全文获取类型
收费全文 | 1091篇 |
免费 | 31篇 |
国内免费 | 11篇 |
专业分类
测绘学 | 23篇 |
大气科学 | 88篇 |
地球物理 | 285篇 |
地质学 | 416篇 |
海洋学 | 56篇 |
天文学 | 162篇 |
综合类 | 2篇 |
自然地理 | 101篇 |
出版年
2021年 | 13篇 |
2020年 | 18篇 |
2019年 | 8篇 |
2018年 | 19篇 |
2017年 | 20篇 |
2016年 | 24篇 |
2015年 | 15篇 |
2014年 | 26篇 |
2013年 | 56篇 |
2012年 | 37篇 |
2011年 | 50篇 |
2010年 | 32篇 |
2009年 | 36篇 |
2008年 | 34篇 |
2007年 | 39篇 |
2006年 | 42篇 |
2005年 | 43篇 |
2004年 | 34篇 |
2003年 | 33篇 |
2002年 | 39篇 |
2001年 | 18篇 |
2000年 | 15篇 |
1999年 | 24篇 |
1998年 | 17篇 |
1997年 | 22篇 |
1996年 | 11篇 |
1995年 | 24篇 |
1994年 | 10篇 |
1993年 | 15篇 |
1992年 | 10篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1987年 | 14篇 |
1986年 | 13篇 |
1985年 | 10篇 |
1984年 | 18篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1980年 | 10篇 |
1979年 | 11篇 |
1978年 | 14篇 |
1977年 | 11篇 |
1976年 | 7篇 |
1975年 | 15篇 |
1974年 | 8篇 |
1973年 | 9篇 |
1971年 | 9篇 |
1970年 | 10篇 |
1954年 | 8篇 |
排序方式: 共有1133条查询结果,搜索用时 265 毫秒
141.
Michael E.?PasyanosEmail author William R.?Walter Megan P.?Flanagan Peter?Goldstein Joydeep?Bhattacharyya 《Pure and Applied Geophysics》2004,161(2):235-281
We construct and evaluate a new three-dimensional model of crust and upper mantle structure in Western Eurasia and North Africa (WENA) extending to 700 km depth and having 1° parameterization. The model is compiled in an a priori fashion entirely from existing geophysical literature, specifically, combining two regionalized crustal models with a high-resolution global sediment model and a global upper mantle model. The resulting WENA1.0 model consists of 24 layers: water, three sediment layers, upper, middle, and lower crust, uppermost mantle, and 16 additional upper mantle layers. Each of the layers is specified by its depth, compressional and shear velocity, density, and attenuation (quality factors, Q
P
and Q
S
). The model is tested by comparing the model predictions with geophysical observations including: crustal thickness, surface wave group and phase velocities, upper mantle
n
velocities, receiver functions, P-wave travel times, waveform characteristics, regional 1-D velocities, and Bouguer gravity. We find generally good agreement between WENA1.0 model predictions and empirical observations for a wide variety of independent data sets. We believe this model is representative of our current knowledge of crust and upper mantle structure in the WENA region and can successfully be used to model the propagation characteristics of regional seismic waveform data. The WENA1.0 model will continue to evolve as new data are incorporated into future validations and any new deficiencies in the model are identified. Eventually this a priori model will serve as the initial starting model for a multiple data set tomographic inversion for structure of the Eurasian continent. 相似文献
142.
