全文获取类型
收费全文 | 1379篇 |
免费 | 31篇 |
国内免费 | 16篇 |
专业分类
测绘学 | 16篇 |
大气科学 | 136篇 |
地球物理 | 377篇 |
地质学 | 563篇 |
海洋学 | 111篇 |
天文学 | 160篇 |
综合类 | 3篇 |
自然地理 | 60篇 |
出版年
2021年 | 12篇 |
2018年 | 26篇 |
2017年 | 16篇 |
2016年 | 25篇 |
2015年 | 18篇 |
2014年 | 34篇 |
2013年 | 40篇 |
2012年 | 33篇 |
2011年 | 52篇 |
2010年 | 37篇 |
2009年 | 51篇 |
2008年 | 55篇 |
2007年 | 39篇 |
2006年 | 52篇 |
2005年 | 39篇 |
2004年 | 34篇 |
2003年 | 38篇 |
2002年 | 54篇 |
2001年 | 19篇 |
2000年 | 21篇 |
1999年 | 16篇 |
1998年 | 27篇 |
1997年 | 17篇 |
1996年 | 19篇 |
1995年 | 23篇 |
1994年 | 12篇 |
1993年 | 19篇 |
1991年 | 11篇 |
1990年 | 16篇 |
1989年 | 14篇 |
1987年 | 14篇 |
1986年 | 12篇 |
1985年 | 24篇 |
1984年 | 21篇 |
1983年 | 26篇 |
1982年 | 18篇 |
1981年 | 17篇 |
1980年 | 14篇 |
1979年 | 21篇 |
1978年 | 18篇 |
1977年 | 17篇 |
1976年 | 15篇 |
1975年 | 11篇 |
1974年 | 11篇 |
1973年 | 17篇 |
1970年 | 11篇 |
1959年 | 15篇 |
1956年 | 11篇 |
1954年 | 12篇 |
1948年 | 13篇 |
排序方式: 共有1426条查询结果,搜索用时 15 毫秒
111.
Tracer experiments were carried out in groyne fields (GF) of the river Elbe near Havelberg (Germany) in order to estimate the hydraulic connectivity with the river channel. The characteristic times of the five groyne fields, which were estimated from the exponentially declining tracer curves in 43 runs, ranged between 15 min and 69 min and did not correlate with the water level. Methodological investigations show that single point injection and two measurements (in the outflowing water and in the dominant region) are sufficient to provide robust in‐situ tracer curves. Using simplified mathematical simulations with connected stirred tanks, the conditions are investigated for the development of breaks in tracer curves and for the occurrence of significant errors in the estimation of intrinsic residence times. It was shown that an initial uniform dye distribution is not mandatory for the estimation during steady states. In special cases, point injections are more advisable. Moreover, the mean hydraulic residence time was found to be not equivalent to the estimated characteristic time. In fact, it is mostly overestimated by tracer experiments. The degree of overestimation depends on mixing and the volumetric proportions between the different parts of the GF and can be calculated from measured dye concentration differences. For example, an overestimation of 32% was calculated for a groyne field with a commonly found circulation flow pattern. 相似文献
112.
The GW-Fauna-Index: A first approach to a quantitative ecological assessment of groundwater habitats 总被引:6,自引:1,他引:6
Between June 2001 and December 2002, 18 hyporheic and groundwater bores were sampled for fauna and environmental data using phreatic traps. The bores were situated in three different natural geographic regions in Palatinate, Southwestern Germany.Faunal data correlated with the relative amount of detritus, bacterial abundances and the standard deviation of temperature, while very few and weak correlations were found with physical–chemical variables. Dissolved oxygen was assumed to be a limiting factor for most metazoans with a critical concentration at around 0.5–1 mg l−1.To quantify the strength of the hydrological exchange with surface water and its effects on fauna, a so-called GW-Fauna-Index was developed and calculated using the relative amount of detritus, standard deviation of temperature, and oxygen concentration. From all environmental data and on all spatial scales, this index best explained the total faunal abundance and taxonomic richness.To describe the availability of organic aliments in the groundwater, the terms of “alimonic” and “alimony” [from lat. alimonium=(food) supply] were proposed.Although stygofauna was different in the geographic regions investigated, the GW-Fauna-Index was independent from these regional particularities. Using the GW-Fauna-Index, three groups of groundwater habitats could be classified according to the alimonic conditions. From oligo-alimonic group I samples, fauna was mostly absent, while meso-alimonic group II samples were prevailingly populated by stygobites, and eu-alimonic group III samples by ubiquists and stygoxenes. Total abundances and taxonomic richness increased significantly from group I to group III. Group I samples were characterized by low index values, group II samples by intermediate and group III samples by high values.The GW-Fauna-Index provides promising perspectives for application, but needs some improvement. First of all, detritus should be analysed quantitatively and qualitatively, rather than semi-quantitatively. Also, a standard protocol for sampling has to be developed. 相似文献
113.
