全文获取类型
收费全文 | 373篇 |
免费 | 15篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 30篇 |
地球物理 | 95篇 |
地质学 | 159篇 |
海洋学 | 47篇 |
天文学 | 44篇 |
综合类 | 2篇 |
自然地理 | 7篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 11篇 |
2017年 | 16篇 |
2016年 | 14篇 |
2015年 | 15篇 |
2014年 | 15篇 |
2013年 | 22篇 |
2012年 | 20篇 |
2011年 | 28篇 |
2010年 | 23篇 |
2009年 | 38篇 |
2008年 | 18篇 |
2007年 | 11篇 |
2006年 | 14篇 |
2005年 | 16篇 |
2004年 | 22篇 |
2003年 | 13篇 |
2002年 | 10篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 3篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 7篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1989年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1952年 | 1篇 |
排序方式: 共有392条查询结果,搜索用时 0 毫秒
61.
62.
Obligatory interactions between species are fundamental to ecosystem functioning and are expected to be particularly sensitive to climate change. Although the effect of past and current climate changes on individual species has been thoroughly investigated, their effect on obligatory interactions has been overlooked. In this review, we present predictions about the effects of climate change on obligatory interactions and illustrate these predictions with examples from the literature. We focus on abrupt past climate change, especially during the Quaternary, because knowing past responses is useful for understanding and predicting the response of organisms and ecosystems to the current climate change. We also pinpoint the need for better time calibration of demographic events from genetic data, and for more studies focused on particularly suitable biological models. We hope that this review will stimulate interaction between the earth sciences and the life sciences on this timely topic. 相似文献
63.
Olivier J. Hardy Céline Born Katarina Budde Kasso Daïnou Gilles Dauby Jérôme Duminil Eben-Ezer B.K. Ewédjé Céline Gomez Myriam Heuertz Guillaume K. Koffi Andrew J. Lowe Claire Micheneau Dyana Ndiade-Bourobou Rosalía Piñeiro Valérie Poncet 《Comptes Rendus Geoscience》2013,345(7-8):284-296
The biogeographic history of the African rain forests has been contentious. Phylogeography, the study of the geographic distribution of genetic lineages within species, can highlight the signatures of historical events affecting the demography and distribution of species (i.e. population fragmentation or size changes, range expansion/contraction) and, thereby, the ecosystems they belong to. The accumulation of recent data for African rain forests now enables a first biogeographic synthesis for the region. In this review, we explain which phylogeographic patterns are expected under different scenarios of past demographic change, and we give an overview of the patterns detected in African rain forest trees to discuss whether they support alternative hypotheses regarding the history of the African rain forest cover. The major genetic discontinuities in the region support the role of refugia during climatic oscillations, though not necessarily following the classically proposed scenarios. We identify in particular a genetic split between the North and the South of the Lower Guinean region. Finally we provide some perspectives for future study. 相似文献
64.
A detailed compilation of distal tephrostratigraphy comprising the last 20,000 yrs is given for the Central Mediterranean region. A total of 47 distinct ash layers identified in the maar lake sediments of Lago Grande di Monticchio (Basilicata, Southern Italy) are compared with proximal and distal terrestrial-marine tephra deposits in the circum-central Mediterranean region. The results of these studies provide valuable information for reconstructing the Late Pleistocene and the Holocene dispersal of pyroclastic deposits from south Italian explosive volcanoes, in particular Somma-Vesuvius, the Campi Flegrei caldera, Ischia Island and Mount Etna. Prominent tephras are discussed with respect to their reliability as dating and correlation tools in sedimentary records. Ashes from Plinian eruptions of Somma-Vesuvius (i.e. Avellino, Mercato, Greenish, Pomici di Base), for instance, are well-defined by their distribution patterns and their unique composition. The widespread Y-1 tephra from Mount Etna, on the other hand, derived most likely from two distinct Plinian events with changing wind conditions, and therefore becomes a less reliable stratigraphic marker. Statistical–numerical calculations are presented in order to discriminate between Holocene tephras from the Campi Flegrei caldera (i.e. Astroni 1–3, Agnano Monte Spina, Averno 1, Lagno Amendolare), since these ashes are characterized by an almost indistinguishable chemical fingerprint. As a highlight, numerous Campanian eruptions of proposed low-intensity have been identified in the distal site of Monticchio suggesting a revision of existing tephra dispersal maps and re-calculation of eruptive conditions. In summary, the tephra record of Monticchio is one of the key successions for linking both, terrestrial records from Central-southern Italy and marine sequences from the Tyrrhenian, Adriatic and Ionian Seas. 相似文献
65.
