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421.
422.
海量巡天数据在线可视化是多波段数据融合的应用之一,对大数据时代天文科研工作和科学普及具有重要意义。近年来,国外出现越来越多类似谷歌地图等互联网地图的天图在线可视化系统。为解决拼接生成的大巡天数据文件所导致的在线加载显示缓慢的问题,天文界普遍采用瓦片地图技术。该技术对数据进行分层保存,在浏览器端按需加载、分层显示。HiPS(hierarchicalprogressive survey)和TOAST(tessellated octahedral adaptive subdivision transform)等分层可视化技术以及一些巡天数据拼接和瓦片生成工具,如Hipsgen.jar和Montage等,目前已应用于Aladin Lite,ESASky,WWT(WorldWide Telescope)等在线可视化系统的开发。海量巡天数据在线可视化也遇到一些需要解决的问题,如数据分层导致了数据量的再次增加,巡天图像拼接耗时较长,多信使数据融合显示等。综述了分层可视化技术、瓦片地图金字塔的创建等内容,并对几款主流的在线可视化系统进行了对比分析,讨论了在线可视化遇到的问题及发展方向。 相似文献
423.
Vera Pessina 《Journal of Seismology》1999,3(3):265-277
Simplified approaches for prediction of strong ground shaking, that can be efficiently implemented through a Geographical Information System (GIS), are applied to constructing earthquake scenarios for the Catania municipal area. Ground shaking maps in terms of peak ground acceleration and response spectral ordinates are developed both for a repetition of the catastrophic 1693 earthquake (M7.3), and for a lower energy event, like that which occurred in 1818 (M6.2). The maps account for amplification due to local site conditions. According to the commonly used attenuation relations, the local amplification is taken into account either in a simpler way or in a more detailed approach, derived from an extensive geotechnical zonation. The approximation introduced by the simpler methodology, to be used whenever accurate data are not available, is estimated by a comparison with damage distribution. 相似文献
424.
The main purpose of this study is to obtain the damage scenario for residential buildings in the occurrence of a destructive earthquake (M = 7+) in the city area of Catania, Eastern Sicily, and to illustrate the comparative performance of two alternative methods used for this purpose. The methods are representative of two different approaches to estimating the seismic vulnerability of structures, i.e., an empirical approach based on statistical score assignments (widely used in Italy and other countries) and a more recent, mechanical approach that uses displacement limit states associated with well-defined thresholds of structural damage. A special concern for seismic vulnerability in Catania is caused by the fact that earthquake design norms were enforced in its municipal area only since 1981. We emphasise some typical problems encountered in earthquake scenario work, such as the difficulty of assembling a reliable building inventory, and the uncertainties inherent in the vulnerability assessments through different probabilistic assumptions. Different criteria for the representation of damage are applied and discussed. It is shown that the main scenarios obtained by the two methods are in reasonable agreement, provided a suitable percentile level for damage is chosen in the statistical score assignment approach. 相似文献
425.
从实用角度出发, 讨论了字符识别技术的原理和方法, 分析提取了基本比例尺地形图图幅编号的特征, 提出了图幅编号自动识别的方法。 相似文献
426.
Gunnar Østrem & Nils Haakensen 《Geografiska Annaler: Series A, Physical Geography》1999,81(4):703-711
A number of Norwegian glaciers were selected in the 1960s for long-term mass-balance measurements, to produce necessary hydrological information for hydropower exploitation. Special large-scale glacier maps were produced for field work and data processing, and some glaciers have been mapped more than once. Thus, comparison of glacier maps can be used to calculate changes in glacier volume for some of the glaciers, provided they are of sufficient accuracy.
Conventional mass-balance measurements were carried out on all the selected glaciers. A cumulative calculation of net balances for a series of years is used to indicate the change in a glacier's volume during that period. However, various errors originate in the field, some of which are systematic, particularly on glaciers with large winter accumulation.
The present study indicates that certain errors are difficult to define and determine, For the maritime glacier Ålfotbreen, a cumulative mass-balance calculation gives a positive total balance (+3.4 m water equivalent in the period 1968–88), whereas the map comparison indicates a total negative balance (−5.8 m water equivalent). This indicates a discrepancy between the methods, which must be accounted for.
