全文获取类型
收费全文 | 679篇 |
免费 | 55篇 |
国内免费 | 137篇 |
专业分类
测绘学 | 18篇 |
大气科学 | 19篇 |
地球物理 | 131篇 |
地质学 | 142篇 |
海洋学 | 463篇 |
天文学 | 1篇 |
综合类 | 51篇 |
自然地理 | 46篇 |
出版年
2024年 | 1篇 |
2023年 | 11篇 |
2022年 | 21篇 |
2021年 | 16篇 |
2020年 | 17篇 |
2019年 | 17篇 |
2018年 | 18篇 |
2017年 | 23篇 |
2016年 | 22篇 |
2015年 | 20篇 |
2014年 | 31篇 |
2013年 | 38篇 |
2012年 | 21篇 |
2011年 | 49篇 |
2010年 | 40篇 |
2009年 | 45篇 |
2008年 | 56篇 |
2007年 | 33篇 |
2006年 | 45篇 |
2005年 | 28篇 |
2004年 | 32篇 |
2003年 | 29篇 |
2002年 | 26篇 |
2001年 | 27篇 |
2000年 | 23篇 |
1999年 | 33篇 |
1998年 | 30篇 |
1997年 | 18篇 |
1996年 | 28篇 |
1995年 | 17篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 5篇 |
1984年 | 9篇 |
1983年 | 2篇 |
1981年 | 5篇 |
1980年 | 1篇 |
排序方式: 共有871条查询结果,搜索用时 13 毫秒
481.
Surface currents measured by high frequency (HF) radar arrays are assimilated into a regional ocean model over Qingdao coastal waters based on Kalman filter method. A series of numerical experiments are per- formed to evaluate the performance of the data assimilation schemes. In order to optimize the analysis pro- cedure in the traditional ensemble Kalman filter (ENKF), a different analysis scheme called quasiensemble Kaman filter (QENKF) is proposed. The comparisons between the ENKF and the QENKF suggest that both them can improve the simulated error and the spatial structure. The estimations of the background error covariance (BEC) are also assessed by comparing three different methods: Monte Carlo method; Canadian quick covariance (CQC) method and data uncertainty engine (DUE) method. A significant reduction of the root-mean-square (RMS) errors between model results and the observations shows that the CQC method is able to better reproduce the error statistics for this coastal ocean model and the corresponding external forcing. In addition, the sensibility of the data assimilation system to the ensemble size is also analyzed by means of different scales of the ensemble size used in the experiments. It is found that given the balance of the computational cost and the forecasting accuracy, the ensemble size of 50 will be an appropriate choice in the Qingdao coastal waters. 相似文献
482.
S. Wohnlich 《Environmental Geology》1996,27(2):108-109
The famous spa of Baden-Baden is situated in the northern Black Forest area not far from the upper Rhine valley in southwestern Germany. Its natural sodium chloride thermal water (68°C), together with its extremely mild climate and pleasant landscape, made Baden-Baden one of the most favored spas in Germany. Baden-Baden was a former capital of the German state of Baden (which means bath or spa), and its name is now included in the name of the state of Baden-Württemberg. Thus, Baden-Württemberg is the only area in Germany where a geologic phenomenon is part of the name of the state. 相似文献
483.
The geochemical characteristics of hydrothermal waters from the Phlegraean Fields (P.F.) (Naples, Italy) were analysed for minor and trace elements, selectively mobilised in hydrothermal systems such as B, F, Hg, As, Pb and Tl.The water samples, collected from a shallow aquifer likely to be fed by deeper fluids, showed various geochemical features, resulting from the mixing of three components: (1) surface waters of meteoric origin; (2) hot deep waters deriving from water-rock interaction and including deep waters of marine origin; (3) magmatic fluids rising from the local magma chamber, lying a few kilometres below the town of Pozzuoli.This setting, although very complex, provides a reliable means of studying the distribution of the investigated trace elements. In particular, within the Phlegraean area, high contents of B (0.1-48 mg/l), F (0.5-8 mg/l), As (16-6050 μg/l) and Hg (0.7-232 μg/l) were observed. The levels of thallium in the springs close to Solfatara (about 7 μg/l) were in line with those normally recorded in hydrothermal areas, whereas high levels of this element (up to 23.3 μg/l) were identified in other wells of the study area. Lead (1.3 to 29.1 μg/l) appears to be anomalous with respect to its normal content in groundwater (about 1 μg/l), owing to the presence of high-density brines at depth, which enhance the solubility of Pb in volcanic rocks under hydrothermal conditions.The distribution of the investigated trace elements in the Phlegraean Fields thermal area is probably related to the different ascent pathways of the fluids. Clearly, apart from the influence exerted by anomalous thermal conditions, each element shows a different behaviour, depending on its geochemical affinity with mineral phases and as a consequence of the different enthalpy values, which determine ion partitioning in gaseous phases.Based on geochemical evidences and on the distribution of minor and trace elements, the source processes of the investigated hydrothermal waters were defined. Five main groups were identified: (1) acid sulphate waters, resulting from mixing of meteoric water with magmatic gases (mainly H2S); (2) high sulphate-chloride waters, from a deep reservoir located in the major upflow zone; (3) waters associated with significant degassing of magmatic CO2; (4) waters from a deep geothermal neutral chloride reservoir, resulting from heating of marine water modified by water-rock interaction processes; (5) cold waters from the inner area, influenced by low-temperature, water-rock interaction processes. 相似文献
484.
