全文获取类型
收费全文 | 1458篇 |
免费 | 62篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 59篇 |
大气科学 | 224篇 |
地球物理 | 381篇 |
地质学 | 517篇 |
海洋学 | 40篇 |
天文学 | 217篇 |
综合类 | 2篇 |
自然地理 | 83篇 |
出版年
2021年 | 21篇 |
2020年 | 24篇 |
2019年 | 16篇 |
2018年 | 58篇 |
2017年 | 45篇 |
2016年 | 75篇 |
2015年 | 60篇 |
2014年 | 62篇 |
2013年 | 107篇 |
2012年 | 36篇 |
2011年 | 43篇 |
2010年 | 59篇 |
2009年 | 65篇 |
2008年 | 34篇 |
2007年 | 46篇 |
2006年 | 51篇 |
2005年 | 26篇 |
2004年 | 15篇 |
2003年 | 30篇 |
2002年 | 33篇 |
2001年 | 27篇 |
2000年 | 29篇 |
1999年 | 20篇 |
1998年 | 18篇 |
1997年 | 30篇 |
1996年 | 20篇 |
1995年 | 25篇 |
1994年 | 22篇 |
1993年 | 17篇 |
1991年 | 20篇 |
1990年 | 17篇 |
1988年 | 11篇 |
1987年 | 14篇 |
1984年 | 14篇 |
1983年 | 22篇 |
1982年 | 16篇 |
1980年 | 13篇 |
1979年 | 13篇 |
1978年 | 17篇 |
1977年 | 11篇 |
1976年 | 12篇 |
1975年 | 12篇 |
1974年 | 16篇 |
1973年 | 20篇 |
1972年 | 13篇 |
1971年 | 10篇 |
1970年 | 12篇 |
1969年 | 11篇 |
1968年 | 12篇 |
1965年 | 14篇 |
排序方式: 共有1523条查询结果,搜索用时 31 毫秒
91.
Hydraulic roughness over simple subaqueous dunes 总被引:2,自引:1,他引:1
Jesper Bartholdy Burg W. Flemming Verner B. Ernstsen Christian Winter Alex Bartholom ä 《Geo-Marine Letters》2010,30(1):63-76
Detailed studies of flow over subaqueous dunes in laboratory flumes were used to suggest a virtual near-bed layer of twice
the dune height in which the mean velocity is accelerated towards the crest by contraction. The mean flow velocity in this
layer above the crest, transformed into friction velocity by means of the surface skin roughness, is shown to give values
consistent with measured values. The resulting dimensionless shear stress due to skin friction is depth-independent, in contrast
to that derived by means of often cited traditional methods. As a result of the relationship between dune height and the thickness
of the near-bed layer, an expression for the expansion loss behind dunes was formulated and used to relate form resistance
directly to dune height. 相似文献
92.
93.
O. Candan O.E. Koralay C. Akal O. Kaya R. Oberhänsli O.Ö. Dora N. Konak F. Chen 《Precambrian Research》2011,184(1-4):1-23
Well-preserved primary contact relationships between a Late Proterozoic metasedimentary and the metagranitic core and Palaeozoic cover series of the Menderes Massif have been recognized in the eastern part of the Çine submassif on a regional-scale. Metaconglomerates occur as laterally discontinuous channel-fill bodies close the base of the metaquartzarenite directly above the basement. The pebbles in the metaconglomerates consist mainly of different types of tourmaline-rich leucocratic granitoids, tourmalinite and schist in a sandy matrix. Petrographic features, geochemical compositions and zircon radiometric ages (549.6 ± 3.7–552.3 ± 3.1 Ma) of the diagnostic clasts of the metaconglomerates (e.g. leucocratic granitoids and tourmalinites) show excellent agreement with their in situ equivalents (549.0 ± 5.4 Ma) occurring in the Pan-African basement as stocks and veins.The correlation between clasts in the metaconglomerates and granitoids of the basement suggests that the primary contact between the basement and cover series is a regional unconformity (supra-Pan-African Unconformity) representing deep erosion of the Pan-African basement followed by the deposition of the cover series. Hence the usage of ‘core–cover’ terminology in the Menderes Massif is valid. Consequently, these new data preclude the views that the granitic precursors of the leucocratic orthogneisses are Tertiary intrusions. 相似文献
94.
