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151.
Presence of groundwater flow in the ‘Somontano de Huesca’ Area, derived from low‐permeability detrital Tertiary rocks, is considered. A groundwater flow model is constructed for these Tertiary rocks. This model explains both water flow through them and the chemical characteristics of the water. Groundwater flow has clear surface manifestations: it causes wetlands (which are called ‘paules’ in the area) with sodic waters, it produces saline, sodic or alkaline soils, and it produces modifies the chemical composition of rivers in Somontano. Irrigation has increased the volume of filtered water, especially in the interfluve areas, causing the extension of the wetlands in the valley thalwegs, and also the greater movement of salts has increased the problems of saline and/or sodic soils in the area. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
152.
Seismic vulnerability and risk assessment: case study of the historic city centre of Coimbra, Portugal 总被引:5,自引:4,他引:1
Romeu Vicente Sonia Parodi Sergio Lagomarsino Humberto Varum J. A. R. Mendes Silva 《Bulletin of Earthquake Engineering》2011,9(4):1067-1096
Seismic risk evaluation of built-up areas involves analysis of the level of earthquake hazard of the region, building vulnerability
and exposure. Within this approach that defines seismic risk, building vulnerability assessment assumes great importance,
not only because of the obvious physical consequences in the eventual occurrence of a seismic event, but also because it is
the one of the few potential aspects in which engineering research can intervene. In fact, rigorous vulnerability assessment
of existing buildings and the implementation of appropriate retrofitting solutions can help to reduce the levels of physical
damage, loss of life and the economic impact of future seismic events. Vulnerability studies of urban centres should be developed
with the aim of identifying building fragilities and reducing seismic risk. As part of the rehabilitation of the historic
city centre of Coimbra, a complete identification and inspection survey of old masonry buildings has been carried out. The
main purpose of this research is to discuss vulnerability assessment methodologies, particularly those of the first level,
through the proposal and development of a method previously used to determine the level of vulnerability, in the assessment
of physical damage and its relationship with seismic intensity. Also presented and discussed are the strategy and proposed
methodology adopted for the vulnerability assessment, damage and loss scenarios for the city centre of Coimbra, Portugal,
using a GIS mapping application. 相似文献
153.
Vyacheslav M. Zobin Juan José Ramírez Hydyn Santiago Eliseo Alatorre Carlos Navarro 《Bulletin of Volcanology》2011,73(1):91-99
Continuous tilt changes during the 2004–2005 effusive-explosive episodes at Volcán de Colima (México) were recorded simultaneously
by two tiltmeters installed on opposite sides of the volcano at elevations of 2200 m and 3060 m above sea level. Data indicate
that the 2004 lava extrusion was preceded by an inflation accompanied by a deflation. The 2005 explosion sequences were associated
with a deflationary–inflationary tilt. The period between the 2004 extrusion and the 2005 explosions was characterized by
an inflationary tilt during a 3 month period. Two deformation sources were located. The first was situated at a depth between
300 m and 1800 m beneath the crater at the northern flank of the volcano and was responsible for volcano deformation during
the preliminary September 2004 stage, the October 2004 extrusion, and the initial stage of the transition period and the March
2005 explosion sequence. The second source was located at a depth between 1800 m and 2800 m beneath the crater at the southern
flank of the volcano and was responsible for volcano deformation during the final stage of the transition period and the May–June
2005 explosion sequence. 相似文献
154.
Grain size is a fundamental property of sediments and is commonly used to describe sedimentary facies and classify sedimentary environments. Among the various conventional techniques utilized to determine grain‐size frequency distributions, sieving is the most widely applied procedure. The accuracy of such analyses is, among other factors, strongly dependent on the sieving time. However, despite a substantial amount of research in this field, optimal sieving times for different types of sediments have, to date, not been established. In this article, the influence of sieving time on grain‐size analyses of medium‐grained microtidal and mesotidal beach and dune sands has been determined. To assess the precision of important textural parameters, such as median grain size, sorting, skewness and kurtosis, an error analysis was carried out for different sieving times (2, 5, 10, 15 and 20 minutes). After calibrating the analytical and sampling methodologies, significant deviations were registered when sieving time was less than 10 minutes. However, such deviations were very small and grain‐size distributions remained almost identical for sieving times of 10 minutes and longer, relative errors being as low as 0% in some cases. 相似文献
155.
