全文获取类型
收费全文 | 934篇 |
免费 | 31篇 |
国内免费 | 21篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 124篇 |
地球物理 | 195篇 |
地质学 | 368篇 |
海洋学 | 36篇 |
天文学 | 223篇 |
综合类 | 4篇 |
自然地理 | 27篇 |
出版年
2021年 | 13篇 |
2020年 | 13篇 |
2019年 | 12篇 |
2018年 | 13篇 |
2017年 | 13篇 |
2016年 | 24篇 |
2015年 | 27篇 |
2014年 | 28篇 |
2013年 | 45篇 |
2012年 | 42篇 |
2011年 | 44篇 |
2010年 | 35篇 |
2009年 | 40篇 |
2008年 | 49篇 |
2007年 | 33篇 |
2006年 | 33篇 |
2005年 | 44篇 |
2004年 | 37篇 |
2003年 | 25篇 |
2002年 | 29篇 |
2001年 | 20篇 |
2000年 | 23篇 |
1999年 | 20篇 |
1998年 | 15篇 |
1997年 | 9篇 |
1996年 | 14篇 |
1995年 | 11篇 |
1994年 | 15篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 17篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 13篇 |
1983年 | 14篇 |
1981年 | 16篇 |
1980年 | 14篇 |
1979年 | 7篇 |
1978年 | 13篇 |
1977年 | 9篇 |
1976年 | 14篇 |
1975年 | 10篇 |
1974年 | 7篇 |
1973年 | 12篇 |
1972年 | 8篇 |
1970年 | 5篇 |
排序方式: 共有986条查询结果,搜索用时 15 毫秒
471.
VGDI – Advancing the Concept: Volunteered Geo‐Dynamic Information and its Benefits for Population Dynamics Modeling 下载免费PDF全文
Christoph Aubrecht Dilek Özceylan Aubrecht Joachim Ungar Sérgio Freire Klaus Steinnocher 《Transactions in GIS》2017,21(2):253-276
The concept of Volunteered Geographic Information (VGI) has progressed from being an exotic prospect to making a profound impact on GIScience and geography in general, as initially anticipated. However, while massive and manifold data is continuously produced voluntarily and applications are built for information and knowledge extraction, the initially introduced concept of VGI lacks certain methodological perspectives in this regard which have not been fully elaborated. In this article we highlight and discuss an important gap in this concept, i.e. the lack of formal acknowledgment of temporal aspects. By coining the proposed advanced framework ‘Volunteered Geo‐Dynamic Information’ (VGDI), we attempt to lay the ground for full conceptual and applied spatio‐temporal integration. To illustrate that integrative approach of VGDI and its benefits, we describe the potential impact on the field of dynamic population distribution modeling. While traditional approaches in that domain rely on survey‐based data and statistics as well as static geographic information, the use of VGDI enables a dynamic setup. Foursquare venue and user check‐in data are presented for a test site in Lisbon, Portugal. Two core modules of spatio‐temporal population assessment are thereby addressed, namely time use profiling and target zone characterization, motivated by the potential integration in existing population dynamics frameworks such as the DynaPop model. 相似文献
472.
Ulrich Cubasch Klaus Hasselmann Heinke Höck Ernst Maier-Reimer Uwe Mikolajewicz Benjamin D Santer Robert Sausen 《Climate Dynamics》1992,8(2):55-69
Climate changes during the next 100 years caused by anthropogenic emissions of greenhouse gases have been simulated for the Intergovernmental Panel on Climate Change Scenarios A (business as usual) and D (accelerated policies) using a coupled ocean-atmosphere general circulation model. In the global average, the near-surface temperature rises by 2.6 K in Scenario A and by 0.6 K in Scenario D. The global patterns of climate change for both IPCC scenarios and for a third step-function 2 x CO2 experiment were found to be very similar. The warming delay over the oceans is larger than found in simulations with atmospheric general circulation models coupled to mixed-layer models, leading to a more pronounced land-sea contrast and a weaker warming (and in some regions even an initial cooling) in the Southern Ocean. During the first forty years, the global warming and sea level rise due to the thermal expansion of the ocean are significantly slower than estimated previously from box-diffusion-upwelling models, but the major part of this delay can be attributed to the previous warming history prior to the start of present coupled ocean-atmosphere model integration (cold start). 相似文献
473.
