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排序方式: 共有207条查询结果,搜索用时 15 毫秒
21.
Erling K. Stenevik Webjrn Melle Eilif Gaard Astthor Gislason Cecilie T.. Broms Irina Prokopchuk Bjrnar Ellertsen 《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2672
Egg production of Calanus finmarchicus was studied during joint basin-scale surveys in April–June 2003 in the Norwegian Sea. Surveys covered the whole Norwegian Sea and were conducted from Norwegian, Icelandic and Faroese research vessels. Stations were classified as being in pre-bloom, bloom or post-bloom phase according to levels of chlorophyll a and nitrate. Individual egg production rates and population egg production rates were calculated and compared between areas. Both individual egg production rates (eggs female−1 day−1) and population egg production rates (eggs m−2 day−1) were significantly higher in bloom areas compared with pre-bloom and post-bloom areas. However, when integrated over an estimated duration of the three phases, the time-integrated egg production (eggs m−2) in most years was highest in the pre-bloom phase, and this was explained by the longer duration of this phase compared with the two other phases. 相似文献
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Thermal characteristics of anisotropic media with inclusions 总被引:1,自引:0,他引:1
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David Savage Josep M. SolerKohei Yamaguchi Colin WalkerAkira Honda Manabu InagakiClaire Watson James WilsonSteven Benbow Irina GausJoerg Rueedi 《Applied Geochemistry》2011,26(7):1138-1152
The use of cement and concrete as fracture grouting or as tunnel seals in a geological disposal facility for radioactive wastes creates potential issues concerning chemical reactivity. From a long-term safety perspective, it is desirable to be able model these interactions and changes quantitatively. The ‘Long-term Cement Studies’ (LCS) project was formulated with an emphasis on in situ field experiments with more realistic boundary conditions and longer time scales compared with former experiments. As part of the project programme, a modelling inter-comparison has been conducted, involving the modelling of two experiments describing cement hydration on one hand and cement-rock reaction on the other, with teams representing the NDA (UK), Posiva (Finland), and JAEA (Japan).This modelling exercise showed that the dominant reaction pathways in the two experiments are fairly well understood and are consistent between the different modelling teams, although significant differences existed amongst the precise parameterisation (e.g. reactive surface areas, dependences of rate upon pH, types of secondary minerals), and in some instances, processes (e.g. partition of alkali elements between solids and liquid during cement hydration; kinetic models of cement hydration). It was not conclusive if certain processes such as surface complexation (preferred by some modellers, but not by others) played a role in the cement-rock experiment or not. These processes appear to be more relevant at early times in the experiment and the evolution at longer timescales was not affected. The observed permeability profile with time could not be matched. The fact that no secondary minerals could be observed and that the precipitated mass calculated during the simulations is minor might suggest that the permeability reduction does not have a chemical origin, although a small amount of precipitates at pore throats could have a large impact on permeability.The modelling exercises showed that there is an interest in keeping the numerical models as simple as possible and trying to obtain a reasonable fit with a minimum of processes, minerals and parameters. However, up-scaling processes and model parameterisation to the timescales appropriate to repository safety assessment are of considerable concern. Future modelling exercises of this type should focus on a suitable natural or industrial analogue that might aid assessing mineral-fluid reactions at these longer timescales. 相似文献
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Regional climate change patterns identified by cluster analysis 总被引:1,自引:0,他引:1
Climate change caused by anthropogenic greenhouse emissions leads to impacts on a global and a regional scale. A quantitative
picture of the projected changes on a regional scale can help to decide on appropriate mitigation and adaptation measures.
In the past, regional climate change results have often been presented on rectangular areas. But climate is not bound to a
rectangular shape and each climate variable shows a distinct pattern of change. Therefore, the regions over which the simulated
climate change results are aggregated should be based on the variable(s) of interest, on current mean climate as well as on
the projected future changes. A cluster analysis algorithm is used here to define regions encompassing a similar mean climate
and similar projected changes. The number and the size of the regions depend on the variable(s) of interest, the local climate
pattern and on the uncertainty introduced by model disagreement. The new regions defined by the cluster analysis algorithm
include information about regional climatic features which can be of a rather small scale. Comparing the regions used so far
for large scale regional climate change studies and the new regions it can be shown that the spacial uncertainty of the projected
changes of different climate variables is reduced significantly, i.e. both the mean climate and the expected changes are more
consistent within one region and therefore more representative for local impacts. 相似文献
28.
