全文获取类型
收费全文 | 149篇 |
免费 | 5篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 16篇 |
地球物理 | 34篇 |
地质学 | 41篇 |
海洋学 | 14篇 |
天文学 | 35篇 |
综合类 | 1篇 |
自然地理 | 11篇 |
出版年
2021年 | 2篇 |
2020年 | 4篇 |
2019年 | 1篇 |
2018年 | 2篇 |
2017年 | 5篇 |
2016年 | 3篇 |
2015年 | 2篇 |
2014年 | 3篇 |
2013年 | 15篇 |
2012年 | 4篇 |
2011年 | 8篇 |
2010年 | 15篇 |
2009年 | 8篇 |
2008年 | 6篇 |
2007年 | 3篇 |
2006年 | 8篇 |
2005年 | 1篇 |
2004年 | 11篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2001年 | 2篇 |
2000年 | 6篇 |
1999年 | 2篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1992年 | 1篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有154条查询结果,搜索用时 78 毫秒
21.
Challenges in global ballast water management 总被引:3,自引:0,他引:3
Endresen Ø Lee Behrens H Brynestad S Bjørn Andersen A Skjong R 《Marine pollution bulletin》2004,48(7-8):615-623
Ballast water management is a complex issue raising the challenge of merging international regulations, ship's specific configurations along with ecological conservation. This complexity is illustrated in this paper by considering ballast water volume, discharge frequency, ship safety and operational issues aligned with regional characteristics to address ecological risk for selected routes. A re-estimation of ballast water volumes gives a global annual level of 3500 Mton. Global ballast water volume discharged into open sea originating from ballast water exchange operations is estimated to approximately 2800 Mton. Risk based decision support systems coupled to databases for different ports and invasive species characteristics and distributions can allow for differentiated treatment levels while maintaining low risk levels. On certain routes, the risk is estimated to be unacceptable and some kind of ballast water treatment or management should be applied. 相似文献
22.
23.
24.
Frey Øivind Planke Sverre Symonds Phillip A. Heeremans Michel 《Marine Geophysical Researches》1998,20(4):293-311
Interpretation of deep seismic reflection data across the Gascoyne Margin reveals six distinct seismic facies units related to the tectono-magmatic breakup history. On the outer Exmouth Plateau four large scale units are identified: (1) an extensively block-faulted upper crust; (2) a middle-crustal unit of discontinuous, undulatory reflectors; (3) a reflection-free deep crustal unit; and (4) a lower-crustal band of low-frequency, high-amplitude reflectors. Two additional units are found near the continent-ocean boundary (COB); (5) seaward-dipping reflectors (SDR); and (6) landward-dipping reflectors in the lower crust below the SDR. The lower-crustal high-reflectivity band, located near the top of a high-velocity unit (Vp > 7 kms–1), is interpreted as magmatic underplating. There is a spatial correlation between the underplated area and the presence of extensive upper-crustal block-faulting and intrusive rocks in the shallow crust. The undulatory middle-crustal reflector unit is also only identified in the outer plateau area, and is interpreted as a zone in which the upper-crustal faults terminate. The inner parts of the margin consist of a deep basin showing little upper-crustal faulting and no evidence of middle crustal deformation or underplating. Theoretical modeling of the effect of rifting and magmatic underplating on crustal strength profiles suggests that the brittle-ductile transition may migrate at least 5 km upwards during several million years after the underplating event. Based on the seismic interpretation and crustal strength modeling we propose that the seismic structure of the outer Exmouth Plateau is severely modified by a transient change in the crustal rheological structure associated with magmatic underplating. 相似文献
25.
Cessation of the Norwegian drift net fishery: changes observed in Norwegian and Russian populations of Atlantic salmon 总被引:3,自引:2,他引:1
26.
PETER STRØMGAARD M.Sc. 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):6-12
Stromgaard, Peter: Potential Crop Production—illustrated by an example from West Africa, Geografisk Tidsskrift, 77: 6—12, København, June 1, 1978. Different ways of describing and modelling the process of primary production are compared, and the concept of potential crop production is elaborated. Two mathematical models are suggested, converted into FORTRAN IV, and used for an estimation of potential productivity in Ghana. 相似文献
27.
Trond Reitan Asgeir Petersen-Øverleir 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(3):351-365
This paper presents a Bayesian approach for fitting the standard power-law rating curve model to a set of stage-discharge
measurements. Methods for eliciting both regional and at-site prior information, and issues concerning the determination of
prior forms, are discussed. An efficient MCMC algorithm for the specific problem is derived. The appropriateness of the proposed
method is demonstrated by applying the model to both simulated and real-life data. However, some problems came to light in
the applications, and these are discussed. 相似文献
28.
