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51.
Berto S Crea F Daniele PG De Stefano C Prenesti E Sammartano S 《Annali di chimica》2006,96(7-8):399-420
In this paper we report the results of an investigation performed by potentiometric (H+-glass electrode) and visible spectrophotometric measurements on the interaction of UO2(2+) ion towards some carboxylic ligands (acetate, malonate, succinate, azelate). The measurements were carried out at T= 25 degrees C in different ionic media (KNO3 and NaCl) at different ionic strengths (0.1 < or = I/mol L(-1) < or = 1.0, NaCl; I/mol L(-1) = 0.1, KNO3). The dependence on ionic strength of formation constants was taken into account by using both a simple Debye-Hückel type equation and the SIT (Specific ion Interaction Theory) approach. Different speciation models (depending on concentration of reagents, ionic strength, pH-range) both for different carboxylates and different ionic media have been obtained. Linear combinations between formation constants, stoichiometric coefficients and length of alkyl chain of dicarboxylates have been observed and predicted formation constants at I= 0 mol L(-1) are reported for the interaction of UO2(2+) with HOOC-(CH2)n-COOH with 1 < or = n < or = 7. Finally, a visible absorption spectrum for each complex reaching a significant percentage of formation in solution (KNO3 medium) has been calculated to characterise the compounds found by pH-metric refinement. 相似文献
52.
A straightforward procedure for the preparation of nucleoside analogue 1 and its regioisomer 2 containing a dihydro-1,4-dithiin as sugar moiety has been accomplished in four steps by our readily available heterocyclic system 5. Nucleobase insertion was carried out by direct addition of N4-acetylcytosine to sulfoxide derivatives via Pummerer-type glycosidation reaction. 相似文献
53.
An efficient and low-cost protocol for the manual synthesis of Peptide Nucleic Acids is reported here. The protocol relies on coupling reactions carried out with 2.5 equiv of PNA monomers activated with HOBT/HBTU, in the presence of pyridine/NMM. The protocol has been tested on four PNA oligomers with a length ranging from 9 to 12 bases and a purine content up to 67%. 相似文献
54.
Concetta De Stefano Ottavia Giuffrè Alberto Pettignano Silvio Sammartano 《Journal of solution chemistry》2003,32(11):967-976
Enthalpies of protonation of polyacrylates and polymethacrylates with different molecular weights in aqueous NaCl solutions, 0 I 2 mol-L–1 were determined by titration calorimetry at 25°C. H values are dependent on both the neutralization degree, , and the molecular weight of polyacids. T S of protonation was obtained using pK values already reported and the present H results. Empirical equations for the dependence on I, , and molecular weight are reported for both H and T S. 相似文献
55.
Bruzzoniti MC Andrensek S Novic M Perrachon D Sarzanini C 《Journal of chromatography. A》2004,1034(1-2):243-247
This work is an upgrade of a previously developed method (J. Chromatogr. A 884 (2000) 251] for epichlorohydrin determination by ion chromatography (IC) and conductivity detection. Here, an ion chromatography-mass spectrometry (IC-MS) coupling has been employed for the separation and the identification of products of epichlorohydrin when reacted with the nucleophilic agent SO3(2-). The high capacity column (IonPac AS11-HC) used for separation provided good resolution. This allowed evaluation of the IC behavior and mass spectrometric identification of epichlorohydrin sulfite derivatives. By using atmospheric pressure interfaces (ESI and APCI) the following species were tentatively identified: 2,3-dihydroxy-1-propanesulfonic, 2,3-epoxy-1-propanesulfonic,1,3-dihydroxy-2-propanesulfonic and 3-oxetanesulfonic acids and 2-hydroxy-1,3-propanedisulfonic acid (or its isomer 3-hydroxy-1,2-propanedisulfonic acid). The study showed that chlorine atoms are displaced from epichlorohydrin during the reaction, while mass spectrometry confirmed that none of the products formed contains chlorine atoms. 相似文献
56.
