | 364篇 |
2012年 | 2篇 |
2011年 | 3篇 |
2010年 | 2篇 |
2009年 | 5篇 |
2008年 | 2篇 |
2007年 | 4篇 |
2006年 | 2篇 |
2005年 | 2篇 |
2004年 | 1篇 |
2003年 | 1篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 4篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有1003条查询结果,搜索用时 7 毫秒
881.
Precession electron diffraction (PED) has been carried out on a fully ordered Fe–40at.%Al solid solution in order to explore its suitability for determining the state of order. The integrated intensity ratio of a superlattice reflection with respect to a fundamental reflection was measured as a function of the sample thickness and the results are well fitted by dynamical simulations. It is proposed that, in addition to conventional X-ray diffraction, PED may provide access to the state of order at microscopic and nanoscopic scales. 相似文献
882.
Kazuhiro Mitsui 《Philosophical Magazine Letters》2013,93(4):225-233
The changes in the electrical resistivity of thermally disordered Cu-15at.%Pd alloys during isothermal annealing at various temperatures has been investigated. The results obtained are compared with the changes in electrical resistivity calculated under the assumption that ordering proceeds only during isothermal annealing. The electrical resistivity in this alloy first increases and then decreases during isothermal annealing, and the magnitude of the increase decreases as the annealing temperature is lowered. A comparison between the results of measurement and calculation shows that the increase in electrical resistivity is considerably larger than that deduced at the early stage of ordering and occurs after the start of the ordering. An electron micrograph of a sample annealed at 643K for 42000s (11.7h) revealed that not only swirl-like antiphase domains but also fine domains with narrow stripes are present. Furthermore, it is shown that the electron diffraction pattern from the fine domains includes somewhat diffuse extra spots, which have never been observed in the L1 2 -type ordered structure, and that the fine domains disappear after a long anneal. These results indicate that the formation and disappearance of any quasistable phase influence the large increase and subsequent decrease in electrical resistivity during isothermal annealing. 相似文献
883.
ABSTRACTThe wear behaviour of hypereutectic Al–Si alloys, which are suitable for use in automobile engines as a replacement for cast iron, has not been explored at higher temperatures. In the present study, the wear behaviour of Al-17Si-5Cu alloy (AR alloy) has been studied in as-received condition as well as after applying a short-duration isothermal heat treatment developed by the present research team. It was found that AR alloy exhibits severe wear, whereas heat-treated alloy (HT alloy) shows mild wear at higher temperatures (up to 300°C) at all applied loads. This severe-to-mild wear transition is addressed here. 相似文献
884.
Considering recently computed formation and migration energies of kinks on nondissociated dislocations, we have compared the relative mobilities of glide partial and shuffle perfect dislocations in silicon. We found that the latter should be more mobile over all the available stress range, invalidating the model of a stress driven transition between shuffle and glide dislocations. We discuss several hypotheses that may explain the experimental observations. 相似文献
885.
We have combined high-angle annular dark field/scanning transmission electron microscopy (HAADF-STEM) tomography with bright field (BF)-TEM tomography to characterize small inclusions of Pb at a grain boundary in Al. It was found that the shape of the grain boundary inclusions is more complex than previously thought. By using moiré fringes observed at some orientations of the specimen in a BF-TEM tomographic tilt series, we were able to determine the orientation of each grain, the axis and angle of misorientation of the grain boundary, and the facet planes of the grain boundary inclusions. The 3D shape of the inclusions was determined by merging this information with the HAADF-STEM tomography. 相似文献
886.
Plate-shaped Guinier–Preston (G–P) zone formation in an Al–Zn–Mg–Cu–Zr alloy has been studied using transmission electron microscopy. The results provide, for the first time, direct evidence showing nucleation and growth of plate-shaped coherent G–P zones during natural aging. 相似文献
887.
Upward directional non-steady-state solidification experiments have been performed on a hypomonotectic Al–5.5?wt%In alloy. The alloy developed cellular as-solidified microstructure for tip growth rates, V L, higher than 0.95?mm/s. The casting regions associated with V L?<?0.95?mm/s were shown to be characterized by a microstructure formed by In droplets disseminated in the Al matrix. Tip growth rate and microstructural features, such as cell spacing and interphase spacing, have been experimentally determined. The experimental cell spacings have been compared with theoretical predictions furnished by the Hunt–Lu model. It was found that the experimental scatter lies below the minimum range of values theoretically predicted. Moreover, the experimental cell spacing evolution with V L is characterized by a ?1.1 power law. The droplets’ interphase spacing, λ, is related to the growth rate by the Jackson–Hunt relationship (λ 2 V L?=?constant). 相似文献
888.
The influences of doping elements (Ti, Zr, Hf, V, Ta, Cr, Mo, W and Al) on the heats of formation of Nb, Nb5Si3 and Nb3Si have been studied using first-principles pseudopotential plane-wave method based on density functional theory. Site preferences of dopants in Nb5Si3 and Nb3Si intermetallics are first determined by comparing the heats of formation of the systems with different site occupations of the doping atoms. The partitionings of dopants between the equilibrium phases Nb and Nb5Si3 of Nb–Si in situ composites are then discussed and compared with experimental results. Phase partitioning behaviours of the alloying elements are found to depend strongly on the number of their valence electrons. By calculating the enthalpy of reaction regarding the eutectoid decomposition of Nb3Si phase, we conclude that Ta is a Nb3Si stabiliser while other dopants destabilise Nb3Si at the investigated concentration. 相似文献
889.
A fine-grained Cu–30%Zn alloy sheet was rolled at 77 K to induce ultrafine mechanical twins. Subsequent annealing of the rolled alloy at temperatures up to 543 K led to the uniform appearance of recrystallized ultrafine grains (UFGs), which contained numerous annealing twins. Average grain sizes of 150 ~ 300 nm were produced in this way. The formation of such UFGs during annealing is attributed to the high nucleus density associated with the fine initial grain size as well as to the high densities of mechanical twins and dislocations produced by cryorolling. The high driving force for recrystallization enabled the use of relatively low annealing temperatures, which limited the subsequent grain growth. 相似文献
890.
Jidong Kang Raja K. Mishra David S. Wilkinson Odd S. Hopperstad 《Philosophical Magazine Letters》2013,93(11):647-655
Experimental measurements of stress drops and band strains in type-B Portevin–Le Chatelier (PLC) bands were carried out for 5xxx series Al–Mg sheets with Mg content between 1.8 and 4.5?wt%. While the stress drops increase with global strain, the band strain values in all the samples follow a common linear relationship with global strain. The results indicate that the type-B PLC band strain is independent of solute content at given strain rate. 相似文献