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411.
On the basis of our predecessors' research,we study the distribution and the space-time evolution characteristics of the seismic apparent strain field in Yunnan since the 1970's using the seismic data of Yunnan and its surrounding areas.The result shows that there is a rather strong corresponding relationship between the anomaly region of seismic apparent strain and strong earthquakes.In the nine earthquakes studied,anomaly areas of seismic apparent strain had appeared before eight earthquakes,including five occurring in the anomaly region and three on the edge.Finally,the investigative result is demonstrated primarily. 相似文献
412.
413.
Stochastic modelling of soil moisture dynamics in a grassland of Qilian Mountain at point scale 总被引:2,自引:0,他引:2
Stochastic modeling of soil moisture dynamics is crucial to the quantitative understanding of plant responses to water stresses,hydrological control of nutrient cycling processes,water competition among plants,and some other ecological dynamics,and thus has become a hotspot in ecohydrology at present.In this paper,we based on the continuously monitored data of soil moisture during 2002―2005 and daily precipitation date of 1992―2006,and tried to make a probabilistic analysis of soil moisture dynamics at point scale in a grassland of Qilian Mountain by integrating the stochastic model improved by Laio and the Monte Carlo method.The results show that the inter-annual variations for the soil moisture patterns at different depths are very significant,and that the coefficient of variance(CV) of surface soil moisture(20 cm) is almost continually kept at about 0.23 whether in the rich or poor rainy years.Interestingly,it has been found that the maximal CV of soil moisture has not always appeared at the surface layer.Comparison of the analytically derived soil moisture probability density function(PDF) with the statistical distribution of the observed soil moisture data suggests that the stochastic model can reasonably describe and predict the soil moisture dynamics of the grassland in Qilian Mountain at point scale.By extracting the statistical information of the historical precipitation data in 1994―2006,and inputting them into the stochastic model,we analytically derived the long-term soil moisture PDF without considering the inter-annual climate fluctuations,and then numerically derived the one when considering the inter-annual fluctuation effects in combination with a Monte-Carlo procedure.It was found that,though the peak position of the probability density distribution significantly moved towards drought when considering the disturbance forces,and its width was narrowed,accordingly its peak value was increased,no significant bimodality was observed in the soil moisture dynamics under the given intensity of random fluctuation disturbance. 相似文献
414.
415.
Steve Wallis 《Acta Geophysica》2007,55(1):85-94
The simulation of solute transport in rivers is frequently based on numerical models of the Advection-Dispersion Equation.
The construction of reliable computational schemes, however, is not necessarily easy. The paper reviews some of the most important
issues in this regard, taking the finite volume method as the basis of the simulation, and compares the performance of several
types of scheme for a simple case of the transport of a patch of solute along a uniform river. The results illustrate some
typical (and well known) deficiencies of explicit schemes and compare the contrasting performance of implicit and semi-Lagrangian
versions of the same schemes. It is concluded that the latter have several benefits over the other types of scheme. 相似文献
416.
Tomasz Niedzielski 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(6):649-664
This paper aims to compare the performances of multivariate autoregressive (MAR) techniques and univariate autoregressive
(AR) methods applied to regional scale rainfall-runoff modelling. We focus on the case study from the upper and middle reaches
of the Odra River with its main tributaries in SW Poland. The rivers drain both the mountains (the Sudetes) and the lowland
(Nizina Śląska). The region is exposed to extreme hydrologic and meteorological events, especially rain-induced and snow-melt
floods. For the analysis, four hydrologic and meteorological variables are chosen, i.e., discharge (17 locations), precipitation
(7 locations), thickness of snow cover (7 locations) and groundwater level (1 location). The time period is November 1971–December
1981 and the temporal resolution of the time series is of 1 day. Both MAR and AR models of the same orders are fitted to various
subsets of the data and subsequently forecasts of discharge are derived. In order to evaluate the predictions the stepwise
procedure is applied to make the validation independent of the specific sample path of the stochastic process. It is shown
that the model forecasts peak discharges even 2–4 days in advance in the case of both rain-induced and snow-melt peak flows.
