全文获取类型
收费全文 | 189篇 |
免费 | 3篇 |
专业分类
化学 | 147篇 |
晶体学 | 6篇 |
力学 | 3篇 |
数学 | 8篇 |
物理学 | 28篇 |
出版年
2023年 | 1篇 |
2022年 | 5篇 |
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 9篇 |
2015年 | 1篇 |
2014年 | 4篇 |
2013年 | 15篇 |
2012年 | 6篇 |
2011年 | 7篇 |
2010年 | 15篇 |
2009年 | 2篇 |
2008年 | 12篇 |
2007年 | 25篇 |
2006年 | 11篇 |
2005年 | 7篇 |
2004年 | 8篇 |
2003年 | 5篇 |
2002年 | 6篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1995年 | 1篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1958年 | 2篇 |
排序方式: 共有192条查询结果,搜索用时 328 毫秒
51.
Alka V. Deshmukh S.M. Yusuf N.P. Lalla 《Journal of magnetism and magnetic materials》2010,322(5):536-1217
Present study reports the detailed structural and magnetic, as well as chemical analysis of polycrystalline Zn1−xMnxO (where x=0, 0.005, 0.01, 0.03, 0.05 and 0.1) samples synthesized by the high-temperature solid state reaction route. X-ray diffraction studies reveal the presence of secondary phase for higher Mn-doping concentrations (x≥0.03). Secondary phase formation having spinel structure is confirmed and reported as an evidence for the first time using transmission electron microscopy study. Chemical investigations using X-ray photoelectron spectroscopy showed the presence of Mn in two valence states. From the observed results we are of the opinion that Zn2+ ions, mainly present at or near grain boundaries, diffuse into manganese oxide to form a stable spinel phase ZnxMn3−xO4 at or near the grain boundaries of ZnO/Zn1−xMnxO. Magnetization measurements did not show any magnetic transition down to 5 K. 相似文献
52.
Solid phase extraction and HPLC determination of veterinary pharmaceuticals in wastewater 总被引:1,自引:0,他引:1
This work focuses on the application of SPE-HPLC analysis of important veterinary pharmaceuticals from different classes in highly complex wastewater matrix. The pharmaceutical investigated included three sulfonamides (sulfamethazine, sulfadiazine and sulfaguanidine), a sulfonamide synergist (trimethoprim), a tetracycline (oxytetracycline), a fluoroquinolone (enrofloxacine) and a β-lactame (penicillin G/procaine). The method involves pre-concentration and clean-up by solid phase extraction (SPE) using Oasis HLB extraction catridges. Final analysis of the selected pharmaceutical compounds was carried out by high-performance liquid chromatography (HPLC) coupled with diode array detector (DAD). Recoveries were ranged from 68.3 to 97.9% with relative standard deviation below 8.4%. Only for sulfaguanidine low recovery was obtained. Limits of quantification were in the range 1.5-100 μg/L depending on pharmaceutical. The described method was applied to the determination of pharmaceuticals in wastewater samples from pharmaceutical industry. 相似文献
53.
Suni V Prathapachandra Kurup MR Nethaji M 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,63(1):174-181
A new thiosemicarbazone, HL is synthesized from di-2-pyridyl ketone and 4-phenyl-3-thiosemicarbazide and structurally and spectrochemically characterized. 1H NMR, 13C NMR, COSY, HMQC and IR spectra of the compound are studied and the proton magnetic resonance spectrum reveals some unprecedented observations. The thione form is predominant in the solid state, as supported by the crystal structure and IR data, while a thiol-thione equilibrium is proposed in the solution state by NMR studies. The compound crystallizes into a monoclinic lattice with space group C2/c and the ZE conformation is exhibited by the thiosemicarbazone. Intra- and intermolecular hydrogen-bonding interactions give rise to a two-dimensional packing in the crystal lattice. 相似文献
54.
Alka Chadha Swaroop Nandan Bora 《Stochastics An International Journal of Probability and Stochastic Processes》2018,90(5):663-681
The paper is mainly concerned with a class of neutral stochastic fractional integro-differential equation with Poisson jumps. First, the existence and uniqueness for mild solution of an impulsive stochastic system driven by Poisson jumps is established by using the Banach fixed point theorem and resolvent operator. The exponential stability in the pth moment for mild solution to neutral stochastic fractional integro-differential equations with Poisson jump is obtained by establishing an integral inequality. 相似文献
55.
Sandra Babić Dragana Mutavdžić Pavlović Danijela Ašperger Martina Periša Mirta Zrnčić Alka J. M. Horvat Marija Kaštelan-Macan 《Analytical and bioanalytical chemistry》2010,398(3):1185-1194
An analytical method for multi-class pharmaceuticals determination in wastewater has been developed and validated. Target
compounds were: sulfonamides (sulfadiazine, sulfaguanidine, sulfamethazine, sulfamethoxazole), fluoroquinolones (ciprofloxacin,
enrofloxacin, norfloxacin), diaminopyrimidine (trimethoprim), anaesthetic (procaine), anthelmintic (praziquantel and febantel),
and macrolide (roxithromycin). The method involves pre-concentration and clean-up by solid-phase extraction (SPE) using Strata-X
extraction cartridges at pH 4.0. Target analytes were identified and quantitatively determined by liquid chromatography–tandem
mass spectrometry using multiple reaction monitoring (MRM). Recoveries were higher than 50% with relative standard deviation
(RSD) below 18.3% for three concentrations. Only for sulfaguanidine was low recovery obtained. Matrix effect was evaluated
using matrix-matched standards. The method detection limit (MDL) was between 0.5 and 5 ng L−1 in spiked water samples. The precision of the method, calculated as relative standard deviation, ranged from 0.5 to 2.0%
and from 1.4 to 8.3 for intra-day and inter-day analysis, respectively. The described analytical method was used for determination
of pharmaceuticals in effluent wastewaters from the pharmaceutical industry. 相似文献
56.
