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131.
The dynamic characteristics of two representative R/C bridges on Egnatia Odos motorway in Greece are estimated based on low amplitude ambient and earthquake-induced vibrations. The present work outlines the instrumentation details, algorithms for computing modal characteristics (modal frequencies, damping ratios and modeshapes), modal-based finite element model (FEM) updating methods for estimating structural parameters, and numerical results for the modal and structural dynamic characteristics of the two bridges based on ambient and earthquake induced vibrations. Transverse, bending and longitudinal modes are reliably identified and stiffness-related properties of the piers, deck and elastomeric bearings of the FEMs of the two bridges are estimated. Results provide qualitative and quantitative information on the dynamic behavior of the bridge systems and their components under low-amplitude vibrations. Modeling assumptions are discussed based on the differences in the characteristics identified from ambient and earthquake vibration measurements. The sources of the differences observed between the identified modal and structural characteristics of the bridges and those predicted by FEMs used for design are investigated and properly justified.  相似文献   
132.
该研究利用学术论文数据库筛选出中国鲤科鱼类游泳能力相关论文115篇,并用Origin软件进行了数据统计分析,旨在归纳和分析中国鲤科鱼类游泳能力并建立估算方法,可为正处于规划阶段和可行性研究阶段的过鱼设施流速设计提供依据.结果表明:(1)鱼类游泳速度与鱼体长度具有显著的非线性相关关系,据此建立了一系列幂函数经验公式,可为游泳能力和过鱼设施研究及设计提供依据.(2)依据所得到的经验公式和协方差分析可知,喜流水型鲤科鱼类的游泳能力>广适型>喜静水型.根据该研究得到的经验公式并结合行业规范和文献资料,对正处于规划阶段和可行性研究阶段过鱼设施流速设计的建议如下:西南地区以裂腹鱼成鱼为主要过鱼对象的过鱼设施进鱼口吸引流速范围为0.61~0.76m/s,通道内最高流速阈值为1.28 m/s;长江中下游以四大家鱼成鱼为主要过鱼对象的进鱼口吸引流速范围为0.76~0.93m/s,通道内最高流速阈值为1.49 m/s,以四大家鱼幼鱼为主要过鱼对象的进鱼口吸引流速范围为0.42~0.62 m/s,通道内最高流速阈值可为0.82 m/s.  相似文献   
133.
Synoptic climatology relates the atmospheric circulation with the surface environment. The aim of this study is to examine the variability of the surface meteorological patterns, which are developing under different synoptic scale categories over a suburban area with complex topography. Multivariate Data Analysis techniques were performed to a data set with surface meteorological elements. Three principal components related to the thermodynamic status of the surface environment and the two components of the wind speed were found. The variability of the surface flows was related with atmospheric circulation categories by applying Correspondence Analysis. Similar surface thermodynamic fields develop under cyclonic categories, which are contrasted with the anti-cyclonic category. A strong, steady wind flow characterized by high shear values develops under the cyclonic Closed Low and the anticyclonic H–L categories, in contrast to the variable weak flow under the anticyclonic Open Anticyclone category.  相似文献   
134.
Due to their ready availability and temporal and spatial consistency, reanalysis data are widely used within the climate community. Nevertheless, higher spatial resolutions are often required and statistical interpolation techniques are applied to increase the data resolution. This work aims to derive a set of high spatial resolution data through three-dimensional interpolation of daily temperature and precipitation. Thin plate spline interpolation has been chosen and used to interpolate ERA-40 temperature and precipitation from a coarse grid (110 km) into a finer one of 1-km spatial resolution. The study evaluates the method by comparing the simulated variables with available in situ meteorological measurements. The chosen stations are distributed over the study region and, most importantly, contain information from a range of altitudes. The results indicate that accounting for the topography in the interpolation process improves the comparisons, with the biggest improvements being evident in the most mountainous areas. The method is found to be better in estimating temperature than precipitation fields. Moreover, the method performs better for maximum temperature in high altitudes and for minimum temperature in low altitudes.  相似文献   
135.
136.
