全文获取类型
收费全文 | 295篇 |
免费 | 12篇 |
国内免费 | 3篇 |
专业分类
化学 | 242篇 |
晶体学 | 3篇 |
力学 | 1篇 |
数学 | 31篇 |
物理学 | 33篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 11篇 |
2015年 | 10篇 |
2014年 | 9篇 |
2013年 | 20篇 |
2012年 | 18篇 |
2011年 | 13篇 |
2010年 | 21篇 |
2009年 | 15篇 |
2008年 | 17篇 |
2007年 | 16篇 |
2006年 | 21篇 |
2005年 | 16篇 |
2004年 | 16篇 |
2003年 | 7篇 |
2002年 | 19篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1971年 | 2篇 |
1961年 | 1篇 |
1960年 | 2篇 |
1959年 | 2篇 |
排序方式: 共有310条查询结果,搜索用时 0 毫秒
61.
JPC – Journal of Planar Chromatography – Modern TLC - 相似文献
62.
R. Antalík 《Czechoslovak Journal of Physics》1991,41(5):427-440
We investigate the dependence of the neutron-proton matrix element ratios (η) on radial neutron and proton ground state density distribution differences (Δ np) within the framework of the shell model quasiparticle random phase approximation. We show that theη ratios are linearly dependent onΔ rms np differences. We prove the consistency of empirical and theoretical methods by agreement of theη ratios obtained from the 1 GeV proton inelastic scattering analysis and from the QRPA calculations. 相似文献
63.
The numbers are twin primes.
64.
Pál?SohárEmail author Antal?Csámpai Gábor?Magyarfalvi Angela E.?Szabó Géza?Stájer 《Monatshefte für Chemie / Chemical Monthly》2004,135(12):1519-1527
Summary. t-2-Benzoyl-t-4-phenylcyclohexane-r-1-carboxylic acid reacts with hydrazine to give the saturated 1,7-diphenyl-trans-phthalazin-4(3H)-one. The reaction of the acid with ethylenediamine yields diastereomeric trans-imidazo[2,3-a]isoindoles, which differ in their C-1 configuration. The cyclizations of the acid with cis-2-aminocyclohexane- or 4-cyclohexenemethanol result in trans-isoindolo[2,1-a][3,1]benzoxazines, while in its reactions with the analogous di-endo- and di-exo-norbornane- and -norborneneamino alcohols, the acid gives methylene-bridged isomeric di-endo-norbornanes or a norbornene derivative; the corresponding diastereomeric di-exo derivatives have also been prepared. After isolation, the structures were established by means of 1H and 13C NMR spectroscopy, with application of DIFFNOE, DEPT, HMQC, HMBC, and 2D-COSY techniques. 相似文献
65.
Péter A Arki A Vékes E Tourwé D Lázár L Fülöp F Armstrong DW 《Journal of chromatography. A》2004,1031(1-2):171-178
Direct and indirect reversed-phase (RP) high-performance liquid chromatographic methods were developed for the separation of enantiomers of 18 unnatural beta-amino acids, including several beta-3-homo amino acids. The direct separations of the underivatized analytes were performed on chiral stationary phases (CSPs) containing macrocyclic glycopeptide antibiotic teicoplanin (Chirobiotic T column) and teicoplanin aglycone (Chirobiotic TAG column). The indirect method involved pre-column derivatization with a new chiral derivatizing agent (CDA), (S)-N-(4-nitrophenoxycarbonyl)phenylalanine methoxyethyl ester ((S)-NIFE), and subsequent separation of diastereomers on Discovery C18 and Hyperpep 300 C18 columns. The different methods were compared in systematic chromatographic examinations. The effects of organic modifier, mobile phase composition, pH and flow rate on the separation were investigated. 相似文献
66.
Arkosi Z Szabó-Plánka T Rockenbauer A Nagy NV Lázár L Fülöp F 《Inorganic chemistry》2003,42(16):4842-4848
We have studied the complex equilibria of copper(II) with a series of beta-substituted beta-amino acids (R: H, Me, Et, iBu, iPr, cHex, 1-EtPr, and tBu) in aqueous solution by pH potentiometry and electron paramagnetic resonace (EPR) spectroscopy in the range pH = 2-8 at various metal and ligand concentrations. The basicities of the corresponding donor groups differed only slightly in the series of ligands. A purely mathematical method, the matrix rank analysis carried out on the EPR spectrum package recorded in the presence of copper(II), indicated the formation of 6 independent paramagnetic species. Accordingly, Cu(2+) (aqua complex) and the complexes [CuLH](2+), [CuL](+), [CuL(2)H(2)](2+), [CuL(2)H](+), and [CuL(2)] were considered in the subsequent analysis of series of spectra, and also two isomers of [CuL(2)] were identified. The formation constants and the EPR parameters, e.g. the isotropic g-factors and the copper and nitrogen hyperfine couplings for the above species, were determined in the same optimization procedure by the simultaneous evaluation of spectra. The ligands "LH" are suggested to bind in equatorial positions through their carboxylate groups, while the amino acids in the L protonation state are likely to occupy two equatorial sites via the amino and carboxylate groups. For the isomers of [CuL(2)], the donors of the same kind are in the cis or trans position. As far as we know, this is the first reported case in which a strong correlation has been found between the steric effects of substituents characterized by Meyer's steric parameter V(a) and the protonation constants of metal complexes. The observed trend for the preference for nonprotonated complexes [CuL](+) and [CuL(2)] to increase with the steric demand of the substituent was explained by the increasing shielding effect of the substituent hindering protonation of the nonprotonated complex. 相似文献
67.
Two-step synthesis of the novel fused heterocycles pyrazolo[4′,3′:5,6]pyrido[2,3-b][1,5]benzoxazepine ( 8 ) and pyrazolo[4′,3′:5,6]pyrido[2,3-b][1,5]benzothiazepine ( 9 ) from the pyrazolo[3,4-b]pyridine derivative 1 is described. 相似文献
68.
A solid-phase extraction sample preparation method using a molecularly imprinted polymer (MIP) selective for the triazine type pesticide terbutylazine has been developed. The method involves preconcentration from large volumes of water samples on a C18 disk coupled to selective clean-up on the MIP. The method has been optimised by studying the recovery and retention of terbutylazine and some other structurally related triazine derivates as a function of the selective washing solvent used. The effect of the water content of the selective washing solvent was also investigated on the recovery of the MIP. River water samples were analysed with the coupled technique, and efficient clean-up of the samples was observed. 相似文献
69.
The enantiomers of 1-(alpha-aminobenzyl)-2-naphthol and 2-(alpha-aminobenzyl)-1-naphthol analogs were separated isothermally on a cellulose-tris-3,5-dimethylphenyl carbamate-based chiral stationary phase (Chiralcel OD-H), at 10 degrees C increments in the range of 5-35 degrees C, using n-hexane/2-propanol/diethylamine as mobile phase. The mobile phase composition and temperature were varied to achieve baseline resolutions in a single chromatographic run. The dependence of the natural logarithms of selectivity factors, In alpha, on the inverse of temperature, 1/T, was used to determine the thermodynamic data of the enantiomers. The thermodynamic data revealed that all the compounds in this study separate via the same enthalpy-driven chiral recognition mechanism. 相似文献
70.