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排序方式： 共有453条查询结果，搜索用时 31 毫秒
421.
Schipper J Chanson JS Chiozza F Cox NA Hoffmann M Katariya V Lamoreux J Rodrigues AS Stuart SN Temple HJ Baillie J Boitani L Lacher TE Mittermeier RA Smith AT Absolon D Aguiar JM Amori G Bakkour N Baldi R Berridge RJ Bielby J Black PA Blanc JJ Brooks TM Burton JA Butynski TM Catullo G Chapman R Cokeliss Z Collen B Conroy J Cooke JG da Fonseca GA Derocher AE Dublin HT Duckworth JW Emmons L Emslie RH Festa-Bianchet M Foster M Foster S Garshelis DL Gates C Gimenez-Dixon M Gonzalez S 《Science (New York, N.Y.)》2008,322(5899):225-230
Knowledge of mammalian diversity is still surprisingly disparate, both regionally and taxonomically. Here, we present a comprehensive assessment of the conservation status and distribution of the world's mammals. Data, compiled by 1700+ experts, cover all 5487 species, including marine mammals. Global macroecological patterns are very different for land and marine species but suggest common mechanisms driving diversity and endemism across systems. Compared with land species, threat levels are higher among marine mammals, driven by different processes (accidental mortality and pollution, rather than habitat loss), and are spatially distinct (peaking in northern oceans, rather than in Southeast Asia). Marine mammals are also disproportionately poorly known. These data are made freely available to support further scientific developments and conservation action. 相似文献
422.
Balogh A Dougherty MK Forsyth RJ Southwood DJ Smith EJ Tsurutani BT Murphy N Burton ME 《Science (New York, N.Y.)》1992,257(5076):1515-1518
The Jovian flyby of the Ulysses spacecraft presented the opportunity to confirm and complement the findings of the four previous missions that investigated the structure and dynamics of the Jovian magnetosphere and magnetic field, as well as to explore for the first time the high-latitude dusk side of the magnetosphere and its boundary regions. In addition to confirming the general structure of the dayside magnetosphere, the Ulysses magnetic field measurements also showed that the importance of the current sheet dynamics extends well into the middle and outer magnetosphere. On the dusk side, the magnetic field is swept back significantly toward the magnetotail. The importance of current systems, both azimuthal and field-aligned, in determining the configuration of the field has been strongly highlighted by the Ulysses data. No significant changes have been found in the internal planetary field; however, the need to modify the external current densities with respect to previous observations on the inbound pass shows that Jovian magnetic and magnetospheric models are highly sensitive to both the intensity and the structure assumed for the current sheet and to any time dependence that may be assigned to these. The observations show that all boundaries and boundary layers in the magnetosphere have a very complex microstructure. Waves and wave-like structures were observed throughout the magnetosphere; these included the longest lasting mirror-mode wave trains observed in space. 相似文献
423.
W. G. Burton 《Potato Research》1968,11(4):249-265
Summary The external oxygen concentration in which the greatest number of buds started to grow at 10–20 C rose during the storage
season, from 2–4% in January to 14–23% in June. There was a similar rise in the concentration which was optimal for the rate
of sustained sprout growth, from 4–5% to 17–20%. 5% O2, which stimulated growth early in the storage season, caused marked suppression late in the season, this effect showing earlier
in tubers previously stored at 2 or 4 C than in those stored at 10 C. It is suggested that two effects of oxygen may be discernible,
involving an optimally anaerobic reversible metabolism of a growth inhibitor and an aerobic requirement for growth. The possibilities
are discussed that the enzyme system concerned in the former may be sulphydryl dependant, and that the direction of reaction
may show parallelism with sucrose accumulation in the tuber.
Zusammenfassung Der Beginn des Keimwachstums und das Ausmass der anschliessenden Entwicklung wurden in O2-Konzentrationen von 1–50% bestimmt, wobei der Rest der Atmosph?re aus N2 (kein CO2) bestand. Die interzellularen O2-Konzentrationen wurden entsprechend den verschiedenen Aussenkonzentrationen errechnet. Das Keimgewicht in Prozenten, die Anzahl der messbaren Keime (> 1 mm) und die durchschnittliche L?nge und Dicke des l?ngsten Keimes pro Knolle wurden notiert (Tabellen 1, 2 und 3), ebenso wurden die H?ufigkeitsverteilungen der verschiedenen Keiml?ngen in den Keimpopulationen (Tabellen 4, 5 und 6) zusammengestellt. In einer Versuchsserie wurde das weitere Wachstum des l?ngsten Keimes jeder Knolle in vier aufeinanderfolgenden Versuchen w?hrend der Lagerung gemessen (Abb. 1). Bei Knollen, die sich am Anfang eines Versuches offenbar noch in der Keimruhe befanden, begann das Wachstum in 5% O2 früher als in Luft Die ?ussere Sauerstoffkonzentration, in der die gr?sste Anzahl der Knospen bei 10–20 C zu wachsen begann, stieg w?hrend der Lagerungszeit von 2–4% im Januar auf 14–23% im Juni (Tabellen 2 und 3) an. Ahnlich stieg die Konzentration, die für die Schnelligkeit des ununterbrochenen Keimwachstums optimal war, von 4–5% auf 17–20% (Tabellen 2 und 3). Eine Konzentration von 5% O2, die das Wachstum w?hrend der Lagerung schon frühzeitig anregte, verursachte zu einem sp?teren Zeitpunkt eine deutliche Hemmung; diese Beeinflussung zeigte sich bei Knollen, die vorher bei 2 oder 4 C gelagert wurden, früher als bei solchen, bei denen die Lagertemperatur 10 C betrug (Tabelle 1). Es wird darauf hingewiesen, dass zwei Wirkungen des Sauerstoffes erkennbar sein dürften, n?mlich ein optimal anaerober reversibler Stoffwechsel eines Wachstumshemmstoffes sowie aerobe Voraussetzung für das Wachstum. Es werden die M?glichkeiten diskutiert, wonach bei der erstgenannten Wirkung das beteiligte Enzymsymstem von Sulphydryl abh?ngig w?re und die Reaktionsrichtung eine Parallelit?t zur Saccharoseakkumulation in der Knolle zeigen k?nne.
