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81.
Wong PS Srinivasan N Kasthurikrishnan N Cooks RG Pincock JA Grossert JS 《The Journal of organic chemistry》1996,61(19):6627-6632
Membrane introduction mass spectrometry (MIMS) allows on-line monitoring of the products of photolysis (254 nm) of benzyl acetate in aqueous methanol and 3,5-dimethoxybenzyl acetate in water. The reaction mixture is continuously exposed to a silicone membrane through which analyte molecules permeate into a triple quadrupole mass spectrometer for qualitative and quantitative analysis. Ionization is achieved by either isobutane or ammonia chemical ionization, and ions characteristic of the reactant ester and its products are monitored simultaneously and continuously. Three products, benzyl methyl ether, ethylbenzene, and bibenzyl are observed in the benzyl acetate photolysis. Two products, 3,5-dimethoxybenzyl alcohol and 3,5-dimethoxyethylbenzene, are formed in the photolysis of 3,5-dimethoxybenzyl acetate. Quantitation is achieved through calibration using external standard solutions and, in the case of benzyl methyl ether, tandem mass spectrometry is used to verify product identification. During the photolysis of benzyl acetate, benzyl methyl ether and ethylbenzene are produced at onset with similar efficiencies. For the 3,5-dimethoxy ester photolysis, performed in aqueous solution, the efficiency of formation of the polar product 3,5-dimethoxybenzyl alcohol is about 300 times greater than that of the nonpolar product 3,5-dimethoxyethylbenzene. The results show that the relative reaction rates are dependent on the solvent and on the photon intensity and are consistent with earlier off-line experiments by Pincock et al. which showed that the photolysis proceeds through both ion and radical pair intermediates. To the best of our knowledge, the work reported here describes the first analysis of the photochemistry of an aralkyl ester in water and the first use of on-line mass spectrometry in a mechanistic study. 相似文献
82.
Fabian Gerson William B. Martin Georges Plattner Franz Sondheimer Henry N. C. Wong 《Helvetica chimica acta》1976,59(6):2038-2048
ESR. studies are reported for the radical anions of 5,6-didehydro- and 5,6,11,12-tetradehydro-dibenzo[a,e]cyclooctene (III and IV, resp.), in addition to that of dibenzo[a,e]cyclooctene (II) itself, the spectrum of which has been reexamined. Comparison of the proton and 13C coupling constants for II·?, III·? and IV·? indicates that the three radical anions do not differ greatly in their electronic and molecular structures. This statement implies that II·? should also be substantially planar, i.e., the tub-shaped eight-membered ring in II is expected to flatten on passing from the neutral molecule to its radical anion. Support for postulating such a change in geometry, analogous to that encountered with the parent cyclooctatetraene (I), is provided by INDO calculations. 相似文献
83.
84.
Jonathan B. Ball Margaret G. Wong Benny Capuano Jacqueline M. Gulbis Maureen F. Mackay Paul F. Alewood 《Journal of heterocyclic chemistry》1990,27(2):279-286
The constrained dipeptide mimic 1 was synthesized from 2 in three steps with 65% overall yield. Analyses of the 1H nmr data of a number of 3-amino-2,5-dioxo-2,3,4,5-tetrahydro-1H-1-benzazepine derivatives led to the conclusion that these compounds adopt a similar conformation and that this ring system is rigid. X-ray crystallography was used to define the structure of 3 , and computer-aided energy minimization of 6 gave a preferred conformation similar to that observed in the crystal of 3 . 相似文献
85.
Wong PS Yoshioka K Xie F Kissinger PT 《Rapid communications in mass spectrometry : RCM》1999,13(5):407-411
Liquid chromatography/tandem mass spectrometry (LC/MS/MS) has been coupled to in vivo microdialysis for on-line monitoring of melatonin in a freely moving rat for a period of 15 hours. A microdialysis probe was surgically implanted into the jugular vein of the rat, and deionized water was used as the perfusion medium at a flow rate of 1.0 microL/min. Microdialysis samples were collected in an on-line injector with sample injection every 30 minutes. Melatonin was dosed by intraperitoneal (i.p.) injection and then monitored by microdialysis/LC/MS/MS. The whole experiment, including the microdialysis sampling and sample injection into the LC/MS system, was fully automated. Metabolites of melatonin were identified off-line by LC/MSn experiments. Two metabolites were identified as 6-hydroxymelatonin and cyclic 2-hydroxymelatonin, consistent with ones found previously in the literature. 相似文献
86.
The molecular structures of 1,3-benzodioxole and 1,3-indandione partially oriented in nematic solvents have been studied by NMR. Results for 1,3-indandione agree well with a planar model. The structural parameters are similar to those obtained by X-ray studies. No keto-enol tautomerism is observed. An anomalous structural result is obtained for 1,3-benzodioxole if the molecule is assumed to be planar. Dipolar couplings agree well with puckered model. The puckering angle is found to be about 15.5° ± 2°, similar to the values observed for TTF, TSeF and 2,5-dihydrofuran. 相似文献
87.
From proton magnetic resonance spectra of TTF and TCNQ partially oriented in nematic liquid crystal solvents the ratio of length to width of the proton rectangle is 3.124 ± 0.03 for TTF and 1.765 ± 0.024 for TCNQ. Values of JCH obtained for TTF dissolved in d6-acetone, are JCH = 187.9 ± 0.3 Hz, JCCH = 6.7 ±0.1 Hz and JCSCH = 9.0 ±0.2 Hz. 相似文献
88.
Angelo J. Amoroso Brian F. G. Johnson Jack Lewis Chi-Keung Li Catherine A. Morewood Paul R. Raithby Maria D. Vargas Wing-Tak Wong 《Journal of Cluster Science》1995,6(1):163-173
Reduction of the heptaosmium cluster [Os7(CO)21] With [Et4N][NH4) gives the cluster dianion [Os7(CO)20]2–,1, in high yield. The reaction of the dianion with [AuPR
3Cl] (R=Et or Ph) in the presence of TlPF6 forms [Os7((CO)20(AuPR
3)2] [R=Et (2a);R = Ph(2b)] in 80% yield, while the corresponding reaction with (Os(C6H6)(CH3CN)3]2+ gives [Os8(CO)20 (
6-C6H6)] (3) in reasonable yield (ca. 30%). The dianion,1, and the clusters2 and3 have been fully characterized by bout spectroscopic and crystallographic methods. The crystal structure of the [Ph4P]+ salt of1 shows that the metals in the anion adopt a capped octahedral geometry, with all twenty carbonyl ligands in terminal sites. The metal core geometry in2a is best described as a tricapped octahedron, and is based on the structure of the dianion1 with two adjacent octahedral faces capped by the Au atoms of the two AuPEt3 groups. In a similar fashion, the geometry of3 is related to that of1 with the addition of an Os(C6H6) unit capped to a triangular face, to give a bicapped octahedral framework. 相似文献
89.
90.