全文获取类型
收费全文 | 2339篇 |
免费 | 75篇 |
国内免费 | 20篇 |
专业分类
化学 | 1422篇 |
晶体学 | 11篇 |
力学 | 34篇 |
数学 | 437篇 |
物理学 | 530篇 |
出版年
2023年 | 17篇 |
2022年 | 48篇 |
2021年 | 64篇 |
2020年 | 48篇 |
2019年 | 66篇 |
2018年 | 62篇 |
2017年 | 54篇 |
2016年 | 79篇 |
2015年 | 90篇 |
2014年 | 76篇 |
2013年 | 159篇 |
2012年 | 134篇 |
2011年 | 162篇 |
2010年 | 113篇 |
2009年 | 112篇 |
2008年 | 163篇 |
2007年 | 139篇 |
2006年 | 171篇 |
2005年 | 137篇 |
2004年 | 92篇 |
2003年 | 82篇 |
2002年 | 89篇 |
2001年 | 36篇 |
2000年 | 28篇 |
1999年 | 28篇 |
1998年 | 22篇 |
1997年 | 24篇 |
1996年 | 32篇 |
1995年 | 15篇 |
1994年 | 11篇 |
1993年 | 14篇 |
1992年 | 10篇 |
1991年 | 9篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1969年 | 2篇 |
排序方式: 共有2434条查询结果,搜索用时 15 毫秒
51.
Joy Chakraborty Brajagopal Samanta Andrei S. Batsanov Joan Ribas M. Salah El Fallah Samiran Mitra 《Structural chemistry》2006,17(4):401-407
A ligand–metal–ligand type co-ordination polymer [Ni (C6H12N4)(NCS)2(H2O)2]
n
has been synthesised under controlled hydrothermal conditions. Here 1,3,5,7-tetraazatricyclo[3.3.1]decane [or hexamethylenetetramine (hmt)] has been used as a μ-(N,N′) bidentate spacer molecule. The prepared polymeric complex has been characterised by elemental and spectral analyses. The structure has been confirmed by a single crystal X-ray diffraction study. Magneto-structural correlation has been drawn from cryomagnetic susceptibility measurements (2–300 K) which unequivocally reflects very weak magnetic spin interactions among the long distant octahedral Ni(II) metal centres mediated by hmt and weak hydrogen bonding interactions between the adjacent zigzag one-dimensional polymeric chains carrying into a two-dimensional infinite polymeric framework. 相似文献
52.
53.
Spectra of single tetra-tert-butylterrylene chromophore molecules embedded in an amorphous polyisobutylene matrix as microprobes were recorded. The individual temperature dependences of the spectral linewidths for the same single molecules (SMs) in a broad temperature interval (1.6 < T < 40 K) have been measured. This enabled us to separate the contributions of tunneling two-level systems and quasilocalized low-frequency vibrational modes (LFMs) to the observed linewidths. The analysis of the T dependences yields the values of LFM frequencies and SM-LFM coupling constants for the LFMs in the local environment of a given chromophore. Pronounced distributions of the observed parameters of LFMs were found. This result can be regarded as the first direct experimental proof of the localized nature of LFMs in glasses. 相似文献
54.
[reaction: see text] Straightforward methods for palladium-catalyzed alkenylation of aziridines with alkenyl halides and copper-catalyzed alkenylation of aziridines with alkenyl boronic acids have been developed. This methodology offers attractive alternatives to the known methods requiring activated alkenyl halides and acetylenes. A wide variety of N-alkenyl aziridines containing substituents other than electron-withdrawing substituents such as cyano groups and sulfones have been synthesized in good yields. Furthermore, these N-alkenyl aziridines exhibit quite a different reactivity from conventional enamines, as demonstrated by their reactivity. 相似文献
55.
[reaction: see text] The combination of diethyl phosphite and DMAP as ligands for nickel in an 8:1 THF-N-ethylpyrrolidinone (NEP) mixture allows a very efficient cross-coupling reaction to be performed between various functionalized arylzinc halides and aryl bromides, triflates and activated chlorides. The reaction proceeds at 25 degrees C within 1-48 h and requires only 0.05 mol % of the nickel catalyst. 相似文献
56.
57.
Andrei Rotaru 《Journal of Thermal Analysis and Calorimetry》2012,110(3):1283-1291
Solid fuels represent one of the most used sources of energy in many countries. In terms of ranking for the coal deposits, Romania occupies the 26th place in the world, and the 11th place in Europe, with reserves of 22 million tones of bituminous coal (BC) and 472 million tones of lignite. The National Bituminous Coal Company extracts the most significant amount of BC from the Jiu Valley area, a Subcharpatian basin in the Parang Mountains. In the present article, the BC extracted from the Livezeni depth mine next to Petro?ani city is investigated from the microstructural, thermal, and kinetic point of view, in comparison with a sample from Ural Mountains in Russia. Scanning electron microscopy, FTIR spectroscopy, and thermal analysis (TG/DSC/DTA in air and inert atmosphere) measurements were performed. The KAS isoconversional kinetic method was applied for the in-depth understanding of thermal decompositions and burning processes that occur. Even if the thermal behavior of the two samples is generally similar, the non-isothermal kinetic study revealed important differences in the pathways of the oxidative decomposition of volatiles and formation of coke. Also, the kinetics of coke burning depends only on the amount of fix carbon, regardless of the provenience of BC. 相似文献
58.
59.
60.