全文获取类型
收费全文 | 2087篇 |
免费 | 335篇 |
国内免费 | 449篇 |
专业分类
测绘学 | 388篇 |
大气科学 | 317篇 |
地球物理 | 420篇 |
地质学 | 1064篇 |
海洋学 | 171篇 |
天文学 | 102篇 |
综合类 | 138篇 |
自然地理 | 271篇 |
出版年
2024年 | 9篇 |
2023年 | 61篇 |
2022年 | 68篇 |
2021年 | 94篇 |
2020年 | 127篇 |
2019年 | 127篇 |
2018年 | 86篇 |
2017年 | 132篇 |
2016年 | 97篇 |
2015年 | 97篇 |
2014年 | 135篇 |
2013年 | 165篇 |
2012年 | 140篇 |
2011年 | 127篇 |
2010年 | 111篇 |
2009年 | 134篇 |
2008年 | 142篇 |
2007年 | 135篇 |
2006年 | 121篇 |
2005年 | 95篇 |
2004年 | 100篇 |
2003年 | 95篇 |
2002年 | 70篇 |
2001年 | 78篇 |
2000年 | 55篇 |
1999年 | 45篇 |
1998年 | 43篇 |
1997年 | 41篇 |
1996年 | 27篇 |
1995年 | 21篇 |
1994年 | 17篇 |
1993年 | 21篇 |
1992年 | 14篇 |
1991年 | 13篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有2871条查询结果,搜索用时 15 毫秒
351.
基于事件数据的雅鲁藏布江-布拉马普特拉河国际河流安全分析 总被引:3,自引:0,他引:3
雅鲁藏布江-布拉马普特拉河是我国重要的国际河流,近年的水电开发活动,使其日益成为国内外国际河流研究关注的热点。本文基于国际关系研究中常用的事件分析方法,在构建事件数据库的基础上,从事件类型、涉及国别、事件频率、影响程度四方面进行分析,结果表明:水资源分配问题是雅江流域主要问题;中国在雅江国际河流问题上与下游国家的联系主要以与印度或孟加拉国的双边联系为主;随着时间的推移,雅江冲突与合作事件的频率都表现出增加的趋势;雅江围绕国际河流的国际关系局势大致可分为4个阶段:60年代的平稳阶段、70年代的紧张阶段、80年代的沉寂阶段、90年代后的持续关注阶段。 相似文献
352.
Ling Bian Shixiong Hu 《International journal of geographical information science》2013,27(9):1009-1032
The development of interoperable environmental process models is widely supported by both the research community and government agencies. This paper discusses a conceptual framework to guide the delineation of process components, the basic unit of interoperable models. The concepts of semantic reference system and dual hierarchy are explored to establish the conceptual framework. Based on this discussion, the Formal Concept Analysis is used as an analytical approach to decompose and fuse existing environmental process models in order to identify environmental process components. For purposes of discussion, a hydrological process, surface runoff, is used throughout the paper as an example of an environmental process to support the conceptual discussion and to illustrate the application of the conceptual framework and analytical approach. 相似文献
353.
为解决常规射电望远镜归心测量工作耗时耗力的问题,引入GNSS (Global Navigation Satellite System)同步监测技术实现了一种针对射电望远镜参考点的无人值守监测方法.设计了针对GNSS靶标点观测数据的归算方法,包括数据匹配、数据检核以及后续精度评估等步骤,并对2018年佘山25-m射电VLBI (Very Long Baseline Interferometry)望远镜的GNSS靶标点实测数据开展了数据预处理、解析与归心解算等,证明了该方法的可行性.结果表明基于该方法,采用单日内部分(5%)数据(约7600个靶标点),所测定的VLBI望远镜参考点的点位形式精度可达3 mm.总结了针对射电望远镜采用GNSS开展无人值守归心测量先行试验中的一些经验教训,明确了利用该方法测量过程中应该注意的问题,为今后更高精度射电望远镜参考点无人值守归心监测提供重要参考. 相似文献
354.
