全文获取类型
收费全文 | 100篇 |
免费 | 4篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 4篇 |
地球物理 | 24篇 |
地质学 | 31篇 |
海洋学 | 22篇 |
天文学 | 5篇 |
自然地理 | 16篇 |
出版年
2021年 | 1篇 |
2020年 | 1篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 6篇 |
2014年 | 5篇 |
2013年 | 12篇 |
2012年 | 8篇 |
2011年 | 10篇 |
2010年 | 4篇 |
2009年 | 2篇 |
2008年 | 6篇 |
2007年 | 8篇 |
2006年 | 9篇 |
2005年 | 1篇 |
2004年 | 2篇 |
2003年 | 1篇 |
2002年 | 4篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1997年 | 5篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有106条查询结果,搜索用时 31 毫秒
91.
92.
A model for underpressure development in a glacial valley,an example from Adventdalen,Svalbard
下载免费PDF全文
![点击此处可从《Basin Research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The underpressure observed in the glacial valley Adventdalen at Svalbard is studied numerically with a basin model and analytically with a compartment model. The pressure equation used in the basin model, which accounts for underpressure generation, is derived from mass conservation of pore fluid and solid, in addition to constitutive equations. The compartment model is derived as a similar pressure equation, which is based on a simplified representation of the basin geometry. It is used to derive analytical expressions for the underpressure (overpressure) from a series of unloading (loading) intervals. The compartment model gives a characteristic time for underpressure generation of each interval, which tells when the pressure state is transient or stationary. The transient pressure is linear in time for short‐time spans compared to the characteristic time, and then it is proportional to the weight removed from the surface. We compare different contributions to the underpressure generation and find that porosity rebound from unloading is more important than the decompression of the pore fluid during unloading and the thermal contraction of the pore fluid during cooling of the subsurface. Our modelling shows that the unloading from the last deglaciation can explain the present day underpressure. The basin model simulates the subsurface pressure resulting from erosion and unloading in addition to the fluid flow driven by the topography. Basin modelling indicates that the mountains surrounding the valley are more important for the topographic‐driven flow in the aquifer than the recharging in the neighbour valley. The compartment model turns out to be useful to estimate the orders of magnitude for system properties like seal and aquifer permeabilities and decompaction coefficients, despite its geometric simplicity. We estimate that the DeGeerdalen aquifer cannot have a permeability that is higher than 1 · 10?18 m2, as otherwise, the fluid flow in the aquifer becomes dominated by topographic‐driven flow. The upper value for the seal permeability is estimated to be 1 · 10?20 m2, as higher values preclude the generation and preservation of underpressure. The porosity rebound is estimated to be <0.1% during the last deglaciation using a decompaction coefficient αr = 1 · 10?9 Pa?1. 相似文献
93.
94.
Metop-GRAS in-orbit instrument performance 总被引:2,自引:1,他引:1
The GRAS instrument on the Metop-A satellite provides more than 600 radio occultation measurement profiles per day. The instrument
is characterized by its wide antenna coverage, high signal-to-noise ratio and an ultra-stable clock reference. The conventional
dual-frequency tracking of GPS signals is under dynamic atmosphere conditions complemented by open loop tracking with sampling
of the signal at a 1 kHz rate, providing an unprecedented view of the signal spectral environment. This paper presents the
instrument performance as derived from analysis of in-orbit measurement data. We show that the noise figure is low enough
to enable mapping of external radio noise variations over the earth’s surface. An error propagation model is presented to
relate instrument characteristics to bending angle performance. This model is also used to illustrate the relation between
filter bandwidth, resolution and measurement noise. The Doppler model, guiding open loop measurements, is found to be accurate
to better than 20 Hz with a possibility for improvement to 10 Hz. The high performance at low altitudes enables the presence
of surface reflections at the −20-dB level to be identified in more than 50% of the occultations. The potential performance
improvements for next generation receivers are discussed. 相似文献
95.
96.
97.
98.
A new predictive formula for the total longshore sediment transport (LST) rate was developed from principles of sediment transport physics assuming that breaking waves mobilize the sediment, which is subsequently moved by a mean current. Six high-quality data sets on hydrodynamics and sediment transport collected during both field and laboratory conditions were employed to evaluate the predictive capability of the new formula. The main parameter of the formula (a transport coefficient), which represents the efficiency of the waves in keeping sand grains in suspension, was expressed through a Dean number based on dimensional analysis. The new formula yields predictions that lie within a factor of 0.5 to 2 of the measured values for 62% of the data points, which is higher than other commonly employed formulas for the LST rate such as the CERC equation or the formulas developed by Inman–Bagnold and Kamphuis, respectively. The new formula is well suited for practical applications in coastal areas, as well as for numerical modeling of sediment transport and shoreline change in the nearshore. 相似文献
99.
A revised ab initio calculation of the H2-H2 collision-induced absorption results in significant differences compared with the work of J. Borysow et al. [Borysow, J., Trafton, L., Frommhold, L., Birnbaum, G., 1985. Astrophys. J. 296, 644-654] for wavenumbers greater than 600 cm−1 and temperatures below 120 K. The revision has significant influence on the spectra of Uranus and Neptune, and essentially removes the need for models with “super-solar” helium abundances or stratospheric hazes to explain the spectrum of Uranus. 相似文献
100.
Alasdair Skelton Lillemor Claesson Govinda Chakrapani Chandan Mahanta Joyanto Routh Magnus Mörth Param Khanna 《Pure and Applied Geophysics》2008,165(1):45-61
Transient hydrogeochemical anomalies were detected in a granite-hosted aquifer, which is located at a depth of 110 m, north
of the Shillong Plateau, Assam, India, where groundwater chemistry is mainly buffered by feldspar alteration to kaolinite.
Their onsets preceded moderate earthquakes on December 9, 2004 (MW = 5.3) and February 15, 2005 (MW = 5.0), respectively, 206 and 213 km from the aquifer. The ratios [Na+K]/Si, Na/K and [Na+K]/Ca, conductivity, alkalinity
and chloride concentration began increasing 3–5 weeks before the MW = 5.3 earthquake. By comparison with field, experimental and theoretical studies, we interpret a transient switchover between
source aquifers, which induced an influx of groundwater from a second aquifer, where groundwater chemistry was dominantly
buffered by the alteration of feldspar to smectite. This could have occurred in response to fracturing of a hydrological barrier.
The ratio Ba/Sr began decreasing 3–6 days before the MW = 5.0 earthquake. We interpret a transient switchover to anorthite dissolution caused by exposure of fresh plagioclase to
groundwater interaction. This could have been induced by microfracturing, locally within the main aquifer. By comparison with
experimental studies of feldspar dissolution, we interpret that hydrogeochemical recovery was facilitated by groundwater interaction
and clay mineralization, which could have been coupled with fracture sealing. The coincidence in timing of these two hydrogeochemical
events with the only two MW ≥ 5 earthquakes in the study area argues in favor of cause-and-effect seismic-hydrogeochemical coupling. However, reasons
for ambiguity include the lack of similar hydrogeochemical anomalies coupled with smaller seismic events near the monitoring
station, the >200 km length scale of inferred seismic-hydrogeochemical coupling, and the potential for far-field effects related
to the Great Sumatra–Andaman Islands Earthquake of December 26, 2004. 相似文献