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61.
A study has been made of the time evolution of the flux of moisture E over grassland. The parameterization of E has been examined in order to formulate an equation depending on the net radiation flux and on bulk parameters which depend on the daily average meteorological situation and soil conditions. In particular the gradient of soil moisture has been recognized as playing a fundamental role in the time evolution of E(t). A time-dependent equation is proposed to compute in a statistical sense the irrigation needs or to forecast the hourly values of E(t), the maximum value E
0 and the time at which this maximum happens. 相似文献
62.
Experiments on degassing of water-saturated granite melts with a pressure drop from 100 and 450 MPa to 40 and 120 MPa, respectively,
at temperatures close to feldspar liquidus (750–700 °C), were carried out to determine the modality of water exsolution and
vesicle formation at the liquidus temperature. Pressure-drop rates as small as approximately 100 bar/day were used. Uniform
space distributions of bubbles of exsolved water were obtained with starting glass containing a small fraction (≈0.5 vol.%)
of trapped air bubbles. Volume crystallization of feldspar was observed in degassed melts supplied with seeds. Bubble size
distributions (BSD) measured in granite glasses after degassing are presented. Data on vesicle characteristics (number, radius,
area, elongation) were acquired on images digitized with standard software, while the reconstruction of size distributions
was performed with the Schwartz-Saltikov "unfolding" procedure. Bubble size distributions of size classes in the range 5–1000 μm
were acquired with proper magnification and satisfactory statistical reliability of determined number densities. The BSDs
of the experimental samples are compared with the results of measurements of rapidly degassed products of Mt. Etna and Vulcano
Island. Many particular features of the bubble nucleation and growth can be distinguished in an individual BSD. However, the
general BSD of the whole data set, including natural ones, can be relatively well described with linear regression in bilogarithmic
coordinates. The slope of this regression is approximately 2.8±0.1. This dependence is in striking contrast with distributions
theoretically predicted with classical nucleation models based on homogeneous nucleation of vesicles. The theoretical distribution
requires the occurrence of strong maxima that are not observed in our experimental and natural samples, thus arguing for heterogeneous
nucleation mechanisms.
Received: 1 October 1998 / Accepted: 25 June 1999 相似文献
63.
A warning system for rainfall-induced shallow failures 总被引:22,自引:0,他引:22
It is widely recognised that soil slips and debris flows are triggered by short intense storms. Owing its geologic, geomorphologic and climatic settings, the Piedmont Region (NW Italy) is highly prone to the occurrence of this kind of landslides. In the last two centuries, in fact, a total of 105 severe meteoric events which triggered shallow failures occurred and, of these, 18 events took place from 1990 to 2002. A fair number of rainfall thresholds have been proposed in the literature, defined both on empirical or on physical bases. Empirical thresholds are defined collecting rainfall data for landslide meteoric events and for events without landslides, while physical thresholds are based on numerical models that consider the relation between rainfall, pore pressure and slope stability. The main objective of this paper is the identification of the empirical triggering thresholds for the Piedmont Region. Four meteoric events were selected and analysed (November 4–5, 1994; July 7–8, 1996; April 27–30, 2000; October 13–16, 2000) because they supply a wide range of variation for both rainfall parameters (duration, intensity, cumulative rainfalls) and the number of induced landslides. In the intensity–duration plot, the critical limit is described by the equation: I=19D−0.50 (where I=rainfall intensity expressed in mm/h and D=rainfall duration expressed in hours). Such a limit is traced to envelop 90% of the points on the graph. In the NI–D diagram the triggering thresholds are given by the equations NI=0.76D−0.33 and NI=4.62D−0.79 (where NI=normalised intensity with respect to the annual precipitation, MAP, expressed in %, [(mm/h)/PMA]×100). In the article the different meaning of these thresholds is discussed. Finally, the diagram NI–NCR is proposed; the triggering threshold is given by the expression: NI=−0.09ln[NCR]+0.54 (where NCR is the normalised cumulative critical rainfall, [mm/PMA]×100). The application of the triggering thresholds as a fundamental element in a warning system dedicated to the safeguarding of population in landslide-prone areas is discussed. In detail an operating procedure which is presently being verified and tested in the studied area is described. 相似文献
64.
