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991.
A combination of statistical hypothesis testing methods (Mann-Whitney, Mann-Kendall and Spearman’s rho) and visual exploratory analysis were used to investigate trends in Irish 7-day sustained low-flow (7SLF) series possibly driven by changes in summer rainfall patterns. River flow data from 33 gauging stations covering most major Irish rivers were analysed, after excluding catchments where low flows are influenced by significant human interventions. A statistically significant increasing trend in the 7SLF series was identified by all three tests at eight gauging stations; in contrast, a statistically significant decreasing trend was identified by all three tests at four stations. The stations with increasing trends are mainly located within the western half of the country, while there is no particular spatial clustering of the stations showing a decreasing trend. Further analysis suggests that the increasing trend in the 7SLF time series persists regardless of the starting year of analysis. However, the decreasing trend occurs only when years prior to 1970 are included in the analysis, and disappears, or is reversed, if only the data from 1970 and onwards are considered. There is strong evidence that the direction of the trends in the 7SLF series is determined mainly by trends in total summer rainfall amounts, i.e. is linked to weather.

EDITOR Z.W. Kundzewicz

ASSOCIATE EDITOR not assigned  相似文献   
992.
Large‐scale inversion methods have been recently developed and permitted now to considerably reduce the computation time and memory needed for inversions of models with a large amount of parameters and data. In this work, we have applied a deterministic geostatistical inversion algorithm to a hydraulic tomography investigation conducted in an experimental field site situated within an alluvial aquifer in Southern France. This application aims to achieve a 2‐D large‐scale modeling of the spatial transmissivity distribution of the site. The inversion algorithm uses a quasi‐Newton iterative process based on a Bayesian approach. We compared the results obtained by using three different methodologies for sensitivity analysis: an adjoint‐state method, a finite‐difference method, and a principal component geostatistical approach (PCGA). The PCGA is a large‐scale adapted method which was developed for inversions with a large number of parameters by using an approximation of the covariance matrix, and by avoiding the calculation of the full Jacobian sensitivity matrix. We reconstructed high‐resolution transmissivity fields (composed of up to 25,600 cells) which generated good correlations between the measured and computed hydraulic heads. In particular, we show that, by combining the PCGA inversion method and the hydraulic tomography method, we are able to substantially reduce the computation time of the inversions, while still producing high‐quality inversion results as those obtained from the other sensitivity analysis methodologies.  相似文献   
993.
Oceanic tidal fluctuations which propagate long distances up coastal rivers can be exploited to constrain hydraulic properties of riverbank aquifers. These estimates, however, may be sensitive to degree of aquifer confinement and aquifer anisotropy. We analyzed the hydraulic properties of a tidally influenced aquifer along the Meghna River in Bangladesh using: (1) slug tests combined with drilling logs and surface resistivity to estimate Transmissivity (T); (2) a pumping test to estimate T and Storativity (S) and thus Aquifer Diffusivity (DPT); and (3) the observed reduction in the amplitude and velocity of a tidal pulse to calculate D using the Jacob‐Ferris analytical solution. Average Hydraulic Conductivity (K) and T estimated with slug tests and borehole lithology were 27.3 m/d and 564 m2/d, respectively. Values of T and S determined from the pumping test ranged from 400 to 500 m2/d and 1 to 5 × 10?4, respectively with DPT ranging from 9 to 40 × 105 m2/d. In contrast, D estimated from the Jacob‐Ferris model ranged from 0.5 to 9 × 104 m2/d. We hypothesized this error resulted from deviations of the real aquifer conditions from those assumed by the Jacob‐Ferris model. Using a 2D numerical model tidal pulses were simulated across a range of conditions and D was calculated with the Jacob‐Ferris model. Moderately confined (Ktop/Kaquifer < 0.01) or anisotropic aquifers (Kx/Kz > 10) yield D within a factor of 2 of the actual value. The order of magnitude difference in D between pumping test and Jacob‐Ferris model at our site argues for little confinement or anisotropy.  相似文献   
994.
Bentekhici  Nadjla  Bellal  Sid-Ahmed  Zegrar  Ahmed 《Natural Hazards》2020,104(1):811-831
Natural Hazards - Forest fires are one of the major environmental problems that cause harmful economic and ecological damage. The Algerian forest and in particular the Tlemcen forest massif where...  相似文献   
995.
Sagardari union is facing groundwater crisis because of contaminations from agriculture and urban sewage, which bring a considerable change in water quality. In view of this, hydro-chemical analyses were undertaken on 35 groundwater samples and the following hydro-geochemical parameters, pH, total dissolved solids (TDS), total hardness (TH), electrical conductivity (EC), cations and anions, were analyzed. From the analytical results, it is found that pH value was lower than WHO drinking water standard and the middle-downstream portions of the investigation region show higher EC. The piper plot indicates that the groundwater in Sagardari falls in the categories of NaClHCO3 hydro-chemical facies. Higher TH in groundwater was detected, but still in an acceptable range. In addition, salinity and arsenic ratio are higher and moderately higher, respectively. The spatial distribution of Groundwater Quality Index (GWQI) was determined by geo-statistical modelling of Sagardari union. The study provides information and supports the administration which to make better groundwater utilization and quality control in the Sagardari union.  相似文献   
996.