Polarizability is a property of molecules that has long been of interest to scientists from a variety of viewpoints. However, in the area of the QSAR of chemical-biological interactions, it has received little attention. Recently we have shown that one can use the simple summation of the valence electrons (H = 1, C = 4, O = 6, etc.) in a molecule as a measure of its polarizability. We have found this parameter to correlate nerve toxicity of a wide variety of chemicals acting on nerves of frogs, rabbits, cockroaches, and humans. 相似文献
57.
A novel mixed ligand nickel complex [NiLB] [H2L-N-4-diethylaminosalicylidine-N′-4-nitrobenzoyl hydrazone and B-4-picoline] has been synthesized and characterized by elemental analysis, IR spectrum, UV-Vis spectrum and structure has been confirmed by single crystal X-ray structure analysis. The crystal structure reveals that the complex adopts distorted square planar structure with ONO donor atoms of primary ligand and N donor atom of the secondary ligand 4-picoline. 相似文献
58.
Rojo John Vijay M. Tangde Niraj T. Khaty Alka S. Dhondge Sudhakar S. Dhondge 《印度化学会志》2022,99(3):100370
Densities and speed of sound of l-arginine hydrochloride and l-proline within the concentration range (0.03–0.2) mol.kg?1 in water and in aqueous NaCl and Urea are determined between temperatures 288.15 K and 318.15 K and at one atmospheric pressure. Densities and speeds of sound have been used to calculate apparent molar volume of solute (), isentropic compressibility of solution (), apparent molar isentropic compressibility () of solute, limiting apparent molar volume (), limiting apparent molar volume of transfer (), limiting apparent molar expansibility (), limiting apparent molar isentropic compressibility () and limiting apparent molar isentropic compressibility of transfer (). These results are then interpreted in terms of intermolecular interactions. The concentration dependencies of the calculated quantities, their limiting values and temperature characteristics are discussed in terms of solute - solvent and solute - solute interactions at experimental conditions. 相似文献
59.
Marthakutty Joseph V. Suni Maliyeckal R. Prathapachandra Kurup Munirathinam Nethaji Archana Kishore Sarita G. Bhat 《Polyhedron》2004,23(18):3069-3080
Six new copper(II) complexes of 2-benzoylpyridine N(4)-cyclohexyl thiosemicarbazone (HL) have been synthesized and characterized by different physicochemical techniques like molar conductivity measurements, magnetic studies and electronic, infrared and EPR spectral studies. Five of the complexes have been found to possess the stoichiometry [CuLX], where X = Cl (1), Br (2), NO3 (3), NCS (4), N3 (5). The complex prepared from copper sulfate has the composition [Cu2L2SO4] · (H2O)2 (6). In all the complexes the deprotonated ligand, L and the anion were found to be coordinated to the Cu(II) ion. The terdentate nature of the ligand is evident from the IR spectra. The metal ligand bonding parameters evaluated from the EPR spectra indicate strong in-plane σ and in-plane π bonding. The magnetic and spectroscopic data indicate a square planar geometry for complexes 1, 3, 4 and 5, while the complexes 2 and 6 are assigned a square pyramidal geometry. Crystal structure of the complex [CuLCl] reveals two molecules per asymmetric unit of a monoclinic lattice, with space group symmetry P21/n. The complexes [ CuLBr 2] (2) and [CuLNCS] (4) crystallized into triclinic lattices with space group . Compound 2 exists as a thiolate bridged copper(II) dimer. The antimicrobial activity of the ligand and the copper complexes were tested against five types of bacteria isolated from clinical samples. The complexes were found to be active against Bacillus sp., Vibrio cholera O1, Staphylococcus aurus and Salmonella paratyphi. 相似文献
60.
Four novel molecular square grids were achieved by self-assembly using the flexible ligands bis(di-2-pyridyl ketone) thiocarbohydrazone (H2L1), bis(quinoline-2-carbaldehyde) thiocarbohydrazone (H2L2), bis(di-2-pyridyl ketone) carbohydrazone (H2L3) and bis(2-benzoylpyridine) carbohydrazone (H2L4). Three complexes were given a general formula of [Ni(HL)]4[PF6]4 · nH2O and one [Ni2(HL2)L2]2(PF6)2 · 7H2O. The MALDI-MS spectra reveal the formation of tetranuclear molecular squares. The square grid of the Ni(II) centers in all the complexes were organized by deprotonated ligands. The complex [Ni(HL1)]4[PF6]4 · 11H2O crystallized as [Ni(HL1)]4(PF6)4 · 0.5 CH3CH2OH · 2.8H2O and X-ray study revealed octahedral geometries around the Ni(II) centers. Variable temperature magnetic studies suggest intramolecular antiferromagnetic coupling between the Ni(II) electrons by a super exchange mechanism through intervening sulfur/oxygen atoms. 相似文献