全文获取类型
收费全文 | 3694篇 |
免费 | 98篇 |
国内免费 | 60篇 |
专业分类
测绘学 | 403篇 |
大气科学 | 306篇 |
地球物理 | 732篇 |
地质学 | 1588篇 |
海洋学 | 190篇 |
天文学 | 489篇 |
综合类 | 59篇 |
自然地理 | 85篇 |
出版年
2023年 | 19篇 |
2022年 | 64篇 |
2021年 | 78篇 |
2020年 | 68篇 |
2019年 | 85篇 |
2018年 | 273篇 |
2017年 | 261篇 |
2016年 | 268篇 |
2015年 | 167篇 |
2014年 | 240篇 |
2013年 | 322篇 |
2012年 | 198篇 |
2011年 | 186篇 |
2010年 | 176篇 |
2009年 | 159篇 |
2008年 | 150篇 |
2007年 | 103篇 |
2006年 | 95篇 |
2005年 | 70篇 |
2004年 | 58篇 |
2003年 | 46篇 |
2002年 | 31篇 |
2001年 | 36篇 |
2000年 | 53篇 |
1999年 | 33篇 |
1998年 | 27篇 |
1997年 | 21篇 |
1996年 | 20篇 |
1995年 | 21篇 |
1994年 | 29篇 |
1993年 | 26篇 |
1992年 | 20篇 |
1991年 | 52篇 |
1990年 | 27篇 |
1989年 | 32篇 |
1988年 | 21篇 |
1987年 | 36篇 |
1986年 | 26篇 |
1985年 | 23篇 |
1984年 | 22篇 |
1983年 | 22篇 |
1982年 | 19篇 |
1981年 | 12篇 |
1980年 | 17篇 |
1979年 | 19篇 |
1978年 | 14篇 |
1976年 | 13篇 |
1974年 | 22篇 |
1973年 | 12篇 |
1972年 | 12篇 |
排序方式: 共有3852条查询结果,搜索用时 31 毫秒
91.
92.
93.
94.
95.
96.
97.
José Tasso Felix Guimarães Prafulla Kumar Sahoo Mariana Maha Jana Costa De Figueiredo Karen da Silva Lopes Markus Gastauer Silvio Junio Ramos Cecilio Frois Caldeira Pedro Walfir M. Souza-Filho Luiza Santos Reis Marcio Sousa Da Silva Paulo Rogenes Pontes Renato Oliveira Da Silva Junior Tarcísio Magevski Rodrigues 《第四纪科学杂志》2021,36(2):255-272
This study addresses paleoclimate influences in a southern Amazonia ecotone based on multiproxy records from lakes of the Carajás region during the last 45k cal a bp. Wet and cool environmental conditions marked the initial deposition in shallow depressions with detrital sediments and high weathering rates until 40k cal a bp. Concomitantly, forest and C3 canga plants, along with cool-adapted taxa, developed; however, short drier episodes enabled expansion of C4 plants and diagenetic formation of siderite. A massive event of siderite formation occurred approximately 30k cal a bp under strong drier conditions. Afterwards, wet and cool environmental conditions returned and persisted until the Last Glacial Maximum (LGM). The LGM was marked by lake-level lowstands and subaerial exposure. The transition from the LGM to the Holocene is marked by the onset of oscillations in temperature and humidity, with an expansion of forest and canga plants. Cool taxa were present for the last time in the Carajás region ~ 9.5–9k cal a bp. After 10k cal a bp , shallow lakes became upland swamps due to natural infilling processes, but the current vegetation types and structures of the plateaus were acquired only after 3k cal a bp under wetter climatic conditions. 相似文献
98.
The concentration of dissolved and particulate Re have been measured in the Narmada, Tapi and the Mandovi estuaries in the Arabian Sea and the Hooghly estuary in the Bay of Bengal. Re concentration in water and particulate matter of these estuaries is highly variable. Re in river waters analysed varies from 1 to 41 pmol/kg, the lowest in the Mandovi and the highest in the Mahi river. Re concentrations in the rivers analysed except in the Mandovi river are higher than the average global riverine Re concentration of 2.1 pmol/kg. Based on this study and the available data, the contemporary global annual flux of dissolved riverine Re is estimated to be ~ 350 × 103 mol with an average concentration of ~ 9.2 pmol/kg, much higher than the earlier estimates. Residence time of Re in the oceans based on this estimate is 175,000 years, ~ 4 times lower compared to earlier estimates. Re behaves conservatively in all the estuaries studied. Re concentrations of seawater in the Bay of Bengal and in the Arabian Sea, estimated from the data of the Hooghly and the Mandovi estuaries respectively are ~ 40 pmol/kg, similar to the open ocean Re values of the Arabian Sea measured in this study and the values reported for in other oceanic regions. However, the dissolved Re in the Gulf of Cambay is 2 to 5 times higher, consistent with the high Re measured in the Mahi estuary and in the coastal waters of the Gulf of Cambay. The source of high Re in the Gulf of Cambay seems to be anthropogenic, measurements of Re in rivers and industrial waste waters draining into the Gulf supply amount to ~ 2300 mol of Re annually. This anthropogenic supply coupled with high residence time of water in the Gulf contribute to its high Re. Re concentration in suspended sediments of the Narmada estuary varies from 1 to 2 pmol/g, and does not show any discernible trend with salinity.The contemporary global riverine Re supply to the oceans estimated in this study is ~ 2–4 times higher compared to its removal in the reducing (anoxic/suboxic) sediments, indicating non-steady state of Re in the ocean. High dissolved riverine Re flux coupled with high Re content in the Gulf of Cambay highlights the need of a detailed study of Re in the various global rivers and in oceans including coastal regions and semi enclosed basins of the world to understand its behaviour in various reservoirs and to constrain the residence time of Re in the ocean. 相似文献
99.
100.
D. C. Singhal V. K. Sharma Manish Tungaria 《Journal of the Geological Society of India》2016,88(4):449-463
In the present case study, impact of urbanization and industrial development on the shallow groundwater regime of Saharanpur town of Uttar Pradesh in India is examined with the aim of planning groundwater protection for better governance. The hazardous physicochemical and bacteriological parameters and heavy metals detected in the shallow aquifer include harmful pathogens like fecal coliforms, heavy metals like cadmium, chromium, nitrates and sulphates. An assessment of ground water vulnerability using the well known DRASTIC method has confirmed that the shallow groundwater in some central and southern localities of Saharanpur town fall in the medium risk zones. Further, using field data of 32 electrical resistivity soundings, the protective capacity of the unconfined aquifer is assessed in terms of a ‘total longitudinal conductance’ of the semi-pervious to impervious sediments overlying the unconfined aquifer. However, some areas aligned along a northwest-southeast and in the western parts of the town seem to have relatively higher protective capacity against infiltrating waste pollutants. A ground water protection planning map prepared by combining the DRASTIC map and the ‘potentially hazardous pollutants’ map has brought out the need to install eleven new groundwater quality monitoring wells in the town at locations near the line sources and point sources of pollution. This approach can be readily employed by the decision makers in framing sound guidelines for groundwater protection and governance. 相似文献