全文获取类型
收费全文 | 355篇 |
免费 | 32篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 27篇 |
地球物理 | 90篇 |
地质学 | 106篇 |
海洋学 | 68篇 |
天文学 | 41篇 |
综合类 | 3篇 |
自然地理 | 50篇 |
出版年
2022年 | 2篇 |
2021年 | 11篇 |
2020年 | 8篇 |
2019年 | 7篇 |
2018年 | 11篇 |
2017年 | 11篇 |
2016年 | 19篇 |
2015年 | 9篇 |
2014年 | 13篇 |
2013年 | 39篇 |
2012年 | 20篇 |
2011年 | 14篇 |
2010年 | 25篇 |
2009年 | 19篇 |
2008年 | 15篇 |
2007年 | 13篇 |
2006年 | 12篇 |
2005年 | 9篇 |
2004年 | 8篇 |
2003年 | 10篇 |
2002年 | 8篇 |
2001年 | 4篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1984年 | 2篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 2篇 |
1968年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有390条查询结果,搜索用时 15 毫秒
371.
The predictability of near-coastal currents using a baroclinic unstructured grid model 总被引:1,自引:1,他引:0
Cheryl Ann Blain Mustafa Kemal Cambazoglu Robert S. Linzell Kendra M. Dresback Randall L. Kolar 《Ocean Dynamics》2012,62(3):411-437
A limited domain, coastal ocean forecast system consisting of an unstructured grid model, a meteorological model, a regional
ocean model, and a global tidal database is designed to be globally relocatable. For such a system to be viable, the predictability
of coastal currents must be well understood with error sources clearly identified. To this end, the coastal forecast system
is applied at the mouth of Chesapeake Bay in response to a Navy exercise. Two-day forecasts are produced for a 10-day period
from 4 to 14 June 2010 and compared to real-time observations. Interplay between the temporal frequency of the regional model
boundary forcing and the application of external tides to the coastal model impacts the tidal characteristics of the coastal
current, even contributing a small phase error. Frequencies of at least 3 h are needed to resolve the tidal signal within
the regional model; otherwise, externally applied tides from a database are needed to capture the tidal variability. Spatial
resolution of the regional model (3 vs 1 km) does not impact skill of the current prediction. Tidal response of the system
indicates excellent representation of the dominant M
2 tide for water level and currents. Diurnal tides, especially K
1, are amplified unrealistically with the application of coarse 27-km winds. Higher-resolution winds reduce current forecast
error with the exception of wind originating from the SSW, SSE, and E. These winds run shore parallel and are subject to strong
interaction with the shoreline that is poorly represented even by the 3-km wind fields. The vertical distribution of currents
is also well predicted by the coastal model. Spatial and temporal resolution of the wind forcing including areas close to
the shoreline is the most critical component for accurate current forecasts. Additionally, it is demonstrated that wind resolution
plays a large role in establishing realistic thermal and density structures in upwelling prone regions. 相似文献
372.
Triassic stretching directions in Iberia and North Africa inferred from magnetic fabrics 总被引:1,自引:0,他引:1
Ruth Soto Antonio M. Casas‐Sainz Beln Oliva‐Urcia Cristina García‐Lasanta Esther Izquierdo‐Llavall Bennacer Moussaid Jos Carlos Kullberg Teresa Romn‐Berdiel Yolanda Snchez‐Moya Alfonso Sopea Sara Torres‐Lpez Juan Jos Villalaín Hamidou El‐Ouardi Inmaculada Gil‐Pea Ann M. Hirt 《地学学报》2019,31(5):465-478
During the Triassic, Iberia and western North Africa displayed a unique situation in relation with the Central and North Atlantic opening and westward expansion of the Tethys. Unravelling the stretching direction in Triassic deposits of the studied area can help in our understanding of this scenario. The tectonic setting is characterized by localized basins with strong thickness variations greatly influenced by previous post‐Variscan mechanical discontinuities. In this work, we revise and compile magnetic fabric data from eight Triassic depocentres in terms of defining the stretching direction (i.e. magnetic lineation), resulting from extensional deformation of this period. Data show the importance of the opening of the Atlantic rift as the leading process during the Triassic. Dextral transtension can explain the deflection of the extensional direction observed in most studied depocentres that is caused by the activity of previous major oblique faults. 相似文献
373.
