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  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Tetrahedron 29 (1973), S. 2323-2325 
    ISSN: 0040-4020
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Tetrahedron 30 (1974), S. 3519-3523 
    ISSN: 0040-4020
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0022-328X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    European Journal of Political Economy 8 (1992), S. 477-490 
    ISSN: 0176-2680
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Economics
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Biology and fertility of soils 23 (1996), S. 50-56 
    ISSN: 1432-0789
    Keywords: Agroforestry ; 15N ; Nitrogen fixation ; Phenolics ; 13C ; Tree fallows
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The natural abundance of 15N and 13C, conventional soil analyses, and biomass production by maize were used to study the influence of five tropical tree species on soils and their fertility. The experiment was conducted in Morogoro, Tanzania, to compare Cassia (Senna) siamea, Eucalyptus camaldulensis, E. tereticornis (all non-N2-fixing), Leucaena leucocephala, Prosopis chilensis (both N2-fixing), and a grass fallow. Maize biomass production, which was correlated with N uptake (P=0.001), was higher on soils from plots with 5-year-old Leucaena and Prosopis spp. compared to the grass fallow, while other tree species had less favourable effects on maize growth. The per cent N was higher in soil and δ15N of soil total N was lower under Prosopis sp. compared to soil under other tree species, which suggests an input from N2 fixation by Prosopis sp. A transfer of fixed N to maize or to understorey grass species was, however, not indicated by the 15N natural abundance. Prosopis sp. contributed more C to the soil than the other four tree species; the difference in δ13C between soils from Prosopis sp. plots and from grass fallow plots showed that the tree contributed 11% to the total C of the soil over a period of 8 years. The leaves of the N2-fixing species had a low ratio of lignin+phenols to N, and maize growth was negatively correlated with this parameter. The Eucalyptus spp. had leaves with a high lignin+phenols to N ratio, contributed very little C to the soil, and lowered the soil pH.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Biology and fertility of soils 23 (1996), S. 50-56 
    ISSN: 1432-0789
    Keywords: Key words Agroforestry ; 15N ; Nitrogen fixation ; Phenolics ; 13C ; Tree fallows
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The natural abundance of 15N and 13C, conventional soil analyses, and biomass production by maize were used to study the influence of five tropical tree species on soils and their fertility. The experiment was conducted in Morogoro, Tanzania, to compare Cassia (Senna) siamea, Eucalyptus camaldulensis, E. tereticornis (all non-N2-fixing), Leucaena leucocephala, Prosopis chilensis (both N2-fixing), and a grass fallow. Maize biomass production, which was correlated with N uptake (P=0.001), was higher on soils from plots with 5-year-old Leucaena and Prosopis spp. compared to the grass fallow, while other tree species had less favourable effects on maize growth. The per cent N was higher in soil and δ15N of soil total N was lower under Prosopis sp. compared to soil under other tree species, which suggests an input from N2 fixation by Prosopis sp. A transfer of fixed N to maize or to understorey grass species was, however, not indicated by the 15N natural abundance. Prosopis sp. contributed more C to the soil than the other four tree species; the difference in δ13C between soils from Prosopis sp. plots and from grass fallow plots showed that the tree contributed 11% to the total C of the soil over a period of 8 years. The leaves of the N2-fixing species had a low ratio of lignin+phenols to N, and maize growth was negatively correlated with this parameter. The Eucalyptus spp. had leaves with a high lignin+phenols to N ratio, contributed very little C to the soil, and lowered the soil pH.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Fresenius' Zeitschrift für analytische Chemie 109 (1937), S. 436-441 
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1615-6102