Pietro Passerini 《Environmental Geology》1984,6(4):211-221
The anthropostrome is used to denote the collective constructs of human artifacts and is characterized by repetitive geometrical
moduli, centralized energetic cyclons, and constrictive restraints to functional freedom of both human and non-human elements.
This unified, self-perpetuating, man-made environment is a high-level integrative structure where organism-like features are
developing while ocosystem-like features persist. Due to pervasive integration, urban-industrial men generally fail to perceive
the colonial nature of the autonomous unit which produced them Direct contacts with the world outside the anthropostrome are
scare, and most information and sensory experience are supplied by the anthropostrome itself
In spite of temporary or localized regressions, the global trend is apparently toward growth of the total anthropostrome Expansion
of urban systems will presumably be accelerated until environmental degradation and resource shortages act as natural constraints
The need for containment of the anthropostrome’s growth and for control of its swift noogentic development while avoiding
injury to men is possibly the next challenge to man’s evolutionary potential 相似文献
65.
Guglielmo Rossi Luca Tanteri Veronica Tofani Pietro Vannocci Sandro Moretti Nicola Casagli 《Landslides》2018,15(5):1045-1052
This paper presents the preliminary results of the IPL project 196 “Development and applications of a multi-sensor drone for geohazards monitoring and mapping.” The objective of the project is to test the applicability of a multi-sensor drone for the mapping and monitoring of different types of geohazards. The Department of Earth Sciences of the University of Florence has developed a new type of drone airframe. Several survey campaigns were performed in the village of Ricasoli, in the Upper Arno river Valley (Tuscany, Italy) with the drone equipped with an optical camera to understand the possibility of this rising technology to map and characterize landslides. The aerial images were combined and analyzed using Structure-from-Motion (SfM) software. The collected data allowed an accurate reconstruction and mapping of the detected landslides. Comparative analysis of the obtained DTMs also permitted the detection of some slope portions being prone to failure and to evaluate the area and volume of the involved mass. 相似文献
66.
Gazzola Laura Ferronato Massimiliano Frigo Matteo Janna Carlo Teatini Pietro Zoccarato Claudia Antonelli Massimo Corradi Anna Dacome Maria Carolina Mantica Stefano 《Computational Geosciences》2021,25(5):1751-1751
Computational Geosciences - A Correction to this paper has been published: https://doi.org/10.1007/s10596-021-10079-6 相似文献
67.
Land subsidence due to subsurface fluid (water, gas, oil) withdrawal is often predicted by either finite element or finite difference numerical models based on coupled poroelastic theory, where the soil is represented as a semi-infinite medium bounded by the traction-free (ground) surface. One of the variables playing a most important role on the final outcome is the flow condition used on the traction-free boundary, which may be assumed as either permeable or impermeable. Although occasionally justified, the assumption of no-flow surface seems to be in general rather unrealistic. A permeable boundary where the fluid pressure is fixed to the external atmospheric pressure appears to be more appropriate. This paper addresses the response, in terms of land subsidence, obtained with a coupled poroelastic finite element model that simulates a distributed pumping from a horizontal aquifer confined between two relatively impervious layers, and takes either a permeable boundary surface, i.e., constant hydraulic potential, or an impermeable boundary, i.e., a zero Neumann flow condition. The analysis reveals that land subsidence is rather sensitive to the flow condition implemented on the traction-free boundary. In general, the no-flow condition leads to an overestimate of the predicted ground surface settlement, which could even be 1 order of magnitude larger than that obtained with the permeable boundary. 相似文献
68.
The reported data present the stratigraphy of several sections across a Middle-Late Jurassic Radiolaritic Unit, well exposed
in different thrust sheets pertaining to the Maghrebian chain of Southwestern Sicily. The aim was to define the chronostratigraphical
distribution of the Jurassic biosiliceous sedimentation in the Sicanian palaeogeographical zone, a deep water basin belonging
to the Southern Tethys continental margin.
