全文获取类型
收费全文 | 1426篇 |
免费 | 106篇 |
国内免费 | 136篇 |
专业分类
测绘学 | 159篇 |
大气科学 | 149篇 |
地球物理 | 280篇 |
地质学 | 418篇 |
海洋学 | 118篇 |
天文学 | 306篇 |
综合类 | 53篇 |
自然地理 | 185篇 |
出版年
2023年 | 15篇 |
2022年 | 19篇 |
2021年 | 23篇 |
2020年 | 33篇 |
2019年 | 46篇 |
2018年 | 35篇 |
2017年 | 43篇 |
2016年 | 39篇 |
2015年 | 41篇 |
2014年 | 66篇 |
2013年 | 64篇 |
2012年 | 49篇 |
2011年 | 66篇 |
2010年 | 37篇 |
2009年 | 91篇 |
2008年 | 85篇 |
2007年 | 97篇 |
2006年 | 87篇 |
2005年 | 77篇 |
2004年 | 81篇 |
2003年 | 68篇 |
2002年 | 49篇 |
2001年 | 50篇 |
2000年 | 54篇 |
1999年 | 34篇 |
1998年 | 42篇 |
1997年 | 26篇 |
1996年 | 26篇 |
1995年 | 24篇 |
1994年 | 14篇 |
1993年 | 21篇 |
1992年 | 25篇 |
1991年 | 19篇 |
1990年 | 12篇 |
1989年 | 23篇 |
1988年 | 10篇 |
1987年 | 14篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1980年 | 4篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1974年 | 1篇 |
1973年 | 4篇 |
1972年 | 10篇 |
1971年 | 7篇 |
排序方式: 共有1668条查询结果,搜索用时 15 毫秒
991.
Geoffrey M. Jacquez 《Journal of Geographical Systems》2000,2(1):91-97
This paper summarizes contributions of GIS in epidemiology, and identifies needs required to support spatial epidemiology
as science. The objective of spatial epidemiology is to identify disease causes and correlates by relating spatial disease
patterns to geographic variation in health risks. GIS supports disease mapping, location analysis, the characterization of
populations, and spatial statistics and modeling. Although laudable, these accomplishments are not sufficient to fully identify
disease causes and correlates. One reason is the failure of present-day GIS to provide tools appropriate for epidemiology.
Two needs are most pressing. First, we must reject the static view: meaningful inference about the causes of disease is impossible
without both spatial and temporal information. Second, we need models that translate space-time data on health outcomes and putative exposures into
epidemiologically meaningful measures. The first need will be met by the design and implementation of space-time information
systems for epidemiology; the second by process-based disease models. 相似文献
992.
使用反映降水强度的各时段最大降水、各量级降水等气象观测资料,应用累积距平法、M-K法和YAMA法对东莞降水强度进行初步的气候诊断分析.分析表明:从1980年代起,东莞的降水强度在6小时以内时段呈多波动变化,9小时以上时段的趋势大体上振荡下降.20分钟、30分钟、3小时的最大降水量在1980年代初发生突变,1988-1997年为谷底,其后是增强的趋势.大量级(100 mm及以上)最大降水量显著增强、增多.5分钟、20分钟、45分钟、1.5小时和12小时时段的最大降水量出现了均值的突变,其中1.5小时的突变(2002年)较强,突变之后的均值较之前增大.大量级的降水日数均值未发生突变.近年东莞的6小时以内时段的降水强度是增大的,但这种趋势变化未达到显著程度,2小时内的降水强度在2004-2005年间是个转折点,可能是一个趋势突变点. 相似文献
993.
994.
人工神经网络法反演晴空大气湿度廓线的研究 总被引:4,自引:0,他引:4
高光谱分辨率大气红外探测器AIRS(Atmospheric Infrared Sounder)作为第一个超高光谱大气红外探测仪,开辟了卫星大气探测的新时代.以无线电探空值与SARTA(Stand-Alone Radiative Transfer Algorithm辐射传输模式)v1.05版的前向模式模拟出的AIRS辐射... 相似文献
995.
996.
