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951.
952.
Marco A. Liñán‐Cabello Laura A. Flores‐Ramírez Tania Zenteno‐Savin Norma O. Olguín‐Monroy Ramón Sosa‐Avalos Manuel Patiño‐Barragan Aramis Olivos‐Ortiz 《Marine Ecology》2010,31(3):407-417
The physiological responses of the coral Pocillopora capitata to environmental conditions common in winter and summer were studied in 2007 during February–March (winter) and June–July (summer) at La Boquita reef (Manzanillo, Colima, Mexico). Shallow and deep sampling stations were established at different distances from a small jetty built next to the Juluapan Lagoon. We analyzed superoxide radicals () and lipid peroxidants (TBARS); the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), and glutathione‐S‐transferase (GST); chlorophyll a (Chl a), zooxanthellae density (ZD); and mycosporine‐like amino acids (MAAs). Our results showed that the , TBARS, CAT, GST, MAAs, and Chl a, levels were significantly higher in summer (P < 0.05); no seasonal difference was found for GPx, GR or ZD. We found significant differences (P < 0.05) in winter only for Chl a and ZD at shallow sites and, in contrast, for at deeper sites. The results of this study indicate that increasing temperature and radiation associated with seasonal changes (from winter to summer), the efficiency of the enzymes GST, CR and GPX, and the production of MAAs together form a powerful mechanism for P. capitata to offset the detrimental effects of environmental change. 相似文献
953.
Gianni Cortecci Tiziano Boschetti Enrico Dinelli Rosa Cidu Francesca Podda Marco Doveri 《Applied Geochemistry》2009
Trace element geochemistry of the Arno River and its main tributaries was investigated on the basis of two sampling campaigns carried out in November 1996 and June 1997. By analyzing filtered and unfiltered water samples, Fe and Al are found in solution mainly as colloidal particles of size lower than 0.45 μm. In June (lower flow rate), Fe and Al are enriched in the filtered waters from the main river, and this feature was interpreted in terms of higher water temperature promoting the formation of smaller particles, thus reducing their aggregation properties. Iron and Al show perfectly synchronous downstream profiles along the Arno River, correlate quite well each to other, and display abrupt concentration increases near to Florence, where the lithology of the catchment changes from siliciclastic dominated to clay-sand (lacustrine-marine)-dominated. The same behaviour is shown by most of the other trace elements in the river, thus supporting a general lithological control. Trace elements in the final part of the Arno River are influenced by flocculation processes in addition to mixing. Adsorption phenomena on oxy-hydroxides are denoted by good elemental correlations with Fe (and Al). Sporadic anomalous concentration values, possibly related to anthropogenic contributions, may prevent such correlations. Referring to the quality of waters for potable use and fish life, toxic elements are below the acceptable limits of current European regulations, with few exceptions for Hg exceeding guideline values. Multivariate analysis groups trace elements according to geochemical affinities and natural or anthropogenic sources, thus distinguishing contaminated from uncontaminated samples. The results achieved in this work will help regional and national Authorities for compliance with the EU water policy, especially in assessing the water quality at the river basin scale and its vulnerability to human activities. 相似文献
954.
We study the Byzantine-to-Ummayad (6th–8th century) archaeological site of Umm-El-Qanatir, located 10 km east of the Dead
Sea Transform (DST) in northern Israel. The site was damaged by an earthquake-induced landslide, and in this work we use slope
stability analysis to constrain the historical seismic acceleration that occurred along the northern segment of the DST. Umm-El-Qanatir
archaeological site is located on a slope of a canyon and contains evidence for earthquake-related damage, including fallen
columns and walls, horizontal shift of heavy masonry blocks, and complete burial of ceramic pots and farming tools beneath
fallen ceilings. A water pool that collected spring water is displaced nearly one meter by the landslide. The artifacts from
the village and the spring area indicate that people inhabited the site until the middle of the 8th century. We argue that
the destruction, which forced the abandonment of Umm-El-Qanatir together with nearby settlements, was associated with the
earthquake of January 18, 749 CE. In order to evaluate the ground acceleration related to the above earthquake, we back-analyze
the stability of a failed slope, which cut and displaced the water-pool, using slope stability software (Slope/W). The results
show that the slope is statically stable and that high values of horizontal seismic acceleration (>0.3 g) are required to
induce slope failure. Subsequently, we use the Newmark displacement method to calculate the earthquake magnitude needed to
cause the slope failure as a function of distance from the site. The results (attributed to the 749 CE earthquake) show that
a MW > 7.0 earthquake up to 25 km from the site could have induced the studied landslide. 相似文献
955.
956.
