全文获取类型
收费全文 | 2354篇 |
免费 | 59篇 |
国内免费 | 197篇 |
专业分类
化学 | 2292篇 |
晶体学 | 24篇 |
力学 | 7篇 |
综合类 | 4篇 |
物理学 | 283篇 |
出版年
2024年 | 7篇 |
2023年 | 69篇 |
2022年 | 21篇 |
2021年 | 24篇 |
2020年 | 39篇 |
2019年 | 81篇 |
2018年 | 34篇 |
2017年 | 84篇 |
2016年 | 49篇 |
2015年 | 61篇 |
2014年 | 58篇 |
2013年 | 79篇 |
2012年 | 279篇 |
2011年 | 125篇 |
2010年 | 100篇 |
2009年 | 113篇 |
2008年 | 152篇 |
2007年 | 171篇 |
2006年 | 127篇 |
2005年 | 120篇 |
2004年 | 123篇 |
2003年 | 68篇 |
2002年 | 78篇 |
2001年 | 77篇 |
2000年 | 69篇 |
1999年 | 65篇 |
1998年 | 46篇 |
1997年 | 39篇 |
1996年 | 31篇 |
1995年 | 32篇 |
1994年 | 31篇 |
1993年 | 25篇 |
1992年 | 17篇 |
1991年 | 36篇 |
1990年 | 24篇 |
1989年 | 22篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有2610条查询结果,搜索用时 1 毫秒
181.
Elvira M. Bauer Marcello Colapietro Said A. Ibrahim Gustavo Portalone 《Journal of solid state chemistry》2006,179(2):389-397
Co[(CH3PO3)(H2O)] (1) and Co[(C2H5PO3)(H2O)] (2) were prepared by the hydrothermal method and isolated as blue-violet platelet crystals. They were characterized by X-ray diffraction, FT-IR, TGA-DSC techniques and their magnetic properties studied by a dc-SQUID magnetometer. Compound (1) shows an hybrid layered structure, made of alternating inorganic and organic layers along the a-direction of the unit cell. The inorganic layers contain Co(II) ions six-coordinated by five phosphonate oxygen atoms and one from the water molecule. These layers are separated by bi-layers of methyl groups and van der Waals contacts are established between them. In compound (2), the layered hybrid structure is rather similar to that described for compound (1), but the alternation of the inorganic and organic layers is along the b-direction of the unit cell. The magnetic behavior of (1) and (2) as function of temperature and magnetic field was studied. The compounds obey the Curie-Weiss law at temperatures above 100 K, the Curie C, and Weiss θ constants for the methyl derivative being and and for the ethyl derivative and , respectively. The observed magnetic moments for Co atom at room temperature (i.e. μeff=5.18 and 5.38 BM, respectively) are higher than those expected for a spin-only value for high spin Co(II) (S=3/2), revealing a substantial orbital contribution to the magnetic moment. The negative values of θ are an indication of the presence of antiferromagnetic exchange couplings between the near-neighbors Co(II) ions, within the layers. [Co(CnH2n+1PO3)(H2O)] (n=1,2) are 2D Ising antiferromagnets at low temperatures. 相似文献
182.
In the present work, studies have been conducted on the equilibrium distribution of cobalt (II) and nickel (II) between aqueous
hydrochloric solution and macromolecular resin impregnated with bis(2,4,4-trimethylpentyl)monothiophosphinic acid (Cyanex302,
HL). Effects of extraction time, pH values, metal ion concentration, and temperature were investigated. Analysis of the results
shows that the extraction of the two metal ions can be explained assuming the formation of metal complexes in the resin phase
with a general composition ML
2. An extraction reaction is proposed and the equilibrium constants of the complexes were determined. The Freundlich isotherm
and thermodynamic quantities, i.e., ΔG, ΔH and ΔS were also obtained. Both of the extraction reactions of cobalt (II) and nickel (II) are endothermic ones. The efficiency
of the resin in the separation of cobalt (II) and nickel (II) is provided according to the separation factors. Under the experimental
conditions employed, pH50 values for cobalt (II) and nickel (II) are 3.76, 5.01, respectively. The logarithmic value of separation factor was calculated
as 2.50. 相似文献
183.
