全文获取类型
收费全文 | 278篇 |
免费 | 7篇 |
专业分类
化学 | 122篇 |
力学 | 2篇 |
数学 | 104篇 |
物理学 | 57篇 |
出版年
2021年 | 3篇 |
2018年 | 3篇 |
2016年 | 3篇 |
2015年 | 3篇 |
2014年 | 8篇 |
2013年 | 14篇 |
2012年 | 13篇 |
2011年 | 11篇 |
2010年 | 6篇 |
2009年 | 4篇 |
2008年 | 9篇 |
2007年 | 10篇 |
2006年 | 14篇 |
2005年 | 20篇 |
2004年 | 6篇 |
2003年 | 6篇 |
2002年 | 8篇 |
2001年 | 8篇 |
2000年 | 13篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1927年 | 4篇 |
1926年 | 3篇 |
1921年 | 5篇 |
1919年 | 4篇 |
1918年 | 2篇 |
1912年 | 6篇 |
1911年 | 5篇 |
1910年 | 6篇 |
排序方式: 共有285条查询结果,搜索用时 156 毫秒
31.
The 13C n.m.r. spectra of a series of 52 substituted norbornanes, norbornenes, bicyclo[2.2.2]octanes and -octenes have been recorded to examine the stereochemical effects of closely neighboring substituents on the carbon shieldings of these well-defined molecular frameworks. These moderately rigid skeletons permit detailed examination of a variety of orientations of substituents and, in this study, attention has been focused on a series of vicinally substituted systems. The substituents include methyl, hydroxymethyl and carboxylic acid groups for comparison with earlier data for several bicyclic alcohols and hydrocarbons, from which conclusions regarding the conformational preferences of the hydroxyl group may be drawn. The deviations of the observed shieldings from those predicted by simple additivity follow definite patterns which should be useful for stereochemical assignments in related systems. 相似文献
32.
Wilson's construction for mutually orthogonal Latin squares is generalized. This generalized construction is used to improve known bounds on the function nr (the largest order for which there do not exist r MOLS). In particular we find n7?780, n8?4738, n9?5842, n10?7222, n11?7478, n12?9286, n13?9476, n15?10632. 相似文献
33.
34.
A.E Brouwer 《Journal of Combinatorial Theory, Series B》1975,18(2):184-185
A question of Entringer and Erdös concerning the number of unique subgraphs of a graph is answered. 相似文献
35.
36.
van Zutphen S Pantoja E Soriano R Soro C Tooke DM Spek AL den Dulk H Brouwer J Reedijk J 《Dalton transactions (Cambridge, England : 2003)》2006,(8):1020-1023
New asymmetric trans-platinum(II) complexes, composed of an isopropylamine, an azole and two carboxylate leaving groups, are presented. The crystal and molecular structures of one of the complexes has been determined and the cytotoxicity and reactivity with 5'-guanosine monophosphate is reported. The complexes show a reduced reactivity, but no decrease in cytotoxic activity compared to their chloro-counterparts. Furthermore the complexes largely overcome cisplatin resistance, they therefore present an interesting class of antitumour active trans-platinum complexes. 相似文献
37.
In many point-line geometries, to cover all points except one, more lines are needed than to cover all points. Bounds can
be given by looking at the dimension of the space of functions induced by polynomials of bounded degree. 相似文献
38.
39.
40.
Marqués-Gallego P den Dulk H Brouwer J Kooijman H Spek AL Roubeau O Teat SJ Reedijk J 《Inorganic chemistry》2008,47(23):11171-11179
Two new cytotoxic fluorescent platinum(II) compounds, cis-[Pt(A9opy)Cl2] (1) and cis-[Pt(A9pyp)(DMSO)Cl2] (2),have been designed, synthesized, and characterized by IR, 1H NMR, and 195Pt NMR spectroscopy; electrospray ionization mass spectrometry (ESI-MS); and single-crystal X-ray diffraction. The carrier ligands selected for thesynthesis of these fluorescent platinum(II) compounds are E-2-[1-(9-anthryl)-3-oxo-3-prop-2-enylpyridine] (abbreviatedas A9opy) and E-1-(9-anthryl)-3-(2-pyridyl)-2-propenone (abbreviated as A9pyp). The compound cis-[Pt(A9opy)Cl2](1) comprises a peculiar cis-platinum(II) organometallic compound, in which the platinum(II) ion is bound to the photoisomerizable carbon-carbon double bond of the carrier ligand. The effects of the metal-ion coordination on the photoisomerization of the carbon-carbon double bond of the ligand have been studied. In contrast, the carrier ligand A9pyp used for the synthesis of the cis-[Pt(A9pyp)(DMSO)Cl2] compound (2) does not undergo such anisomerization process and remains in the E conformation, while coordinated to the platinum(II) ion through the nitrogen of the pyridine ring. In addition to the synthesis and characterization, solution studies of both compounds have also been performed in detail, including NMR and ESI-MS spectroscopy. Moreover, a high degree of cytotoxicactivity of compound 1 was found, as compared to cisplatin and its corresponding platinum-free molecule, in a series of human tumor cell lines. Compound 2 was also found to be highly active against these cell lines but appeared less active compared to the platinum-free molecule. 相似文献