全文获取类型
收费全文 | 592篇 |
免费 | 75篇 |
国内免费 | 119篇 |
专业分类
化学 | 678篇 |
晶体学 | 6篇 |
综合类 | 5篇 |
物理学 | 15篇 |
综合类 | 82篇 |
出版年
2023年 | 5篇 |
2022年 | 17篇 |
2021年 | 13篇 |
2020年 | 23篇 |
2019年 | 24篇 |
2018年 | 19篇 |
2017年 | 21篇 |
2016年 | 31篇 |
2015年 | 26篇 |
2014年 | 20篇 |
2013年 | 54篇 |
2012年 | 39篇 |
2011年 | 24篇 |
2010年 | 25篇 |
2009年 | 34篇 |
2008年 | 45篇 |
2007年 | 46篇 |
2006年 | 38篇 |
2005年 | 45篇 |
2004年 | 33篇 |
2003年 | 31篇 |
2002年 | 25篇 |
2001年 | 12篇 |
2000年 | 18篇 |
1999年 | 21篇 |
1998年 | 11篇 |
1997年 | 11篇 |
1996年 | 9篇 |
1995年 | 17篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 14篇 |
1991年 | 5篇 |
1989年 | 9篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有786条查询结果,搜索用时 31 毫秒
761.
二茂铁基环氧的分子结构中同时含有环氧和二茂铁,是一类兼具化学活性和多功能性的特殊材料。这类材料具有单体结构多样性和聚合物的多功能性,近年来对其制备方法和应用的研究受到广泛关注。研究者们已利用二茂铁醛、酮、烯、氯醇、双醇、乙酰氯等为中间体,制备出二十多种小分子化合物。采用二茂铁接枝环氧聚合物或含烯单体自由基聚合,分别得到多种结构的聚合物。本文在综述二茂铁基环氧制备方法的基础上,进一步讨论了这类材料的结构稳定性。研究发现,当二茂铁处于环氧的邻位时,极易形成卡宾结构,使得环氧开环并重排成醛。通过列举典型研究实例,阐明其在功能材料、传感介质、燃速催化、催化剂配体以及药物合成等方面的应用,并就其在材料表界面的发展趋势进行了展望。 相似文献
762.
763.
764.
Ludmila L. Troitskaya 《Journal of organometallic chemistry》2005,690(17):3976-3982
Cyclopalladation of the Schiff bases of general formula McCHN-CH(Me)Fc (McFc, Ru) (1a,b) with a chiral centre leads to the mixtures of three products, two of which (2 and 3) are planar chiral diastereomers formed from homoannular substitution into the aldehyde fragment. The third product 4 is a result of the unusual heteroannular palladation of the amine fragment in starting aldimine. This ansa-structure 4 having 3-atomic C-N-Pd bridge is without precedent in metallocenes. The molecular structures of all organopalladium compounds obtained have been proved using X-ray analysis of single crystals. 相似文献
765.
E. I. Klimova L. Ruiz Ramirez T. Klimova Berestneva M. Martinez Garcia R. Moreno-Esparza C. Alvarez Toledano R. A. Toscano 《Russian Chemical Bulletin》1998,47(3):482-489
Crystalline 3-ferrocenyl-3-(1-naphthyl)cyclopropene was prepared by dehydrobromination ofZ- andE-2-bromo-1-ferrocenyl-1-(1-naphthyl)-cyclopropanes by ButOK in DMSO. The resulting compound and the startingZ-monobromocyclopropane were characterized by X-ray diffraction analysis. The obtained cyclopropene reacts with 1,3-diphenylisobenzofuran
to give a [4+2]-cycloadduct. The small ring opens upon treatment with HBF4 etherate to afford isomericZ- andE-prop-1-enes and 1-ferrocenyl-3H-benzo[e]indene. Thermolysis of this cyclopropene results in the formation of 1-ferrocenyl-9bH-benzo[e]indene. In all cases, opening of the small ring is accompanied by exclusive alkylation of the naphthalene moiety.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 499–506, March, 1998. 相似文献
766.
The interaction of silver triflate (OTf−=SO3(CF3)−) and dppf [(C5H4PPh2)2Fe)] gave different complexes, depending on the stoichiometric proportions and reaction conditions. Under limiting dppf conditions, three different forms (1-3) of [Ag2(OTf)2(dppf)]x were isolated. Single crystal X-ray diffraction analyses showed that the structure of 1 (x=2n) consists of a 2-D polymer comprising a tetra-silver basic unit, while that of 2 (x=2) possesses a discrete tetra-silver framework and that of 3 (x=n) is a linear polymer based on a di-silver repeating unit. The structures are supported by bridging dppf ligands and triflate groups. The crystal lattices of the compounds are stabilized by extensive intermolecular C-H?X hydrogen bonding (H=ring proton of Cp or Ph of dppf; X=O or F of OTf). [Ag(dppf)(OTf)] (4) and the structurally characterized mononuclear [Ag(dppf)2](OTf) (5) were the sole products obtained from treatment of AgOTf with dppf in molar ratios of 1:1 and 1:2, respectively. 相似文献
767.
