全文获取类型
收费全文 | 4088篇 |
免费 | 83篇 |
国内免费 | 25篇 |
专业分类
4196篇 |
出版年
2023年 | 23篇 |
2022年 | 31篇 |
2021年 | 34篇 |
2020年 | 49篇 |
2019年 | 46篇 |
2018年 | 52篇 |
2017年 | 29篇 |
2016年 | 48篇 |
2015年 | 41篇 |
2014年 | 55篇 |
2013年 | 193篇 |
2012年 | 53篇 |
2011年 | 330篇 |
2010年 | 265篇 |
2009年 | 361篇 |
2008年 | 278篇 |
2007年 | 268篇 |
2006年 | 273篇 |
2005年 | 268篇 |
2004年 | 310篇 |
2003年 | 90篇 |
2002年 | 168篇 |
2001年 | 57篇 |
2000年 | 51篇 |
1999年 | 66篇 |
1998年 | 133篇 |
1997年 | 49篇 |
1996年 | 74篇 |
1995年 | 147篇 |
1994年 | 65篇 |
1993年 | 17篇 |
1992年 | 34篇 |
1991年 | 15篇 |
1990年 | 22篇 |
1989年 | 16篇 |
1988年 | 14篇 |
1987年 | 17篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 17篇 |
1983年 | 16篇 |
1982年 | 22篇 |
1981年 | 10篇 |
1980年 | 15篇 |
1979年 | 15篇 |
1978年 | 10篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1974年 | 3篇 |
排序方式: 共有4196条查询结果,搜索用时 15 毫秒
941.
The mixed-metal trinuclear cluster cations [H3Ru2(C6Me6)2Os(C6H6)(O)]+ (1), [H3Ru2(1,2,4,5-C6H2Me4)2Os(p-MeC6H4iPr)(O)]+ (2) and [H3Ru2(1,2,4,5-C6H2Me4)2Os(C6H6)(O)]+ (3) have been synthesised from the corresponding dinuclear precursors [H3Ru2(arene)2]+ and the corresponding mononuclear complexes [Os(arene)(H2O)3]2+, isolated and characterised as the tetrafluoroborate and hexafluorophosphate salts. The cations 1, 2 and 3 are heteronuclear analogues of the cluster cation [H3Ru3(C6H6)(C6Me6)2(O)]+ that possesses a homonuclear metallic core. The single-crystal X-ray structure analyses of [1][BF4], [2][PF6] and [3][PF6] reveal an equiangular metal triangle despite the presence of an osmium atom in the metallic core. 相似文献
942.
The dinuclear arene ruthenium complexes [RuCl2{C6H5(CH2)3OCO-p-C6H4-OC8H17}]2 (1) and [RuCl2{p-C6H4(CH2COOCH2CH3)2}]2 (2) have been obtained by dehydrogenation of the corresponding cyclohexadiene derivative with ruthenium chloride hydrate. The single-crystal X-ray structure analysis of 2 shows the arene ligands to be involved in slipped-parallel π-π stacking interactions with neighbouring molecules, thus forming infinite chains along the b-axis. The dinuclear complexes 1 and 2 react with two equivalents of triphenylphosphine (PPh3) to give in excellent yield the corresponding mononuclear phosphine complexes [RuCl2{C6H5(CH2)3OCO-p-C6H4-OC8H17}(PPh3)] (3) and [RuCl2{p-C6H4(CH2COOCH2CH3)2}(PPh3)] (4), respectively. The single-crystal X-ray structure analysis of 4 reveals the formation of a dimer through two C-H?Cl interactions in the solid state. 相似文献
943.
Rodolphe F.R. Jazzar Andrew D. Burrows Stuart A. Macgregor Mary F. Mahon 《Inorganica chimica acta》2006,359(3):815-820
Two isomers of the N,O-coordinated acetylpyrrolyl complex [Ru(PPh3)2(CO)(NC4H3C(O)CH3)H] {cis-N,H (1) and trans-N,H (2)} have been prepared as models for catalytic intermediates in the Murai reaction. Complex 2 isomerises to 1 upon heating via a dissociative pathway (ΔH‡ = 195 ± 41 kJ mol−1; ΔS‡ = 232 ± 62 J mol−1 K−1); the mechanism of this process has been modeled using density functional calculations. Complex 2 displays moderate catalytic activity for the Murai coupling of 2′-methylacetophenone with trimethylvinylsilane, but 1 proved to be catalytically inactive under the same conditions. 相似文献
944.
Mousa Z. Al-Noaimi Salim F. Haddad Robert J. Crutchley 《Inorganica chimica acta》2006,359(8):2395-2399
The novel azoimine ligand α-acetyl-α-phenylazo-4-chlorophenylazomethine (L) was prepared and characterized. Its coordination chemistry to Ru(II) was investigated by the preparation and characterization of the complex trans-[Ru(bpy)LCl2] where bpy is 2,2′-bipyridine. A crystal structure of this complex showed that L is a bidentate ligand and coordinates to Ru(II) by azo-and imine-nitrogen donor atoms. Cyclic voltammetry and spectroelectrochemistry were performed on this complex and the visible region absorption bands assigned. L is shown to be a strong π-acid ligand. 相似文献
945.
