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排序方式: 共有113条查询结果,搜索用时 15 毫秒
1.
Manoj K. Pandit Helga de Wall Narendra K. Chauhan 《Journal of Earth System Science》2008,117(3):201-209
A number of fine-grained sericite bearing pelitic, schistose lithologies occur along the Archean (Banded Gneiss Complex)-Proterozoic
(Aravalli Supergroup) contact (APC) in the Udaipur valley in NW Indian craton. These Al-rich lithologies (subsequently metamorphosed)
have been described as ‘paleosols’, developed over a 3.3 Ga old Archean gneissic basement and are overlain by Paleoproterozoic
Aravalli quartzite. The paleosol was developed between 2.5 and 2.1, coincident with the globally recognized Great Oxidation
Event (GOE). In previous studies these paleosol sections were interpreted to have developed under reducing environment, however,
the finding of a ‘ferricrete’ zone in the upper part of Tulsi Namla section (east of Udaipur) during the present study (in
addition to earlier reported lithologies) has led to an alternative suggestion of oxygen-rich conditions during paleosol development.
The Tulsi Namla paleosol section shows all the features characteristic of a complete paleosol section described from other
Archean cratons. The paleosol includes sericite schist with kyanite as the prevalent Al-silicate in the lower part of profile
while chloritoid and Fe-oxides typify the Fe-rich upper part. Alumina has remained immobile during the weathering process
while Fe and Mn show a decrease in the lower part of the section and an abrupt rise in the upper part, in the ferricrete zone.
The field and geochemical data indicate that the Tulsi Namla section is an in situ weathering profile and at least the upper part shows evidence of oxidizing conditions. 相似文献
2.
Frances Wall 《Geology Today》2003,19(6):206-211
Numerous world class mineral deposits make the Kola Peninsula a 'Mecca' for mineralogists, and key economic deposits make it one of Russia's most important industrial areas. For geologists there is the challenge of explaining how this situation has come about. 相似文献
3.
4.
Manoj K. Pandit Ramona Dotzler Helga De Wall 《Journal of the Geological Society of India》2016,87(1):35-42
Mafic dykes intrude the composite Mt. Abu granite batholith as a minor and the last phase of magmatism. The dykes are sub-vertical, variable in width and visibly compact, however, features of alteration and shearing can be seen. The dykes occurring within the recently identified and described, Delwara Shear Zone (DWSZ), from the western margin of the Mt. Abu batholith are intensely to moderately sheared and intricately mixed with the host granitoids. The mafic dykes occurring within the shear zone bear evidence of assimilating the host granitoids during their ascent, seen as relicts, streaks and sub-rounded K-feldspar clasts in mafic dykes. The hybridization has resulted in unusual geochemical signatures of the mafic dykes such as higher silica levels, erratic and high incompatible trace element abundances and lack of any systematic trends. Mixing line calculations on the mafic dyke samples reveal between 30 to 60% felsic input into the mafic dykes. Mafic dykes outside the shear zone in the Mt. Abu are meter scale in width and generally free of felsic inclusions owing to small volumes of mafic melts. Large volume of mafic melts are required for assimilating up to 60% felsic component which has been identified as approximately 100 m wide zone within the DWSZ. Shearing has played an important role in providing the channel ways and for sustained high temperatures to allow such hybridization. 相似文献
5.
6.
Hugh St. C. O'Neill Mark I. Pownceby Victor J. Wall 《Contributions to Mineralogy and Petrology》1989,103(2):216-222
The activity of FeTiO3 in the binary ilmenitepyrophanite (FeTiO3-MnTiO3) solid solution has been determined for the temperature range 1050–1300 K by displacement of the reaction: 2 FeTiO3=2 Fe+2 TiO2+O2 in T-O2 space, using an electrochemical technique with calcia- and yttria-stabilized zirconia solid electrolytes. The activities show small positive deviations from ideality, which, although the data are unusually precise, may be perfectly described by the simple regular solution model, with an interaction parameter, W
Fe-Mn
ilm
, of 2.2±0.3 kJ g-atom–1, which is independent of temperature. This value, together with the experimental data on the partitioning of Fe and Mn between ilmenite and garnet (Pownceby et al. 1987), gives W
Fe-Mn
gt
=1.2±0.5 kJ g-atom–1 for the almandine-spessartine (Fe3Al2Si3O12-Mn3Al2Si3O12) solid solution. 相似文献
7.
Laminar sheetflows, transporting sediment at their capacity rates, both with and without rainfall disturbance, were investigated. Values of flow depth and relative submergence were very small. In the flows without rainfall, measured velocities exceeded the predictions of the smooth-surface, clear-water laminar model by an average of 12 per cent. Reduced flow resistance due to high sediment concentrations may explain this result. Velocities in the rainfall-disturbed flows were not significantly different from the predictions of the smooth-surface, clear-water model, and the velocity reduction due to rainfall was about 12 per cent. Although the uniformity of rainfall intensity under the single-nozzle rainfall simulator is high, variation of momentum and kinetic energy fluxes along the 1-5 m long flume was significant. The rainfall angle of incidence was highly correlated with deviations from expected flow velocities in the upper and lower sections of the flume. 相似文献
8.
