全文获取类型
收费全文 | 677篇 |
免费 | 25篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 19篇 |
大气科学 | 42篇 |
地球物理 | 178篇 |
地质学 | 225篇 |
海洋学 | 81篇 |
天文学 | 109篇 |
综合类 | 2篇 |
自然地理 | 48篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 11篇 |
2020年 | 14篇 |
2019年 | 17篇 |
2018年 | 21篇 |
2017年 | 31篇 |
2016年 | 35篇 |
2015年 | 21篇 |
2014年 | 31篇 |
2013年 | 36篇 |
2012年 | 31篇 |
2011年 | 44篇 |
2010年 | 36篇 |
2009年 | 36篇 |
2008年 | 39篇 |
2007年 | 29篇 |
2006年 | 34篇 |
2005年 | 27篇 |
2004年 | 25篇 |
2003年 | 21篇 |
2002年 | 19篇 |
2001年 | 13篇 |
2000年 | 15篇 |
1999年 | 13篇 |
1998年 | 9篇 |
1997年 | 7篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 4篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1975年 | 2篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1970年 | 4篇 |
1966年 | 2篇 |
1963年 | 4篇 |
1961年 | 2篇 |
1940年 | 2篇 |
排序方式: 共有704条查询结果,搜索用时 15 毫秒
131.
Filippo?RidolfiEmail author Alberto?Renzulli 《Contributions to Mineralogy and Petrology》2012,163(5):877-895
The following article presents constraints of the stability of Mg-rich (Mg/(Mg + Fe2+) > 0.5) calcic amphibole in both calc-alkaline and alkaline magmas, testing of previous thermobarometers, and formulation
of new empirical equations that take into consideration a large amount of literature data (e.g. more than one thousand amphibole
compositions among experimental and natural crystals). Particular care has been taken in choosing a large number of natural
amphiboles and selecting quality experimental data from literature. The final database of experimental data, composed of 61
amphiboles synthesized in the ranges of 800–1,130°C and 130–2,200 MPa, indicates that amphibole crystallization occurs in
a horn-like P–T stability field limited by two increasing curves (i.e. the thermal stability and an upper limit), which should start to bend
back to higher pressures. Among calcic amphiboles, magnesiohornblendes and tschermakitic pargasites are only found in equilibrium
with calc-alkaline melts and crystallize at relatively shallow conditions (P up to ~1 GPa). Kaersutite and pargasite are species almost exclusively found in alkaline igneous products, while magnesiohastingsite
is equally distributed in calc-alkaline and alkaline rocks. The reliability of previous amphibole applications was checked
using the selected experimental database. The results of this testing indicate that none of the previous thermobarometers
can be successfully used to estimate the P, T and fO2 in a wide range of amphibole crystallization conditions. Multivariate least-square analyses of experimental amphibole compositions
and physico-chemical parameters allowed us to achieve a new thermobarometric model that gives reasonably low uncertainties
(T ± 23.5°C, P ± 11.5%, H2Omelt ± 0.78wt%) for calc-alkaline and alkaline magmas in a wide range of P–T conditions (up to 1,130°C and 2,200 MPa) and ∆NNO values (±0.37 log units) up to 500 MPa. The AK-[4]Al relation in amphibole can be readily used to distinguish crystals of calc-alkaline liquids from those of alkaline magmas.
In addition, several chemometric equations allowing to estimate the anhydrous composition of the melts in equilibrium with
amphiboles of calc-alkaline magmas were derived. 相似文献
132.
