全文获取类型
收费全文 | 2634篇 |
免费 | 265篇 |
国内免费 | 715篇 |
出版年
2024年 | 10篇 |
2023年 | 29篇 |
2022年 | 54篇 |
2021年 | 91篇 |
2020年 | 103篇 |
2019年 | 80篇 |
2018年 | 101篇 |
2017年 | 117篇 |
2016年 | 77篇 |
2015年 | 83篇 |
2014年 | 73篇 |
2013年 | 231篇 |
2012年 | 166篇 |
2011年 | 222篇 |
2010年 | 188篇 |
2009年 | 192篇 |
2008年 | 207篇 |
2007年 | 295篇 |
2006年 | 277篇 |
2005年 | 244篇 |
2004年 | 160篇 |
2003年 | 117篇 |
2002年 | 72篇 |
2001年 | 57篇 |
2000年 | 43篇 |
1999年 | 63篇 |
1998年 | 34篇 |
1997年 | 32篇 |
1996年 | 26篇 |
1995年 | 27篇 |
1994年 | 18篇 |
1993年 | 22篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 4篇 |
1986年 | 11篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 3篇 |
排序方式: 共有3614条查询结果,搜索用时 15 毫秒
991.
X. H. Zhang 《Philosophical Magazine Letters》2013,93(12):797-805
A polymorphous crystallization process in an amorphous FeZr2 alloy has been investigated by means of accurate electrical resistance measurements (ERMs) at elevated temperatures. It was found that, upon crystallization of the amorphous alloy, the electrical resistance increased with increasing temperature, exhibiting three distinct stages. Quantitative microscopy observations revealed that the three stages originated from crystal nucleation, from subsequent growth of crystal nuclei and from coarsening of the crystallites respectively. The activation energies for the crystal nucleation and growth determined from the ERM data agree satisfactorily with the data in the literature. The success in identification of the crystal nucleation and growth processes by means of ERMs may originate from differences in electrical resistance changes due to the crystal formation and the crystalline-amorphous interface formation processes from the amorphous phase. 相似文献
992.
The Ag-(Bi(Pb)-Sr-Ca-Cu-O (BSCCO)) interface region has been studied by scanning electron microscopy and transmission electron microscopy to a distance of 2µm away from the silver in the Ag-sheathed multifilamentary Bi(Pb)2Sr2Ca2Cu3O (Bi(Pb)-2223) tapes. Owing to undulation of the silver surface, silver was found to play an important but not always positive role in the alignment of BSCCO grains. Based on the kink angle variation, the effective thickness of multifilamentary Bi(Pb)-2223 tapes capable of carrying a large current has been defined. We believe that the difference in effective thickness is the key reason leading to different critical current densities J c for these tapes. 相似文献
993.
994.
In this paper, the probability of fatigue cracking along different kinds of grain boundary (GB) and persistent slip bands (PSBs) is considered in the light of data obtained by cyclic deformation of copper bicrystals and columnar crystals. It is found that, in copper bicrystals, fatigue cracks always nucleate and propagate along large-angle GBs, irrespective of whether the GB is perpendicular, parallel or inclined to the stress axis. On the contrary, for columnar copper crystals containing small-angle GBs, PSB-matrix interfaces become the preferential sites for initiation of fatigue crack; fatigue cracking along the small-angle GBs was never observed. For a special [1-34]/[182-7] copper bicrystal with a Sigma = 19b GB and a common primary slip plane, GB cracking also results in fatigue failure. Based on the results above, the interactions of dislocations carried by PSBs with GBs, including 'pile-up of dislocations', 'passing through of dislocations' and 'partial passing-through dislocations', are discussed. It is suggested that the probability of fatigue cracking in fatigued copper crystals increases in the order of small-angle GBs, PSBs and large-angle GBs. 相似文献
995.