C. C. Wallén 《Theoretical and Applied Climatology》1958,9(2):113-123
Summary Different measures of variability of precipitation are discussed and it is concluded that it is preferable to apply therelative intersequential variability in cases when overall trends are feared in the records. 127 stations in Sweden have been studied for the period 1901–1950 as to the relative interannual variability of precipitation. For a selection of these stations other measures have also been calculated and a comparison has been made between the coefficient of variation and the intersequential variability. As the relation between these measures varies with the existence of serial correlations in the records the serial correlation coefficient for a lag of one element has been calculated. The value of the coefficient has indicated the existence of trends in certain areas of Sweden generally in agreement with earlier investigations byÅngström.The geographical distribution of the relative interannual variability in Sweden is discussed and also the distribution of anomalies of relative variability compared with the world's normal curve completed byConrad. It is shown that the relationship between relative variability and precipitation amount for Swedish stations can be expressed by a hyperbolic function deviating fromConrad's world normal curve only by an additive constant.
With 5 Figures
Dedicated to Dr.Anders K. Ångström on the occasion of his 70th birthday. 相似文献
Zusammenfassung Der Verfasser erörtert verschiedene Maße für die Variabilität des Niederschlages und kommt zu der Feststellung, daß in den Fällen, in denen eine einseitige Tendenz in den Beobachtungsreihen zu befürchten ist, die Verwendung derrelativen reiheninternen Variabilität am geeignetsten ist. 127 Stationen in Schweden sind für die Periode 1901–1950 im Hinblick auf die relative interannuelle Variabilität des Niederschlags untersucht worden. Für eine Auswahl dieser Stationen wurden auch andere Maße berechnet und der Schwankungskoeffizient mit der reiheninternen Variabilität verglichen. Da die Beziehung zwischen diesen Maßen mit dem Auftreten von Serienkorrelationen in der Beobachtungsreihe variiert, wurde der Serienkorrelationskoeffizient für eine Verschiebung eines Elements berechnet. Die erhaltenen Werte des Koeffizienten deuten auf das Vorhandensein gesetzmäßiger Tendenzen in gewissen Gebieten Schwedens hin und stehen im allgemeinen in guter Übereinstimmung mit älteren Untersuchungen vonÅngström.Die geographische Verteilung der relativen interannuellen Variabilität in Schweden sowie die Verteilung der Anomalien der relativen Variabilität, verglichen mit der vonConrad aufgestellten Weltnormalkurve, werden erörtert. Schlie\lich wird gezeigt, daß es möglich ist, den Zusammenhang zwischen relativer Variabilität und Niederschlagsmenge für schwedische Stationen durch eine hyperbolische Funktion zu beschreiben, die vonConrads Weltnormalkurve nur durch eine additive Konstante abweicht.
Résumé L'auteur mentionne différentes mesures de la variabilité des précipitations et conclut qu'il est préférable d'appliquer la variabilité relative interséquentielle lorsqu'une tendance unilatérale des séries d'observations est à craindre. Il a étudié la variabilité relative interannuelle des précipitations pour 127 stations suédoises (1901/50) ainsi que d'autres mesures de variabilité pour un choix restreint de stations et il a comparé le coefficient de variation à la variabilité relative interséquentielle. Comme la relation entre ces mesures varie avec l'existence de corrélations de série dans les séries d'observations, le coefficient de corrélation de série a été calculé pour un déplacement d'un terme; la valeur de ce coefficient indique l'existence de tendances générales dans certaines régions de Suède, ce qui confirme les résultats anciens deÅngström.La distribution géographique de la variabilité relative interannuelle en Suède ainsi que celle des anomalies de la variation relative comparée à la courbe normale mondiale dressée parConrad fait l'objet d'un examen. Enfin on montre qu'il est possible d'exprimer la relation entre la variabilité relative et la quantité de précipitations en Suède par une fonction hyperbolique qui ne diffère de la courbe normale deConrad que par une constante additive.
With 5 Figures
Dedicated to Dr.Anders K. Ångström on the occasion of his 70th birthday. 相似文献
9.
Geoffrey Wall 《Climatic change》1998,40(2):371-389
Tourism and recreation are important economic activities which are major agents of change globally and, more specifically, in wetland areas. There is a regular round of activities associated with the seasons and anything which influences operating seasons is likely to have substantial consequences for tourism businesses Atmospheric conditions influence both whether or not people will participate as well as the quality of the experience. In marine coasts, wetland recreations may be threatened by rising sea levels but recreation in inland water bodies may be affected more by deficiencies rather than superabundance of water. Marinas and recreational boating are harmed by extremes of both high and low water, particularly the latter which is the most likely situation under global climate change. Two main groups can be considered with respect to the potential to adapt to climate change. These are the participants themselves and the businesses which cater to them. It is argued that the former are likely to be much more adaptable than the latter. 相似文献
10.