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Fu-Peng Wu Yang Yuan Claas Schünemann Prof. Dr. Paul C. J. Kamer Prof. Dr. Xiao-Feng Wu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(26):10537-10541
The borocarbonylative coupling of unactivated alkenes with alkyl halides remains a challenge. In this communication, a Cu-catalyzed borocarbonylative coupling of unactivated alkenes with alkyl halides for the synthesis of β-boryl ketones has been developed. A broad range of β-boryl ketone derivatives was prepared in moderate to excellent yields with complete regioselectivity. 相似文献
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Sebastian Brückner Enrique Barrigón Oliver Supplie Peter Kleinschmidt Anja Dobrich Claas Löbbel Ignacio Rey‐Stolle Henning Döscher Thomas Hannappel 《固体物理学:研究快报》2012,6(4):178-180
Ge(100) substrates essential for subsequent III–V integration were studied in the hydrogen ambient of a metalorganic vapor phase epitaxy reactor. We confirmed thermal oxide and carbon removal by X‐ray photoelectron spectroscopy, characterized the (2 × 1)/(1 × 2) surface reconstruction by low energy electron diffraction, and employed reflection anisotropy spectroscopy for optical in situ analysis. Our Ge(100) spectra de‐ viate from reference data of clean surfaces prepared in ultra‐high vacuum, most probably due to the presence of hydrogen bonds. The observation was correlated with Fourier‐transform infrared spectroscopy showing coupled H–Ge–Ge–H stretch modes associated with a monohydride termination of the Ge(100) surface. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Summary Seven aminoalkanols were separated after their derivatization to fluorescent salicylaldehydeazomethine diphenylboron chelates by high-performance liquid chromatography. Separation is performed on HPLC column Si 60 with mixtures of dichloromethane/acetone using fluorimetric detection. The peak areas are linear-proportional to the concentration in the range between 6·10–6 and 1·10–4 mol/l. With the determination of 6·10–5 mol/l derivatized 2-amino-1-ethanol the relative standard deviation was 0.03 (3.0%). The smallest detectable amount of one of the aminoalkanols ranged from 3.3 to 8.8 ng dissolved in the injected volume of 50 l.
Boron Chelates and Boron Metal Chelates, Part XVI. For Part XV see ref. [1]
Dedicated to Prof. Dr. H. Monien on the occasion of his 60th birthday 相似文献
Vorsäulen-Fluorescenz-Derivatisierung in der Hochleistungsflüssigkeits-Chromatographie mit 2,2-Diphenyl-1-oxa-3-oxonia-2-boratanaphthalin (DOOB): Bestimmung von Aminoalkanolen
Zusammenfassung Sieben Aminoalkanole werden nach der Derivatisierung zu fluorescierenden Salicylaldehydazomethin-diphenylborchelaten hochleistungsflüssigkeits-chromatographisch getrennt. Die Trennung erfolgt auf einer HPLC-Säule Si 60 mit Dichlormethan/Aceton-Gemischen und fluorimetrischer Detektion. Die Peakflächen sind im Konzentrationsbereich von 6·10–6 bis 1·10–4 mol/l linear proportional. Bei der Bestimmung von 6 · 10–5 mol/l derivatisiertem 2-Amino-1-ethanol wurde die relative Standardabweichung zu 0,03 (3,0%) berechnet. Die kleinste bestimmbare Menge eines der Aminoalkanole liegt im Bereich zwischen 3,3 und 8,8 ng gelöst im Injektionsvolumen von 50 l.
