全文获取类型
收费全文 | 1481篇 |
免费 | 184篇 |
国内免费 | 458篇 |
专业分类
化学 | 1543篇 |
晶体学 | 40篇 |
力学 | 31篇 |
综合类 | 19篇 |
数学 | 2篇 |
物理学 | 488篇 |
出版年
2024年 | 1篇 |
2023年 | 16篇 |
2022年 | 24篇 |
2021年 | 49篇 |
2020年 | 57篇 |
2019年 | 54篇 |
2018年 | 46篇 |
2017年 | 55篇 |
2016年 | 70篇 |
2015年 | 57篇 |
2014年 | 69篇 |
2013年 | 115篇 |
2012年 | 139篇 |
2011年 | 86篇 |
2010年 | 85篇 |
2009年 | 108篇 |
2008年 | 128篇 |
2007年 | 126篇 |
2006年 | 106篇 |
2005年 | 92篇 |
2004年 | 76篇 |
2003年 | 60篇 |
2002年 | 83篇 |
2001年 | 71篇 |
2000年 | 51篇 |
1999年 | 47篇 |
1998年 | 48篇 |
1997年 | 42篇 |
1996年 | 32篇 |
1995年 | 30篇 |
1994年 | 16篇 |
1993年 | 20篇 |
1992年 | 18篇 |
1991年 | 9篇 |
1990年 | 3篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有2123条查询结果,搜索用时 625 毫秒
961.
《Analytical letters》2012,45(7):1224-1241
The combined use of a competing ligand exchange (CLE) method and a diffusive gradient in thin films (DGT) technique in a quasi-labile system provides a better understanding of dynamic metal (Cu and Ni) complexes in the presence of humic substances of different origins. The CLE and DGT techniques provide total labile (dynamic) metal complexes (Cu and Ni) and their dissociation rate constants in environmental systems. DGT was found to estimate lower concentrations of labile metal complexes than CLE. These discrepancies were caused by diffusion controlled metal flux (towards the binding resin gel) in the diffusive gel of DGT. The interactions of Cu and Ni with humic acids are stronger than their interactions with fulvic acid and natural organic matter. Changes in the lability of Ni and Cu complexes (complexed with humic substances of different origins) with the changing analytical detection window indicate that the complexes of these metals were formed with different binding sites with diverse binding energies in the humic substances. The combination of these two techniques was found to be very useful in determining diffusion coefficients of labile metal-humate complexes in quasi-labile systems. The values of diffusion coefficients of labile Ni and Cu complexes determined in this study are in good agreement with limited results from the literature. This finding is novel and can be very useful in further improving our understanding of the metal-humate interactions in natural environments. 相似文献
962.
963.
《Journal of Coordination Chemistry》2012,65(9):723-729
A novel tetradentate, N2O2-type Schiff base, synthesized from 1,2-bis-(o-aminophenoxy)ethane and 2-hydroxynaphthalin-1-carbaldehyde, forms stable complexes with transition metal ions such as Cu(II), Ni(II), VO(IV) and Zn(II) in DMF. Microanalytical data, elemental analyses, magnetic measurements, 1H NMR, UV, visible and IR-spectra as well as conductance measurements were used to confirm the structures. 相似文献
964.
965.
《Journal of Coordination Chemistry》2012,65(15):2666-2681
Two new complexes, [Ni(en)2(mtt)2] (1) and [Co(en)2(mtt)2](mtt) (2) (Hmtt = 5-methyl-1,3,4-thiadiazole-2-thiol and en = ethylenediamine), have been synthesized and characterized by various physicochemical techniques. Complexes 1 and 2 crystallize in monoclinic and orthorhombic system with space groups P 21/n and P 21 21 21, respectively. The molecular structures of 1 and 2 show that the metal ions are six-coordinate bonded through four equatorial nitrogens of two en and two axial nitrogens of mtt ligands. The crystal structures of the complexes reveal that mtt is present in thione form and bound to the metal ion through the thiadiazole nitrogen. The crystal structures of the complexes are stabilized by various intermolecular hydrogen bonding providing supramolecular architecture. Complex 2 is also stabilized by weak π···π interactions occurring between two thiadiazole rings. The bioefficacies of the ligand and complexes have been examined against the growth of bacteria to evaluate their antimicrobial potential. The biological results suggest that 2 is more active than the ligand and 1 against the tested bacteria. The geometries of the ligand and the complexes have been optimized by the DFT method and the results are compared with the X-ray diffraction data. The Co(III) complex exhibits an irreversible Co(III)/Co(II) process while the Ni(II) complex displays quasi-reversible Ni(II)/Ni(III) redox processes with large peak separation as compared to that expected for a one electron process which is thought to be coupled with some chemical reaction. 相似文献
966.
《Journal of Coordination Chemistry》2012,65(22):3887-3899
The complexes [NiCl2(PyTn)2]?·?2H2O (1), [Ni(H2O)2(PyTn)2](NO3)2 (2), [Ni(H2O)2(PzTz)2]Cl2 (3) and [Ni(H2O)2(PzTz)2](NO3)2 (4) [PyTn?=?2-(1-pyrazolyl)-2-thiazoline; PzTz?=?2-(1-pyrazolyl)-1,3-thiazine] have been prepared and characterized by elemental analysis, electronic spectroscopy, IR spectroscopy and single crystal X-ray diffraction to determine if the size of the S,N-heterocycle influences coordination to Ni(II). The four complexes are six coordinate as a distorted octahedron. The disposition of chlorides and water is trans in 1 and 2, whereas 3 and 4 are cis, as a consequence of the steric strain induced by the larger S,N-ring. 相似文献
967.