Furthermore, the accuracy of discharge predictions increases if one analyses the combined data on discharge, precipitation,
snow cover, and groundwater level instead of the pure discharge multivariate time series. MAR-based discharge forecasts based
on multivariate data on discharges are more accurate than AR-based univariate predictions for a year with a flood, however,
this relation is reverse in the case of the free-of-flooding year. In contrast, independently of the occurrence of floods
within a year, MAR-based discharge forecasts based on discharges, precipitation, snow cover, and groundwater level are more
precise than AR-based predictions. 相似文献
417.
A simple two-domain bucket model of fractured soil was coupled with a stochastic model of rainfall variability, in order to investigate the climate and soil controls upon the stochastic properties of the triggering of fracture flow and surface runoff, and the partitioning of rainfall between the matrix and fracture domains and surface runoff. Conventionally, soils are regarded as time domain filters between rainfall and hydrological response. This investigation highlights an additional type of threshold filtering especially important in understanding the infiltration behaviour of fractured soils, for which an event-based characterisation of rainfall in modelling is crucial. A priori-definable indices were derived which are capable of describing elements of this threshold filtering, by allowing the statistical properties of fracture flow- and surface runoff-triggering storms (i.e., mean and variance of storm duration, intensity and effective inter-storm period, as well as cumulative partitioning of rainfall), to be inferred directly from average storm and soil properties. Using these indices, the long-term response of fractured soils, including the long-term hydrological importance of fractures, can be estimated without simulation. 相似文献
418.
Active meandering rivers are capable of reworking and removing large quantities of valuable land. Therefore, understanding the characteristics of meandering rivers and predicting future meander behaviour can be of great value for local authorities. In this study, we apply a topographic steering meander model to the Geul River (southern Netherlands), using field data to calibrate the model. The present channel characteristics of the Geul River were mapped in the field. Cut‐banks were classified as erosive, unstable or stable. The model outcomes were compared with these field data. Several model runs were carried out, using different sets of parameter values. After studying the results and using the field data, we introduced the concept of a variable channel width in the simulation model. In reality, the river has different channel widths varying from 8 to more than 15 m. These widths are a linear function of local curvature. The model runs using a variable channel width show that the model is capable of predicting locations of lateral migration in conformity with observed active lateral migration and erosive banks. With both models, the sediment reworking time of the floodplain can be calculated. Floodplain reworking times of 200–300 years were calculated. In combination with the lateral migration rate, this reworking time is an important element in catchment sediment budget calculations. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
419.
The concept of distributed strain‐sensing techniques has been proposed in our recent research, which was dedicated to utilizing the strain distributions throughout the full or partial areas of structures to detect arbitrary and unforeseen damage. An algorithm not requiring a detailed analytical model is presented for damage locating in flexural structures through the direct use of dynamic responses recorded by distributed long‐gauge strain sensors. The modal macro‐strain vector (MMSV), which has been proven to have a mapping relation with displacement mode shape, can be extracted directly from macro‐strain time‐series data, from which a damage evaluating index can be derived and used as an indicator for locating damage. Numerical examples are simulated to verify the sensitivity and effectiveness of the index in different cases. Furthermore, experimental investigations on a cantilevered beam with various long‐gauge fibre optic sensors placements are carried out to examine the feasibility and applicability of the proposed method. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
420.
This paper examines the limitations and deficiencies of the current British archaeomagnetic calibration curve and applies several mathematical approaches in an attempt to produce an improved secular variation curve for the UK for use in archaeomagnetic dating. The dataset compiled is the most complete available in the UK, incorporating published results, PhD theses and unpublished laboratory reports. It comprises 620 archaeomagnetic (directional) data and 238 direct observations of the geomagnetic field, and includes all relevant information available about the site, the archaeomagnetic direction and the archaeological age. A thorough examination of the data was performed to assess their quality and reliability. Various techniques were employed in order to use the data to construct a secular variation (SV) record: moving window with averaging and median, as well as Bayesian statistical modelling. The SV reference curve obtained for the past 4000 years is very similar to that from France, most differences occurring during the early medieval period (or Dark Ages). Two examples of dating of archaeological structures, medieval and pre-Roman, are presented based on the new SV curve for the UK and the implications for archaeomagnetic dating are discussed. 相似文献