全文获取类型
收费全文 | 3538篇 |
免费 | 529篇 |
国内免费 | 888篇 |
学科分类
地球科学 | 4955篇 |
出版年
2024年 | 15篇 |
2023年 | 65篇 |
2022年 | 152篇 |
2021年 | 180篇 |
2020年 | 167篇 |
2019年 | 239篇 |
2018年 | 142篇 |
2017年 | 192篇 |
2016年 | 163篇 |
2015年 | 199篇 |
2014年 | 269篇 |
2013年 | 366篇 |
2012年 | 195篇 |
2011年 | 294篇 |
2010年 | 193篇 |
2009年 | 227篇 |
2008年 | 226篇 |
2007年 | 235篇 |
2006年 | 186篇 |
2005年 | 178篇 |
2004年 | 154篇 |
2003年 | 161篇 |
2002年 | 104篇 |
2001年 | 97篇 |
2000年 | 92篇 |
1999年 | 83篇 |
1998年 | 82篇 |
1997年 | 49篇 |
1996年 | 69篇 |
1995年 | 32篇 |
1994年 | 36篇 |
1993年 | 37篇 |
1992年 | 25篇 |
1991年 | 19篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有4955条查询结果,搜索用时 15 毫秒
961.
962.
963.
Extended severe dry and wet periods are frequently observed in the northern continental climate of the Canadian Prairies. Prairie streamflow is mainly driven by spring snowmelt of the winter snowpack, whilst summer rainfall is an important control on evapotranspiration and thus seasonality affects the hydrological response to drought and wet periods in complex ways. A field‐tested physically based model was used to investigate the influences of climatic variability on hydrological processes in this region. The model was set up to resolve agricultural fields and to include key cold regions processes. It was parameterized from local and regional measurements without calibration and run for the South Tobacco Creek basin in southern Manitoba, Canada. The model was tested against snow depth and streamflow observations at multiple scales and performed well enough to explore the impacts of wet and dry periods on hydrological processes governing the basin scale hydrological response. Four hydro‐climatic patterns with distinctive climatic seasonality and runoff responses were identified from differing combinations of wet/dry winter and summer seasons. Water balance analyses of these patterns identified substantive multiyear subsurface soil moisture storage depletion during drought (2001–2005) and recharge during a subsequent wet period (2009–2011). The fractional percentage of heavy rainfall days was a useful metric to explain the contrasting runoff volumes between dry and wet summers. Finally, a comparison of modeling approaches highlights the importance of antecedent fall soil moisture, ice lens formation during the snowmelt period, and peak snow water equivalent in simulating snowmelt runoff. 相似文献
964.
965.
利用MODIS资料监测和预警干旱新方法 总被引:11,自引:2,他引:11
为了提高遥感监测土壤水分和干旱的技术水平,在对常用遥感监测土壤水分和干旱方法进行评价的基础上,根据土壤热力学理论,提出了利用EOS/MODIS资料遥感监测农业干旱的新方法———能量指数模式。实际监测应用结果表明,能量指数模式更适合农作物土壤水分和干旱的监测,监测效果明显优于已经业务化的其它模式。农作物生长季节干旱的预警应当在土壤水分遥感监测的基础上,考虑未来预警期内的预报降水量和最高气温,并且把这个预报降水量和最高气温定量转化为土壤水分订正值,按照当地的标准划分成干旱预警等级。 相似文献
966.
A Comparative Analysis of Primary and Extreme Characteristics of Dry or Wet Status between Asia and North America 总被引:1,自引:0,他引:1
In this study, the Palmer Drought Severity Index (PDSI) was used to analyze the average and extreme dry/wet states of Asia and North America from 1953 to 2003. The results indicate that the two continents underwent drying trends during this period. Compared with North America, Asia showed more severe drought trends. However, more significant and regular seasonal variation for drought was found in North America. The driest regions in Asia were located in the northern region of China, Mongolia, and eastern mid-Siberian plateau. Most regions in central North America were relatively wetter than other regions. The northern and southwestern regions of North America, as well as the Atlantic and Pacific coastal areas, experienced the most drought during this period. A sharp increase of the drought area and the number of extreme drought events took place from 1997 to 2003 in both Asia and North America. Severe drought events were more likely to occur during the summer on both continents. Asia had the most extreme drought events during July, but North America reached its highest drought frequency from June to September. In Asia, a persistent increasing trend of extreme drought emerged throughout the studied period. However, a more complex evolution of drought emerged in North America: a decreasing trend appeared before the mid-1960s and an increasing trend appeared after the late 1970s. A relatively steady dry/wet status was observed between the mid-1960s and the late 1970s. The role of exceptional, extreme drought events with respect to the La Nin?a event was considered during 1997–2003. 相似文献
967.