A sample containing single-wall carbon nanotubes (SWCNTs) has been annealed at 900°C and then irradiated by high-energy electrons in an ultrahigh-vacuum transmission electron microscope. Sequential high-resolution images showed that the structures of SWCNT bundles and individual SWCNT segments first collapsed into disordered and fullerene-like carbon materials and then reorganized into graphitic particles under continuous electron irradiation. The speed of structural evolution is dependent on the flux density of the electron irradiation. 相似文献
996.
The influence of ruthenium (Ru) on the partitioning behavior of W, Re and Cr in γ′-Ni3Al has been studied using the Dmol3 method based on the density functional theory. The calculated results show that W, Re and Cr have a preference for the Ni site in γ′-Ni3Al alloyed with Ru. When Ru substitutes the central Ni atom, the site preference for W, Re and Cr varies. Furthermore, an electronic structure analysis of the alloy in terms of the Mulliken population and partial density of states was performed to elucidate the alloying mechanism of Ru in γ′-Ni3Al. The results show that the strengthening effect of Ru in the alloy arises from a reduction in the binding energy of Ru as well as p-orbital hybridization between Ru and the host atoms. 相似文献
997.
A phase-transformation-induced hardening effect is reported in Zn–22Al (Al: 22?wt.%) alloys. The Zn–22Al specimens were held at 300?°C for 10?h and then quenched in water. A hardening effect took place in subsequent artificial aging at 100–200?°C, which was accompanied by a phase decomposition of a soft α 2 phase and a grain coarsening. The phase-transformation-induced hardening affects the hardness more than the grain-coarsening-induced softening, which leads to the age-hardening phenomenon. 相似文献
998.
Zhiguo Chen Jishuai Zhang Jun Shu Gang Sha Junhai Xia Shiyong Wang 《Philosophical Magazine Letters》2013,93(11):648-654
The precipitation behaviour and age-hardening response of Al–1.5Cu–4.0Mg (wt.%) alloys microalloyed with Si have been investigated by means of hardness measurement, TEM and HRTEM. Compared to the ternary alloy, the quaternary alloys exhibit a higher hardness. It is found that the underaged microstructure in the Al–1.5Cu–4.0?Mg alloy contains some fine precipitates, which are identified as the T phase by FFT spectra. The peak-aged microstructures of the ternary alloy is dominated by the T phase, while the peak-aged microstructures of the Si-containing alloys are dominated by the S phase. The volume fraction of the S phase is found to increase as more Si is added. 相似文献
999.
A Ni53Nb20Ti10Zr8Co6Cu3 fully amorphous metallic coating has been deposited by means of kinetic metallization (KM) using gas atomized powders. As the thickness of the amorphous metallic coating is increased to 400?µm, it attains the excellent corrosion resistance of the amorphous alloy, as indicated by the extremely low passive current density and wide passive region in 1?kmol/m3 HCl aqueous solution. The corrosion rate is as low as 10–3?mm/year in the extremely corrosive environment of 6?kmol/m3 HCl aqueous solution. 相似文献
1000.
B. J. Derksen M. C. Duff K. Weldon J. Zhang K. D. Zamba D. Tranel 《Memory (Hove, England)》2013,21(4):612-624
Learning and memory abilities tend to decline as people age. The current study examines the question of whether a learning situation that emphasises collaborative social interaction might help older persons overcome age-related learning and memory changes and thus perform similarly to younger persons. Younger and Older participants (n = 34 in each group) completed the Barrier Task (BT), a game-like social interaction where partners work together to develop labels for a set of abstract tangrams. Participants were also administered standard clinical neuropsychological measures of memory, on which the Older group showed expected inferiority to the Younger group. On the BT, the Older group performed less well than the Younger group early on, but as the task progressed, the performance of the Older group caught up and became statistically indistinguishable from that of the Younger group. These results can be taken to suggest that a learning milieu characterised by collaborative social interaction can attenuate some of the typical memory disadvantages associated with being older. 相似文献