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81.
Two-photon sequential absorption spectroscopy has been used to selectively excite rotational structure in the B---X absorption transition of the 129I2 molecule up to within 2 cm−1 of the dissociation limit. Vibrational and rotational constants have been obtained for the B state levels with υ = 71–79. Le Roy's equations for long-range behaviour are expressed in mass-reduced form, and it is shown that these equations can be successfully used to combine the spectroscopic constants for 127I2 and 129I2 to give improved values of the long range constants for the B state. The improved values are only slightly different from those previously obtained by the same technique for 127I2 alone. 相似文献
82.
83.
[reaction: see text] 6-(Imidazol-1-yl)-, 6-(benzimidazol-1-yl)-, and 6-(1,2,4-triazol-4-yl)purine nucleosides undergo a nickel-mediated C-C cross-coupling of azole-substituted purine derivatives with arylboronic acids to give good yields of 6-arylpurine nucleosides. 相似文献
84.
Thomas Novinson Roland K. Robins Darrell E. O'Brien 《Journal of heterocyclic chemistry》1973,10(5):835-837
Nucleophilic displacement reactions under acidic and basic conditions have been studied with 4,6-dinitro-3-methoxypyridazine 1-oxide ( 1 ) and with 6-chloro-3-methoxy-4-nitropyridazine 1-oxide ( 2 ). Depending on the nature of the nucleophilic reagent and the conditions of the reaction we have found that the chloro group, the nitro group, as well as the methoxy group of 1 and 2 may be displaced by the nucleophile. This type of compound possesses significant in vitro antifungal activity. 相似文献
85.
Naeem B. Hanna Slobodan D. Dimitrijevich Steven B. Larson Roland K. Robins Ganapathi R. Revankar 《Journal of heterocyclic chemistry》1988,25(6):1857-1868
1-β-D-Ribofuranosyl- 21 , 1-(2-deoxy-β-D-erytftro-pento fur anosyl)- 27 and 1-β-D-arabinofuranosyl- 29 derivatives of 1,2,4-triazole-3-sulfonamide ( 19 ) have been prepared. Glycosylation of the silylated 19 with 1,2,3,5-tetra-0-acetyl-β-D-ribofuranose ( 5 ) in the presence of trimethylsilyl triflate gave the corresponding blocked nucleoside ( 20 ), which on ammonolysis afforded 1-β-D-ribofuranosyl-1,2,4-triazole-3-sulfonamide ( 21 ). Stereospecific glycosylation of the sodium salt of 19 with either 1-chloro-2-deoxy-3,5-di-O-p-toluoyl-α-D-erythro-pentofuranose ( 22 ) or 1-chloro-2,3,5-tri-0-benzyl-α-D-arabinofuranose ( 23 ) provided the corresponding protected nucleosides 26 and 28. Deprotection of 26 and 28 furnished 1-(2-deoxy-β-D-erythro-pentofuranosyl)-1,2,4-triazole-3-sulfonamide ( 27 ) and 1-β-D-arabinofuranosyl-1,2,4-triazole-3-sulfonamide ( 29 ), respectively. 2-0-D-Ribofuranosyl-1,2,4-triazole-3(4H)-thione ( 7 ) and 4-β-D-ribofuranosyl-1,2,4-triazole-3(2H)-thione ( 9 ) were also prepared utilizing either an acid catalyzed fusion of 1,2,4-triazole-3(1H,2H)-thione ( 4 ) with 5 , the reaction of 5 with silylated 4 in the presence of trimethylsilyl triflate, or by ring closure of 4-(2,3,5-tri-0-benzoyl-β-D-ribofuranosyl)thiosemicarbazide ( 10 ) with mixed anhydride and subsequent deacylation. The synthesis of 1-β-D-ribofuranosyl-3-benzylthio-1,2,4-triazole ( 15 ) has also been accomplished by the silylation procedure employing 3-benzylthio-1,2,4-triazole ( 13 ) and 5 to give 1-(2,3,5-tri-0-acetyl-β-D-ribofuranosyl)-3-benzylthio-1,2,4-triazole ( 14 ). Deacetylation of 14 furnished 15 . The structural assignments of 7, 14 and 21 were made by single-crystal X-ray diffraction analysis and their hydrogen bonding characteristics have been studied. The sulfonamido-1,2,4-triazole nucleosides are devoid of any significant antiviral or antitumor activity in cell culture. 相似文献
86.