Groundwater flow model, recharge estimation and sustainability in an arid region of Patagonia, Argentina 总被引:2,自引:2,他引:0
María del Pilar Alvarez María Marta Trovatto Mario Alberto Hernández Nilda González 《Environmental Earth Sciences》2012,66(7):2097-2108
The Península Valdés, in northeastern Patagonia, Argentina, is characterised by its arid climate and the lack of perennial watercourses; thus, all economic activities depend on the groundwater resources. Water demand is mainly associated with tourism, which is centralised in Puerto Pirámides and supplied by a water desalination plant, and to sheep farming, supplied by the local aquifer. Due to the exponential growth of tourism, the government is planning to exploit groundwater and convey it by aqueduct to the abovementioned locality. The objectives of this study were to corroborate the conceptual geohydrological model, to develop a mathematical model to simulate the response of the aquifer to different scenarios, and to assess the incidence of water input into the system as a variable—a function that poses difficulties in the models for arid regions. The Visual Modflow 4.1 code was used, calibrating it in trial-and-error mode, changing the recharge and hydraulic conductivity parameters with different variants in the recharge zone and in the inclusion or exclusion of the evapotranspiration module. Results indicate the importance of the recharge analysis by treating rainfall at daily time steps. The adjusted model was exposed to four scenarios with variations in water input and in output by pumping. It can be concluded that under different input conditions, but with a controlled extraction, the system responds in a sustainable manner. 相似文献
133.
Mariano García F. Mark Danson David Riaño Emilio Chuvieco F. Alberto Ramirez Vishal Bandugula 《International Journal of Applied Earth Observation and Geoinformation》2011
This paper evaluates the potential of a terrestrial laser scanner (TLS) to characterize forest canopy fuel characteristics at plot level. Several canopy properties, namely canopy height, canopy cover, canopy base height and fuel strata gap were estimated. Different approaches were tested to avoid the effect of canopy shadowing on canopy height estimation caused by deployment of the TLS below the canopy. Estimation of canopy height using a grid approach provided a coefficient of determination of R2 = 0.81 and an RMSE of 2.47 m. A similar RMSE was obtained using the 99th percentile of the height distribution of the highest points, representing the 1% of the data, although the coefficient of determination was lower (R2 = 0.70). Canopy cover (CC) was estimated as a function of the occupied cells of a grid superimposed upon the TLS point clouds. It was found that CC estimates were dependent on the cell size selected, with 3 cm being the optimum resolution for this study. The effect of the zenith view angle on CC estimates was also analyzed. A simple method was developed to estimate canopy base height from the vegetation vertical profiles derived from an occupied/non-occupied voxels approach. Canopy base height was estimated with an RMSE of 3.09 m and an R2 = 0.86. Terrestrial laser scanning also provides a unique opportunity to estimate the fuel strata gap (FSG), which has not been previously derived from remotely sensed data. The FSG was also derived from the vegetation vertical profile with an RMSE of 1.53 m and an R2 = 0.87. 相似文献
134.
This article presents a methodology for designing a WebGIS framework intended for automatically analyzing spatial data and updating statistics of interest with new information inserted daily by multiple users via a Web portal. A practical example is used on vehicle accident data for assessing risk in specific road segments. Two main blocks integrated together will be described: the collaborative block and the data‐analysis block. The former gives end‐users computer‐aided tools to view, insert, modify and manage data related to accidents and traffic monitoring sensors, whereas the latter is developed to automatically analyze the accident data coming from user's collaboration. Because different agencies can survey accident sites, a collaborative environment is necessary – and a Web‐based solution is ideal – for permitting multi‐user access and data insertion. A centralized approach to process the data in real time is described in all its components. Server‐side Structured Query Language functions optimize performance by using dedicated libraries for spatial processing and re‐structuring the attributes associated with elements which are consequently re‐classified for correct color‐scaling. The end‐product is a system that provides a seamless integration of front‐end tools for user collaboration and back‐end tools to update accident risk statistics in real time and provide them to stakeholders. 相似文献
135.
