全文获取类型
收费全文 | 3243篇 |
免费 | 72篇 |
国内免费 | 8篇 |
专业分类
化学 | 1803篇 |
晶体学 | 22篇 |
力学 | 74篇 |
数学 | 332篇 |
物理学 | 1092篇 |
出版年
2022年 | 26篇 |
2021年 | 29篇 |
2020年 | 29篇 |
2019年 | 28篇 |
2017年 | 26篇 |
2016年 | 44篇 |
2015年 | 50篇 |
2014年 | 67篇 |
2013年 | 88篇 |
2012年 | 128篇 |
2011年 | 147篇 |
2010年 | 75篇 |
2009年 | 59篇 |
2008年 | 142篇 |
2007年 | 116篇 |
2006年 | 136篇 |
2005年 | 139篇 |
2004年 | 110篇 |
2003年 | 84篇 |
2002年 | 76篇 |
2001年 | 67篇 |
2000年 | 54篇 |
1999年 | 37篇 |
1998年 | 31篇 |
1997年 | 44篇 |
1996年 | 73篇 |
1995年 | 65篇 |
1994年 | 61篇 |
1993年 | 73篇 |
1992年 | 47篇 |
1991年 | 27篇 |
1990年 | 39篇 |
1989年 | 41篇 |
1988年 | 35篇 |
1987年 | 35篇 |
1986年 | 37篇 |
1985年 | 29篇 |
1984年 | 31篇 |
1983年 | 30篇 |
1982年 | 29篇 |
1981年 | 24篇 |
1980年 | 31篇 |
1978年 | 25篇 |
1975年 | 31篇 |
1974年 | 21篇 |
1973年 | 21篇 |
1968年 | 50篇 |
1967年 | 117篇 |
1966年 | 110篇 |
1965年 | 71篇 |
排序方式: 共有3323条查询结果,搜索用时 15 毫秒
81.
Alessandro D'Aprano Ines Dorina Donato Vincenzo Turco Liveri 《Journal of solution chemistry》1989,18(8):785-793
Static dielectric constants, refractive indices and viscosities of 1-pentanol +2-methyl-2-butanol mixtures were measured at 5, 25 and 45°C. The results show that the mixing of the two isomers modifies the polarizability and the resistence of viscous flow of the system depending on the composition and temperature. Short range intermolecular interactions producing hetero-alcohol open dimers are considered. 相似文献
82.
Graziano Guella Ines Mancini Giuseppe Chiasera Francesco Pietra 《Helvetica chimica acta》1992,75(1):310-322
83.
Reported here are two novel quasi-racemic (bis)indole alkaloids, cycloaplysinopsin A (5) and cycloaplysinopsin B (6), isolated from tropical Indo-Pacific (Comoros, Philippines) scleractinian corals of the family Dendrophylliidae. Although their structures suggest a Diels-Alder cycloaddition origin from aplysinopsin-type precursors, neither experiments, nor theory allowed us to clearly distinguish an enzymatic process with scarce enantioselection from the intrusion of an adventitious catalyst in the coral extracts, where the chiral environment caused a slight asymmetric induction. 相似文献
84.
It is shown that an unidentified marine demosponge of Brittany contains two unique lipids consisting of glycerol etherified by a C12 trienic linear alcohol and esterified by 4-hydroxybenzoic acid. The latter is attached to the secondary position of glycerol in bretonin A (= 3-[((4E, 6E, 8E)-dodeca-4,6,8-trienyl)oxy]-2-(4-hydroxy-benzoyl)propan-1-ol; 1a ), and to the other primary position of glycerol in isobretonin A ( = (+)-3-[((4E, 6E, 8E)-dodeca-4,6,8-trienyl)oxy]-1-(4-hydroxybenzoyl)propan-2-ol; (+) -2 ). The structures are based on NMR and MS data, including the ones of the acetylation product (?)- 1b of 1a . 相似文献
85.
86.
87.
An infrared spectral investigation of a number of pyrimidine and pyrimidone hexachloroantimonates is reported. Typical aromatic absorption bands found in pyrimidinium salts were absent in the pyrimidone cations. 2-And 4-Pyrimidone hexachloroantimonates, as well as their N-methyl- and N,N'-dimethyl derivatives, exhibit intense carbonyl absorption bands between 1720–1729 cm?1 (solid state) which corroborates N-protonation of pyrimidones. 相似文献
88.
H. Bauer 《Fresenius' Journal of Analytical Chemistry》1962,191(3):205
Ohne Zusammenfassung 相似文献
89.
The complexing ligand EDTA can be determined as its complex with bismuth by indirect anodic stripping voltammetry down to 0.1 μg/L without a concentration step. Interfering copper and excess bismuth have to be removed by cation exchange, although in presence of these metals EDTA can be determined down to 0.5 μg/L only. If NTA, EDTA, and DTPA are present simultaneously, the accumulation curves for the corresponding bismuth-complexes can overlap, preventing a separate determination of the three chelons. Due to the interaction of NTA and DTPA with soil normally only EDTA is present in ground-waters. Similarly, EDTA also dominates in surface-waters. Thus it seems to be sufficient to determine the sum of the three chelons as EDTA (index of bismuth-complexation) using suitable electrochemical conditions. 相似文献
90.
Optical resolution by counter-current distribution has been demonstrated on a preparative scale for two chiral ferrocene derivatives, e.g. 1.2-(α-oxotetramethylene)ferrocene (1), and 1.2-(α-butenylene)ferrocene (2), resp., in the system cyclohexane—(+)-diethyltartrate. The optical yields were 12 and 1%, resp., and are in good agreement with the values calculated from the partition coefficients of the enantiomers. The optical purity of1 could be increased to 40% by crystallization from cyclohexane. A resolution of1 with an optical yield of 14% was also possible by thin layer partition chromatography on silica gel using the same solvents. 相似文献