全文获取类型
收费全文 | 611篇 |
免费 | 27篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 22篇 |
地球物理 | 173篇 |
地质学 | 235篇 |
海洋学 | 55篇 |
天文学 | 121篇 |
综合类 | 3篇 |
自然地理 | 28篇 |
出版年
2023年 | 4篇 |
2022年 | 8篇 |
2021年 | 12篇 |
2020年 | 14篇 |
2019年 | 14篇 |
2018年 | 35篇 |
2017年 | 24篇 |
2016年 | 31篇 |
2015年 | 22篇 |
2014年 | 34篇 |
2013年 | 30篇 |
2012年 | 31篇 |
2011年 | 49篇 |
2010年 | 30篇 |
2009年 | 37篇 |
2008年 | 30篇 |
2007年 | 26篇 |
2006年 | 24篇 |
2005年 | 26篇 |
2004年 | 25篇 |
2003年 | 23篇 |
2002年 | 20篇 |
2001年 | 8篇 |
2000年 | 9篇 |
1999年 | 10篇 |
1998年 | 8篇 |
1997年 | 5篇 |
1996年 | 9篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1968年 | 1篇 |
1955年 | 1篇 |
1948年 | 1篇 |
1946年 | 2篇 |
1944年 | 2篇 |
1941年 | 1篇 |
1940年 | 3篇 |
排序方式: 共有642条查询结果,搜索用时 15 毫秒
91.
92.
The landscape setting of estuaries varies widely and is an important aspect of determining how they evolve. This paper focusses on alluvial estuaries in river valleys and how they respond to sea level rise. We examine the implications of marine transgression, as a response to sea level rise, where the estuary moves upwards and landwards to maintain its position in the tidal frame (so-called stratigraphic rollover). Here we encapsulate such kinematic movement of the estuary morphology using a ‘morphokinematic’ model, to assess the potential response to sea level rise and sediment supply. The model of the estuary form includes a single convergent channel, intertidal and surrounding floodplains (the valley) and allows the relative importance of the space available for deposition of sediments, the accommodation space, to be investigated as a function of rates of sea level rise and sediment supply. The transgression of the system is determined using a sediment mass balance, taking account of any supply from the river and marine environment. Model results confirm that the transgression distance, measured as the distance the entity moves landward, varies in proportion to the change in accommodation space, which mainly depends on the floodplain area. As the size of the floodplain reduces, the transgression distance is less and the system becomes much more sensitive to changes in the rate of sea level rise or changes in sediment supply. The greater demand for sediment when a floodplain is present results in greater cannibalization of the estuary form (i.e. greater landward movement) to meet the sediment demand. When the floodplain is disconnected from the estuary, the synergistic relationship is lost and the accommodation space increases. The capacity for restoration will depend on the availability of sediment and the prevailing rate of sea level rise. 相似文献
93.
94.
Marco Brandano Laura Tomassetti Guillem Mateu‐Vicens Giovanni Gaglianone 《Sedimentology》2019,66(6):2268-2296
Seagrasses are marine angiosperms that form extensive submarine meadows in the photic zone where carbonate producing biota dwell as epiphytes on the leaves or as infaunal forms, and act as prolific carbonate sediment factories. Because seagrasses have a low preservation potential and records of exceptionally well‐preserved and plant material from marine settings are rare, these palaeoenvironments are difficult to identify in the rock record. Consequently, sedimentological and palaeontological proxies are the main indicators of the presence of seagrass‐dominated ecosystems. This work investigates the skeletal assemblage of Modern (Maldivian and western Mediterranean) and fossil (Eocene; Apula and Oman carbonate platforms and Oligocene; Malta platform) seagrass examples to characterize the skeletal assemblage of modern and fossil seagrasses. Two main types of grains, calcareous algae and foraminifera, constitute around 50% of the bioclastic sediment in both tropical Maldivian and temperate Mediterranean scenarios. However, in the tropical setting they are represented by green algae (Halimeda), while in the Mediterranean they are represented by corallinacean red algae. In contrast, in the Eocene examples, the foraminifera are the most conspicuous group and the green algae are also abundant. The opposite occurs in the Maltese Chattian, which is dominated by coralline algae (mean 42%), although the foraminifera are still abundant. It is suggested to use the term foralgal to identify the seagrass skeletal assemblage. To discriminate between red algae and green algae dominance, the introduction of the prefixes ‘GA’ (green algae) and ‘RA’ (red algae) is proposed. The investigated examples provide evidence that the green algae–foralgal assemblage is typical of tropical, not excessively dense seagrass meadows, characterized by a well‐illuminated substrate to support the development and calcification of the Halimeda thallus. Contrarily, the red algae‐foralgal assemblage is typical of high density tropical to subtropical seagrass meadows which create very dense oligophotic conditions on the sea floor or in temperate settings where Halimeda cannot calcify. 相似文献
95.
