全文获取类型
收费全文 | 388篇 |
免费 | 14篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 13篇 |
大气科学 | 60篇 |
地球物理 | 78篇 |
地质学 | 150篇 |
海洋学 | 13篇 |
天文学 | 82篇 |
综合类 | 2篇 |
自然地理 | 10篇 |
出版年
2024年 | 2篇 |
2021年 | 5篇 |
2020年 | 6篇 |
2019年 | 8篇 |
2018年 | 9篇 |
2017年 | 12篇 |
2016年 | 15篇 |
2015年 | 12篇 |
2014年 | 10篇 |
2013年 | 37篇 |
2012年 | 17篇 |
2011年 | 28篇 |
2010年 | 30篇 |
2009年 | 22篇 |
2008年 | 23篇 |
2007年 | 20篇 |
2006年 | 15篇 |
2005年 | 10篇 |
2004年 | 16篇 |
2003年 | 18篇 |
2002年 | 13篇 |
2001年 | 12篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 9篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1994年 | 4篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1987年 | 2篇 |
1984年 | 6篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1937年 | 1篇 |
1931年 | 1篇 |
1930年 | 1篇 |
1914年 | 1篇 |
1912年 | 1篇 |
排序方式: 共有408条查询结果,搜索用时 46 毫秒
351.
352.
The glacially formed northeastern German lowlands are characterized by extensive floodplains, often interrupted by relatively steep moraine hills. The hydrological cycle of this area is governed by the tight interaction of surface water dynamics and the corresponding directly connected shallow groundwater aquifer. Runoff generation processes, as well as the extent and spatial distribution of the interaction between surface water and groundwater, are controlled by floodplain topography and by surface water dynamics. A modelling approach based on extensive experimental analyses is presented that describes the specific water balance of lowland areas, including the interactions of groundwater and surface water, as well as reflecting the important role of time‐variable shallow groundwater stages for runoff generation in floodplains. In the first part, experimental investigations of floodplain hydrological characteristics lead to a qualitative understanding of the water balance processes and to the development of a conceptual model of the water balance and groundwater dynamics of the study area. Thereby model requirements which allow for an adequate simulation of the floodplain hydrology, considering also interactions between groundwater and surface water have been characterized. Based on these analyses, the Integrated Modelling of Water Balance and Nutrient Dynamics (IWAN) approach has been developed. This consists of coupling the surface runoff generation and soil water routines of the deterministic, spatially distributed hydrological model WASIM‐ETH‐I with the three‐dimensional finite‐difference‐based numerical groundwater model MODFLOW and Processing MODFLOW. The model was applied successfully to a mesoscale subcatchment of the Havel River in northeast Germany. It was calibrated for two small catchments (1·4 and 25 km2), where the importance of the interaction processes between groundwater and surface waters and the sensitivity of several controlling parameters could be quantified. Validation results are satisfying for different years for the entire 198 km2 catchment. The model approach was further successfully tested for specific events. The experimental area is a typical example of a floodplain‐dominated landscape. It was demonstrated that the lateral flow processes and the interactions between groundwater and surface water have a major importance for the water balance and periodically superimposed on the vertical runoff generation. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
353.
Christian Motch Adriana M. Pires Frank Haberl Axel Schwope 《Astrophysics and Space Science》2007,308(1-4):217-224
The excellent spatial resolution of the Chandra observatory offers the unprecedented possibility to measure proper motions
at X-ray wavelength with relatively high accuracy using as reference the background of extragalactic or remote galactic X-ray
sources. We took advantage of this capability to constrain the proper motion of RX J0806.4-4123 and RX J0420.0-5022, two X-ray
bright and radio quiet isolated neutron stars (INSs) discovered by ROSAT and lacking an optical counterpart. In this paper,
we present results from a preliminary analysis from which we derive 2σ upper limits of 76 mas/yr and 138 mas/yr on the proper motions of RX J0806.4-4123 and RX J0420.0-5022 respectively. We use
these values together with those of other ROSAT discovered INSs to constrain the origin, distance and evolutionary status
of this particular group of objects. We find that the tangential velocities of radio quiet ROSAT neutron stars are probably
consistent with those of ‘normal’ pulsars. Their distribution on the sky and, for those having accurate proper motion vectors,
their possible birth places, all point to a local population, probably created in the part of the Gould Belt nearest to the
earth.
相似文献
354.
Lutz HECHT Axel WITTMANN Ralf‐Thomas SCHMITT Dieter STFFLER 《Meteoritics & planetary science》2004,39(7):1169-1186
Abstract Petrographical and chemical analysis of melt particles and alteration minerals of the about 100 m‐thick suevitic sequence at the Chicxulub Yax‐1 drill core was performed. The aim of this study is to determine the composition of the impact melt, the variation between different types of melt particles, and the effects of post‐impact hydrothermal alteration. We demonstrate that the compositional variation between melt particles of the suevitic rocks is the result of both incomplete homogenization of the target lithologies during impact and subsequent post‐impact hydrothermal alteration. Most melt particles are andesitic in composition. Clinopyroxene‐rich melt particles possess lower SiO2 and higher CaO contents. These are interpreted by mixing of melts from the silicate basement with overlying carbonate rocks. Multi‐stage post‐impact hydrothermal alteration involved significant mass transfer of most major elements and caused further compositional heterogeneity between melt particles. Following backwash of seawater into the crater, palagonitization of glassy melt particles likely caused depletion of SiO2, Al2O3, CaO, Na2O, and enrichment of K2O and FeOtot during an early alteration stage. Since glass is very susceptible to fluid‐rock interaction, the state of primary crystallization of the melt particles had a significant influence on the intensity of the post‐impact hydrothermal mass transfer and was more pronounced in glassy melt particles than in well‐crystallized particles. In contrast to other occurrences of Chicxulub impactites, the Yax‐1 suevitic rocks show strong potassium metasomatism with hydrothermal K‐feldspar formation and whole rock K20 enrichment, especially in the lower unit of the suevitic sequence. A late stage of hydrothermal alteration is characterized by precipitation of silica, analcime, and Na‐bearing Mg‐rich smectite, among other minerals. This indicates a general evolution from a silica‐undersaturated fluid at relatively high potassium activities at an early stage toward a silica‐oversaturated fluid at relatively high sodium activities at later stages in the course of fluid rock interaction. 相似文献
355.