ABSTRACTFollowing the June 2013 disaster in the Uttarakhand Himalayas, many discussions are ongoing with regard to how climate change is seeking revenge on mankind by endowing us with disasters! The event was mostly linked with the occurrence of an extreme event due to climate change. In view of this, an attempt has been made in this paper to analyse the extreme rainfall events experienced by the Uttarakhand during 1901–2013 using more than 100 stations’ daily rainfall data. The study revealed that during the 113-year period, the highest numbers of extreme events were recorded during the decade 1961–1970, and to some extent in the decade 1981–1990. Thereafter, there is a decrease in extreme rainfall events. The comparative study of extreme events prior to 1901 showed that on 17–18 September 1880, a rainstorm which occurred in close vicinity to Uttarakhand caused serious floods and damage to lives and properties. The extreme rainfall recorded by some stations during this unprecedented rainstorm has not been surpassed to date. 相似文献
355.
Historical trends in Florida temperature and precipitation 总被引:1,自引:0,他引:1
Michelle M. Irizarry‐Ortiz Jayantha Obeysekera Joseph Park Paul Trimble Jenifer Barnes Winifred Park‐Said Erik Gadzinski 《水文研究》2013,27(16):2225-2246
Because of its low topographic relief, unique hydrology, and the large interannual variability of precipitation, Florida is especially vulnerable to climate change. In this paper, we investigate a comprehensive collection of climate metrics to study historical trends in both averages and extremes of precipitation and temperature in the state. The data investigated consist of long‐term records (1892–2008) of precipitation and raw (unadjusted) temperature at 32 stations distributed throughout the state. To evaluate trends in climate metrics, we use an iterative pre‐whitening method, which aims to separate positive autocorrelation from trend present in time series. Results show a general decrease in wet season precipitation, most evident for the month of May and possibly tied to a delayed onset of the wet season. In contrast, there seems to be an increase in the number of wet days during the dry season, especially during November through January. We found that the number of dog days (above 26.7 °C) during the year and during the wet season has increased at many locations. For the post‐1950 period, a widespread decrease in the daily temperature range (DTR) is observed mainly because of increased daily minimum temperature (Tmin). Although we did not attempt to formally attribute these trends to natural versus anthropogenic causes, we find that the urban heat island effect is at least partially responsible for the increase in Tmin and its corresponding decrease in DTR at urbanized stations compared with nearby rural stations. In the future, a formal trend attribution study should be conducted for the region. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
356.
Trend analysis of reference evapotranspiration in Northwest China: The roles of changing wind speed and surface air temperature 总被引:2,自引:0,他引:2
Reference evapotranspiration (ET0) is an important element in the water cycle that integrates atmospheric demands and surface conditions, and analysis of changes in ET0 is of great significance for understanding climate change and its impacts on hydrology. As ET0 is an integrated effect of climate variables, increases in air temperature should lead to increases in ET0. However, this effect could be offset by decreases in vapor pressure deficit, wind speed, and solar radiation which lead to the decrease in ET0. In this study, trends in the Penman–Monteith ET0 at 80 meteorological stations during 1960–2010 in the driest region of China (Northwest China) were examined. The results show that there was a change point for ET0 series around the year 1993 based on the Pettitt's test. For the region average, ET0 decreased from 1960 to 1993 by ?2.34 mm yr?2, while ET0 began to increase since 1994 by 4.80 mm yr?2. A differential equation method based on the Food and Agriculture Organization Penman–Monteith formula was used to attribute the change in ET0. The attribution results show that the significant decrease in wind speed dominated the change in ET0, which offset the effect of increasing air temperature and led to the decrease in ET0 from 1960 to 1993. However, wind speed began to increase, and the amplitude of increase in air temperature also rose significantly since the mid‐1990s. Increases in air temperature and wind speed together reversed the trend in ET0 and led to the increase in ET0 since 1994. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
357.
