全文获取类型
收费全文 | 910篇 |
免费 | 9篇 |
国内免费 | 5篇 |
专业分类
化学 | 759篇 |
力学 | 16篇 |
数学 | 87篇 |
物理学 | 62篇 |
出版年
2022年 | 8篇 |
2021年 | 11篇 |
2020年 | 7篇 |
2016年 | 11篇 |
2015年 | 11篇 |
2014年 | 7篇 |
2013年 | 23篇 |
2012年 | 38篇 |
2011年 | 54篇 |
2010年 | 33篇 |
2009年 | 16篇 |
2008年 | 45篇 |
2007年 | 50篇 |
2006年 | 55篇 |
2005年 | 49篇 |
2004年 | 48篇 |
2003年 | 40篇 |
2002年 | 32篇 |
2001年 | 14篇 |
2000年 | 7篇 |
1999年 | 11篇 |
1998年 | 17篇 |
1997年 | 20篇 |
1996年 | 20篇 |
1995年 | 14篇 |
1994年 | 10篇 |
1993年 | 14篇 |
1992年 | 18篇 |
1991年 | 16篇 |
1990年 | 16篇 |
1989年 | 8篇 |
1988年 | 15篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 14篇 |
1979年 | 12篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1976年 | 9篇 |
1975年 | 12篇 |
1974年 | 8篇 |
1973年 | 14篇 |
1972年 | 3篇 |
1971年 | 4篇 |
1967年 | 3篇 |
排序方式: 共有924条查询结果,搜索用时 15 毫秒
151.
Dynamic polymers (dynamers) based on reversible imine interactions were generated and found to respond to changes in neat/solution environment, thus displaying adaptive behavior through modification of their constitution in order to maximize the stability of their mesoscopic state as a function of conditions. 相似文献
152.
The long oligopyridinedicarboxamide strand 9, containing 15 heterocyclic rings has been synthesized and its helical structure determined by X-ray crystallography. It was shown that the shorter analogue 6 displays induced circular dichroism and amplification of induced chirality upon dissolution in an optically active solvent, diethyl-L-tartrate. A novel class of helical foldamers was prepared, strands 14-16, based on two oligopyridine carboxamide segments linked through a L-tartaric acid derived spacer. These tartro strands display internal chirality induction as well as chirality amplification. NMR spectroscopy (on 8 and 9) and circular dichroism (on 16) studies show that the oligopyridine carboxamide strands undergo reversible unfolding/folding upon protonation. The protonation-induced unfolding has been confirmed by X-ray crystallographic determination of the molecular structure of the extended protonated heptameric form 8(+). The molecular-scale mechano-chemical motions of the protonation-induced structural switching consist of a change of the length of the molecule, from 6 angstroms (6, coiled form) to 29 angstroms (8(+), uncoiled form) for the heptamer and from 12.5 angstroms (9, coiled form, X-ray structure) to 57 angstroms (9(+), uncoiled form, from modeling) for the pentadecamer. Similar unfolding/folding motional processes take place in the L-tartro strands 15 and 16 upon protonation/deprotonation, with loss of helicity-induced circular dichroism on unfolding as shown for the protonated form 16(+). 相似文献
153.
154.
Guillemot G Thieuleux C Copéret C Soulivong D Spitzmesser S Basset JM 《Dalton transactions (Cambridge, England : 2003)》2007,(40):4589-4593
Grafting the well-defined molecular complexes [(ArO)Zr(CH2tBu)3], , and [(ArO)2Zr(CH2tBu)2], , on SiO2-(700) (ArO=2,6-Ph2C6H3O) gives the corresponding monosiloxy surface complexes [([TRIPLE BOND]SiO)Zr(CH2tBu)2(OAr)] and [([TRIPLE BOND]SiO)Zr(CH2tBu)(OAr)2] as major surface species as evidenced by mass balance analysis, IR and NMR spectroscopies. In both cases, minor cyclometallated species (ca. 20%) are also probably formed during the grafting process. While /SiO2-(700) catalytically transforms propane into its lower and higher homologues, /SiO2-(700) remains inactive. Moreover, the formation of butane as the major higher homologues is consistent with the formation of metallocarbene intermediates in this system in contrast to what was observed for the corresponding homologation reaction on silica supported zirconium hydrides. 相似文献
155.
l,2-Bis(2,2'-bipyridinyl)ethylene(1) ligand was synthesized by Wittig-Horner reaction and 1, 2-Bis(2, 2'-bipyridinyl)ethane(2) ligand(which can be obtained via another route ) was prepared by hydrogenation of (1). The formation of complexes of (1) and (2) with copper (I) has been studied. The influence of the different bridge chains (CH =CH, CH2CH2) on complexation is discussed on the basis of 1H NMR spectra. Keywords Dipyridine aldehyde, Dipyridine derivative, Copper complex 相似文献
156.
157.
158.
Bernold Hasenknopf Jean-Marie Lehn Nedjia Boumediene Emmanuelle Leize Alain Van Dorsselaer 《Angewandte Chemie (International ed. in English)》1998,37(23):3265-3268
NMR and MS analysis as a function of time has shown that the self-assembly of a linear ligand with Fe2+ or Ni2+, metal ions of octahedral coordination geometry, generates first a triple helicate and thereafter the circular helicate 1 as kinetic and thermodynamic products, respectively. The results provide insight into features of the energy hypersurface on which this self-assembly operates and point to the general role of kinetic and thermodynamic control in such processes. 相似文献
159.
160.