全文获取类型
收费全文 | 64126篇 |
免费 | 9767篇 |
国内免费 | 7262篇 |
专业分类
化学 | 45089篇 |
晶体学 | 860篇 |
力学 | 3776篇 |
综合类 | 515篇 |
数学 | 7889篇 |
物理学 | 23026篇 |
出版年
2024年 | 134篇 |
2023年 | 1148篇 |
2022年 | 1705篇 |
2021年 | 1959篇 |
2020年 | 2279篇 |
2019年 | 2193篇 |
2018年 | 1938篇 |
2017年 | 1833篇 |
2016年 | 2739篇 |
2015年 | 2718篇 |
2014年 | 3302篇 |
2013年 | 4387篇 |
2012年 | 5310篇 |
2011年 | 5718篇 |
2010年 | 3969篇 |
2009年 | 3911篇 |
2008年 | 4299篇 |
2007年 | 3883篇 |
2006年 | 3614篇 |
2005年 | 2965篇 |
2004年 | 2362篇 |
2003年 | 1971篇 |
2002年 | 1874篇 |
2001年 | 1548篇 |
2000年 | 1453篇 |
1999年 | 1366篇 |
1998年 | 1192篇 |
1997年 | 1092篇 |
1996年 | 1134篇 |
1995年 | 982篇 |
1994年 | 884篇 |
1993年 | 754篇 |
1992年 | 731篇 |
1991年 | 597篇 |
1990年 | 519篇 |
1989年 | 426篇 |
1988年 | 359篇 |
1987年 | 299篇 |
1986年 | 291篇 |
1985年 | 299篇 |
1984年 | 204篇 |
1983年 | 133篇 |
1982年 | 129篇 |
1981年 | 88篇 |
1980年 | 67篇 |
1979年 | 68篇 |
1978年 | 40篇 |
1976年 | 37篇 |
1974年 | 40篇 |
1973年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
NianYuanTAN XiaoMingXIAO ZeLinLI TakekoMATSUMURA-INOUE 《中国化学快报》2004,15(6):687-690
A new cobalt(Ⅱ) complex with tridentate ligand 2, 6-bis (benzimidazol-2-yl)pyridine has been synthesized by microwave irradiation method and characterized by elemental analysis,electrochemical and spectral methods. The binding of the complex with calf thymus DNA has also been investigated by absorption and fluorescence spectra. 相似文献
172.
The electronic structure and chemical bonding in a recently synthesized inorganic fullerene-like molecule, [CuCl]20[Cp*FeP5]12[Cu-(CH3CN) +
2Cl−]5 has been studied by a density functional approach. Geometrical optimization of the three basic structural units of the molecule
is performed with Amsterdam Density Functional Program. The results are in agreement with the experiment. Localized MO’s obtained
by Boys-Foster method give a clear picture of the chemical bonding in this molecule. The reason why CuCl can react with Cp*FeP5 in solvent CH3CN to form the fullerene-like molecule is explained in terms of the soft-hard Lewis acid base theory and a new concept of
covalence. 相似文献
173.
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
174.
175.
176.
We observe enhanced terahertz (THz) radiation generated from a Si3N4 film-coated GaAs photoconductive dipole antenna. Compared to an uncoated antenna with identical electrode geometry and optical excitation power, the Si3N4 film-coated antenna has a higher effective DC resistance and larger breakdown voltage. As a result, the peak amplitude of generated THz radiation is significantly enhanced due to the Si3N4 film-coated layer. 相似文献
177.
Thermal oxidation of polyethylene filled with dispersed copper and containing an amine antioxidant was studied. The concentration ranges in which the catalytic effect of the metal on the polymer oxidation or the stabilizing effect of the antioxidant prevails were determined. Under certain conditions, dispersed copper enhances the stabilizing effect of the antioxidant. 相似文献
178.
179.
LiAlO2 single crvstals doped with Ti at concentration 0.2at.% are grown by the Czochralskl technique with dimensions φ42×55mm. Ti ions in the crystal are quadrivalence proven by comparing the absorption and fluorescence spectra of pure LiAlO2 and Ti: LiAlO2. After air and Li-rich atmosphere annealing, the absorption peaks in the range of 600-800nm disappear. We conclude that 682 and 756nm absorption peaks are attributed to the VLi and Vo absorptions, respectively: The peaks at 716nm and 798nm may stem from the VLi^+ and absorptions. The colour-centre model can be applied to explain the experimental phenomena. Ti^4+-doping produces more lithium vacancies in the LiAlO2 crystal. The intensities of [LiO4] and the associated bonds remain unchanged, which improves the anti-hydrolyzation and thermal stability of LiAlO2 crystals. 相似文献
180.
The ρ-T curves in our single phase HgBa2Ca2Cu3O8+δ superconductor were measured as a function of temperature and magnetic field, ρ=ρ0exp(−Ueff/κBT). It can be transformed to another form d(lnρ)/d(1/T)=−Ueff+TdUeff/dT, then this becomes a plot of the activation energy Ueff as a function of temperature. Our data plotted in these ways show a clear crossover from high-temperature two-dimensional vortex-liquid to a critical region associated with the low-temperature three-dimensional vortex-glass phase transition. The critical exponents v(z−1)=3.9±1.9 in this system are little different with previous measurements in BSCCO and YBCO systems. 相似文献