The radiolarian biostratigraphy indicates that the switching from carbonate to siliceous sedimentation in the Sicanian Basin
is referable to the Bajocian, as shown by the section of Campofiorito, near Corleone. The biostratigraphical dataset allows
the correlation between the onset of biosiliceous sedimentation and the fall of biodiversity in the Sicanian basin with the
carbonate productivity crisis, indicated by the highest eutrophication that affected Western Tethys during Middle Jurassic
times.
Editorial handling: J.-P. Billon-Bruyat & M. Chiari (Guest) 相似文献
69.
Shujun Ye Yue Luo Jichun Wu Xuexin Yan Hanmei Wang Xun Jiao Pietro Teatini 《Hydrogeology Journal》2016,24(3):695-709
Shanghai, in China, has experienced two periods of rapid land subsidence mainly caused by groundwater exploitation related to economic and population growth. The first period occurred during 1956–1965 and was characterized by an average land subsidence rate of 83 mm/yr, and the second period occurred during 1990–1998 with an average subsidence rate of 16 mm/yr. Owing to the establishment of monitoring networks for groundwater levels and land subsidence, a valuable dataset has been collected since the 1960s and used to develop regional land subsidence models applied to manage groundwater resources and mitigate land subsidence. The previous geomechanical modeling approaches to simulate land subsidence were based on one-dimensional (1D) vertical stress and deformation. In this study, a numerical model of land subsidence is developed to simulate explicitly coupled three-dimensional (3D) groundwater flow and 3D aquifer-system displacements in downtown Shanghai from 30 December 1979 to 30 December 1995. The model is calibrated using piezometric, geodetic-leveling, and borehole extensometer measurements made during the 16-year simulation period. The 3D model satisfactorily reproduces the measured piezometric and deformation observations. For the first time, the capability exists to provide some preliminary estimations on the horizontal displacement field associated with the well-known land subsidence in Shanghai and for which no measurements are available. The simulated horizontal displacements peak at 11 mm, i.e. less than 10 % of the simulated maximum land subsidence, and seems too small to seriously damage infrastructure such as the subways (metro lines) in the center area of Shanghai. 相似文献
70.
Jan Pietroń Jeffrey A. Nittrouer Sergey R. Chalov Tian Y. Dong Nikolay Kasimov Galina Shinkareva Jerker Jarsjö 《水文研究》2018,32(2):278-292
The Selenga River delta (Russia) is a large (>600 km2) fluvially dominated fresh water system that transfers water and sediment from an undammed drainage basin into Lake Baikal, a United Nations Educational, Scientific, and Cultural Organization World Heritage Site. Through sedimentation processes, the delta and its wetlands provide important environmental services, such as storage of sediment‐bound pollutants (e.g., metals), thereby reducing their input to Lake Baikal. However, in the Selenga River delta and many other deltas of the world, there is a lack of knowledge regarding impacts of potential shifts in the flow regime (e.g., due to climate change and other anthropogenic impacts) on sedimentation processes, including sediment exchanges between deltaic channels and adjacent wetlands. This study uses field measurements of water velocities and sediment characteristics in the Selenga River delta, investigating conditions of moderate discharge, which have become more frequent over the past decades (at the expense of peak flows, Q > 1,350 m3 s?1). The aims are to determine if the river system under moderate flow conditions is capable of supporting sediment export from the main distributary channels of the delta to the adjacent wetlands. The results show that most of the deposited sediment outside of the deltaic channels is characterized by a large proportion of silt and clay material (i.e., <63 μm). For example, floodplain lakes function as sinks of very fine sediment (e.g., 97% of sediment by weight < 63 μm). Additionally, bed material sediment is found to be transported outside of the channel margins during conditions of moderate and high water discharge conditions (Q ≥ 1,000 m3 s?1). Submerged banks and marshlands located in the backwater zone of the delta accumulate sediment during such discharges, supporting wetland development. Thus, these regions likely sequester various metals bound to Selenga River sediment. 相似文献