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1.
E. C. Hopewell M. J. Barlow J. E. Drew Y. C. Unruh Q. A. Parker M. J. Pierce P. A. Crowther C. Knigge S. Phillipps A. A. Zijlstra 《Monthly notices of the Royal Astronomical Society》2005,363(3):857-866
We report the discovery of five massive Wolf–Rayet (WR) stars resulting from a programme of follow-up spectroscopy of candidate emission-line stars in the Anglo-Australian Observatory United Kingdom Schmidt Telescope (AAO/UKST) Southern Galactic Plane Hα survey. The 6195–6775 Å spectra of the stars are presented and discussed. A WC9 class is assigned to all five stars through comparison of their spectra with those of known late-type WC stars, bringing the known total number of Galactic WC9 stars to 44. Whilst three of the five WC9 stars exhibit near-infrared (NIR) excesses characteristic of hot dust emission (as seen in the great majority of known WC9 stars), we find that two of the stars show no discernible evidence of such excesses. This increases the number of known WC9 stars without NIR excesses to seven. Reddenings and distances for all five stars are estimated. 相似文献
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David Drew Houghton 《Meteorology and Atmospheric Physics》1962,12(4):407-425
Summary The large scale three-dimensional diabatic heating in the atmosphere is computed at 12 isentropic surfaces for a particular twelve hour time period. Using a method due toErtel, the continuity equation is combined with the equations of motion to give an explicit relation between diabatic heating and changes in potential vorticity and stability along isentropic surface trajectories. The results are barely of useful accuracy and reliability and this only under favorable conditions. The distribution of diabatic heating is qualitatively reasonable in the regions near the tropopause, close to the ground, above a cloud or moist layer, and within an area of general condensation. Errors and approximations make the computed values completely unreliable in areas of large anticyclonic vorticity or large baroclinity. Comparison of magnitudes with those computed from rainfall observations and with those measured directly at the earth's surface shows agreement in sign and within a factor of three in the areas of best data. The results emphasize that there are regions and periods where diabatic heating in the free atmosphere may be important in controlling atmospheric behavior. Sample calculations in one of these regions using values of diabatic heating computed by this study illustrate that this process is of comparable importance with the adiabatic process in determining vertical velocity.
With 7 Figures 相似文献
Zusammenfassung Die großräumige nichtadiabatische Erwärmung der Atmosphäre in 12 isentropen Flächen während eines 12stündigen Zeitabschnittes wird berechnet. Unter Verwendung einer Methode vonErtel liefert eine Kombination der Kontinuitätsgleichung mit den Bewegungsgleichungen eine explizite Beziehung zwischen der nichtadiabatischen Erwärmung, der potentiellen Vorticity und der Stabilität entlang der isentropen Trajektorien. Das Resultat ist von beschränkter Genauigkeit — und auch dies nur unter günstigen Bedingungen. Qualitativ brauchbare Verteilungen der nichtadiabatischen Erwärmung erhält man nahe der Tropopause, in Bodennähe, über einer Schicht von Wolken oder feuchter Luft und innerhalb der Zonen mit verbreiteter Kondensation. In Gebieten mit großer antizyklonaler Vorticity oder großer Baroklinität werden die berechneten Werte infolge von Meß- und Approximationsfehlern völlig ungenau. In den Gebieten mit optimalen Voraussetzungen stimmen die berechneten Werte mit den aus Niederschlagsmessungen abgeleiteten oder am Boden direkt beobachteten im Vorzeichen und innerhalb eines Faktors von 3 überein. Die Ergebnisse der vorliegenden Untersuchung weisen erneut darauf hin, daß in manchen Gebieten bzw. Zeitabschnitten das Verhalten der freien Atmosphäre durch nichtadiabatische Erwärmung wesentlich beeinflußt sein kann. Stichprobenweise Berechnungen für eines dieser Gebiete zeigen, daß die theoretisch ermittelte nichtadiabatische Erwärmung für die resultierende Vertikalgeschwindigkeit der Luft quantitativ von ähnlicher Bedeutung ist wie der adiabatische Prozeß.