Robust numerical implementation of a 3D rate-dependent model for reservoir geomechanical simulations
Giovanni Isotton Pietro Teatini Massimiliano Ferronato Carlo Janna Nicolò Spiezia Stefano Mantica Giorgio Volonte 《国际地质力学数值与分析法杂志》2019,43(18):2752-2771
A 3D elasto-plastic rate-dependent model for rock mechanics is formulated and implemented into a Finite Element (FE) numerical code. The model is based on the approach proposed by Vermeer and Neher (A soft soil model that accounts for creep. In: Proceedings of the International Symposium “Beyond 2000 in Computational Geotechnics,” pages 249-261, 1999). An original strain-driven algorithm with an Inexact Newton iterative scheme is used to compute the state variables for a given strain increment.The model is validated against laboratory measurements, checked on a simplified test case, and used to simulate land subsidence due to groundwater and hydrocarbon production. The numerical results prove computationally effective and robust, thus allowing for the use of the model on real complex geological settings. 相似文献
96.
Elyas Hayati Ehsan Abdi Mohsen Mohseni Saravi John L. Nieber Baris Majnounian Giovanni B. Chirico 《水文研究》2018,32(16):2570-2583
An experimental campaign was set up to quantify the contribution of evapotranspiration fluxes on hillslope hydrology and stability for different forest vegetation cover types. Three adjacent hillslopes, respectively, covered by hardwood, softwood, and grass were instrumented with nine access tubes each to monitor soil water dynamics at the three depths of 30, 60, and 100 cm, using a PR2/6 profile probe (Delta‐T Devices Ltd) for about 6 months including wet periods. Soil was drier under softwood and wetter under grass at all the three depths during most of the monitoring period. Matric suction derived via the soil moisture measurements was more responsive to changes in the atmospheric conditions and also recovered faster at the 30 cm depth. Results showed no significant differences between mean matric suction under hardwood (101.6 kPa) with that under either softwood or grass cover. However, a significant difference was found between mean matric suction under softwood (137.5 kPa) and grass (84.3 kPa). Results revealed that, during the wettest period, the hydrological effects from all three vegetation covers were substantial at the 30 cm depth, whereas the contribution from grass cover at 60 cm (2.0 kPa) and 100 cm (1.1 kPa) depths and from hardwood trees at 100 cm depth (1.2 kPa) was negligible. It is surmised that potential instability would have occurred at these larger depths along hillslopes where shallow hillslope failures are most likely to occur in the region. The hydrological effects from softwood trees, 8.1 and 3.9 kPa, were significant as the corresponding factor of safety values showed stable conditions at both depths of 60 and 100 cm, respectively. Therefore, the considerable hydrological reinforcing effects from softwood trees to the 100 cm depth suggest that a hillslope stability analysis would show that hillslopes with softwood trees will be stable even during the wet season. 相似文献
97.
98.
99.
In laboratory experiments, the influence of inflow and outflow sequences on the behavior of fine sedi-ment was investigated. The experimental set-up consisted of two interconnected rectangular basins, between which water was moved back and forth. Suspended sediment concentration in the main basin as well as the sediment exchange rates were derived from turbidity measurements.The suspended sediment ratio, SSR, and sediment exchange rates (influx sediment rate, ISR, and evacuated sediment rate, ESR) were measured. In twenty test runs, a parametric study on the magnitude and frequency of inflow and outflow cycles, the relative duration between inflow and outflow sequences, the initial sediment concentration, and the intake position was done. An initial test with stagnant water described the set-tling behavior of fine sediment and served as a reference scenario.The test results show that settling of fine particles near the intake/outlet structure can be considerably reduced by the nature of the inflow and outflow sequences. High cycle magnitude and frequency lead to maximum suspended sediment ratio in the system. For low discharges, the evolution of suspended sediment concentration cannot be directly correlated to the inflow and outflow cycles. However, compared to"no operation"conditions, the suspended sediment ratio could be increased by 10%to 40%locally. For high discharge, the evolution of suspended sediment concentration correlated with discharge cycles and suspended sediment ratios between 50%and 80%higher than for stagnant water could be achieved. Similar ratios could be obtained when the intake is located closer to the bottom or to the free water surface.Meanwhile, the overall sediment balance remained in equilibrium over the test period, indicating that the influx and evacuated sediment rates are not significantly influenced by the inflow and outflow cycles. 相似文献
100.
Giovanni Boschian 《Geoarchaeology》1997,12(3):227-249
The deposits of Grotta dell'Edera have been studied by both standard sedimentological and soil micromorphological techniques, and have been divided into four main stages. The two older ones have not been dated, as they did not yield any human artefacts; nevertheless, according to their stratigraphic position and sedimentological-micromorphological characteristics, they may be considered as Tardiglacial. They testify to a thermoclastic event followed by loess deposition, both accompanied by strong inputs from outside the cave. The two following stages were ascribed to the Mesolithic (stage 3) and to the Neolithic-Copper Age (stage 4). In these two intervals sedimentation was strongly affected by human activity, while external inputs decreased. Mesolithic occupation produced sediments rich in ash and decayed organic matter. During the final stage, the cave was a shelter for domestic animals, and the deposits are mainly composed of their droppings. © 1997 John Wiley & Sons, Inc. 相似文献