Abstract The spatio-temporal variations of reference crop evapotranspiration (ETref) reflect the combined effects of meteorological variables, primarily wind speed, relative humidity, net radiation and air temperature. This study investigated the spatial distribution and temporal trends of ETref (calculated by the FAO-56 Penman-Monteith equation), pan evaporation (Epan) and pan coefficient (Kp) in a 140?×?103 km2 semi-humid to semi-arid area in China. The results show that: (i) although the spatial distributions of ETref and Epan are roughly similar and their spatial correlation is high over the growing season, Kp varied considerably in space due to high humidity in the east of the region and low humidity in the southwest; (ii) the monthly variations of ETref and Epan are similar to that of net radiation and opposite to that of relative humidity, while the monthly variation of Kp is similar to that of relative humidity and opposite to that of wind speed, and the long-term trend is slightly increasing for ETref and Epan, while significantly (10% significance level) increasing for Kp; and (iii) generally, the time series of ETref and Epan from 1951 to 2001 could be divided into three phases due to variations of meteorological variables. Citation Liang, L.-Q., Li, L.-J. & Liu, Q. (2011) Spatio-temporal variations of reference crop evapotranspiration and pan evaporation in the West Songnen Plain of China. Hydrol. Sci. J. 56(7), 1300–1313. 相似文献
358.
R. Domínguez M. 《水文科学杂志》2013,58(3):460-478
Abstract The estimation and review of discharge flow rates in hydraulic works is a fundamental problem in water management. In the case of dams with large regulating capacity, in order to estimate return periods of discharge flow rates from the spillways, it becomes necessary to consider both peak flow and volume of the incoming floods. In this paper, the results of the validation for several methods of assessing design floods for spillways of dams with a large flood control capacity are presented; the validation is performed by comparing the maximum outflows (or the maximum levels reached in the reservoir) obtained from the routing of the design floods with those obtained from the routing of the historical annual maximum floods. The basin of Malpaso Dam, Mexico, is used as the case study. Editor D. Koutsoyiannis Citation Domínguez, M.R. and Arganis, J.M.L., 2012. Validation of methods to estimate design discharge flow rates for dam spillways with large regulating capacity. Hydrological Sciences Journal, 57 (3), 460–478. 相似文献
359.
Nancy Pérez-Morga Thomas Kretzschmar Tereza Cavazos Stephen V. Smith Francisco Munoz-Arriola 《Geofísica Internacional》2013,52(3):277-291
Extreme wet and dry years (± 1 standard deviation, respectively), as well as the top 95 percentile (P95) of daily precipitation events, derived from tropical cyclone (TC) and nontropical cyclone (NTC) rainfall, were analyzed in coastal river basins in Southern Oaxaca, Mexico (Río Verde, Río Tehuantepec, and the Southern Coast). The study is based on daily precipitation records from 47 quality-controlled stations for the 1961 to 1990 period and TC data for the Eastern Tropical Pacific (EPAC). The aim of this study was to evaluate extreme (dry and wet) trends in the annual contribution of daily P95 precipitation events and to determine the relationship of summer precipitation with El Niño Southern Oscillation (ENSO) and the Pacifical Decadal Oscillation (PDO). A regionalization based on a rotated principal component analysis (PCA) was used to produce four precipitation regions in the coastal river basins. A significant negative correlation (significance at the 95% level) was only found with ONI in rainfall Region 3, nearest to the Gulf of Tehuantepec. Wet years, mainly linked to TC-derived P95 precipitation events, were associated with SST anomalies (≥?0.6°C) similar to weak La Niña and Neutral cool conditions, while dry years were associated with SST positive anomalies similar to Neutral warm conditions (≤?0.5°C). The largest contribution of extreme P95 precipitation derived from TCs to the annual precipitation was observed in Region 3. A significant upward trend in the contribution of TC-derived precipitation to the annual precipitation was found only in Region 1, low Río Verde. 相似文献
360.
《水文科学杂志》2013,58(2)
Abstract Abstract The Chronology of British Hydrological Events (CBHE) has been created as an on-line information resource (http://www.dundee.ac.uk/geography/cbhe/) in order to enhance access to and use of historical facts pertaining to British hydrological phenomena. Its scope covers floods, droughts and all other notable historical phenomena of hydrological interest. This paper sets out the technical means by which the CBHE has been created, explains the benefits to hydrologists in creating such a facility, and illustrates its utility with a number of examples. Benefits include hydrological risk assessments, historical studies of individual events and objectives in environmental education. The scope for establishing comparable national chronologies for other countries is identified, along with prospects for enhancing the utility of such systems with additional functionality such as links to on-line gazetteers and maps. 相似文献