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901.
Most downstream hydraulic geometry exponents have been found to be very close to the classic values reported by Leopold and Maddock (1953). These have been viewed as the simplified cases to general trends because the hydraulic geometry of alluvial channels is actually the product of ‘multivariate controls’ (Richards, 1982). This paper is an attempt to develop a soundly based foundation for the explanation of the physical mechanisms of these controls. A quantitative relationship between channel shape and boundary shear distribution developed from experimental flume results is found to be applicable in some instances to alluvial channels, particularly to stable canals. On the basis of this relationship, it is shown that downstream hydraulic geometry is determined not only by flow discharge, but also by channel slope, channel average roughness and sediment composition of the channel boundary. This is strongly supported by our analysis of 529 observations from both stable canals and natural rivers in the U.S.A. and the U.K. The difference between regime relations in canals and the hydraulic geometry of rivers appears to be caused mainly by channel slope and average roughness, which can be regarded as constants only in stable canals. The close relationship between discharge and channel average roughness observed in canals is not repeated in natural channels, partly because of the variety of flow values used to define the channel-forming discharge. Furthermore, it is indicated that the effects of the sediment composition of the channel boundary on hydraulic geometry are significant and need further investigation. 相似文献
902.
胜利油田渤南洼陷沙四上段沉积环境分析 总被引:12,自引:0,他引:12
通过地质和物探手段相结合,宏观和微观方法相结合,对渤南洼陷构造发育特征和沙四上段沉积相特征进行了深入的研究。根据沉积旋回性、韵律性等特征,确定渤南洼陷沙四上段沉积环境为滨(浅)湖-半深湖和湖底扇。根据沉积学标志,测井相标志和地震相标志,对沙四上段沉积环境为滨(浅)湖-半深湖和湖底扇。根据沉只学标志,测井相标志和地震相标志,对沙四上段湖底扇沉积微相进行了详细划分和描述,将湖底扇划分为内扇、中扇和外扇3个亚相,并进一步划分为5个微相。在上述基础上,揭示了湖底扇的平面展布规律,建立了沙四上段湖底扇的沉积模式。 相似文献
903.
904.
Recent studies of turbidite bed thickness distributions have demonstrated power-law as well as log-normal statistical distributions. The different distributions may reflect different fan processes and environments and, therefore, could be used as a quantitative method to help identify those environments, including those devoid of sequential patterns. The cumulative distributions of well-known turbidite deposits spanning a range of interpreted fan subenvironments are used to illustrate the potential correlation between cumulative distribution and environments. Assuming that power-law distributions may, for some systems, be the primary input signal, one-dimensional modelling allows semi-quantitative characterization of the effects of different fan processes such as erosion and bed amalgamation. Environments indicative of different fan processes may be characterized based on the degree to which processes have acted as a 'filter' to modify the assumed power-law distribution systematically. This model of the effect of fan processes on the power-law distribution is used to help to account for bed thickness distributions observed in several field sites. 相似文献
905.
The main objective of the present paper is to present an integrated approach to the study of faulting stages in coarse alluvial deposits. The study site is the alluvial fan of Nahal Shehoret, presently under an extremely arid regime. The exposure of fault scarps on the fan surfaces enables the identification of several geomorphic indicators employed in analysing and separating faulting events and periods of quiescence: (a) the nature of fault scarp topography; (b) soil catenary development on fault scarps; (c) buried paleosols in alluvial deposits; (d) colluvial bodies; (e) rotated clasts along fault planes. These indicators enable us to determine, at all sites studied, the total amount of displacement, to separate faulting events and the amount of their displacement per event, and to evaluate scarp stability and the duration of periods of tectonic quiescence. 相似文献
906.
907.
908.
单断式盆地充填模式与油气聚集──东濮凹陷东南部实例分析 总被引:3,自引:0,他引:3
在东濮凹陷东南部的盆地构造岩相带分析中,发现单断式盆地有三种对沉积体系、油气分布及盆地本身演化具有控制作用的正断层:犁式边界断层、箕式边界断层和多米诺式断层。它们分别形成了犁式河湖充填模式、箕式扇体充填模式和多米诺式三角洲-重力流充填模式;前者制约着生油洼陷的发育和盆地的生油潜力,后两者主要控制着油气聚集区的发育。 相似文献
909.
Dilip Saha 《Journal of Earth System Science》1990,99(2):339-355
A small thrust sheet, named Pedda Gutta thrust sheet, consisting of calcareous to cherty argillites and cherts, and juxtaposed
against tidal-intertidal cross-bedded quartzites and stromatolitic and sileceous limestone in the eastern Proterozoic belt,
Godavari Valley, exhibits structures comparable in style to those of the external zone of a fold-thrust mountain belt. A wide
spectrum of periodic and aperiodic mesoscopic folds varying from upright ones with rounded hinges and attenuated limbs, through
noncylindrical kinks to whalebacks and sheath-like forms have developed within the small volume of the thrust sheet, the preserved
thickness of which is of the order of 50 metres (comparable in scale to cleavage duplexes). Cleavage development is also heterogeneous
across the width of the sheet. Displacement transfer from faults to folds and vice-versa is a common feature.
On the basis of the distribution of the mesoscopic structures of varying style within the sheet and localization of fault
rocks, three slices (wedges) have been recognized, each bounded on the east by a thrust which is steep at the current erosion
level but interpreted to be of listric form making the thrust network comparable in architecture, though not in scale, to
a hinterland (west) dipping imbricate fan. 相似文献
910.
D. Bowman 《地球表面变化过程与地形》1988,13(3):239-249
Laboratory experiments investigating the effects of a lowering base level do not simulate natural eustatic lowering along concave river profiles. The field data on this issue are also quite limited. In evaluating the control exercised by lowering base level on a drainage network, distinction must be made between its influence and those of other hydromorphological processes operating within the basin. Field data on morphological relations, based on photogrammetric mapping and longitudinal profiling, have been gathered in the Dead Sea area, Israel, where a rapid fall in base level has occurred during the Holocene. The study area is an entrenched fan delta with a sequence of 14 unpaired fan terraces which die out at intersection points within an alluvial fan system. The results suggest that the intersection points did not function as base levels. The receding base level played only a passive role, allowing entrenchment without transmitting a head-cutting feedback basinwards. The arid environment caused a delay in transmission of information through the system. The results support the model of short, episodic, and discontinuous erosional events, inherent in the evolution of drainage basins. It is suggested that base level effects in temperate and humid regions are not transferrable to arid zones. 相似文献