全文获取类型
收费全文 | 846篇 |
免费 | 26篇 |
国内免费 | 16篇 |
专业分类
化学 | 512篇 |
晶体学 | 1篇 |
力学 | 18篇 |
数学 | 125篇 |
物理学 | 232篇 |
出版年
2021年 | 8篇 |
2020年 | 6篇 |
2019年 | 11篇 |
2018年 | 10篇 |
2016年 | 15篇 |
2015年 | 11篇 |
2014年 | 19篇 |
2013年 | 37篇 |
2012年 | 42篇 |
2011年 | 40篇 |
2010年 | 27篇 |
2009年 | 18篇 |
2008年 | 54篇 |
2007年 | 47篇 |
2006年 | 31篇 |
2005年 | 40篇 |
2004年 | 44篇 |
2003年 | 25篇 |
2002年 | 45篇 |
2001年 | 19篇 |
2000年 | 20篇 |
1999年 | 14篇 |
1998年 | 17篇 |
1997年 | 18篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1994年 | 9篇 |
1993年 | 12篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 13篇 |
1985年 | 18篇 |
1984年 | 5篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 14篇 |
1980年 | 12篇 |
1979年 | 10篇 |
1978年 | 14篇 |
1977年 | 10篇 |
1976年 | 15篇 |
1975年 | 11篇 |
1974年 | 8篇 |
1973年 | 9篇 |
1972年 | 5篇 |
1971年 | 4篇 |
排序方式: 共有888条查询结果,搜索用时 15 毫秒
1.
2.
Burford N Ragogna PJ McDonald R Ferguson MJ 《Chemical communications (Cambridge, England)》2003,(16):2066-2067
Polyphosphorus dications have been synthesised and comprehensively characterised as diphosphine (dppe, dmpe and dpph) linked Ar2P+ Lewis acids (Ar = C6H5); this application of unique homoatomic coordination chemistry provides important building blocks for extended systems. 相似文献
3.
4.
Two series of monodisperse cross-conjugated oligomers based on enyne repeat units have been realized. The first class of molecules, iso-polytriacetylenes (iso-PTAs, 2), was divergently synthesized using an iterative sequence of palladium-catalyzed cross-coupling reactions of vinyl triflate 5 with terminal alkynes. The second series of oligoenynes (17-20) are based on an octatetrayne backbone, and result from homocoupling of the differentially protected iso-PTA oligomers 8-11. The longest member of this series, 20, spans ca. 5.6 nm from Si atom to Si atom and is composed of a contiguous sequence of 44 sp and sp(2) carbons. The lowest energy electronic absorption band for iso-PTA dimers in the progression 13 --> 9 --> 16 is consistently red-shifted as a result of extending the cross-conjugated structure. A similar comparison within each series (i.e., 16, 6-7, or 17-20), however, suggests little effect on the electronic characteristics of these molecules as oligomer length is increased. The solid-state properties of one derivative, 17, are also described. 相似文献
5.
Samples taken from 61 slabs of cannabis resin originating in The Lebanon were examined by high performance liquid chromatography. The slabs were derived from seizures of cannabis resin made over a three-year period. From a study of 14 of these samples, taken from bags which bore a number of identical stamp marks, it was shown that there was a correlation between the cannabinoid distribution and the marks. The remaining 47 samples of cannabis resin, all of which were from bags with different marks, were each found to have a unique cannabinoid distribution. Such an examination can therefore be used to aid investigations where evidence of a common origin is sought. 相似文献
6.
H. Huber Ch. Koeberl I. McDonald W.U. Reimold 《Journal of Radioanalytical and Nuclear Chemistry》2000,244(3):603-607
We used - coincidence spectrometry to investigate the possible presence of a meteoritical component in 27 samples of South African diamictites. Recently, several studies have suggested that some tillites/diamictites may represent impact breccias, but a petrographical study by our group found no evidence for the presence of impact-characteristic shocked minerals. The siderophile elements, such as Cr, Co, Ni, and, especially, the platinum group elements, have high abundances in meteorites, but low abundances in terrestrial crustal rocks. The Ir content of the diamictites was measured with the new iridium coincidence spectrometer (ICS) at the University of Vienna, with detection limits of around 0.02 ppb. No enrichments in the contents of Ir and other siderophile elements compared to average crustal concentrations were found; thus, no unequivocal evidence for an impact origin of these diamictites of the South African Dwyka Group can be documented. 相似文献
7.
Deconvolutions of measured absorption line profiles in the 1n0 (n = 0 to 5) and the 320 bands of the Ã2A2X?2B1 electronic transition of ClO2 reveal subnanosecond lifetimes for all rotational levels of the 2A2 state. Observed ratios of radiationless rates from spin-doublet components identify direct spin-orbit coupling of the 2A2 state with 2A1 and/or 2B1 vibronic states as a predominant predissociation mechanism. Variations of rates with ν′1 locate an intersection of a second potential surface with that of the 2A2 state. 相似文献
8.
Phase transitions in C6H4Cl2 and C6H4I2 were monitored by observing the frequencies and apparent spin-spin relaxation times of the 35Cl and 127I nuclear quadrupole resonances. Decreases in the apparent spin-spin relaxation times were found to accompany the onset of the transitions. 相似文献
9.
J.R. McDonald 《Chemical physics》1976,13(4):339-347
The fluorescence emission spectrum and analysis of NSF vapor is presented. Single vibronic level excitation near the S1 origin gives rise to a 10 μs radiative decay. The fluorescence lifetime for excitation of levels with ? 4500 cm?1 excess vibrational energy becomes controlled by a unimolecular radiationless process which is likely photodissociation; the dependence of this radiationless rate on energy and vibrational mode is investigated. The perturbations resulting from coupling of zero-order S1 states with other vibronic levels which control the excited state dynamics of SO2 are apparently not operative for NSF. Attempts are made to rationalize the grossly different dynamic behavior of the S1 levels of these two otherwise very similar systems. 相似文献
10.