Alla Shogenova Anne Kleesment Ann Hirt Enn Pirrus Toivo Kallaste Kazbulat Shogenov Rein Vaher 《Studia Geophysica et Geodaetica》2009,53(1):111-131
The formation of hematite and goethite concretions in different sedimentary rocks including sandstones is an important diagenetic
process in the geologic history of the Earth. Its interpretation can also contribute to understanding the diagenetic history
of Martian iron hydroxide concretions.
A case study of iron-rich concretions from Estonian Middle Devonian sandstones exposed in ancient river valleys in southeastern
Estonia was carried out based on the results of mineralogical, petrographical, geochemical, petrophysical and magnetic analyses.
It was found that the high Fe2O3(total) content (25.0–39.5%), high magnetic susceptibility, bulk and grain density, very low porosity, corrosion and fracturing
of the quartz grains of the platy iron concretions are in contrast with properties of the Devonian host sandstones. However
the ferrous iron content (measured as FeO) of iron-rich concretions was as low as in the other Devonian rocks, suggesting
an oxidizing environment and arid climate during the cementation by iron-hydroxides. The fracturing of quartz grains cemented
by iron hydroxides could take place at near-surface conditions including vadose and phreatic zones in arid climate with high
evaporation rates. Such climatic conditions have been reported for the Baltic region during Devonian, Upper Permian and Triassic
times.
We have found that goethite is prevalent in the cement, replacing clay and carbonate minerals. We assume that this iron-rich
cement is originated from the mobilization of iron in host sandstones by groundwater, associated with tectonic activity at
the end of the Middle Devonian, evidenced by fracturing in Devonian outcrops and caves. Although this mobilization could occur
under reducing conditions, precipitation of goethite and hematite for the cementation could take place in oxidizing environment
along bedding planes close to the surface during short sedimentation breaks. Another possible time for the formation of iron
concretions could be Permian, under the condition of both arid climate and tectonic activity. 相似文献
374.
375.
Macrofaunal nematodes of the deep Whittard Canyon (NE Atlantic): assemblage characteristics and comparison with polychaetes
下载免费PDF全文
![点击此处可从《Marine Ecology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Laetitia M. Gunton Brian J. Bett Andrew J. Gooday Adrian G. Glover Ann Vanreusel 《Marine Ecology》2017,38(2)
Large nematodes form an important component of deep‐sea macrofaunal assemblages, but are often considered to be part of the meiobenthos and are rarely studied. We analysed the standing stocks, diversity, and functional group and genus‐level composition of macrofaunal nematodes at lower bathyal depths (3,500 m water depth) in the Whittard Canyon system (NE Atlantic) and on the adjacent continental slope. Five replicate sample sets were obtained using a Megacorer, at four locations (three canyon branches, one slope). Sediment samples were processed on a 500‐μm mesh to provide both nematode and polychaete data from the same samples. The dominant nematode genera included Paramesacanthion, Metacylicolaimus, Cylicolaimus and Phanodermopsis. Nematode standing stocks (density and biomass) increased significantly from slope to canyon locations. Similarly, nematode dominance increased substantially (and diversity decreased) from slope to canyon locations. Nematode feeding groups and tail shape groups also appeared to exhibit common trends across study locations. Nematode genus‐level faunal composition varied significantly between slope and canyon locations. We describe and discuss the broadly similar trends detected in the matching polychaete data, noting some differences in the polychaete density and diversity responses. We suggest that the similar trends in macrofaunal nematode and polychaete ecology across our four study locations reflect responses to both changing sedimentology and food availability. 相似文献
376.
