全文获取类型
收费全文 | 601篇 |
免费 | 41篇 |
国内免费 | 23篇 |
专业分类
测绘学 | 20篇 |
大气科学 | 62篇 |
地球物理 | 188篇 |
地质学 | 238篇 |
海洋学 | 68篇 |
天文学 | 61篇 |
综合类 | 5篇 |
自然地理 | 23篇 |
出版年
2024年 | 2篇 |
2023年 | 3篇 |
2022年 | 12篇 |
2021年 | 23篇 |
2020年 | 16篇 |
2019年 | 16篇 |
2018年 | 31篇 |
2017年 | 31篇 |
2016年 | 42篇 |
2015年 | 33篇 |
2014年 | 21篇 |
2013年 | 42篇 |
2012年 | 34篇 |
2011年 | 42篇 |
2010年 | 38篇 |
2009年 | 39篇 |
2008年 | 40篇 |
2007年 | 31篇 |
2006年 | 22篇 |
2005年 | 22篇 |
2004年 | 17篇 |
2003年 | 12篇 |
2002年 | 18篇 |
2001年 | 16篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1968年 | 1篇 |
1966年 | 1篇 |
1952年 | 4篇 |
1950年 | 1篇 |
1920年 | 1篇 |
1914年 | 1篇 |
1913年 | 1篇 |
排序方式: 共有665条查询结果,搜索用时 15 毫秒
301.
Snow zonation on Hielo Patagónico Sur, Southern Patagonia, derived from Landsat 5 TM data 总被引:1,自引:1,他引:0
Hielo Patagónico Sur (HPS), an icefield in Southern Patagonia, is the largest temperate ice mass in the southern hemisphere. Despite continued research efforts during the last decade many glaciological variables, especially mass balance, are still poorly known. This is partly because access to the icefield is difficult due to remoteness and persistent harsh weather conditions. Therefore, remote sensing appears to be a more suitable tool for the acquisition of data. In this work we present a remote sensing study of snow zonation on HPS using Landsat 5 Thematic Mapper data acquired on 12 March 2001. By using image processing and classification techniques, proved to be useful in other glaciated regions, we map for the first time the extent and occurrence of major snow zones on the whole HPS. We separate between two classes of ice and three classes of snow. Ice facies are classified as bare or debris (i.e. dirt) covered ice, covering 2454 km2 and 777 km2 respectively, or 18.4% and 5.8% of the icefield on the day of image acquisition. Snow types are classified according to spectral differences in the images, following the glacier facies concept. Two of the three snow cover types are interpreted to represent differences in snow grain size within a fairly homogeneous snow pack whereas the third one is interpreted to represent the slush zone. A first order altitudinal control on the distribution of these snow facies is evident. In addition, our results show that snow accumulation on HPS is markedly controlled by the interaction of strong west–northwest snow-bearing winds and the rough mountainous terrain. In order of decreasing altitude we find that the two snow facies and the slush facies occupy 3819 km2, 3292 km2 and 2295 km2 respectively, or 28.6%, 24.6% and 17.2% of the icefield, on the day of image acquisition. Estimates of equilibrium line altitude using our results yield values of 800–900 m above sea level for the western side and 1500–1600 m above sea level for the eastern side, with an accumulation area ratio of 0.74. 相似文献
302.
Pedro J. Amado Susana Martín-Ruíz Juan Carlos Suárez Armando Arellano Ferro Andrés Moya Ignasi Ribas Ennio Poretti 《Astrophysics and Space Science》2006,304(1-4):173-175
Photometric and spectroscopic results for the star HD 172189, member of the open cluster IC 4756 in the summer field of the space mission COROT, are presented. From photometric observations in the Strömgren system carried out at various epochs, its binary nature as well as the presence of a δ Scuti-type pulsating component have been discovered. The frequency analysis of the whole dataset confirms a dominant frequency of 19.5974 c d?1 with a maximum amplitude near 0.02 mag plus other frequencies in the range 18–20 c d?1. A preliminary orbital solution from the light curve and from four FEROS spectra reveals two similar components of around 1.5 M ⊙ orbiting with a period of 5.702 d. 相似文献
303.
304.
Tomás Morales-Juberías Martín Olazar Jose María Arandes Pedro Zafra Iñaki Antigüedad Félix Basauri 《Environmental Geology》1997,30(3-4):143-151
A model based on numerical solutions, which allows for solving the dispersion equation under variable recharge and velocity conditions, is developed to simulate solute transport in conduit flow aquifers during flow recession periods. As an example, the evolution of a tracer in the little known karst conduit that links the sinking stream of Oma valley to the Olalde spring is investigated in the karstic region of Santa Eufemia-Ereñozar (Basque Country, Spain). The model, with different hypothetical structures, allows for obtaining series of tracer breakthrough curves, which are fitted to experimental data using an optimization algorithm. These results, although they can be used to simulate the tracer evolution between the two points considered, do not allow for determining the internal structure and spatial disposition of contributions in the aquifer. 相似文献
305.
Gutiérrez Pedro J. Ortiz José L. Rodrigo Rafael López-Moreno José J. Jorda Laurent 《Earth, Moon, and Planets》2002,90(1-4):239-247
A simplified thermal model has been used to calculate thenon-gravitational forces acting on small irregular nuclei in the
orbit ofComet 46P/Wirtanen. The torque of thenon-gravitational force has beencalculated and the Euler equations have been
solved in order toinvestigate the rotational evolution of several irregular nuclei duringa single orbital step. Several initial
spin axis orientations andactivity patterns on their surfaces have been considered. The nucleiconsidered have a mean radius
of 1 km and their inertia moments havebeen calculated assuming a homogeneous bulk density of 500 kg/m3. Inall the simulations, the initial spin period is 6h and the nucleiinitially rotate around their shortest axis. Under these
assumptions,significant changes in the angular momentum and in spin period have beenobtained in all the simulations, but the
nucleus is found to practicallyremain in its spin state of lowest energy during the entire orbitalperiod. 相似文献
306.