The ionosphere: effects,GPS modeling and the benefits for space geodetic techniques 总被引:12,自引:8,他引:4
Manuel Hernández-Pajares J. Miguel Juan Jaume Sanz Àngela Aragón-Àngel Alberto García-Rigo Dagoberto Salazar Miquel Escudero 《Journal of Geodesy》2011,85(12):887-907
The main goal of this paper is to provide a summary of our current knowledge of the ionosphere as it relates to space geodetic
techniques, especially the most informative technology, global navigation satellite systems (GNSS), specifically the fully
deployed and operational global positioning system (GPS). As such, the main relevant modeling points are discussed, and the
corresponding results of ionospheric monitoring are related, which were mostly computed using GPS data and based on the direct
experience of the authors. We address various phenomena such as horizontal and vertical ionospheric morphology in quiet conditions,
traveling ionospheric disturbances, solar flares, ionospheric storms and scintillation. Finally, we also tackle the question
of how improved knowledge of ionospheric conditions, especially in terms of an accurate understanding of the distribution
of free electrons, can improve space geodetic techniques at different levels, such as higher-order ionospheric effects, precise
GNSS navigation, single-antenna GNSS orientation and real-time GNSS meteorology. 相似文献
136.
Borja A Barbone E Basset A Borgersen G Brkljacic M Elliott M Garmendia JM Marques JC Mazik K Muxika I Magalhães Neto J Norling K Rodríguez JG Rosati I Rygg B Teixeira H Trayanova A 《Marine pollution bulletin》2011,62(3):499-513
In recent times many benthic indices have been proposed to assess the ecological quality of marine waters worldwide. In this study we compared single metrics and multi-metric methods to assess coastal and transitional benthic status along human pressure gradients in five distinct environments across Europe: Varna bay and lake (Bulgaria), Lesina lagoon (Italy), Mondego estuary (Portugal), Basque coast (Spain) and Oslofjord (Norway). Hence, 13 single metrics (abundance, number of taxa, and several diversity and sensitivity indices) and eight of the most common indices used within the European Water Framework Directive (WFD) for benthic assessment were selected: index of size spectra (ISS), Benthic assessment tool (BAT), Norwegian quality index (NQI), Multivariate AMBI (M-AMBI), Benthic quality index (BQI), (Benthic ecosystem quality index (BEQI), Benthic index based on taxonomic sufficiency (BITS), and infaunal quality index (IQI). Within each system, sampling sites were ordered in an increasing pressure gradient according to a preliminary classification based on professional judgement. The different indices are largely consistent in their response to pressure gradient, except in some particular cases (i.e. BITS, in all cases, or ISS when a low number of individuals is present). Inconsistencies between indicator responses were most pronounced in transitional waters (i.e. IQI, BEQI), highlighting the difficulties of the generic application of indicators to all marine, estuarine and lagoonal environments. However, some of the single (i.e. ecological groups approach, diversity, richness) and multi-metric methods (i.e. BAT, M-AMBI, NQI) were able to detect such gradients both in transitional and coastal environments, being these multi-metric methods more consistent in the detection than single indices. This study highlights the importance of survey design and good reference conditions for some indicators. The agreement observed between different methodologies and their ability to detect quality trends across distinct environments constitutes a promising result for the implementation of the WFD’s monitoring plans. Moreover, these results have management implications, regarding the dangers of misclassification, uncertainty in the assessment, use of conflicting indices, and testing and validation of indices. 相似文献
137.
Roberto Tonini Alberto Armigliato Stefano Tinti 《Pure and Applied Geophysics》2011,168(6-7):1113-1123
The tsunamigenic earthquake (Mw?=?8.1) that occurred on 29 September 2009 at 17:48 UTC offshore of the Samoa archipelago east of the Tonga trench represents an example of the so-called ??outer-rise?? earthquakes. The areas most affected were the south coasts of Western and American Samoa, where almost 200 people were killed and run-up heights were measured in excess of 5?m at several locations along the coast. Moreover, tide gauge records showed a maximum peak-to-peak height of about 3.5?m near Pago Pago (American Samoa) and of 1.5?m offshore of Apia (Western Samoa). In this work, different fault models based on the focal mechanism solutions proposed by Global CMT and by USGS immediately after the 2009 Samoan earthquake are tested by comparing the near-field recorded signals (three offshore DART buoys and two coastal tide gauges) and the synthetic signals provided by the numerical simulations. The analysis points out that there are lights and shadows, in the sense that none of the computed tsunamis agrees satisfactorily with all the considered signals, although some of them reproduce some of the records quite well. This ??partial agreement?? and ??partial disagreement?? are analysed in the perspective of tsunami forecast and of Tsunami Early Warning System strategy. 相似文献
138.
