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81.
Ganymede crater dimensions – Implications for central peak and central pit formation and development
Veronica J. Bray Paul M. Schenk H. Jay Melosh Joanna V. Morgan Gareth S. Collins 《Icarus》2012,217(1):115-129
The morphology of impact craters on the icy Galilean satellites differs from craters on rocky bodies. The differences are thought due to the relative weakness of ice and the possible presence of sub-surface water layers. Digital elevation models constructed from Galileo images were used to measure a range of dimensions of craters on the dark and bright terrains of Ganymede. Measurements were made from multiple profiles across each crater, so that natural variation in crater dimensions could be assessed and averaged scaling trends constructed. The additional depth, slope and volume information reported in this work has enabled study of central peak formation and development, and allowed a quantitative assessment of the various theories for central pit formation. We note a possible difference in the size-morphology progression between small craters on icy and silicate bodies, where central peaks occur in small craters before there is any slumping of the crater rim, which is the opposite to the observed sequence on the Moon. Conversely, our crater dimension analyses suggest that the size-morphology progression of large lunar craters from central peak to peak-ring is mirrored on Ganymede, but that the peak-ring is subsequently modified to a central pit morphology. Pit formation may occur via the collapse of surface material into a void left by the gradual release of impact-induced volatiles or the drainage of impact melt into sub-crater fractures. 相似文献
82.
Environmental and land use factors affecting phosphate hysteresis patterns of stream water during flood events (Carpathian Foothills,Poland) 总被引:1,自引:0,他引:1
Flood events play a substantial role in the circulation of catchment phosphate (PO43?). The purpose of the research was to analyze the factors determining PO43? hysteresis patterns (direction and width) during four types of floods: short and long rainfall floods and snowmelt floods on frozen and thawed soil. The research took place in small catchments (forested, agricultural, mixed‐use) in the Carpathian Foothills in Poland. Anticlockwise hysteresis was identified in the forested catchment during short and long rainfall floods. Under the same conditions, the clockwise direction was observed in the agricultural catchment. In the mixed‐use catchment, the direction of PO43? hysteresis loops was various, driven by the share of water flowing from each part of the catchment. For snowmelt floods, the PO43? hysteresis pattern was similar in all the streams studied (usually clockwise). The direction of PO43? hysteresis loops depends on water circulation patterns, which are determined by the different influx times of particular runoff components. The stream recharge mechanism during a flood event is affected both by the factor initiating the event (precipitation, snowmelt) as well as by land use in the given catchment. Hysteresis loop width was determined by the pool of PO43? in a given catchment during the time period immediately preceding a flood event as well as by the quantity of PO43? flushed out of the soil. The greater a catchment's pool of PO43? and the greater its ability to flush PO43? out of the soil and into surface flow, the wider the hysteresis loops. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
83.
84.
Climate Change Impact on Hydrological Extremes: Preliminary Results from the Polish-Norwegian Project 总被引:2,自引:1,他引:1
Renata J. Romanowicz Ewa Bogdanowicz Sisay E. Debele Joanna Doroszkiewicz Hege Hisdal Deborah Lawrence Hadush K. Meresa Jaroslaw J. Napiórkowski Marzena Osuch Witold G. Strupczewski Donna Wilson Wai Kwok Wong 《Acta Geophysica》2016,64(2):477-509
This paper presents the background, objectives, and preliminary outcomes from the first year of activities of the Polish–Norwegian project CHIHE (Climate Change Impact on Hydrological Extremes). The project aims to estimate the influence of climate changes on extreme river flows (low and high) and to evaluate the impact on the frequency of occurrence of hydrological extremes. Eight “twinned” catchments in Poland and Norway serve as case studies. We present the procedures of the catchment selection applied in Norway and Poland and a database consisting of near-natural ten Polish and eight Norwegian catchments constructed for the purpose of climate impact assessment. Climate projections for selected catchments are described and compared with observations of temperature and precipitation available for the reference period. Future changes based on those projections are analysed and assessed for two periods, the near future (2021–2050) and the far-future (2071–2100). The results indicate increases in precipitation and temperature in the periods and regions studied both in Poland and Norway. 相似文献
85.
Joanna Dzido Agnieszka Kijewska Magdalena Rokicka Agnieszka Świątalska-Koseda Jerzy Rokicki 《Polar Science》2009,3(3):207-211
The aim of this study is to extend our knowledge of the distribution of anisakid nematode parasites in Arctic and Antarctic polar regions. We examined vertebrate (fish) taxa characteristic of the faunas in both polar regions for the presence of parasitic nematodes. The material was collected from Svalbard (Arctic) between July and August 2008 and from King George Island (South Shetland Islands, Antarctic Peninsula) between November 2007 and January 2008. In addition, faecal, bird, and invertebrate samples were collected and examined for the presence of anisakid nematodes or eggs. Anisakis simplex s.s. was found in the body cavity of Arctic cod, and Contracaecum sp. and Pseudoterranova sp. were found in Antarctic notothenioids. Eggs of Anisakis sp. and Contracaecum sp. were recovered from the faeces of Mirounga leonina. We present the first record of the occurrence of A. simplex C in the Antarctic fishes Notothenia coriiceps and Notothenia rossii. 相似文献
86.