Evidence for Holocene environmental changes in the northern Fertile Crescent provided by pedogenic carbonate coatings 总被引:1,自引:0,他引:1
Holocene environmental changes in the northern Fertile Crescent remain poorly understood because of the scarcity of local proxy records in the region. In this study we investigated pedogenic (soil-formed) carbonate coatings on stones at the Pre-Pottery Neolithic site Göbekli Tepe as an indicator of local early-mid Holocene environmental changes. The 14C ages and stable isotopic composition of carbon and oxygen in thin (0.2–0.3 mm thick) pedogenic carbonate lamina indicate two main periods of coating formation: the early-Holocene (ca. 10000–6000 cal yr BP) and the mid-Holocene (ca. 6000–4000 cal yr BP). During the first period, there was an inverse relationship between δ13C and δ18O curves: a decrease in δ13C values coincide with an increase in δ18O values. For this period a trend towards higher temperatures is suggested. In the mid-Holocene, the mean rate of coating growth was 2–3 times higher than in the early Holocene. Both δ13C and δ18O reached their maximum values during this time and the direction of changes of the δ13C and δ18O curves became similar. The combination of data suggests that this period was the most humid in the Holocene and on average warmer than the early Holocene. At ca. 4000 cal yr BP secondary accumulation of carbonate ceased, presumably reflecting a shift to a more arid climate. 相似文献
474.
Marghaleray Amini Anton Eisenhauer Florian Böhm Chris Holmden Katharina Kreissig Folkmar Hauff Klaus Peter Jochum 《Geostandards and Geoanalytical Research》2009,33(2):231-247
We report δ44/40Ca(SRM 915a) values for eight fused MPI‐DING glasses and the respective original powders, six USGS igneous rock reference materials, the U‐Th disequilibria reference material TML, IAEA‐CO1 (Carrara marble) and several igneous rocks (komatiites and carbonatites). Sample selection was guided by three considerations: (1) to address the need for information values on reference materials that are widely available in support of interlaboratory comparison studies; (2) support the development of in situ laser ablation and ion microprobe techniques, which require isotopically homogenous reference samples for ablation; and (3) provide Ca isotope values on a wider range of igneous and metamorphic rock types than is currently available in the scientific literature. Calcium isotope ratios were measured by thermal ionisation mass spectrometry in two laboratories (IFM‐GEOMAR and Saskatchewan Isotope Laboratory) using 43Ca/48Ca‐ and 42Ca/43Ca‐double spike techniques and reported relative to the calcium carbonate reference material NIST SRM 915a. The measurement uncertainty in both laboratories was better than 0.2‰ at the 95% confidence level. The impact of different preparation methods on the δ44/40Ca(SRM 915a) values was found to be negligible. Except for ML3‐B, the original powders and the respective MPI‐DING glasses showed identical δ44/40Ca(SRM 915a) values; therefore, possible variations in the Ca isotope compositions resulting from the fusion process are excluded. Individual analyses of different glass fragments indicated that the glasses are well homogenised on the mm scale with respect to Ca. The range of δ44/40Ca(SRM 915a) values in the igneous rocks studied was larger than previously observed, mostly owing to the inclusion of ultramafic rocks from ophiolite sections. In particular, the dunite DTS‐1 (1.49 ± 0.06‰) and the peridotite PCC‐1 (1.14 ± 0.07‰) are enriched in 44Ca relative to volcanic rocks (0.8 ± 0.1‰). The Carrara marble (1.32 ± 0.06‰) was also found to be enriched in 44Ca relative to the values of assumed precursor carbonates (< 0.8‰). These findings suggest that the isotopes of Ca are susceptible to fractionation at high temperatures by, as yet, unidentified igneous and metamorphic processes. 相似文献
475.
Piero Bellanova Mike Frenken Bruce Richmond Jan Schwarzbauer Seanpaul La Selle Frances Griswold Bruce Jaffe Alan Nelson Klaus Reicherter 《Sedimentology》2020,67(3):1230-1248
Far-field tsunami deposits observed in the Kahana Valley, O‘ahu, Hawai‘i (USA), were investigated for their organic-geochemical content. During short high-energy events, (tsunamis and storms) organic and chemical components are transported with sediment from marine to terrestrial areas. This study investigates the use of anthropogenic based organic geochemical compounds (such as polycyclic aromatic hydrocarbons, pesticides and organochlorides) as a means to identify tsunami deposits. Samples were processed by solid–liquid extraction and analyzed using gas chromatography–mass spectrometry. A total of 21 anthropogenic marker compounds were identified, of which 11 compounds were selected for detailed analysis. Although the tsunami deposits pre-date industrial activity in Hawai‘i by several hundred years, distinct changes were found in the concentrations of anthropogenic marker compounds between sandy tsunami deposits and the surrounding mud/peat layers, which may help in identifying tsunami deposits within cores. As expected, low overall concentrations of anthropogenic markers and pollutants were observed due to the lack of industrial input-sources and little anthropogenic environmental impact at the study site. This geochemical characterization of tsunami deposits shows that anthropogenic markers have significant potential as another high-resolution, multi-proxy method for identifying tsunamis in the sedimentary record. 相似文献
476.
