全文获取类型
收费全文 | 143篇 |
免费 | 7篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 15篇 |
地球物理 | 42篇 |
地质学 | 34篇 |
海洋学 | 21篇 |
天文学 | 29篇 |
自然地理 | 6篇 |
出版年
2022年 | 1篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 6篇 |
2015年 | 6篇 |
2014年 | 2篇 |
2013年 | 12篇 |
2012年 | 5篇 |
2011年 | 11篇 |
2010年 | 9篇 |
2009年 | 9篇 |
2008年 | 17篇 |
2007年 | 5篇 |
2006年 | 5篇 |
2005年 | 4篇 |
2004年 | 5篇 |
2003年 | 5篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有150条查询结果,搜索用时 484 毫秒
61.
Balaena Bay, Wellington Harbour, New Zealand, has a small pocket beach that was covered originally by pebbles and cobbles. In February and October 1982, the beach was nourished with sandy granular gravel, the stability of which was monitored until February 1984. Although isolated from oceanic swell, the new beach readily responded to locally generated wind waves which induced both northwards and southwards longshore drift. The net effect was erosion of the southern beach, aggradation over the central beach, and minor fluctuations at the northern end. Yet despite this mobility nearly all the nourishment sediment was retained in the littoral zone. Beach volumes, calculated for each survey, varied little and sediment distribution patterns revealed negligable transport of nourishment sediment to adjacent beaches and offshore areas. Stability is further confirmed by compositional data which record no preferential loss of the sandstone, argillite, and quartz components. The only compositional changes were the incorporation into the new beach of small (< 10%) quantities of sediment derived from the old beach surface and from biogenic productivity. 相似文献
62.
Soil erosion induces soil redistribution within the landscape and thus contributes to the spatial variability of soil quality. This study complements a previous experimentation initiated by the authors focusing on soil redistribution as a result of soil erosion, as indicated by caesium‐137 (137Cs) measurements, in a small agricultural field in Canada. The spatial variability of soil organic matter (SOM) was characterized using geostatistics, which consider the randomized and structured nature of spatial variables and the spatial distribution of the samples. The spatial correlation of SOM (in percentages) patterns in the topsoil was established taking into account the spatial structure present in the data. A significant autocorrelation and reliable variograms were found with a R2 ≥ 0·9, thus demonstrating a strong spatial dependence. Ordinary Kriging (OK) interpolation provided the best cross validation (r2 = 0·35). OK and inverse distance weighting power two (IDW2) interpolation approaches produced similar estimates of the total SOM content of the topsoil (0–20 cm) of the experimental field, i.e. 211 and 213 tonnes, respectively. However, the two approaches produced differences in the spatial distribution patterns and the relative magnitude of some SOM content classes. The spatialization of SOM and soil redistribution variability – as evidenced by 137Cs measurements – is a first step towards the assessment of the impact of soil erosion on SOM losses to recommend conservation measures. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
63.
The Solomon Sea is a key region in the Pacific Ocean where equatorial and subtropical circulations are connected. The region
exhibits the highest levels in sea level variability in the entire south tropical Pacific Ocean. Altimeter data was utilized
to explore sea level and western boundary currents in this poorly understood portion of the ocean. Since the geography of
the region is extremely intricate, with numerous islands and complex bathymetry, specifically reprocessed along-track data
in addition to standard gridded data were utilized in this study. Sea level anomalies (SLA) in the Solomon Sea principally
evolve at seasonal and interannual time scales. The annual cycle is phased by Rossby waves arriving in the Solomon Strait,
whereas the interannual signature corresponds to the basin-scale ENSO mode. The highest SLA variability are concentrated in
the eastern Solomon Sea, particularly at the mouth of the Solomon Strait, where they are associated with a high eddy kinetic
energy signal that was particularly active during the phase transition during the 1997–1998 ENSO event. Track data appear
especially helpful for documenting the fine structure of surface coastal currents. The annual variability of the boundary
currents that emerged from altimetry compared quite well with the variability seen at the thermocline level, as based on numerical
simulations. At interannual time scales, western boundary current transport anomalies counterbalance changes in western equatorial
Pacific warm water volume, confirming the phasing of South Pacific western boundary currents to ENSO. Altimetry appears to
be a valuable source of information for variability in low latitude western boundary currents and their associated transport
in the South Pacific. 相似文献
64.
