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21.
The delay coordinate technique is examined as an indicator of the regime of particle dynamics for the system of single charged particle motion in magnetic reversals. Examples of numerically integrated trajectories in both static (zero electric field) and time dependent (corresponding nonzero induction electric field) simple models for magnetic reversals are considered. In the static case, the dynamics can in principle be directly classified by constructing Poincaré surfaces of section; here we demonstrate that whilst the Poincaré surface contains the relevant information to classify the dynamics, the corresponding delay coordinate plot can provide a far more sensitive indication of the onset of nonregular behaviour. In the case of nonperiodic time dependence considered here Poincaré plots cannot in general be constructed directly. Nevertheless, delay coordinate plots can still reveal details of the phase space portrait of the system, and here are shown to indicate whether segments of stochastic motion exist in a given trajectory. It is anticipated that the delay coordinate plot technique as realized here will be a valuable tool in characterizing the behaviour in large numbers of trajectories that are evolved in time-dependent systems, thereby giving us insight into the evolution of the distribution function as a whole, either in prescribed fields or in self-consistent numerical simulations. 相似文献
22.
Oscar Escolero Luis E. Marin Eloisa Domínguez-Mariani Sandra Torres-Onofre 《Environmental Geology》2007,51(5):719-723
A hydraulic analysis of the interface between freshwater–saltwater behavior was done in the Merida Yucatan zone, two machines
that constantly register the groundwater levels were installed, and three electric conductivity logs were taken from wells.
When comparing the measured results with the ones obtained using theoretical equations developed to calculate the freshwater–saltwater
interface position, it was proved that in some cases these equations can be applied, and in others not. Two effects that rule
the behavior of karst aquifers in extraordinary conditions were found. 相似文献
23.
Christian Tiberius Thomas Pany Bernd Eissfeller Peter Joosten Sandra Verhagen 《GPS Solutions》2002,6(1-2):96-99
In this short contribution it is demonstrated how integer carrier phase cycle ambiguity resolution will perform in near future,
when the US GPS gets modernized and the European Galileo becomes operational. The capability of ambiguity resolution is analyzed
in the context of precise differential positioning over short, medium and long distances. Starting from dual-frequency operation
with GPS at present, particularly augmenting the number of satellites turns out to have beneficial consequences on the capability
of correctly resolving the ambiguities. With a 'double' constellation, on short baselines, the confidence of the integer ambiguity
solution increases to a level of 0.99999999 or beyond.
Electronic Publication 相似文献
24.
Ideas of complexity theory – including self-organized criticality – are being applied to the study of turbulence and astroplasmas in the solar system. An RAS MIST meeting in London brought together researchers from different disciplines to compare established paradigms with more recent ideas. Sandra Chapman , Mervyn Freeman and Sean Oughton report. 相似文献
25.
Sandra L. Macfarlane 《Estuaries and Coasts》1996,19(2):311-319
Concern about declining stocks of municipally managed shellfish species in Orleans, Massachusetts, led to several shellfish enhancement programs. Projects included bottom and raft culture of hatchery-raised seed, hatchery and upweller techniques, transplants of seed and adult shellfish, and other management options. However, deterioration of water quality and habitat prompted the town to initiate a multifaceted program to address the issues causing environmental degradation. A water-quality task force, appointed to determine solutions to the problems, recommended changes in land-use practices. A drainage remediation program was undertaken at five sites, resulting in the reopening of a viable shellfish area for the first time in 12 yr. Issues concerning nutrient enrichment, groundwater flow and depth, flushing characteristics of the embayments, proliferation of private docks and piers in the public tidelands, effect of barrier beach dynamics including erosion control measures, and the number of users and diversity of their activies employed on the waters themselves will be addressed in current municipal planning initiatives. 相似文献
26.