The footprint assemblage of Vieux Emosson, located at 2400 m altitude in the Swiss Alps, was first described in 1982. The
assemblage was regarded as Late Ladinian or Carnian in age, but the dating was questioned because the taxa show few affinities
with other Triassic assemblages. Here we describe a short trackway with shallow but well-preserved tracks referred to the
ichnogenus Isochirotherium, showing affinities with Isochirotherium soergeli and Isochirotherium lomasi. The trackway is present on a piece of slab ex situ lying on a mass of fallen rocks, but the slab can be attributed with confidence to the same level as the main one previously
mapped. Preliminary observations in situ and of the footprint casts made in 1979 and deposited in the Natural History Museum of Geneva suggest that none of these
are attributable to dinosaurs and that the Vieux Emosson footprints are mainly “track preservation variations” of chirotherian
tracks. The occurrence of the ichnogenus Isochirotherium favours an older age, probably Early or Middle Triassic, than previously suggested for the Vieux Emosson tracksite. 相似文献
957.
Contrasting sediment flux in Val Lumnezia (Graubünden, Eastern Swiss Alps), and implications for landscape development 总被引:1,自引:0,他引:1
Marco Schwab Fritz Schlunegger Heinz Schneider Gregor Stöckli Dirk Rieke-Zapp 《Swiss Journal of Geoscience》2009,102(2):211-222
This paper presents qualitative estimates of sediment discharge from opposite valley flanks in the S–N-oriented Val Lumnezia,
eastern Swiss Alps, and relates inferred differences in sediment flux to the litho-tectonic architecture of bedrock. The valley
flank on the western side hosts the deep-seated Lumnezia landslide where an area of ca. 30 km2 has experienced slip rates of several centimetres per year, potentially resulting in high sediment discharge to the trunk
stream (i.e. the Glogn River). High slip rates have resulted in topographic changes that are detectable on aerial photographs
and measurable with geodetic tools. In contrast, a network of tributary channels dissects the valley flank on the eastern
side. There, an area of approximately 18 km2 corresponding to < 30% of the surface has experienced a change in the landscape mainly by rock avalanche and rock fall, and
the magnitudes of changes are below the calibration limit of digital photogrammetry. We thus infer lower magnitudes of sediment
discharge on the eastern tributaries than on the western valley side, where landsliding has been the predominant erosional
process. These differences are interpreted to be controlled by the dip-slope situation of bedrock on the western side that
favours down-slope slip of material.
Morphometric investigations reveal that the western valley side is characterized by a low topographic roughness because this
valley flank has not been dissected by a channel network. It appears that high sediment discharge of the Lumnezia landslide
has inhibited the establishment of a stable channel network and has largely controlled the overall evolution of the landscape.
This contrasts to the general notion that channelized processes exert the first-order control on landscape evolution and formation
of relief and needs to be considered in future studies about landscape architecture, drainage network and sediment discharge. 相似文献
958.
1951-2002年长江流域降水特征 总被引:2,自引:0,他引:2
The monthly, seasonal, and annual precipitation trends in the Yangtze river catchment have been detected through analysis of 51 meteorological stations‘ data between 1950-2002 provided by National Meteorological Administration. Results reveal that: 1) Summer precipitation in the Yangtze river catchment shows significant increasing tendency. The Poyanghu lake basin, Dongtinghu lake basin and Taihu lake basin in the middle and lower reaches are the places showing significant positive trends. Summer precipitation in the middle and lower reaches experienced an abrupt change in the year 1992; 2) The monthly precipitation in months just adjoining to summer shows decreasing tendency in the Yangtze river catchment. The upper and middle reaches in Jialingjiang river basin and Hanshui river basin are the places showing significant negative trends; 3) Extreme precipitation events show an increasing tendency in most places, especially in the middle and lower reaches of the Yangtze river catchment. 相似文献
959.
Flow and transport in channels with submerged vegetation 总被引:3,自引:0,他引:3
This paper reviews recent work on flow and transport in channels with submerged vegetation, including discussions of turbulence
structure, mean velocity profiles, and dispersion. For submerged canopies of sufficient density, the dominant characteristic
of the flow is the generation of a shear-layer at the top of the canopy. The shear-layer generates coherent vortices by Kelvin-Helmholtz
(KH) instability. These vortices control the vertical exchange of mass and momentum, influencing both the mean velocity profile,
as well as the turbulent diffusivity. For flexible canopies, the passage of the KH vortices generates a progressive wave along
the canopy interface, termed monami. The KH vortices formed at the top of the canopy penetrate a distance δ
e
into the canopy. This penetration scale segregates the canopy into an upper layer of rapid transport and a lower layer of
slow transport. Flushing of the upper canopy is enhanced by the energetic shear-scale vortices. In the lower layer turbulence
is limited to length-scales set by the stem geometry, and the resulting transport is significantly slower than that of the
upper layer. 相似文献
960.
Theoretical and practical issues concerning the multi-faceted task of mitigating the latero-torsional seismic response of a prototypal frame structure with asymmetric mass distribution are approached.Chevron braces with embedded magnetorheological dampers acting on the interstory drift are used to ensure additional energy dissipation.The semi-active control strategy employed to govern the modifi cation of the damper characteristics via feedback is based on the selection of optimal forces according to a H2/L... 相似文献