全文获取类型
收费全文 | 207篇 |
免费 | 12篇 |
国内免费 | 3篇 |
专业分类
化学 | 122篇 |
力学 | 2篇 |
数学 | 48篇 |
物理学 | 50篇 |
出版年
2022年 | 4篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 3篇 |
2017年 | 8篇 |
2016年 | 6篇 |
2015年 | 5篇 |
2014年 | 4篇 |
2013年 | 6篇 |
2012年 | 11篇 |
2011年 | 15篇 |
2010年 | 3篇 |
2009年 | 4篇 |
2008年 | 9篇 |
2007年 | 8篇 |
2006年 | 10篇 |
2005年 | 6篇 |
2004年 | 11篇 |
2003年 | 16篇 |
2002年 | 10篇 |
2001年 | 7篇 |
2000年 | 8篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 1篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1987年 | 2篇 |
1985年 | 4篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1969年 | 4篇 |
1968年 | 1篇 |
1911年 | 2篇 |
排序方式: 共有222条查询结果,搜索用时 15 毫秒
1.
Declan J. Maher 《Tetrahedron letters》2004,45(6):1301-1305
It has been shown that catalytic amounts (20-40 mol %) of bis-aryl (thio)ureas greatly accelerate the DABCO-promoted Baylis-Hillman reaction between a range of aromatic aldehydes and methyl acrylate in the absence of solvent. These robust organocatalysts are superior mole per mole promoters of the reaction than either methanol or water and are recoverable in high yield after the reaction by column chromatography. 相似文献
2.
M. Keane 《Applied Acoustics》2007,68(10):1104-1117
A new method is presented for splitting musical notes into tonal and broadband components by removing the harmonic peaks from the spectra. This method was used to analyse the key vibrations of eight pianos (four grand and four upright). The broadband component of vibrations was found to be more intense in the upright pianos than in the grand pianos, while no such difference was found in the tonal component. As grands are considered to be superior to uprights, this suggests that it may be possible to improve upright pianos by reducing the strength of the broadband component of vibrations. 相似文献
3.
Held GA Solina DH Solina H Keane DT Haag WJ Horn PM Grinstein G 《Physical review letters》1990,65(9):1120-1123
4.
5.
Two results on site percolation on thed-dimensional lattice,d1 arbitrary, are presented. In the first theorem, we show that for stationary underlying probability measures, each infinite cluster has a well-defined density with probability one. The second theorem states that if in addition, the probability measure satisfies the finite energy condition of Newman and Schulman, then there can be at most one infinite cluster with probability one. The simple arguments extend to a broad class of finite-dimensional models, including bond percolation and regular lattices. 相似文献
6.
Roucoules V Fail CA Schofield WC Teare DO Badyal JP 《Langmuir : the ACS journal of surfaces and colloids》2005,21(4):1412-1415
A substrate-independent method has been devised for ring formation at solid surfaces. This entails the aminolysis reaction of allylamine with maleic anhydride pulsed plasma polymer films to yield terminal alkene groups at the surface. Subsequent exposure to 1,3-cyclohexadiene leads to a Diels-Alder type (4 + 2) cycloaddition reaction to give a mixture of endo- and exo-bicyclo[2.2.2]oct-2-ene rings. 相似文献
7.
Praic M. Keane Kyra O'Sullivan Fergus E. Poynton Bjrn C. Poulsen Igor V. Sazanovich Michael Towrie Christine J. Cardin Xue-Zhong Sun Michael W. George Thorfinnur Gunnlaugsson Susan J. Quinn John M. Kelly 《Chemical science》2020,11(32):8600
Ruthenium polypyridyl complexes which can sensitise the photo-oxidation of nucleic acids and other biological molecules show potential for photo-therapeutic applications. In this article a combination of transient visible absorption (TrA) and time-resolved infra-red (TRIR) spectroscopy are used to compare the photo-oxidation of guanine by the enantiomers of [Ru(TAP)2(dppz)]2+ in both polymeric {poly(dG-dC), poly(dA-dT) and natural DNA} and small mixed-sequence duplex-forming oligodeoxynucleotides. The products of electron transfer are readily monitored by the appearance of a characteristic TRIR band centred at ca. 1700 cm−1 for the guanine radical cation and a band centered at ca. 515 nm in the TrA for the reduced ruthenium complex. It is found that efficient electron transfer requires that the complex be intercalated at a G-C base-pair containing site. Significantly, changes in the nucleobase vibrations of the TRIR spectra induced by the bound excited state before electron transfer takes place are used to identify preferred intercalation sites in mixed-sequence oligodeoxynucleotides and natural DNA. Interestingly, with natural DNA, while it is found that quenching is inefficient in the picosecond range, a slower electron transfer process occurs, which is not found with the mixed-sequence duplex-forming oligodeoxynucleotides studied.Efficient electron transfer requires the complex to be intercalated at a G-C base-pair. Identification of preferred intercalation sites is achieved by TRIR monitoring of the nucleobase vibrations before electron transfer. 相似文献
8.
The ferric ion binding characteristics of a novel chelating probe for detecting reactive oxygen and nitrogen species are reported. The probe comprises a polyaminocarboxylic acid chelator (EDTA) conjugated with aromatic amino acids. The probe (i) complexes redox-active and non-redox active metal ions and (ii) differentiates between different reactive oxygen/nitrogen species based upon the reaction products with same. The ferric ion binding characteristics were measured using species distribution and electronic absorption spectroscopic investigations. Over the physiological pH range a favoured one to one complex exists. 相似文献
9.
10.
Previous work on the electrochemistry of palladium in aqueous acid solution demonstrated the existence of two multilayer
hydrous oxide reduction peaks, one at ca. 0.24 V and another at ca. 0.55 V vs. RHE, plus the presence of a reversible active
surface state transition at ca. 0.24 V. In the present work with thermally activated palladium it was observed that, in agreement
with the hydrous oxide reduction behaviour of the system, there is a second active state transition at E≥ca. 0.45 V. In most of its reactions in aqueous acid solution, apart from its unusual capacity to absorb hydrogen, palladium
exhibits properties very similar to those of platinum; however, palladium seems to be more prone to dissolution and subsurface
oxygen formation. Also the premonolayer oxidation responses of these two metals are often different as the more active state
of the palladium surface is not as readily generated as that of platinum. The electrocatalytic properties of palladium, as
reported earlier, correlate quite well with the hydrous oxide and premonolayer oxidation behaviour of this electrode system.
Electronic Publication 相似文献