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131.
Lithospheric structure of the Tornquist Zone resolved by nonlinear P and S teleseismic tomography along the TOR array 总被引:1,自引:1,他引:1
Z. Hossein Shomali Roland G. Roberts Laust B. Pedersen the TOR Working Group 《Tectonophysics》2006,416(1-4):133
The main aim of the TOR project is to study the lithospheric–asthenospheric boundary structure under the Sorgenfrei–Tornquist Zone, across northern Germany, Denmark and southern Sweden. Relative arrival-time residuals of teleseismic P and S phases from 51 earthquakes, recorded by 150 seismic stations along the TOR array, were used to delineate the transition zone in the studied area. The effects of crustal structures were investigated by correcting the teleseismic residuals for travel-time variations in the crust based on a 3D crustal model derived from other data. The inversion was carried out for S phases. The results were then compared with the corresponding P-wave models. As expected, the derived models show that the relatively old and cold Baltic Shield has higher velocity at depth than the younger lithosphere farther South. The models show two sharp and distinct increases in depth to velocities which are low compared to our reference model, as we move from South to North. The location and sharpness of these boundaries suggests that the features resolved are, at least partially, compositional in origin, presumably related to mantle depletion. A sharp and steep subcrustal boundary is found roughly coincident with the southern edge of Sweden. This is below where the edge of the Baltic Shield is usually placed, based on surface geological evidence (the Sorgenfrei–Tornquist Zone). Another less significant transition is recognised more or less beneath the Elbe-lineament. Relatively high d(Vp / Vs) ratios under the central part of the profile (Denmark) indicate relatively low S-velocity in an area where a gravity high supports the hypothesis of extensive mafic intrusions. 相似文献
132.
Empirical laws and statistics of earthquakes are valuable as a basis for a better understanding of the earthquake cycle. In this paper we focus on the postseismic phase and the physics of aftershock sequences. Using interevent time distributions for a catalogue of Icelandic seismicity, we infer that the parameter C2 in the Omori law, often considered to represent incomplete detection of aftershocks, is at least in part related to the physics of the earthquake process. We investigate the role of postseismic pore pressure diffusion after two Icelandic earthquakes on the rate of aftershocks and what we can infer about the physical meaning of C2 from the diffusion process. Using the Mohr–Coulomb failure criterion we obtain a rate of triggered points in our diffusion model that agrees with the modified Omori law, with a value of C2 that is consistent with data. Our pore pressure diffusion model suggests that C2 is related to the process of reducing high pore pressure gradients existing across a fault zone at short times after a main shock. 相似文献
133.
Karin A. Koinig Christian Kamenik Roland Schmidt Anna Agustí-Panareda Peter Appleby Andrea Lami Miroslava Prazakova Neil Rose Øyvind A. Schnell Richard Tessadri Roy Thompson Roland Psenner 《Journal of Paleolimnology》2002,28(1):147-160
Changes in microfossils (diatoms, chrysophytes, chironomids and cladocera remains), geochemistry and deposition of atmospheric pollutants have been investigated in the sediment records of the alpine lake Gossenköllesee (Tyrol, Austria) spanning the last two centuries. The sediment records were compared with seasonal and annual air temperature trends calculated for the elevation (2417 m a.s.l.) and the geographical position (47° 1346N, 11° 0051E) of the lake, and with precipitation records available since 1866 from Innsbruck. Temperature trends followed a 20–30 year oscillation between cold and warm periods. Regarding long-term changes, temperature trends showed a U-shaped trend between 1780 and 1950, followed by a steep increase since 1975.Physical, geochemical, and organic parameters were not controlled by air temperature. Among the biological records only diatoms and chrysophytes reacted to air temperature changes: the relative abundance of planktonic diatoms increased during warm periods and changes in mean annual alpine air temperature explained 36.5% of their variation. The relation between abundance of seasonal stomatocyst types and air temperature varied on two different time scales: while summer stomatocysts were influenced by short term temperature fluctuations, the autumn stomatocysts were affected only by the long term changes. Other biological parameters exhibited a constant species composition (chironomids, pigments) or changes were small and independent of temperature (cladocera). Spheroidal carbonaceous fly-ash particles, and trends in Pb and Cr indicated increasing deposition of atmospheric pollutants but had no detectable effects on the biological parameters either. In respect to temperature variations over the last 200 years, this alpine lake is much less sensitive than expected and has thus to be regarded as a well buffered site. However, temperature alone is not sufficient to understand changes in species composition and other biogeochemical processes with unknown historical patterns might have affected species composition more strongly. 相似文献
134.