Susanna Carbonin Gabriella Salviulol Rosalba Munno Mirella Desiderio A. Dal Negro 《Mineralogy and Petrology》1989,41(1):1-10
Summary The crystal structures of 20 natural diopsides have been refined. For some samples, microprobe analyses show a Si deficiency in the tetrahedron with no A1 present; this suggests that some Ti4+ may enter the tetrahedral site. Geometrical variations in these samples with respect to the others are discussed in the light of this Si Ti4+ substitution. The volumes of their M1 sites are larger because of the absence of R3+ cations, the octahedron being very regular; in the same way, the volumes of M2 sites of these samples are greater not because of different site occupancies but because of significant charge modifications around the O3 and O1 oxygens, caused by the tetrahedral site. The low distortion of M1 site and the lengthening of (M2-O1) and M2-O3 bond lengths are a clue to the presence of small amounts of Ti at the tetrahedral site.
Kristallchemische untersuchung natürlicher diopside: Geometrische hinweise für tetraedrische Si-Ti substitution
Zusammenfassung Die Kristallstrukturen von zwanzig natürlichen Diopsiden sind verfeinert worden. In einigen Proben zeigen Mikrosondenanalysen zu geringe Si-Werte im Tetraeder ohne daß A1 anwesend wäre. Dies weist darauf hin, daß Ti4+ Tetraederplätze einnehmen könnte. Geometrische Variationen in diesen Proben werden im Lichte der genannten Substitution diskutiert. Die Volumen von M1-Plätzen sind größer wegen der Abwesenheit von R3+ Kationen, wobei das Oktaeder sehr gleichmäßig ist. Die Volumina von M2-Plätzen sind noch größer nicht wegen verschiedener Besetzungen dieser Plätze sondern wegen signifikanter Ladungsmodifikationen im Bereich von O3 und O1 Sauerstoffen, die durch die tetraedrische Position bewirkt wird. Die geringe Distortion der M1-Plätze und die Verlängerung der (M2-O1) und (M2-O3) Abstände weisen auf die Anwesenheit von geringen Titangehalten auf Tetraederplätzen hin.相似文献
95.
E. S. Mo T. Throndsen P. Andresen S. A. Bäckström A. Forsberg S. Haug B. Tørudbakken 《International Journal of Earth Sciences》1989,78(1):305-317
The Midgard Field offshore mid-Norway is a gas-condensate accumulation with a thin oil leg reservoired in Early and Middle Jurassic sandstones. There are two potential source rocks in the area; the Late Jurassic Spekk Formation is a marine shale with type II kerogen and a rich potential for oil, and the Åre Formation of Early Jurassic age which is a thick coal-bearing sequence with type III kerogen and potential mainly for gas. Geochemical analyses indicate that both the condensate and the oil leg are sourced mainly from the coal-bearing Åre Formation. Any contribution from the Spekk Formation appears to be of minor importance. Computer simulation of hydrocarbon generation in the drainage area for the Midgard Field indicates that huge volumes are formed, and confirms that hydrocarbon generation from the Åre Formation is volumetrically far more important than from the Spekk Formation. The simulation results also exclude any contribution to the reservoired gas from the Spekk Formation.