Meta-sedimentary rocks including marbles and calcsilicates in Central Dronning Maud Land (CDML) in East Antarctica experienced
a Pan-African granulite facies metamorphism with peak metamorphic conditions around 830 ± 20 °C at 6.8 ± 0.5 kbar which was
accompanied by the post-kinematic intrusion of huge amounts of syenitic (charnockitic) magmas at 4.5 ± 0.7 kbar. The marbles
and calcsilicates may represent meta-evaporites as indicated by the occurrence of metamorphic gypsum/anhydrite and Cl-rich
scapolite that formed in the presence of saline fluids with X
NaCl in the range 0.15–0.27. The marbles and calcsilicates bear biotite, tremolite and/or hornblende and humite group minerals
(clinohumite, chondrodite and humite) which are inferred to have crystallized at about 650 °C and 4.5 kbar. The syenitic intrusives
contain late-magmatic biotite and amphibole (formed between 750 and 800 °C) as well as relictic magmatic fayalite, orthopyroxene
and clinopyroxene. Two syenite and two calcsilicate samples contain fluorite. Corona textures in the marbles and calcsilicates
suggest very low fluid-rock ratios during the formation of the retrograde (650 °C) assemblages. Biotite in all but two syenite
samples crystallized at log(f
H
2
O/f
HF) ratios of 2.9 ± 0.4, while in the calcsilicates, both biotite and humite group minerals indicate generally higher log(f
H
2
O/f
HF) values of up to 5.2. A few samples, though, overlap with the syenite values. Log(f
H
2
O/f
HCl) derived from biotite covers the range 0.5–2.6 in all rock types. Within a single sample, the calculated values for both
parameters vary typically by 0.1 to 0.8 log units. Water and halogen acid fugacities calculated from biotite-olivine/orthopyroxene-feldspar-quartz
equilibria and the above fugacity ratios are 1510–2790 bars for H2O, 1.3–5.3 bars for HF and 7–600 bars for HCl. The results are interpreted to reflect the reaction of relatively homogeneous
magmatic fluids [in terms of log(f
H
2
O
/f
HF)] derived from the late-magmatic stages of the syenites with both earlier crystallized, still hotter parts of the syenites
and with adjacent country rocks during down-temperature fluid flow. Fluorine is successively removed from the fluid and incorporated
into F-bearing minerals (close to the syenite into metamorphic fluorite). In the course of this process log(f
H
2
O
/f
HF) increases significantly. Chlorine preferably partitions into the fluid and hence log(f
H
2
O
/f
HCl) does not change markedly during fluid-rock interaction.
Received: 28 November 1997 / Accepted: 27 April 1998 相似文献
27.
28.
Spijker Jeroen Recaño Joaquín Martínez Sandra Carioli Alessandra 《Journal of Geographical Systems》2021,23(2):161-207
Journal of Geographical Systems - Colombia is undergoing major changes in mortality patterns. National- and department-level cause-specific analyses have previously been carried out, but very... 相似文献
29.
Francisco Carreño Conde Sandra García Martínez Javier Lillo Ramos Raquel Fernández Martínez Ariana Mabeth-Montoya Colonia 《Environmental Earth Sciences》2014,71(1):61-66
Water resources management of protected sites requires a powerful tool to analyze the process and changes that are occurring in the environment. This paper describes a 3D geomodel design of the Jarama River Detrital Aquifer located in Madrid (Spain). That hydrogeological unit is included in the “Parque Regional de los Cursos Bajos de los Ríos Manzanares y Jarama” (Regional Park of the Lower Courses of Manzanares and Jarama Rivers). The goal of this work is to define a method by which a three-dimensional (3D) model can be created with hydrogeologic geometry real of main aquifer, to accomplish an adequate management of the groundwater resources. All data used in this study were integrated in a geographic database: geological and hydrogeological information, geological map (1:25,000), eleven cross-sections, piezometric maps and a digital elevation model. The constructed 3D model of the Jarama Aquifer shows geometric features and spatial distribution and variations of geologic units. Thus, the 3D model allows the assessment of volumes of each unit, the depth and thickness variations of the main aquifer, and the spatial and temporal variations of water tables. From the 3D model, the most suitable areas (in terms of groundwater protection) for managed recharge and mining works have been identified. 相似文献
30.