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921.
Polycyclic aromatic hydrocarbons (PAH) and alkylphenols (AP) that are present in routine discharges of produced water (PW) from the offshore industry continue to cause concern. The suitability of biological methods and chemical based passive samplers to determine exposure to these compounds was tested by deploying them around an oil installation and at reference locations in the North Sea. PAH and AP were analysed either as parent compounds in passive samplers and mussel tissue or as metabolites in fish bile. Generally the pattern of exposure relative to proximity to the discharge was represented by mussels, SPMDs and fish for PAH. Fish and SPMDs showed good correlation for PAH accumulations, whereas some differences were apparent between mussels and SPMDs. POCIS was the only technique tested that could accurately measure the most abundant AP in PW. The advantages of biologically independent measures of exposure for inclusion in discharge monitoring studies are outlined. 相似文献
922.
The gross distribution of seismicity in North America suggests the interior platform and shield provinces are relatively stable and significantly affect the intraplate stress field. Focal mechanisms and in-situ stress measurements indicate the cratonic areas of North America must be relatively immobile with respect to the eastern and western portions of the continent. Simple kinematic models are presented to illustrate the importance of the craton in any attempt to explain the general pattern of intraplate stress and seismicity in North America. 相似文献
923.
Christopher J. Potter Richard W. Allmendinger Ernest C. Hauser Jack E. Oliver 《Geophysical Journal International》1987,89(1):99-104
Summary. COCORP seismic reflection traverses of the U.S. Cordillera at 40°N and 48.5°N latitude reveal some fundamental similarities as well as significant differences in reflection patterns. On both traverses, autochthonous crust beneath thin-skinned thrust belts of the eastern part of the Cordillera is unreflective; immediately to the west the Cordilleran interior is very reflective above a flat, prominent reflection Moho. Mesozoic accreted terranes in the western part of the orogen are underlain on both traverses by very complex reflection patterns, in constrast to more easily deciphered patterns beneath areas of Cenozoic accretion. The prominent reflection Moho beneath the orogenic interior on both transects probably evolved through a combination of magmatic and deformational processes during Cenozoic extension. The main differences between the two traverses lie in the reflection patterns of the middle and lower crust in the Cordilleran interior; these differences are probably related to the way Cenozoic extension was accommodated at depth. Laminated middle and lower crust above the reflection Moho in the western Basin and Range (40°N) may be related to magmatism, ductile pure shear and large-scale transposition during Cenozoic extension. By contrast, beneath the eastern Basin and Range (40°N), and the orogenic interior in the NW United States (48.5°N), Cenozoic extension was probably accommodated along dipping deformation zones throughout the crust. 相似文献
924.
Alex Ruzicka Jeffrey Grossman Audrey Bouvier Christopher D. K. Herd Carl B. Agee 《Meteoritics & planetary science》2015,50(9):1662-1662
Meteoritical Bulletin 102 contains 3141 meteorites including 12 falls (Boumdeid (2003), Boumdeid (2011), Braunschweig, Chelyabinsk, Dongyang, Draveil, Heyetang, Indian Butte, Katol, Ladkee, Ouadangou, Xining), with 2611 ordinary chondrites, 264 HED achondrites, 124 carbonaceous chondrites, 30 ureilites, 20 Martian meteorites, 16 primitive achondrites, 16 Rumuruti chondrites, 15 mesosiderites, 12 iron meteorites, 10 lunar meteorites, 9 enstatite chondrites, 4 enstatite achondrites, 4 Pallasites, 4 ungrouped achondrites, and 2 angrites, and with 1708 from Antarctica, 956 from Africa, 294 from South America, 126 from Asia, 47 from North America, 6 from Europe (including Russia), and 4 from Oceania. Information about approved meteorites can be obtained from the Meteoritical Bulletin Database (MBD) available on line at http://www.lpi.usra.edu/meteor/ . 相似文献
925.
Christopher R. Kelble Peter B. Ortner Gary L. Hitchcock Michael J. Dagg Joseph N. Boyer 《Estuaries and Coasts》2010,33(3):723-737
Quantifying the relationship between mesozooplankton and water quality parameters identifies the factors that structure the
mesozooplankton community and can be used to generate hypotheses regarding the mechanisms that control the mesozooplankton
population and potentially the trophic network. To investigate this relationship, mesozooplankton and water quality data were
collected in Florida Bay from 1994 to 2004. Three key characteristics were found in the mesozooplankton community structure:
(1) there are significant differences between the four sub-regions of Florida Bay; (2) there is a break in May of 1997 with
significant differences before and after this date; and (3) there is a positive correlation between mesozooplankton abundance
and salinity. The latter two characteristics are closely correlated with predator abundance, indicating the importance of
top-down control. Hypersaline periods appear to provide a refuge from predators, allowing mesozooplankton to increase in abundance
despite the increased physiological stress. 相似文献
926.