Matthew J. Wooller John W. Pohlman Benjamin V. Gaglioti Peter Langdon Miriam Jones Katey M. Walter Anthony Kevin W. Becker Kai-Uwe Hinrichs Marcus Elvert 《Journal of Paleolimnology》2012,48(1):27-42
Atmospheric contributions of methane from Arctic wetlands during the Holocene are dynamic and linked to climate oscillations. However, long-term records linking climate variability to methane availability in Arctic wetlands are lacking. We present a multi-proxy ~12,000?year paleoecological reconstruction of intermittent methane availability from a radiocarbon-dated sediment core (LQ-West) taken from a shallow tundra lake (Qalluuraq Lake) in Arctic Alaska. Specifically, stable carbon isotopic values of photosynthetic biomarkers and methane are utilized to estimate the proportional contribution of methane-derived carbon to lake-sediment-preserved benthic (chironomids) and pelagic (cladocerans) components over the last ~12,000?years. These results were compared to temperature, hydrologic, and habitat reconstructions from the same site using chironomid assemblage data, oxygen isotopes of chironomid head capsules, and radiocarbon ages of plant macrofossils. Cladoceran ephippia from ~4,000?cal?year BP sediments have ??13C values that range from ~?39 to ?31??, suggesting peak methane carbon assimilation at that time. These low ??13C values coincide with an apparent decrease in effective moisture and development of a wetland that included Sphagnum subsecundum. Incorporation of methane-derived carbon by chironomids and cladocerans decreased from ~2,500 to 1,500?cal?year BP, coinciding with a temperature decrease. Live-collected chironomids with a radiocarbon age of 1,640?cal?year BP, and fossil chironomids from 1,500?cal?year BP in the core illustrate that ??old?? carbon has also contributed to the development of the aquatic ecosystem since ~1,500?cal?year BP. The relatively low ??13C values of aquatic invertebrates (as low as ?40.5??) provide evidence of methane incorporation by lake invertebrates, and suggest intermittent climate-linked methane release from the lake throughout the Holocene. 相似文献
143.
Wan-Li Cheng Li-Wei Lai Walter Den Shu-Ying Wang Pay-Liam Lin Chueh-Ying Pai 《Meteorology and Atmospheric Physics》2012,117(3-4):153-166
This study investigated the potential factors contributing to a series of ozone (O3) episodes in the Taichung metropolis, which occurred during the first half of May 2007. Surface data of the meteorological parameters and air pollutant concentrations, supported by Taiwan Environmental Protection Administration, and vertical data monitored via tethersonde sampling were analysed. The analyses showed that local anthropogenic activities and physical factors such as the sea–air interaction were not the main factors contributing to the O3 events. Excluding these potential causes, the results suggest that, during the aforementioned period, the stronger Mainland High and Pacific Low may have been responsible for the long-range transport of large quantities of O3 from Mainland China to Taiwan. Furthermore, O3 photochemical activity also played an important role in the O3 episodes. The faster consumption of NO lead to a more rapid increase in the O3 concentration. 相似文献
144.
145.
Christian Pfister Emmanuel Garnier Maria-João Alcoforado Dennis Wheeler Jürg Luterbacher Maria Fatima Nunes João Paulo Taborda 《Climatic change》2010,101(1-2):281-310
Three violent eighteenth-century storms that ravaged the North Sea area (1703), western central Europe (1739) and Portugal (1739) are investigated from the point of view of their meteorological setting, their socio-economic impact, and whether and by what means they secured an enduring place in the cultural memory. The evidence draws on individual narrative sources such as chronicles and poems, and institutional sources such as ship’s logbooks and state-organised ‘windthrow’ inventories of tree loss. Each of the three storms had socio-economic impacts that could be described as ‘war-like’ in the damage caused to buildings and the destruction of forests. The “Great Storm” of December 1703 jeopardized English naval supremacy in the War of the Spanish Succession by sinking a number of Royal Navy ships and taking the life of more than 8000 seamen. In January 1739 two similarly destructive storms swept over mainland Europe. The cultural memory of the three events here considered was however strikingly different. The sequence of storms in January 1739 though being the most protracted of the last centuries, and well-chroniceled, did not persist in the collective memories of those in France, Switzerland and elsewhere who experienced them. Likewise, the “Great Storm” was quickly forgotten on the continent, whereas its memory remained deeply rooted in England through the writings of Defoe (1704). In Portugal the 1739 storm won a lasting place in the country’s cultural memory owing to two poems that it inspired. Furthermore, it was recorded in the Kingdom’s official newspaper, in the astronomical prognoses and in written records of the Old Regime’s cultural elite. 相似文献
146.
This paper is concerned with the use of Royal Navy ships’ logbooks for the period 1685 to 1750, thereby embracing the oldest members of this documentary series that extends to the present day. The geographic range of the undertaking is confined to the English Channel and its western approaches where the abundance of logbooks for this period allows for the abstraction of a daily series of wind force and direction data. These are verified and processed for inclusion in a database from which indices are derived for air circulation patterns based on the frequency of winds from north, east, south and west quarters, and of gale frequency, based on the contemporary terminology of wind force. The methods by which the data are abstracted and processed are described, as is the nature of the raw data and source material. The results provide a uniquely detailed insight into the changing patterns of air circulation over this critical period that marked the transition from the depths of the Little Ice Age in the late seventeenth century. Attention is also drawn to the changing nature of gale frequency, which revealed a notable decrease over the study period. Associations between changing circulation patterns and temperature regimes are also explored. 相似文献
147.