Boron Chelates and Boron Metal Chelates, Part XVI. For Part XV see ref. [1]
Dedicated to Prof. Dr. H. Monien on the occasion of his 60th birthday 相似文献
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H. Monique H. Hurks Coby Out-Luiting Bert-Jan Vermeer Frans H. J. Claas A. Mieke Mommaas 《Photochemistry and photobiology》1997,66(1):76-81
Abstract— The mixed epidermal cell lymphocyte reaction (MECLR) is a commonly used method to study the immunomodulatory effects of UV radiation. The in vitro action spectrum for the MECLR showed that the UV-induced suppression of the MECLR responses is associated with UV-induced DNA damage. To investigate whether in vivo DNA damage also leads to the abrogation of the MECLR, in situ action spectra were made for the MECLR and the induction of thymine dimers (T<>T). Human skin, obtained from plastic surgery, was exposed to monochromatic light of 254, 297, 302 and 312 nm. After irradiation, epidermal cells were isolated and used as stimulator cells in the MECLR or processed for flow cytometric detection of T<>T. On the basis of dose-response curves for each wavelength, the action spectra for suppression of the MECLR and the induction of T<>T were calculated. These spectra showed close similarities, suggesting that, also in situ, UV-induced DNA damage is involved in the UV-induced suppression of the MECLR. Both action spectra showed a small decline from 254 nm to 302 nm, followed by a steep decline to 312 nm. These data show that, in situ, UVC can efficiently induce DNA damage and modulate cutaneous immune responses. 相似文献
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H. M. H. Hurks C. Out-Luiting R. G. Van der Molen B. J. Vermeer F. H. J. Claas A. M. Mommaas 《Photochemistry and photobiology》1997,65(4):616-621
Abstract— Cis -urocanic acid (UCA), formed in the stratum corneum by UV irradiation of trans -UCA has been proposed as a mediator of UV-induced immunosuppression in the skin. In this study, we examined the in vitro effect of cis -UCA (6-100 μg/mL) on the human mixed lymphocyte reaction (MLR) and the mixed epidermal cell lymphocyte reaction (MECLR). Addition of cis -UCA (purified or in a mixture with trans -UCA) did not affect the MLR but was able to induce a 20% suppression of the MECLR responses. Because this effect of cis -UCA on the MECLR was not as strong as could be expected from previous in vivo results, we designed a set of experiments in order to enhance the in vitro immunosuppressive capacity of cis -UCA. Firstly, we preincubated epidermal cells with UCA (50 u.g/mL) for 3 or 6 days before culture in the MECLR because in vivo repeated UV exposure can lead to a photostationary state, where cis -UCA may be present for several weeks. This pretreatment with cis-UCA resulted in a maximal decrease of the MECLR responses of 27%, whereas trans -UCA had no effect. Secondly, we investigated whether UVB irradiation of epidermal cells could make cells more sensitive to cis -UCA. However, addition of trans- or cis -UCA did not potentiate the reduced alloac-tivating capacity of UVB-irradiated cells. Finally, we examined the possibility of a synergistic effect of cis -UCA with histamine. Addition of histamine suppressed the MLR and MECLR responses, but neither cis - nor trans -UCA were able to modulate this decrease. We conclude that cis -UCA can partly downregulate the human MECLR but not the MLR. The mechanism involved in this differential downregulation is not known. In this respect it is striking that cis -UCA does not potentiate the UVB- or histamine-induced suppression of the MECLR. 相似文献
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Surprisingly Different Reaction Behavior of Alkali and Alkaline Earth Metal Bis(trimethylsilyl)amides toward Bulky N‐(2‐Pyridylethyl)‐N′‐(2,6‐diisopropylphenyl)pivalamidine
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Diana Kalden Ansgar Oberheide Dr. Claas Loh Dr. Helmar Görls Dr. Sven Krieck Prof. Dr. Matthias Westerhausen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(31):10944-10959
N‐(2,6‐Diisopropylphenyl)‐N′‐(2‐pyridylethyl)pivalamidine (Dipp‐N=C(tBu)‐N(H)‐C2H4‐Py) ( 1 ), reacts with metalation reagents of lithium, magnesium, calcium, and strontium to give the corresponding pivalamidinates [(tmeda)Li{Dipp‐N=C(tBu)‐N‐C2H4‐Py}] ( 6 ), [Mg{Dipp‐N=C(tBu)‐N‐C2H4‐Py}2] ( 3 ), and heteroleptic [{(Me3Si)2N}Ae{Dipp‐N=C(tBu)‐N‐C2H4‐Py}], with Ae being Ca ( 2 a ) and Sr ( 2 b ). In contrast to this straightforward deprotonation of the amidine units, the reaction of 1 with the bis(trimethylsilyl)amides of sodium or potassium unexpectedly leads to a β‐metalation and an immediate deamidation reaction yielding [(thf)2Na{Dipp‐N=C(tBu)‐N(H)}] ( 4 a ) or [(thf)2K{Dipp‐N=C(tBu)‐N(H)}] ( 4 b ), respectively, as well as 2‐vinylpyridine in both cases. The lithium derivative shows a similar reaction behavior to the alkaline earth metal congeners, underlining the diagonal relationship in the periodic table. Protonation of 4 a or the metathesis reaction of 4 b with CaI2 in tetrahydrofuran yields N‐(2,6‐diisopropylphenyl)pivalamidine (Dipp‐N=C(tBu)‐NH2) ( 5 ), or [(thf)4Ca{Dipp‐N=C(tBu)‐N(H)}2] ( 7 ), respectively. The reaction of AN(SiMe3)2 (A=Na, K) with less bulky formamidine Dipp‐N=C(H)‐N(H)‐C2H4‐Py ( 8 ) leads to deprotonation of the amidine functionality, and [(thf)Na{Dipp‐N=C(H)‐N‐C2H4‐Py}]2 ( 9 a ) or [(thf)K{Dipp‐N=C(H)‐N‐C2H4‐Py}]2 ( 9 b ), respectively, are isolated as dinuclear complexes. From these experiments it is obvious, that β‐metalation/deamidation of N‐(2‐pyridylethyl)amidines requires bases with soft metal ions and also steric pressure. The isomeric forms of all compounds are verified by single‐crystal X‐ray structure analysis and are maintained in solution. 相似文献