全文获取类型
收费全文 | 252篇 |
免费 | 10篇 |
专业分类
化学 | 181篇 |
晶体学 | 1篇 |
力学 | 14篇 |
数学 | 29篇 |
物理学 | 37篇 |
出版年
2024年 | 1篇 |
2022年 | 8篇 |
2021年 | 17篇 |
2020年 | 10篇 |
2019年 | 11篇 |
2018年 | 7篇 |
2017年 | 7篇 |
2016年 | 14篇 |
2015年 | 6篇 |
2014年 | 13篇 |
2013年 | 12篇 |
2012年 | 12篇 |
2011年 | 11篇 |
2010年 | 13篇 |
2009年 | 9篇 |
2008年 | 13篇 |
2007年 | 19篇 |
2006年 | 12篇 |
2005年 | 9篇 |
2004年 | 13篇 |
2003年 | 8篇 |
2002年 | 10篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1994年 | 2篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1984年 | 1篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1974年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有262条查询结果,搜索用时 359 毫秒
71.
72.
Two 1-aryl-3-cyclohexylurea and two 1-aryl-3-cyclohexylurethane with and without alkyl tail in aryl fragments were synthesized and their variable-temperature 1H NMR spectra in chloroform, DMSO and DMF were recorded. The temperature dependences of chemical shift of NH protons for all compounds have been observed. The type of dependence has been explained by the aggregation of molecules and formation of ionic structures. The formation of intermolecular complexes leads to possible formation of symmetrical N1 … … H ……N3 intramolecular hydrogen bond in urea fragment. As a result,4hJH1H3 trans-hydrogen bond scalar coupling constants have been observed for the first time in low molecular weight compounds using a simple one-dimensional 1H NMR experiment. The formation of strong intramolecular H-bond leads to π-conjugation not only with spacer but with phenyl ring too. It support the Gilli conception that RAHB formation is a result of π-electron delocalization. The presence in urea fragment of such kind interaction leads to formation of ionic structure, which has been detected by NMR and UV spectroscopies. The formation of ionic structure can explain the catalytic activity of such compounds and the mechanism of transformation in organic and bioorganic reactions in which involved the urea compounds. 相似文献
73.
Rashidian M Dozier JK Lenevich S Distefano MD 《Chemical communications (Cambridge, England)》2010,46(47):8998-9000
An aldehyde-containing alternative substrate for protein farnesyltransferase was prepared and shown to be enzymatically incorporated into a peptide and a protein. The protein was subsequently immobilized onto aminooxy-functionalized agarose beads or labeled with a fluorophore. This method for protein modification provides an alternative to the commonly employed Cu(I)-catalyzed click reaction. 相似文献
74.
Decreasing and fast solutions for a second-order difference equation related to Fisher-Kolmogorov's equation 总被引:1,自引:0,他引:1
Meline Aprahamian Stepan Tersian 《Journal of Mathematical Analysis and Applications》2010,363(1):97-110
We prove the existence of so-called fast solutions of a second-order difference equation related to traveling wave solutions of Fisher-Kolmogorov's equation. Variational approach is used and the fast solutions are obtained as minimizers of an energy functional on a weighted Hilbert space. Numerical experiments are presented. 相似文献
75.
The anisotropic components of van der Waals radii for 5b, 6b and 7b Group elements were determined from the structures of gaseous van der Waals complexes and of crystalline molecular solids. The transition from the gaseous to the solid state reduces the anisotropy of a van der Waals atomic shape. This anisotropy is largely responsible for the changes of intermolecular distances, which are often misinterpreted as an effect of hydrogen bonds. 相似文献
76.
77.
Stepan Tersian Julia Chaparova 《Journal of Mathematical Analysis and Applications》2002,272(1):223-239
In this paper we study the existence of periodic solutions of the sixth-order equation
uvi+Auiv+Bu″+u−u3=0, 相似文献
78.
V. P. Chizhkov V. N. Boitsov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(3):440-444
Results of a thermodynamic analysis of a liquid extraction process in which the separation of the components of the mixture is associated with the presence of thermodynamically nonequilibrium phases were summarized and compared to the available data on the act of separation of a mixture due to the energy supplied from an external source. A thermodynamic interpretation was proposed for optimum conditions of separation of an equimolar binary mixture by liquid extraction. 相似文献
79.
V. M. Boitsov R. R. Kostikov A. P. Molchanov A. V. Stepakov M. S. Baird 《Russian Journal of Organic Chemistry》2004,40(12):1760-1763
The synthesis and dehydrohalogenation of diethyl halocyclopropane-1,1-dicarboxylates prepared from diethyl ethylidene- and benzylidenemalonates are described.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 12, 2004, pp. 1811–1814.Original Russian Text Copyright © 2004 by Boitsov, Kostikov, Molchanov, Stepakov, Baird. 相似文献
80.
Igor V Ivanov Stepan G RomanovValery P Shevchenko Elena A RozhkovaMikhail A Maslov Nataliya V GrozaNikolai F Myasoedov Hartmut KuhnGalina I Myagkova 《Tetrahedron》2003,59(41):8091-8097
17(R)-OH-AA and 14,15-dehydro-17(R)-OH-AA were synthesized from a common tetraacetylenic precursor and their azide derivatives were obtained in moderate yields via the corresponding p-toluenesulfonates. Since the azido group remained stable during tritiation procedure on Lindlar's catalyst in benzene, both 14,15-dehydro-17(S)-N3-AA and 14,15-dehydro-17(R)-OH-AA constitute useful intermediates in the synthesis of radio-labelled 17(S)-N3-AA and 17(R)-OH-AA. In contrast, reduction of azide in methanol afforded 17(S)-NH2-AA with 95% yield. 相似文献