全文获取类型
收费全文 | 1542篇 |
免费 | 83篇 |
国内免费 | 18篇 |
专业分类
测绘学 | 31篇 |
大气科学 | 111篇 |
地球物理 | 404篇 |
地质学 | 565篇 |
海洋学 | 136篇 |
天文学 | 235篇 |
综合类 | 12篇 |
自然地理 | 149篇 |
出版年
2023年 | 9篇 |
2022年 | 5篇 |
2021年 | 36篇 |
2020年 | 27篇 |
2019年 | 27篇 |
2018年 | 50篇 |
2017年 | 47篇 |
2016年 | 55篇 |
2015年 | 50篇 |
2014年 | 67篇 |
2013年 | 107篇 |
2012年 | 63篇 |
2011年 | 95篇 |
2010年 | 79篇 |
2009年 | 112篇 |
2008年 | 86篇 |
2007年 | 67篇 |
2006年 | 66篇 |
2005年 | 63篇 |
2004年 | 59篇 |
2003年 | 52篇 |
2002年 | 60篇 |
2001年 | 21篇 |
2000年 | 23篇 |
1999年 | 23篇 |
1998年 | 21篇 |
1997年 | 18篇 |
1996年 | 27篇 |
1995年 | 18篇 |
1994年 | 15篇 |
1993年 | 3篇 |
1992年 | 20篇 |
1991年 | 5篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 11篇 |
1986年 | 7篇 |
1985年 | 12篇 |
1984年 | 15篇 |
1983年 | 13篇 |
1982年 | 15篇 |
1981年 | 10篇 |
1980年 | 13篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 4篇 |
1973年 | 2篇 |
排序方式: 共有1643条查询结果,搜索用时 15 毫秒
151.
152.
Adam Kovach Harold W. Fairbairn Patrick M. Hurley Miguel A.S. Basei Umberto G. Cordani 《Precambrian Research》1976,3(5):471-480
Rb/Sr whole rock as well as K/Ar whole rock and mineral age determinations have been carried out on drill core samples obtained from the crystalline basement underlying the Amazonas and Maranhão Basins in Brazil. The data confirm the existence of an ancient basement under the Upper and Middle Amazonas Basin. The primary age of the granitic rocks is estimated at about 1560 Ma which correlates with recent age data obtained on granitic rocks on both sides of the Amazonas syneclise. In some areas the K/Ar ages show a decrease probably due to the effect of the Nickerie thermal episode described previously in the Guayana Shield.In the basement of the interconnected Lower Amazonas and Maranhão Basins Late Precambrian (Caririan) metamorphism and igneous activity seems to have been pervasive. The data allow the continuation of the Brazilian age province known in northeastern Brazil under the Maranhão Basin, linking this province to the Brasilia-Paraguay orogenic belt of similar age. 相似文献
153.
Deep and surface magnetic measurements, gravity and subbottom seismic profiling data have been gathered across a part of the northwest Atlantic smooth-rough magnetic border. These data indicate that the transition involves only a change in the magnetic field, without associated gravity or subbottom topographic signature. Model studies suggest that a change in basement magnetization from 0.010 emu/cm3 to 0.005 emu/cm3 could account for the magnetic field change across the boundary from the rough to the smooth sectors. Various theories previously proposed to explain this magnetic boundary are discussed with respect to these newer data; reduction of basement magnetization by weathering of the proto-Atlantic Ocean floor as described by Drake et al. (1968) is the preferred explanation. 相似文献
154.
Organic carbon from sediments collected in Texas seagrass meadows was enriched in 13C by an average of 6.6% relative to organic carbon from offshore sediments. Within the South Texas hay system examined. δ13C values became increasingly more typical of offshore sediments with increasing distance from seagrass meadows. This permits the use of carbon isotope data as a measure of the relative contributions of seagrasses and plankton to sedimentary organic matter. 相似文献
155.
156.
Jeffrey Neal Guy Schumann Paul Bates Wouter Buytaert Patrick Matgen Florian Pappenberger 《水文研究》2009,23(25):3641-3649
River discharge is currently monitored by a diminishing network of gauges, which provide a spatially incomplete picture of global discharges. This study assimilated water level information derived from a fused satellite Synthetic Aperture Radar (SAR) image and digital terrain model (DTM) with simulations from a coupled hydrological and hydrodynamic model to estimate discharge in an un‐gauged basin scenario. Assimilating water level measurements led to a 79% reduction in ensemble discharge uncertainty over the coupled hydrological hydrodynamic model alone. Measurement bias was evident, but the method still provided a means of improving estimates of discharge for high flows. The study demonstrates the potential of currently available synthetic aperture radar imagery to reduce discharge uncertainty in un‐gauged basins when combined with model simulations in a data assimilation framework, where sufficient topographic data are available. The work is timely because in the near future the launch of satellite radar missions will lead to a significant increase in the volume of data available for space‐borne discharge estimation. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
157.