The determination of high-resolution geoid for marine regions requires the integration of gravity data provided by different sources, e.g. global geopotential models, satellite altimetry, and shipborne gravimetric observations. Shipborne gravity data, acquired over a long time, comprises the short-wavelengths gravitation signal. This paper aims to produce a consistent gravity field over the Red Sea region to be used for geoid modelling. Both, the leave-one-out cross-validation and Kriging prediction techniques were chosen to ensure that the observed shipborne gravity data are consistent as well as free of gross-errors. A confidence level equivalent to 95.4% was decided to filter the observed shipborne data, while the cross-validation algorithm was repeatedly applied until the standard deviation of the residuals between the observed and estimated values are less than 1.5 mGal, which led to the elimination of about 17.7% of the shipborne gravity dataset. A comparison between the shipborne gravity data with DTU13 and SSv23.1 satellite altimetry-derived gravity models is done and reported. The corresponding results revealed that altimetry models almost have identical data content when compared one another, where the DTU13 gave better results with a mean and standard deviation of ?2.40 and 8.71 mGal, respectively. A statistical comparison has been made between different global geopotential models (GGMs) and shipborne gravity data. The Spectral Enhancement Method was applied to overcome the existing spectral gap between the GGMs and shipborne gravity data. EGM2008 manifested the best results with differences characterised with a mean of 1.35 mGal and a standard deviation of 11.11 mGal. Finally, the least-squares collocation (LSC) was implemented to combine the shipborne gravity data with DTU13 in order to create a unique and consistent gravity field over the Red Sea with no data voids. The combined data were independently tested using a total number of 95 randomly chosen shipborne gravity stations. The comparison between the extracted shipborne gravity data and DTU13 altimetry anomalies before and after applying the LSC revealed that a significant improvement is procurable from the combined dataset, in which the mean and standard deviation of the differences dropped from ?3.60 and 9.31 mGal to ?0.39 and 2.04 mGal, respectively.  相似文献   
997.
Natural Resources Research - Unlike in coastal and sedimentary basins, regional-scale exploration of groundwater resources using only geophysical methods is costlier in consolidated rocks such as...  相似文献   
998.
The phytoplankton group’s composition is an excellent indicator of the state of coastal waters. The aim of this study is to explore spatial variability of phytoplankton in shallow coastal areas from different regions (East, Center and West) of the Algerian coast. The quantitative and qualitative study of the phytoplankton population was conducted on samples taken during the 2012-2013 period by the research vessel GRINE BELKACEM. The qualitative results show a significant diversity of diatoms and dinoflagellates, which rank first and second in the total flora (Fr > 50%). This finding is also confirmed quantitatively by the abundance values in both 2013 and 2012 samples which largely exceeds the average value in most other areas of the western region (56%) and slightly exceeding 52% in all central areas which represent an equi-distribution between diatoms and dinoflagellates. The Dinoflagellates contribute significantly to the quantitative richness in the eastern region (>60%). The minimum value of Dia/Dino index, recorded in the eastern region confirms the dominance of the dinoflagellates especially in Skikda (0.31) (Skikda).However, our results reveal the presence, in smaller proportion, of other groups such as the cocolithophoridae and euglenophyceae.  相似文献   
999.
Mean bulk chemical data of recently found H5 and L6 ordinary chondrites from the deserts of Oman generally reflect isochemical features which are consistent with the progressive thermal metamorphism of a common, unequilibrated starting material. Relative differences in abundances range from 0.5–10% in REE (Eu = 14%), 6–13% in siderophile elements (Co = 48%), and >10% in lithophile elements (exceptions are Ba, Sr, Zr, Hf, U = >30%) between H5 and L6 groups. These differences may have accounted for variable temperature conditions during metamorphism on their parent bodies. The CI/Mg‐normalized mean abundances of refractory lithophile elements (Al, Ca, Sm, Yb, Lu, V) show no resolvable differences between H5 and L6 suggesting that both groups have experienced the same fractionation. The REE diagram shows subtle enrichment in LREE with a flat HREE pattern. Furthermore, overall mean REE abundances are ~0.6 × CI with enriched La abundance (~0.9 × CI) in both groups. Precise oxygen isotope compositions demonstrate the attainment of isotopic equilibrium by progressive thermal metamorphism following a mass‐dependent isotope fractionation trend. Both groups show a ~slope‐1/2 line on a three‐isotope plot with subtle negative deviation in ?17O associated with δ18O enrichment relative to δ17O. These deviations are interpreted as the result of liberation of water from phyllosilicates and evaporation of a fraction of the water during thermal metamorphism. The resultant isotope fractionations caused by the water loss are analogous to those occurring between silicate melt and gas phase during CAI and chondrule formation in chondrites and are controlled by cooling rates and exchange efficiency.  相似文献   
1000.
Numerical simulations have been carried out to determine the incompressible free surface flow around a VLCC hull form for which experimental results are available. A commercial viscous flow finite volume code using the two-phase Eulerian–Eulerian fluid approach and a potential flow code based on the Rankine source method have been used in this study. The simulation conditions are the ones for which experimental results exist. The shear stress transport (SST) turbulence model has been used in the viscous flow code. A tetrahedral unstructured grid was used with the viscous flow code for meshing the computational domain, while quadrilateral structural patches were used with the potential flow code for meshing the VLCC hull surface and the water surface around it. The results compare well with the available experimental data and they allow an understanding of the differences that can be expected from viscous and potential flow methods as a result of their different mathematical formulations, which make their complementary application useful for determining the total ship resistance.  相似文献   
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