Average ice crystal size and bulk short-wave single-scattering properties of cirrus clouds 总被引:1,自引:0,他引:1
The bulk single-scattering properties of cirrus clouds required for driving the radiation scheme in large-scale climate models are computed with respect to various size distributions and ice crystal shapes. It is shown that the average ice crystal size, defined as the ratio of total volume to the total projected area, can well-characterize the effect of various size distributions in determining the bulk radiative properties of cirrus clouds. Details of the size distributions are not significant in specifying the radiative properties of these clouds if the effective average size is thus defined. Therefore, the ratio of the total volume to the total projected area is an ideal parameter for describing the bulk single-scattering properties. The effect of ice crystal shape is not critical in the parameterization of the extinction coefficient and single-scattering albedo. However, the various crystal habits must be accounted for in the parameterization of the asymmetry parameter. The resulting parameterization is intended for radiative transfer calculations involving cirrus clouds in large-scale models. 相似文献
477.
The Eastern Weddell Ice Shelves (EWIS) are believed to modify the water masses of the coastal current and thus preconditions
the water mass formation in the southern and western Weddell Sea. We apply various ocean warming scenarios to investigate
the impact on the temperature–salinity distribution and the sub-ice shelf melting in the Eastern Weddell Sea. In our numerical
experiments, the warming is imposed homogeneously along the open inflow boundaries of the model domain, leading to a warming
of the warm deep water (WDW) further downstream. Our modelling results indicate a weak quadratic dependence of the melt rate
at the ice shelf base on the imposed amount of warming, which is consistent with earlier studies. The total melt rate has
a strong dependence on the applied ocean warming depth. If the warming is restricted to the upper ocean (above 1,000 m),
the water column (aside from the mixed surface layer) in the vicinity of the ice shelves stabilises. Hence, reduced vertical
mixing will reduce the potential of Antarctic Bottom Water formation further downstream with consequences on the global thermohaline
circulation. If the warming extends to the abyss, the WDW core moves significantly closer to the continental shelf break.
This sharpens the Antarctic Slope Front and leads to a reduced density stratification. In contrast to the narrow shelf bathymetry
in the EWIS region, a wider continental shelf (like in the southern Weddell Sea) partly protects ice shelves from remote ocean
warming. Hence, the freshwater production rate of, e.g., the Filchner–Ronne Ice Shelf increases much less compared with the
EWIS for identical warming scenarios. Our study therefore indicates that the ice-ocean interaction has a significant impact
on the temperature-salinity distribution and the water column stability in the vicinity of ice shelves located along a narrow
continental shelf. The effects of ocean warming and the impact of increased freshwater fluxes on the circulation are of the
same order of magnitude and superimposed. Therefore, a consideration of this interaction in large-scale climate studies is
essential. 相似文献
478.
Evaristo Vázquez-Domínguez Carlos M. Duarte Klaus Jürgens Josep M. Gasol 《Progress in Oceanography》2008,79(1):83-94
The role of microorganisms in the transfer of carbon of marine systems is very important in open oligotrophic oceans. Here, we analyze the picoplankton structure, the heterotrophic bacterioplankton activity, and the predator-prey relationships between heterotrophic bacteria and nanoflagellates during two large scale cruises in the Central Atlantic Ocean (∼29°N to ∼40°S). Latitud cruises were performed in 1995 between March-April and October-November. During both cruises we crossed the regions of different trophic statuses; where we measured different biological variables both at the surface and at the deep chlorophyll maximum (DCM). The concentration of chlorophyll a varied between 0.1 and 0.8 mg m−3, the abundance of heterotrophic bacteria varied between <1.0 × 105 and >1.0 × 106 cells ml−1, and that of heterotrophic nanoflagellates between <100 and >1.0 × 104 cells ml−1. The production of heterotrophic bacteria varied more than three orders of magnitude between <0.01 and 24 μgC L−1 d−1; and the growth rates were in the range <0.01-2.1 d−1. In the Latitud-II cruise, Prochlorococcus ranged between <103 and >3 × 105 cells ml−1, Synechococcus between <100 and >1.0 × 104 cells ml−1, and picoeukaryotes between <100 and >104 cells ml−1.Two empirical models were used to learn more about the relationship between heterotrophic bacteria and nanoflagellates. Most bacterial production was ingested when this production was low, the heterotrophic nanoflagellates could be controlled by preys during Latitud-I cruise at the DCM, and by predators in the surface and in the Latitud-II cruise. Our results were placed in context with others about the structure and function of auto- and heterotrophic picoplankton and heterotrophic nanoplankton in the Central Atlantic Ocean. 相似文献
479.
