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281.
Channel samples of the Springfield (No. 9) and Herrin (No. 11) (Pennsylvanian, Desmoinesian/Westphalian D) coals were acquired in three mines each in the Western Kentucky coal field. Pyrite was characterized petrographically in terms of its size, form, and microlithotype association. Within each coal seam significant variations in the amount of pyrite of certain forms occurred between the sites. Pyritic sulfur as determined chemically did not exhibit significant variation between the seams or between the sites. The variation in dendritic pyrite in vitrite plus clarite between seams and between sites was highly significant and the variation in framboidal pyrite in vitrite plus clarite between sites was also highly significant. 相似文献
282.
Emma L. Yates Angela M. Detweiler Laura T. Iraci Brad M. Bebout Christopher P. McKay Kathleen Schiro Edwin J. Sheffner Cheryl A. Kelley Jovan M. Tadić Max Loewenstein 《Environmental Earth Sciences》2013,70(3):1047-1056
Alkaline soils occupy approximately 5 % of the Earth’s land surface (7 million km), and this may increase due to the global trend towards increasing desertification, yet the extent to which these soils modulate carbon dynamics on regional and global scales is inadequately studied and poorly understood. Railroad Valley (RRV) playa (Nevada, USA) is a semi-arid playa with highly alkaline soils (pH > 10) and no vegetation. The extreme, alkaline environment and absence of vascular vegetation make RRV an ideal site to investigate the role of physiochemical processes of soil-atmosphere CO2 exchange. Both field and laboratory investigations were conducted. This work shows how the atmospheric CO2 mixing ratio decreases at nighttime at RRV playa to a value well below the average global background CO2 concentration. Laboratory investigations using soil samples collected at RRV playa confirmed that CO2 uptake by RRV playa soils occurs when temperatures are decreased. Both field and laboratory studies suggest that the alkaline RRV soil acts as a CO2 reservoir during colder periods, such as at nighttime. These results highlight the importance of investigating carbon dynamics in previously understudied environments. Given how little information is available on the CO2 flux in desert and semi-arid alkaline ecosystems lacking vegetation, our findings draw attention to these environments as becoming increasingly important for carbon fluxes on regional and global scales. 相似文献
283.
First results of renewed excavations at the Middle Stone Age spring site of Florisbad are reported. Seven meters of deposits dating possibly from the later mid-Pleistocene to the mid-Holocene contain several cultural phases and record alternating periods of increased spring flow versus more stabilized conditions. The archaic Homo sapiens cranium discovered in 1932 and the Florisian Land Mammal Age fauna retrieved from the springs are argued to derive from the earliest deposits, estimated to be ca. 100,000–200,000 years old. In an Upper Pleistocene layer beyond the range of Carbon-14 dating, a Middle Stone Age occupation floor has been excavated. This we interpret as a multiple-occupation kill, butchery, or scavenging site. The presence of a hearth, of chipping debris under 10 mm in size, and the limited displacement of artifacts which have been refitted as conjoining pieces demonstrate a minimally disturbed, primary context site. 相似文献
284.
Urban karst systems are typically considered more vulnerable to contamination and excess storm discharge because of potential
source areas, increased sediment loading, and focusing of water from impervious surfaces. However, urban hydrology can lead
to unexpected patterns, such as pirating of recharge into man-made storm systems. Valley Creek Basin in southeastern Pennsylvania,
presents such an urban karst system. Four springs were monitored for suspended sediment, water chemistry, and storm response
for an 18-month period. The baseflow suspended sediment concentrations were low, less than 4.0 mg/l. Furthermore, trace metal
analysis of baseflow water samples and spring mouth sediment showed only low concentrations. The response to storms within
the system was rapid, on the order of 1–3 h. The maximum water stage increases at the urban springs were typically less than
15 cm, with springs from more commercialized areas showing <2 cm increase. A nearby retention basin, in contrast, had water
level rises of 100 cm, suggesting that pirating of recharge into stormwater systems occurs. Thus, the concept of an urban
karst system as a contaminant conduit is not the only one that applies. In Valley Creek Basin, reduced infiltration due to
paving led to smaller storm response and less contaminant input, and the smaller capture area due to diversion of stormwater
led to short flow paths and rapid storm response. Although contaminant levels have not increased due to urbanization, the
springs may be at risk for future contamination. Short flow paths may reduce flushing, which means that the system will not
cleanse itself if contamination occurs. 相似文献
285.