Joanna Mirosław-Grabowska Monika Niska Elwira Sienkiewicz 《Journal of Paleolimnology》2009,42(4):467-481
We present isotope, cladoceran and diatom results from investigations of Eemian sediments of the palaeolake at Ruszkówek,
central Poland. Our analyses of the 15-m-thick sediments indicate that sandy silts occur on the bottom, followed by calcareous
gyttja, interbedded with lake marl. The upper part of the sequence contains peat and peaty sands. Values of δ18O change from −9.4‰ to −3.3‰ and δ13C values oscillate between −3.2‰ and +7.0‰. Nine isotope zones (Is) were defined and characterized using stable isotope analysis
of carbonates. Fifteen species of subfossil Cladocera were found and six faunal zones were distinguished (Cladocera zones).
One hundred and twenty-three diatom taxa, representing 31 genera were identified, enabling us to discern six Diatom Assemblage
Zones. The isotope, cladoceran, and diatom data correlate well with pollen data that define seven phases of evolution of the
palaeolake at Ruszkówek. The palaeolake began during the final phase of the Wartanian (Late Saalian Glaciation). During the
early Eemian, the palaeolake reached its maximum depth. During the Early Vistulian glaciation, the palaeolake declined. Changes
in the cladoceran and diatom communities indicate initial oligotrophic conditions in the lake, then an increase to mesotrophy,
and finally eutrophic conditions. 相似文献
87.
We developed, and applied in two sites, novel methods to measure ground water-borne nitrogen loads to receiving estuaries from plumes resulting from land disposal of waste water treatment plant (WWTP) effluent. In addition, we quantified nitrogen losses from WWTP effluent during transport through watersheds. WWTP load to receiving water was estimated as the difference between total measured ground water-transported nitrogen load and modeled load from major nitrogen sources other than the WWTP. To test estimated WWTP loads, we applied two additional methods. First, we quantified total annual waste water nitrogen load from watersheds based on nitrogen stable isotopic signatures of primary producers in receiving water. Second, we used published data on ground water nitrogen concentrations in an array of wells to estimate dimensions of the plume and quantify the annual mass of nitrogen transported within the plume. Loss of nitrogen during transport through the watershed was estimated as the difference between the annual mass of nitrogen applied to watersheds as treatment plant effluent and the estimated nitrogen load reaching receiving water. In one plume, we corroborated our estimated nitrogen loss in watersheds using data from multiple-level sampling wells to calculate the loss of nitrogen relative to a conservative tracer. The results suggest that nitrogen from the plumes is discharging to the estuaries but that substantial nitrogen loss occurs during transport through the watersheds. The measured vs. modeled and stable isotopic approaches, in comparison to the plume mapping approach, may more reliably quantify ground water-transported WWTP loads to estuaries. 相似文献
88.
Organochlorine pesticides in fish from the southern Baltic Sea: levels, bioaccumulation features and temporal trends during the 1995-2006 period 总被引:1,自引:0,他引:1
The levels of HCH isomers, HCB and summation DDTs were determined in five species of Baltic fish collected during 1995-2006. Some downward time trends of HCH isomer, pp'-DDE and pp'-DDD concentrations in Baltic fish were observed; in contrast, HCB and DDT concentrations did not exhibit any obvious trend. Concentrations of summation HCHs expressed on a lipid weight basis were very similar in all species studied. In contrast, concentrations of summation DDTs varied in tested species. The most abundant HCH isomer was beta-HCH and among DDT-related compounds, pp'-DDE prevailed. In our investigations the sampling sites were not a crucial factor for organochlorine pesticide concentrations and patterns observed in fish, but the occurrence of several inter-species differences in the bioaccumulation features of OC pesticides were observed. For cod there was a positive correlation between fish size (length) and summation DDT concentration. In herring, sprat and salmon samples, summation DDT concentrations were negatively correlated with fat content. 相似文献
89.
Svetlana A. Suleymanova Vera A. Izvekova Joanna M. Rankin N. Rathnasree 《Journal of Astrophysics and Astronomy》1998,19(1-2):1-18
The characteristics of the “burst” (B) mode and “quiescent” (Q) mode pulse sequences–long known from studies at or below 103
MHz–are identified at 430 MHz for the first time. An 18-minute, Polarimetrie observation begins with a long Bmode sequence,
which has a higher average intensity, regular drifting subpulses, and a preponderance of primary polarisationmode radiation.
An abrupt transition to a Q-mode sequence is then marked by a) weaker average intensity, but occasional very bright individual
subpulses, b) a complete cessation of drifting subpulses, with disorganized subpulses now being emitted over a much wider
longitude interval, and c) near parity between the primary and secondary polarisation modes, resulting in pronounced depolarisation,
both of individual pulses and the average profile.
Careful study, however, of profile changes before and after this mode change reveals slower variations which both anticipate
the abrupt transition and respond to it. A slow attenuation of the intensity level of the dominant component is observed throughout
the duration of the B-mode sequence, which then accelerates with the onset of the Q-mode sequence. This slow variation appears
to represent a “preswitching transition” process; and the combination of effects on slow and abrupt time scales are finally
responsible for the formation of the characteristic B and Q-mode average profiles. 相似文献
90.