《Journal of Coordination Chemistry》2012,65(1-3):51-64
Abstract The new 1,2-dithiolene, 1,4-butanediyldithioethylene-1,2-dithiolate, has been isolated. In addition, new monoanionic bis-complexes with nickel and copper have been prepared and isolated. The formal Ni(III) complex crystallizes in the orthorombic space group, Pbca, with a = 9.762(9), b = 12.53(2), and c = 23.166(3) Å, with 4 molecules in the unit cell. The structure was refined to an R = 9.01% (Rw = 8.95%). The formal Cu(III) complex crystallizes in the monoclinic space group, C2/c, with a = 25.567(6), b = 8.011(3), c = 14.504(3) Å, and β = 106.17(2)° with 4 molecules in the unit cell. The structure refined to R = 4.2% with R w = 4.3%. Comparisons to similar 1,2-dithiolenes suggest this ligand produces only modest structural and electronic differences when compared to the 1,3-propanediyldithioethylene-1,2-dithiolate complexes. The oxidation (to a neutral complex) and reduction (to a dianion) for the Ni(III) and Cu(III) complexes show large differences from those of maleonitriledithiolate. Other physical data are presented as well. 相似文献
968.
《Journal of Coordination Chemistry》2012,65(2):359-368
Abstract A new soluble vic-dioxime, l,4-bis(2-methoxyethyl-2, 3-bis(hydroxyimino)-5, 6-diphenylpiper-azine (LH2) has been synthesized as a mixture of isomers from dicyan di-N-oxide and 1, 2-diphe-nyl-l,2-bis(2′-methoxyethylamino)ethane, 1, which has been prepared through the reduction of the condensation product of benzaldehyde and 2-methoxyethylamine with the aluminium amalgam. LH2 gives N,N-coordinated planar metal complexes with CoII, NiII, CuII and PdII Oxidation of (LH)2Co in the presence of a base such as py or triphenylphoshine leads to octahedral complexes (LH)2Co(B)Cl. The uranyl complex of LH2 has a 1 :1 metal-ligand ratio and a binuclear structure with μ-hydroxo bridges. 相似文献
969.
《Journal of Coordination Chemistry》2012,65(8):1418-1429
New bi- and trihomonuclear Mn(II), Co(II), Ni(II), and Zn(II) complexes with sulfa-guanidine Schiff bases have been synthesized for potential chemotherapeutic use. The complexes are characterized using elemental and thermal (TGA) analyses, mass spectra (MS), molar conductance, IR, 1H-NMR, UV-Vis, and electron spin resonance (ESR) spectra as well as magnetic moment measurements. The low molar conductance values denote non-electrolytes. The thermal behavior of these chelates shows that the hydrated complexes lose water of hydration in the first step followed by loss of coordinated water followed immediately by decomposition of the anions and ligands in subsequent steps. IR and 1H-NMR data reveal that ligands are coordinated to the metal ions by two or three bidentate centers via the enol form of the carbonyl C=O group, enolic sulfonamide S(O)OH, and the nitrogen of azomethine. The UV-Vis and ESR spectra as well as magnetic moment data reveal that formation of octahedral [Mn2L1(AcO)2(H2O)6] (1), [Co2(L1)2(H2O)8] (2), [Ni2L1(AcO)2(H2O)6] (3), [Mn3L2(AcO)3(H2O)9] (5), [Co3L2(AcO)3(H2O)9] · 4H2O (6), [Ni3L2(AcO)3(H2O)9] · 7H2O (7), [Mn3L3(AcO)3(H2O)6] (9), [Co2(HL3)2(H2O)8] · 4H2O (10), [Ni3L3(AcO)3(H2O)9] (11), [Mn3L4(AcO)3(H2O)9] · H2O (13), [Co2(HL4)2(H2O)8] · 5H2O (14), and [Ni3L4(AcO)3(H2O)9] (15) while [Zn2L1(AcO)2(H2O)2] (4), [Zn3L2(AcO)3(H2O)3] · 2H2O (8), [Zn3L3(AcO)3(H2O)3] · 3H2O (12), and [Zn3L4(AcO)3(H2O)3] · 2H2O (16) are tetrahedral. The electron spray ionization (ESI) MS of the complexes showed isotope ion peaks of [M]+ and fragments supporting the formulation. 相似文献
970.
《Journal of Coordination Chemistry》2012,65(18):3012-3019
In this article, the electrochemical behavior of the complexation of (2E,3E)-2H-1,4-benzothiazine-2,3 (4 H)-dionedioxime with Ni(II) is studied. The experiments were performed in DMF in the presence of tetraethylammoniumtetrafluoroborate (0.1 M) as a supporting electrolyte and studied by using square-wave voltammetry, cyclic voltammetry, and differential pulse polarography. Reductions of the complexes are irreversible. The ligand forms 1 : 1 and 1 : 2 (metal : ligand) complexes with Ni(II). Stability constants of the formed complexes were evaluated with the modified DeFord–Hume method at different ligand concentrations as 3.21(±0.03) × 106 and 2.73(±0.03) × 106, respectively. 相似文献