Ann M. Schmiedekamp Anthony Ginnetti Brian Piccione Kevin Cannon M. Dominic Ryan 《International journal of quantum chemistry》2007,107(6):1415-1429
Octahedral, six‐coordinate Co2+ can exist in two spin states: S = 3/2 and S = 1/2. The difference in energy between high spin (S = 3/2) and low spin (S = 1/2) is dependent on both the ligand mix and coordination stereochemistry. B3LYP calculations on combinations of neutral imidazole, NH3, and H2O ligands show that low‐spin isomers are stabilized by axial H2O ligands and in structures that also include trans pairs of equatorial NH3 and protonated imidazole ligands, spin crossover structures are predicted from spin state energy differences. Occupied Co d orbitals from the DFT calculations provide a means of estimating effective ligand strength for homoleptic and mixed ligand combinations. These calculations suggest that in a labile biological system, a spin crossover environment can be created. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
184.
185.
《Journal of Coordination Chemistry》2012,65(24):4180-4193
AbstractA series of six new mononuclear Schiff base complexes, 1–6 of cobalt(III) of the general formula, [CoLX] or its adduct with methanol, is reported. The pentadentate Schiff base ligand (H2L) was obtained by the condensation of N-(3-aminopropyl)-N-methylpropane-1,3-diamine with 1-(2-hydroxyphenyl)ethanone (H2L1) or 1-(2-hydroxyphenyl)propan-1-one (H2L2). X stands for the pseudohalides, N3–, N(CN)2? , and NCS–. The complexes have been synthesized by the reaction of equimolar amounts of cobalt(II) nitrate with H2L1 or H2L2 in the presence of the respective pseudohalide in methanol medium. All the complexes have been characterized by microanalytical, spectroscopic, single crystal XRD (except 3), and other physicochemical studies. Structural studies reveal that the central Co(III) ion in 1, 2, 4, 5, and 6 adopts a distorted octahedral geometry with a CoN4O2 chromophore. Weak intermolecular H-bonding and/or π-interactions are operative in these complexes to bind the molecular units. The antimicrobial activity of all the complexes and their constituent Schiff bases has been tested against some common bacteria and fungi. 相似文献
186.
吡啶-2-羧酸钴催化氯苄双羰化合成新型α-酮酸研究 总被引:3,自引:0,他引:3
α-酮酸在生物化学、农药、医药、食品生产及精细有机合成中具有潜在的应用价值[1] .从有机卤化物一步双羰化合成α-酮酸或其衍生物是近年来有机过渡金属化学中新发现的反应之一 [2 ,3] .迄今为止 ,双羰化合成α-酮酸的催化剂主要为羰基钴类络合物 [4 ] 或钯络合物 [5] ,合成产物均为苯丙酮酸 .我们在进行吡啶 - 2 -羧酸钴氧化羰化合成碳酸二甲酯研究的基础上 [6 ] ,发现吡啶 - 2 -羧酸钴具有良好的双羰化性能 ,在 333K,3.0 MPa条件下 ,可使氯苄一步双羰化合成一种新的α-酮酸 ( 1 ) :β-苄基 -α-苯丙酮酸( BPPA) .反应式如下 :CH2 Cl+… 相似文献
187.
