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991.
An Urban Surface Exchange Parameterisation for Mesoscale Models 总被引:9,自引:11,他引:9
A scheme to represent the impact of urban buildings on airflow in mesoscale atmospheric models is presented. In the scheme, the buildings are not explicitly resolved, but their effects on the grid-averaged variables are parameterised. An urban quarter is characterised by a horizontal building size, a street canyon width and a building density as a function of height. The module computes the impact of the horizontal (roof and canyon floor) and vertical (walls) surfaces on the wind speed, temperature and turbulent kinetic energy. The computation of the shortwave and longwave radiation, needed to compute the temperature of the urban surfaces, takes into account the shadowing and radiation trapping effects induced by the urban canyons. The computation of the turbulent length scales in the TKE equation is also modified to take into account the presence of the buildings.The parameterisation is introduced into a mesoscale model and tested in a bidimensional case of a city over flat terrain. The new parameterisation is shown to be able to reproduce the most important features observed in urban areas better than the traditional approach which is based only on the modification of the roughness length, thereby retaining the Monin–Obukhov similarity theory. The new surface exchange parameterisation is furthermore shown to have a strong impact on the dispersion characteristics of air pollutants in urban areas. 相似文献
992.
993.
GPS变形监测系统中消除噪声的一种有效方法 总被引:21,自引:1,他引:21
GPS变形监测系统的观测资料可看成为与时间有关的数据序列,应用小波分析理论,研究了时间序列观测数据的误差消除问题。结果表明,借助于小波分解与重构,可有效地从强噪声干扰的观测数据序列中提取变形特征。该方法解决了传统处理技术对非平稳、非等时间间隔观测数据序列滤波的局限性问题。 相似文献
994.
小波理论用于地图数据处理中若干理论问题的探讨 总被引:4,自引:0,他引:4
从理论上分析用紧支集小波处理地图矢量数据时遇到的点位漂移和端点附近图形畸变等问题,给出解决上述问题的具体方法,并用实例验证所给方法的正确性,为小波理论在地图数据分析和处理中的应用做必要的理论准备。 相似文献
995.
996.
Factors controlling the magnitudes of, and short-term variations in, the potential temperatures of the snow surface and the
air at the height of 2 m θS and θ2 m over Arctic sea ice in winter are analysed. The study addresses the winters of 1986–1987 and 1987–1988, and is based on the
temperature, wind, and cloud observations made by Russian drifting ice stations. It also relies on the ERA40 re-analyses of
the European Centre for Medium-Range Weather Forecasts, which were utilised to calculate the lateral heat advection at the
sites of the ice stations. The cloud cover and wind speed were more important than the heat advection in controlling the magnitudes
of θ2 m and θS, while on a time scale of 24 h, during steady forcing conditions, the heat advection was the most important factor affecting
the changes in θS and θ2 m. During changing conditions, and considering individual factors separately, the monthly mean 24-h temperature changes were
less than ± 5 °C: the effect of the cloud cover was the largest, and that of the heat advection was the smallest. When simultaneous
changes in the three factors were analysed, the seasonal mean temperature changes were even of the order of ±15 °C, with the
strongest warming events exceeding 35 K in a single day. The difference θS − θ2 m reached its lowest seasonal mean values during conditions of clear skies (−1.3 °C), light winds (−1.3 °C) and warm-air advection
(−0.8 °C). θS and θ2 m followed each other closely, even during major synoptic-scale temperature variations. 相似文献
997.
Wavelet analysis of rainfall variation in the Hebei Plain 总被引:5,自引:0,他引:5
XU Yueqing LI Shuangcheng & CAI Yunlong Key Laboratory for Earth Surface Process Ministry of Education Department of Resources Environmental Geosciences College of Environmental Sciences Peking University Beijing China 《中国科学D辑(英文版)》2005,48(12):2241-2250
Rainfall is an important climate factor, which has significant impacts on agricultural production and na-tional economic development[1]. Being part of the North China Plain, the Hebei Plain is an agricultural region. Under the continental monsoon climate, it is cold and dry in winter, hot and rainy in summer, and its variable rainfall is concentrated in summer. Droughts and floods occur frequently and impose sig-nificant impacts on agricultural production. Studies on the characteristics and … 相似文献
998.
地震道的奇性检测与提高分辨率 总被引:2,自引:0,他引:2
地震道蕴涵有丰富的奇性特征,而地震子波的起跳点是形成地震道奇性特征的主要原因。样条函数是间段性和连续性的对立统一体。对于地震道,子波起跳点(波至)具有某种意义上的间断性。针对地震道的奇性特征,应用了奇性检测算法,具体过程为:首先以样条函数为尺度函数,构造一个低通滤波器,采用小波包的思想,定义一个算子,使低频分量逐步迭代地从原始信号中分离出,便可以对地震道信号进行奇性分解。经过理论模型和实际资料的处理,能显著提高分辨率,对于面波的去除也很理想;此算法没有任何假设条件的约束。 相似文献
999.
用小波变换提取雷达回波图像中的辐合特征线 总被引:1,自引:1,他引:0
采用小波变换的方法对滨州雷达资料的反射率图像进行处理,得到特征线增强后的图像,将其输入自动预报系统实现特征识别,可为雷暴预报提供初步资料。 相似文献
1000.
小波变换理论的线状要素制图综合研究 总被引:1,自引:0,他引:1
空间数据的多尺度表达问题已成为G IS研究的重点,也是地图自动综合的瓶径,如何解决智能化的多尺度表达是迫切需要解决的问题。基于小波分析原理和制图综合原理,利用线状要素的极角变化,对线状要素进行平滑和综合,实现了线状要素数据的制图综合。 相似文献