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81.
Adler S Atiya MS Chiang IH Diwan MV Frank JS Haggerty JS Jain V Kettell SH Kycia TF Li KK Littenberg LS Ng C Strand RC Witzig C Kazumori M Komatsubara TK Kuriki M Muramatsu N Otomo A Sugimoto S Inagaki T Kabe S Kobayashi M Kuno Y Sato T Shinkawa T 《Physical review letters》2000,84(17):3768-3770
A search for additional evidence for the rare kaon decay K+-->pi(+)nunu; has been made with a new data set comparable in sensitivity to the previous exposure that produced a single event. No new events were found in the pion momentum region examined, 211
pi(+)nunu;) = 1.5(+3.4)(-1.2)x10(-10). 相似文献
82.
[structure: see text] A stereocontrolled convergent synthesis of the annonaceous acetogenin pyragonicin (1) is presented. The key intermediates were accessed using asymmetric Horner-Wadsworth-Emmons (HWE) methodology. A reagent controlled zinc-mediated stereoselective coupling, joining the two highly functionalized intermediates 3 and 4, then provided the core structure. 相似文献
83.
Østby KA Gundersen G Haaland A Nöth H 《Dalton transactions (Cambridge, England : 2003)》2005,(13):2284-2291
The molecular structures of dimethylamino[(dimethylboryl)methylamino]methylborane, Me2NBMeNMeBMe2 (1) and 1,1-bis(dimethylboryl)-2,2-dimethylhydrazine, (Me2B)2NNMe2 (2) have been determined by gas electron diffraction (GED), density functional theory calculations at the B3PW91/6-311++G** level and ab initio calculations at the MP2/6-311++G** level. 1 adopts an open structure similar to that of the isoelectronic hydrocarbon molecule permethylbutadiene; the central B-N bond distance at 148.0/149.3(7) pm (MP2/GED) corresponds to a single covalent N--B bond distance, the two terminal distances, 140.9/140.5(4) pm and 141.8/141.3(4) pm, correspond to the distance between N and B atoms joined by a covalent sigma-bond and a dative pi-bond. A closed form where the establishment of a dative bond between the terminal N and B atoms has led to the formation of a four-membered ring also corresponds to a minimum on the potential energy surface, but the energy is calculated to be 14.3 kJ mol(-1) higher at the MP2 level. This structure is also incompatible with the GED data. 2 adopts a structure in which a dative sigma-bond between the dimethylamino N atom and one of the boron atoms has led to the formation of a three-membered N(2)B ring. The dative sigma-bond distance is 165.5/164.0(13) pm, the two other bond distances in the ring are N-B=150.6/148.9(9) pm corresponding to a covalent sigma-bond and N-N=145.1/145.4(3) pm. The terminal B--N distance 139.6/138.9(9) pm is consistent with a covalent sigma-bond augmented by a dative pi-bond. An open Y-shaped structure also corresponds to a minimum on the potential energy surface, but the energy is 18.7 kJ mol(-1) higher (MP2) and it is incompatible with the GED data. 相似文献
84.
Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is frequently used to identify and quantify drugs in human biological samples due to the high selectivity and sensitivity of this technique. However, ion suppression effects caused by co-eluting compounds: drugs, metabolites, matrix components, impurities and degradation products, are a major concern. Stable isotope labelled internal standards (SIL ISs), usually deuterium ((2)H) labelled, are often used to compensate for these effects. In many LC separations the retention times of (2)H labelled ISs and their analogues will differ. Ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) is increasingly being used for bio-analysis. With the better chromatographic resolution provided with sub 2 μm particles, larger separation between analytes and their (2)H labelled analogues can be expected, which might reduce the benefits of the SIL IS. There is a greater difference in physico-chemical properties between hydrogen isotopes than between isotopes of other elements. (13)C, (15)N and (18)O labelled ISs are more similar to their analytes than (2)H labelled ISs and thereby expected to behave more similarly in chromatographic separations. In this study we have investigated the use of (13)C and (2)H labelled ISs for the determination of amphetamine and methamphetamine by UPLC-MS/MS. The (13)C labelled ISs were co eluting with their analytes under different chromatographic conditions while the (2)H labelled ISs and their analytes were slightly separated. An improved ability to compensate for ion suppression effects were observed when the (13)C labelled ISs were used. Furthermore, an UPLC-MS/MS method for determination of amphetamine and methamphetamine in urine using (13)C labelled ISs has been developed and validated. Unfortunately, there are few (13)C labelled ISs commercial available today. If more (13)C labelled ISs become commercial available they may well be the coming solution to minimize ion suppression/enhancement effects in LC-MS/MS analyses of drugs in biological samples. 相似文献
85.
F. F. Tisdall A. R. Ling J. H. Bushill A. C. Alport K. Ohmi L. Condorelli J. S. Sharpe K. Myrbäck R. V. Stanford A. H. M. Wheatley A. Mirkin S. J. Druskin W. Mestrezat R. Fabre Détrois K. Blühdorn Grete Genck A. Hirth A. Klotz G. de Toni P. Ronaund H. Kleinmann Leonia Kriss F. Lebermann B. Kramer Shun-Ichi Yoshimatsu C. H. Fiske G. Litarczek D. Olmer L. Payan J. Berthier und I. Gittleman 《Fresenius' Journal of Analytical Chemistry》1928,74(3-4):151-160
Ohne Zusammenfassung 相似文献
86.
Hellmut Fischer und Grete Leopoldi 《Fresenius' Journal of Analytical Chemistry》1940,119(5-6):161-188
Ohne Zusammenfassung 相似文献
87.
Dr. Grete Lasch 《Monatshefte für Chemie / Chemical Monthly》1913,34(10):1653-1664
Ohne Zusammenfassung 相似文献
88.
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90.