全文获取类型
收费全文 | 209篇 |
免费 | 13篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 18篇 |
地球物理 | 45篇 |
地质学 | 51篇 |
海洋学 | 29篇 |
天文学 | 72篇 |
综合类 | 2篇 |
自然地理 | 7篇 |
出版年
2022年 | 1篇 |
2021年 | 4篇 |
2020年 | 3篇 |
2019年 | 9篇 |
2018年 | 10篇 |
2017年 | 8篇 |
2016年 | 13篇 |
2015年 | 12篇 |
2014年 | 6篇 |
2013年 | 12篇 |
2012年 | 15篇 |
2011年 | 8篇 |
2010年 | 13篇 |
2009年 | 15篇 |
2008年 | 17篇 |
2007年 | 8篇 |
2006年 | 5篇 |
2005年 | 10篇 |
2004年 | 8篇 |
2003年 | 12篇 |
2002年 | 5篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1986年 | 2篇 |
1982年 | 3篇 |
1981年 | 1篇 |
排序方式: 共有225条查询结果,搜索用时 0 毫秒
61.
A detailed reconstruction of the morphology and recent tectonic activity of the Northern Ionian basin is provided on the basis
of newly acquired high-resolution swath bathymetric and single and multichannel seismic profiles. The tectonic domains in
this area are the Calabrian accretionary wedge and the Apulian foreland. The contact between the two domains, oriented NW–SE,
morphologically coincides with a sea-bottom erosional channel (Taranto canyon) characterized on both sides by mass movements
induced by slope instability. Along the accretionary wedge/Apulian foreland boundary three different morphological sectors
have been recognized whose main characters are represented by a southward stepped increase of erosional canyon activity resulting
in a pronounced slope acclivity and a superficial sediment instability. By means of seismic data we correlate the morphology
of the sea-bottom to different contractional and flexural processes of the accretionary wedge/foreland system. The interaction
between the different rheological domains in the subduction/collision processes could have also induced horizontal stress
represented by areas of tectonic release. In an area like this, where very few detailed surveys have been carried out, this
study represents the first attempt in correlating the recent tectonic activity to the morphological features and in locating
possible slope instability that has to be evaluated for the positioning of offshore infrastructures. 相似文献
62.
Giorgio Bartolini Valentina di Stefano Giampiero Maracchi Simone Orlandini 《Theoretical and Applied Climatology》2012,107(1-2):279-295
We created a new homogenized daily minimum and maximum temperature data set (1955–2007) for the central Mediterranean area of Tuscany (Italy). Yearly and seasonal long-term trends of some climatic and extreme climatic indices were investigated. The results highlighted a positive trend for mean temperature of about 0.9°C per 50 years with a slightly more pronounced increase in maximum temperature. Seasonal analysis revealed a by far much greater increase in summer (June, July, August) and spring (March, April, May) temperature in respect of autumn and winter, this finding consistent with most recent Mediterranean evidences. Warm extremes showed an overall tendency to increase, while a slight not significant decrease trend was found in regard to frost days and cold extremes. Comparisons with different patterns of Mediterranean warming confirmed the magnitude of recent very fast rise in temperature, especially during summer. This change could be due to last decades modifications of general circulation patterns and land–temperature, land–precipitation positive feedback processes dependent from soil moisture. All these results confirm that the Mediterranean is a region especially responsive and thus very vulnerable to climate change. 相似文献
63.
The impact of a railway tunnel on groundwater and surface waters in the Northern Apennines (Italy) was demonstrated and characterised by multi-tracer tests and hydrological observations. The 15-km-long Firenzuola tunnel crosses turbidite marls and sandstones previously not considered as aquifers. During the drilling, water inrushes occurred at fracture zones, and the tunnel still continues to drain the aquifer. The water table dropped below the level of the valleys, and gaining streams transformed into losing streams or ran completely dry, as did many springs, causing severe damage to the aquatic fauna and other elements of the ecosystem. Two multi-tracer tests, each using uranine and sulforhodamine G, were carried out in two impacted catchments in order to confirm and quantify the stream–aquifer–tunnel interrelations. The results proved connection between losing streams and numerous water inlets in the tunnel, with maximum linear distances of 1.4 km and velocities up to 135 m/d. Several of the demonstrated flowpaths pass under previous groundwater divides (mountain ridges), proving that the tunnel has completely modified the regional flow system. Water balance estimations demonstrate that the observed water losses cannot be explained by climate change but can largely be attributed to the tunnel drainage. 相似文献
64.
65.