E. Mahieu R. Zander L. Delbouille P. Demoulin G. Roland C. Servais 《Journal of Atmospheric Chemistry》1997,28(1-3):227-243
Since 1984, about 15000 high quality infrared solar spectra have beenrecorded with state-of-the-art grating and Fourier transform spectrometersat the International Scientific Station of the Jungfraujoch, Switzerland.Nonlinear least squares spectral curve fitting of selected microwindowscontaining isolated and well characterized lines of 20 telluric gases haveallowed to retrieve their total vertical column abundances above thestation, leading to observational data bases essential to derive long- andshort-term changes experienced by these species during the last 12 years. Inthis paper, we focus on atmospheric gases of particular interest within thecontext of the EUROTRAC/TOR (Tropospheric Ozone Research) project; secularevolution as well as seasonal cycles of the minor constituentsCH4, CO and of the trace gasesC2H6, OCS, C2H2, HCNand H2CO are reported and discussed. The long-livedN2O is included as a tracer of the dynamic activity of theatmosphere. 相似文献
135.
A general method is presented for analyzing how climatic conditions affect plant disease severity. An example of its application is given for the analysis of stripe rust (caused by Puccinia striiformis) data on winter wheat cultivar Gaines and climatic data collected at Pullman, WA. for 1968–1986. A computer program WINDOW was written to identify the climatic factors most highly correlated with disease. This program is designed to utilize meteorological data for an entire growing season of a crop as well as to include climatic conditions preceding planting. This program uses an iterative process to examine variable-length segments of meteorological data in a more exhaustive analysis than previously possible. Climatic factors considered include: mean maximum, minimum, and average temperature; total and frequency of precipitation; consecutive days with and without precipitation; accumulation of negative and positive degree days; and number of days with extreme temperature events. Variables that were highly correlated with disease were the basis for regression models that were developed to predict disease severity index for each of the three cultivars. Two- and three-variable models explained, respectively, 75 and 76% of the variation in disease from year to year. Predictions (which could be made early enough in the growing season to allow application of chemical control) were evaluated on the basis of whether years with severe disease were accurately predicted. Models were validated using Allen's PRESS statistic and by application to new data. The method is potentially applicable to studies of how climatic conditions affect the populations or productivity of other types of organisms.This research was supported by a National Science Foundation Grant (ATM 85-03115), Climate Dynamics Program, Division of Atmospheric Sciences. 相似文献
136.
Roland Schmidt 《Aquatic Sciences - Research Across Boundaries》1989,51(4):317-337
Three cores from Traunsee were investigated and compared with respect to diatom stratigraphy concerning dating of incursions into and rate of accumulation of industrial tailings in the profundal zone. 相似文献
137.
Roland Psenner 《Aquatic Sciences - Research Across Boundaries》1989,51(2):108-128
Alpine lakes in siliceous catchments of Tyrol and Carinthia (Austria) show signs of acidification. About 9% of the studied lakes have no alkalinity, more than 20% are below pH 6. About two thirds of all lakes have acid neutralizing capacities below 100 eq 1–1. In spite of moderate precipitation acidity, some lakes show considerable concentrations of dissolved reactive aluminum during or shortly after snowmelt. High altitude lakes of the Alps are definitely more acidic than high mountain lakes in remote areas. Large differences in water and soil chemistry of nearby situated lakes were attributed to heterogeneities of bedrock geology. Paleolimnological investigations on former pH values of five lakes, based on diatom assemblages in the sediment, showed different developments: recent and past acidification, stable conditions, and alkalinization. 相似文献
138.