Gerhard Krinner Annette Rinke Klaus Dethloff Irina V. Gorodetskaya 《Climate Dynamics》2010,35(4):619-633
This paper describes atmospheric general circulation model climate change experiments in which the Arctic sea-ice thickness
is either fixed to 3 m or somewhat more realistically parameterized in order to take into account essentially the spatial
variability of Arctic sea-ice thickness, which is, to a first approximation, a function of ice type (perennial or seasonal).
It is shown that, both at present and at the end of the twenty-first century (under the SRES-A1B greenhouse gas scenario),
the impact of a variable sea-ice thickness compared to a uniform value is essentially limited to the cold seasons and the
lower troposphere. However, because first-year ice is scarce in the Central Arctic today, but not under SRES-A1B conditions
at the end of the twenty-first century, and because the impact of a sea-ice thickness reduction can be masked by changes of
the open water fraction, the spatial and temporal patterns of the effect of sea-ice thinning on the atmosphere differ between
the two periods considered. As a consequence, not only the climate simulated at a given period, but also the simulated Arctic
climate change over the twenty-first century is affected by the way sea-ice thickness is prescribed. 相似文献
29.
Wolfram Kloppmann Haim Chikurel Géraldine Picot Joseph Guttman Marie Pettenati Avi Aharoni Catherine Guerrot Romain Millot Irina Gaus Thomas Wintgens 《Applied Geochemistry》2009
Boron and Li isotopes have been tested as environmental tracers of treated sewage injected into a sandy aquifer (Shafdan reclamation project, Israel). During a 38 days injection test in a newly dug injection well, a conservative artificial tracer (Br−) was monitored together with δ11B and δ7Li in the injectate, in the unsaturated soil zone (porous cup) and an observation well in the aquifer. In spite of B and Li concentrations in the injectate close to background values, significant shifts of the isotope signatures could be observed over the duration of the injection test. Boron isotope ratios show a breakthrough curve delayed with respect to Br− breakthrough due to some reversible sorption on the aquifer material. No isotope fractionation was observed in the unsaturated or the saturated zone so that B isotopes can be considered as conservative in the investigated part of the aquifer system. Lithium isotopes are strongly fractionated, probably due to sorption processes. Lithium concentrations point to a Li sink in the system, δ7Li values vary strongly with a tendency of 7Li depletion in the liquid phase over the duration of the experiment. This is opposite to the expected preferential sorption of 6Li onto clay minerals. Boron isotopes reveals a valuable tracer of artificial recharge of freshwaters derived from treated sewage, both for short term tracer tests and for long-term monitoring of artificial recharge, even if in aquifers with higher clay contents, sorption-linked isotope fractionation cannot be excluded. More data are needed on Li isotope fractionation in natural groundwater systems to assess the potential of this tracer as monitoring tool. 相似文献
30.
Irina G. Kudintseva Alexander P. Nickolaenko Masashi Hayakawa 《Surveys in Geophysics》2010,31(4):427-448
We describe the space–time distribution of the pulsed electric field in the middle atmosphere above a positive Γ-shaped lightning
stroke. The channel of such a discharge contains a vertical and a horizontal section. The current wave moves initially vertically
and then turns horizontally so that radiation appears from the vertical electric dipole followed by that from the horizontal
dipole. Combined with reflection from the perfectly conducting ground, the source provides three subsequent pulses in the
atmosphere, with the lag being determined by the finite velocity of the current wave in the Γ-shaped stroke. The pulses are
reproduced by reflections from the air-ground and the air-ionosphere interfaces and the waveform resembles the M-component,
which is often noted in the negative strokes (e.g. Yashunin et al., J Geophys Res 112:D10109, 2007). The non-stationary fine structure appears in the spatial distribution of electric field, which persists for 2 ms or even
more and exceeds the runaway electron threshold. Estimates support the idea of free electron bunching in the mesosphere by
the pulsed electric field. Focusing may occur about 10 km away from the point of electron- field interaction; it is delayed
by a few ms from the moment of interaction. The data presented might be helpful in realistic modeling of the red sprite formation. 相似文献