全文获取类型
收费全文 | 71594篇 |
免费 | 11822篇 |
国内免费 | 8747篇 |
专业分类
化学 | 50454篇 |
晶体学 | 929篇 |
力学 | 4606篇 |
综合类 | 691篇 |
数学 | 8817篇 |
物理学 | 26666篇 |
出版年
2024年 | 137篇 |
2023年 | 1330篇 |
2022年 | 1840篇 |
2021年 | 2364篇 |
2020年 | 2808篇 |
2019年 | 2693篇 |
2018年 | 2300篇 |
2017年 | 2156篇 |
2016年 | 3114篇 |
2015年 | 3187篇 |
2014年 | 3908篇 |
2013年 | 5077篇 |
2012年 | 6224篇 |
2011年 | 6419篇 |
2010年 | 4442篇 |
2009年 | 4370篇 |
2008年 | 4718篇 |
2007年 | 4238篇 |
2006年 | 3967篇 |
2005年 | 3398篇 |
2004年 | 2775篇 |
2003年 | 2154篇 |
2002年 | 2048篇 |
2001年 | 1764篇 |
2000年 | 1545篇 |
1999年 | 1615篇 |
1998年 | 1381篇 |
1997年 | 1253篇 |
1996年 | 1297篇 |
1995年 | 1085篇 |
1994年 | 1035篇 |
1993年 | 801篇 |
1992年 | 726篇 |
1991年 | 633篇 |
1990年 | 582篇 |
1989年 | 403篇 |
1988年 | 370篇 |
1987年 | 348篇 |
1986年 | 268篇 |
1985年 | 260篇 |
1984年 | 214篇 |
1983年 | 186篇 |
1982年 | 142篇 |
1981年 | 103篇 |
1980年 | 82篇 |
1979年 | 56篇 |
1978年 | 43篇 |
1976年 | 42篇 |
1975年 | 46篇 |
1973年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
271.
研究了应用于锂二次电池正极的新型高能量密度存贮材料Li(AlxCo1-x)O2 (x=01—05)的磁性.发现Al3+的掺杂可导致Co3+中d电子自旋态发生变化,即有部分d电子进入高自旋态.伴随Co3+中电子状态的改变,材料结构演化也发生了相应变化,表现为c/a比增大明显减缓,较好地解释了材料结构对Vegard定律的正偏离.这对材料的微观结构与性能设计具有重要意义.
关键词:
锂电池材料
Li(AlxCo1-x)O2
磁性
自旋态
结构演化 相似文献
272.
273.
274.
Yang Ruike Wu Zhensen You Jinguang 《International Journal of Infrared and Millimeter Waves》2003,24(8):1383-1392
The influence of sand and dust storms on modern MMW and satellite communication systems reliability have been paid more attention to. The attenuations induced by sand and dust storms are estimated by means of Mie-theory and Rayleigh approximation, in the case of the tenuous distribution of particles. With the particle density increasing, however, these method become inadequate, the multiple scattering effects then become dominant for attenuation estimation. The attenuations considering multiple scattering effects are estimated by Monte-Carlo and four fluxes method at horizontal paths. At slant paths, based on multi-layer media model, the attenuations considering multiple scattering effects are calculated by layered Monte-Carlo method at 100, 37, 24, and 14GHz. It is shown that the multiple scattering effects should be considered at the attenuation prediction in the sand and dust storm, which the visibility is about 0.5km and smaller than 0.5km and frequency is about 20GHz. Above 30GHz, the multiple scattering effects due to sand and dust particles should be considered, as visibility is about 1km and smaller than 1km at slant paths. 相似文献
275.
276.
277.
Yingyu Hu Guoqiao Lai Yongjia Shen Yongfang Li 《Monatshefte für Chemie / Chemical Monthly》2004,33(2):1167-1172
Zinc(II) and magnesium(II) phthalocyanines bearing four substituted propylenedithiotetrathiafulvalene (PDT-TTF) units were synthesized and characterized by NMR, MS, EA, and UV/VIS spectra. The absorption peaks of two target molecules were hypsochromically shifted compared with the phthalocyanine parent compound. Studies using cyclic voltammetry indicated that introduction of Zn and Mg as central metals enhanced the electronwithdrawing between the phthalocyanine core and the PDT-TTF unit, thus losing one electron to form (PDT-TTF)+ becomes more difficult. 相似文献
278.
Hong-wei Zhang Shao-ying Zhang Bao-gen Shen Helmut Kronmüller 《Journal of magnetism and magnetic materials》2003,260(3):352-360
The magnetization behavior in nanocrystalline permanent magnets has been investigated using mean field Stoner–Wohlfarth model. The model is comparatively simple but allows the numerical treatment of extended nanostructures. The predominant intergrain exchange coupling is expressed by a mean field constant Nm in spite of no explicit relationship between Nm and the microstructure. By this model, the experimental phenomena, such as the remanence enhancement, the shape of demagnetization curve, the irreversible magnetization, the exchange bias field and their respective temperature dependence, can be well explained. The Nm dependence of magnetic properties has been extensively discussed in the present paper. 相似文献
279.
280.