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21.
Mathematical Geosciences - Geological facies modeling is a key component in exploration and characterization of subsurface reservoirs. While traditional geostatistical approaches are still commonly... 相似文献
22.
Flood-prone areas assessment using linear binary classifiers based on flood maps obtained from 1D and 2D hydraulic models 总被引:3,自引:0,他引:3
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This paper presents the earliest temperature observations, scheduled every 3–4 h in the 1654–1670 period, which have been
recovered and analysed for the first time. The observations belong to the Medici Network, the first international network
of meteorological observations, based on eleven stations, the two main ones being Florence and Vallombrosa, Italy. All observations
were made with identical thermometers and operational methodology, including outdoor exposure in the shade and in the sunshine
to evaluate solar heating, state of the sky, wind direction and precipitation frequency. This paper will consider only the
regular temperature series taken in the shade. The observations were made with the newly invented spirit-in-glass thermometer,
also known as Little Florentine Thermometer (LFT). The readings have been transformed into modern units of temperature (°C)
and time (TMEC). The LFT has been analysed in detail: how it was made, its linearity, calibration and performances. Since
the middle of the LIA, the climate in Florence has shown less than 0.18°C warming. However, although the yearly average showed
little change, the seasonal departures are greater, i.e. warmer summers, colder winters and unstable mid seasons. The temperature
in the Vallombrosa mountain station, 1,000 m a.m.s.l, apparently rose more, i.e. 1.41°C. A discussion is made on the interpretation
of this finding: how much it is affected by climate change or bias. A continuous swinging of the temperature was observed
in the Mediterranean area, as documented by the long instrumental observations over the 1654–2009 period. However, changes
in vegetation, or exposure bias might have contributed to reduce the homogeneity of the series over the centuries. 相似文献
26.
Dario Camuffo C. Bertolin N. Diodato M. Barriendos F. Dominguez-Castro C. Cocheo A. della Valle E. Garnier M. -J. Alcoforado 《Climatic change》2010,100(1):137-142
The paper discusses the newly produced temperature and precipitation series from instrumental observations in the Western
Mediterranean (WM) area, dating back to 1654. The two series had a continuous swing and unstable coupling passing from correlation
to anti-correlation. Only after 1950 are they permanently anti-correlated with increasing temperature and decreasing precipitation.
It is not clear how long this coupling will persist. The analysis of the correlation between the Northern Hemisphere (NH)
and the WM temperature anomalies and their trends shows a certain variability from 1850 to 1950; later a strong coupling between
NH and WM. Results suggest that the WM climate is approaching a turning point that might locally oppose the adverse effects
of Global Warming. 相似文献
27.
Riccardo Campana Enrico Massaro Dario Gasparrini † Sara Cutini † Andrea Tramacere 《Monthly notices of the Royal Astronomical Society》2008,383(3):1166-1174
We developed a source detection algorithm based on the Minimal Spanning Tree (MST), that is a graph-theoretical method useful for finding clusters in a given set of points. This algorithm is applied to γ-ray bi-dimensional images where the points correspond to the arrival direction of photons, and the possible sources are associated with the regions where they clusterize. Some filters to select these clusters and to reduce the spurious detections are introduced. An empirical study of the statistical properties of MST on random fields is carried out in order to derive some criteria to estimate the best filter values. We also introduce two parameters useful to verify the goodness of candidate sources. To show how the MST algorithm works in practice, we present an application to an EGRET observation of the Virgo field, at high Galactic latitude and with a low and rather uniform background, in which several sources are detected. 相似文献
28.
Emplacement of small‐volume (<0·1 km3) pyroclastic flows is significantly influenced by topography. The Arico ignimbrite on Tenerife (Canary Islands) is a characteristic small‐volume pyroclastic flow deposit emplaced on high relief topography. The pyroclastic flow flowed down pre‐existing valleys on the southern slopes of the island. In proximal areas deep (up to 100 m) valleys acted as efficient conduits for the pyroclastic flow, which was mostly channelled; in this particular area the ignimbrite corresponds to a homogeneous, moderately welded deposit, consisting of flattened pumices in an abundant ashy matrix with a relatively low lithic fragment content. In intermediate zones significant changes occur in the steepness of the slope and, although still channelled, here the pyroclastic flow was influenced by hydraulic jumps. In this area, two different units can be clearly distinguished in the ignimbrite: the lower unit is composed of a lithic‐rich ground‐layer deposit that formed at the turbulent, highly concentrated head of the flow; the upper unit consists of a well welded pumice‐rich deposit that occasionally reveals a basal layer formed by shearing with the lower part. This division into two units is maintained as far as distal areas near the present‐day coastline, where the slope is very gentle or null and the ignimbrite is not channelled. The ground layer is not found in distal areas. The ignimbrite here only consists of the upper unit, which is occasionally repeated due to a surging process provoked by the lower flow speed, as the pyroclastic flow spread out of the channelled zone. A theoretical model on how topography controlled the deposition of the Arico ignimbrite is derived by interpreting the observed lithological and sedimentological variations in terms of changes in topography and bedrock morphology. This new model is of general applicability and will help to explain other deposits of similar characteristics. 相似文献
29.
Statistical facies classification from multiple seismic attributes: comparison between Bayesian classification and expectation–maximization method and application in petrophysical inversion 下载免费PDF全文
We present here a comparison between two statistical methods for facies classifications: Bayesian classification and expectation–maximization method. The classification can be performed using multiple seismic attributes and can be extended from well logs to three‐dimensional volumes. In this work, we propose, for both methods, a sensitivity study to investigate the impact of the choice of seismic attributes used to condition the classification. In the second part, we integrate the facies classification in a Bayesian inversion setting for the estimation of continuous rock properties, such as porosity and lithological fractions, from the same set of seismic attributes. The advantage of the expectation–maximization method is that this algorithm does not require a training dataset, which is instead required in a traditional Bayesian classifier and still provides similar results. We show the application, comparison, and analysis of these methods in a real case study in the North Sea, where eight sedimentological facies have been defined. The facies classification is computed at the well location and compared with the sedimentological profile and then extended to the 3D reservoir model using up to 14 seismic attributes. 相似文献
30.
Mohammad Koneshloo Saman A. Aryana Dario Grana John W. Pierre 《Mathematical Geosciences》2017,49(8):995-1020
Realistic and accurate static geologic models are an essential element needed to predict the behavior of subsurface reservoirs and play an important role in petroleum engineering. Data used in the development of a static geologic model are gathered from various sources, such as seismic, log, and core data, each of them providing information on different physical properties of interest and with varying degrees of resolution. Compiling all data from various sources into a single representation of the subsurface formation of interest is a daily challenge for many petroleum geologists and engineers. This paper describes a framework to develop and select process-mimicking models that are consistent with available seismic attributes, namely impedance. Using a process-mimicking modeling package, 75 models of a fluvial meandering system are generated, one of which is chosen as the “true” model and masked thereafter. The implemented selection method relies on the degree of similarity in the histogram of representations of clusters of all possible patterns in the seismic impedance domain based on each process-mimicking model and that of the “true” model at several resolutions. The results demonstrate the effectiveness of the use of a weighted average divergence distance across multiple levels to select process-mimicking models that honor seismic data the best. 相似文献