全文获取类型
收费全文 | 5390篇 |
免费 | 1138篇 |
国内免费 | 670篇 |
专业分类
化学 | 3512篇 |
晶体学 | 39篇 |
力学 | 189篇 |
综合类 | 20篇 |
数学 | 54篇 |
物理学 | 1988篇 |
综合类 | 1396篇 |
出版年
2024年 | 21篇 |
2023年 | 71篇 |
2022年 | 153篇 |
2021年 | 184篇 |
2020年 | 253篇 |
2019年 | 204篇 |
2018年 | 166篇 |
2017年 | 184篇 |
2016年 | 260篇 |
2015年 | 256篇 |
2014年 | 347篇 |
2013年 | 427篇 |
2012年 | 358篇 |
2011年 | 367篇 |
2010年 | 290篇 |
2009年 | 324篇 |
2008年 | 343篇 |
2007年 | 322篇 |
2006年 | 312篇 |
2005年 | 281篇 |
2004年 | 277篇 |
2003年 | 245篇 |
2002年 | 182篇 |
2001年 | 160篇 |
2000年 | 158篇 |
1999年 | 147篇 |
1998年 | 125篇 |
1997年 | 109篇 |
1996年 | 112篇 |
1995年 | 87篇 |
1994年 | 89篇 |
1993年 | 64篇 |
1992年 | 61篇 |
1991年 | 49篇 |
1990年 | 44篇 |
1989年 | 34篇 |
1988年 | 25篇 |
1987年 | 19篇 |
1986年 | 20篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 2篇 |
排序方式: 共有7198条查询结果,搜索用时 15 毫秒
71.
The effect of Ni substitution for Mn on magnetic and transport properties has been investigated for layered manganese oxides LaSr2Mn2-xNixO7. Nickel doping hampered the canted antiferromagnetic (AFM) exchange at low temperature and their Neel temperature (TN) decreased from 138 K (x=0) to 102 K (x=0.3). Meanwhile, spin glass, charge ordering and metal-insulator transition are suppressed by Ni addition. The resistivity increases obviously with increasing x due to double exchange interaction channel broken by Ni2+ addition. The resistivity of all samples in low temperature range fits to the Mott′s variable rang hopping (VRH) model, while it fits to nearest neighbor hopping of small polarons model in high temperature range. 相似文献
72.
The influence of the pH of precipitation and the ionic medium nature on the composition, surface charge, and kinetic sorption characteristics of aluminum oxyhydroxides formed by alkaline hydrolysis of an aqueous solution of aluminum nitrate was studied. The methods of drop titration with alkali, argentometric titration, point of zero charge, and indicator reactions of heterogeneous hydrolysis were used. The composition of the freshly precipitated hydrogels of aluminum(iii) oxyhydroxide, rate constants of heterogeneous hydrolysis of the IrCl6
2– ions as indicator reactions, and the pH of the point of zero charge were determined. The rate of indicator reactions (as for other oxyhydroxide hydrogels) depends strongly on the pH of precipitation. However, it is lower than the rates characteristics of iron(iii) and chromium(iii) oxyhydroxides obtained under similar conditions. The pH of the point of zero charge for the alumogels in a chloride medium is 8.3 and that in a sulfate medium is 9.5. 相似文献
74.
Zou JW Jiang YJ Guo M Hu GX Zhang B Liu HC Yu QS 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(2):740-751
Ab initio calculations have been performed on a series of complexes formed between halogen-containing molecules and ammonia to gain a deeper insight into the nature of halogen bonding. It appears that the dihalogen molecules form the strongest halogen-bonded complexes with ammonia, followed by HOX; the charge-transfer-type contribution has been demonstrated to dominate the halogen bonding in these complexes. For the complexes involving carbon-bound halogen molecules, our calculations clearly indicate that electrostatic interactions are mainly responsible for their binding energies. Whereas the halogen-bond strength is significantly enhanced by progressive fluorine substitution, the substitution of a hydrogen atom by a methyl group in the CH(3)X...NH(3) complex weakened the halogen bonding. Moreover, remote substituent effects have also been noted in the complexes of halobenzenes with different para substituents. The influence of the hybridization state of the carbon atom bonded to the halogen atom has also been examined and the results reveal that halogen-bond strengths decrease in the order HC triple bond CX > H(2)C=CHX approximately O=CHX approximately C(6)H(5)X > CH(3)X. In addition, several excellent linear correlations have been established between the interaction energies and both the amount of charge transfer and the electrostatic potentials corresponding to an electron density of 0.002 au along the R-X axis; these correlations provide good models with which to evaluate the electron-accepting abilities of the covalently bonded halogen atoms. Finally, some positively charged halogen-bonded systems have been investigated and the effect of the charge has been discussed. 相似文献
75.
76.
77.
Yong Zhao Xianliang Sheng Jin Zhai Lei Jiang Chunhe Yang Zhongwei Sun Yongfang Li Daoben Zhu 《Chemphyschem》2007,8(6):856-861
Titanium dioxide (TiO(2)) photoelectrodes with micro/nano hierarchical branched inner channels have been prepared by an electrohydrodynamic (EHD) technique and assembled to form dye-sensitized solar cells (DSSCs). Excellent penetration of ionic-liquid electrolytes and enhanced light harvesting in the longer wavelength region are realized within the composite-structure electrode, thus a better fill factor (ff) of 75.3 % and higher conversion efficiency (eta) of 7.1 % are obtained for viscous ionic-liquid electrolytes compared to pure nanostructured films. Hierarchical branched channels in the photoanodes can efficiently improve the transport properties of redox-active species in viscous electrolytes, which is demonstrated by electrical impedance spectroscopy (EIS). The incident monochromatic photon-to-electron conversion efficiency (IPCE) shows that enhanced light scattering in the composite film is of benefit for light harvesting and thus for solar energy conversion efficiency. 相似文献
78.
79.
80.
研究了4-位苯基取代基旋转受阻和旋转自由的2,4,6-三苯基氧盐的光物理性质。实验结果表明,当4-位苯基取代基旋转受阻时,氧盐化合物在激发态时引起的分子内极化程度比4-位取代基旋转自由的氧盐化合物大,即在激发态时旋转受阻氧盐化合物发生的分子内电荷转移能力较强;4-位取代基旋转自由的化合物的荧光量子产率随溶剂粘度的增大而有所增大,但旋转受阻化合物在相同的条件下则出现相反的结果。实验结果还表明,4-位取代苯基旋转受阻对化合物的荧光发射不利。 相似文献