全文获取类型
收费全文 | 679篇 |
免费 | 30篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 32篇 |
大气科学 | 119篇 |
地球物理 | 149篇 |
地质学 | 244篇 |
海洋学 | 49篇 |
天文学 | 73篇 |
综合类 | 3篇 |
自然地理 | 42篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 13篇 |
2019年 | 10篇 |
2018年 | 24篇 |
2017年 | 30篇 |
2016年 | 37篇 |
2015年 | 22篇 |
2014年 | 23篇 |
2013年 | 40篇 |
2012年 | 34篇 |
2011年 | 37篇 |
2010年 | 44篇 |
2009年 | 41篇 |
2008年 | 36篇 |
2007年 | 32篇 |
2006年 | 23篇 |
2005年 | 28篇 |
2004年 | 20篇 |
2003年 | 11篇 |
2002年 | 24篇 |
2001年 | 18篇 |
2000年 | 5篇 |
1999年 | 21篇 |
1998年 | 5篇 |
1997年 | 10篇 |
1996年 | 11篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1984年 | 4篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1971年 | 2篇 |
1951年 | 2篇 |
1948年 | 1篇 |
排序方式: 共有711条查询结果,搜索用时 171 毫秒
161.
162.
163.
164.
165.
B. Keating N. Z. Cherkis P. W. Fell D. Handschmacher R. N. Hey A. Lazarewicz D. F. Naar R. K. Perry D. Sandwell D. C. Schwank P. Vogt B. Zondek 《Marine Geophysical Researches》1984,7(1-2):69-71
Knowledge of the locations and sizes of seamounts is of great importance in applications such as inertial navigation and ocean
mining. The quality and density of bathymetry data in the equatorial regions and the southern hemisphere are, unifortunately,
highly variable. Our present knowledge of bathymetry, and in particular of seamount locations and characteristics, is based
upon ship surveys, which are both time-consuming and expensive. It is likely that a significant number of uncharted seamounts
exist throughout the oceans, and remote-sensing techniques may be the most effective means of locating them. 相似文献
166.
The stratigraphic evolution of the Indus Fan and the history of sedimentation in the Arabian Sea 总被引:6,自引:1,他引:6
Clift Peter Gaedicke Christoph Edwards Rosemary Il Lee Jae Hildebrand Peter Amjad Shahid White Robert S. Schlüter Hans-Ulrich 《Marine Geophysical Researches》2002,23(3):223-245
The Indus Fan records the erosion of the western Himalayas and Karakoram since India began to collide with Asia during the Eocene, 50 Ma. Multi-channel seismic reflection data from the northern Arabian Sea correlated to industrial well Indus Marine A-1 on the Pakistan Shelf show that sedimentation patterns are variable through time, reflecting preferential sedimentation in deep water during periods of lower sea-level (e.g., middle Miocene, Pleistocene), the diversion of sediment toward the east following uplift of the Murray Ridge, and the autocyclic switching of fan lobes. Individual channel-levee systems are estimated to have been constructed over periods of 105–106 yr during the Late Miocene. Sediment velocities derived from sonobuoys and multi-channel stacking velocities allow sections to be time-depth converted and then backstripped to calculate sediment budgets through time. The middle Miocene is the period of most rapid accumulation, probably reflecting surface uplift in the source regions and strengthening of the monsoon at that time. Increasing sedimentation during the Pleistocene, after a late Miocene-Pliocene minimum, is apparently caused by faster erosion during intense glaciation. The sediment-unloaded geometry of the basement under the Pakistan Shelf shows a steep gradient, similar to the continent-ocean transition seen at other rifted volcanic margins, with basement depths on the oceanward side indistinguishable from oceanic crust. Consequently we suggest that the continent-ocean transition is located close to the present shelf break, rather than >350 km to the south, as previously proposed. 相似文献
167.
Anja Guhl Pascal Bertran Christoph Zielhofer Kathryn E. Fitzsimmons 《Boreas: An International Journal of Quaternary Research》2013,42(2):317-332
Two sand wedge structures and their host sediments, from Jonzac in SW France, were successfully dated using Optically Stimulated Luminescence (OSL) measurements on both small aliquots and single grains of quartz from the 180–212 μm size fraction. One of the sand wedges clearly contains primary infilling. However, grain‐size analysis and field observations do not clearly indicate whether the other feature represents a primary sand wedge or a composite sand wedge with primary and secondary infilling. OSL results and the geological setting justify using the Central Age Model (CAM) for the calculation of age estimates. Grain‐size analysis and detailed investigations of OSL results revealed the contamination of one sand wedge sample with host sediment. However, age calculation using the Finite Mixture Model (FMM) provided what is considered to be a reliable age estimate for the contaminated sample. The age estimates for all samples correspond to Marine Isotope Stage (MIS) 3. While fine‐grained sediments were deposited in the middle of MIS 3 (c. 43–55 ka), the sand wedges unexpectedly correspond to the end of this period (c. 33 ka) or the onset of MIS 2 (c. 27 ka). The sand wedges were probably formed during intense but short cold periods, possibly correlated with a Heinrich event (H2 and/or H3). The results help us to assess how effective luminescence dating is on sand wedges and the limitations involved in correlating sand wedge ages with Heinrich events, and contribute to the debate on the timing of cryogenic formation processes and the permafrost distribution in SW France. 相似文献
168.
