全文获取类型
收费全文 | 2474篇 |
免费 | 98篇 |
国内免费 | 1篇 |
专业分类
2573篇 |
出版年
2023年 | 20篇 |
2022年 | 14篇 |
2021年 | 22篇 |
2020年 | 49篇 |
2019年 | 61篇 |
2018年 | 84篇 |
2017年 | 71篇 |
2016年 | 67篇 |
2015年 | 66篇 |
2014年 | 56篇 |
2013年 | 256篇 |
2012年 | 97篇 |
2011年 | 96篇 |
2010年 | 71篇 |
2009年 | 55篇 |
2008年 | 81篇 |
2007年 | 92篇 |
2006年 | 82篇 |
2005年 | 52篇 |
2004年 | 71篇 |
2003年 | 43篇 |
2002年 | 47篇 |
2001年 | 121篇 |
2000年 | 117篇 |
1999年 | 75篇 |
1998年 | 17篇 |
1997年 | 28篇 |
1996年 | 22篇 |
1994年 | 18篇 |
1992年 | 40篇 |
1991年 | 54篇 |
1990年 | 39篇 |
1989年 | 42篇 |
1988年 | 42篇 |
1987年 | 28篇 |
1986年 | 18篇 |
1985年 | 23篇 |
1984年 | 22篇 |
1983年 | 18篇 |
1981年 | 15篇 |
1979年 | 20篇 |
1976年 | 15篇 |
1975年 | 13篇 |
1974年 | 16篇 |
1973年 | 16篇 |
1971年 | 17篇 |
1970年 | 14篇 |
1969年 | 15篇 |
1968年 | 16篇 |
1967年 | 16篇 |
排序方式: 共有2573条查询结果,搜索用时 15 毫秒
851.
Structurally complicated ξ′- and ξ-phases have been found, for the first time, in as-cast Al73Ni5Rh22 and Al75Ni15Rh10 alloys. The lattice parameters of these two phases were determined by means of electron diffraction and high-resolution transmission electron microscopy (HREM). These two phases have similar orthorhombic structures but with different lattice parameters of a?=?23.2?Å, b?=?16.4?Å, c?=?12.0?Å for the ξ′-phase and a?=?20.3?Å, b?=?16.4?Å, c?=?14.8?Å for the ξ-phase. A new two-dimensional domain-boundary network has also been observed in these two phases. Domain boundaries with normals closely parallel to the [001] direction are actually phason planes represented by a translation vector of r?=(1/2)a?+(1/2τ)c in the ξ′-phase and r=±(1/2τ2) a?+(τ/2)c in the ξ-phase, whereas the newly-found wide and zigzag boundaries perpendicular to the above set were attributed from the step-like boundary structures of domains related by a translation vector of r?=(1/τ)((1/2)a?+(1/2τ)c). The structural difference between the two types of planar faults is discussed. 相似文献
852.
CeO2-doped diamond-like carbon (DLC) films with thicknesses of 180–200 nm were deposited by unbalanced magnetron sputtering. When the CeO2 concentration is in the range 5–8%, the residual compressive stress of the deposited films is reduced by 90%, e.g. from about 4.1 GPa to 0.5 GPa, whereas their adhesion strength increases. These effects are attributed to the dissolution of CeO2 within the DLC amorphous matrix and a widening interface between the DLC film and the Si substrate, respectively. 相似文献
853.
We report on the formation of a new crystalline approximant phase of the icosahedral (i-)Al–Cu–Fe quasicrystal. This phase is formed during sintering of Al-based composites reinforced with i-AlCuFeB quasicrystalline particles. The structure of this phase has been characterized by transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). TEM revealed that it is a B-centred orthorhombic phase with lattice parameters a = 1.166 nm, b = 1.195 nm and c = 3.44 nm. Its chemical composition, as determined by electron energy loss spectroscopy (EELS), is close to Al76.9Cu2.7Fe20.4, with an average number of valence electrons per atom e/a of 1.92, similar to the value in all other approximants of the i-phase discovered thus far. Initial results on local atomic arrangements along one of its pseudo-5-fold axes are also presented. 相似文献
854.
