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481.
Barbara Hennemuth 《Boundary-Layer Meteorology》1986,36(4):371-394
Wind observations from a small Alpine valley are used to investigate the problem of cross-valley winds. The observed daytime windfield is a superposition of dynamically and thermally forced cross-winds. Prevailing cross-winds above the valley result in a recirculation cell above the lee slope. The return flow is strengthened or weakened by thermal effects which induce a wind that blows from the shaded to the sunny side of the valley. The reaction time of the thermally induced cross-winds is only 4 min. The horizontal and vertical motions of the cross-valley circulation transport heat in such a way that the insolation differences between the two sides of the valley are nearly equalized. 相似文献
482.
Couplings of watersheds and coastal waters: Sources and consequences of nutrient enrichment in Waquoit Bay,Massachusetts 总被引:1,自引:0,他引:1
Ivan Valiela Kenneth Foreman Michael LaMontagne Douglas Hersh Joseph Costa Paulette Peckol Barbara DeMeo-Andreson Charlene D’Avanzo Michele Babione Chi-Ho Sham John Brawley Kate Lajtha 《Estuaries and Coasts》1992,15(4):443-457
Human activities on coastal watersheds provide the major sources of nutrients entering shallow coastal ecosystems. Nutrient loadings from watersheds are the most widespread factor that alters structure and function of receiving aquatic ecosystems. To investigate this coupling of land to marine systems, we are studying a series of subwatersheds of Waquoit Bay that differ in degree of urbanization and hence are exposed to widely different nutrient loading rates. The subwatersheds differ in the number of septic tanks and the relative acreage of forests. In the area of our study, groundwater is the major mechanism that transports nutrients to coastal waters. Although there is some attenuation of nutrient concentrations within the aquifer or at the sediment-water interface, in urbanized areas there are significant increases in the nutrient content of groundwater arriving at the shore’s edge. The groundwater seeps or flows through the sediment-water boundary, and sufficient groundwater-borne nutrients (nitrogen in particular) traverse the sediment-water boundary to cause significant changes in the aquatic ecosystem. These loading-dependent alterations include increased nutrients in water, greater primary production by phytoplankton, and increased macroaglal biomass and growth (mediated by a suite of physiological responses to abundance of nutrients). The increased macroalgal biomass dominates the bay ecosystem through second- or third-order effects such as alterations of nutrient status of water columns and increasing frequency of anoxic events. The increases in seaweeds have decreased the areas covered by eelgrass habitats. The change in habitat type, plus the increased frequency of anoxic events, change the composition of the benthic fauna. The data make evident the importance of bottom-up control in shallow coastal food webs. The coupling of land to sea by groundwater-borne nutrient transport is mediated by a complex series of steps; the cascade of processes make it unlikely to find a one-to-one relation between land use and conditions in the aquatic ecosystem. Study of the process and synthesis by appropriate models may provide a way to deal with the complexities of the coupling. 相似文献
483.
Barbara J. Leitner Donald J. Weidner Robert C. Liebermann 《Physics of the Earth and Planetary Interiors》1980,22(2):111-121
The elastic moduli of a synthetic single crystal of pyrope (Mg3Al2Si3O12) have been determined using a technique based on Brillouin scattering. These results are used in an evaluation of the effect of composition on the elastic properties of silicate garnet solid solution series (Mg, Fe, Mn, Ca)3 (Al, Fe, Cr)2 Si3O12. In the pyralspites (Mg FeMn aluminum garnets), for which a large amount of data is available, this analysis indicates that the bulk modulus K is independent of the Fe2+/Mg2+ ratio, which is similar to the behavior observed in olivines and pyroxenes. However, the shear modulus μ of the garnets increases by 10% from the Mg to the Fe end member, in contrast to the decrease of μ with Fe content which is observed in olivines and pyroxenes. This contrasting behavior is most probably related to the oxygen coordination of the cation site occupied by Mg2+ and Fe2+ in these different minerals. 相似文献
484.
485.
Dynamic capillary effects in heterogeneous porous media 总被引:1,自引:0,他引:1
In standard multi-phase flow models on porous media, a capillary pressure saturation relationship developed under static conditions
is assumed. Recent experiments have shown that this static relationship cannot explain dynamic effects as seen for example
in outflow experiments. In this paper, we use a static capillary pressure model and a dynamic capillary pressure model based
on the concept of Hassanizadeh and Gray and examine the behavior with respect to material interfaces. We introduce a new numerical
scheme for the one-dimensional case using a Lagrange multiplier approach and develop a suitable interface condition. The behavior
at the interface is discussed and verified by various numerical simulations. 相似文献
486.
K. David Newell John H. Doveton Daniel F. Merriam Barbara Sherwood Lollar William M. Waggoner L. Michael Magnuson 《Natural Resources Research》2007,16(3):277-292
In late 2005 and early 2006, the WTW Operating, LLC (W.T.W. Oil Co., Inc.) #1 Wilson well (T.D. = 5772 ft; 1759.3 m) was drilled
for 1826 ft (556.6 m) into Precambrian basement underlying the Forest City Basin in northeastern Kansas. Approximately 4500
of the 380,000 wells drilled in Kansas penetrate Precambrian basement. Except for two previous wells drilled into the arkoses
and basalts of the 1.1-Ga Midcontinent Rift and another well drilled in 1929 in basement on the Nemaha Uplift east of the
Midcontinent Rift, this well represents the deepest penetration into basement rocks in the state to date. Granite is the typical
lithology observed in wells that penetrate the Precambrian in the northern Midcontinent. Although no cores were taken to definitively
identify lithologies, well cuttings and petrophysical logs indicate that this well encountered basement metamorphic rocks
consisting of schist, gneiss, and amphibolitic gneiss, all cut by aplite dikes.
