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81.
Orm Hager AntonioL. Llamas-Saiz Concepcin Foces-Foces RosaM. Claramunt Concepcin Lpez Jos Elguero 《Helvetica chimica acta》1999,82(12):2213-2230
The crystal and molecular structure of two salts, I and III , and one molecular complex, II , formed by combining 1,1′-binaphthyl-2,2′-dicarboxylic acid (BNDA) with pyrazole ( 3 ) and 3,5-dimethylpyrazole ( 4 ) has been determined by X-ray crystallography. The most striking feature is the spontaneous resolution of the racemic BNDA host by co-crystallization with 4 , an achiral guest, to form the salt III . The absolute configuration of three manually selected crystals of III have been established by crystallographic methods. The two crystals formed by the (P)-enantiomer display a negative Cotton effect. 13C-CPMAS-NMR Spectroscopy has been used to compare the compounds obtained by crystallization with those prepared by mechanical grinding. 相似文献
82.
Ranjana Aggarwal Shilpa Sharma Mona Hooda Dionisia Sanz Rosa M. Claramunt Brendan Twamley Isabel Rozas 《Tetrahedron》2019,75(50):130728
The first visible-light mediated, simple, efficient and ecofriendly protocol for the regioselective synthesis of novel [1,2,4]triazolo[3,4-b][1,3,4]thiadiazines has been developed by the reaction of α-bromodiketones, generated in situ by the bromination of a diverse array of β-diketones with N-bromosuccinimide, with 4-amino-[1,2,4]triazole-3-thiols. The methodology does not require the presence of any additives and this reaction proceeded in the presence of EDG (OMe), EWG (Cl) and heteroarenes (thiophenyl) giving the expected products in good to excellent yields. A solvent free protocol was also established to accomplish the synthesis of target compounds but it required PTSA as a catalyst and yields are comparatively poor. The structure of the regioisomer has been confirmed unambiguously by heteronuclear 2D-NMR [(1H-13C) HMBC, (1H-15N) HMBC, (1H-13C) HMQC] spectroscopic and X-ray crystallographic studies. 相似文献
83.
Mariusz Pietrzak Dr. Jens P. Wehling Shushu Kong Peter M. Tolstoy Dr. Ilya G. Shenderovich Dr. Concepción López Dr. Rosa María Claramunt Prof. Dr. José Elguero Prof. Dr. Gleb S. Denisov Prof. Dr. Hans‐Heinrich Limbach Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(5):1679-1690
The properties of the intramolecular hydrogen bonds of doubly 15N‐labeled protonated sponges of the 1,8‐bis(dimethylamino)naphthalene (DMANH+) type have been studied as a function of the solvent, counteranion, and temperature using low‐temperature NMR spectroscopy. Information about the hydrogen‐bond symmetries was obtained by the analysis of the chemical shifts δH and δN and the scalar coupling constants J(N,N), J(N,H), J(H,N) of the 15NH15N hydrogen bonds. Whereas the individual couplings J(N,H) and J(H,N) were averaged by a fast intramolecular proton tautomerism between two forms, it is shown that the sum |J(N,H)+J(H,N)| generally represents a measure of the hydrogen‐bond strength in a similar way to δH and J(N,N). The NMR spectroscopic parameters of DMANH+ and of 4‐nitro‐DMANH+ are independent of the anion in the case of CD3CN, which indicates ion‐pair dissociation in this solvent. By contrast, studies using CD2Cl2, [D8]toluene as well as the freon mixture CDF3/CDF2Cl, which is liquid down to 100 K, revealed an influence of temperature and of the counteranions. Whereas a small counteranion such as trifluoroacetate perturbed the hydrogen bond, the large noncoordinating anion tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate B[{C6H3(CF3)2}4]? (BARF?), which exhibits a delocalized charge, made the hydrogen bond more symmetric. Lowering the temperature led to a similar symmetrization, an effect that is discussed in terms of solvent ordering at low temperature and differential solvent order/disorder at high temperatures. By contrast, toluene molecules that are ordered around the cation led to typical high‐field shifts of the hydrogen‐bonded proton as well as of those bound to carbon, an effect that is absent in the case of neutral NHN chelates. 相似文献
84.
85.
