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排序方式: 共有172条查询结果,搜索用时 218 毫秒
71.
72.
M. Martínez García P. Arroyo Ortega F. Lara Ochoa G. Espinosa Pérez S. Hernández Ortega M.I. Chávez Uribe M. Salmón R. Cruz-Almanza 《Tetrahedron》1997,53(52):4415-17642
A conformational study of cycloveratrilenes 3 and 4 by high resolution NMR at low temperature for 3 and room temperature for 4 along with X-ray crystallography is reported. From these experiments we found a dynamic process, where magnetic and topologic environment are exchanged by conformational variations through rotations. A conformational study of two cyclotetraveratrilenes by high resolution NMR at low and room temperature along with X-ray crystallography is reported. From these experiments we found a dynamic process, where magnetic and topologic environment are exchanged by conformational variations through rotations. 相似文献
73.
Margarita Surez Estael Ochoa Beatriz Pita Remberto Espinosa Leandro Gonzlez Nazario Martín Margarita Quinteiro Carlos Seoane Jose L. Soto 《Journal of heterocyclic chemistry》1997,34(3):931-935
Novel 4,7-dihydrothieno[2,3-b]pyridines 10a-d have been prepared in a one step procedure from the readily available o-chloroformyl substituted 1,4-dihydropyridines 9a-d and ethyl mercaptoacetate in good yields. Semiempirical calculations reveal a favoured geometry with a boat conformation in the dihydropyridine system and a planar thieno ring. The calculated charge density values for the olefmic carbons (C5 and C6) are in agreement with the experimental push-pull effect observed in the 13C nmr. 相似文献
74.
[reaction: see text] A synthetic supramolecular system is described that models the effect of phosphoryl transfer in molecular recognition. beta-Cyclodextrin-6A-phosphate (pCD), which is shown to be a substrate of alkaline phosphatase, binds cationic aromatic guests, including anticancer agents, up to 100-fold better than native beta-CD. The above observations demonstrate that pCD is capable of releasing the guests from its cavity upon hydrolysis with the phosphatase, as also confirmed by monitoring the hydrolysis in the presence of a guest. 相似文献
75.
Margarita Surez Esperanza Salfrn Estael Ochoa Yamila Verdecia Livan Alba Nazario Martín Carlos Seoane Roberto Martínez‐Alvarez Hector Novoa De Armas Norbert M. Blaton Oswald M. Peeters Camiel J. De Ranter 《Journal of heterocyclic chemistry》2003,40(2):269-275
Two dihydropyridines endowed with fluorine atoms ( 3 ) and fluorine and chlorine atoms ( 4 ) have been synthesized and structurally characterized by experimental X‐ray analyses and theoretical calculations at the semiempirical (AMI) and ab initio (HF/6–31G*) levels. The results show that these compounds meet the required criteria to act as potential calcium channel modulators. 相似文献
76.
Synthesis and structural study of novel 5-aryl substituted 2-amino-4,7-dioxopyrido[2,3-d]pyrimidines
Ren Rodríguez Margarita Surez Estael Ochoa Beatriz Pita Remberto Espinosa Nazario Martín Margarita Quinteiro Carlos Seoane Jose L. Soto 《Journal of heterocyclic chemistry》1997,34(3):957-961
The tide compounds 4a-c have been prepared in a one-step procedure from 2,4-diamino-6-hydroxy-pyrimidine (1) and the corresponding arylidene substituted Meldrum's acids 2a-e in very good yields. Semiempirical theoretical calculations (AMI) reveal two favoured conformations ( A and B ) for compounds 4a-e. The 1H-nmr determinations, by using Karplus and Altona equations, clearly indicate that conformation A, with the aryl group on C5 in a pseudoaxial position, is that predominant in solution. The calculated charge density values for the olefinic carbons are in agreement with the experimental push-pull effect observed in the 13C-nmr spectra. 相似文献
77.