Résumé L'auteur a calculé le réchauffement non adiabatique, à grande échelle, de l'atmosphère à 12 niveaux isentropes pendant un intervalle de 12 heures. Une méthode établie parErtel combine l'équation de continuité et les équations de mouvement et aboutit à une relation explicite entre le réchauffement non adiabatique, la vorticity potentielle et la stabilité le long de trajectoires isentropes. Le résultat n'a qu'une exactitude approchée, et cela dans des conditions favorables seulement. On obtient une répartition utilisable du réchauffement non adiabatique au voisinage de la tropopause, du sol, au-dessus d'une couche de nuages ou d'air humide, ainsi qu'à l'intérieur des zones à forte condensation. Dans les régions à grande vorticity anticyclonique et à grande baroclinité, les valeurs calculées deviennent tout à fait inexactes par suite d'une approximation insuffisante et d'erreurs de mesure. Dans les régions à conditions favorables par contre, les valeurs calculées correspondent à celles que l'on peut tirer de la mesure des précipitations ou de celles que l'on mesure au sol, cela au signe et à un facteur 3 près. Le résultat de cette étude montre à nouveau que dans certaines régions ou certains laps de temps l'état de l'atmosphère peut être notablement conditionné par un réchauffement non adiabatique. Des épreuves faites pour l'une de ces régions montrent que le réchauffement non adiabatique obtenu par calcul est quantitativement aussi important pour la vitesse verticale résultante de l'air que le processus adiabatique.
With 7 Figures 相似文献
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Multi-proxy evidence of long-term changes in ecosystem structure in a Danish marine estuary, linked to increased nutrient loading 总被引:3,自引:0,他引:3
Marianne Ellegaard Annemarie L. Clarke Nina Reuss Simon Drew Kaarina Weckstrm Stephen Juggins N. John Anderson Daniel J. Conley 《Estuarine, Coastal and Shelf Science》2006,68(3-4):567
This paper presents a study of changes in eutrophication over the past 100 years in a fertile estuary. The Danish estuary Mariager Fjord is a long, narrow sill-fjord with a permanently anoxic basin. In 1997 anoxia spread from the basin to the entire inner estuary, killing almost all eukaryotes and prompting debate on the causes. This paper reports a multi-proxy survey of 210Pb-dated sediment cores from the anoxic basin. Analyses of diatoms, dinoflagellates, pigments and geochemical proxies were used to determine changes in ecosystem structure over the past 100 years. The aim was to establish ‘base-line conditions’, for management purposes, of the biological structure prior to 1900, and to examine possible causes of changes observed. Geochemical proxies total nitrogen (TN), total carbon (TC) and biogenic silica (BSi) were consistently high throughout the sediment record. Increased concentrations of pigments and natural isotopes (δ13C, δ15N) suggested increasing production and nutrient loading. The main changes in the biological proxies occurred between 1915 and the 1940s, and indicated that the estuary has been somewhat eutrophic since 1900, but that the eutrophication process increased over the past 100 years. A reconstruction of TN concentration by a diatom-based transfer function supports this interpretation, with inferred TN ca. 1900 around 60 μmol l−1, and an increase in TN concentration over the past century to ca. 130 μmol l−1 by 1995. Inferred TN decreased to ca. 100 μmol l−1 by 2001, similar to present day monitoring data. 相似文献
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Two widely-used techniques to estimate the volume of remaining oil and gas resources are discovery process modeling and geologic assessment. Both were used in a recent national assessment of oil and gas resources of the United States. Parallel estimates were obtained for 27 provinces. Geological-based estimates can typically see into areas not available to discovery process models (that is areas with little or no exploration history) and thus, on average, yield higher estimates. However, a linear relation does exist between the mean estimates obtained from these two methods. In addition, other variables were found in a multiple regression model that explained much of the difference. Thus, it is possible to perform discovery process modeling and adjust the estimates to yield results that might be expected from geological-based assessments. 相似文献
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