Kowalska E. Byszewski P. Klusek Z. Popławska M. Radomska J. 《Journal of Thermal Analysis and Calorimetry》2003,74(2):459-463
Molecules that may adopt various stable conformations might be applied to store information. The conformational changes could
be induced by suitable polarized tip of STM. For the STM experiments two types of fullerene:ferrocene cycloadducts (C60:Fn) were selected where ferrocene fragment is bound to C60 at the 6-6 bond by different heterocyclic pentagon rings. According to semiempirical quantum chemistry calculation one of
them may be used to STM observation without any modification, while the second cycloadduct must be exposed to thermal treatment
in order to obtain bistable molecule.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
768.
Leonard R. MacGillivray Heather A. Spinney Jennifer L. Reid John A. Ripmeester 《Journal of chemical crystallography》1999,29(8):865-869
The crystal and molecular structure of 1,1-ferrocene-dicarbaldehyde 1 is reported. Crystal data for 1: monoclinic, space group P21/n, a = 5.876(1), b = 11.349(1), c = 29.460(3) Å, = 95.067(2)°, V = 1956.9(3) Å3, and D
c = 1.64 g/cm3, for Z = 8. The complex crystallizes such that two molecules are located in the asymmetric unit in which the complexes display different degrees of twisting of the cyclopentadienyl (Cp) rings and formyl substituents about the Cp—Fe—Cp and Cp—COH axes, respectively. The molecule self-assembles in the solid state to form a 2D layered structure held together by - interactions and C—H···O hydrogen bonds. 相似文献
769.
Frank W. Heinemann Immo Weber Ulrich Zenneck 《Journal of chemical crystallography》2007,37(3):165-170
The absolute configuration at the chiral sulfurs centers of (−)-(S
S
, 1R, 2S, 5R)-menthyl-p-tolylsulfinate (1) and (S
S
)-[(p-tolyl)sulfinyl]ferrocene (2) were determined by single crystal X-ray diffraction with anomalous dispersion effects and the corresponding calculation
of Flack’s absolute structure parameters. Both compounds crystallize in the monoclinic crystal system in space group P21 (no. 4); chiral sulfinate ester 1: a = 8.2868(6), b = 6.1399(3), c = 16.366(2) ?, β = 91.816(6)°, V = 832.3(2) ?3, Z = 2 and absolute structure parameter −0.03(7); chiral ferrocenyl sulfoxide 2: a = 5.8371(3), b = 15.390(2), c = 16.143(2) ?, β = 97.748(6)°, V = 1436.9(3) ?3, Z = 4 and absolute structure parameter +0.01(1). The trigonal pyramidal geometry at the chiral sulfur atom of 2 is close to expected values while the one of 1 is slightly distorted. With direct determination of the absolute configuration at the chiral sulfur centers an important
gap concerning the widely used precursors 1 and 2 for the syntheses of chiral sulfoxides and 1,2-disubstituted planar chiral ferrocenyl ligands is now closed. The latter substance
class is playing a key role in enantioselective catalysis. 相似文献
770.
Philipp Stegner Dr. Christian Färber Dr. Jan Oetzel Prof. Dr. Ulrich Siemeling Michael Wiesinger Dr. Jens Langer Dr. Sudip Pan Dr. Nicole Holzmann Prof. Dr. Gernot Frenking Dr. Uta Albold Prof. Dr. Biprajit Sarkar Prof. Dr. Sjoerd Harder 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(34):14723-14728
Double deprotonation of the diamine 1,1′-(tBuCH2NH)-ferrocene ( 1 -H2) by alkaline-earth (Ae) or EuII metal reagents gave the complexes 1 -Ae (Ae=Mg, Ca, Sr, Ba) and 1 -Eu. 1 -Mg crystallized as a monomer while the heavier complexes crystallized as dimers. The Fe⋅⋅⋅Mg distance in 1 -Mg is too long for a bonding interaction, but short Fe⋅⋅⋅Ae distances in 1 -Ca, 1 -Sr, and 1 -Ba clearly support intramolecular Fe⋅⋅⋅Ae bonding. Further evidence for interactions is provided by a tilting of the Cp rings and the related 1H NMR chemical-shift difference between the Cp α and β protons. While electrochemical studies are complicated by complex decomposition, UV/Vis spectral features of the complexes support Fe→Ae dative bonding. A comprehensive bonding analysis of all 1 -Ae complexes shows that the heavier species 1 -Ca, 1 -Sr, and 1 -Ba possess genuine Fe→Ae bonds which involve vacant d-orbitals of the alkaline-earth atoms and partially filled d-orbitals on Fe. In 1 -Mg, a weak Fe→Mg donation into vacant p-orbitals of the Mg atom is observed. 相似文献