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271.
Ohnsmann J Quintás G Garrigues S De La Guardia M 《Analytical and bioanalytical chemistry》2002,374(3):561-565
A sustainable and environmentally friendly procedure has been developed for the FTIR determination of caffeine in tea leaf samples. The method is based on the extraction with ammonia and CHCl3 and direct determination of caffeine on the chloroform extracts using peak height absorbance measurements at 1658.5 cm(-1) and external calibration. The method provides a sensitivity of 0.2142 absorbance units mg(-1) mL and a limit of detection of 1 mg L(-1), corresponding to 0.002% m/m caffeine in tea leaves. As compared with a reference procedure, based on UV absorbance measurement at 276 nm after low pressure column chromatography, the developed procedure reduces the consume of CHCl3 by a factor of 10, that of NH4OH by a factor of 20 and avoids the use of diethyl ether and Celite. The time required to do the analysis of a sample is 15 minutes as compared with the 6 hours for the reference one. 相似文献
272.
Zusammenfassung Es wurden mechanische Gemenge sowie Gemeinschaftsfällungen von röntgenamorphen Eisen(III)-hydroxid und Aluminiumoxidhydrat untersucht, die sich röntgenographisch nicht, wohl aber in ihrem katalytischen Vorhalten voneinander unterscheiden. 相似文献
273.
Wiktor Wawrzyczek Helena Majkowska und Janina Soboczyska 《Fresenius' Journal of Analytical Chemistry》1962,188(2):88-89
Ohne Zusammenfassung 相似文献
274.
Ohne Zusammenfassung 相似文献
275.
276.
Janina Karolak-Wojciechowska Witold Kwiatkowski Stanisław W. Markowicz 《Journal of chemical crystallography》1993,23(5):423-429
Two independent molecules in the unit cell are the same enantiomer of the title compound but possess slightly different conformations. Both conformers are joined by H-bonds to one water molecule. The configuration at C11 was established asR.Crystal data: C14H19O3N×1/2H2O; trigonal,P32;a=17.486(2),b=17.486(2),c=8.024(1)Å;V=2124.72(6)Å3;Z=6; (CuK)=1.54178 Å;F(000)=834; finalR=0.0495 for 2376 reflections (of 2747 unique data). 相似文献
277.
Tingting Fu Janina Oetjen Manuel Chapelle Alexandre Verdu Matthias Szesny Arnaud Chaumot Davide Degli‐Esposti Olivier Geffard Yohann Clment Arnaud Salvador Sophie Ayciriex 《Journal of mass spectrometry : JMS》2020,55(9)
The highly diverse chemical structures of lipids make their analysis directly from biological tissue sections extremely challenging. Here, we report the in situ mapping and identification of lipids in a freshwater crustacean Gammarus fossarum using matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) in combination with an additional separation dimension using ion mobility spectrometry (IMS). The high‐resolution trapped ion mobility spectrometry (TIMS) allowed efficient separation of isobaric/isomeric lipids showing distinct spatial distributions. The structures of the lipids were further characterized by MS/MS analysis. It is demonstrated that MALDI MSI with mobility separation is a powerful tool for distinguishing and localizing isobaric/isomeric lipids. 相似文献
278.
Janina Diekmann Isabell Theves Kristoffer A. Thom Peter Gilch 《Molecules (Basel, Switzerland)》2020,25(22)
The psoralens 8-methoxypsoralen (8-MOP), 4,5′,8-trimethylpsoralen (TMP) and 5-methoxypsoralen (5-MOP) find clinical application in PUVA (psoralen + UVA) therapy. PUVA treats skin diseases like psoriasis and atopic eczema. Psoralens target the DNA of cells. Upon photo-excitation psoralens bind to the DNA base thymine. This photo-binding was studied using steady-state UV/Vis and IR spectroscopy as well as nanosecond transient UV/Vis absorption. The experiments show that the photo-addition of 8-MOP and TMP involve the psoralen triplet state and a biradical intermediate. 5-MOP forms a structurally different photo-product. Its formation could not be traced by the present spectroscopic technique. 相似文献
279.
Steven E. J. Bell Gaëlle Charron Emiliano Corts Janina Kneipp Marc Lamy de la Chapelle Judith Langer Marek Prochzka Vi Tran Sebastian Schlücker 《Angewandte Chemie (International ed. in English)》2020,59(14):5454-5462
Experimental results obtained in different laboratories world‐wide by researchers using surface‐enhanced Raman scattering (SERS) can differ significantly. We, an international team of scientists with long‐standing expertise in SERS, address this issue from our perspective by presenting considerations on reliable and quantitative SERS. The central idea of this joint effort is to highlight key parameters and pitfalls that are often encountered in the literature. To that end, we provide here a series of recommendations on: a) the characterization of solid and colloidal SERS substrates by correlative electron and optical microscopy and spectroscopy, b) on the determination of the SERS enhancement factor (EF), including suitable Raman reporter/probe molecules, and finally on c) good analytical practice. We hope that both newcomers and specialists will benefit from these recommendations to increase the inter‐laboratory comparability of experimental SERS results and further establish SERS as an analytical tool. 相似文献
280.
Baccarelli I Gianturco FA Grandi A Sanna N Lucchese RR Bald I Kopyra J Illenberger E 《Journal of the American Chemical Society》2007,129(19):6269-6277
Electron attachment experiments are carried out on the beta-d-ribose molecule in the gas phase for the energy region around 8 eV, and clear fragmentation products are observed for different mass values. A computational analysis of the relevant dynamics is also carried out for the beta-d-ribose in both the furanosic and pyranosic form as gaseous targets around that energy range. The quantum scattering attributes obtained from the calculations reveal in both systems the presence of transient negative ions (TNIs). An analysis of the spatial features of the excess resonant electron, together with the computation and characterization of the target molecular normal modes, suggests possible break-up pathways of the initial, metastable molecular species. 相似文献