首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   3955篇
  免费   147篇
  国内免费   32篇
测绘学   88篇
大气科学   293篇
地球物理   1459篇
地质学   1214篇
海洋学   299篇
天文学   586篇
综合类   16篇
自然地理   179篇
  2021年   63篇
  2020年   60篇
  2019年   49篇
  2018年   132篇
  2017年   138篇
  2016年   220篇
  2015年   157篇
  2014年   187篇
  2013年   250篇
  2012年   166篇
  2011年   173篇
  2010年   181篇
  2009年   200篇
  2008年   164篇
  2007年   155篇
  2006年   99篇
  2005年   95篇
  2004年   111篇
  2003年   93篇
  2002年   63篇
  2001年   58篇
  2000年   61篇
  1999年   48篇
  1998年   57篇
  1997年   48篇
  1996年   56篇
  1995年   35篇
  1994年   48篇
  1993年   43篇
  1992年   37篇
  1991年   29篇
  1990年   45篇
  1989年   33篇
  1988年   35篇
  1987年   30篇
  1986年   41篇
  1985年   27篇
  1984年   44篇
  1983年   40篇
  1982年   41篇
  1981年   27篇
  1980年   24篇
  1979年   38篇
  1978年   33篇
  1977年   29篇
  1975年   24篇
  1974年   30篇
  1973年   28篇
  1972年   29篇
  1971年   30篇
排序方式: 共有4134条查询结果,搜索用时 15 毫秒
51.
52.
53.
54.
55.
International Journal of Earth Sciences - The Juchatengo complex (JC) suite is located between the Proterozoic Oaxacan complex to the north and the Xolapa complex to the south, and was amalgamated...  相似文献   
56.
Given its geological and climatic conditions and its rugged orography, Asturias is one of the most landslide prone areas in the North of Spain. Most of the landslides occur during intense rainfall episodes. Thus, precipitation is considered the main triggering factor in the study area, reaching average annual values of 960 mm. Two main precipitation patterns are frequent: (i) long-lasting periods of moderate rainfall during autumn and winter and (ii) heavy short rainfall episodes during spring and early summer. In the present work, soil moisture conditions in the locations of 84 landslides are analysed during two rainfall episodes, which represent the most common precipitation patterns: October–November 2008 and June 2010. Empirical data allowed the definition of available water capacity percentages of 99–100% as critical soil moisture conditions for the landslide triggering. Intensity-duration rainfall thresholds were calculated for each episode, considering the periods with sustained high soil moisture levels before the occurrence of each analysed landslide event. For this purpose, data from daily water balance models and weather stations were used. An inverse relationship between the duration of the precipitation and its intensity, consistent with published intensity-duration thresholds, was observed, showing relevant seasonal differences.  相似文献   
57.
The method of water quality index is widely used in evaluation of the surface water quality because of its capability to summarize a number of water quality parameters into one numeric value, along with defined scale of water quality range. The current investigation includes application of modified model for calculating water quality index values, generated using experimental data and literary models. Software was created using modular design. Fourteen physical, chemical and biological parameters representing water quality state along with the assigned weights were elected. Comparison between models generated based on Serbian and American models of water quality index was done. Selected parameters differ mutually in number of parameters used in calculation of index, as well as in values of the weighting factors. In order to enable an efficient water quality analysis and to reconcile the requirements of both Serbian and American model, two software solutions were generated and processed on the example of the water quality of the Danube River in Serbia. Danube water quality was assessed at seventeen measuring locations along the river flow. Index values obtained from the two generated software applications were compared with the results of the official Serbian online calculator. Water quality determined using new generated models shows stricter approach and one class lower water quality compared to the existing Serbian model. Therefore, modular and open-generated simulation software is of great significance for the comparison and testing of different water quality models, not just those two shown in this study.  相似文献   
58.
An unsupervised machine-learning workflow is proposed for estimating fractional landscape soils and vegetation components from remotely sensed hyperspectral imagery. The workflow is applied to EO-1 Hyperion satellite imagery collected near Ibirací, Minas Gerais, Brazil. The proposed workflow includes subset feature selection, learning, and estimation algorithms. Network training with landscape feature class realizations provide a hypersurface from which to estimate mixtures of soil (e.g. 0.5 exceedance for pixels: 75% clay-rich Nitisols, 15% iron-rich Latosols, and 1% quartz-rich Arenosols) and vegetation (e.g. 0.5 exceedance for pixels: 4% Aspen-like trees, 7% Blackberry-like trees, 0% live grass, and 2% dead grass). The process correctly maps forests and iron-rich Latosols as being coincident with existing drainages, and correctly classifies the clay-rich Nitisols and grasses on the intervening hills. These classifications are independently corroborated visually (Google Earth) and quantitatively (random soil samples and crossplots of field spectra). Some mapping challenges are the underestimation of forest fractions and overestimation of soil fractions where steep valley shadows exist, and the under representation of classified grass in some dry areas of the Hyperion image. These preliminary results provide impetus for future hyperspectral studies involving airborne and satellite sensors with higher signal-to-noise and smaller footprints.  相似文献   
59.
Natural Hazards - The seismically induced ground failure is defined as any earthquake-generated process that leads to deformations within a soil medium, which in turn results in permanent...  相似文献   
60.
Geoarchaeological investigations on the northeastern shore of Lake Ohrid revealed 3.5 m thick deepwater lacustrine sediments overlying terrestrial vegetation macrofossils, worked wood and abundant potsherds dated to the Late Bronze Age (LBA). Distinct contact of deepwater sediment with the sub-aerial weathered limestone bedrock point to a sudden increase in lake level. According to radiocarbon data, catastrophic flooding occurred shortly after 1214 yr bc. Because the area is located in a highly active seismic zone, we propose that this event was caused by tectonically induced, metre-scale coseismic subsidence related to faults bordering the Ohrid alluvial plain. Moreover, this event coincides well with a dramatic switch in the habitation and settlement strategy in the region. More important, however, is the finding that the age of the proposed massive tectonic event and change in habitation lies within the interval of the proposed ‘earthquake storm’ in the eastern Mediterranean dated to 1225–1175 bc. As the Ohrid-Korça zone belongs to the same tectonic province, a relationship between the abovementioned earthquakes and the proposed event can be expected. This research therefore might provide the first direct evidence of a large-scale earthquake event linkable to the LBA collapse of Europe's first urban civilisation in the Aegean.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号