The coastal zones are facing the prospect of changing storm surge statistics due to anthropogenic climate change. In the present study, we examine these prospects for the North Sea based on numerical modelling. The main tool is the barotropic tide-surge model TRIMGEO (Tidal Residual and Intertidal Mudflat Model) to derive storm surge climate and extremes from atmospheric conditions. The analysis is carried out by using an ensemble of four 30-year atmospheric regional simulations under present-day and possible future-enhanced greenhouse gas conditions. The atmospheric regional simulations were prepared within the EU project PRUDENCE (Prediction of Regional scenarios and Uncertainties for Defining EuropeaN Climate change risks and Effects). The research strategy of PRUDENCE is to compare simulations of different regional models driven by the same global control and climate change simulations. These global conditions, representative for 1961–1990 and 2071–2100 were prepared by the Hadley Center based on the IPCC A2 SRES scenario. The results suggest that under future climatic conditions, storm surge extremes may increase along the North Sea coast towards the end of this century. Based on a comparison between the results of the different ensemble members as well as on the variability estimated from a high-resolution storm surge reconstruction of the recent decades it is found that this increase is significantly different from zero at the 95% confidence level for most of the North Sea coast. An exception represents the East coast of the UK which is not affected by this increase of storm surge extremes. 相似文献
114.
Using paleoclimate proxy-data to select optimal realisations in an ensemble of simulations of the climate of the past millennium 总被引:1,自引:0,他引:1
Hugues Goosse Hans Renssen Axel Timmermann Raymond S. Bradley Michael E. Mann 《Climate Dynamics》2006,27(2-3):165-184
We present and describe in detail the advantages and limitations of a technique that combines in an optimal way model results and proxy-data time series in order to obtain states of the climate system consistent with model physics, reconstruction of past radiative forcing and proxy records. To achieve this goal, we select among an ensemble of simulations covering the last millennium performed with a low-resolution 3-D climate model the ones that minimise a cost function. This cost function measures the misfit between model results and proxy records. In the framework of the tests performed here, an ensemble of 30 to 40 simulations appears sufficient to reach reasonable correlations between model results and reconstructions, in configurations for which a small amount of data is available as well as in data-rich areas. Preliminary applications of the technique show that it can be used to provide reconstructions of past large-scale temperature changes, complementary to the ones obtained by statistical methods. Furthermore, as model results include a representation of atmospheric and oceanic circulations, it can be used to provide insights into some amplification mechanisms responsible for past temperature changes. On the other hand, if the number of proxy records is too low, it could not be used to provide reconstructions of past changes at a regional scale. 相似文献
115.
Peter Brack Hans Rieber Roland Mundil Wolfgang Blendinger Florian Maurer 《Swiss Journal of Geoscience》2007,100(3):327-348
The depositional architecture and the geometric relationships between platform-slope deposits and basinal sediments along
with paleontological evidence indicate the time interval of the younger Anisian Reitziites reitzi ammonoid zone to largely represent the main stage of platform aggradation at the Cernera and Bivera/Clapsavon carbonate platforms.
Published and new U-Pb age data of zircons from volcaniclastic layers bracketing the stratigraphic interval of platform growth
constrain the duration of platform evolution to a time span shorter than 1.8±0.7m.y., probably in the order of 0.5-1m.y.,
reflecting fast rates of vertical platform aggradation exceeding 500 m/m.y. In the range of growth potentials for shallow-water
carbonate systems estimated in relation to the time span of observation, this high rate is in agreement with values for short
intervals of 105-106yrs (e.g., Schlager 1999).
After drowning, the platforms at Cernera and Bivera/Clapsavon were blanketed by thin pelagic carbonates. On the former platform
flanks the draping sediments in places comprise red nodular pelagic limestones (Clapsavon Limestone) similar in facies to
the Han Bulog Limestones occurring elsewhere in Middle Triassic successions of the Mediterranean Tethys. The drowning of vast
areas of former carbonate platforms possibly triggered the onset of bottom-water circulation in adjacent basins as suggested
by the abrupt transition from laminated to bioturbated pelagic nodular limestones in the Buchenstein Formation which occurred
close to the time of initial platform submergence. During the Late Ladinian the topographic features of the drowned platforms
were onlapped by rapidly deposited, predominantly clastic successions including coarse breccias and volcanic rocks sealing
and preserving the peculiar stratigraphic setting. 相似文献
116.