2006年川渝地区夏季干旱的成因分析 总被引:1,自引:1,他引:1
利用NCEP/NCAR再分析月平均资料、全国160站降水资料、向外长波辐射OLR(outgoinglongwave radiation)资料和所计算的热源资料,分析了2006年夏季东亚大气环流的异常特征,并研究了热力异常与川渝地区夏季降水的关系。结果表明,2006年夏季由南向北的水汽输送较常年偏弱;西太洋副热带高压较常年异常偏强,脊线位置明显偏北,川渝地区受高压系统影响盛行下沉气流,中高纬环流场则表现为乌拉尔山地区和东北亚区域无明显阻塞高压形势,冷空气活动比常年弱;南亚高压比常年偏北偏强,持续控制川渝地区;2006年夏季青藏高原热源偏弱,热带西太平洋暖池区热源偏强,是引起西太平洋副热带高压偏北偏强的重要原因之一。川渝地区夏季降水与西太平洋副热带高压的异常变化有密切关系,川渝地区夏季干旱年,西太平洋副热带高压偏北,并且引起西太平洋副热带高压偏北的原因与2006年类似。 相似文献
968.
Worldwide, 98% of total electricity is currently produced by thermoelectric power and hydropower. Climate change is expected to directly impact electricity supply, in terms of both water availability for hydropower generation and cooling water usage for thermoelectric power. Improved understanding of how climate change may impact the availability and temperature of water resources is therefore of major importance. Here we use a multi-model ensemble to show the potential impacts of climate change on global hydropower and cooling water discharge potential. For the first time, combined projections of streamflow and water temperature were produced with three global hydrological models (GHMs) to account for uncertainties in the structure and parametrization of these GHMs in both water availability and water temperature. The GHMs were forced with bias-corrected output of five general circulation models (GCMs) for both the lowest and highest representative concentration pathways (RCP2.6 and RCP8.5). The ensemble projections of streamflow and water temperature were then used to quantify impacts on gross hydropower potential and cooling water discharge capacity of rivers worldwide. We show that global gross hydropower potential is expected to increase between +2.4% (GCM-GHM ensemble mean for RCP 2.6) and +6.3% (RCP 8.5) for the 2080s compared to 1971–2000. The strongest increases in hydropower potential are expected for Central Africa, India, central Asia and the northern high-latitudes, with 18–33% of the world population living in these areas by the 2080s. Global mean cooling water discharge capacity is projected to decrease by 4.5-15% (2080s). The largest reductions are found for the United States, Europe, eastern Asia, and southern parts of South America, Africa and Australia, where strong water temperature increases are projected combined with reductions in mean annual streamflow. These regions are expected to affect 11–14% (for RCP2.6 and the shared socio-economic pathway (SSP)1, SSP2, SSP4) and 41–51% (RCP8.5–SSP3, SSP5) of the world population by the 2080s. 相似文献
969.
Since the forest eco-hydrology of arid area shows a well sensitivity of the global climate change, the relationship between forest and water and the hydrological function has attracted the attention of academic communites and management departments. This paper expounds the research progress in arid mountain forest eco-hydrology, and analyses the formation and stable mechanism of forest patch pattern, the relationship between forest and water yield and the response of forest eco-hydrology to climate change from three aspects: Forest spatial pattern, hydrological process and its response to climate change. In addition, combined with the current research progress, the research emphases in the future are put forward: Strengthening the research on the coupling of vegetation pattern and hydrological process; solving the scale problem by using remote sensing technique and model; enhancing the understanding towards the hydrological function of forest; determining the suitable forest scale which can balance the relationship of ecology and hydrological effect. 相似文献
970.
Fluvial terraces along the middle reaches of many Japanese rivers were formed during the last glacial period as a result of changes in sediment discharge related to cooler temperatures and/or reduced water discharge because of lower precipitation. The influence of climate change on these fluvial terraces is not yet fully understood because most previous studies lacked detailed reconstructions of the chronology of terrace development. This study provides a detailed luminescence chronology of fluvial terrace deposits along the Ani River, northeastern Honshu, Japan, and compares that chronology to paleoclimatic records. Eight samples for luminescence dating were obtained from an outcrop of terrace deposits (∼10 m thick) in the Ani River valley. The fading-corrected infrared stimulated luminescence (IRSL) ages are consistent with the fading-corrected post-IR IRSL ages for some samples, which suggests that fading corrections were effective despite the higher fading rates of the IRSL signal. However, for the other samples, the post-IR IRSL ages are significantly older than the fading-corrected IRSL ages due to incomplete bleaching. The pulsed IRSL signals are close to field saturation for older samples, which might have resulted in a greater variation of the ages. Fading-corrected IRSL ages demonstrate periods of rapid aggradation during 105–90 ka and 75–60 ka. Comparison of terrace development with paleoclimatic records indicates that the two periods of fluvial deposition correspond to decreases in precipitation caused by weakened East Asian summer monsoon precipitation and possibly decreases in temperature. The results of this study show that the Ani River responded rapidly to climate change on a time scale of a few tens of thousands of years during the last glacial period. 相似文献