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31.
The formation of colloids during the weathering of phyllite was investigated by exposing ground phyllite to Milli-Q water. Secondary mineral colloids of 101–102 nm were detected in significant concentrations. At pH of about 8.5, the solution concentration of these colloids reached up to 10 mg/L (however, acidification to pH 4.0 prevented the formation of the colloids). The mineralogical composition of the secondary mineral colloids is assumed to be a mixture of ferrihydrite, manganese oxyhydroxides, aluminosilicates, amorphous Al(OH)3 and gibbsite with possible additions of iron silicates and␣iron-alumino silicates. The colloids were stable over longer periods of time (at least several weeks), even in the presence of suspended ground rock. Direct formation of iron-containing secondary mineral colloids at the rock–water interface by the weathering of rock material is an alternative to the well-known mechanism of iron colloid formation in the bulk of water bodies by mixing of different waters or by aeration of anoxic waters. This direct mechanism is of relevance for colloid production during the weathering of freshly crushed rock in the unsaturated zone as for instance crushed rock in mine waste rock piles. Colloids produced by this mechanism, too, can influence the transport of contaminants such as actinides because these colloids have a large specific surface area and a high sorption affinity. 相似文献
32.
An 11-month observation of dissolved and particulate organic matter, chlorophyll a(Chl a), C18 Sep-Pak extractable hydrophobic dissolved organic matter (hDOM) fraction and associated dissolved trace metals (Cd,
Cu, V, Co, Ni, Mo, U) was performed in the Lot–Garonne River system. This system includes the Riou Mort, the Lot River and
the downstream reaches of the Garonne River and represents the fluvial transport path of trace metals between the major point
source of polymetallic pollution, located in the Riou Mort watershed and the Gironde estuary. Spatial and temporal variations
of dissolved and particulate organic carbon and Chl areflect the presence of different types of organic matter and their relation with the hDOM fraction. Maximum Chl a/POC ratios (up to 0.03), indicate intense phytoplankton production from March to May. In the Lot River (Temple), DOC and
POC concentrations were clearly higher and mean Chl a concentration (2.8 mg g−1) was about three times higher than those of the other sites. High Chl a/POC ratios suggest high phytoplankton activity with maxima in spring and late summer. In the Riou Mort River, very high POC
concentrations of up to 40 (mean: 20) occurred, whereas Chl a concentrations were relatively low indicating low phytoplankton activity. High, strongly variable DOC and POC concentrations
suggest important natural (Carboniferous soils, forests) or anthropogenic (e.g., former coal mines, waste areas, agriculture,
sewage) carbon sources within the small Riou Mort watershed. Despite high DOC concentrations in the Riou Mort River, hDOM
metal fractions were generally lower than those at the other sites. The general order of decreasing binding strength between
metals and the organic hydrophobic phase (Cu, U > Co, Ni > V, Mo > Cd) at all four sites was in good agreement with the Irving–William
series of transition element affinity towards organic ligands. Accordingly, the role of the hydrophobic phase in dissolved
Cd transport appeared to be negligible, whereas the hDOM–Cu fraction strongly contributed to dissolved Cu transport. 相似文献
33.
During the late Miocene, the Guadalquivir Basin and its satellite basin, the Ronda Basin, were under Atlantic cool-water influence. The aim of our study is to develop a sequence stratigraphic subdivision of the Ronda Basin fill and to provide models for the cool-water carbonates. The Upper Miocene of the Ronda Basin can be divided into three depositional sequences. Sequence 1 is early Tortonian, Sequence 2 late Tortonian to earliest Messinian, and Sequence 3 Messinian in age. The sediments were deposited in a ramp depositional system. Sequence 1 is dominated by conglomerates and marls. In Sequence 2 and Sequence 3, carbonate deposits dominate in the inner ramp whereas siliciclastics preferentially occur in the middle and outer ramp. Bryomol carbonate sediments occur in all sequences whereas rhodalgal carbonates are restricted to Sequence 3. In bays protected from siliciclastic influx, rhodalgal deposits formed under transgressive conditions. A bryomol factory occurs in zones of continuous siliciclastic supply. This distribution results from facies partitioning during the flooding of the Ronda Basin, which has a rugged and irregular relief. Embayments were protected from siliciclastic influx and provided regions with less hydraulic energy. 相似文献
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J. Steppeler R. Hess U. Schättler L. Bonaventura 《Meteorology and Atmospheric Physics》2003,82(1-4):287-301
Summary ?Currently available computer power allows to run operational numerical weather prediction models at resolutions higher than
10 km. The aim of such high resolution modeling is the prediction of local weather, including orographically induced winds
and local precipitation patterns. In this range the hydrostatic approximation is no longer valid and nonhydrostatic models
have to be used instead. For several decades these models have been developed for research purposes only, but operational
application is now reality. In this paper, the numerical methods used in current nonhydrostatic forecast models will be reviewed
and some promising techniques in this field will be discussed. Special attention is given to aspects such as the choice of
the vertical coordinate, the efficiency of algebraic solvers for semi-implicit time discretizations, and accurate and non-oscillatory
advection schemes.
