全文获取类型
收费全文 | 959篇 |
免费 | 148篇 |
国内免费 | 69篇 |
专业分类
测绘学 | 50篇 |
大气科学 | 29篇 |
地球物理 | 201篇 |
地质学 | 442篇 |
海洋学 | 57篇 |
天文学 | 20篇 |
综合类 | 59篇 |
自然地理 | 318篇 |
出版年
2023年 | 8篇 |
2022年 | 45篇 |
2021年 | 60篇 |
2020年 | 47篇 |
2019年 | 55篇 |
2018年 | 48篇 |
2017年 | 55篇 |
2016年 | 45篇 |
2015年 | 52篇 |
2014年 | 49篇 |
2013年 | 66篇 |
2012年 | 69篇 |
2011年 | 53篇 |
2010年 | 45篇 |
2009年 | 38篇 |
2008年 | 45篇 |
2007年 | 55篇 |
2006年 | 36篇 |
2005年 | 35篇 |
2004年 | 34篇 |
2003年 | 27篇 |
2002年 | 18篇 |
2001年 | 18篇 |
2000年 | 32篇 |
1999年 | 24篇 |
1998年 | 15篇 |
1997年 | 17篇 |
1996年 | 16篇 |
1995年 | 7篇 |
1994年 | 10篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1982年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有1176条查询结果,搜索用时 15 毫秒
991.
992.
Similar to most mountain glaciers in the world, Urumqi Glacier No. 1 (UG1), the best observed glacier in China with continued glaciological and climatological monitoring records of longer than 50 years has experienced an accelerated recession during the past several decades. The purpose of this study is to investigate the acceleration of recession. By taking UG1 as an example, we analyze the generic mechanisms of acceleration of shrinkage of continental mountain glaciers. The results indicate that the accel... 相似文献
993.
Glacial features in the geological record provide essential clues about past behavior of climate. Of the numerous physical systems on earth, glaciers are one of most responsive to climate change, especially small glaciers, their direct marginal response taking only a few years or decades to be expressed. Accelerating recession of modern glaciers raises the issue of the climate’s impact on water runoff. Data based on topographic maps and Advanced Spaceborne Thermal Emission and Radiometer (ASTER) imagery sho... 相似文献
994.
995.
Two decades have passed since China and Japan jointly launched hydrological & climatological observations on the glaciers in Tanggula Pass, Tibetan Plateau. Although the research institutions involved have been either restructured or renamed, their work, between 1989 and 1993, was ground-breaking and remains significant even to this day. Some observation sites established at that time are still utilized for large-scaled projects sponsored by GAME/Tibet, NSFC (Natural Science Foundation of China) and the Major State Basic Research Development Program of China (973 Program). Recently, a glacier monitoring system has been established on the cap of Dongkemadi Glacier, and is expected to make further contributions to research on the change of the cryospheric and climatic environment in the area. 相似文献
996.
1973-2010年青藏高原西部昂拉仁错流域气候、冰川变化与湖泊响应 总被引:11,自引:6,他引:5
采用距离昂拉仁错最近的狮泉河、改则和普兰地区1973-2010年的气象数据和覆盖昂拉仁错流域1973、1976、1990、2000、2001、2002和2009年共7a的Landsat卫星遥感影像提取湖泊变化信息,并选取1976、1990/1992、2001和2009年覆盖全流域的遥感影像分析流域内的冰川变化过程.分析过去近40a内昂拉仁错流域内气候、湖泊和冰川的变化,并探讨了不同时期引起昂拉仁错发生变化的原因.结果表明:昂拉仁错在过去近40a内出现先萎缩后扩张的变化趋势,2000年为转折年,整体的变化趋势为萎缩;流域内冰川在研究时段内一直处于萎缩状态,并持续补给昂拉仁错.分析比较流域附近3个站在气温、降水量和最大潜在蒸发量的变化趋势之后,选用与昂拉仁错流域气候变化最为相近的改则站的气象参数为参照分析引起昂拉仁错湖泊面积发生变化的原因.结果显示,昂拉仁错湖面变化的每个时期内,在气温持续升高、冰川持续消融补给昂拉仁错水量输入的背景环境下,蒸发量和降水量差值的变化主要调控了湖泊面积的变化;区域冰川量的减少与温度持续升高相匹配;当持续增加的冰雪融水与降水量对湖泊水量输入小于流域蒸发量时,湖泊面积萎缩;当冰川冻土随着温度进一步升高而加速融化、流域的降水量逐步上升;当二者的水量输入总和超过流域内蒸发量时,湖泊面积开始扩张. 相似文献
997.
目前,世界上还有许多国家的海洋边界没得到确定,由此引起的国家间海上争端事件不断。因此,开展海洋划界技术和方法研究,科学精确地确定两国间海洋边界显得十分必要。本文阐述了基于墨卡托投影的海图进行海上划界方法的不足,研究了利用高斯平均引数大地主题解算计算点到大地线的球面距离模型,最后设计了基于地球椭球面模型的等比例海上划界算法,并基于ArcGIS Engine实现划界功能。 相似文献
998.