286.
In this study, we compiled unpublished archival documentation of archaeological site locations from the southern part of the Cuyahoga River Valley in northeastern Ohio, USA, registered at the State of Ohio Historic Preservation Office into a Geographic Information Systems (GIS) database. Using digitized soil shapefiles to generate a geomorphic data layer, we assessed the spatial and temporal distribution of 79 known archaeological sites by landform association. This digital compilation indicates that Woodland period, Late Prehistoric, and Historic sites occur in most geomorphic settings along the river valley. In contrast, Paleoindian and Archaic sites only occur on Wisconsinan cut terraces and in upland interfluve settings, indicating that most of these documented sites are in primary contexts and have not been reworked. We discuss the distribution of archaeological sites in the study region as a function of various factors, including cultural activities, taphonomic processes, landform development, and the nature and extent of the original archaeological surveys. Observed spatial patterns of known sites clearly reflect local geomorphological controls; artifactual contexts from the earlier prehistoric periods are underrepresented in the database. We conclude that additional site surveys, as well as the excavation and documentation of new sites in this part of Ohio, are required to understand local prehistoric economies and to ascertain patterns of culturally mediated land use. © 2004 Wiley Periodicals, Inc. 相似文献
287.
Vulnerability of water supply from the Oregon Cascades to changing climate: Linking science to users and policy 总被引:1,自引:0,他引:1
Despite improvements in understanding biophysical response to climate change, a better understanding of how such changes will affect societies is still needed. We evaluated effects of climate change on the coupled human-environmental system of the McKenzie River watershed in the Oregon Cascades in order to assess its vulnerability. Published empirical and modeling results indicate that climate change will alter both the timing and quantity of streamflow, but understanding how these changes will impact different water users is essential to facilitate adaptation to changing conditions. In order to better understand the vulnerability of four water use sectors to changing streamflow, we conducted a series of semi-structured interviews with representatives of each sector, in which we presented projected changes in streamflow and asked respondents to assess how changing water availability would impact their activities. In the McKenzie River watershed, there are distinct spatial and temporal patterns associated with sensitivity of water resources to climate change. This research illustrates that the implications of changing streamflow vary substantially among different water users, with vulnerabilities being determined in part by the spatial scale and timing of water use and the flexibility of those uses in time and space. Furthermore, institutions within some sectors were found to be better positioned to effectively respond to changes in water resources associated with climate change, while others have substantial barriers to the flexibility needed to manage for new conditions. A clearer understanding of these opportunities and constraints across water use sectors can provide a basis for improving response capacity and potentially reducing vulnerability to changing water resources in the region. 相似文献
288.
Martitia P. Tuttle Robert H. Lafferty Margaret J. Guccione Eugene S. Schweig Neal Lopinot Robert F. Cande Kathleen Dyer-Williams Marion Haynes 《Geoarchaeology》1996,11(6):451-480
Prehistoric earthquake-induced liquefaction features occur in association with Native American occupation horizons in the New Madrid seismic zone. Age control of these liquefaction features, including sand-blow deposits, sand-blow craters, and sand dikes, can be accomplished by extensive sampling and flotation processing of datable materials as well as archaeobotanical analysis of associated archaeological horizons and pits. This approach increases both the amount of carbon for radiocarbon dating and the precision dating of artifact assemblages. Using this approach, we dated liquefaction features at four sites northwest of Blytheville, Arkansas, and found that at least one significant earthquake occurred in the New Madrid seismic zone between A.D. 1180 and 1400, probably about A.D. 1300 ± 100 yr. In addition, we found three buried sand blows that formed between 3340 B.C. and A.D. 780. In this region where very large to great earthquakes appear to be closely timed, archaeology is helping to develop a paleoearthquake chronology for the New Madrid seismic zone. © 1996 John Wiley & Sons, Inc. 相似文献
289.