In watershed modelling, the traditional practice of arbitrarily filling topographic depressions in digital elevation models has raised concerns. Advanced high‐resolution remote sensing techniques, including airborne scanning laser altimetry, can identify naturally occurring depressions that impact overland flow. In this study, we used an ensemble physical and statistical modelling approach, including a 2D hydraulic model and two‐point connectivity statistics, to quantify the effects of depressions on high‐resolution overland flow patterns across spatial scales and their temporal variations in single storm events. Computations for both models were implemented using graphic processing unit‐accelerated computing. The changes in connectivity statistics for overland flow patterns between airborne scanning laser altimetry‐derived digital elevation models with (original) and without (filled) depressions were used to represent the shifts of overland flow response to depressions. The results show that depressions can either decrease or increase (to a lesser degree and shorter duration) the probability that any two points (grid locations) are hydraulically connected by overland flow pathways. We used macro‐connectivity states (Φ) as a watershed‐specific indicator to describe the spatiotemporal thresholds of connectivity variability caused by depressions. Four states of Φ are identified in a studied watershed, and each state represents different magnitudes of connectivity and connectivity changes (caused by depressions). The magnitude of connectivity variability corresponds to the states of Φ, which depend on the topological relationship between depressions, the rising/recession limb, and the total rainfall amount in a storm event. In addition, spatial distributions of connectivity variability correlate with the density of depression locations and their physical structures, which cause changes in streamflow discharge magnitude. Therefore, this study suggests that depressions are “nontrivial” in watershed modelling, and their impacts on overland flow should not be neglected. Connectivity statistics at different spatial scales and time points within a watershed provide new insights for characterizing the distributed and accumulated effects of depressions on overland flow. 相似文献
997.
The hydroclimatology of prairie‐dominated portions of the Lake Winnipeg watershed was investigated to determine the possible presence of trends and shifts in variables that may influence the streamflow regimes and water quality of Lake Winnipeg. The total annual streamflow, precipitation, runoff ratio and daily maximum streamflow in the two major tributaries of the Assiniboine River and Red River were analysed for a range of nonstationary behaviours. Each of these rivers has been gauged for more than 90 years. The methods used included a nonparametric Mann–Kendall test modified to account for diverse memory properties (i.e. short term versus long term) and a Bayesian change point detection model to identify possible segments of time series with inconsistent nonstationary behaviour. Although there is no evidence of statistically significant trends in precipitation and streamflow in the Assiniboine River watershed, a shift‐type nonstationarity in annual runoff and runoff ratio was observed in this area, which is manifested in the form of a sequence of wet and dry spells during the last century. Precipitation and runoff metrics in the American portion of the study area (i.e. Red River watershed) were characterised with both gradual and abrupt changes with an extremely increasing rate of streamflow beyond that of intensified precipitation. The nonproportional watershed runoff response is attributed to the dynamic nature of contributing areas that, together with the semiarid climate, leads to sudden changes of streamflow due to major or even some times minor changes in climate inputs. It is evident that streamflow in the depression‐dominated landscapes of the semiarid glaciated plains of North America is particularly sensitive and vulnerable to minor climate variability and change. This study provides valuable insights into the highly complex precipitation–runoff relationship in depression‐dominated landscapes and could have important implications for water management in this part of North America and comparable regions. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
998.
999.
传统的地震统计学多局限于规则的统计范围,或是需要较多的人工干预,本文引入了基于地理信息系统的空间统计学方法,将其应用于地震空间统计中,能够高效、快速地挖掘含有地理信息的各要素之间的相互联系。本文以川滇地区2019年发生的ML≥1.0地震数量的空间统计为例,详述了对地震数据进行空间统计的流程。统计结果表明,0.5°×0.5°是最适合该地震数据集空间统计的矩形范围,发生地震次数最多的区域位于四川盆地西南缘的威远?长宁地区,此外龙门山断裂带、龙门山断裂带与鲜水河?小江断裂系交汇处、丽江?小金河断裂沿线以及滇南地区均为地震发生次数较高的区域。此外,还利用该方法计算了2015—2019年全国各省地震能量释放情况。结果显示在该时间段内,释放地震能量总量最多的省份为四川省,新疆维吾尔自治区和西藏自治区次之,而台湾地区陆地区域、四川省、西藏自治区等地区具有较高的每万平方公里地震能量释放量和每万人地震能量承受量。并通过上述应用实例,探索了地理信息系统在地震统计领域的初步应用。 相似文献
1000.
Annalise G. Blum Stacey A. Archfield Robert M. Hirsch Richard M. Vogel Julie E. Kiang Robert W. Dudley 《水文科学杂志》2013,58(12):1404-1414
ABSTRACTAccurate estimators of streamflow statistics are critical to the design, planning, and management of water resources. Given increasing evidence of trends in low-streamflow, new approaches to estimating low-streamflow statistics are needed. Here we investigate simple approaches to select a recent subset of the low-flow record to update the commonly used statistic of 7Q10, the annual minimum 7-day streamflow exceeded in 9 out of 10 years on average. Informed by low-streamflow records at 174 US Geological Survey streamgages, Monte Carlo simulation experiments evaluate competing approaches. We find that a strategy which estimates 7Q10 using the most recent 30 years of record when a trend is detected, reduces error and bias in 7Q10 estimators compared to use of the full record. This simple rule-based approach has potential as the basis for a framework for updating frequency-based statistics in the context of possible trends. 相似文献