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611.
Pier G. Daniele Giorgio Ostacoli Orfeo Zerbinati Silvio Sammartano Alessandro De Robertis 《Transition Metal Chemistry》1988,13(2):87-91
Summary A thermodynamic study of CuII–MII-citrate (MII=NiII, ZnII or CdII) ternary systems has been performed by means of potentiometric measurements of hydrogen ion concentration at different temperatures (10, 25, 35 and 45°C) and at I=0.1 mol dm–3 (KNO3).The different binary and ternary systems involved have been further characterized by visible spectra and by calculating the spectra ( versus ) of all the CuII complexes.The thermodynamic data suggest strong entropic stabilization for the species under discussion. As regards the visible spectral characteristics of CuII(d-d transitions), the substitution of one CuII ion in the dimer [Cu2(cit)2H–2]4– by NiII or ZnII to form heterobinuclear [CuM(cit)2H–2]4– complexes, gives rise to a change in the visible spectrum. 相似文献
612.
Antonio da Settimo Giampaolo Prirnofiore Oreste Livi Pier Luigi Ferrarini Silvano Spinelli 《Journal of heterocyclic chemistry》1979,16(1):169-174
Isatoic acid reacts with 7-mcthyl-2,3-dihydro-1,8-naphthyridin-4(1H) one ( 8 ) to give 3-methyl-5,6-dihvdroquino[3,2-c][1,8]naphthyriclin-7-carboxylic acid ( 9a ), which was transformed into the 3-methylquino[3,2-c][1,8]naphthyridine ( 7a ) by refluxing with copper chromite in quinoline. The same product ( 7a ) was also obtained by aromatization of the 3-methyl-5,6-dihydroquino-[3,2-c][1.8]naphthvridine ( 10a ), prepared by condensation of the ketone ( 8 ) and o-aminobenzaldehyde. Other 3-substituted quino[3,2-c][1,8]naphthyridines ( 7b,c,d,e ), which contain a new heterocyclic, ring structure, have been prepared using o-aminobenzaldehyde and 7-sub-stituted-2,3-dihv dro-1,8-naphthyridin-4(1H) ones ( 12 and 13 ) as starting materials. Also, the preparation of the parent nucleus ( 7f ) is described. 相似文献
613.
The chemical characterization of horse liver alcohol dehydrogenase solubilized in isooctane via reverse micelles formed by the anionic surfactant di (2-ethyl-hexyl) sodium sulfosuccinate (AOT) and water (0.6 to 4% v/v) is presented. The enzyme’s catalytic activity toward acetaldehyde reduction is markedly dependent upon w0 = [H2O]/[AOT], and upon the pH of the stock aqueous solution (pHst), from which the hydrocarbon enzyme solution is prepared. Kinetically, the micellar solution appears to follow a normal Michaelis-Menten behavior, with a turnover number which, under the optimal conditions (w0 = 42, pHst = 8.8), appears to be higher than in bulk water. The affinity between enzyme and NADH, as judged from direct binding studies (quenching of the protein fluorescence), is much reduced with respect to water if concentrations refer to the water pool of the micelles, and comparable to water if concentrations refer to the overall volume (hydrocarbon plus water pool). Also, the Km values are much higher if concentrations refer to the water pool. Ultraviolet absorption studies show that the aromatic chromophores are not significantly perturbed on going from a water solution to the micellar solution. The essentially aqueous environment of the protein in the reverse micelles is confirmed by fluoresence studies. Circular dichroism studies show that the enzyme’s conformation in the micelles is similar to that in water; however, under certain conditions, small but significant changes of the main chain folding seem to occur, which do not impair enzymatic activity. The spectroscopic properties of NADH in the hydrocarbon phase (fluorescence and circular dichroism) are also investigated. The potential of the LADH-NADH system for technical applications (oxidoreduction of lipophylic substrates) is discussed. 相似文献
614.
615.
616.
As a last part of an investigation on all 2-pH-unit intervals of carrier ampholytes (CAs) for IEF (see Electrophoresis 2006, 27, 3919-3934; 2006, 27, 4849-4858; 2007, 28, 715-723) two different lots of Servalyt CAs, in the pH 9-11 range, have been analyzed by a 2-D technique based on preparative Rotofor fractionation followed by capillary electrophoresis mass-spectrometry of 10 out of 20 fractions harvested, in the second dimension. The findings: the two lots contain 65 and 69 different M(r) compounds, in the M(r) interval of 232-667 Da, for a total of 341-387 isoforms, respectively. Since this is a chaotic organic synthesis, the high reproducibility (here demonstrated for the first time during the 40 years of existence of CAs) of the synthetic process (for two batches produced at 6 years of distance) is remarkable, considering that a 94% agreement for the individual chemicals and 88% agreement for the total number of isoforms for the two lots is found. It is additionally demonstrated that the lower pI species are accompanied by considerably more isoforms than the high pI forms and that in all cases such isoforms consist of family of compounds clustered around the pI of the parental form, with a pI spread of ca. 0.1-0.2 pH units. 相似文献
617.