A lattice distortion, represented by microstrain and lattice parameter change, is frequently observed in nanocrystalline (NC) materials. In this letter, we develop a quantitative model to account for this phenomenon. The internal stress induced by the excess volume at grain boundaries is suggested to be the main reason for the lattice distortion. NC materials, prepared by the milling and crystallization method, were used for analysis and comparison. Theoretical calculation shows a reasonable agreement with experimental observations in the grain-size range from 5 to 100 nm. Our results indicate that there is an inherent relationship between microstrain and lattice parameter change in NC materials. 相似文献
855.
Y. Cai A. Zimmermann S. Prinz S. Krämer F. Philipp W. Sigle 《Philosophical Magazine Letters》2013,93(10):553-558
An abnormally large phase, which was found in the precursor-derived Si 3.0 B 1.1 C 5.3 N 3.0 ceramics after crystallization under a nitrogen pressure of 100bar at 1800C for 3h, has been characterized by means of transmission electron microscopy and electron-energy-loss spectroscopy (EELS). EELS analysis shows that this phase consists of only silicon and nitrogen, no other elements being detected. The analysis of selected-area diffraction and convergent-beam electron diffraction in conjunction with EELS reveals that the unknown phase is a variant of silicon nitride. It has a hexagonal structure with lattice parameters a =0.737nm and c =0.536nm, and the space group P62c. . 相似文献
856.
Changes in the structure and mechanical properties of Ti50Zr25Co25 melt-spun ribbons upon electrolytic hydrogenation have been investigated. Structural analyses of the as-spun ribbons revealed the sporadic presence of icosahedral (i) quasicrystalline short-range order (SRO) in the amorphous structure. Upon cathodic charging with hydrogen, the i-SRO vanished for a hydrogen content of about 21 at.% (hydrogen-to-metal atom ratio, H/M: 0.26), resulting in a fully amorphous structure. Simultaneously, the fracture strength was found to increase while the ribbons preserved their bending ductility. However, a significant reduction in the fracture strength and ductility of the ribbons was observed for hydrogen concentrations larger than 26 at.%. Variations in the mechanical stability are discussed based on a structure-property correlation. 相似文献
857.
858.
Gong Li Y.P. Gao Z.H. Chi J. Liu T. Zhang R.P. Liu 《Philosophical Magazine Letters》2013,93(7):543-551
A 52 m drop tube has been used to solidify bulk-glass-forming Zr41Ti14Cu12.5Ni10Be22.5 alloy. Glassy balls with different sizes solidified from the droplets whose structural features, glass-transition behaviour and crystallization kinetics have been investigated. The results indicate that the apparent activation energies of the glass transition and main crystallization reaction are significantly different from those of samples prepared by water quenching. The structural difference between the two types of glassy specimen is revealed by compression studies and in situ energy-dispersive X-ray diffraction. The results are important for understanding the structural features of bulk-forming glasses. 相似文献
859.
The effects of irradiation with electrons having energies in the range 0.7–1.7 MeV on the dark conductivity and the network of hydrogenated amorphous silicon (a-Si:H) thin films have been studied. The dark conductivity measurements show that electron irradiation leads to a degradation in the dark conductivity, with the degradation being greater at lower electron energies. The Raman results suggest that the irradiation induces structural defects in the a-Si:H films, with the lower energy electrons producing more disorder in the amorphous network. 相似文献
860.
Mechanical tests have been carried out on Fe–15%Cr ferritic stainless steel with various microstructures. Ultrafine-grained microstructures with grain sizes of 0.2–0.3 µm were developed by large-strain cold-working and light annealing. The effects of severe deformation on the mechanical behaviour of as-processed and recovered steel were evaluated with reference to the same material having conventional work-hardened and recrystallised microstructures. Despite the low dislocation density in the fine grain interiors in the as-processed state, the samples with strain-induced submicrocrystalline structure were characterised by high internal stresses that resulted in a higher strength than could be expected from simple grain-size strengthening. These internal stresses were associated with a non-equilibrium state of strain-induced grain boundaries after severe deformation. 相似文献