Frédéric Castruccio Jacques Verron Lionel Gourdeau Jean-Michael Brankart Pierre Brasseur 《Ocean Dynamics》2008,58(1):43-63
The altimetric satellite signal is the sum of the geoid and the dynamic topography, but only the latter is relevant to oceanographic
applications. Poor knowledge of the geoid has prevented oceanographers from fully exploiting altimetric measurements through
its absolute component, and applications have concentrated on ocean variability through analyses of sea level anomalies. Recent
geodetic missions like CHAMP, GRACE and the forthcoming GOCE are changing this perspective. In this study, data assimilation
is used to reconstruct the Tropical Pacific Ocean circulation during the 1993–1996 period. Multivariate observations are assimilated
into a primitive equation ocean model (OPA) using a reduced order Kalman filter (the Singular Evolutive Extended Kalman filter).
A 6-year (1993–1998) hindcast experiment is analyzed and validated by comparison with observations. In this experiment, the
new capability offered by an observed absolute dynamic topography (built using the GRACE geoid to reference the altimetric
data) is used to assimilate, in an efficient way, the in-situ temperature profiles from the TAO/TRITON moorings together with
the T/P and ERS1&2 altimetric signal. GRACE data improves compatibility between both observation data sets. The difficulties
encountered in this regard in previous studies such as Parent et al. (J Mar Syst 40–41:381–401, 2003) are now circumvented. This improvement helps provide more efficient data assimilation, as evidenced, by assessing the results
against independent data. This leads in particular to significantly more realistic currents and vertical thermal structures. 相似文献
65.
The influence of riverine inputs on biogeochemical cycling and organic matter recycling in sediments on the continental shelf off the Rhône River mouth (NW Mediterranean Sea) was investigated by measuring sediment oxygen uptake rates using a combination of in situ and laboratory techniques. Four stations were investigated during two cruises in June 2001 and June 2002, with depths ranging from 9 to 192 m and over a distance to the Rhône River mouth ranging from 4 to 36 km. Diffusive oxygen uptake (DOU) rates were determined using an in situ sediment microprofiler and total oxygen uptake (TOU) rates were measured using sediment core incubations. There was good agreement between these two techniques which indicates that the non-diffusive fraction of the oxygen flux was minimal at the investigated stations. DOU rates ranged from 3.7±0.4 mmol O2 m−2 d−1 at the continental shelf break to 19.3±0.5 mmol O2 m−2 d−1 in front of the Rhône River mouth. Sediment oxygen uptake rates mostly decreased with increasing depth and with distance from the Rhône mouth. The highest oxygen uptake rate was observed at 63 m on the Rhône prodelta, corresponding to intense remineralization of organic matter. This oxygen uptake rate was much larger than expected for the increasing bathymetry, which indicates that biogeochemical cycles and benthic deposition are largely influenced by the Rhône River inputs. This functioning was also supported by the detailed spatial distribution of total organic carbon (TOC), total nitrogen (TN) and C/N atomic ratio in surficial sediments. Sediments of the Rhône prodelta are enriched in organic carbon (2–2.2%) relative to the continental shelf sediments (<1%) and showed C/N ratios exceeding Redfield stoichiometry for fresh marine organic matter. A positive exponential correlation was found between DOU and TOC contents (r2=0.98, n=4). South-westward of the Rhône River mouth, sediments contained highly degraded organic matter of both terrestrial and marine origin, due to direct inputs from the Rhône River, sedimentation of marine organic matter and organic material redeposition after resuspension events. 相似文献
66.