Determination of errors in mass-balance measurements is difficult. Sinking of stakes in the accumulation area and the use of sounding sticks (steel probes) in heavy snowlayers cause problems. 相似文献
Conventional mass-balance measurements were carried out on all the selected glaciers. A cumulative calculation of net balances for a series of years is used to indicate the change in a glacier's volume during that period. However, various errors originate in the field, some of which are systematic, particularly on glaciers with large winter accumulation.
The present study indicates that certain errors are difficult to define and determine, For the maritime glacier Ålfotbreen, a cumulative mass-balance calculation gives a positive total balance (+3.4 m water equivalent in the period 1968–88), whereas the map comparison indicates a total negative balance (−5.8 m water equivalent). This indicates a discrepancy between the methods, which must be accounted for.
Determination of errors in mass-balance measurements is difficult. Sinking of stakes in the accumulation area and the use of sounding sticks (steel probes) in heavy snowlayers cause problems. 相似文献
427.
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429.
Extending self-organizing maps for supervised classification of remotely sensed data 总被引:1,自引:0,他引:1
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CHEN Yongliang 《世界地质(英文版)》2009,12(1):46-56
An extended self-organizing map for supervised classification is proposed in this paper. Unlike other traditional SOMs, the model has an input layer, a Kohonen layer, and an output layer. The number of neurons in the input layer depends on the dimensionality of input patterns. The number of neurons in the output layer equals the number of the desired classes. The number of neurons in the Kohonen layer may be a few to several thousands, which depends on the complexity of classification problems and the classification precision. Each training sample is expressed by a pair of vectors: an input vector and a class codebook vector. When a training sample is input into the model, Kohonens competitive learning rule is applied to selecting the winning neuron from the Kohonen layer and the weight coefficients connecting all the neurons in the input layer with both the winning neuron and its neighbors in the Kohonen layer are modified to be closer to the input vector, and those connecting all the neurons around the winning neuron within a certain diameter in the Kohonen layer with all the neurons in the output layer are adjusted to be closer to the class codebook vector. If the number of training samples is sufficiently large and the learning epochs iterate enough times, the model will be able to serve as a supervised classifier. The model has been tentatively applied to the supervised classification of multispectral remotely sensed data. The author compared the performances of the extended SOM and BPN in remotely sensed data classification. The investigation manifests that the extended SOM is feasible for supervised classification. 相似文献
430.
It is suggested that the multiple samples in a correlation map or a set of correlation maps should be examined with sig-nificance tests as per the Bernoulli probability, model. Therefore, both the contemporaneous and lag correlations of summertime pre-cipitation R in any one of the three regions of Northern China (NC), the Changjiang-Huaihe River Valley (CHRV), and Southern China (SC) with the SSTA in the global domain have been tested in the present article, using our significance test method and the method proposed by Livezey and Chen (1983) respectively. Our results demonstrate that the contemporaneous correlations of sum-mer R in CHRV with the SSTA are larger than those in NC. Significant correlations of SSTA with CHRV R are found to be in some warm SST regions in the tropics, whereas those of SSTA with NC R, which are opposite in sign as compared to the SSTA-CHRV R correlations, are found to be in some regions where the mean SSTs are low. In comparison with the patterns of the contemporaneous correlations, the 1 to 12 month lag correlations between NC R and SSTA, and those between CHRV summer R and SSTA show simi-lar patterns, including the magnitudes and signs, and the spatial distributions of the coefficients. However, the summer rainfall in SC is not well correlated with the SSTA, no matter how long the lag interval is. The results derived from the observations have set up a relationship frame connecting the precipitation anomalies in NC, CHRV, and SC with the SSTA in the global domain, which is criti-cally useful for our understanding and predicting the climate variabilities in different parts of China Both NC and CHRV summer R are connected with El Nino events, showing a'--'pattern in an El Nino year and a'+ +'pattern in the subsequent year. 相似文献