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91.
Frédéric Liébault Hervé Bellot Margot Chapuis Sébastien Klotz Michaël Deschâtres 《地球表面变化过程与地形》2012,37(4):385-399
This paper reports a radiofrequency identification (RFID) tracing experiment implemented in a high‐sediment‐load mountain stream typical of alpine gravel‐bed torrents. The study site is the Bouinenc Torrent, a tributary to the Bléone River in southeast France that drains a 38·9‐km² degraded catchment. In spring 2008, we deployed 451 tracers with b‐axis ranging from 23 to 520 mm. Tracers were seeded along eight cross‐sections located in the upstream part of the lowest 2·3 km of the stream. Three tracer inventories were implemented in July 2008, 2009 and 2010. Recovery rates calculated for mobile tracers declined from 78% in 2008 to 45% in 2009 and 25% in 2010. Observations of tracer displacement revealed very high sediment dispersion, with frontrunners having travelled more than 2 km only three months after their deployment. The declining recovery rate over time was interpreted as resulting from rapid dispersion rather than deep burial. We evaluated that 64% of the tracers deployed in the active channel were exported from the 2·3‐km study reach three years after the onset of the tracing experiment. Travel distances were characterized by right‐skewed and heavy‐tailed distributions, correctly fitted by a power‐law function. This supports the idea that in gravel‐bed rivers with abundant sediment supply relative to transport capacity, bedload transport can be viewed as a superdiffusive sediment dispersion process. It is also shown that tracers initially deployed in the low‐flow channel were characterized by a 15‐ to 30‐fold increase of mobility compared to tracers deployed in gravel bars. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
92.
We inferred the temperature and environmental conditions of Smreczynski Staw Lake in the Tatra Mountains, southern Poland,
from a sediment record covering the last 1,500 years. Paleobiological methods (cladocera, chironomid, and diatom analyses)
were used together with sedimentological analysis and dating. These studies provide new information about the timing and character
of climate fluctuations during the Little Ice Age (LIA). The Medieval Warm Period ended in the Tatra region at the beginning
of the thirteenth century, followed by the first episode of the LIA. The LIA was a relatively long but unstable period. The
first part of the LIA was cold in the Tatra Mountains, without evidence of increasing precipitation, while the second part,
after AD 1540, was cold and humid. The LIA terminated in the Tatra Mountains at the beginning of the twentieth century, although
some aspects of its climatic and sedimentological regime continued until the 1920s. We also found some evidence of warming
and acidification during the twentieth century. 相似文献
93.
The rate of sedimentation in Lake Kinneret was measured over several years by means of sediment traps, in up to seven different locations in the lake. Gross sedimentation rates measured in the sediment traps vary from about 1·5 kg m−2 a−1 in the deepest part of the lake up to 10 kg m−2 a−1 near the mouth of the upper Jordan river. The rate of sedimentation near the Jordan's inflow is highly correlated to flow discharge in the river, while in the centre of the lake the seasonal sedimentation pattern is mainly correlated to the bloom period of Peridinium gatunense. During the bloom period of Peridinium gatunense sedimentation rates all over the lake are very similar, indicating that the Peridinium is evenly distributed in the lake. The average suspended sediment discharge of the upper Jordan river flowing into the lake is 41 000 ton a−1.Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
94.
95.
Several researchers have investigated morphological changes on the south-eastern Mediterranean coast during the late Holocene.
However, very few of these studies include quantitative data covering the last 200 years. In this study, topographical maps,
nautical charts and aerial photographs are used to estimate the shoreline migrations and beach–nearshore sand balance over
the last 200 years in Haifa Bay, Israel, the northernmost final depositional sink of the Nile littoral cell. The findings
reflect two main periods. During the first period, between 1799 and 1928, human intervention along the bay’s coast was negligible,
a significant coastal expansion of ∼50 to 150 m (averages of 0.4–1.2 m/year) was measured, and sand accumulation was estimated
at ∼70,000 m3 annually in the beach–nearshore area. A dramatic change in the sedimentological pattern was observed during the second period,
between 1928 and 2006, following the completion of Haifa Port’s main breakwater (1929–1933). During this period, most of the
bay’s coast was in a steady state, with seasonal fluctuations of less than about ±20 m, and slight erosion of ∼7,000 m3 annually. These findings are consistent with previous studies which conclude that from approximately 4,000 years ago until
the construction of Haifa Port, sea level remained relatively stable, and a continuous accumulation of Nile-derived sand dried
up the Zevulun Plain and shifted the Haifa Bay shoreline westwards to its present location. This long-term trend ceased after
completion of the Haifa Port main breakwater. 相似文献
96.