Sabine Hanisch Martin Wessels Frank Niessen Antje Schwalb 《Journal of Paleolimnology》2009,41(3):393-406
This study used organic matter in oligotrophic Lake Constance (southern Germany) to reconstruct lake environment and to disentangle
the multiple factors, such as climate change and human impacts, which influence sedimentation in large lakes. A sediment core
from Upper Lake Constance, which represents 16,000 years of Late Glacial and Holocene lake history, was analysed for organic
biomarkers, hydrogen index and elements calcium, strontium, and magnesium. Magnetic susceptibility was measured to establish
a high-resolution stratigraphic framework for the core and to obtain further information about changes with respect to relative
allochthonous versus autochthonous sedimentation. Dinosterol—a biomarker for dinoflagellates—and calcium have low concentrations
in Younger Dryas sediments and consistently high concentrations between 10,500 and 7,000 cal. years BP. These variations are
attributed to changes in lake productivity, but are not reflected in the proportion of total organic carbon within the sediment.
During the Younger Dryas and between 6,000 and 2,800 cal. years BP, concentrations and accumulation rates of land-plant-derived
C29-steroids (β-sitosterol, stigmastanol and stigmasterol), in combination with a relatively low HI, indicate periods of enhanced
terrigenous input to the lake. For the Younger Dryas, higher runoff can be attributed to a cold climate, leading to decreased
vegetation cover and increased erosion. After 6,000 cal. years BP, high terrestrial input may be explained by enhanced precipitation.
Biomarker and HI results, in combination with archaeological studies, raise the question as to whether lakeshore settlements
affected sedimentation in Upper Lake Constance between 6,000 and 2,800 cal. years BP. 相似文献
66.
F. Lohou A. Druilhet B. Campistron J.-L. Redelspergers F. Saïd 《Boundary-Layer Meteorology》2000,97(3):361-383
In two preceding papers, coherent structures of theatmospheric boundary layer (ABL), such as rollvortices or cells, were investigated through radar andaircraft observations collected during the TRAC-93(Turbulence Radar Aircraft Cells) experiment held inFrance in June 1993. The analysis of this experimentaldata set provided information on the spatialcharacteristics of these organisations (length scale,orientation, type ... ), their temporal and verticalevolution, and their relation with the dynamic andthermodynamic conditions of the ABL. For the thirdpaper in this series, a large eddy simulation model is used to examine the impact of thecoherent structures on the ABL vertical fluxes. Theanalysis of the simulated horizontal fields is madewith two-dimensional auto and cross-correlationsapplied on different pertinent ABL variables. Theresults emphasise a directional anisotropy of theseorganised fields throughout the ABL, much morepronounced in the heat flux fields, not only at thelength scale of organisations but also at theturbulence scales. This finding has an importantconsequence for traditional ABL flux measurementsbased on the hypothesis of isotropic and homogeneousturbulence. It can explain part of the underestimationof the surface fluxes often mentioned in theliterature. This approach makes it possible tomodify the concept of diffusion time (in chemicalmodelling) and could also lead to revised ABLparameterisations in Range Scale models. 相似文献
67.