Glaciological controls on debris cover formation are investigated from the perspective of primary dispersal of supraglacial debris across a melting ice surface. This involves the migration of angled debris septa outcrops across a melting, thinning glacier ablation zone. Three measures of a glacier's ability to evacuate supraglacial debris are outlined: (1) a concentration factor describing the focusing of englacial debris into specific supraglacial mass loads; (2) the rate of migration of a septum outcrop relative to the local ice surface; and (3) a downstream velocity differential between a slower septum outcrop and the faster ice surface velocity. Measures (1) and (2) are inversely related, while measure (3) increases down‐glacier to explain why slow‐moving, thinning ice rapidly becomes debris covered. Data from Glacier d'Estelette (Italian Alps) are used to illustrate these processes, and to explore the potential for debris cover formation and growth in different glaciological environments. The transition from a ‘clean’, transport‐dominated to a debris‐covered ablation‐dominated glacier is explained by the melting out of more closely‐spaced debris septa, in combination with the geometric interactions of angled septa and ice surface in a field of reducing flow and increasing ablation. The growth and shrinkage of debris covers are most sensitive to glaciological changes at glaciers with gently‐dipping debris‐bearing foliation, but less sensitive at high‐compression glaciers whose termini are constrained by moraine dams and other forms of obstruction. These findings show that a variety of debris‐covered glacier types will show a spectrum of response characteristics to negative mass balance. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
999.
Biswajit Mukhopadhyay 《水文科学杂志》2013,58(12):2062-2085
AbstractField observations and geodetic measurements suggest that in the Karakoram Mountains, glaciers are either stable or have expanded since 1990, in sharp contrast to glacier retreats that are prevalently observed in the Himalayas and adjoining high-altitude terrains of central Asia. Decreased discharge in the rivers originating from this region is cited as a supporting evidence for this somewhat anomalous phenomenon. Here, we show that river discharge during the melting season of the glaciers in the eastern and western Karakoram, respectively, exhibits rising and falling trends. We have implemented a statistical procedure involving non-parametric tests combined with a benchmark smoothing technique that has proven to be a powerful method for separating the stochastic component from the trend component in a time series. Precipitation patterns determined from ERA-40 and GPCP data indicate that summer-monsoonal precipitation has increased over the Karakoram Mountains in recent decades. Increasing flows in June and July in the eastern Karakoram are due to an increase in summer-monsoonal precipitation. The rising trend of August discharge is due to an increase in the loss of glacier storage at an approximate average rate of 0.186–0.217 mm d-1 year-1 during the period 1973–2010. Moreover, this rate is higher than the rate of increase in monsoonal snowfall during the months of August and September. Therefore, most plausibly, glacier mass balance in the eastern Karakoram is negative. In the western Karakoram, river flows show declining trends for all summer months for the period 1966–2010, corresponding to a rate of increase of glacier storage by approximately 0.552–0.644 mm d-1 year-1, which is also higher than the rate of increase in summer-monsoonal precipitation. The gain of the cryospheric mass in the western Karakoram is in the form of increased thickness of the glaciers and perennial snowpacks instead of areal expansion. This investigation shows two contrasting patterns of trends of river flows that signify both negative and positive mass balance of the Karakoram glaciers. Trends of river flows are spatially and temporally integrated responses of a watershed to changing climate and thereby are important signals of the conditions of the cryospheric component of a watershed where it is highly significant. However, they cannot unequivocally provide indications of the state and fate of the glaciers in the complex hydrometeorological setting of the Karakoram. Extreme caution and care must be exercised in interpreting trends of river discharge in conjunction with climatic data. 相似文献
1000.
Glaciers are widely recognized as key indicators of climate change, and melt water obtained from them is an important source of fresh water and for hydropower generation. Regular monitoring of a large number of Himalayan glaciers is important for improving our knowledge of glacier response to climate change. In the present study, Survey of India topographical maps (1966) and Landsat datasets as ETM+ (2000, 2006) and TM (2011) have been used to study glacier fluctuations in Tirungkhad basin. A deglaciation of 26.1% (29.1?km2) in terms of area from 1966 to 2011 was observed. Lower altitude small glaciers (area?<?1?km2) lost more ice (34%), while glaciers with an area <10?km2 lost less (20%). The percentage of change in glacier length was 26% (31.9?km) from 1966 to 2011. The south-facing glaciers showed high percentages of loss. From 2000 to 2011, debris cover has increased by 1.34%. The analysis of the trend in meteorological data collected from Kalpa and Purbani stations was carried out by Mann Kendall non-parametric method. During the last two decades, the mean annual temperature (Tmax and Tmin) has increased significantly, accompanied with a fall in snow water equivalent (SWE) and rainfall. The increasing trend in temperature and decreasing trend in SWE were significant at 95% confidence level. This observation shows that the warming of the climate is probably one of the major reasons for the glacier change in the basin. 相似文献