Rosa M. Claramunt Concepción López Carlos Pérez-Medina M. Rosario Torres 《Tetrahedron》2006,62(50):11704-11713
Multinuclear magnetic resonance spectroscopy allowed us to characterize four 1(2),5,6,7-tetrahydro-4H-indazol-4-one derivatives (1-4) and establish the most stable tautomer in each case. The crystal structure of 6,6-dimethyl-1(2),5,6,7-tetrahydro-4H-indazol-4-one (2) (orthorhombic space group P2(1)2(1)2(1), a=10.1243(8), b=21.526(2), c=24.992(2) Å, Z=4, 293 K) presents two different trimers, bonded through N-H?N hydrogen bonds involving tautomers 1H and 2H. In crystalline 3,6,6-trimethyl-2,5,6,7-tetrahydro-4H-indazol-4-one (4) (monoclinic space group P2(1)/c, a=5.9827(7), b=16.494(2), c=11.012(1) Å, β=93.464(2)°, Z=4, 293 K) only tautomer 2H exists forming a hydrogen-bonded network through the 4-oxo group and a water molecule. 相似文献
86.
Infantes L Mó O Yáñez M Roux MV Jiménez P Dávalos JZ Temprado M Ribeiro da Silva MA Ribeiro da Silva Md Amaral LM Cabildo P Claramunt R Elguero J 《The journal of physical chemistry. A》2006,110(7):2535-2544
The enthalpies of combustion, heat capacities, enthalpies of sublimation and enthalpies of formation of 2-tert-butylbenzimidazole (2tBuBIM) and 2-phenylimidazole (2PhIM) are reported and the results compared with those of benzene derivatives and a series of azoles (imidazoles, pyrazoles, benzimidazoles and indazoles). Theoretical estimates of the enthalpies of formation were obtained through the use of atom equivalent schemes. The necessary energies were obtained in single-point calculations at the B3LYP/6-311++G(d,p) on B3LYP/6-31G optimized geometries. The comparison of experimental and calculated values of all studied compounds bearing H (unsubstituted), methyl (Me) ethyl (Et), propyl (Pr), isopropyl (iPr), tert-butyl (tBu), benzyl (Bn) and phenyl (Ph) groups show remarkable homogeneity. The remarkable consistency of both the calculated and experimental results allows us to predict with reasonable certainty the missing experimental values. The crystal and molecular structure of the 2-benzylbenzimidazole (2BnBIM) has been determined by X-ray analysis. The observed molecular conformation permits the crystal being built up through N-H...N hydrogen bonds and van der Waals contacts between the molecules. An attempt has been made to relate the crystal structure to the enthalpies of sublimation. 相似文献
87.
New Schiff bases have been prepared by reacting 3-hydroxy-4-pyridine- carboxaldehyde with various amines. NMR spectroscopic methods provided clear evidence that the Schiff bases exist in the solid state and in solution as hydroxyimino tautomers with the E-configuration. A study of the stabilities of the tautomeric forms and the different conformers has been carried out using density functional calculations at the B3LYP/6-31G** level. 相似文献
88.
89.
An NMR and Computational Study of Azolo[a]pyrimidines with Special Emphasis on Pyrazolo[1,5‐a]pyrimidines 下载免费PDF全文
Ranjana Aggarwal Virender Kumar Gulshan Singh Dionisia Sanz Rosa M. Claramunt Ibon Alkorta Goar Sánchez‐Sanz José Elguero 《Journal of heterocyclic chemistry》2015,52(2):336-345
The reaction of 3(5)‐amino‐5(3)‐hydrazinopyrazole, a bifunctional compound, with 3‐oxo‐3‐phenylpropanenitrile and two of its p‐substituted derivatives affords 2,5‐diaryl‐7‐aminopyrazolo[1,5‐a]pyrimidines. A mechanism for this unexpected reaction involving the formation of hydrazine is proposed. The position of the aryl substituents on the bicyclic ring has been established by the combined use of NMR and DFT calculations. Moreover, the chemical shifts have been calculated, and some general rules have been withdrawn. 相似文献
90.
M. Ángeles García Rosa M. Claramunt Tomáš Solčan Viktor Milata Ibon Alkorta José Elguero 《Magnetic resonance in chemistry : MRC》2009,47(2):100-104
The 13C [hexadeutero‐dimethylsulfoxide (DMSO‐d6), hexamethyl‐phosphoramide (HMPA)‐d18and solid‐state] and 15N (solid‐state) NMR spectra of six C‐aminobenzimidazoles have been recorded. The tautomerism of 4(7)‐aminobenzimidazoles and 5(6)‐aminobenzimidazoles has been determined and compared with B3LYP/6‐311 + + G(d,p) calculations confirming the clear predominance of the 4‐amino tautomer and the slight preference for the 6‐amino tautomer. GIAO‐calculated absolute shieldings compare well with experimental chemical shifts. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献