Natalia G. Zhukova Valentina N. Nesterova Irina P. Prokopchuk Galina B. Rudneva 《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(21-22):1959
The purpose of the study is to analyze the state of the Barents Sea euphausiids populations in the warm period (2000–2005) based on the study of their structure dynamics and distribution under the influence of abiotic and biotic factors. For estimation of their aggregations in the bottom layer, the traditional method was used with the help of the modified egg net (0.2 m2 opening area, 564 μm mesh size). The net is used for collecting euphausiids in the autumn–winter period when their activity is reduced, which results in high-catch efficiency. The findings confirmed the major formation patterns of the euphausiids species composition associated with climate change in the Arctic basin. As before, in the warm years, one can see a clear-cut differentiation of space distribution of the dominant euphausiids Thysanoessa genus with localization of the more thermophilic Thysanoessa inermis in the north-west Barents Sea and Thysanoessa raschii in the east. The major euphausiids aggregations are formed of these species. In 2004, the first data of euphausiids distribution in the northern Barents Sea (77–79°N) were obtained, and demonstrated extremely high concentrations of T. inermis in this area, with the biomass as high as 1.7–2.4 g m−2 in terms of dry weight. These data have improved our knowledge of the distribution and euphausiids abundance during periods of elevated sea-water temperatures in the Barents Sea. The oceanic Atlantic species were found to increase in abundance due to elevated advection to the Barents Sea during the study period. Thus, after nearly a 30-year-long absence of the moderate subtropical Nematoscelis megalops in the Barents Sea, they were found again in 2003–2005. However in comparison with 1960, the north-east border of its distribution considerably shifted to 73°50′N 50°22′E. The portion of Meganyctiphanes norvegica also varied considerably—from 10% to 20% of the total euphausiids population in the warm 1950s–1960s almost to complete disappearing in 1970–1990s. The peak of this species’ occurrence (18–26%) took place in the beginning of warm period (1999–2000) after a succession of cold years. The subsequent reduction of the relative abundance of M. norvegica to 7% might have been mostly caused by fish predation during a period of low population densities of capelin. This high predation pressure may therefore have been mediated both by other pelagic fishes (i.e. herring, blue whiting, polar cod) but also by demersal fishes such as cod and haddock. Similar sharp fluctuations in the capelin stock (the major consumer of euphausiids) created marked perturbations in the food web in the Barents Sea in the middle 1980s and the early 1990s. 相似文献
66.
In this paper we present the first results of the analysis of intermediate resolution (Δλ ~ 3.5 Å) spectra of giants of the Sagittarius dwarf galaxy acquired using the ESO NTT telescope. From the deep CCD photometry of Marconi et al. (1998a) we have selected a sample of giants representative of the metallicity spread suggested by the comparison of the colour-magnitude diagram of Sagittarius with those of galactic globular clusters. The spectra have been used to measure radial velocities, to confirm the membership to Sagittarius, and to provide a metallicity estimate by using spectral synthesis techniques. The analyzed stars show a spread in metallicities in the range ?1.0≤ [Fe/H]≤ +0.7, some 0.5 dex more metal-rich than the photometric estimates. 相似文献
67.
M. Guainazzi G. Matt L. A. Antonelli L. Bassani A. C. Fabian R. Maiolino A. Marconi F. Fiore K. Iwasawa L. Piro 《Monthly notices of the Royal Astronomical Society》1999,310(1):10-20
We present an X-ray spectroscopic study of the bright Compton-thick Seyfert 2 galaxies NGC 1068 and the Circinus Galaxy, performed with BeppoSAX . Matt et al. interpreted the spectrum above 4 keV as the superposition of Compton reflection and warm plasma scattering of the nuclear radiation. When this continuum is extrapolated downwards to 0.1 keV, further components arise. The NGC 1068 spectrum is rich in emission lines, mainly owing to K α transitions of He-like elements from oxygen to iron, plus a K α fluorescent line from neutral iron. If the ionized lines originate in the warm scatterer, its thermal and ionization structure must be complex. From the continuum and line properties, we estimate a column density, N warm , of the warm scatterer less than a few×1021 cm−2 . In the Circinus Galaxy, the absence of highly ionized iron is consistent with a scattering medium with U X ≲5 and N warm ∼ a few×1022 cm−2 . In both cases the neutral iron line is most naturally explained as fluorescence in the medium responsible for the Compton reflection continuum. In NGC 1068 an optically thin plasma emission with kT ≃500 eV and strongly sub-solar metallicity is required, while such a component is only marginal in the Circinus Galaxy. We tentatively identify this component as emission of diffuse hot gas in the nuclear starbursts. Possible causes for the metal depletion are discussed. 相似文献
68.
69.
S. Degl’Innocenti P. G. Prada Moroni M. Marconi A. Ruoppo 《Astrophysics and Space Science》2008,316(1-4):25-30
We summarize the main physical assumptions and numerical procedures adopted by the FRANEC code to compute stellar models in all the evolutionary phases at hydrostatic and thermal equilibrium. An application to the Standard Solar Model is also briefly presented. 相似文献
70.