Low-divergence synchrotron-sourced X-rays enable a radiographic imaging scheme for full characterization of binary chemical reactions and characterization by type of more complex reactions, in situ, in diamond anvil cells (DAC). Spatially resolved reactants are induced to react by laser heating of their interface. The spatially intermediate products are observed through X-ray absorption contrast. Limits to the technique include the ability to maintain controlled experiment geometry during compression and the ability to resolve chemical differences between reactants and products by X-ray absorption. The ability to make in situ observations at experimental pressure and temperature obviates the problem with quenching techniques for capturing liquid compositions in experiments with dimensions smaller than the diffusion length during quenching time. Partially molten Fe-alloy systems, of poor quenchability, are examined at DAC pressures and temperatures for relevance to Earth's core constitution and evolution. Determinations of eutectic melting in Fe–FeS match known results. Of the probable light elements that may alloy with Fe in the Earth's liquid outer core, Fe–FeS experiments show only modest quenching problems, but C and Si alloy experiments are highly vulnerable to quenching artifacts. The observed reactivity of FeS, Fe3C, FeSi, and FeO(OH) with Fe in DAC makes the observed non-reactivity between Fe and FeO more significant, reducing the probability that oxygen alone is the major alloy in Earth's molten outer core. 相似文献
148.
The broad-spectrum herbicide glyphosate has become the largest-selling crop-protection product worldwide. The increased use of glyphosate is associated with the appearance of a growing number of tolerant or resistant weeds, with socio-environmental consequences apart from the loss of productivity. In 2002, a glyphosate-resistant biotype of johnsongrass (Sorghum halepense (L.)) appeared in Argentina and now covers at least 10,000 ha. This paper analyzes the driving forces behind the emergence and spread of this weed and also examines management responses and their implications.Preventive strategies against glyphosate-resistant johnsongrass fail because of the institutional setting. Reactive measures, however, transfer the risks to the society and the environment through the introduction of novel genetically modified crops that allow the use of yet more herbicide. This in turn reinforces the emergence of herbicide-resistant weeds, constituting a new phenomenon of intensification, the “transgenic treadmill”. 相似文献
149.
New age constraints on the western Betic intramontane basins: A late Tortonian closure of the Guadalhorce Corridor?
下载免费PDF全文
![点击此处可从《地学学报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Marlies van der Schee Bas C. J. van den Berg Walter Capella Dirk Simon Francisco J. Sierro Wout Krijgsman 《地学学报》2018,30(5):325-332
Several gateways connected the Mediterranean with the Atlantic during the late Miocene but the timing of closure and therefore their role prior to and during the Messinian Salinity Crisis (5.97–5.33 Ma) is still under debate. The timing of closure of the Guadalhorce Corridor is especially disputed as the common lack of marine microfossils hampers precise age determination. Here we present new biostratigraphic age constraints on the sediments of the Ronda, Antequera and Arcos regions, which formed the northern part of the Guadalhorce Corridor. The general presence of Globorotalia menardii 4 in the youngest deep‐marine sediments of all three regions indicates a late Tortonian age, older than 7.51 Ma. We conclude that the Guadalhorce Corridor closed during the late Tortonian, well before the onset of the Messinian Salinity Crisis and that the late Tortonian tectonic uplift of the eastern Betics extended into the western Betics. 相似文献
150.
Joshua Fisher Hannah Stutzman Mariana Vedoveto Debora Delgado Ramon Rivero Walter Quertehuari Dariquebe 《社会与自然资源》2020,33(4):538-553
AbstractGiven the linkages between natural resources and social conflicts, evidence increasingly shows that successful natural resource management requires conflict mitigation and prevention. However, there may be a gap in practice between knowing what processes and tools need to be used to manage conservation conflicts and how to actually implement them. We present learning from a practice-based case study of conflict management in the Amarakaeri Communal Reserve in the Peruvian Amazon that aimed to develop natural resource governance institutions and build stakeholder capacity, including of indigenous groups, to navigate existing conflict resolution mechanisms. Through applying good practices in conservation conflict management and collaborative governance, we generated important lessons on the practical considerations involved in collaborative conservation. These lessons, while specific to our case, could be applied to a variety of protected areas facing complex social-ecological systems dynamics and wicked problems. 相似文献