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61.
62.
Action-angle variables for the Levi-Civita regularized planar Kepler problem were introduced independently first by Chenciner and then by Deprit and Williams. The latter used explicitly the so-called Lissajous variables. When applied to the transformed Keplerian Hamiltonian, the Lissajous transformation encounters the difficulty of being defined in terms of the constant frequency parameter, whereas the Kepler problem transformed into a harmonic oscillator involves the frequency as a function of an energy-related canonical variable. A simple canonical transformation is proposed as a remedy for this inconvenience. The problem is circumvented by adding to the physical time a correcting term, which occurs to be a generalized Kepler’s equation. Unlike previous versions, the transformation is symplectic in the extended phase space and allows the treatment of time-dependent perturbations. The relation of the extended Lissajous–Levi-Civita variables to the classical Delaunay angles and actions is given, and it turns out to be a straightforward generalization of the results published by Deprit and Williams. 相似文献
63.
Maciej Pawlikowski Witold P. Alexandrowicz Ladislav Banesz Josef Hromada Janusz K. Kozlowski Krzysztof Sobczyk Barbara Kazior 《Geoarchaeology》1998,13(6):565-594
Moravany-Lopata, located in the complex of sites in the middle Vah basin, dates to the period immediately preceding the LGM. The authors use this site to demonstrate the usefulness of mineralogical, sedimentological, palaeomalacological, and anthropogenic criteria for the correlation of loess profiles. This analysis is especially concerned with sites in loess territories where the loess layers covering archaeological levels are not thick. Such sites occur frequently on the plateaus of the northern part of Central Europe, though they appear most notably in the areas in which the last loess cover, corresponding to the period after the last Pleniglacial and/or Late Glacial postloess sediments, is absent. The archaeological levels dated to before or directly after the LGM occur in the upper portion of the loess, overlain by the Holocene soil. The investigations at the Moravany-Lopata site have confirmed the usefulness of the anthropogenic indicators in the 0.1–1.0 mm fraction for the identification of occupation levels extending even beyond the area of occurrence of macrofinds and evident type structures. On this basis, a relationship could be established between two occupational levels and two ice-wedge generations in the period from 21.4 to 20 ky. Gravettian settlement in western Slovakia seems to have persisted up to the maximum of the LGM. Population groups representing the end of the shouldered points horizon (pointes à cran) appeared in western Slovakia in the intervals between the formation of large networks of ice wedges. The next settlement phase in that territory falls at about 18–17 ky B.P. This is the Epigravettian settlement, which is culturally unrelated to the shouldered points horizon. © 1998 John Wiley & Sons, Inc. 相似文献
64.
Krzysztof P. Teisseyre 《Acta Geophysica》2007,55(4):535-553
Analysis of a group of seismic events which took place in central Italy and have been recorded at the l’Aquila Observatory
reveals proportionality between the maximum seismic signal (the displacement velocity) and the maximum amplitudes of rotational
components. To compare the seismic events in the aspect of energy emitted as rotational motions, the rotation indices are
used; these indices help us also to differentiate between the results obtained for different frequency spectra.
In the adopted higher frequency range, 2.6–43 Hz, the relation between maximum displacement velocities and the rotation indices
is roughly reciprocal, while for the lower frequencies, 0.3–3 Hz, there is no clear relationship.
The share of rotation motions in the whole seismic energy emitted from the source varies during the seismic event. Research
on the rotational components hidden in the seismic field gives a new insight into the processes in the source. 相似文献
65.
Exact distributions for apparent waves in irregular seas 总被引:2,自引:0,他引:2
We discuss the long-run distributions of several characteristics for the apparent waves in a Gaussian sea. Three types of one-dimensional wave records are considered: 1) the seaway in time at a fixed position; 2) the instantaneous profile along a horizontal line; 3) the encountered seaway. Exact integral forms of the joint long run distributions are derived for the apparent periods, lengths, and heights. Results of numerical approximations of these distributions are presented in examples. For the computations we considered, as the input spectra, empirical estimates of the frequency spectra as well as JONSWAP type spectra. Effective algorithms are discussed and utilized in the form of a comprehensive computer package of numerical routines. 相似文献
66.