Clay-based layers which serve to minimize infiltration of surface water into waste piles seem to form a promising concept, since their hydraulic conductivity can be kept so low that the net effect of cyclic drying and wetting in Sweden will be that no water penetrates. Problems may arise, however, from physico/chemical processes as well as from swelling, one example being given in this paper. 相似文献
139.
This study investigated the distribution of subfossil diatom assemblages in surficial sediments of 100 lakes along steep ecological and climatic gradients in northernmost Sweden (Abisko region, 67.07° N to 68.48° N latitude, 17.67° E to 23.52° E longitude) to develop and cross-validate transfer functions for paleoenvironmental reconstruction. Of 19 environmental variables determined for each site, 15 were included in the statistical analysis. Lake-water pH (8.0%), sedimentary loss-on-ignition (LOI, 5.9% and estimated mean July air temperature (July T, 4.8%) explained the greatest amounts of variation in the distribution of diatom taxa among the 100 lakes. Temperature and pH optima and tolerances were calculated for abundant taxa. Transfer functions, based on WA-PLS (weighted averaging partial least squares), were developed for pH (r2 = 0.77, root-mean-square-error of prediction (RMSEP) = 0.19 pH units, maximum bias = 0.31, as assessed by leave-one-out cross-validation) based on 99 lakes and for July T (r2 = 0.75, RMSEP = 0.96 °C, max. bias = 1.37 °C) based on the full 100 lake set. We subsequently assessed the ability of the diatom transfer functions to estimate lake-water pH and July T using a form of independent cross-validation. To do this, the 100-lake set was divided in two subsets. An 85-lake training-set (based on single limnological measurements) was used to develop transfer functions with similar performance as those based on the full 100 lakes, and a 15-lake test-set (with 2 years of monthly limnological measurements throughout the ice-free seasons) was used to test the transfer functions developed from the 85-lake training-set. Results from the intra-set cross-validation exercise demonstrated that lake-specific prediction errors (RMSEP) for the 15-lake test-set corresponded closely with the median measured values (pH) and the estimations based on spatial interpolations of data from weather stations (July T). The prediction errors associated with diatom inferences were usually within the range of seasonal and interannual variability. Overall, our results confirm that diatoms can provide reliable and robust estimates of lake-water pH and July T, that WA-PLS is a robust calibration method and that long-term environmental data are needed for further improvement of paleolimnological transfer functions. 相似文献
140.
Martin Gude Gerhard Daut Susanne Dietrich Roland Mäusbacher Christer Jonasson Annett Bartsch & Dieter Scherer 《Geografiska Annaler: Series A, Physical Geography》2002,84(3-4):205-212
The analysis of Holocene geomorphic process activity demands long–term data sets, which are available for the Kärkevagge catchment due to 50 years of intensive geomorphologic field studies. This data set is used in combination with additional field measurements, remote sensing and digital elevation model (DEM) analysis to provide input data for modelling Holocene valley development. On the basis of this information, geomorphic process units (GPUs) are defined by means of GIS modelling. These units represent areas of homogeneous process composition that transfer sediments. Since the data base enables the quantification of single processes, the interaction of processes within the units can also be quantified. Applying this concept permits calculation of recent sediment transfer rates and hence leads to a better understanding of actual geomorphic landscape development activity. To extrapolate these data in time and space the process–related sediments in the valley are analysed for depth and total volume, primarily using geophysical methods. In this fashion the validity of measured process rates is evaluated for the Holocene time scale. Results from this analysis are exemplified in a cross–profile showing some of the principal sediment units in the valley. For example, the measured modern rates on a slush torrent debris fan seem to represent the Holocene mean rate. This approach should also be suitable for revealing Holocene geomorphic landscape development in terms of climate change. 相似文献