The well was cased and perforated in the Precambrian, and then acidized. After several days of swabbing operations, the well
produced shows of low-Btu gas, dominated by the non-flammable component gases of nitrogen (20%), carbon dioxide (43%), and
helium (1%). Combustible components include methane (26%), hydrogen (10%), and higher molecular-weight hydrocarbons (1%).
Although Coveney and others [Am. Assoc. Petroleum Geologists Bull., v. 71, no, 1, p. 39–48, 1987] identified H2-rich gas in two wells located close to the Midcontinent Rift in eastern Kansas, this study indicates that high levels of
H2 may be a more widespread phenomenon than previously thought. Unlike previous results, the gases in this study have a significant
component of hydrocarbon gas, as well as H2, N2, and CO2. Although redox reactions between iron-bearing minerals and groundwater are a possible source of H2 in the Precambrian basement rocks, the hydrocarbon gas does not exhibit the characteristics typically associated with proposed
abiogenic hydrocarbon gases from Precambrian Shield sites in Canada, Finland, and South Africa. Compositional and isotopic
signatures for gas from the #1 Wilson well are consistent with a predominantly thermogenic origin, with possible mixing with
a component of microbial gas. Given the geologic history of uplift and rifting this region, and the major fracture systems
present in the basement, this hydrocarbon gas likely migrated from source rocks and reservoirs in the overlying Paleozoic
sediments and is not evidence for abiogenic hydrocarbons generated in situ in the Precambrian basement. 相似文献
487.
A spatial analysis of structural controls on Karst groundwater geochemistry at a regional scale 总被引:7,自引:0,他引:7
Danile Valdes Jean-Paul Dupont Benoît Laignel Sylvie Ogier Thierry Leboulanger Barbara J. Mahler 《Journal of Hydrology》2007,340(3-4):244-255
The coupled spatial investigation of the geometrical and geochemical properties of a chalk karstic aquifer provides information on the degree to which geologic structure controls aquifer functioning and groundwater quality. Major ion concentrations in the chalk aquifer of the Haute-Normandie region (France) were measured at a high spatial resolution (more than 100 sampling sites over a 6000 km2 area) and mapped. The first observation is a continuity of the geochemical properties, in spite of the karstic properties of the aquifer principal components analysis of geochemical maps revealed two types of spatial distributions: ions with an autochthonous origin (Ca2+, HCO3), and ions with a principally allochthonous origin (Cl−, Na+, , ). Mg2+ was categorised as both autochthonous (chalk dissolution) and allochthonous (brought in by infiltration of Tertiary deposits). To better understand the spatial distribution of the geochemistry, the aquifer geochemistry was compared to the physical properties of the aquifer, in particular aquifer thickness (representing aquifer geometry) and piezometric level (representing aquifer flow). Use of spatial correlation between the geochemical and the geometrical properties provided insight regarding the directional structure of the data and give evidence of directional relations between geochemical and geometrical properties. The degree of mineralisation (principally composed of Ca2+ and ions) increased along the direction of flow, corresponding to an increase in chalk dissolution rate along the flowpath. The steepest mineralisation gradients were related to an increase in the Mg/Ca ratio, evidence of longer residence times and corresponding to zones where aquifer flow capacity is limited because of a decrease of the thickness of the flow section (anticlines or faults). These results highlight the dominant role played by the geometry and the structural context in controlling aquifer geochemistry. 相似文献
488.
Genetic algorithms have been shown to be powerful tools for solving a wide variety of water resources optimization problems. Applying these approaches to complex, large-scale water resources applications can be difficult due to computational limitations, especially when a numerical model is needed to evaluate different solutions. This problem is particularly acute for solving field-scale groundwater remediation design problems, where fine spatial grids are often needed for accuracy. Finer grids usually improve the accuracy of the solutions, but they are also computationally expensive. In this paper we present multiscale island injection genetic algorithms (IIGAs), in which the optimization algorithms have different multiscale populations working on different islands (groups of processors) and periodically exchanging information. This new approach is tested using a field-scale pump-and-treat design problem at the Umatilla Army Depot in Oregon, USA. The performance of several variations of this approach is compared with the results of a simple genetic algorithm. The new approach found the same solution as much as 81% faster than the simple genetic algorithm and 9–53% faster than other previously formulated multiscale strategies. These findings indicate substantial promise for multiscale IIGA approaches to improve solution of complex water resources applications at the field scale. 相似文献
489.
490.
ABSTRACTStreamflow data are important for river management and the calibration of hydrological models. However, such data are only available for gauged catchments. Citizen science offers an alternative data source, and can be used to estimate streamflow at ungauged sites. We evaluated the accuracy of crowdsourced streamflow estimates for 10 streams in Switzerland by asking citizens to estimate streamflow either directly, or based on the estimated width, depth and velocity of the stream. Additionally, we asked them to estimate the stream level class by comparing the current stream level with a picture that included a virtual staff gauge. To compare the different estimates, the stream level class estimates were converted into streamflow. The results indicate that stream level classes were estimated more accurately than streamflow, and more accurately represented high and low flow conditions. Based on this result, we suggest that citizen science projects focus on stream level class estimates instead of streamflow estimates. 相似文献