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  • Chemistry  (7)
  • Cell & Developmental Biology  (2)
  • Anaerobiosis
  • Nuclear Reactions
  • 1995-1999  (7)
  • 1965-1969  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    Thoracic structure of the adult mecopteron, Bittacus strigosus Hagen (Mecoptera: Bittacidae) (1968)
    New York, NY : Wiley-Blackwell
    Journal of Morphology 126 (1968), S. 199-210 
    Details
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The thoracic skeleton and musculature of the adult bittacid mecopteron Bittacus strigosus Hagen is described. In its musculature, Bittacus shows only moderate differences from two panorpids (Neopanorpa, Panorpa) that have been studied by Maki ('38) and by Hasken ('39), respectively. Not only are these three genera much alike in their musculature generally, but in all of them, and in Boreus (Boreidae) too, the mesothorax is extremely similar to the metathorax. Functional emphasis (for flight) on either of the two pterothoracic segments has not appeared among neuropteroid insects at the metopteran evolutionary level.Although the “snowfleas” of the genus Boreus possess striking alterations of pterothoracic structure in comparison with other mecopterons (Füller, '54, '55), these are related to their unusual activities and have not, to any great extent, affected the two pterothoracic segments differentially.In terms of thoracic specialization, the overall mecopteran pattern represents a stage somewhat advanced beyond the primitive conditions exemplified by the Megaloptera and certain coleopterous larvae, but one that is in general less highly developed than is charatceristic of such neuropteroid orders as the Siphonaptera, Diptera, Trichoptera, and Lepidoptera.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jmor.1051260204
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  • 2
    Electronic Resource
    Electronic Resource
    Propylene polymerization with catalysts containing divalent titanium (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 2645-2652 
    Details
    ISSN: 0887-624X
    Keywords: propylene polymerization ; titanium oxidation state ; hydrogen activation ; catalyst decay ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The behavior in propylene polymerization of divalent titanium compounds of type [η6-areneTiAl2Cl8], both as such and supported on activated MgCl2, has been studied and compared to that of the simple catalyst MgCl2/TiCl4. Triethylaluminium was used as cocatalyst. The Ti-arene complexes were active both in the presence and in the absence of hydrogen, in contrast to earlier reports that divalent titanium species are active for ethylene but not for propylene polymerization. 13C-NMR analysis of low molecular weight polymer fractions indicated that the hydrogen activation effect observed for the MgCl2-supported catalysts should be ascribed to reactivation of 2,1-inserted (“dormant”) sites via chain transfer, rather than to (re)generation of active trivalent Ti via oxidative addition of hydrogen to divalent species. Decay in activity during polymerization was observed with both catalysts, indicating that for MgCl2/TiCl4 catalysts decay is not necessarily due to overreduction of Ti to the divalent state during polymerization. In ethylene polymerization both catalysts exhibited an acceleration rather than a decay profile. It is suggested that the observed decay in activity during propylene polymerization may be due to the formation of clustered species that are too hindered for propylene but that allow ethylene polymerization. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2645-2652, 1997
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Regio- and stereospecificity in propene polymerization with MgCl2-supported Ziegler-Natta catalysts: effects of hydrogen and the external donor (1995)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 196 (1995), S. 1431-1437 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Investigation of the effects of hydrogen and different external donors on the stereoregularity and chain-end distribution of polypropylene prepared using MgCl2/TiCl4/phthalate ester-AlEt3-alkoxysilane catalyst systems has not only confirmed the importance of regiospecificity in relation to hydrogen activation but has also indicated a significant effect of stereospecificity. Alkoxysilanes giving high isospecificity also give high molecular weight polypropylene. Polymer stereoregularity also increases with increasing hydrogen concentration in polymerization. These effects indicate that not only regioirregular but also stereoiregular insertion slows down chain propagation. In each case the probability of chain transfer with hydrogen is higher than that following a stereoregular insertion, and in each case chain transfer with hydrogen leads to the regeneration of isospecific propagation.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1995.021960506
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  • 4
    Electronic Resource
    Electronic Resource
    Isotactic 1-butene polymerization promoted by C2-symmetric metallocene catalysts (1997)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 198 (1997), S. 1257-1270 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 1-Butene polyinsertion promoted by two typical C2-symmetric zirconocene catalysts (i.e. rac-ethylenebis(1-indenyl)ZrCl2 (1) and rac-dimethylsilylbis(1-indenyl)ZrCl2) (2) was investigated under both hydrooligomerization and polymerization conditions and compared with that of propene. It was found that, in spite of a similar regiospecificity for the two monomers, the fraction of “dormant” sites is higher in 1-butene polymerization, as a result of a (much) lower reactivity of a 2,1 last-inserted unit. Accordingly, in the investigated cases, 2,1 units of 1-butene were not incorporated in the growing chains but either isomerized to 4,1 units or remained at the chain end until they underwent chain transfer via β-hydrogen elimination. Experimental evidence is also presented of an epimerization reaction of the growing poly(1-butene) chain with a 1,2 last-inserted unit, leading to a decrease of polymer stereoregularity with decreasing monomer concentration.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1997.021980427
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  • 5
    Electronic Resource
    Electronic Resource