Michel Michaelovitch de Mahiques Rubens Cesar Lopes Figueira Alexandre Barbosa Salaroli Daniel Pavani Vicente Alves Cristina Gonçalves 《Environmental Earth Sciences》2013,68(4):1073-1087
The Cananéia–Iguape system consists of a complex of estuarine and lagoonal channels located in the coastal region of southeastern Brazil known as Lagamar, a Biosphere Reserve recognized by the United Nations Educational, Scientific and Cultural Organization (UNESCO) in 1991. The area suffered dramatic environmental changes along the last ca. 150 years initiated by the 1852 opening of an artificial channel, the Valo Grande, connecting the Ribeira de Iguape River to the estuarine system. Due to Au, Ag, Zn, and Pb mining activities that took place in the upstream regions of the Ribeira de Iguape River since the seventeenth century, the system has acted as a final destination of contaminated sediments. Analysis of cores located along the estuarine system revealed a history of contamination, with an increase of anthropogenic metal input between the decades of 1930 and 1990. The anthropogenic influence can be traced in locations as far as 20 km from the mouth of the artificial channel. 相似文献
156.
Estimation of daytime downward longwave radiation under clear and cloudy skies conditions over a sub-humid region 总被引:1,自引:0,他引:1
Facundo Carmona Raúl Rivas Vicente Caselles 《Theoretical and Applied Climatology》2014,115(1-2):281-295
Downward longwave radiation (LW ↓ ) is a relevant variable for meteorological and climatic studies. Good estimates of this term are vitally important in correct determining of the net radiation, which, in turn, modulates the magnitude of the terms in the surface energy budget (e.g., evaporation). In remote sensing applications, the determination of daytime LW↓ is required for estimation of the net radiation using satellite data. LW↓ is not directly measured in weather stations and then is estimated using models with surface air temperature and humidity as input. In this paper, we identify the best models to estimate daytime downward longwave radiation from meteorological data in the sub-humid Pampean region. Several well-known models to estimate LW↓ under clear and cloudy skies were tested. We use downward radiation components and meteorological data registered at Tandil (Argentina) from 2006 to 2010 (840 days). In addition, we propose two multiple linear regression models (MLRM-1 and MLRM-2) to estimate LW↓ at the surface for all sky conditions. The new equations show better performance than the others models tested with root mean square errors between 12 and 16 W m?2, bias close to zero and best agreements with measured data (r 2?≥?0.85). 相似文献
157.
Local governance involves coalitions between public and private actors on policy issues. Actors participating in these coalitions may vary according to the issue in question, even within the same city. Based on a survey carried out among actors from different sectors of the local political community in four Spanish cities, governance networks are analyzed across five different issues: public housing, cultural tourism, urban regeneration, social policy, and citizen participation. Using network analysis and indexes in a comparative examination of 20 policy networks, we show that variations across networks are explained by policy issue content and supra-municipal regulations, regardless of the cities’ political characteristics. 相似文献
158.
Seismic vulnerability assessment of historical urban centres: case study of the old city centre in Seixal, Portugal 总被引:1,自引:1,他引:0
Tiago Miguel Ferreira Romeu Vicente J. A. R. Mendes da Silva Humberto Varum Aníbal Costa 《Bulletin of Earthquake Engineering》2013,11(5):1753-1773
The seismic vulnerability assessment of old masonry buildings is essential not only to buildings with recognised historical and heritage value but also to ordinary residential masonry buildings. This paper approaches the seismic vulnerability assessment of masonry buildings by applying a simplified methodology to the old city centre of Seixal in Portugal. The methodology adopted in this study was based on a vulnerability index used for the evaluation of damage and the study of loss scenarios on a large scale. Over 500 buildings were assessed using this methodology, and the results were analysed using an integrated Geographical Information System tool. The integration of the vulnerability and loss results could allow city councils or regional authorities to plan interventions based on a global view of the site under analysis, leading to more accurate and comprehensive risk mitigation strategies that support the requirements of safety and emergency planning. 相似文献
159.
