全文获取类型
收费全文 | 1051篇 |
免费 | 13篇 |
国内免费 | 115篇 |
专业分类
化学 | 975篇 |
晶体学 | 8篇 |
力学 | 5篇 |
综合类 | 5篇 |
物理学 | 186篇 |
出版年
2024年 | 2篇 |
2023年 | 13篇 |
2022年 | 4篇 |
2021年 | 16篇 |
2020年 | 12篇 |
2019年 | 18篇 |
2018年 | 16篇 |
2017年 | 17篇 |
2016年 | 16篇 |
2015年 | 23篇 |
2014年 | 36篇 |
2013年 | 55篇 |
2012年 | 66篇 |
2011年 | 67篇 |
2010年 | 59篇 |
2009年 | 53篇 |
2008年 | 46篇 |
2007年 | 70篇 |
2006年 | 70篇 |
2005年 | 60篇 |
2004年 | 64篇 |
2003年 | 53篇 |
2002年 | 48篇 |
2001年 | 34篇 |
2000年 | 36篇 |
1999年 | 33篇 |
1998年 | 23篇 |
1997年 | 20篇 |
1996年 | 24篇 |
1995年 | 22篇 |
1994年 | 12篇 |
1993年 | 19篇 |
1992年 | 19篇 |
1991年 | 13篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1988年 | 9篇 |
1987年 | 1篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有1179条查询结果,搜索用时 328 毫秒
981.
This article reports the use of a cascade Suzuki-Heck reaction for the polymerization of suitable aryldibromides with potassium vinyltrifluoroborate resulting in the synthesis of a series of poly(fluorenylenevinylene)s. The protocol is characterized by a great versatility, deriving from the use of easily attainable substrates, and yields polymers with low percentages of structural 1,1-diarylenevinylene defects. 相似文献
982.
983.
The nanosecond desorption of ground-state K atoms from potassium halides was investigated for the first time using a laser-induced fluorescence method with synchrotron radiation and laser pulses. It was found that the desorption consists of a nanosecond component and a slow one of > 180 ns response time. The fast desorption is several orders of magnitude faster than existing results for the time response of ground-state alkali desorption. Therefore, the fast desorption of ground-state alkali atoms cannot be interpreted in terms of the existing mechanisms based on thermal processes and requires a new desorption model. We suggest that the lattice instability due to electronic excitation in the surface layer may play an important role in the fast desorption of ground-state alkali atoms. 相似文献
984.
The novel redox system, potassium diperiodatonickelate (Ni(IV))-casein, was used to initiate graft copolymerization of butyl acrylate onto casein under heterogeneous conditions in aqueous 5% potassium hydroxide solution, which showed high grafting efficiency and percent grafting. FT i.r. spectroscopy, thermal analysis and scanning electron microscopy characterized the structures and properties of the grafted copolymer. The effects of synthesis variables in the graft copolymerization have been discussed in the light of grafting efficiency, percent grafting and the rate of polymerization. A possible initiation mechanism is proposed. 相似文献
985.
Shangwu Ding Nathan D. Jones Charles A. McDowell 《Solid state nuclear magnetic resonance》1998,10(4):205-210
Prudent analysis of the solid state 13C MAS NMR spectra of polycrystalline K2Pt(CN)4 · 3H2O (KTCP)− reveals that in crystals of this compound there are two types of carbon nuclei with slightly different 13C chemical shift tensors, contrary to what is found for the solution NMR spectrum and previous static powder NMR studies on this compound and the high resolution solid state NMR studies on other similar compounds. The 13C MAS spectra measured at different rotor spinning speeds are satisfactorily simulated though the use of a newly developed computer program based on a novel density matrix formulation. The present method is eminently successful even though the spectra are rather complicated because of (1) the relatively large anisotropies of the chemical shift tensors; (2) the high-order dipolar interactions between 13C and 14N nuclei because of the strong quadrupolar coupling constants of 14N nuclei; and (3) the indirect J-coupling between the 13C and 195Pt. The principal elements as well as their orientations of the two 13C chemical shift tensors are evaluated from the spectral simulations. 相似文献
986.
987.
988.
A series of 1,3-alternate calix[4]azacrown ethers for which the monoaza and unsymmetrical crowned-azacrown with different side arms were examined as an ionophore for ion-selective polymeric membrane electrode toward potassium ion. Among them, the electrode based on calix[4]crown-5-azacrown-5 with a phenyl group exhibited near Nernstian response for K+ ions over a wide concentration range (1×10−5 to 1×10−1 M) with a limit of detection of 2×10−6 M. It has a fast response time of approximately 2-3 s and can be used for at least 2 months without observing any major deterioration. Selectivity coefficients indicated that interference from all common alkali, alkaline and transition metal ions was very small. 相似文献
989.
催化动力学光度法测定痕量亚硝酸根 总被引:6,自引:2,他引:6
研究了在磷酸介质中 ,亚硝酸根 (NO- 2 )对溴酸钾氧化二甲基黄催化作用的反应条件 ,建立了测定亚硝酸根的光度法。最大吸收波长在 5 15nm ,表观摩尔吸光系数为 3.0× 10 5L·mol- 1·cm- 1,方法的检出限为 9.16× 10 - 10 g·ml- 1,NO- 2 在 0~ 10 0ng·ml- 1范围内符合比耳定律。用于人唾液及洋葱中亚硝酸根的测定 ,结果满意 相似文献
990.
喷流型发生器、氢化物-原子吸收光谱法测定岩石、矿物中的铅 总被引:1,自引:0,他引:1
本文采用喷流型连续氢化物发生器,氢化物-火焰原子吸收光谱法对岩石、矿物中微量铅的测定条件进行了研究。用铁氰化钾作为铅的氧化剂,草酸为干扰抑制剂,于217.0nm波长,测得铅的特征浓度为0.012μg/ml(1%吸收)。相对标准偏差(对0.6μg/ml Pb)为0.97%。 相似文献