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991.
Martin Reich Carlos Palacios Gabriel Vargas Shangde Luo Eion M. Cameron Matthew I. Leybourne Miguel A. Parada Alejandro Zúñiga Cheng-Feng You 《Mineralium Deposita》2009,44(5):497-504
Supergene enrichment of Cu deposits in the Atacama Desert has played a critical role in making this the prime Cu-producing
province of the world. Previously, this has been believed to have occurred exclusively over a long period from the middle
Eocene to the late Miocene, which ended when climatic conditions changed from arid to hyperarid. Here, we report U-series
disequilibrium ages in atacamite-bearing supergene assemblages that provide a new conceptualization on both the supergene
enrichment process and the onset of extreme hyperaridity in the Atacama Desert. 230Th–234U ages of gypsum intergrown with atacamite in supergene veins from Cu deposits cluster at ~240 ka (Chuquicamata), 130 ka (Mantos
Blancos, Spence), and 80 ka (Mantos de la Luna, Michilla). When coupled with previous data, these results indicate that supergene
enrichment of Cu deposits did not cease after the onset of hyperaridity. We propose that supergene enrichment in the Atacama
region developed in two main stages. The main phase, caused by downward circulation of meteoric waters in a semi-arid setting,
was active from 45 until ~9 Ma, with a last pulse ca. 5 Ma in the southern Atacama Desert. During this phase, atacamite-bearing
supergene assemblages were not preserved because atacamite requires saline water for its formation and rapidly dissolves when
contacted by meteoric water. This was followed by a second stage starting at ~2–1.5 Ma and continuing until at least the late
Pleistocene, when deep formation waters derived from the basement passed up through and modified the pre-existing supergene
Cu oxide minerals. Atacamite has then been preserved in the prevailing hyperarid climate. 相似文献
992.
Earth fissures triggered by groundwater withdrawal and coupled by geological structures in Jiangsu Province,China 总被引:3,自引:0,他引:3
Earth fissures in Jiangsu Province, China have caused serious damages to properties, farmlands, and infrastructures and adversely
affected the local or regional economic development. Under the geological and environmental background in Jiangsu Province,
this paper presents the earth fissures caused by excessive groundwater withdrawal and coupled by distinctive geological structures
such as Ancient Yellow River Fault in Xuzhou karst area, and Ancient Yangtze River Course and bedrock hills in Suzhou, Wuxi,
and Changzhou area. Although all the earth fissures are triggered by groundwater exploitation, the characteristics are strongly
affected by the specific geological and hydrogeological settings. In particular, in the water-thirsty Xuzhou city, the cone
of depression caused by groundwater extraction enlarged nearly 20 times and the piezometric head of groundwater declined 17 m
over a decade. As groundwater is extracted from the shallowly buried karst strata in the Ancient Yellow River Fault zone,
the development of earth fissures is highly associated with the development of karstic cavities and sinkholes and their distribution
is controlled by the Ancient Yellow River Fault with all the 17 sinkholes on the fault. On the other hand, in the rapidly
developing Southern Jiangsu Province, groundwater is mainly pumped from the second confined aquifer in the Quaternary, which
is distributed neither homogeneously nor isotropically. The second confined aquifer comprises more than 50 m thick sand over
the Ancient Yangtze River Course, but this layer may completely miss on the riverbank and bedrock hills. With a typical drawdown
rate of 4–6 m per annum, the piezometric head of groundwater in the second confined aquifer has declined 76 m at Maocunyuan
since 1970s and 40 m at Changjing since mid-1980s, and a large land subsidence, e.g., 1,100 mm at Maocunyuan, is triggered.
Coupled with the dramatic change of the bedrock topography that was revealed through traditional geological drilling and modern
seismic reflection methods, the geological-structure-controlled differential settlement and earth fissures are phenomenal
in this area. 相似文献
993.
昌都盆地古油藏的流体包裹体证据 总被引:4,自引:0,他引:4
青藏高原隆升与油气保存是当今油气勘探理论与实践面临挑战课题之一。本文利用在昌都盆地采集的51块储层岩石样品,运用流体包裹体系统分析的技术和方法,不仅揭示了工区中生界三叠系和侏罗系在早侏罗世—早白垩世的前陆盆地发育阶段发生4期油气充注,形成了古油藏,而且这些古油藏在新生代的走滑拉分盆地发育阶段遭到破坏而演化成沥青砂岩。同时,在古生界—中生界储层检测到大量纯气相包裹体,并且与高温盐水包裹体共生,暗示工区晚期存在天然气运聚过程。由此认为,昌都盆地以寻找天然气为主;在盆地南部的芒康深凹陷中生界可能是天然气勘探的有利地区。 相似文献
994.
Dissolved chemical compositions in rainwater have provided valuable information on pollutant sources in the atmosphere and short-term environmental changes. However, baseline chemical data associated with typhoon is rather limited. In this study, a suite of time-series rain specimens including four typhoon events are collected from Tainan city, southern Taiwan and analyzed for major ions, heavy metals and Pb isotopes to elucidate mechanisms causing dissolved components variation in rainwater and to understand how heavy metals are transported by air-mass along typhoon pathways. 相似文献
995.