Lidia Romero-Viana Brendan J. Keely Antonio Camacho Eduardo Vicente M. Rosa Miracle 《Journal of Paleolimnology》2010,43(4):771-786
We analysed photosynthetic pigments in annually laminated sediment of meromictic Lake La Cruz, Spain, to cope with the timing
and characterisation of primary productivity changes over the last four centuries. The photosynthetic pigments identified
included chlorophyll a and b (and its derivatives) and specific carotenoids of different algal groups, such as zeaxanthin, lutein, alloxanthin, diadinoxanthin
and diatoxanthin among others. Marker pigments of phototrophic sulfur bacteria were also observed, including bacteriochlorophyll
a derivatives, homologue series of bacteriophaeophytins d and bacterial carotenoids okenone and chlorobactene. We investigated the diagenetic processes of pigment alteration in anoxic
sediments and the possible implications for paleoproductivity reconstruction and interpretation. The lack of systematic down-core
changes in diagenetic indicators suggests that variability of sedimentary pigment concentrations is the result of changes
in lake productivity. The lower concentration of algal photosynthetic pigments in the bottom of sediment sequence corresponds
to the onset of meromictic conditions. Before that, sediment was not continuously anoxic and the preservation of pigments
was reduced. Regarding photosynthetic bacteria, green sulfur bacteria derivatives indicate that population growth was limited
until the settled organic matter was sufficient to provide enough sulphide. Moreover, the presence of bacterioviridine, an
oxidised derivative of bacteriochlorophyll a, suggest the competitive relation among photosynthetic bacteria. The high relative abundance of zeaxanthin indicates the
dominance of picocyanobacteria in the primary productivity over the last centuries. Fluctuations of the pigment signal observed
in the sediment sequence during the meromictic period were well correlated with fluctuations of solar activity. 相似文献
160.
Inmaculada de Vicente Eva Ortega-Retuerta Ignacio P. Mazuecos Michael L. Pace Jonathan J. Cole Isabel Reche 《Aquatic Sciences - Research Across Boundaries》2010,72(4):443-453
In inland waters, transparent exopolymer particles (TEP) can affect carbon export and sequestration in sediments with consequences
for lake C budgets. We measured TEP concentration in 32 lakes from two contrasting lake districts covering wide ranges in
biological and chemical characteristics. North temperate lakes, located in a wet region, have low to moderate ionic strength
and low to high dissolved organic carbon with corresponding variation in color (light absorbance). Mediterranean lakes located
in a semiarid region were characterized by high ionic strength and high concentrations of dissolved organic carbon but low
color. TEP concentrations were large relative to the living portion of the particulate organic carbon pool in both Mediterranean
(36%) and north temperate (33%) lakes. TEP concentrations ranged from 36 to 1,462 μg [as Gum Xanthan equivalents (GX eq)] L−1 in north temperate lakes. In the Mediterranean lakes, concentrations were higher that previously reported for other systems
and ranged from 66 to 9,038 μg GX eq L−1. TEP concentration was positive and significantly related to chlorophyll a (chl a) in north temperate lakes and in the entire data set. Although a significant and positive relationship between TEP and chl
a was also detected in the Mediterranean lakes, bacterial abundance was most strongly related to TEP. In contrast with the
positive influence of phytoplankton and bacteria on TEP, there were weaker relationships between TEP and the chemical variables
tested. We observed a significant and positive relationship between pH and TEP (for all lakes) but this relationship was indirectly
driven by a co-variation of pH with phytoplankton biomass based on multiple regression analysis. For the Mediterranean lakes,
the negative (but not significant) trends between TEP and both conductivity and divalent cations suggest thresholds above
which TEP will likely be destabilized. Under these conditions, TEP may flocculate or disperse in the water column. 相似文献