Zuccarello F Buemi G Gandolfo C Contino A 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(1):139-151
A conformational study on Barbituric (BA) and Thiobarbituric (TBA) acids was performed at ab initio MP2/6-31G** level on the neutral, protonated, mono- and di-anionic forms. Acid-base equilibria were studied by comparing the electronic transitions evaluated for the most stable conformations and the experimental spectra at different pH values. The electronic transitions were obtained through the ZINDO approach. 相似文献
57.
Pier G. Daniele Alessandro De Robertis Concetta De Stefano Silvio Sammartano 《Journal of solution chemistry》1989,18(1):23-36
Imidazole protonation constants were determined potentiometrically, using a (H+)-glass electrode, in LiCl, NaCl, KCl, CaCl2, MgCl2, tetramethylammonium (Me4N-) iodide and chloride, Et4N-, Pr4N- and Bu4N-iodides. Salt effects were tentatively explained by assuming that complexes [H(Im)X]o (Im = imidazole, X–=Cl– or I–), [M(Im)]2+ (M2+=Mg2+ or Ca2+) and [A(Im)]+ (A+ = tetraalkylammonium cation) were formed in solution. Calcium(II)-selective electrode measurements confirmed our hypothesis about the formation of the Ca2+-imidazole complex. The reliability of the complex formation model is discussed on the basis of its self consistency and in light of previous results. 相似文献
58.
New mesoionic compounds (2H, 3H-thiazolo[3,2-c]oxazol-7-ones) (β) or ketenes ((3-acyl-1,3-thiazolidin-2-ylidene)methanone) (β′) were generated from N-acetyl and N-benzoyl-thiazolidine-2-carboxylic acids (7a,b) using different methods, and their reactivity towards N-(phenylmethylene)benzenesulfonamide (2) and N-(phenylmethylene)aniline (3) was tested. When (7a,b) were treated with (2) and acetic anhydride in refluxing toluene solution, only imidazo[5,1-b]thiazoles (8a,b) were obtained from the mesoionic compound intermediates (β). When the ketene intermediates (β′) were generated from (7a,b) by means of Mukaiyama's reagent, only spiro-β-lactams (9a,b) were isolated. 相似文献
59.
Alessandro de Robertis Concetta de Stefano Rosario Scarcella Carmelo Rigano 《Thermochimica Acta》1984,80(2):197-208
The formation constants for the complexes Mg2+ -, Ca2+ -, Sr2+ - and Ba2+ - succinate (succ2−) have been determined by potentiometric measurements, in aqueous solution, at different temperatures and ionic strengths. The species [M(succ)]0 and [M(succ)H]+ were found for all systems. For the stability constant the ionic strength dependence has been found, and general parameters for the relation log β = f(I) have been obtained. From the temperature dependence of stability constants ΔH values have been deduced. The procedure adopted in calculating all the thermodynamic parameters for the systems under study, where weak complexes are formed, is discussed. The stability of the complexes follows the order Mg < Ca Sr ≈ Ba. 相似文献
60.
Esposito V Randazzo A Piccialli G Petraccone L Giancola C Mayol L 《Organic & biomolecular chemistry》2004,2(3):313-318
NMR, molecular dynamics and mechanics calculations, and CD spectroscopy were used to characterise three tetramolecular quadruplex complexes: [d(TG(Br)GGT)](4), [d(TGG(Br)GT)](4) and [d(TGGG(Br)T)](4), where G(Br) indicates an 8-bromoguanine residue. All three quadruplexes are characterised by a 4-fold symmetry with all strands parallel to each other and, differently to what has been observed for other parallel quadruplex structures, with a tetrad (formed by 8-Br-dGs) in a syn conformation. The whole of the data demonstrates that the replacement in turn of different dG residues with 8-Br-dG in the sequence 5[prime or minute]-TGGGT-3[prime or minute] affects the resulting structures in different ways, leading to different CD profiles and thermal stabilities. Particularly, [d(TG(Br)GGT)](4) and [d(TGG(Br)GT)](4) are more stable than the unmodified sequence, whereas [d(TGGG(Br)T)](4) is much less stable than the natural counterpart. The conformational features found in the three quadruplexes might, in principle, amplify the range of applicability of synthetic oligonucleotides as aptamers or catalysts, by providing novel structural motifs with different molecular recognition capabilities from those of native DNA sequences. 相似文献