356.
357.
358.
Zoisite-bearing high-pressure pegmatites from the MünchbergMassif, Germany, provide an excellent example of the characteristicsof the onset of metabasite melting at eclogite-facies conditions.The pegmatites were derived by partial melting of a mid-oceanridge basalt (MORB)-like eclogite at T 680°C/2·3GPa to 750°C/3·1 GPa, which produced small amountsof tonalitic to trondhjemitic melt. The melt concentrated locallyin isolated, small melt pockets and crystallized primary zoisiteas liquidus phase at P 2·3 GPa/680°C to 2·1GPa/750°C. Compositional zoning of pegmatite zoisite recordsan ensuing multi-stage uplift history with successive, discretecrystallization events at 1·4 ± 0·2 GPa/650700°Cand 1·0 ± 0·1 GPa/620650°C.Resorption textures indicate reheating and thermal perturbationof the whole system prior to each successive crystallizationevent. Final solidification of zoisite-pegmatites occurred at0·9 ± 0·1 GPa/620650°C. Thedata suggest that isolated melt + zoisite crystal mush pocketsformed an integral part of the eclogite throughout uplift frommelt formation at T 680°C/2·3 GPa to 750°C/3·1GPa to final solidification at 0·9 GPa/620630°C;that is, over a depth range of 4560 km. The entire pegmatite-formingprocess was probably fluid conserving: fluid present duringmelt formation was trapped by fully or nearly water-saturatedsiliceous melts, whereas fluid liberated during pegmatite crystallizationinteracted with dehydrated eclogite-facies assemblages to formamphibolite-facies hydrous minerals. A set of empirical Dmelt/eclogitevalues based on mean zoisite-pegmatite and eclogite compositionwere used to model the onset of partial high-pressure meltingof metabasites. KEY WORDS: adakite; high-pressure melting; pegmatite; trondhjemite; zoisite 相似文献
359.
The role of market mechanisms was far from certain in the lead up to the 2015 Paris Climate Conference. The use of ‘constructive ambiguity’ led to Article 6 of the Paris Agreement, with Article 6.2 specifying a mechanism with limited international oversight, and Article 6.4 establishing a ‘Sustainable Development Mechanism’ (SDM) subject to detailed rules. Clear operationalization of these mechanisms remains a challenge, especially regarding the critical accounting issue that could not be resolved at the 2018 Katowice Climate Conference (COP24) – how to apply corresponding adjustments, especially regarding sectors not covered by targets under nationally-determined contributions (NDCs). By using fictitious examples, we explain two possible approaches to using Internationally Transferred Mitigation Outcomes (ITMOs) under Article 6.2 for achieving NDCs: a ‘target-based’ one where the acquiring Party adds the ITMO amount to the target level of its NDC; and a ‘tally-based’ one where the acquiring Party removes the ITMO amount from the final tally of its NDC. We discuss how these approaches influence the way to make corresponding adjustments and to avoid ‘double counting’. The first one leads to ‘target/budget-based accounting’, the second one to ‘emission-based accounting’. For mitigation outside the scope of the host Party's NDC, we propose using a tally-based interpretation of ITMO use, as opposed to the target-based variety used in the 1997 Kyoto Protocol, and stress the need for additionality testing. This interpretation allows for mandatory corresponding adjustments for all ITMO usage, while the host Party NDC level remains unchanged. A buffer registry is created for corresponding non-NDC adjustments of the selling party.
Key policy insights
Under the Paris Agreement, transfers of emissions units between two countries through the Article 6 mechanisms need a corresponding adjustment on both sides to prevent double counting.
Corresponding adjustments can be applied either to emissions targets under NDCs or measured emissions levels.
The transfer of emissions reduction credits generated outside an NDC should lead to a corresponding adjustment of a buffer registry of the selling country, but not its emissions level/NDC target. Such credits should only be generated if additionality of the reductions is shown.
360.
The middle Silurian ‘big crisis’ refers to a graptolite extinction event and faunal turnover at the onset of a double‐peaked positive carbon isotope excursion. The crisis has been proposed to affect conodonts, giving rise to a sophisticated palaeoecological model of their stepwise extinction, known as the Mulde Event. However, the impact of the event on conodont faunas outside Gotland and the Silurian Baltic Basin remains unknown. Here, it is examined in the Widowo IG‐1 core (E Poland). The middle Silurian succession in this core represents foreshoal, shoal, and lagoonal settings on a tropical carbonate ramp on the shelf of the Eastern European Craton. Three positive δ13Ccarb excursions have been identified; the two upper excursions correlate with the Mulde isotope anomaly and with two global eustatic regressions. Conodont species proposed to be affected by the extinction event either were not observed or ranged through the extinction interval. Changes in their frequencies are best explained by the sequence stratigraphic architecture of the late Wenlock strata in the Widowo IG‐1 core. The little impact of the ‘big crisis’ may reflect facies homogeneity across the studied interval, supporting the hypothesis that the late Wenlock conodont turnover in epicontinental settings was primarily driven by eustatically controlled facies shifts. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献