Mary Ann Levine 《Geoarchaeology》2007,22(1):49-66
Although native copper has attracted the scholarly attention of both geologists and archaeologists since the middle of the 19th century, it is only recently that native copper studies have benefited from interdisciplinary research. This history of disciplinary solitude can be traced to the professionalization of the two fields in the early 20th century, an era in which crossdisciplinary communication began to wane. The effects of this phenomena resulted in the development of a model of aboriginal native copper procurement by archaeologists that did not take into account the geological literature, which had long identified numerous—rather than a single—source of native copper in North America. In this article, the author discusses how this disciplinary solitude developed and how it resulted in the creation of a dominant model for native copper procurement that constrained our understanding of aboriginal lifeways for generations. The author also considers how increasing collaboration between geologists and archaeologists since the 1970s has led to the reevaluation of an old model of native copper procurement that has been uncritically accepted by most archaeologists for over a century and a half. © 2007 Wiley Periodicals, Inc. 相似文献
377.
In western Jutland deposits with a texture and structure similar to Dutch cover sands have been found. Investigations have been carried out on the lithology and the lithostratigraphic sequences. Pollen analysis is used for biostratigraphic correlation, and ages have been obtained by the radiocarbon method as well as by thermoluminescence techniques using both quartz and eldspar. The five sites are presented separately and the data are integrated into a general stratigraphic outline of the Late Glacial cover-sand sequence in Jutland. During the latest part of the Upper Pleniglacial and the earliest Late Glacial, older cover-sand type was deposited. Locally this sediment was also deposited during the later parts of the Late Glacial. Younger cover-sand type was deposited primarily during the Early Dryas and Late Dryas, but some sand of this type was also laid down during the Allerød and the earliest Holocene. The palaeobotanical records are discontinuous, but plant growth was probably present throughout the Late Glacial; only during the Altered did the deposition of sand decrease long enough to allow a relatively stable vegetational development. The investigation shows that the sequence of events in Jutland is similar to the Dutch record. 相似文献
378.
Single-crystal structure determinations at pressure have shown that the structural response of synthetic (Mg0.6Fe0.4)SiO3 orthopyroxene to compression is the same as that previously observed in MgSiO3 orthoenstatite. At pressure below ~4?GPa there is no significant compression of the SiO4 tetrahedra, while above ~4?GPa the tetrahedra decrease in volume as a result of Si?O bond shortening. A study of the compressional behaviour of synthetic FeSiO3 orthoferrosilite also shows the same behaviour below 4?GPa, but studies at higher pressures are precluded due to the transformation of the sample to the higher density C2/c high-clinoferrosilite polymorph. A further single-crystal study to 6?GPa of a Ca2+-containing natural orthopyroxene shows that chemical substitution of, primarily, Al3+ and Ca2+ into the structure of orthopyroxene inhibits the initial rapid compression of the M2?O3 bonds observed in the synthetic samples, and no significant tetrahedral compression is observed in this sample. Raman data collected from synthetic MgSiO3 orthoenstatite show that there is a change in the rate of change of frequency with pressure, δν/δP, between 3.5 and 6.0?GPa, but no changes in the number of observed bands. These observations indicate a non-symmetry-breaking change in the properties of the orthoenstatite, which is associated with the change in compression mechanism observed using X-ray diffraction techniques at this pressure. 相似文献
379.
The loamy ?brickearth’? deposits overlying coarse cold climate Kempton Park, Lynch Hill and Taplow Gravels of the R. Thames in west London are dated by thermoluminescence and mineralogical comparisons with loesses of three known ages. Although much of the ?brickearth’? resembles loess, it often contains more sand or clay than typical loess, and the mineralogical studies suggest that even the coarse silt (16–63 μm) fraction is rarely similar in composition to any known English loess. The thermoluminescence measurements suggest that most of the ?brickearth’? on the Taplow and Lynch Hill Gravels was deposited in the late Devensian, whereas that on the Park Gravel is mainly Flandrian. It is suggested that the latter is mainly floodloam, whereas the earlier ?brickearth’? is a mixed aeolian sediment derived from various local sources in and close to the Thames Valley. 相似文献
380.