In this paper seven of the ten Water Control Zones (WCZs) in Hong Kong’s coastal waters with monthly or bi-weekly sampling
data of 17 parameters collected at 37 monitoring stations from 1988 to 1999 were selected to analyze the spatial and temporal
variations of chlorophyll-a and its influencing factors. Cluster analysis was employed to group the monitoring stations based
on the structure of the data set. Multiple step regression was employed to determine the significant influencing factors of
chlorophyll-a level. The results suggest that all the monitoring stations could be grouped into two clusters. Cluster I with
frequent red tide incidents comprises two WCZs which are semi-enclosed bays. Cluster II with less red tide occurrence comprises
the other five WCZs in an estuarine environment in the west. For both clusters, the organic contents indicator, BOD5, was
a common significant influencing factor of the chlorophyll-a level. Nitrogen and light penetration condition related to turbidity,
total volatile solids and suspended solids had more influence on the cholophyll-a level in Cluster I than in Cluster II, while
phosphorus and oceanographic conditions associated with salinity, temperature, dissolved oxygen and pH were more important
in Cluster II than in Cluster I. Generally, there was a higher average chlorophyll-a level in winter and autumn in a year.
The chlorophyll-a level was much higher in Cluster I than in Cluster II among all seasons. Although the chlorophyll-a concentration
had great variations from place to place in Hong Kong’s coastal waters, it seemed to have a common long term fluctuation period
of 8–10 years with a high-low-high variation in the period in the whole region, which might be influenced by other factors
of global scale. 相似文献
485.
Gabriela-Raluca Babaua Anca-Iulia Stoica Petre Capota George-Emil Baiulescu 《Environmental Geology》2003,45(1):58-64
Using two analytical techniques, CSV/ASV and ICP–AES, the concentration of some microelements (lead, zinc, manganese) in mineral waters from the Covasna and Harghita districts of Romania were determined. The optimum parameters for the voltammetric determination of manganese, copper, zinc and lead were established (electrolyte, deposition time, pulse duration, pulse amplitude, etc.) and then the content of these elements in twelve samples of mineral water were determined. The results obtained by both techniques led to the conclusion that the concentration of microelements in mineral waters from Covasna and Harghita districts is connected to the mineral content underground. 相似文献
486.
The spatial and temporal discharge regime and its effects on benthic communities were studied in two small temporary karstic stream systems of the Paderborner Hochfläche (East Westphalia, Germany). Both streams are characterized by very small perennial springbrook sections. Benthic invertebrates were sampled three times at 12 sites and discharge was measured monthly from March to September 2000. The spatial extension of streamflow was observed regularly to evaluate the duration of drought. Both streams showed a longitudinal gradient of hydrological intermittency from very small perennial reaches with low intermittency to an extremely harsh hydrological situation. The benthic communities displayed a decreasing species richness at increasing intermittency. The different hydrological stream sections were colonized by different lotic communities, characterized by typical species of temporary streams and by several typical species of springs. Particularly the perennial springs and springbrooks are very important for the species richness in these karstic stream systems. 相似文献
487.
J. Marques Monteiro F. Santos R. Graça R. Castro L. Aires-Barros L. Mendes Victor 《Hydrogeology Journal》2001,9(6):584-596
The Vilarelho da Raia-Chaves region, located in northern Portugal adjacent to the Spanish border, is characterized by both
hot and cold CO2-rich mineral waters issuing from springs and drilled wells. The present paper updates the conceptual circulation model of
the Vilarelho da Raia cold CO2-rich mineral waters. Vilarelho da Raia mineral waters, dominated by Na and HCO3 ions, have formed mainly by interaction with CO2 of deep-seated mantle origin. The δ
18O, δ
2H and 3H values indicate that these waters are the result of meteoric waters infiltrating into Larouco Mountain, NW of Vilarelho
da Raia, circulating at shallow depths in granitic rocks and moving into Vilarelho da Raia area. The conceptual geochemical
and geophysical circulation model indicates that the hot and cold CO2-rich mineral waters of Chaves (76 °C) and Vilarelho da Raia (17 °C) should be considered manifestations of similar but not
the same geohydrological systems.
Electronic Publication 相似文献
488.
Granite fines are inorganic wastes produced in the elaboration of dimension stone. Because of the increasing development of that industry in NW Spain, some concerns related to their classification as type of waste and their environmental impact have been raised. We have performed a detailed physicochemical, mineralogical and geomechanical characterization of the fines and the results make up the basis of several modeling exercises addressed to give answers to particular topics: the impact of high pH waters on the environment and the mobility of some toxic metals. Based on our analyses, we conclude that granite fines do not constitute a significant hazard to the quality of natural waters. 相似文献
489.
The state and its agencies in coastal resources management: The political ecology of fisheries management in Pattani, southern Thailand 总被引:1,自引:0,他引:1
May Tan-Mullins 《Singapore journal of tropical geography》2007,28(3):348-361
Various stakeholders contribute to the current state of resource management in the inshore fisheries of Pattani, southern Thailand. Taking the state, empowered by national legislation, as the main agent of enforcement, this paper uses an actor-oriented approach derived from political ecology to evaluate how key agents in state agencies at provincial and district levels translate Thai political and legal systems at the local level; more specifically, how cross-scalar institutional linkages and translations affect coastal resources management and the access of village-based, small-scale fishermen to coastal resources. The paper shows that trans-scalar interpretations have created a space of contestation and negotiation in resource governance at the local level that reveals intrastate tensions. Based on extensive fieldwork, the paper demonstrates that access to environmental resources at the local level is highly influenced or regulated by the unequal power relations between different actors at various levels. 相似文献
490.