Journal of Geographical Sciences - Water depths and flow velocities decisively influence the damage caused by flash floods. Geographic Information System (GIS) is a powerful and useful tool,... 相似文献
307.
Performance of intertidal topography video monitoring of a meso-tidal reflective beach in South Portugal 总被引:2,自引:1,他引:1
Michalis Ioannis Vousdoukas Pedro Manuel Ferreira Luis Pedro Almeida Guillaume Dodet Fotis Psaros Umberto Andriolo Rui Taborda Ana Nobre Silva Antonio Ruano Óscar Manuel Ferreira 《Ocean Dynamics》2011,61(10):1521-1540
This study discusses site-specific system optimization efforts related to the capability of a coastal video station to monitor
intertidal topography. The system consists of two video cameras connected to a PC, and is operating at the meso-tidal, reflective
Faro Beach (Algarve coast, S. Portugal). Measurements from the period February 4, 2009 to May 30, 2010 are discussed in this
study. Shoreline detection was based on the processing of variance images, considering pixel intensity thresholds for feature
extraction, provided by a specially trained artificial neural network (ANN). The obtained shoreline data return rate was 83%,
with an average horizontal cross-shore root mean square error (RMSE) of 1.06 m. Several empirical parameterizations and ANN
models were tested to estimate the elevations of shoreline contours, using wave and tidal data. Using a manually validated
shoreline set, the lowest RMSE (0.18 m) for the vertical elevation was obtained using an ANN while empirical parameterizations
based on the tidal elevation and wave run-up height resulted in an RMSE of 0.26 m. These errors were reduced to 0.22 m after
applying 3-D data filtering and interpolation of the topographic information generated for each tidal cycle. Average beach-face
slope tan(β) RMSE were around 0.02. Tests for a 5-month period of fully automated operation applying the ANN model resulted in an optimal,
average, vertical elevation RMSE of 0.22 m, obtained using a one tidal cycle time window and a time-varying beach-face slope.
The findings indicate that the use of an ANN in such systems has considerable potential, especially for sites where long-term
field data allow efficient training. 相似文献
308.
Elisa Villa Heather Stoll Pedro Farias Luna Adrados R. Lawrence Edwards Hai Cheng 《Quaternary Research》2013,79(1):1-5
Cemented calcareous breccias appear in the Picos de Europa (Cantabrian Mountains, Spain) resting on glacially abraded surfaces and covered by moraines. U/Th dating of the calcite coating the clasts was successful in two samples, the oldest one indicating that the breccias accumulated during or prior to Marine Isotope Stage (MIS) 11, and the youngest indicating later cementation during MIS 8. The former introduces a limit for the age of the glaciation preceding the breccias, which cannot correspond to an event younger than MIS 12. This is the oldest absolute age so far obtained for intercalated glacial/interglacial deposits of the Iberian Peninsula. 相似文献
309.
Abstract The first numerical age determinations from radiocarbon dating establish the chronology of glacial events in Redes Natural Park (Cantabrian Mountain, NW Spain). A core drilled in an ice-dammed deposit provided a minimum age of 28 990 ± 230 years BP for the maximum glacial expansion (phase I). Another core from a cirque bottom-fill provided organic sediment with 20 640 ± 300 years BP, a minimum age for the first glacial retreat (phase II). Radiometric dating of proglacial deposits interpreted as synchronous with the last glacial maximum phase in neighbouring Cornelia basin (Picos de Europa), yield ages of 40 480 ± 820 years BP. The chronological data presented in this work are consistent with the model of glacier evolution established in the Pyrénées, with a glacial maximum phase for the last glacial period older than 18 ka. © 2002 Éditions scientifiques et médicales Elsevier SAS. AU rights reserved. 相似文献
310.
Manuela Morales Demarco Pedro Oyhantçabal Karl-Jochen Stein Siegfried Siegesmund 《Environmental Earth Sciences》2013,69(4):1361-1395
Slates are internationally known as roof and façade-cladding material since prehistoric times. The methods required to mine and manufacture these dimensional stones are relatively simple in comparison to those utilized in granitic dimensional stones. This has led to a worldwide rentable commercialization of slate in the last centuries and also to the development of characteristic cultural landscapes. In Uruguay several slates are mined and used in architecture, especially as façade cladding and floor slabs. The most important slates regarding their production and utilization are the dolomitic slates. These dolomitic slates are associated with the Neoproterozoic thrust and fold belt of the Dom Feliciano belt. Representative samples have been geochemically and petrographically characterized, as well as petrophysically and petromechanically analyzed. The petrophysical and petromechanical properties were investigated in a very systematic way with respect to the new European standards, showing values comparable to those registered for internationally known slates. Detailed structural and deposit analysis were carried out in Uruguay in order to evaluate the dolomitic slate deposits. The slates are linked to calc-silicate strata in a greenschist facies volcano-sedimentary sequence and the deposits are located in the limb of a regional fold, where bedding and cleavage are parallel. The main lithotype is a layered and fine-grained dolomitic slate with a quite diverse palette of colors: light and dark green, gray, dark gray, reddish and black. The mined slate is split into slabs 0.5–2 cm thick. In the past, the average production in Uruguay was around 4,000 tons/year and a historical maximum of 13,000 tons was reached in 1993 (Oyhantçabal et al. in Z dt Ges Geowiss 158(3):417–428, 2007). The oscillations in the regional demand were the cause of several flourishing and decay cycles in the activity, but our investigation shows a considerable volume of indicated resources and therefore a very good potential. 相似文献