Timothy j. Fagan Edward r. d. Scott Klaus Keil Thomas f. Cooney Shiv k. Sharma 《Meteoritics & planetary science》2000,35(2):319-329
Abstract— The enstatite chondrite reckling peak (rkp) a80259 contains feldspathic glass, kamacite, troilite, and unusual sets of parallel fine‐grained enstatite prisms that formed by rapid cooling of shock melts. Metallic Fe,Ni and troilite occur as spherical inclusions in feldspathic glass, reflecting the immiscible Fe‐Ni‐S and feldspathic melts generated during the impact. The Fe‐Ni‐S and feldspathic liquids were injected into fractures in coarse‐grained enstatite and cooled rapidly, resulting in thin (≤ 10 μm) semicontinuous to discontinuous veins and inclusion trails in host enstatite. Whole‐rock melt veins characteristic of heavily shocked ordinary chondrites are conspicuously absent. Raman spectroscopy shows that the feldspathic material is a glass. Elevated MgO and SiO2 contents of the glass indicate that some enstatite and silica were incorporated in the feldspathic melt. Metallic Fe,Ni globules are enclosed by sulfide and exhibit Nienrichment along their margins characteristic of rapid crystallization from a Fe‐Ni‐S liquid. Metal enclosed by sulfide is higher in Si and P than metal in feldspathic glass and enstatite, possibly indicating lower O fugacities in metal/sulfide than in silicate domains. Fine‐grained, elongate enstatite prisms in troilite or feldspathic glass crystallized from local pyroxene melts that formed along precursor grain boundaries, but most of the enstatite in the target rock remained solid during the impact and occurs as deformed, coarsegrained crystals with lower CaO, Al2O3, and FeO than the fine‐grained enstatite. Reckling Peak A80259 represents an intermediate stage of shock melting between unmelted E chondrites and whole‐rock shock melts and melt breccias documented by previous workers. The shock petrogenesis of RKPA80259 reflects the extensive impact processing of the enstatite chondrite parent bodies relative to those of other chondrite types. 相似文献
480.
Reinhard Calov Andrey Ganopolski Martin Claussen Vladimir Petoukhov Ralf Greve 《Climate Dynamics》2005,24(6):545-561
We study the mechanisms of glacial inception by using the Earth system model of intermediate complexity, CLIMBER-2, which
encompasses dynamic modules of the atmosphere, ocean, biosphere and ice sheets. Ice-sheet dynamics are described by the three-dimensional
polythermal ice-sheet model SICOPOLIS. We have performed transient experiments starting at the Eemiam interglacial, at 126 ky
BP (126,000 years before present). The model runs for 26 kyr with time-dependent orbital and CO2 forcings. The model simulates a rapid expansion of the area covered by inland ice in the Northern Hemisphere, predominantly
over Northern America, starting at about 117 kyr BP. During the next 7 kyr, the ice volume grows gradually in the model at
a rate which corresponds to a change in sea level of 10 m per millennium. We have shown that the simulated glacial inception
represents a bifurcation transition in the climate system from an interglacial to a glacial state caused by the strong snow-albedo
feedback. This transition occurs when summer insolation at high latitudes of the Northern Hemisphere drops below a threshold
value, which is only slightly lower than modern summer insolation. By performing long-term equilibrium runs, we find that
for the present-day orbital parameters at least two different equilibrium states of the climate system exist—the glacial and
the interglacial; however, for the low summer insolation corresponding to 115 kyr BP, we find only one, glacial, equilibrium
state, while for the high summer insolation corresponding to 126 kyr BP only an interglacial state exists in the model.
相似文献
Reinhard CalovEmail: |