    Polymerization of 3-methyl-1-butene promoted by metallocene catalysts (1996)
    Weinheim : Wiley-Blackwell
    Macromolecular Rapid Communications 17 (1996), S. 589-597 
    Details
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 3-Methyl-1-butene was polymerized in the presence of a number of homogeneous metallocene catalysts (co-catalyst methylalumoxane). Contrary to literature reports, it was found that even the simplest C2-symmetric metallocenes promote the isotactic polymerization of this monomer with reasonable productivities. Quite surprisingly, a prevailingly isotactic polymer was also obtained in the presence of Cs-symmetric metallocenes, which are instead syndiotactic-specific in propene polymerization.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/marc.1996.030170813
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  • 6
    Electronic Resource
    Electronic Resource
    Aspects of hydrogen activation in propene polymerization using MgCl2/TiCl4/diether catalysts (1996)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 197 (1996), S. 2501-2510 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 13C NMR analysis of the chain-end distribution of poly(propylenes) prepared using the highly active catalyst system MgCl2/TiCl4/diether - AlEt3 has revealed particularly high proportions of butyl chain-ends in polymers prepared at relatively low hydrogen pressures. This indicates that the high sensitivity of this type of catalyst to hydrogen, both with respect to catalyst activity and polymer molecular weight, can largely be ascribed to chain transfer following regioirregular (2,1-) insertion, such an insertion leading to a species having low activity in chain propagation. Isotactic stereoregularity increases with increasing hydrogen pressure, indicating that a stereoirregular insertion may also slow down the chain propagation, again leading to chain transfer and resulting in the conversion of a potential chain defect into an isobutyl chain-end. Analysis of highly isotactic polymer fractions isolated via temperature rising elution fractionation revealed the presence of both butyl and isobutyl chain-ends, indicating that even the most highly stereo-specific sites in MgCl2-supported catalysts are not totally regiospecific.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1996.021970814
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  • 7
    Electronic Resource
    Electronic Resource
    Propene polymerization with MgCl2-supported catalysts: effects of using a diether as external donor (1997)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 198 (1997), S. 1181-1188 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 13C NMR analysis of poly(propylene) fractions of different tacticity, obtained using a catalyst system of type MgCl2/TiCl4/diisobutyl phthalate - AlEt3 - diether, has provided further evidence that the active species in this system are similar to those in which the ether is used as “internal” rather than “external” donor. Chain-end analysis of relatively low molecular weight polymer fractions indicated, for polymers of similar molecular weight, similar proportions of butyl-terminated chain-ends, indicative of chain transfer with hydrogen following regioirregular (2,1-) insertion. The relatively high hydrogen response of diether-containing catalyst systems can therefore be largely ascribed to this phenomenon, irrespective of whether the diether is used as internal or external donor. At relatively low hydrogen concentrations, chain transfer to hydrogen takes place predominantly after the occasional secondary insertion, while the additional presence of vinylidene chain-ends in certain xylene-soluble fractions indicates that chain transfer via β-H transfer takes place mainly after primary insertion.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1997.021980419
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of polymerization temperature on the microtacticity of isotactic poly(propylene) prepared using heterogeneous (MgCl2-supported) Ziegler-Natta catalysts (1998)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 199 (1998), S. 1873-1878 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A study of the effect of polymerization temperature on the microtacticity of poly(propylene) prepared using various MgCl2-supported catalysts has shown that, in almost all cases, an increase in temperature leads not only to higher proportions of isotactic polymer but also to increased stereoregularity of the isotactic fraction. The results indicate a greater relative increase in productivity, with increasing temperature, for highly isospecific as opposed to moderately isospecific centres. It is suggested that easier propagation after the occasional regioirregular (2,1-) insertion may contribute to this effect.
    Additional Material: 2 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Synthesis of antibody by spleen cells after exposure to kiloroentgen doses of ionizing radiationResearch jointly sponsored by the National Cancer Institute, and the U.S. Atomic Energy Commission under contract with the Union Carbide Corporation. (1967)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 69 (1967), S. 355-366 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Mouse spleen cells in diffusion chambers were studied in an effort to assess the radiation survival curves of lymphoid cells during the different serological phases of immune response and to characterize morphologically and metabolically these radiation-resistant cells. The results showed that the capacity of immunocompetent progenitor cells to proliferate and differentiate into antibody-synthesizing cells was highly sensitive to x-irradiation. Their fully differentiated progenies, which were made up mainly of mature plasma cells, were resistant in that they were able to synthesize antibody effectively for as long as several days after their exposure to radiation doses up to 10,000 R.As a result of these studies, a method with a high recovery yield was devised for obtaining a highly purified preparation of dispersed monospecific antibody-synthesizing cells. This was done by simply exposing primed spleen cells to 10,000 R at the end of the log phase of response and harvesting the culture several days later.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1040690312
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