87.
Felpin FX Girard S Vo-Thanh G Robins RJ Villiéras J Lebreton J 《The Journal of organic chemistry》2001,66(19):6305-6312
An enantiomeric synthesis of six piperidine and pyrrolidine alkaloids, (S)-nornicotine 1, (S)-nicotine 2, (S)-anatabine 3, (S)-N-methylanatabine 4, (S)-anabasine 5, and (S)-N-methylanabasine 6, known as natural products in tobacco, was established from a common chiral homoallylic (S)-3-(1-azido-but-3-enyl)-pyridine 15. An intramolecular hydroboration-cycloalkylation of the homoallylic azide intermediate 15 served as the key step in the pyrrolidine ring formation. A ring closing metathesis reaction (RCM) of a diethylenic amine intermediate (S)-allyl-(1-pyridin-3-yl-but-3-enyl)-carbamic acid benzyl ester 20 served as the key step in the piperidine ring formation. From the commercially available 3-pyridinecarboxaldehyde 13, a short and convenient enantiomeric synthesis of tobacco alkaloids is described: (S)-nornicotine 1 (5 steps, with an overall yield of 70%), (S)-nicotine 2 (6 steps, 65%), (S)-anatabine 3 (8 steps, 30%), (S)-N-methylanatabine 4 (8 steps, 25%), (S)-anabasine 5 (8 steps, 35%), and (S)-N-methylanabasine 6 (8 steps, 25%). 相似文献
88.
89.
Eliot P. Botosoa Virginie Silvestre Richard J. Robins Jose Manuel Moreno Rojas Claude Guillou Gérald S. Remaud 《Journal of chromatography. A》2009,1216(42):7043-7048
Quantitative isotopic 13C NMR at natural abundance has been used to determine the site-by-site 13C/12C ratios in vanillin and a number of related compounds eluted from silica gel chromatography columns under similar conditions. Head-to-tail isotope fractionation is observed in all compounds at the majority of carbon positions. Furthermore, the site-specific isotope deviations show signatures characteristic of the position and functionality of the substituents present. The observed effects are more complex than would be obtained by simply summing the individual effects. Such detail is hidden when only the global 13C content is measured by mass spectrometry. In particular, carbon positions within the aromatic ring are found to show site-specific isotope fractionation between the solute and the stationary phase. These interactions, defined as non-covalent isotope effects, can be normal or inverse and vary with the substitution pattern present. 相似文献
90.
Katarzyna Kosieradzka Illa Tea Emmanuel Gentil Richard J. Robins 《Analytical and bioanalytical chemistry》2010,396(4):1405-1414
An important route for the detoxification of tropane alkaloids involves N-demethylation to the nor-compounds followed by further degradation. In order to study the mechanisms of the pertinent reactions,
a suitable means to determine the isotope ratios of the substrates and products is required. However, the polarity and functionality
of the nortropane compounds makes their analysis as free bases difficult. A method is described which allows both the quantification
of nortropane alkaloids and the determination of their natural abundance δ15N values. The protocol exploits the derivatisation of the alkaloids by reaction with ethyl chloroformate in aqueous medium
and the quantitative extraction of the ensuing ethylcarbamate esters. The improved chromatographic properties of these derivatives
gives ample separation of the isomeric nortropine and norpseudotropine for measurement of their δ15N (‰) values by isotope ratio mass spectrometry interfaced to gas chromatography. Adequate separation could not be achieved
with the underivatised compounds. Repeatability and precision are sufficient to allow differences in the δ15N values (∆δ15N) > 0.8‰ to be measured, with a standard deviation routinely ∼0.3‰. The methodology has been tested by determining the changes
in the δ15N values of nortropine and norpseudotropine during degradation by cell suspension cultures of a Pseudomonas strain expressing a specific capacity for tropine catabolism. The precision and reproducibility are shown sufficient to allow
the evolution of the δ15N values to be followed during the fermentation. 相似文献