An analytical solution is presented for the response of a non-homogeneous, compressible, elastic half-space to a time-harmonic vertical point load on its surface. The shear modulus is assumed to increase continuously with depth. The model is chosen so as to describe uniformly deposited cohesionless soils. Expressions for displacements and stresses in the interior of the half-space medium are derived by means of Hankel transforms and contour integration. Selected numerical results are presented to demonstrate the influence of non-homogeneity. Finally, some effects are pointed out to be used in connection with vibration tests for subsoil investigation.  相似文献   
137.
Nine methods to determine local-scale aerodynamic roughness length \((z_{0})\) and zero-plane displacement \((z_{d})\) are compared at three sites (within 60 m of each other) in London, UK. Methods include three anemometric (single-level high frequency observations), six morphometric (surface geometry) and one reference-based approach (look-up tables). A footprint model is used with the morphometric methods in an iterative procedure. The results are insensitive to the initial \(z_{d}\) and \(z_{0}\) estimates. Across the three sites, \(z_{d}\) varies between 5 and 45 m depending upon the method used. Morphometric methods that incorporate roughness-element height variability agree better with anemometric methods, indicating \(z_{d}\) is consistently greater than the local mean building height. Depending upon method and wind direction, \(z_{0}\) varies between 0.1 and 5 m with morphometric \(z_{0}\) consistently being 2–3 m larger than the anemometric \(z_{0}\). No morphometric method consistently resembles the anemometric methods. Wind-speed profiles observed with Doppler lidar provide additional data with which to assess the methods. Locally determined roughness parameters are used to extrapolate wind-speed profiles to a height roughly 200 m above the canopy. Wind-speed profiles extrapolated based on morphometric methods that account for roughness-element height variability are most similar to observations. The extent of the modelled source area for measurements varies by up to a factor of three, depending upon the morphometric method used to determine \(z_{d}\) and \(z_{0}\).  相似文献   
138.
139.
An investigation was carried out to delineate the hydrogeologic framework and to understand groundwater quality of the Kompsatos River fan aquifer system, northeastern Greece, as well as to assess environmental impact induced by human activities. As groundwater is the only major source of water in this area, it is important to know the effect of geological formations, and anthropogenic activities on groundwater chemistry and environment. A thorough hydrogeological study was performed during the period 2004–2007. The differential river gauging method was used for estimating the volume of water leaking from (or discharging into) the river. Groundwater samples were collected from 89 monitoring wells, during the summer period of 2007, and analyzed for major ions and trace elements. A potential reservoir of groundwater is formed within the Kompsatos River fan. The aquifer system/Kompsatos River interaction is the outstanding feature of this area. Ca–Mg–HCO3–SO4 is the dominant water type as a result of dissolving carbonate salts. B, Ba, Mn, Li, Sr, and Zn are the most abundant trace elements in groundwater. Both the major-ion chemistry and trace element enrichment of the groundwater are controlled by mineral dissolution and water–rock interaction. Nitrate contamination of groundwater is related to agricultural practices. An improperly constructed drainage system led locally to salinization of groundwater. Channelization has caused considerable disruption to the river ecosystem. The eventual construction of a dam on the river will adversely affect the environment and the aquifer system. The lack of managerial policy for water is putting environmental resources and water supply in jeopardy.  相似文献   
140.
Anhydritic claystones are among the most problematic rocks in tunnelling. Their swelling has caused serious damage and high repair costs in a number of tunnels, especially in Switzerland and southwest Germany. The swelling is usually attributed to the transformation of anhydrite into gypsum. It is a markedly time-dependent process which might take several decades to complete in nature. The present paper focusses on simultaneous anhydrite dissolution and gypsum precipitation in a closed system, i.e. disregarding the transport processes that may also be important for the evolution of the swelling process. The paper begins with a presentation of the governing equations and continues with parametric studies in order to investigate the role of the initial volumetric fractions of the constituents and the specific surface areas of the minerals involved. A simplified model for the hydration of anhydrite is also proposed, which identifies the governing process and the duration of the swelling process. Finally, parametric studies are performed in order to investigate the effect of the anhydrite surface being sealed by the formation of gypsum. The latter slows down the swelling process considerably.  相似文献   
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