全文获取类型
收费全文 | 15271篇 |
免费 | 2071篇 |
国内免费 | 1950篇 |
专业分类
测绘学 | 2393篇 |
大气科学 | 1474篇 |
地球物理 | 2201篇 |
地质学 | 5508篇 |
海洋学 | 694篇 |
天文学 | 149篇 |
综合类 | 1512篇 |
自然地理 | 5361篇 |
出版年
2024年 | 39篇 |
2023年 | 120篇 |
2022年 | 457篇 |
2021年 | 584篇 |
2020年 | 529篇 |
2019年 | 644篇 |
2018年 | 495篇 |
2017年 | 667篇 |
2016年 | 644篇 |
2015年 | 718篇 |
2014年 | 825篇 |
2013年 | 995篇 |
2012年 | 984篇 |
2011年 | 1019篇 |
2010年 | 896篇 |
2009年 | 840篇 |
2008年 | 861篇 |
2007年 | 964篇 |
2006年 | 925篇 |
2005年 | 797篇 |
2004年 | 791篇 |
2003年 | 634篇 |
2002年 | 568篇 |
2001年 | 513篇 |
2000年 | 463篇 |
1999年 | 383篇 |
1998年 | 352篇 |
1997年 | 308篇 |
1996年 | 234篇 |
1995年 | 192篇 |
1994年 | 215篇 |
1993年 | 163篇 |
1992年 | 130篇 |
1991年 | 73篇 |
1990年 | 67篇 |
1989年 | 68篇 |
1988年 | 42篇 |
1987年 | 29篇 |
1986年 | 16篇 |
1985年 | 10篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
941.
942.
松嫩平原近20年土壤盐渍化动态变化及驱动力分析 总被引:1,自引:0,他引:1
利用1986年(TM)和2001年(ETM)卫星遥感影像数据和RS-GIS集成技术,对松嫩平原盐渍化土地的现状、程度和发展趋势进行了量化分析.结果表明,这15年中,松嫩平原盐碱地面积增加了21.7112×104 hm2,每年增加1.45×104 hm2,年平均增长率为1.4%.其中轻度盐渍化土地增加8812 hm2,年平均增长0.16%;中度盐渍化土地增加3.8306×104 hm2,年平均增长0.64%;重度盐渍化土地面积增加了16.9994×104 hm2,年平均增长了4.2%.气候变暖,降水减少,人为活动增强是盐渍化程度加重的主要驱动力. 相似文献
943.
944.
945.
收缩城市建设用地利用效率时空分异及影响机制——以黑龙江省伊春市为例 总被引:1,自引:1,他引:0
建设用地是城镇经济社会活动的空间载体,其利用效率是调控建设用地扩张和配置的重要基础.论文以收缩型城市——黑龙江省伊春市为例,利用DEA模型测算了1995-2015年伊春市建设用地利用效率分析其时空演变规律,并运用地理探测器模型探究伊春市建设用地利用效率空间分异的影响机制,结论如下:①1995-2015年伊春市建设用地利... 相似文献
946.
Simona Avnaim‐Katav Ahuva Almogi‐Labin Amir Sandler Dorit Sivan Naomi Porat Ari Matmon 《第四纪科学杂志》2012,27(7):675-686
The current detailed chronostratigraphic framework of the last 1 Ma of an eastern Mediterranean sequence (Haifa Bay, Israel) aims to examine the relative roles of sea‐level changes, climate and tectonics. Seven continuous marine cores, up to ~120 m long, were recovered from shallow water depths. The cores were dated by optically stimulated luminescence, 14C, magnetostratigraphy, 230Th/234U, 26Al/10Be, occurrence of index fossils and correlated to the global sea‐level curve and Marine Isotope Stages (MIS). The sedimentary sequence accumulated during the last ca. 1.0 Ma consists of 21 transgression–regression units with hiatuses between them. Five marine/terrestrial cycles, which occur in the lower part of the sequence, are attributed to the Jaramillo subchron and the Brunhes–Matuyama boundary, and correspond to MIS 29–21. The top ~50 m includes three sedimentary cycles deposited in the last ca. 400 ka. The regressive phases during this interval correspond to Glacial MIS 8, 6 and 2, while the transgressions correspond to Interglacial MIS 11, 7, 5 and 1. Thus, for the first time, this study documents the longest Quaternary succession dated so far in a key area of the Levant, sensitive to global history of sea‐level changes and glacial/interglacial fluctuations. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
947.
