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81.
82.
α-Haloketones and -dibromides are converted to the corresponding ketones and alkenes respectively with nickel boride generated from sodium borohydride and nickel chloride. 相似文献
83.
t.C4H9+ - chemical ionization mass spectrometry of long chain conjugated dienes was shown to generate branched alkyl cations providing unambiguous location of the unsaturated system. 相似文献
84.
H. E. Audier A. Milliet C. Perret J. C. Tabet P. Varenne 《Journal of mass spectrometry : JMS》1978,13(6):315-318
Chemical ionization mass spectrometry of bifunctional organic molecules can induce fragmentation involving the formation of cyclic ions. 相似文献
85.
The fragmentation mechanism of cyclanones (cycloheptanone, cyclooctanone and some methylated or deuterated derivatives) was reinvestigated. All the peaks observed can be interpreted on the basis of a rearrangement of the molecular ion. This rearrangement is particularly important at low voltage. 相似文献
86.
Jean-Claude Tabet Yves Tondeur Yves Troin Danielle Vallee-Goyet Jean-Claude Gramain Daniel Fraisse 《Journal of mass spectrometry : JMS》1985,20(12):770-776
Stereospecific decomposition reactions of isomeric (cis and trans) deprotonated molecules from azabicycloalkane derivatives as azetidinols generated under negative chemical ionization (NCI)/OH? have been examined using mass-analysed ion kinetic energy (MIKE) and collisional activation (CA)/MIKE spectra. These measurements together with the ones obtained on specifically labelled compounds enabled us to determine the origin of the stereochemical effects. The results indicate that the hydroxylic proton constitutes the preferential (?90%) site for the deprotonation process. Subsequent fragmentations of the deprotonated species observed in the second field-free region of a reversed geometry instrument are affected by the stereochemistry of the hydroxylic group. The isomer with the hydroxyl group in the cis position relative to the hydrogen at the ring junction mainly loses H2O, while the trans isomer eliminates CH3˙, both processes occurring with high specificity. Labelling studies indicate that two major pathways exist for the elimination of H2O from the cis isomer and the loss of CH3˙ from the trans isomer. The course of the reaction is determined by the ability of the stereoisomers to transfer a proton during the first decomposition step. When the size of the lactam ring is increased from a five-membered ring to a six- or seven-membered ring, these stereochemical effects tend to become less pronounced. 相似文献
87.
Mezzache S Bruneleau N Vekey K Afonso C Karoyan P Fournier F Tabet JC 《Journal of mass spectrometry : JMS》2005,40(10):1300-1308
Proton affinity (PA) of compounds such as proline, cis-3-methylproline, cis-3-ethylproline, cis-3-isopropylproline and cis-3-isopentanylproline was determined by kinetic method with amines as the reference bases. The effective temperatures determined using ion trap and triple quadrupole mass spectrometers were found to be significantly different. In the case of the triple quadrupole instruments, the effective temperature depends significantly on the collision energy. The influence of the apparent basicity (GBapp) on the effective temperature may be used to estimate the difference in protonation entropy (DeltaDeltaS degrees) between the sample and reference compounds. In case of the ion trap mass spectrometer, the variation of the effective temperature as a function of the excitation amplitude is small, so it is difficult to account for the contribution of the entropy effects to the proton affinity value. A better estimation of the PA and DeltaDeltaS degrees values for the investigated molecules is obtained by combining the GBapp and Teff data pairs that are obtained from both the mass spectrometers. 相似文献
88.
Mezzache S Pepe C Karoyan P Fournier F Tabet JC 《Rapid communications in mass spectrometry : RCM》2005,19(16):2279-2283
The proton affinity (PA) of cis/trans-3-prolinoleucines and cis/trans-3-prolinoglutamic acids have been studied by the kinetic method and density functional theory (DFT) calculations. Several conformations of the neutral and the protonated modified prolines, in particular the endo and exo ring conformations, were analyzed with respect to their contribution to the PA values. When the substituent is an alkyl, both the diastereoisomers have the same PA value. However, the PA values for the diastereoisomers are different when the substituted chain contains functional groups (e.g. a carboxyl group). This variation in PA values could be attributed to the existence of intramolecular hydrogen bonds. 相似文献
89.
Lafaye A Junot C Ramounet-Le Gall B Fritsch P Ezan E Tabet JC 《Journal of mass spectrometry : JMS》2004,39(6):655-664
This paper reports a liquid chromatographic/electrospray ionization mass spectrometric (LC/ESI-MS) method for profiling a wide range of structurally different sulfoconjugated compounds in urine and its application to the characterization of biomarkers for heavy metal toxicity in rat urine. Sulfoconjugates were first isolated by solid-phase extraction and the LC separation was performed on a reversed-phase column. Sulfoconjugates were detected in a triple-quadrupole mass spectrometer by simultaneously monitoring constant losses of 80 u (or 80 Th for doubly charged ions), precursors of m/z 80 (SO(3) (-*)) and precursors of m/z 97 (HSO4-). The ESI-MS detection conditions were optimized on dehydroepiandrosterone sulfate and estradiol sulfate and tested on other sulfoconjugates. The analysis of urine samples from humans and rats by using the developed method allowed the detection of about 15 peaks in each mode of detection. It was then applied to the investigation of heavy metal toxicity in rats. Comparative analysis of the chromatographic fingerprints of urine from control and uranium- and cadmium-treated rats showed several variations in the chromatographic pattern of the sulfoconjugates. Diagnostic m/z ratios were confirmed by analyzing individual urine samples and one of the observed variations seemed to be specific to uranium toxicity. The ion responsible for this variation has been identified as 4-ethylphenol sulfate by comparison of its chromatographic retention time and collision-induced dissociation mass spectra (MS(2) and MS(3) performed on a quadrupole ion trap instrument) with those of the synthesized compound. 相似文献
90.
Casper D Becker-Szendy R Bratton CB Cady DR Claus R Dye ST Gajewski W Goldhaber M Haines TJ Halverson PG Jones TW Kielczewska D Kropp WR Learned JG LoSecco JM McGrew C Matsuno S Matthews J Mudan MS Price L Reines F Schultz J Sinclair D Sobel HW Stone JL Sulak LR Svoboda R Thornton G van der Velde JC 《Physical review letters》1991,66(20):2561-2564