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251.
Road building in Congo Basin forests has increased due to expansion of commercial logging, with potential to expose intact forests to greater establishment of agriculture. We developed new knowledge of agriculture clearing sizes, spatial patterns, and relationships with roads in seven case study sites comprising 7,529 km2. Using very high spatial resolution satellite imagery, we mapped roads and rivers, plus clearings for agriculture, settlements, and logging. Mapped clearings (N = 1,781) ranged in size from 0.008 ha to more than 300 ha; most were smallholder agriculture, with 64 percent ≤ 1 ha. Statistical tests of spatial pattern confirmed that agriculture occurred in an inhomogeneous-aggregated pattern, suggesting interactions with other landscape elements. Proximity analyses showed that 76 percent of clearings were within 1 km of a road or river. Thirty-five percent of agriculture clearings were within 1 km of main public roads built before 1990, compared to 17 percent for logging roads built after 2000. Less than 6 percent of agriculture clearings were within 1 km of logging roads with overgrown canopies, suggesting transient relationships. Results based on fine-scale data provide new empirical support for understanding the interactions between agriculture and roads in one of the remaining relatively intact forest areas of the Congo Basin. 相似文献
252.
Laura?Tositti Linda?Pieri Erika?BrattichEmail authorView authors OrcID profile Silvia?Parmeggiani Francesca?Ventura 《Journal of Atmospheric Chemistry》2018,75(1):97-121
This study provides an analysis of a five-year time series chemical composition of the bulk deposition (2009–2013), collected within a farm surrounded by industrial and urban settlements in a semi-rural area of the Po Valley, with the aim of characterizing potential emission sources affecting precipitation composition at the site. Most monitoring efforts in this region, recognized as one of the most polluted in the world both due to the intense industrialisation and urbanisation as well as to frequent air stagnation conditions, are presently devoted more to gaseous and particulate pollutants than to precipitation chemistry. The bulk deposition samples were very concentrated in chemical species, both acidic and alkaline, high compared to other polluted sites in the world and to locations in the same district. The mean ions concentrations (in μeq l?1) are: NO3 ? (243) > SO4 2? (220) > PO4 3? (176) > Cl? (153) > NO2 ? (29) > F? (2.6); NH4 + (504) > Ca2+ (489) > K+ (151) > Na+ (127) > Mg2+ (127). pH data shows a trend toward slightly alkaline conditions attributed to the large presence of ammonium and crustal elements, in spite of high concentrations of nitrates and sulphates. The relevant concentrations of Ca2+ and Mg2+ further suggests that these alkaline conditions might be due to the correspondingly significant concentrations of carbonates/bicarbonates in our dataset. While back-trajectories analysis suggests the stronger importance of local resuspension over long-range transport, statistical analyses on ion composition highlight the key role exerted by agricultural activity, especially in the case of NH4 +, K+, Ca2+ and PO4 3? (especially linked to fertilisation practices and soil resuspension due to mechanical operations). Apart from Na+ and Cl? ions which correlate well as expected, indicating their likely common origin from marine salt, the identification of the origin of the other ions is very complex due to the contribution of diverse local sources, such as industrial and residential settlements. 相似文献
253.
Silvia E. Newell Mark J. McCarthy Wayne S. Gardner Robinson W. Fulweiler 《Estuaries and Coasts》2016,39(6):1626-1638
Coastal ocean primary productivity is often limited by nitrogen (N) availability, which is determined by the balance between N sources (e.g., N-fixation, groundwater, river inputs, etc.) and sinks (e.g., denitrification, sediment burial, etc.). Historically, heterotrophic N-fixation in sediments was excluded as a significant source of N in estuarine budgets, based on low, indirectly measured rates (e.g., acetylene reduction assay) and because it was unnecessary to achieve mass balance. Many recent studies using net N2 flux measurements have shown that sediment N-fixation can equal or exceed N2 loss. In an effort to quantify N2 production and consumption simultaneously, we measured N-fixation and denitrification directly in sediment cores from a temperate estuary (Waquoit Bay, MA). N-fixation, dissimilatory nitrate reduction to ammonium, and denitrification occurred simultaneously, and the net N2 flux shifted from uptake (N-fixation) to efflux (denitrification) over the 120-h incubation. Evidence for N-fixation included net 28N2 and 30N2 uptake, 15NH4 + production from 30N2 additions, 15Norganic matter production, and nifH expression. N-fixation from 30N2 was up to eight times higher than potential denitrification. However, N-fixation calculated from 15NO3 ? was one half of the measured fixation from 30N2, indicating that 15NO3-isotope labeling calculations may underestimate N-fixation. These results highlight the dynamic nature of sediment N cycling and suggest that quantifying individual processes allows a greater understanding of what net N2 fluxes signify and how that balance varies over time. 相似文献
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257.