《Journal of Coordination Chemistry》2012,65(7):605-614
New complexes having the formulae [L2CoX2] and [LCuCl2], [LCuCl] and [LCu](ClO4)2 where L?=?(2-thiophene)-(5,6-diphenyl-[1,2,4]-triazin-3-yl)hydrazone TDPTH; X?=?Cl, OAc or ClO4 have been synthesized and characterized on the basis of elemental analyses, conductance, magnetic moments and infrared, electronic and ESR spectral data. The IR spectra indicate that TDPTH is a neutral bidentate ligand, coordinating via a triazine-N and azomethine-N in [L2CoX2] and [LCuCl2] with the thiophene-S not coordinated but is tridentate in [LCuCl] and [LCu](ClO4)2 through the same two nitrogen atoms and thiophene-S. The magnetic moment and electronic spectral data suggest a distorted octahedral structure for Co(II) complexes, a dimeric square pyramidal geometry for [LCuCl2] through chloride bridges and a dimeric diamagnetic, four-coordinate copper in [LCu](ClO4)2 through thiophene-S bridges. The X-band ESR spectra of Co(II) complexes, in the solid state, are rhombic with three g values consistent with a high-spin distorted octahedral structure. The X-band ESR spectrum of the powdered sample of both [LCuCl2]·2H2O and [LCu](ClO4)2 at room temperature and at 77?K showed only one broad signal due to?ΔM s?=?±?1 transition and a weak signal due to the forbidden?ΔM s?=?±?2 transition, indicating an antiferromagnetic interaction between copper(II) centers whereas [LCuCl] is ESR silent, indicating a monovalent copper ion in this complex. 相似文献
188.
Chandra S Kumar R 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,62(4-5):1050-1057
Reaction of divalent cobalt(II) and trivalent ruthenium(III) salts (NO3, SCN and SO4) with macrocyclic ligands L1, L2 and L3 having N2S2, N4 and N5 core, have been designed and carry out. All these three macrocyclic ligands and their complexes were obtained in pure form. Their structures were investigated by using microanalytical analyses, IR, mass, magnetic moments, electronic and EPR spectral studies. The redox properties of the complexes were also examined by cyclic voltammetry. An interesting feature of complexes is that the relatively large rings of macrocyclic ligands prevent the macrocyclic rings from approaching the metal center as closely as they would, if they were not constrained. So the Ru-N distances are longer than expected due to ring size. Electrochemical studies show that the macrocyclic ligand L1 is more effective electron donors to ruthenium than of L2 and L3. Electronic spectral properties also show that the sulphur donor atom of L1 weakens the ligand field with respect to ligand-to-metal charge-transfer band. However it is expected that second-row transition metal-ligand bonds tend to be weaker than third-row transition metal-ligand bonds. There are well-established examples of reactions in which decreased of reactivity down a triad of transition metals is not observed. These novelties are usually attributed to pi-bonding effects for ligands such as carbon monoxide, solvent effects, or a change in mechanism. 相似文献
189.
190.
Cyclopentadienyl cobalt complexes (η5‐C5H4R) CoLI2 [L = CO,R=‐COOCH2CH=CH2 (3); L=PPh3, R=‐COOCH2‐CH=CH2 (6); L=P(p‐C6H4O3)3, R = ‐COOC(CH3) = CH2 (7), ‐COOCH2C6H5 (8), ‐COOCH2CH = CH2 (9)] were prepared and characterized by elemental analyses, 1H NMR, ER and UV‐vis spectra. The reaction of complexes (η5‐C5H4R)CoLI2 [L= CO, R= ‐COOC(CH3) = CH2 (1), ‐COOCH2C6H5(2); L=PPh3, R=‐COOC (CH3) = CH2 (4), ‐COOCH2C6H5 (5)] with Na‐Hg resulted in the formation of their corresponding substituted cobaltocene (η5‐C5H4R)2 Co[R=‐COOC(CH3) = CH2 (10), ‐COOCH2C6H5 (11)]. The electrochemical properties of these complexes 1–11 were studied by cyclic voltammetry. It was found that as the ligand (L) of the cobalt (III) complexes changing from CO to PPh3 and P(p‐tolyl)3, their oxidation potentials increased gradually. The cyclic voltammetry of α,α′‐substituted cobaltocene showed reversible oxidation of one electron process. 相似文献