David H. Roberts Antony J. Long Bethan J. Davies Matthew J. R. Simpson Christoph Schnabel 《第四纪科学杂志》2010,25(6):850-864
This paper investigates the processes governing bedrock bedform evolution in ice sheet and ice stream areas in central West Greenland, and explores the evidence for a cross‐shelf ice stream at the Last Glacial Maximum (LGM). To the east of Sisimiut the formation of streamlined bedforms with high elongation ratios and high bedform density has been controlled by geological structure and topography in slow‐flowing ice sheet areas. At the coast, the effects of regional flow convergence, caused by coastal fjord orientation, routed ice into the Sisimiut/Itilleq area where it formed an ice stream onset zone. This funnelled ice into an offshore trough (Holsteinsborg Dyb), resulting in a southwesterly regional ice flow direction and the formation of a topographically routed ice stream (Holsteinsborg Isbrae). To the south of this, striae and bedform evidence show that local valley glaciers initially flowed east to west across the coast, but were later redirected by the Itilleq Fjord ice which turned southwestward due to diffluent flow and deflection by Holsteinsborg Isbrae. Roches moutonnées in this area have low elongation ratios and high bedform density, but do not provide unequivocal support for ice streaming, as they are a product of both bedrock structure and changes in ice flow direction, rather than enhanced flow velocities. Cosmogenic surface exposure ages limit maximum ice sheet surface elevation to ca. 755–810 m above sea level in this region. Such ice thickness enabled Holsteinsborg Isbrae to reach the mid/outer continental shelf during the LGM, and to contribute to the formation of a trough mouth fan and the Outer Hellefisk moraines. Initial deglaciation across this region was driven by rising sea level and increasing air temperatures prior to the Bølling Interstadial at ca. 14.5 cal. ka BP. Between 12 and 10 cal. ka BP both increased air and ocean temperatures post the Younger Dryas, and peak sea‐level rise up to the marine limit, caused accelerated thinning and marginal retreat through calving, although dating evidence suggests ice streams remained along the inner shelf/coast boundary until at least ca. 10 cal. ka BP, their longevity maintained by increased ice thickness and ice discharge. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
169.
A. Milkov P. Vogt G. Cherkashev G. Ginsburg N. Chernova A. Andriashev 《Geo-Marine Letters》1999,19(1-2):38-47
A survey of the submarine Håkon Mosby mud volcano (HMMV) area by photo and video cameras permits the classification and mapping of sea-floor terrains. Approximate concentric zoning is seen in the distribution of the terrains, which correlates well with morphostructural elements of the mud volcano. A relatively limited biological community, dominated by tubeworms (Pogonophora and Polychaeta) and demersal fish, exists on the HMMV. Photo and video images show no evidence for gas bubbles in the water column, although methane is present in the mud volcano sediments. White patches, which comprise over 75% of the sea floor in some areas, are interpreted to be bacterial mats and/or gas hydrates. 相似文献
170.
Daniel Schimpf Rolf Kilian Andreas Kronz Klaus Simon Christoph Spötl Gerhard Wörner Michael Deininger Augusto Mangini 《Quaternary Science Reviews》2011,30(3-4):443-459
Stalagmites are important palaeo-climatic archives since their chemical and isotopic signatures have the potential to record high-resolution changes in temperature and precipitation over thousands of years. We present three U/Th-dated records of stalagmites (MA1–MA3) in the superhumid southern Andes, Chile (53°S). They grew simultaneously during the last five thousand years (ka BP) in a cave that developed in schist and granodiorite. Major and trace elements as well as the C and O isotope compositions of the stalagmites were analysed at high spatial and temporal resolution as proxies for palaeo-temperature and palaeo-precipitation. Calibrations are based on data from five years of monitoring the climate and hydrology inside and outside the cave and on data from 100 years of regional weather station records.Water-insoluble elements such as Y and HREE in the stalagmites indicate the amount of incorporated siliciclastic detritus. Monitoring shows that the quantity of detritus is controlled by the drip water rate once a threshold level has been exceeded. In general, drip rate variations of the stalagmites depend on the amount of rainfall. However, different drip-water pathways above each drip location gave rise to individual drip rate levels. Only one of the three stalagmites (MA1) had sufficiently high drip rates to record detrital proxies over its complete length. Carbonate-compatible element contents (e.g. U, Sr, Mg), which were measured up to sub-annual resolution, document changes in meteoric precipitation and related drip-water dilution. In addition, these soluble elements are controlled by leaching during weathering of the host rock and soils depending on the pH of acidic pore waters in the peaty soils of the cave’s catchment area. In general, higher rainfall resulted in a lower concentration of these elements and vice versa. The Mg/Ca record of stalagmite MA1 was calibrated against meteoric precipitation records for the last 100 years from two regional weather stations. Carbonate-compatible soluble elements show similar patterns in the three stalagmites with generally high values when drip rates and detrital tracers were low and vice versa. δ13C and δ18O values are highly correlated in each stalagmite suggesting a predominantly drip rate dependent kinetic control by evaporation and/or outgassing. Only C and O isotopes from stalagmite MA1 that received the highest drip rates show a good correlation between detrital proxy elements and carbonate-compatible elements. A temperature-related change in rainwater isotope values modified the MA1 record during the Little Ice Age (~0.7–0.1 ka BP) that was ~1.5 °C colder than today. The isotopic composition of the stalagmites MA2 and MA3 that formed at lower drip rates shows a poor correlation with stalagmite MA1 and all other chemical proxies of MA1. ‘Hendy tests’ indicate that the degassing-controlled isotope fractionation of MA2 and MA3 had already started at the cave roof, especially when drip rates were low. Changing pathways and residence times of the seepage water caused a non-climatically controlled isotope fractionation, which may be generally important in ventilated caves during phases of low drip rates. Our proxies indicate that the Neoglacial cold phases from ~3.5 to 2.5 and from ~0.7 to 0.1 ka BP were characterised by 30% lower precipitation compared with the Medieval Warm Period from 1.2 to 0.8 ka BP, which was extremely humid in this region. 相似文献