Zusammenfassung Das Midgard Feld vor der Küste Mittelnorwegens ist eine Gas-Kondensat-Akkumulation mit einem nur geringen Ölanteil innerhalb unter- und mitteljurassischer Sandsteine. In diesem Gebiet gibt es zwei mögliche Muttergesteine: Einmal die oberjurassische Spekk-Formation, bei der es sich um einen marinen Schiefer mit Typ II Kerogen handelt und die ein hohes Ölpotential darstellt. Zum anderen gibt es die unterjurassische Åre-Formation, eine mächtige Kohle-führende Folge mit Typ III Kerogen und ein möglicher Gaslieferant. Geochemische Analysen deuten darauf hin, daß sowohl das Gas-Kondensat als auch das Öl des Midgard Feldes auf diese Kohle-führende Åre-Formation zurückzuführen sind. Jede Zufuhr aus der Spekk-Formation scheint von geringer Bedeutung zu sein. Eine durch Computersimulation rekonstruierte Kohlenwasserstofferzeugung im Einzugsgebiet des Midgard Feldes spricht für eine hohe Bildungsrate und bestätigt die Annahme, daß die Kohlenwasserstoff-produktion der Spekk-Formation gegenüber der Åre-Formation zu vernachlässigen ist. Die Simulation ergab ferner, daß keinerlei Gas von der Spekk-Formation dem Reservoir zugeführt wurde.
Résumé Le champ off-shore de Midgard (Norvège moyenne) est une accumulation de gaz condensé accompagnée d'un mince corps d'huile, accumulation renfermée dans des grès d'âge jurassique inférieur et moyen. Il existe dans le secteur deux sources possibles: la formation de Spekk (shale marins du Jurassique tardif, à kérogène de type II, possédant un riche potentiel en huile) et la formation d'Åre (série épaisse jurassique inférieure, à couches de charbon, à kérogène de type III et potentiel essentiellement en gaz). Les analyses géochimiques montrent que le gaz condensé et l'huile ont tous deux comme origine la formation charbonneuse de Åre. La formation de Spekk ne semble être intervenue que de manière subordonnée. Une simulation par ordinateur de la genèse de l'hydrocarbure dans l'aire d'alimentation du champ de Midgard fait apparaître que des volumes importants ont été formés et confirme la large prépondérance de la formation de Åre parmi les roches-mères. De plus, cette simulation exclut toute expèce de contribution de la formation de Spekk dans la genèse du gaz.
Midgard / / . : Spekk — , 2, , Are , 3 . . . , Are. Spekk, , . Midgard , Are . , , Spekk .相似文献
96.
Hannu Savijärvi 《Surveys in Geophysics》1994,15(6):755-773
The thermodynamics, dynamics, weather and general circulation (climate) of the atmospheres of Venus, Earth and Mars is reviewed, in the light of present knowledge. These three terrestrial planets each have a gaseous sunlit envelope, but the realizations of motions in them are quite different. This makes comparisons of their meteorology very interesting and challenging. 相似文献
97.
Erich Bäuerle 《Aquatic Sciences - Research Across Boundaries》1994,56(2):145-160
An episode of velocity measurements in the epilimnion at a midlake station in Lake Überlingen and taken from the campaign in October 1972 discloses a uni-nodal Poincaré-type baroclinic mode response with a 4 h period. We discuss the data and interpret it in terms of a two-layered linear wave model on the rotating Earth.
相似文献
相似文献
98.
99.
Alexandra Schmäh 《Journal of Paleolimnology》1993,9(2):99-108
In paleolimnology, subfossil head capsules of chironomids play an important role as ecological indicators of lake history. It is important to determine, therefore, whether fossil assemblages are representative of former biocoenoses. There is evidence that headcapsules washed in from other places can make up a significant percentage of the total. As interpretations are usually drawn from the examination of a single core, it is of special interest to know whether a fossil assemblage of a single site properly reflects limnological conditions of the whole lake. This study examined the taxonomic distribution of subfossil chironomids in the surficial sediments of the Bodensee-Untersee, with the aim of assessing the variability in chironomid assemblages. Apparently, most of the head capsules of the profundal fossil assemblages in the Untersee had been washed in from the littoral zone or from the slope. Although the Bodensee-Untersee is a rather large lake, variability is surprisingly low among all samples. Therefore a correct interpretation from a single core may be possible. 相似文献
100.