全文获取类型
收费全文 | 5982篇 |
免费 | 147篇 |
国内免费 | 62篇 |
专业分类
测绘学 | 123篇 |
大气科学 | 503篇 |
地球物理 | 1373篇 |
地质学 | 1985篇 |
海洋学 | 592篇 |
天文学 | 957篇 |
综合类 | 14篇 |
自然地理 | 644篇 |
出版年
2021年 | 47篇 |
2020年 | 65篇 |
2019年 | 73篇 |
2018年 | 111篇 |
2017年 | 116篇 |
2016年 | 132篇 |
2015年 | 103篇 |
2014年 | 129篇 |
2013年 | 315篇 |
2012年 | 177篇 |
2011年 | 260篇 |
2010年 | 238篇 |
2009年 | 236篇 |
2008年 | 241篇 |
2007年 | 209篇 |
2006年 | 228篇 |
2005年 | 182篇 |
2004年 | 184篇 |
2003年 | 171篇 |
2002年 | 165篇 |
2001年 | 117篇 |
2000年 | 108篇 |
1999年 | 103篇 |
1998年 | 95篇 |
1997年 | 85篇 |
1996年 | 88篇 |
1995年 | 92篇 |
1994年 | 86篇 |
1993年 | 76篇 |
1992年 | 86篇 |
1991年 | 70篇 |
1990年 | 98篇 |
1989年 | 85篇 |
1988年 | 75篇 |
1987年 | 100篇 |
1986年 | 75篇 |
1985年 | 96篇 |
1984年 | 131篇 |
1983年 | 108篇 |
1982年 | 97篇 |
1981年 | 100篇 |
1980年 | 88篇 |
1979年 | 100篇 |
1978年 | 71篇 |
1977年 | 86篇 |
1976年 | 71篇 |
1975年 | 70篇 |
1974年 | 55篇 |
1973年 | 61篇 |
1972年 | 35篇 |
排序方式: 共有6191条查询结果,搜索用时 0 毫秒
71.
72.
Robert G. Bednarik 《Geoarchaeology》1993,8(6):443-463
This article introduces a new quantitative method of dating petroglyphs and describes its initial application. First, the major recent developments in the field of rock art dating are briefly reviewed, and the continuing difficulties in the dating of petroglyphs are elucidated. The archaeological background of the Lake Onega art, its geological setting and archaeogeophysical dating are explained. The theory of microerosion dating is described, together with its first practical application at the site Besov Nos on the shore of Lake Onega. The article concludes with a brief discussion of the new method's advantages and disadvantages. © 1993 John Wiley & Sons, Inc. 相似文献
73.
74.
Robert E. Reed David A. Dickey JoAnn M. Burkholder Carol A. Kinder Cavell Brownie 《Estuarine, Coastal and Shelf Science》2008
Water level time series records from the Neuse and Pamlico River Estuaries were statistically compared to local and distant wind field data, water level records within the Pamlico Sound and also coastal ocean sites to determine the relative contribution of each time series to water levels in the Neuse and Pamlico Estuaries. The objectives of this study were to examine these time series data using various statistical methods (i.e. autoregressive, empirical orthogonal function analysis (EOF), exploratory data analysis (EDA)) to determine short- and long-time-scale variability, and to develop predictive statistical models that can be used to estimate past water level fluctuations in both the Neuse Estuary (NE) and Pamlico Estuary (PE). Short- and long-time-scale similarities were observed in all time series of estuarine, Pamlico Sound and subtidal coastal ocean water level and wind component data, due to events (nor'easters, fronts and tropical systems) and seasonality. Empirical orthogonal function analyses revealed a strong coastal ocean and wind field contribution to water level in the NE and PE. Approximately 95% of the variation was captured in the first two EOF components for water level data from the NE, sound and coastal ocean, and 70% for the PE, sound and coastal ocean. Spectral density plots revealed strong diurnal signals in both wind and water level data, and a strong cross correlation and coherency between the NE water level and the North/South wind component. There was good agreement between data and predictions using autoregressive statistical models for the NE (R2 = 0.92) and PE (R2 = 0.76). These methods also revealed significant autoregressive lags for the NE (days 1 and 3) and for the PE (days 1, 2 and 3). Significant departures from predictions are attributed to local meteorological and hydrological events. The autoregressive techniques showed significant predictive improvement over ordinary least squares methods. The results are considered within the context of providing long time-scale hindcast data for the two estuaries, and the importance of these data for multidisciplinary researchers and managers. 相似文献
75.