996.
997.
陆相高分辨率层序界面识别的地球化学方法 总被引:8,自引:3,他引:5
粘土矿物、微量元素普遍存在于各种类型的沉积物和沉积岩中,它们对环境的变化敏感,同时它们的沉积分异、组合特征、矿物成分及其含量都从不同的角度记录了形成过程中各种环境因素的变化。这些对恢复古环境,研究陆相湖盆水深变化具有重要的指示意义。通过对东营凹陷胜北断层下降盘沙三段 -沙四上段各层序内部高分辨率层序地层单元中岩石地球化学标型参数的研究发现,在一个高分辨率层序地层单元形成过程中,在古气候驱动下的湖平面变化旋回中,沉积岩中的矿物成分 (主要指粘土矿物和胶结物 )、化学成分 (微量元素 )等皆发生周期性变化。 相似文献
998.
Yuanyuan You Jianyu Liu Yongqiang Zhang Hylke E. Beck Xihui Gu Dongdong Kong 《水文研究》2021,35(10):e14367
Runoff signatures, including low flow, high flow, mean flow and flow variability, have important implications on the environment and society, predominantly through drought, flooding and water resources. Yet, the response of runoff signatures has not been previously investigated at the global scale, and the influencing mechanisms are largely unclear. Hence, this study makes a global assessment of runoff signature responses to the El Niño and La Niña phases using daily streamflow observations from 8217 gauging stations during 1960–2015. Based on the Granger causality test, we found that ~15% of the hydrological stations of multiple runoff signatures show a significant causal relationship with El Niño–southern oscillation (ENSO). The quantiles of all runoff signatures were larger during the El Niño phase than during the La Niña phase, implying that the entire flow distribution tends to shift upward during El Niño and downward during La Niña. In addition, El Niño has different effects on low and high flows: it tends to increase the low and mean flow signatures but reduces the high flow and flow variability signatures. In contrast, La Niña generally reduces all runoff signatures. We highlight that the impacts of ENSO on streamflow signatures are manifested by its effects on precipitation (P), potential evaporation (PET) and leaf area index (LAI) through ENSO-induced atmospheric circulation changes. Overall, our study provides a comprehensive picture of runoff signature responses to ENSO, with valuable insights for water resources management and flood and drought disaster mitigation. 相似文献
999.
Thermal effects of lateral supra‐permafrost water flow around a thermokarst lake on the Qinghai–Tibet Plateau
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Both the inflow and outflow of supra‐permafrost water to lakes play important roles in the hydrologic process of thermokarst lakes. The accompanying thermal effects on the adjacent permafrost are required for assessing their influences on the development of thermokarst lakes. For these purposes, the lake water level, temperature dynamics, and supra‐permafrost water flow of a lake were monitored on the Qinghai‐Tibet Plateau. In addition, the spatial and temporal variation of the active layer thickness and permafrost distribution around the lake were investigated by combining ground penetrating radar, electrical resistivity tomography, and borehole temperature monitoring. The results revealed that the yearly unfrozen supra‐permafrost water flow around the lake lasted approximately 5 months. The temperature and water level measurements during this period indicate that the lake water was recharged by relatively colder supra‐permafrost water from the north‐western lakeshore and was discharged through the eastern lakeshore. This process, accompanied by heat exchange with the underlying permafrost, might cause a directional difference of the active layer thickness and permafrost characteristics around the lake. Specifically, the active layer thickness variation was minimal, and the ice‐rich permafrost was found adjacent to the lakeshore along the recharge groundwater pathways, whereas a deeper active layer and ice‐poor permafrost were observed close to the lakeshore from which the warm lake water was discharged. This study suggests that the lateral flow of warm lake water can be a major driver for the rapid expansion of thermokarst lakes and provides clues for evaluating the relationships between the thermokarst expansion process and climate warming. 相似文献
1000.
Water temperature is an important habitat factor in river ecosystems that exhibits the characteristics of continuous change. Dam construction disrupts the continuity of river water temperature and reset it, thus exerting sharp rise/decrease on the characteristics of water temperature change. The effect of a dam on river continuity is directly related to the dam size. To explain this relationship, two rivers in China were selected: one river without reservoirs and one river with cascade reservoirs. Through the analysis of the longitudinal change of water temperature in free-flowing rivers, we found that water temperature changes continuously and steadily in the longitudinal direction. Based on this, a temperature trend hypothesis in river was proposed, and the discontinuity of the water temperature in the reservoir section was evaluated. The results are as follows: (1) In mixed reservoirs, river water temperature remained as continuous as free-flowing rivers. However, the river water temperature had a large discontinuity in the stratified reservoir. (2) Water residence time was used as an indicator of the continuity of reservoir water temperature. (3) Selective withdrawal of stratified reservoirs in January could not remove the discontinuity caused by itself, but it worked in June. 相似文献