    Keywords: Extracellular matrix ; Tissue culture ; Epithelium ; Mammary gland ; EHS tumour ; Lumen formation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The nature of the substratum profoundly influences the growth and function of epithelia in tissue culture. “Mammospheres”, hollow spherical structures, develop when epithelial clusters are plated on a biomatrix derived from the Engelbreth-Holm-Swarm murine tumour (EHS matrix). Morphologic examination of mammosphere development demonstrates that morphogenesis is a two stage process. Over the first 48 h the cells aggregate into spheres, drawing the matrix up and over themselves to become buried within the material. Changes in matrix morphology emphasize the importance of the quasi-fluid nature of the substratum on which the cells are plated. Lumen formation ensues over the next 2 to 5 days as the cells, polarized by basal contact with the matrix, differentiate. They form tight junctions at their apical borders and synthesize milk proteins, secreting caseins into the enlarging interior cavity and transferrin from their basal surfaces into the medium. These experiments demonstrate that the physical properties of the EHS matrix allow epithelial cells to develop the cuboidal shape necessary for secretory activity.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 620 (1994), S. 1264-1270 
    ISSN: 0044-2313
    Keywords: 1,3-Di-tert-butyl-2,2-dimethyl-4,4-dichalcogen-1,3,2,4-diazasilagermetidines and -stannetidines ; digerma- and distanna- dichalcogencyclobutanes ; oxydation of germylenes and stannylenes by chalcogens ; reaction of a bis(amino)germylene with amine-N-oxide ; X-ray structure analyses ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthesis and Structures of Bis(amino)germa and -stanna ChalcogenidesThe cyclic bis(amino)germylene 1 and the -stannylene 2 react with elemental S, Se and Te to yield oxydation products of the general formula Me2Si(NtBu)2MEl2M(NtBu)2SiMe2 (M = Ge, El = S (4), El = Se (5), El = Te (6); M = Sn, El = Se (9), El = Te (10)). As may be deduced from X-ray structures (4, 5, 6, 9, 10) all compounds show similar central skeletons: the three spirocyclicly connected four-membered rings SiN2M (2x) and MEl2M are oriented in an orthogonal way to oneanother. The germanium and the tin atoms thus are in a distorted tetrahedral coordination while the chalcogen atoms only have two neighbours in acute angles. If 1 is allowed to react with trimethylamine-N-oxide, the oxygen is transferred to germanium and [Me2Si(NtBu)2GeO]3 (3) is formed. Contrarily to the other compounds 3 can be described as a trimer. There is a central almost planar Ge3O3 six-membered ring, the germanium atoms serving as spiro-cyclic centres to three GeN2Si four-membered rings (X-ray structure of 3). In the central four-membered rings of 4, 5, 6, 9 and 10 no transanular bonding between the chalcogen atoms have to be considered although these atoms have small distances to oneanother. The mean M-El distances have been found to be: Ge—O 1.762(5), Ge—S 2.226(3), Ge—Se 2.363(3), Ge—Te 2.592(5), Sn—Se 2.536(3), Sn—Te 2.741(3) Å.
    Notes: Das cyclische Bis(amino)germylen 1 sowie das -stannylen 2 reagieren mit elementarem S, Se oder Te zu Oxidationsprodukten der allgemeinen Formel Me2Si(NtBu)2MEl2M(NtBu)2SiMe2 (M = Ge, El = S (4), El = Se (5), El = Te (6); M = Sn, El = Se (9), El = Te (10)). Nach Röntgenstrukturanalysen (4, 5, 6, 9, 10) bestehen alle Verbindungen aus drei spirocyclisch verbundenen Vierringen SiN2M (2x) und MEl2M, die weitgehend orthogonal zueinander stehen. Die Germanium- und Zinnatome sind folglich verzerrt tetraedrisch koordiniert, während die Chalkogenatome jeweils zwei Nachbaratome unter spitzem Winkel besitzen. Setzt man 1 mit Trimethylamin-N-oxid um, so wird der Sauerstoff an das Germanium übergeben unter Bildung von [Me2Si(NtBu)2GeO]3 (3). Im Gegensatz zu den anderen Verbindungen kann 3 formal als Trimeres aufgefaßt werden: an einem zentralen weitgehend planaren Ge3O3-Sechsring sind spirocyclisch an den Germaniumatomen jeweils drei GeN2Si Vierringe geknüpft (Röntgenstrukturanalyse von 3). In den zentralen Vierringen von 4, 5, 6, 9 und 10 bestehen keine transanularen Wechselwirkungen zwischen den Chalkogenatomen, obwohl diese einen kurzen Abstand untereinander aufweisen. Die gemittelten M—El Abstände betragen: Ge—O 1,762(5), Ge—S 2,226(3), Ge—Se 2,363(3), Ge—Te 2,592(5), Sn—Se 2,536(3), Sn—Te 2,741(3) Å.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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