Pim de Klerk Andreas Haberl Andreas Kaffke Matthias Krebs Izolda Matchutadze Merten Minke Jenny Schulz Hans Joosten 《Quaternary Science Reviews》2009,28(9-10):890-910
The Kolkheti lowlands of western Georgia have a unique vegetation and a rich cultural history. Palynological and macrofossil analysis accompanied by AMS 14C-dates of the deposits of the Ispani 2 mire near Kobuleti allow the reconstruction of regional vegetation, environmental history and local peatland development within the context of Black Sea level and cultural changes. Comparison of two adjacent peatland cores confirms spatial differences in wetland development. Prior to 5400 cal yr BP, the Ispani basin was a floodplain of an active river system where overbank deposits with fluvially transported Castanea pollen were deposited. Subsequently, a lake or lagoon developed in which reeds expanded. These were succeeded by herb-rich open alder carrs. After 1900 cal yr BP, Carpinus and Fagus expanded on the dry grounds, where formerly Quercus was more abundant. Also Castanea declined. Local reedbeds, that burned regularly, succeeded the alder carr. After 1000 cal yr BP, a percolation bog developed resulting in the formation of 4 m of loose, porous, and largely undecomposed Sphagnum austinii peat with Molinia roots. The upper 50 cm of the analysed section show extensive human impact on the landscape during the 20th century. 相似文献
158.
Yasuhiro Hashimoto J. Patrick Henry Hans Böhringer 《Monthly notices of the Royal Astronomical Society》2007,380(2):835-838
We investigated the influence of environment on cluster morphology by examining the alignment of the cluster position angle with respect to the nearest neighbour cluster. The cluster position angle and ellipticity were measured using high spatial resolution X-ray data taken from the Chandra archive, while the nearest neighbour sample was extracted from the Abell cluster catalogue. We found high confidence for an alignment when neighbour distance (Dn) was less than 70 h −1 Mpc, while we found no significant variations of the confidence level at various values of Dn less than 70 h −1 Mpc. 相似文献
159.
A global positioning system and ground penetrating radar surveys is used to produce digital elevation models of the surface and bed of Brewster Glacier. These are used to derive maps of subglacial hydraulic potential and drainage system structure using three different assumptions about the subglacial water pressure (Pw): (i) Pw = ice overburden; (ii) Pw = half ice overburden; (iii) Pw = atmospheric. Additionally, 16 dye‐tracing experiments at 12 locations were performed through a summer melt season. Dye return curve shape, together with calculations of transit velocity, dispersivity and storage, are used to infer the likely morphology of the subglacial drainage system. Taken together, the data indicate that the glacier is underlain by a channelised but hydraulically inefficient drainage system in the early summer in which water pressures are close to ice overburden. By mid‐summer, water pressures are closer to half‐ice overburden and the channelised drainage system is more hydraulically efficient. Surface streams that enter the glacier close to the location of major subglacial drainage pathways are routed quickly to the channels and then to the glacier snout. Streams that enter the glacier further away from the drainage pathways are routed slowly to the channels and then to the snout because they first flow through a distributed drainage system. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
160.
Dominant amphipods of Posidonia oceanica seagrass meadows display considerable trophic diversity 下载免费PDF全文
Loïc N. Michel Patrick Dauby Sylvie Gobert Martin Graeve Fabienne Nyssen Nicolas Thelen Gilles Lepoint 《Marine Ecology》2015,36(4):969-981
Gut content examination and trophic markers (fatty acids, stable isotopes of C and N) were combined to delineate the diet of the dominant species of amphipods from Mediterranean Posidonia oceanica seagrass meadows and to highlight trophic diversity among this community. Our results indicate that, although all dominant species heavily relied on macroalgal epiphytes, considerable interspecific dietary differences existed. Carbon stable isotope ratios notably showed that some of the amphipod species favored grazing on epiphytes from leaves or litter fragments (Apherusa chiereghinii, Aora spinicornis, Gammarus aequicauda), while others such as Dexamine spiniventris preferred epiphytes from rhizomes. The remaining amphipods (Caprella acanthifera, Ampithoe helleri and Gammarella fucicola) readily consumed both groups. In addition, SIAR modeling suggested that most species had a mixed diet, and relied on several food items. Fatty acid analysis and gut contents revealed that contributions of microepiphytic diatoms and of benthic and suspended particulate organic matter to the diet of amphipods were anecdotal. None of the examined species seemed to graze on their seagrass host [low 18:2(n‐6) and 18:3(n‐3) fatty acids contents], but Gammarus aequicauda partly relied on seagrass leaf detritus, as demonstrated by the lesser 13C‐depletion of their tissues. Overall, our findings suggest that amphipods, because of their importance in the transfer of organic matter from primary producers and detritus to higher rank consumers, are key items in P. oceanica‐associated food webs. 相似文献