A global database of 2,626 rainfall events that have resulted in shallow landslides and debris flows was compiled through
a thorough literature search. The rainfall and landslide information was used to update the dependency of the minimum level
of rainfall duration and intensity likely to result in shallow landslides and debris flows established by Nel Caine in 1980.
The rainfall intensity–duration (ID) values were plotted in logarithmic coordinates, and it was established that with increased
rainfall duration, the minimum average intensity likely to trigger shallow slope failures decreases linearly, in the range
of durations from 10 min to 35 days. The minimum ID for the possible initiation of shallow landslides and debris flows was
determined. The threshold curve was obtained from the rainfall data using an objective statistical technique. To cope with
differences in the intensity and duration of rainfall likely to result in shallow slope failures in different climatic regions,
the rainfall information was normalized to the mean annual precipitation and the rainy-day normal. Climate information was
obtained from the global climate dataset compiled by the Climate Research Unit of the East Anglia University. The obtained
global ID thresholds are significantly lower than the threshold proposed by Caine (Geogr Ann A 62:23–27, 1980), and lower than other global thresholds proposed in the literature. The new global ID thresholds can be used in a worldwide
operational landslide warning system based on global precipitation measurements where local and regional thresholds are not
available.. 相似文献
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259.
Jérémy Ragusa Lina Maria Ospina-Ostios Silvia Spezzaferri Pascal Kindler 《Swiss Journal of Geoscience》2018,111(3):461-473
The ages obtained from planktonic foraminiferal assemblages retrieved from two exposures in the Gurnigel Flysch and from the re-examination of similar material gathered by previous researchers from the Voirons Flysch reveal only minor discrepancies with previous studies based on nannofossil biostratigraphy. In contrast, major divergences between this work and previous studies on the Voirons Flysch also based on planktonic foraminifera have been identified. They are generally related to distinct approaches in species classification and the use of different zonal schemes. Based on our data, the age of the Voirons Flysch extends from the Early Eocene (planktonic foraminiferal zone P7) to the Middle Eocene (planktonic foraminiferal zone P12). Contrasting with claims made in earlier studies, no specimen of Late Eocene or Early Oligocene age has been observed in the revised material. However, we cannot exclude a younger age (possibly Late Eocene) for the upper portion of this flysch from which we did not revise any sample. Thus, more research and sampling are needed to resolve this question. The palaeogeographic origin of the Voirons-Wägital complex as well as the sedimentation history of these flyschs need now to be re-evaluated in light of this revised biostratigraphic data. 相似文献
260.
Akram El Kateb Andres Rüggeberg Claudio Stalder Christoph Neururer Silvia Spezzaferri 《Swiss Journal of Geoscience》2018,111(3):501-510
Lake Murten is located in the Lake District in western Switzerland and so far, it has been poorly investigated. The Environmental Service of Fribourg (SEn) has monitored this lake once a month for several years by water profiles (water temperature, pH, dissolved oxygen, conductivity) at its deepest part. The SEn identified the stratification of water masses as one of the main causes for oxygen consumption in the hypolimnion. In the present study, a Lander System was deployed in Lake Murten from April to September 2015 at 20 m depth at the northwestern part of the lake to monitor water temperature and dissolved oxygen at higher resolution (30 s interval). These records were compared with time series of atmospheric parameters like atmospheric temperature, wind speed and precipitation. A clear correlation of lake temperatures with wind speed was observed during the Spring and Autumn. The water mass stratification evolved through the season and reached its peak during Summer, preventing surface turbulences to reach the deeper part (20 m) of the water column and to partially oxygenate the metalimnion. 相似文献