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901.
Federico Marini Fabrizio Balestrieri Remo Bucci Antonio L. Magrì Domenico Marini 《Microchemical Journal》2003,74(3):239-248
Supervised pattern recognition appears to be a useful tool to authenticate foodstuffs according to their geographical or varietal origin, when a set of samples whose classification is known a priori are available. In this work, linear discriminant analysis and artificial neural networks trained by the back-propagation algorithm have been used to discriminate rice bran oils manufactured in three different countries (Italy, Thailand and Switzerland) according to their geographical origin. The variables to be included in the mathematical models have been chosen by means of Fisher F-ratio value among the chemical indices routinely determined on vegetable oils (particularly fatty acids, triglycerides and sterol composition). The prediction ability of all the classifiers was 100% as evaluated by cross-validation. 相似文献
902.
Fabrizio Rodante 《Thermochimica Acta》1979,34(1):29-34
Enthalpic and entropic contributions to substituent effects for the ionization of m-and p-nitrobenzoic acids are examined, ranging from pure water to 0.8 mole fraction DMSO. The effect of the medium on the substituent and reaction constants is explained in terms of solute—solvent interactions. No structure-breaking effect was found. 相似文献
903.
Fabrizio Rodante 《Thermochimica Acta》1979,31(2):221-226
Separate enthalpic and entropic contributions to substituent effects on the dissociation of m- and p-chlorobenzoic acids in water-dimethylsulfoxide mixtures ranging from 0 to 0.8 mole fraction DMSO are presented.The effect of the medium on the substituent and reaction constants for the ionization processes is explained in terms of solute-solvent interactions and related structure breaking. 相似文献
904.
Bergami C Donzello MP Ercolani C Monacelli F Kadish KM Rizzoli C 《Inorganic chemistry》2005,44(26):9852-9861
A new octacationic macrocycle, tetrakis-2,3-[5,6-di{2-(N-methyl)pyridiniumyl}pyrazino]porphyrazine, was obtained in its hydrated form as the water-soluble iodide salt. This compound, abbreviated as [(2-Mepy)(8)TPyzPzH(2)](I(8)).8H(2)O (2-Mepy = 2(N-methyl)pyridiniumyl moiety), was obtained by demetalation of the corresponding Mg(II) complex, [(2-Mepy)(8)TPyzPzMg(H(2)O)](I(8)).5H(2)O, which in turn was prepared from its corresponding neutral hydrated species tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazinato(monoaquo)magnesium(II), [Py(8)TPyzPzMg(H(2)O)].4H(2)O, by reaction with CH(3)I in N,N-dimethylformamide. The quaternization reactions by using CH(3)I or methyl p-toluenesulfonate were also conducted on the monomeric precursor 2,3-dicyano-5,6-di(2-pyridyl)-1,4-pyrazine, [(CN)(2)Py(2)Pyz], with formation of the monoquaternized ion [(CN)(2)Py(2-Mepy)Pyz](+) neutralized by iodide and p-toluenesulfonate anions. Single-crystal X-ray work allowed elucidation of the structure of the two salt-like species. The diquaternized ion [(CN)(2)(2-Mepy)(2)Pyz](2+) could also be obtained as a p-toluenesulfonate salt, but attempts at direct macrocyclization of this dicationic species were unsuccessful. The iodide salt [(2-Mepy)(8)TPyzPzH(2)](I(8)).8H(2)O is water-soluble, with different solubilities depending on the range of pH explored. It was established that the macrocycle [(2-Mepy)(8)TPyzPzH(2)](8+) undergoes facile deprotonation and behaves as a strong acid. Aggregation phenomena are observed for both the octacation [(2-Mepy)(8)TPyzPzH(2)](8+) and its corresponding centrally deprotonated species [(2-Mepy)(8)TPyzPz](6+). Nevertheless, both cationic moieties exist in their monomeric form under specific experimental conditions. UV-visible monitored titrations with NaOH provide information about the type of protonation/deprotonation equilibria which are complicated by the occurrence of aggregation phenomena. 相似文献
905.
Sunto Per un problema relativo allo studio di campi elettrici armonici con una condizione al contorno dissipativa espressa dalla relazione: (*) Et=*Ht×n si perviene a un teorema di esistenza, unicità e dipendenza continua. Cioè si prova la correttezza del problema ehe invece non sussiste se si sostituisce la relazione (*) con la usuale condizione al contorno dei conduttori perfetti: Et×n=0.