A new ichthyofauna from southeastern Morocco, comprising five forms, is briefly discussed. The faunal composition differs from the Early Cenomanian Kem Kem and Early Turonian Goulmima assemblages, but is close to that from Jebel Tselfat. We propose a Late Cenomanian age for the new fauna and that from Jebel Tselfat. The evolution of these fish assemblages shows the Moroccan fish faunas to have been related to those from South America until at least the Early Turonian. Central Tethyan influence on faunas seems to have been restricted to a short period of time during the beginning of the Late Cenomanian transgressive phase. 相似文献
67.
Abstract— ‐Major surface fissures and relatively large‐scale, angular surface irregularities are expected to have been present on many asteroids at early stages in their histories as a byproduct of at least two processes (impact disruption and reassembly into rubble piles for all classes of asteroid and, for carbonaceous chondrite parent bodies, aqueous alteration) which led to the low bulk densities currently being observed for asteroids. However, in all cases where high‐enough resolution images exist, such abrupt, deep irregularities are not observed. We model the spatial redistribution of impact‐generated regolith on an asteroid with an idealized irregular shape to show how the complex gravitational field of such a body will lead to the systematic infilling of deep valleys in the surface. Our analysis emphasizes the high efficiency with which regolith redistribution can act to disguise the internal structures of asteroids with sizes in the 20–100 km range. 相似文献
68.
A GLORIA (Geological Long-Range Inclined Asdic) side-scan sonar survey, covering 23,000 km2, provides the first complete imagery of an active and contiguous, oceanic to continental back-arc system, namely, the Havre
Trough to Taupo Volcanic Zone (TVZ) New Zealand. Havre Trough tectonism and volcanism relates to a series of laterally discontinuous,
mutiple spreading rifts which terminate southward at the 3-km-deep Ngatoro Basin. A 45-km sinistral offset attributed toen echelon synthetic shearing separates the basin from the actively spreading TVZ. Sonographs reveal a youthful and complex volcanic
seascape with 20 newly discovered seamounts, whereas flanking regions are mantled with a largely featureless mud blanket. 相似文献
69.
Lionel Carter 《Geo-Marine Letters》2001,21(1):42-50
The Pacific deep western boundary current (DWBC) encounters an unstable continental margin where it flows across the New Zealand convergent plate boundary. Seismic profiles show the DWBC was intercepted by several submarine landslides, the latest (~38-100 ka) being the newly discovered Matakaoa debris flow. Occupying ~650 km3, the flow extends 200 km from Matakaoa re-entrant to Kermadec Ridge to form a 37-68 m high lobe in the current's path. This deposit appears to have (1) reduced the size of gaps in the western boundary, thereby reducing leakage of the DWBC, and (2) temporarily reduced the terrigenous supply into the flow by impeding the passage of turbidity currents from New Zealand. 相似文献
70.
Iwona Jozwik Jacek Jagielski Grzegorz Gawlik Przemyslaw Jozwik Renata Ratajczak Gerard Panczer Nathalie Moncoffre Anna Wajler Agata Sidorowicz Lionel Thomé 《Physics and Chemistry of Minerals》2016,43(6):439-445
A comparative study of damage accumulation in magnesium aluminate spinel (MgAl2O4) has been conducted using ionoluminescence (IL), cathodoluminescence (CL) and Rutherford Backscattering Spectrometry/channeling (RBS/C) techniques. MgAl2O4 single crystal and polycrystalline samples were irradiated with 320 keV Ar+ ions at fluencies ranging from 1 × 1012 to 2 × 1016 cm?2 in order to create various levels of radiation damage. RBS/C measurements provided quantitative data about damage concentration in the samples. These values were then compared to the luminescence measurements. The results obtained by IL and RBS/C methods demonstrate a two-step character of damage buildup process. The CL data analysis points to the three-step damage accumulation mechanism involving the first defect transformation at fluencies of about 1013 cm?2 and second at about 1015 cm?2. The rate of changes resulting from the formation of nonluminescent recombination centers is clearly nonlinear and cannot be described in terms of continuous accumulation of point defects. Both, IL and CL techniques, appear as new, complementary tools bringing new possibilities in the damage accumulation studies in single- and polycrystalline materials. 相似文献