Résumé On a déterminé le début de la croissance du germe, et l'importance du développement subséquent dans des concentrations en O2 allant de 1–50%, la partie restante de l'atmosphère étant N2, le CO2 étant absent. On a calculé les concentrations intercellulaires en O2 correspondant aux différentes concentrations externes. On a enregistré le pourcentage du poids des germes, le nombre de germes mesurables (> 1 mm), la longueur moyenne et la largeur du plus long germe par tubercule (Tableau 1, 2 et 3) ainsi que la fréquence des distributions de la longueur des germes dans les populations de germes (Tableaux 4, 5 et 6). Dans un essai on a mesuré la progression de la croissance du germe le plus long sur chaque tubercule, dans quatre observations successives pendant la période de stockage (Fig. 1). Chez les tubercules qui apparemment étaient encore dormants au début de l'expérience, la croissance démarrait plus t?t dans 5% O2 que dans l'air. La concentration externe en oxygène dans laquelle le plus grand nombre de bourgeons commen?aient à se développer à 10–20 C augmentait pendant la période de stockage de 2–4% en janvier à 14–23% en juin (Tableaux 2 et 3). Il y avait une progression semblable dans la concentration optimale pour la vitesse de croissance soutenue du germe, de 4–5% à 17–20% (Tableaux 2 et 3). Le taux de 5% O2, qui stimule le développement précoce pendant la période de stockage, cause une suppression marquée tard dans la saison, cet effet se marquant plus t?t chez les tubercules préalablement emmagasinés à 2 ou 4 C que chez ceux emmagasinés à 10 C (Tableau 1). L'auteur suggère qu'on peut discerner deux effets de l'oxygène, comprenant un métabolisme réversible idéalement anaérobie d'un inhibiteur de croissance, et une exigence aérobie de croissance. Il examine les possibilités que le système d'enzymes concernées dans le premier effet puisse dépendre du sulphydril, et que la direction de la réaction puisse montrer un parallélisme avec l'accumulation de sucrose dans le tubercule.相似文献
424.
425.
Cytological abnormalities in the ovaries of triploid yellowtail flounder,Limanda ferruginea (Storer)
Abnormal oocytes were detected in the ovaries of triploid yellowtail flounder of three years of age. Triploidy in these females had been induced artificially by hydrostatic pressure shock. Binucleate oocytes were found in the ovaries of six different triploid females. These cells were always small and in a primary growth stage. Cytoplasmic vacuoles, presumed to be due to nucleoplasmic extrusion, was another abnormal feature observed in two primary growth oocytes, each seen in a separate female. The appearance of binucleate oocytes in triploid females, not previously noted in diploid yellowtail flounder, is proposed to be an ephemeral phenomenon associated with the triploid condition. 相似文献
426.
427.
P.R. Avery J. Burton J.L. Bromberek D.M. Seelig R. Elmslie S. Correa E.J. Ehrhart P.S. Morley A.C. Avery 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2014,28(2):538-546
Background
Canine T‐cell lymphoma (TCL) is conventionally considered an aggressive disease, but some forms are histologically and clinically indolent. CD4 TCL is reported to be the most common subtype of TCL. We assessed flow cytometric characteristics, histologic features when available, and clinical outcomes of CD4+ TCL to determine if flow cytometry can be used to subclassify this group of lymphomas.Objective
To test the hypothesis that canine CD4+ T‐cell lymphoma (TCL) is a homogeneous group of lymphomas with an aggressive clinical course.Animals
Sixty‐seven dogs diagnosed with CD4+ TCL by flow cytometry and treated at 1 of 3 oncology referral clinics.Methods
Retrospective multivariable analysis of outcome in canine CD4+ TCL including patient characteristics, treatment, and flow cytometric features.Results
The majority of CD4+ TCL were CD45+, expressed low class II MHC, and exhibited an aggressive clinical course independent of treatment regimen (median survival, 159 days). Histologically, CD4+ TCL were classified as lymphoblastic or peripheral T cell. Size of the neoplastic lymphocytes had a modest effect on both PFI and survival in this group. A small number of CD4+ TCL were CD45− and class II MHC high, and exhibited an apparently more indolent clinical course (median survival not yet reached).Conclusions and Clinical Importance
Although the majority of CD4+ TCL in dogs had uniform clinical and flow cytometric features and an aggressive clinical course, a subset had a unique immunophenotype that predicts significantly longer survival. This finding strengthens the utility of flow cytometry to aid in the stratification of canine lymphoma. 相似文献428.
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430.