Agricultural management impacts on groundwater: simulations of existing and alternative management options in Peninsular India
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Daniel R. Dourte Sanjay Shukla Dorota Z. Haman M. Devender Reddy M. Uma Devi Adusumilli Mani 《水文研究》2014,28(19):5021-5033
Understanding the principal causes and possible solutions for groundwater depletion in India is important for its water security, especially as it relates to agriculture. A study was conducted in an agricultural watershed in Andhra Pradesh, India to assess the impacts on groundwater of current and alternative agricultural management. Hydrological simulations were used as follows: (1) to evaluate the recharge benefits of water‐harvesting tillage through a modified Soil and Water Assessment Tool (SWAT) model and (2) to predict the groundwater response to changing extent and irrigation management of rice growing areas. The Green–Ampt infiltration routine was modified in SWAT was modified to represent water‐harvesting tillage using maximum depression storage parameter. Water‐harvesting tillage in rainfed croplands was shown to increase basin‐scale groundwater recharge by 3% and decrease run‐off by 43% compared with existing conventional tillage. The groundwater balance (recharge minus irrigation withdrawals), negative 11 mm/year under existing management changed to positive (18–45 mm/year) when rice growing areas or irrigation depths were reduced. Groundwater balance was sensitive to changes in rice cropland management, meaning even small changes in rice cropland management had large impacts on groundwater availability. The modified SWAT was capable of representing tillage management of varying maximum depression storage, and tillage for water‐harvesting was shown to be a potentially important strategy for producers to enhance infiltration and groundwater recharge, especially in semi‐arid regions where rainfall may be becoming increasingly variable. This enhanced SWAT could be used to evaluate the landscape‐scale impacts of alternative tillage management in other regions that are working to develop strategies for reducing groundwater depletion. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
67.
68.
Reza Kalbasi Krzysztof Janowicz Femke Reitsma Luc Boerboom Ali Alesheikh 《Transactions in GIS》2014,18(6):834-851
Ontology‐based information publishing, retrieval, reuse, and integration have become popular research topics to address the challenges involved in exchanging data between heterogeneous sources. However, in most cases ontologies are still developed in a centralized top‐down manner by a few knowledge engineers. Consequently, the role that developers play in conceptualizing a domain such as the geosciences is disproportional compared with the role of domain experts and especially potential end‐users. These and other drawbacks have stimulated the creation of new methodologies focusing around collaboration. Based on a review of existing approaches, this article presents a two‐step methodology and implementation to foster collaborative ontology engineering in the geosciences. Our approach consists of the development of a minimalistic core ontology acting as a catalyst and the creation of a virtual collaborative development cycle. Both methodology and prototypical implementation have been tested in the context of the EU‐funded ForeStClim project which addresses environmental protection with respect to forests and climate change. 相似文献
69.
We aim to numerically study evolution of Alfv′en waves that accompany short-lasting swirl events in a solar magnetic flux-tube that can be a simple model of a magnetic pore or a sunspot. With the use of the FLASH code we numerically solve three-dimensional ideal magnetohydrodynamic equations to simulate twists which are implemented at the top of the photosphere in magnetic field lines of the flux-tube. Our numerical results exhibit swirl events and Alfv′en waves with associated clockwise and counterclockwise rotation of magnetic lines, with the largest values of vorticity at the bottom of the chromosphere, and a certain amount of energy flux. 相似文献
70.
Lithofacies analysis of two transgressive sequences within the Kapp Starostin Formation (Upper Permian, West Spitsbergen), indicates considerable differences in seawater chemistry between their depositional environments. The onshore part of the sequence represented in the Vøringen and Svenskeegga Members is largely calcareous, with allochthonous and corroded siliceous materials. In contrast, in the equivalent sequence within the Hovtinden Member, silica is ubiquitous whereas carbonate materials include mainly corroded bioclasts. These differences are consistent with predictions of the oceanographic model of ‘overfed’ and ‘hungry’ oceans proposed previously on the basis of carbon and oxygen stable isotope analysis. 相似文献