Assessing spatial variability in soil characteristics with geographically weighted principal components analysis 总被引:1,自引:0,他引:1
Sandeep?KumarEmail author Rattan?Lal Christopher?D.?Lloyd 《Computational Geosciences》2012,16(3):827-835
Dimensionality reduction methods such as principal components analysis (PCA) provide a means of identifying trends in soil
characteristics which may be represented by a wide range of variables. However, these characteristics may be highly spatially
variable and so the results from PCA represent, in some sense, an “average” of locally distinct characteristics. One approach
to account for these local differences is to introduce a geographical weighting scheme into the PCA process. In this paper,
such an approach is assessed in the exploration of soil characteristics in the state of Pennsylvania, USA. Data from 878 georeferenced
soil profiles which include different soil parameters (n = 12) were extracted from the National Soil Survey Center database. Where data are parts of compositions (e.g., percentages
of sand, silt, and clay), analysis using raw data is not appropriate and such data were transformed using log ratios (specifically,
balances). Single variables (i.e., those which are not parts of compositions) were logged. The first two principal components
explain over 50% of the variance. The mapped values suggest marked spatial variation in soil characteristics, but it is not
possible to assess which of these variables explain most variation in particular regions from the simple maps of raw variables.
Geographically weighted PCA (GWPCA) provides additional information which is obscured by PCA, and it also provides a set of
component scores and loadings at all data locations. The soil variable with the largest loading at most locations of Pennsylvania
is the logged base saturation (BSln), and this supports the findings of the conventional PCA analysis. While BSln loads most
highly in most of the eastern third, the middle and the south west of the state, the northwest is less spatially consistent
in terms of the variables which explain most variation. For GWPC 1, the variable with the second largest loading at most locations
(i.e., primarily the south and west) is CEC.B1 (the log ratio of Ca, Mg, and Na to K and EXACID), while CEC.B2 (the log ratio
of Ca and Mg to Na), pHln (logged pH) and BSln dominate in other areas. The GWPCA results suggest that there is marked spatial
variation in multivariate soil characteristics across Pennsylvania state and that results from standard PCA obscure this considerable
variation. 相似文献
927.
Christopher Potter Peggy Gross Steven Klooster Matthew Fladeland Vanessa Genovese 《Climatic change》2008,90(3):269-282
A plant and soil simulation model based on satellite observations of vegetation and climate data was used to estimate the
potential carbon pools in standing wood biomass across all forest ecosystems of the conterminous United States up to the year
1997. These modeled estimates of vegetative carbon potential were compared to aggregated measurements of standing wood biomass
from the U. S. Forest Service’s national Forest Inventory and Analysis (FIA) data set and the Carbon Online Estimator (COLE)
to understand: 1) predominant geographic variations in tree growth rate and 2) local land cover and land use history including
the time since the last stand-replacing disturbance (e.g., from wildfire or harvest). Results suggest that although wood appears
to be accumulating at high rates in many areas of the U.S. (Northwest and Southeast), there are still extensive areas of relatively
low biomass forest in the late 1990s according to FIA records. We attribute these low biomass accumulation levels to the high
frequency of disturbances, which can be observed even in high production areas such as the Southeast due to frequent forest
harvests. Ecosystem models like the one presented in this study have been coupled with satellite observations of land cover
and green plant density to uniquely differentiate areas with a high potential for vegetative carbon storage at relatively
fine spatial resolution. 相似文献
928.
Christopher S. Swezey Arthur P. Schultz Wilma Alemán González Christopher E. Bernhardt William R. Doar III Christopher P. Garrity Shannon A. Mahan John P. McGeehin 《Quaternary Research》2013
Sand hills in the Savannah River valley in Jasper County (South Carolina, USA) are interpreted as the remnants of parabolic eolian dunes composed of sand derived from the Savannah River and stabilized by vegetation under prevailing climate conditions. Optically stimulated luminescence ages reveal that most of the dunes were active ca. 40 to 19 ka ago, coincident with the last glacial maximum (LGM) through early deglaciation. Modern surface winds are not sufficient for sustained eolian sand transport. When the dunes were active, winds blew at velocities of at least 4 m/s from west to east, and some vegetation was present. The ratio of annual precipitation to potential evapotranspiration (P:PE) was less than the modern ratio of 1.23 and may have been < 0.30, caused by stronger winds (which would have resulted in greater evaporation) and/or reduced precipitation. The Savannah River dunes are part of a larger assemblage of eolian dunes that were active in the eastern United States during and immediately after the LGM, suggesting that eolian sediment behavior in this region has been controlled by regional forcing mechanisms during the Quaternary. 相似文献
929.
Routine trace-element geochemistry suggests that components in putative marine halite evaporites may be partly of nonmarine origin, but such interpretations are commonly ambiguous. Stable chlorine isotopes may provide a less-ambiguous marker of chloride origin where δ37 Cl departs from the range predicted for evaporite formation from seawater. Bedded halite with primary sedimentary textures preserves original δ37 Cl values. Measurable change in δ37 Cl can be generated by incongruent dissolution of halite, but only if less than half the original halite remains. Badenian (middle Miocene) halite from the Forecarpathian and from the East Slovakian and Transcarpathian basins has a δ37 Cl range of – 0.2 to 0.8‰. Two phenomena cannot be explained by simple evaporation of 0.0‰ seawater. At Wieliczka, the Shaft Salt has distinctive δ37 Cl values (– 0.2 to 0.0‰) relative to neighbouring salt beds (0.2 to 0.6‰), requiring a large, abrupt input of brine with negative δ37 Cl. Halite with high (0.6 – 0.8‰) δ37 Cl near the base of the East Slovakian and Transcarpathian evaporites requires a large input of chloride with positive δ37 Cl into the basins. Expulsion of basin brine with non-0‰δ37 Cl into the evaporite basins may account for the nonmarine chloride sources. 相似文献
930.