《Geoforum》2016
In the Sierra de Perijá, Venezuela, the indigenous Yukpa have long faced reterritorialization and violent displacement through the expansion of cattle farms, so-called haciendas. However, the new Venezuelan constitution in 2000 guaranteed rights to indigenous territory and ushered in an endogenous, community-based development model. By the 2010s, Yukpa had reclaimed a half-dozen haciendas, taking advantage of the political leverage and economic opportunities provided by the endogenous development model. This process of deterritorialization has been accompanied by extensive migration of residents from mountain communities to the lowlands, and these reconfigurations of Yukpa spatiality have prompted reconceptualization of a diasporic, multi-sited indigenous identity. 相似文献
948.
In debris‐flow‐prone channels, normal fluvial sediment transport occurs (nearly exclusively in suspended mode) between episodic debris‐flow events. Observations of suspended sediment transport through a winter season in a steepland gully in logged terrain revealed two event types. When flows exceeded a threshold of 270 l s−1, events yielded significant quantities of sediment and suspended sediment concentration increased with flow. Smaller events were strongly ‘supply limited’; sediment concentration decreased as flow increased. Overall, there is no consistent correlation between runoff and sediment yield. Within the season, three subseasons were identified (demarcated by periods of freezing weather) within which a pattern of fine sediment replenishment and evacuation occurred. Finally, a signature of fine sediment mobilization and exhaustion was observed within individual events. Fine sediment transport occurred in discrete pulses within storm periods, most of the yield occurring within 5 to 15% of storm runoff duration, so that it is unlikely that scheduled sampling programs would identify significant transport. Significant events are, however, generally forecastable on the basis of regional heavy rainfall warnings, providing a basis for targeted observations. Radiative snowmelt events and rain‐on‐snow remain difficult to forecast, since the projection of temperatures from the nearest regular weather station yields variable results. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
949.
The surface energy balance algorithm for land method was used in this study to calculate the evapotranspiration (ET) rate for the middle reaches of the Heihe River Basin, Gansu Province, China, to analyse ET distribution within the oasis and the surrounding desert and, especially, on the edge zone of the oasis. Five profile graphs were created vertical to the river. Because of the inverse humidity phenomenon, the least amount of evapotranspiration occurred on the desert close to the oasis. The average evapotranspiration rate was roughly proportioned from the edge of the oasis to inside and outside its boundary. Two meteorological ground stations located close to the oasis edge showed a notable difference in net radiation flux that led to the difference found in ET. The primary reason for the significant differences observed in net radiation may be largely the result of differences in flux reflectivity and surface temperature. Meteorological data show that water supply also played an important role. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
950.
Global climate change will likely increase temperature and variation in precipitation in the Himalayas, modifying both supply of and demand for water. This study assesses combined impacts of land‐cover and climate changes on hydrological processes and a rainfall‐to‐streamflow buffer indicator of watershed function using the Soil Water Assessment Tool (SWAT) in Kejie watershed in the eastern Himalayas. The Hadley Centre Coupled Model Version 3 (HadCM3) was used for two Intergovernmental Panel on Climate Change (IPCC) emission scenarios (A2 and B2), for 2010–2099. Four land‐cover change scenarios increase forest, grassland, crops, or urban land use, respectively, reducing degraded land. The SWAT model predicted that downstream water resources will decrease in the short term but increase in the long term. Afforestation and expansion in cropland will probably increase actual evapotranspiration (ET) and reduce annual streamflow but will also, through increased infiltration, reduce the overland flow component of streamflow and increase groundwater release. An expansion in grassland will decrease actual ET, increase annual streamflow and groundwater release, while decreasing overland flow. Urbanization will result in increases in streamflow and overland flow and reductions in groundwater release and actual ET. Land‐cover change dominated over effects on streamflow of climate change in the short and middle terms. The predicted changes in buffer indicator for land‐use plus climate‐change scenarios reach up to 50% of the current (and future) range of inter‐annual variability. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献