Ulrich Jürgen Scheele 《Inorganica chimica acta》2006,359(15):4891-4900
A series of six 3,6-bis(imidazolium-3-yl)pyridazine derivatives with different imidazole-N substituents have been synthesized and isolated as the salts [H2L]Cl2 (1a)-(6a) and [H2L](PF6)2 (1b)-(6b). Solid state structures have been determined crystallographically for eleven out of the twelve compounds, revealing diverse hydrogen bonding patterns that involve the imidazolium-C2H units and the anions. N-heterocyclic carbene (NHC) mercury(II) complexes [Hg2L2](PF6)4 (7)-(9) are readily formed in good yields from ligand precursors [H2L](PF6)2 and Hg(OAc)2, as long as imidazole-N substituents are not too bulky. X-ray crystallography reveals double helical bimetallic arrangements for the stable [Hg2L2]4+ cations. Ligand scrambling in [Hg2L2]4+ occurs only in the presence of free carbene precursor, presumably via an associative mechanism. 相似文献
946.
The reaction of [Ti(cp∗)2(BTMSA)] (1) (cp∗ = η5-C5Me5, BTMSA = bis(trimethylsilyl)acetylene) with malonic acids ((HOOC)2CR2, R = H, Me) and N,N-dimethylglycine resulted in the formation of titanium(IV) dicarboxylato complexes [Ti(cp∗)2{(OOC)2CR2}] (R = H, 2; R = Me, 3) and an α-amino acid titanium(III) complex [Ti(cp∗)2(OOCCH2NMe2)] (4). The identities of complexes 2-4 were confirmed by microanalysis, 1H and 13C NMR spectroscopy (2, 3), ESI-MS and CID experiments (2, 3) as well as by ESR and magnetic measurements (μeff = 1.81, 298 K) for 4. Single X-ray diffraction analyses of 2 and 4 exhibited monomolecular complexes in which the titanium atom is distorted tetrahedrally coordinated by two η5-C5Me5 rings and by the chelating bound malonato-κ2O,O′ (2) and N,N-dimethylglycinato-κ2O,O′ ligand (4). 相似文献
947.
Raúl Chiozzone Ricardo González Donatella Armentano Juan Faus 《Inorganica chimica acta》2006,359(7):2194-2200
The reaction of K2[ReX6] (X = Cl, Br) with oxalic acid and triethylamine in dimethylformamide solution yields the substituted complexes [ReX4(ox)]2− and cis-[ReX2(ox)2]2−, which can be obtained separately depending on the amount of added amine. The crystal structures of (PPh4)2[ReBr4(ox)], cis-(PPh4)2[ReBr2(ox)2] and cis-(AsPh4)2[ReCl2(ox)2] have been determined by single-crystal X-ray diffraction. The anionic complexes are octahedral with only slight distortions. The direct isolation of the pure complexes as well as the formation of only the cis isomers - without the presence of trans isomers and/or [Re(ox)3]2− - is probably due to the kinetic inertness of Re(IV)-X bonds, which increases with the number of oxalato ligands bound to the metal ion. 相似文献
948.
Wagner M. Teles Maria Vanda Marinho Nivaldo L. Speziali Carlos B. Pinheiro Alexandre A. Leitão 《Inorganica chimica acta》2006,359(14):4613-4618
The complexes [Cu(DPS)(H2O)Cl2] · H2O (1a) and [{Cu(DPS)Cl}2μ-(Cl)2] (1b) where DPS = Di(2-pyridyl)sulfide have been synthesized and characterized using elemental analysis, thermal analysis (TG/DSC), vibrational and electronic spectroscopies as well as electron paramagnetic resonance (EPR). Additionally, the crystal and molecular structures of both compounds have been determined by X-ray diffraction techniques. 相似文献
949.
Annie Michaud 《Inorganica chimica acta》2006,359(9):2592-2598
The complexes (tpm*)Ni(η2-NO3)(η1-NO3) (1), [(bpm*)2Ni(η2-NO3)]NO3 (2), and [(tpm*)(bpm*)Ni(η1-NO3)]NO3 (3) (tpm* = tris(3,5-dimethylpyrazolyl)methane; bpm* = bis(3,5-dimethylpyrazolyl)methane) have been prepared and characterized by IR and UV-Vis spectroscopy and X-ray diffraction studies. These d8 complexes all adopt variously distorted octahedral structures in the solid state and their magnetic moments are consistent with a paramagnetic state with two unpaired electrons. The solution 1H NMR data show that the paramagnetism is maintained in solution. 相似文献
950.
Christer B. Aakeröy John Desper Jesús Valdés-Martínez 《Inorganica chimica acta》2006,359(4):1255-1262
We have prepared two ligands, 4- and 5-carboxylic acid pyrimidine, and synthesized and crystallographically characterized seven coordination complexes thereof. The need for potentially structurally disruptive counterions is eliminated by deprotonation of the carboxylic acid moieties; the carboxylates present in each structure act as counterions and balance the charge on the divalent metal ions leading to charge-neutral complex ions. The four new M(II)-complexes with 4-carboxylic acid pyrimidine (M = Ni, Cu, Zn, and Co) are isostructural as are the three M(II) complexes with 3-carboxylic acid pyrimidine (M = Ni, Cu, and Zn), indicating robust and reliable coordination modes for both ligands. 相似文献