Rouaida Trabelsi Moncef Zaïri Habib Smida Hamed Ben Dhia 《Comptes Rendus Geoscience》2005,337(5):515-524
The intensive agricultural and economic activities induce the increase of the risk of groundwater quality degradation through high groundwater pumping rates. The salinization and contamination are the main sources of this pollution, especially in coastal aquifers. The explanation of the origin of salinity for the shallow aquifer of Northern Sahel of Sfax was analysed by a chemical study of the groundwater main compounds. The partitioning of groundwaters into homogenous groups is undertaken by graphical techniques, including a Stiff pattern diagram, an expanded Durov diagram and several binary diagrams. The study indicates the presence of various salinization processes. In the recharge area, salinization is the result of dissolution/precipitation of the aquifer formation material (group I). The irrigation water return and the intensive pumping have been identified as major sources of salinization in the south by direct cation exchange and mixing reactions (groups II and III). The anomaly of high groundwater salinity observed near the Hazeg zone was explained by the presence of a seawater intrusion in this area. This hypothesis is related to the high chloride concentration, to the presence of inverse cation exchange reactions (group IV), and to the piezometric level inferior to sea level. To cite this article: R. Trabelsi et al., C. R. Geoscience 337 (2005). 相似文献
68.
69.
滇西保山地块是西南“三江”特提斯构造带的重要组成部分,其大地构造位置处于藏-滇-泰-马中间板块中段,是近年来科学研究和地质找矿的热点地区之一。受区域构造演化的影响,保山地块先后历经原、古、中、新特提斯演化,并发生了多期成岩成矿事件,在北部形成了以金厂河铁铜铅锌矿、核桃坪铅锌矿、陡崖铁铜多金属矿、黑牛凹金矿、黄家地金矿等为代表的金厂河铁铜金铅锌多金属矿集区。区内矿床在成矿空间上具有明显的分带性,单个矿床在垂向上、平面上均呈有规律地分布,其分带标志除了矿床类型外,还表现在有用矿物组合及元素分带。由下往上、由内向外均有Fe→Cu-Fe→Cu-Pb-Zn→Au矿种分带及“矽卡岩型→构造蚀变岩型→石英脉型”的矿床类型分带,成矿元素均从高温到中低温变化。成矿系统的分析表明,区内各代表性矿床中矿石的硫、铅同位素组成和变化范围较为一致性,矿床的形成具有相似的成矿流体,表明不同类型的矿化可能形成于早白垩世中特提斯洋的闭合过程。本文综合区内构造演化、典型矿床地质特征、各地质事件发生的先后关系,建立了金厂河矿集区铁铜金铅锌多金属矿床成矿模式,以期为该区深边部地质找矿提供科学依据。 相似文献
70.
Justus E. E. van Beusekom Sabine Diel-Christiansen 《International Journal of Earth Sciences》2009,98(2):269-280
Phytoplankton plays a dominant role in shelf biogeochemistry by producing the major part of organic matter. Part of the organic
matter will reach the sediment where diagenetic processes like denitrification, apatite formation or burial will remove nutrients
from the biogeochemical cycle. In this article current knowledge on the decadal plankton variability in the North Sea is summarized
and possible implications of these changes for the biogeochemistry of the North Sea are discussed. Most of the observed interdecadal
dynamics seem to be linked to large-scale oceanographic and atmospheric processes. Prominent changes in the North Sea ecosystem
have taken place around 1979 and 1988. In general, the phytoplankton color (CPRS indicator of phytoplankton biomass) reached
minimum values during the end of the 1970s and has increased especially since the mid 1980s. Changes with a similar timing
have been identified in many time series from the North Sea through the entire ecosystem and are sometimes referred to as
regime shifts. It is suggested that the impact of global change on the local biogeochemistry is largely driven by the phyto-
and zooplankton dynamics during spring and early summer. At that time the extent of zooplankton–phytoplankton interaction
either allows that a large part of the new production is settling to the sediment, or that a significant part of the new production
including the fixed nutrients is kept within the pelagic system. The origin of the extent of the phytoplankton–zooplankton
interaction in spring is probably set in the previous autumn and winter. In coastal areas, both large-scale atmospheric and
oceanographic changes as well as anthropogenic factors influence the long-term dynamics. Due to eutrophication, local primary
production nowadays still is up to five times higher than during pre-industrial conditions, despite a decreasing trend. Recently,
introduced species have strengthened the filter feeder component of coastal ecosystems. Especially in shallow coastal seas
like the Wadden Sea, this will enhance particle retention, shift organic matter degradation to the benthic compartment and
enhance nutrient removal from the biogeochemical cycle by denitrification or apatite formation. 相似文献