Trond Reitan Asgeir Petersen-Øverleir 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(5):627-642
This study explores Bayesian methods for handling compound stage–discharge relationships, a problem which arises in many natural
rivers. It is assumed: (1) the stage–discharge relationship in each rating curve segment is a power-law with a location parameter,
or zero-plane displacement; (2) the segment transitions are abrupt and continuous; and (3) multiplicative measurement errors
are of equal variance. The rating curve fitting procedure is then formulated as a piecewise regression problem where the number
of segments and the associated changepoints are assumed unknown. Procedures are developed for describing both global and site-specific
prior distributions for all rating curve parameters, including the changepoints. Estimation and uncertainty analysis is evaluated
using Markov chain Monte Carlo simulation (MCMC) techniques. The first model explored accounts for parameter and model uncertainties
in the interpolated area, i.e. within the range of available stage–discharge measurements. A second model is constructed in
an attempt to include the uncertainty in extrapolation, which is necessary when the rating curve is used to estimate discharges
beyond the highest or lowest measurement. This is done by assuming that the rate of changepoints both inside and outside the
measured area follows a Poisson process. The theory is applied to actual data from Norwegian gauging stations. The MCMC solutions
give results that appear sensible and useful for inferential purposes, though the latter model needs further efforts in order
to obtain a more efficient simulation scheme. 相似文献
29.
A New method for identifying possible causal relationships between CO2, total solar irradiance and global temperature change 总被引:1,自引:0,他引:1
The study compares two formulas for calculating the daily evapotranspiration ET0 for a reference crop. The first formula was proposed by Allen et al. (AL), while the second one was proposed by Katerji and Perrier with the addition of the carbon dioxide (CO2) effect on evapotranspiration (KP). The study analyses the impact of the calculation by the two formulas on the irrigation requirement (IR). Both formulas are based on the Penman-Monteith equation but adopt different approaches for parameterising the canopy resistance r c . In the AL formula, r c is assumed constant and not sensitive to climate change, whereas in the KP formula, r c is first parameterised as a function of climatic variables, then ET0 is corrected for the air CO2 concentration. The two formulas were compared in two periods. The first period involves data from two sites in the Mediterranean region within a measured climate change period (1981–2006) when all the input climatic variables were measured. The second period (2070–2100) involves data from a future climate change period at one site when the input climatic variables were forecasted for two future climate scenarios (A2 and B2). The annual cumulated values of ET0 calculated by the AL formula are systematically lower than those determined by the KP formula. The differences between the ET0 estimation with the AL and KP formulas have a strong impact on the determination of the IR for the reference crop. In fact, for the two periods, the annual values of IR when ET0 is calculated by the AL formula are systematically lower than those calculated by the KP formula. For the actual measured climate change period, this reduction varied from 26 to 28 %, while for the future climate change period, it varied based on the scenario from 16 % (A2) to 20 % (B2). 相似文献
30.
Three-dimensional (3D) seismic data acquired for hydrocarbon exploration reveal that gas accumulations are common within the
2–3 km thick Plio-Pleistocene stratigraphic column of the south-western Barents Sea continental margin. The 3D seismic data
have relatively low-frequency content (<40 Hz) but, due to dense spatial sampling, long source-receiver offsets, 3D migration
and advanced interpretation techniques, they provide surprisingly detailed images of inferred gas accumulations and the sedimentary
environments in which they occur. The presence of gas is inferred from seismic reflection segments with anomalously high amplitude
and reversed phase, compared with the seafloor reflection, so-called bright spots. Fluid migration is inferred from vertical
zones of acoustic masking and acoustic pipes. The 3D seismic volume allows a spatial analysis of amplitude anomalies inferred to reflect the presence of gas and fluids. At several locations, seismic attribute
maps reveal detailed images of flat spots, inferred to represent gas–water interfaces. The data indicate a focused fluid migration
system, where sub-vertical faults and zones of highly fractured sediments are conduits for the migration of gas-bearing fluids
in Plio-Pleistocene sediments. Gas is interpreted to appear in high-porosity fan-shaped sediment lobes, channel and delta
deposits, glacigenic debris flows and sediment blocks, probably sealed by low-permeability, clayey till and/or (glacio)marine
sediments. Gas and fluid flow are here attributed mainly to rapid Plio-Pleistocene sedimentation that loaded large amounts
of sedimentary material over lower-density, fine-grained Eocene oozes. This probably caused pore-fluid dewatering of the high-fluid
content oozes through a network of polygonal faults. The study area is suggested to have experienced cycles of fluid expulsion
and hydrocarbon migration associated with glacial–interglacial cycles. 相似文献