Yimnang Golbuu Katharina Fabricius Steven Victor Robert H. Richmond 《Estuarine, Coastal and Shelf Science》2008
This study analyzed how coral communities change along a gradient of increasing exposure to a mud-discharging river in the Enipein Catchment, Pohnpei, Micronesia. Using video transects, we quantified benthic communities at five sites along a gradient moving away from the river mouth towards the barrier reef. The most river-impacted site was characterized by a high accumulation of mud, low coral cover and low coral diversity. Although coral cover leveled off at ∼400 m from the river mouth to values found at the outer-most sites, coral diversity continued to increase with increasing distance, suggesting that the most distant site was still impacted by the river discharges. Fungiidae, Pavona, Acropora, Pachyseris and Porites rus all significantly increased in cover with distance from the river, while Turbinaria decreased. The combined presence and abundance of these six species groups, together with coral species richness, may help to indicate the effects of terrestrial runoff in similar runoff-exposed settings around Micronesia, whereas coral cover is not a sensitive indicator for river impact. Coral reefs are important resources for the people of Pohnpei. To prevent further degradation of this important resource, an integrated watershed approach is needed to control terrestrial activities. 相似文献
76.
Open coast storm surge water levels consist of wind setup due to wind shear at the water surface; a wave setup component caused by wind induced waves transferring momentum to the water column; an atmospheric pressure head component due to the atmospheric pressure deficit over the spatial extent of the storm system; a Coriolis forced setup or setdown component due to the effects of the rotation of the earth acting on the wind driven alongshore current at the coast; a possible seiche component due to resonance effects initiated by moving wind system, and, if astronomical tides are present, an astronomical tide component (although the tide is typically considered to be a forced astronomical event and not really a direct part of the external wind-driven meteorological component of storm surge). Typically the most important component of a storm surge is the wind setup component, especially on the U.S. East Coast and the Gulf of Mexico shorelines. In many approaches to storm surge modeling, a constant depth approximation is invoked over a limited step size in the computational domain. The use of a constant depth approximation has received little attention in the literature although can be very important to the resulting magnitude of the computed storm surge. The importance of discrete step size to the wind setup storm surge component is considered herein with a simple case computation of the wind setup component on a linear slope offshore profile. The present study findings show that the constant depth approximation to wind setup storm surge estimation is biased on the low side (except in extremely shallow water depths) and can provide large errors if discrete step size is not sufficiently resolved. Guidance has been provided on the error that one might encounter for various step sizes on different slopes. 相似文献
77.
78.
Cindy Lee Robert A. Armstrong J. Kirk Cochran Anja Engel Scott W. Fowler Madeleine Goutx Pere Masqu Juan Carlos Miquel Michael Peterson Christian Tamburini Stuart Wakeham 《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(18):1363-1368
The MedFlux project was devised to determine and model relationships between organic matter and mineral ballasts of sinking particulate matter in the ocean. Specifically we investigated the ballast ratio hypothesis, tested various commonly used sampling and modeling techniques, and developed new technologies that would allow better characterization of particle biogeochemistry. Here we describe the rationale for the project, the biogeochemical provenance of the DYFAMED site, the international support structure, and highlights from the papers published here. Additional MedFlux papers can be accessed at the MedFlux web site (http://msrc.sunysb.edu/MedFlux/). 相似文献
79.
Fluorometric Determination of Chlorophyll 总被引:32,自引:0,他引:32
80.