G. García-Muoz R. Madroero C. Ochoa M. Stud W. Pfleiderer 《Journal of heterocyclic chemistry》1976,13(4):793-796
7-Amino-1H,4H-imidazo[2,3-c][1,2,6]thiadiazine 5,5-dioxide was prepared by a multi-step reaction sequence form 3,5-diamino-4H-1,2,6-thiadiazine 1,1-dioxide. 7-Amino-4H-furazano-[3,4-c][1,2,6]thiadiazine 5,5-dioxide was obtained by lead tetraacetate oxidation of 3,5-diamino-4-hydroxyimino-4H-1,2,6-thiadiazine 1,1-dioxide. 相似文献
78.
Lara KO Godoy-Alcantar C Eliseev AV Yatsimirsky AK 《Organic & biomolecular chemistry》2004,2(12):1712-1718
Complexation of free and N-acetylated alpha-amino acid anions (Gly, Ala, Phe) and some structurally related guests by a dicationic cyclophane-type N,N'-dibenzylated chiral derivative of a bisisoquinoline macrocyclic alkaloid S,S-(+)-tetrandrine (DBT) has been studied by (1)H-NMR titrations in D(2)O. In contrast to other macrocyclic hosts like cyclodextrins and calixarenes, DBT shows highest affinity and large enantioselectivity (K(S)/K(R) >/=10) toward smaller N-acetylalanine and binds larger phenylalanine derivatives more weakly and non-selectively. With 1,2,3,4-tetrahydroisoquinoline-3-carboxylate, a rigid analog of phenylalanine, binding again becomes enantioselective with K(S)/K(R)= 3.8. The binding specificity of DBT is rationalized on the basis of molecular mechanics calculations. 相似文献
79.
Vargas G Hernández I Höpfl H Ochoa ME Castillo D Farfán N Santillan R Gómez E 《Inorganic chemistry》2004,43(26):8490-8500
Three types of homo- and heterotrinuclear boron complexes have been obtained in moderate to good yields from reactions of salen-type ligands with boric acid and combinations of boric acid with phenylboronic and phenylphosphonic acid. The products are air-stable and have relatively high melting points (>290 degrees C) but are poorly soluble or insoluble in common organic solvents. They have been characterized as far as possible by elemental analysis, mass spectrometry, IR, (1)H, (11)B, and (31)P NMR spectroscopy, and X-ray crystallography. Furthermore, theoretical calculations have been performed for representative examples to permit a complete comparison of the different structure types. A detailed analysis of the molecular structures showed that the complexes are constructed around a central B(3)O(3) or B(2)PO(3) ring. The salen ligands are attached to two boron atoms of these rings, which have therefore tetrahedral coordination geometries. The complexes contain seven- and eight-membered heterocycles of the B(2)C(n)ON(2) (n = 2, 3) type with chair or twisted-chair and boat-chair or chair-chair conformations, respectively. In the homotrinuclear complexes one of the three boron atoms is three-coordinate and can therefore still act as Lewis acid, thus making these products interesting for catalytic applications, e.g. in asymmetric synthesis. Depending on the substitutents attached to the boron atoms, these complexes show a relationship with either trimetaboric acid, boroxine, or the tetraborate dianion found in Borax. 相似文献
80.
Palacios F Ochoa de Retana AM Pascual S Oyarzabal J 《The Journal of organic chemistry》2004,69(25):8767-8774
A simple method for preparation of fluoroalkyl beta-enaminophosphonates 1 from alkylphosphonates 2 and perfluoroalkyl nitriles 3 is reported. Olefination reaction of functionalized phosphates 1 with aldehydes gives alpha,beta-unsaturated imines 5. Acid hydrolysis of these fluoroalkyl derivatives 5 affords alpha,beta-unsaturated ketones 6, while their selective reduction with hydrides leads to the formation of allylamines 7, enamines 8, and saturated ketones 9 or amines 10. Selective oxidative cleavage of the carbon-carbon double bond of allylamines 7 gives fluorinated alpha-amino aldehydes 12, alpha-amino ketones 13, or alpha-amino acid derivatives 14. 相似文献