全文获取类型
收费全文 | 70946篇 |
免费 | 10074篇 |
国内免费 | 7492篇 |
专业分类
化学 | 37244篇 |
晶体学 | 543篇 |
力学 | 3451篇 |
综合类 | 399篇 |
数学 | 6068篇 |
物理学 | 20084篇 |
无线电 | 20723篇 |
出版年
2024年 | 258篇 |
2023年 | 1643篇 |
2022年 | 2013篇 |
2021年 | 2609篇 |
2020年 | 2589篇 |
2019年 | 2289篇 |
2018年 | 2002篇 |
2017年 | 1956篇 |
2016年 | 2786篇 |
2015年 | 2986篇 |
2014年 | 3630篇 |
2013年 | 4655篇 |
2012年 | 5727篇 |
2011年 | 5688篇 |
2010年 | 4065篇 |
2009年 | 4082篇 |
2008年 | 4451篇 |
2007年 | 3956篇 |
2006年 | 3895篇 |
2005年 | 3406篇 |
2004年 | 2587篇 |
2003年 | 2154篇 |
2002年 | 1966篇 |
2001年 | 1710篇 |
2000年 | 1563篇 |
1999年 | 1750篇 |
1998年 | 1477篇 |
1997年 | 1322篇 |
1996年 | 1424篇 |
1995年 | 1228篇 |
1994年 | 1116篇 |
1993年 | 932篇 |
1992年 | 864篇 |
1991年 | 672篇 |
1990年 | 570篇 |
1989年 | 420篇 |
1988年 | 375篇 |
1987年 | 306篇 |
1986年 | 231篇 |
1985年 | 229篇 |
1984年 | 189篇 |
1983年 | 158篇 |
1982年 | 112篇 |
1981年 | 85篇 |
1980年 | 67篇 |
1979年 | 40篇 |
1978年 | 30篇 |
1976年 | 31篇 |
1975年 | 36篇 |
1974年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
提出了一种新的高功率宽带放大器,它由速调管和自由电子脉塞组成,用永久周期磁铁聚焦。研究了这种器件的电子束聚焦、群聚和辐射。在速调管提供一阶调制系数为30%,波导管的半径1.51cm,摇摆器的磁场振幅0.16T,周期7.92cm,电子束的电压490kV,电流50A和半径0.368cm的条件下,预估这种器件的辐射波频率为11.4GHz,输出辐射功率为18MW,输出辐射带宽为44%。 相似文献
94.
Fe2(CO)6(μ-S2) was used as a single source precursor in attempt to produce FeS film via MOCVD. Pyrolysis of Fe2(CO)6(μ-S2) at temperature below 500℃ produced Fe1-xS or Fe7S8 powder as indicated by its powder X-ray spectra. At 750 ℃, polycrystalline FeS powder was obtained. In film deposition, polycrystalline Fe1-xS or Fe7Ss films were obtained on Si(100) and Ag/Si(100) substrates below 500 ℃. SEM micrographs showed the film on Si(100) substrate containing whisker like grains. However, pillar like grains were obtained on Ag/Si(100) substrate.Deposition rates are also different for different substrates as evaluated by the thickness of the films, which were obtained by SEM micrographs of the cross section of the films. At 750℃, similar polycrystalline Fe1-xS or Fe7S8 film was obtained. 相似文献
95.
5,6-Dihydro-OSW-1 (1) was synthesized following our previous procedure for the total synthesis of OSW-1. This compound demonstrated slightly stronger potency than that of OSW-1 against the growth of cancer cells. 相似文献
96.
A New Triterpene from the Orchid Pholidota yunnanensis 总被引:2,自引:0,他引:2
ZhiMingBI ZhengTaoWANG LuoShanXU 《中国化学快报》2004,15(10):1179-1181
A new triterpene, 25-methylenecyclopholidonyl p-hydroxy-trans-cinnamate, was isolated from a orchid Pholidota yunnanensis. The structure elucidation and ^1H, ^13C-NMR assignments were achieved by spectral and chemical method. 相似文献
97.
Baker‘s yeast mediated reduction of optically active diketone is described. The two keto groups are efficiently differentiated and the ee value of the recovered material is considerably raised. It affords highly optically active key intermediates efficiently for the synthesis of natural polyhydroxylated agarofuran products. 相似文献
98.
多小波子空间上的单小波表示 总被引:1,自引:0,他引:1
本文在较弱的条件下,建立了2重多小波子空间与单小波子空间的关系.即由2重多小波构造出单小波.一方面,这种单小波的平移伸缩与2重多小波的平移伸缩生成的子空间是完全相同的;另一方面,它具有插值性.因此通过构造出的单小波建立了多小波子空间上的Shannon型采样定理. 相似文献
99.
QiangWU DaChunYANG 《数学学报(英文版)》2005,21(1):81-94
In this paper, two classes of closely related multilinear singular and fractional integrals,which include the commutators as special cases, are studied and their boundedness on Herz type spaces is discussed. In fact, it is proved that these operators are actually not bounded in certain extreme cases. 相似文献
100.
Zhao Zheng Zhang Jian-hua Jiang Ya-ling 《International Journal of Theoretical Physics》1997,36(6):1359-1368
The Hawking effect of a nonuniformly rectilinearly accelerating Kinnersley black hole is studied. Its horizons are rotationally
symmetric. Its Hawking temperature depends not only on the time, but also on the polar angle. When a Kinnersley black hole
touches its Rindler horizon, the Hawking temperature at the contact point is reduced to zero. But at the opposite pole of
the black hole, the Hawking temperature increases rapidly. A jet appears as a tail of the accelerating black hole. 相似文献