Nathan Roche Steve Eales & Hans Hippelein 《Monthly notices of the Royal Astronomical Society》1998,295(4):946-958
We investigate the angular correlation function, ο(θ), of the galaxies detected in the 2.1-μm K ' band in 17 fields (101.5 arcmin2 in total), each containing a z ∼1.1 radio galaxy. There is a significant detection of galaxy clustering at a limit of K ∼20, with a ο(θ) amplitude similar to that estimated by Carlberg et al. at K =21.5. The ο(θ) amplitudes of these K -limited samples are higher than expected from the faint galaxy clustering in the blue and red passbands, but consistent with a pure luminosity evolution model if clustering is stable (ε=0) and the correlation function of early-type galaxies is steeper than that of spirals.
We do not detect a significant cross-correlation between the radio galaxies and the other galaxies in these fields. The upper limits on the cross-correlation are consistent with a mean clustering environment of Abell class 0 for z ∼1.1 radio galaxies, similar to that observed for radio galaxies at z ∼0.5, but would argue against an Abell class 1 or richer environment. As Abell 0 clustering around the radio galaxies would not significantly increase the ο(θ) amplitude of galaxies in these fields, stable clustering with a steep ξ( r ) for E/S0 galaxies appears to remain the most likely interpretation of the ο(θ) amplitude.
At K ≤20, the number of galaxy–galaxy pairs of 2–3 arcsec separation exceeds the random expectation by a factor of 2.15±0.26. The excess of close pairs is comparable to that previously reported for R -band data, and consistent with a ∼(1+ z )2 evolution of the galaxy merger rate. 相似文献
We do not detect a significant cross-correlation between the radio galaxies and the other galaxies in these fields. The upper limits on the cross-correlation are consistent with a mean clustering environment of Abell class 0 for z ∼1.1 radio galaxies, similar to that observed for radio galaxies at z ∼0.5, but would argue against an Abell class 1 or richer environment. As Abell 0 clustering around the radio galaxies would not significantly increase the ο(θ) amplitude of galaxies in these fields, stable clustering with a steep ξ( r ) for E/S0 galaxies appears to remain the most likely interpretation of the ο(θ) amplitude.
At K ≤20, the number of galaxy–galaxy pairs of 2–3 arcsec separation exceeds the random expectation by a factor of 2.15±0.26. The excess of close pairs is comparable to that previously reported for R -band data, and consistent with a ∼(1+ z )
117.
The application of kriging-based geostatistical algorithms to integrate large-scale seismic data calls for direct and cross variograms of the seismic variable and primary variable (e.g., porosity) at the modeling scale, which is typically much smaller than the seismic data resolution. In order to ensure positive definiteness of the cokriging matrix, a licit small-scale coregionalization model has to be built. Since there are no small-scale secondary data, an analytical method is presented to infer small-scale seismic variograms. The method is applied to estimate the 3-D porosity distribution of a West Texas oil field given seismic data and porosity data at 62 wells. 相似文献
118.
119.
120.
This paper presents the results of a detailed structural analysis of the northern Nijar and southern Vera basins with special emphasis on the evolution of the regional stress field and the associated timing of movement of the Serrata, Gafarillos and Palomares strike-slip fault zones. These major fault zones control the Neogene deformation of the SE Internal Betic Cordilleras in Spain. Detailed stress analysis on Neogene sediments of the Vera and Nijar basins shows a strike-slip regime with NW–SE-oriented subhorizontal maximum principal stress (σ1) during Tortonian and earliest Messinian times. Under the influence of this stress field, dextral displacement along the N090E-trending Gafarillos fault zone resulted in deformation of the sediments of the southern Sorbas and northeastern Nijar basins. During the early Messinian a clock-wise rotation of the stress field occurred. Stress analysis in rocks with late–early Messinian up to Quaternary ages in the Nijar and Vera basins indicates a strike-slip regime with N–S-oriented subhorizontal maximum principal stress (σ1). Under the influence of this stress field the main activity along the N010E-striking Palomares strike-slip fault zone took place, resulting in deformation of the Neogene sediments of the southeastern Vera basin and culminating in a maximum sinistral displacement of more than 20 km. At the same time the stress field was not suitably oriented to exert a large shear component on the Gafarillos fault zone, which activity ended after the earliest Messinian. Fault and outcrop patterns of syntectonic Neogene sediments in the Vera basin show that displacement along the Palomares fault zone decreased at the end of the Middle Miocene although minor displacement phases may still have occurred during the Late Miocene and possibly even Pliocene. From the Middle Miocene onward, deformation in the Nijar basin was controlled by sinistral displacement along the N040E-trending Serrata strike-slip fault zone. 相似文献