Marcelli A Foggi P Moroni L Gellini C Salvi PR Badovinac IJ 《The journal of physical chemistry. A》2007,111(12):2276-2282
The fluorescence spectra of unsubstituted porphyrin (H2P), diprotonated porphyrin (H4P2+), and isoelectronic tetraoxaporphyrin dication (TOxP2+) have been measured in solution at room temperature. The S2-->S0 fluorescence has been observed, much more intense for TOxP2+ than for H4P2+ and H2P. In the TOxP2+ case, the S2-->S0 fluorescence spectrum is remarkably sharp and shows an excellent mirror symmetry with respect to S0-->S2 absorption. On the contrary, the spectra of H4P2+ and H2P are shifted and more extended with respect to the absorption counterparts. The differences have been attributed primarily to the change of the equilibrium geometry upon excitation, larger in H2P and H4P2+ than in TOxP2+ and in the case of H4P2+ to the nonplanar conformation of the macrocycle. Also the S1-->S0 spectra of H2P, H4P2+, and TOxP2+ have been measured and more qualitatively discussed. The S1 and S2 fluorescence decays have been observed for H4P2+ and TOxP2+ exciting with ultrashort pulses. The S2 lifetime of TOxP2+ is of the order of the temporal resolution of our experimental apparatus, whereas that of H4P2+ is shorter. The S2-->S0 quantum yield of TOxP2+ has been estimated to be 0.035, approximately 3 orders of magnitude higher than that of H4P2+. It is proposed on the basis of ab initio model calculations that excited states of the H4P2+(CF3COO-)2 complex with charge-transfer character are responsible of the increased extension of the S2-->S0 spectrum with respect to that of H2P. 相似文献
618.
The role played by the carbonyl group in the antenna system of a naturally occurring photochromic chromene, flindersine (FL), has been experimentally investigated and compared with that of a carbonyl group present in a structurally related unreactive heterocyclic compound, 6(5H)-phenanthridinone (PH). Through stationary and time-resolved absorption and emission techniques, the excited-state relaxation dynamics after UV irradiation were determined for FL and PH. The presence of a carbonyl group in both compounds entails the existence of two close-lying, strongly coupled electronic excited states, having n,pi* and pi,pi* character, respectively. Their coupling can be modulated by a careful choice of the solvent proticity and temperature. Moreover, in the case of strong coupling between the n,pi* and pi,pi* states, we have proved that the relaxation dynamics can involve transitions in which the upper of the coupled states acts as an intermediate for radiationless decay, bypassing the lowest emissive state, whereby the fluorescence quantum yield becomes a function of the excitation wavelength. 相似文献
619.
Arvidsson B Johannesson N Citterio A Righetti PG Bergquist J 《Journal of chromatography. A》2007,1159(1-2):154-158
A capillary electrophoresis method for separation and detection with time-of-flight mass spectrometry is described for tryptophan metabolites in the kynurenic pathway. Tryptophan metabolites are usually difficult to detect with electrospray mass spectrometry since they have low surface activity and occur in low nanomolar to micromolar range in body fluids. Modification of the silica-wall with 1-(4-iodobutyl)4-aza-1-azoniabicyclo[2,2,2]octane iodide, also named M7C4I, has successfully been used to deactivate the fused silica wall and generate a stable reversed electroosmotic flow. Utilizing this advantage together with electrospray ionization time-of-flight mass spectrometry, which generates high resolution and fast acquisition monitoring of species, proved to be successful even for such a complex matrix like human cerebrospinal fluid. 相似文献
620.
A series of symmetric and non-symmetric bis(oxazoline) ligands were applied in the Nozaki-Hiyama-Kishi methallylation of a range of aromatic and aliphatic aldehydes. A non-symmetrical ligand with tert-butyl/benzyl-substituted oxazolines provided the highest enantioselectivity of 99.5% for the methallylation of benzaldehyde. 相似文献