Alfredo Alberto Muxel Sonia Maria Nobre Gimenez Flaveli Aparecida de Souza Almeida Rení Ventura da Silva Alfaya Antonio Alberto da Silva Alfaya 《洁净——土壤、空气、水》2011,39(3):289-295
The natural cotton fiber was used to synthesize an anion exchange, containing ZrO2 film on its surface, NCFZC (natural cotton fiber/ZrO2 composite). This anion exchanger was produced by the reaction of the zirconium oxychloride and hydroxyl groups on surface of the natural cotton fiber. The material was used for Cr(VI) ions adsorption studies. Adsorption equilibrium time and optimum pH for Cr(VI) adsorption were found to be 6 h and 4.0, respectively. The Langmuir and Temkin isotherms were used to models adsorption equilibrium data. The adsorption capacity of NCFZC was found to be 1.33 mmol/g. Kinetic studies showed that the rate of adsorption of Cr(VI) on NCFZC obeyed a pseudo‐second‐order kinetic model. 相似文献
139.
Francesco Marazzi Ioannis Politopoulos Alberto Pavese 《Bulletin of Earthquake Engineering》2011,9(2):623-640
This paper presents a synthesis of the activities carried out in the framework of the European project EFAST (design study
of a European Facility for Advanced Seismic Testing) to determine the general characteristics of a new European world-class
facility for earthquake testing of structures. To this end the demands for the necessary testing to support the modern seismic
engineering research have been investigated and compared to the actual capabilities of European laboratories. The outcome
is the determination of performance objectives and requirements in the gross. On the basis of the needs assessment carried
out during the first phase of the project and taking into account the technological advances in both experimental techniques
and equipment (hardware and software) for seismic testing, a modern facility for experimental seismic research should be composed,
mainly, of a high performance shaking tables array and a large reaction structure where both traditional (pseudo-static/dynamic)
and innovative testing techniques (e.g. real time hybrid testing) can be applied and combined. A tentative layout of the facility
is also proposed and issues related to the best utilization of such a laboratory are discussed. 相似文献
140.
Antonio Olita Alberto Ribotti Roberto Sorgente Leopoldo Fazioli Angelo Perilli 《Ocean Dynamics》2011,61(1):89-102
Data reduction and signal decomposition techniques have been applied to a large bio-physical remotely sensed dataset covering the decade 1997–2007. The aim was the estimation of the spatial (basin and sub-basin scales) and temporal (seasonal and interannual) variability of sea level anomalies and chlorophyll-a concentration in the Algero-Provençal Basin, as well as the study of their covariability. Empirical orthogonal functions, wavelet analysis, singular value decomposition and correlation maps have been successfully used to individuate the patterns of (co)variability of the investigated fields. The seasonal variability of the phytoplanktonic biomass is divided in two distinct modes, timewise and spacewise separated. Positive interannual events are related to anomalies in 1999 and 2005, while the main (negative) anomaly is that of summer 2003, associated to the European 2003 heatwave. The analysis of the sea level anomalies shows a minimum in the formation of anticyclonic Algerian eddies during that period. The largest anticorrelation between sea level anomalies and phytoplanktonic biomass is found in the central zone of the basin, suggesting a clear biological response to the shoaling/deepening of the isopycnae and so to the nutrient injection into the euphotic layer. The analysis suggests that the driver of the variability of the nutricline depth in this central area is the displacement (seasonal) of the North Balearic Front and the formation/action of the frontal eddies. 相似文献