Lavoro eseguito nell'ambito delle attività del G.N.F.M. 相似文献
Summary For the problem relating to the study of electromagnetic fields with a dissipative boundary condition expressed by the relation: (*) Et=*Ht×n we prove a theorem of existence, uniqueness and continuous dependence. That is we prove the correctness of the problem that does not exist if we replace the relation (*) by the customary boundary condition for a perfect conducting medium: Et×n=0.
Lavoro eseguito nell'ambito delle attività del G.N.F.M. 相似文献
906.
Ottorino DeLucchi Arif Datan Aliye Altunda Fabrizio Fabris Metin Balci 《Helvetica chimica acta》2004,87(9):2364-2367
An efficient synthetic route to the concave‐shaped, potentially ionophoric syn‐ and anti‐isomers of 5,6,11,12,17,18‐hexahydro‐5,18:6,11:12,17‐triepoxytrinaphthylene ( 4 ) was elaborated. Starting from ‘oxabenzonorbornadiene’ ( 5 ), the stannylated precursor 9 was prepared in three steps, followed by cyclotrimerization catalyzed by copper(I) thiophene‐2‐carboxylate (CuTC) , which afforded 4 in a syn/anti ratio of 5 : 4. 相似文献
907.
Donzello MP Ou Z Monacelli F Ricciardi G Rizzoli C Ercolani C Kadish KM 《Inorganic chemistry》2004,43(26):8626-8636
A new pyrazinoporphyrazine macrocycle carrying externally appended pyridine rings, tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazine (hydrated), [Py(8)TPyzPzH(2)].2H(2)O, was prepared in high yield by direct cyclotetramerization of the precursor, 2,3-dicyano-5,6-di(2-pyridyl)-1,4-pyrazine, [(CN)(2)Py(2)Pyz], in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The single-crystal X-ray structure of [(CN)(2)Py(2)Pyz] shows a noncoplanar positioning of the pyrazine and pyridine rings in the two slightly different independent molecular units present in the crystal. UV-vis spectra of [Py(8)TPyzPzH(2)] were measured in two nondonor solvents (CHCl(3), CH(2)Cl(2)), a slightly basic solvent (pyridine), and an acidic solvent (CH(3)COOH). In all cases, the spectral changes are consistent with the occurrence of molecular aggregation and colloidal dispersions which break up with time to give clear solutions containing exclusively the monomeric form of the macrocycle, either neutral [Py(8)TPyzPzH(2)] (in CHCl(3), CH(2)Cl(2), and CH(3)COOH) or dianionic [Py(8)TPyzPz](2)(-) (in pyridine). A spectrally monitored titration of [Py(8)TPyzPzH(2)] in CH(2)Cl(2) with TBA(OH) shows the loss of two protons from the macrocyclic core and quantitative conversion of [Py(8)TPyzPzH(2)] to [Py(8)TPyzPz](2)(-). Cyclic voltammetry and thin-layer spectroelectrochemical measurements show that [Py(8)TPyzPzH(2)] is present in CH(2)Cl(2) while [Py(8)TPyzPz](2)(-) is present in pyridine, but both forms of the compound exhibit identical electrochemical behavior, consistent with a conversion of the dianion to the neutral porphyrazine in pyridine prior to electroreduction via four reversible one-electron transfer steps. No oxidations of the macrocycle are observed in either solvent containing 0.1 M tetrabuthylammonium perchlorate (TBAP). A comparison of the electrochemical behavior for [Py(8)TPyzPzH(2)] with what is reported for related phthalocyanine and porphyrazine analogues highlights the remarkable electron-accepting properties of the presently investigated free-base macrocycle. 相似文献
908.
909.
910.
Franco Bellesia Laurent De Buyck Franco Ghelfi Adele Mucci Ugo M. Pagnoni Fabrizio Roncaglia 《Tetrahedron》2006,62(4):746-757
Chaetomellic anhydride A was efficiently attained in three steps, starting from 2,2-dichloropalmitic acid and 2-(3-chloro-2-propenylamino)pyridine. Atom transfer radical cyclisation selectively formed the cis-stereoisomer of the trichloropyrrolidin-2-one, which underwent a stereospecific functional rearrangement to form a substituted maleimide. The choice of 2-pyridyl, as ‘cyclisation auxiliary’ in the atom transfer radical cyclisation step, proved beneficial for hydrolysis of the maleimide to form the desired anhydride. 相似文献