Received July 6, 2001; revision October 12, 2001 相似文献
39.
M. Krämer Ri. Müller H. Bovensmann J. Burrows J. Brinkmann E. P. Röth J.-U. Grooß Ro. Müller Th. Woyke R. Ruhnke G. Günther J. Hendricks E. Lippert K. S. Carslaw Th. Peter A. Zieger Ch. Brühl B. Steil R. Lehmann D. S. McKenna 《Journal of Atmospheric Chemistry》2003,45(1):51-77
Several stratospheric chemistry modules from box, 2-D or 3-D models, have been intercompared. The intercomparison was focused on the ozone loss and associated reactive species under the conditions found in the cold, wintertime Arctic and Antarctic vortices. Comparisons of both gas phase and heterogeneous chemistry modules show excellent agreement between the models under constrained conditions for photolysis and the microphysics of polar stratospheric clouds. While the mean integral ozone loss ranges from 4–80% for different 30–50 days long air parcel trajectories, the mean scatter of model results around these values is only about ±1.5%. In a case study, where the models employed their standard photolysis and microphysical schemes, the variation around the mean percentage ozone loss increases to about ±7%. This increased scatter of model results is mainly due to the different treatment of the PSC microphysics and heterogeneous chemistry in the models, whereby the most unrealistic assumptions about PSC processes consequently lead to the least representative ozone chemistry. Furthermore, for this case study the model results for the ozone mixing ratios at different altitudes were compared with a measured ozone profile to investigate the extent to which models reproduce the stratospheric ozone losses. It was found that mainly in the height range of strong ozone depletion all models underestimate the ozone loss by about a factor of two. This finding corroborates earlier studies and implies a general deficiency in our understanding of the stratospheric ozone loss chemistry rather than a specific problem related to a particular model simulation. 相似文献
40.
Meso-gamma scale forecasts using the nonhydrostatic model LM 总被引:10,自引:0,他引:10
J. Steppeler G. Doms U. Schättler H. W. Bitzer A. Gassmann U. Damrath G. Gregoric 《Meteorology and Atmospheric Physics》2003,82(1-4):75-96
Summary ?The nonhydrostatic model LM was developed for small scale operational predictions. Advances in computer development will
give the possibility of operational models of a rather fine scale, which will cover the meso-gamma scale. The LM is currently
applied at a scale of 7 km and an increase of the operational resolution to 2.5 km is planned for the next few years. Predictions
of such high resolution require to abandon the hydrostatic assumption, which is used with most current operational weather
prediction models. The LM was designed to cover all resolutions from 50 m to 50 km with an efficiency making it suitable for
operational use. It is a fully elastic model, using second order centred finite differences. The time integration is done
using the Klemp–Wilhelmson method, treating the slow modes by a larger time step than the fast modes. The vertical propagation
of the fast waves is done implicitly.
After describing the design of the LM, this paper gives examples of model predictions at the meso-γ scale. Some results of
the current operational application at the resolution 7 km are presented. Deficiencies in the localisation of model generated
precipitation are investigated using an idealised bell shaped mountain and applying different resolutions. In this way the
convergence to the correct solution can be investigated. From these results it is concluded, that orographic filtering is
necessary and the effect of such filtering on precipitation forecasts is investigated. Finally, the prediction of a squall
line over northern Germany is shown in order to demonstrate the potential of the model in forecasting the meso-γ scale.
Received May 15, 2001; revised September 21, 2001 相似文献