The anelastic nonhydrostatic model EULAG is a candidate for the future dynamical core of a numerical weather prediction model.
Achieving such an objective requires a number of experiments focused on testing correctness of the solutions and robustness
of the solver. In the spirit of this idea, a set of tests related to standard atmospheric problems was performed, of which
the two regarding development and evolution of a supercell were employed as benchmarks of moist dynamics of the model. Their
results are discussed in this paper. Development and evolution of a stormsystem with a set of characteristic features such
as stormsplitting along with the generation of horizontal vorticity and cold pool formation is investigated. In addition,
the influence of domain geometry, boundary conditions and subgrid-scale mixing is examined. 相似文献
97.
For the last sixty years, two institutions have shaped the destiny of the town of O?wi?cim in southern Poland. One of these institutions is globally recognised, its history and development widely researched; the other is well known only amongst Polish industrialists, perhaps Polish economic geographers, and amongst the people of O?wi?cim. These two institutions are the Auschwitz State Museum and the chemical firm Dwory SA. Both institutions have their roots in the German Occupation of Poland 1939-1945. This paper presents the tale of these two institutions in order not only to highlight the need to embed memorial sites in their wider contexts, but also to indicate the impact of such sites as political-economic institutions, with the influence to shape social and economic landscapes. In laying out the geographies of the town and its two major institutions, we draw attention to the ways in which Holocaust memorialisation and post-socialist transformation are articulated with each other, not only here in O?wi?cim, and also with wider processes of social, economic, political and cultural change. 相似文献
98.
A sediment core from the Arctic Revvatnet (Hornsund area, SW Spitsbergen, Svalbard) provided data on environmental changes over the last 3100 years. Diatom analysis showing the domination of planktonic Cyclotella forms suggested good edaphic conditions until the middle of the nineteenth century, even during the Little Ice Age. A thermally stratified and relatively stable water column with good mixing allowed small, less heavily silicified Cyclotella sensu lato to develop during this time. The climate warming at the beginning of the twentieth century induced intensification of erosion processes in the catchment of the lake and caused an increase in the sedimentation rate. These processes have caused a lack of thermal stratification by disturbances in the water column and an increase of nutrients, consequently driving changes in the diatom species composition, which became dominated by benthic forms. In this period, almost all planktonic taxa disappeared or abruptly decreased in frequency. Higher temperatures accelerated the melting of nearby glaciers, which caused an increase in the activity of diatoms typical of running waters. Also a few Cladocera species appeared at the first time in the youngest samples. 相似文献
99.
Microconchids are a group of tiny, encrusting tubeworms. They appeared in the Late Ordovician, some 450 Myr ago, flourished during the rest of Palaeozoic and Triassic, and became extinct in the Middle Jurassic. Their morphological resemblance to the sedentary polychaete genus Spirorbis, very common in marine environments, misled various authors for decades. This mistake originally gave the genus Spirorbis an enormous stratigraphical range, from Ordovician to Recent. Indeed, microconchids provide an excellent example of evolutionary convergence with respect to both their morphology and ecology. In the late 1970s these ‘spirorbids’ were interpreted as vermetid gastropods on the basis of the inner architecture and microstructure of their tubes. This idea, however, was challenged in the 1990s when detailed microstructural investigation showed them to be neither polychaetes nor gastropods, but closely related to an extinct Palaeozoic enigmatic group of organisms called tentaculitids. No thorough investigation of their origin, phylogeny and ecology has ever been conducted, but new data concerning their palaeobiology has come to the light during the last few years. 相似文献
100.
Andrzej Baran John Telting Roy Østensen Maciej Winiarski Marek Drożdż Dorota Kozieł Mike Reed Raquel Oreiro Roberto Silvotti Michał Siwak Uli Heber Peter Papics 《Astrophysics and Space Science》2010,329(1-2):199-203
We present early results of the application of a method which uses multicolor photometry and spectroscopy for ? discrimination. This method has been successfully applied to the pulsating hot subdwarf Balloon?090100001. Here we apply the method to QQ?Vir (PG1325+101). This star was observed spectroscopically and photometrically in 2008. Details on spectroscopy can be found in Telting et al. (Astrophys. Space Sci. 2010, this volume), while photometry and preliminary results on ? discrimination are provided here. The main aim of this work was to compare the value of the ? parameter derived for the main mode in QQ?Vir to previously published values derived by using different methods. 相似文献