全文获取类型
收费全文 | 498篇 |
免费 | 18篇 |
专业分类
测绘学 | 7篇 |
大气科学 | 53篇 |
地球物理 | 121篇 |
地质学 | 178篇 |
海洋学 | 64篇 |
天文学 | 61篇 |
综合类 | 1篇 |
自然地理 | 31篇 |
出版年
2023年 | 2篇 |
2021年 | 5篇 |
2020年 | 12篇 |
2019年 | 5篇 |
2018年 | 20篇 |
2017年 | 23篇 |
2016年 | 21篇 |
2015年 | 18篇 |
2014年 | 20篇 |
2013年 | 26篇 |
2012年 | 23篇 |
2011年 | 17篇 |
2010年 | 29篇 |
2009年 | 36篇 |
2008年 | 24篇 |
2007年 | 23篇 |
2006年 | 19篇 |
2005年 | 11篇 |
2004年 | 10篇 |
2003年 | 13篇 |
2002年 | 13篇 |
2001年 | 7篇 |
2000年 | 9篇 |
1999年 | 6篇 |
1998年 | 7篇 |
1997年 | 6篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 9篇 |
1992年 | 3篇 |
1990年 | 3篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1984年 | 5篇 |
1983年 | 10篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 9篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1959年 | 1篇 |
1957年 | 1篇 |
1953年 | 1篇 |
排序方式: 共有516条查询结果,搜索用时 343 毫秒
21.
22.
23.
24.
25.
Formic and acetic acids occurred in atmospheric condensate with concentrations similar to rainwater collected in Wilmington, North Carolina, during the sampling period from June to October of 1990. Atmospheric concentrations of these acids (calculated from the condensate concentrations) were higher in continental versus maritime air masses. Concentrations of formic and acetic acids were correlated with each other in both condensate and air. Traffic was a source of acetic acid and of bisulfite to atmospheric condensate in this study. 相似文献
26.
27.
Understanding the ways in which children with different life experiences come to terms with day-to-day contexts and constraints has become an important topic of social science research. This study applies the technique of auto-photography to the study of children-environment transactions. How children apprehend their environments is described through a leitmotif analysis and an interpretation of photographs taken by children from middle-class families, homeless children, and children whose mobility is impaired by cerebral palsy. We speculate upon the social and physical contexts of these children based upon the images that they selected to photograph. Although impressionistic, our findings suggest the importance of auto-photography as a method for uncovering children-environment transactions. 相似文献
28.
Summary A principal component analysis (PCA) based on a network including 179 pluviometric gauges is attempted in order to describe the main patterns governing precipitation in Catalonia (NE Spain). This PCA procedure is applied to the interstation covariance matrix and component loadings are then deduced from it and extensively interpreted. PCA results are used immediately after in a Davis and Kalkstein clustering process, leading to a rainfall division. The homogeneity of the different groups obtained is tested by means of the analysis of their spatial and temporal within-group variances.With 8 Figures 相似文献
29.
In the tidal Potomac River, high river discharges during the spring are associated with high chlorophylla concentrations in the following in the following summer, assuming that summertime light and temperature conditions are favorable. Spring floods deliver large loads of particulate N and P to the tidal river. This particulate N and P could be mineralized by bacteria to inorganic N and P and released to the water column where it is available for phytoplankton use during summertime. However, during the study period relatively low concentrations of chlorophylla (less than 50 μg l?1 occurred in the tidal river if average monthly discharge during July or August exceeded 200 m3s?1. Discharge and other conditions combined to produce conditions favorable for nuisance levels of chlorophylla (greater than 100 μg l?1 approximately one year out of four. Chlorophylla maxima occurred in the Potomac River transition zone and estuary during late winter (dinoflagellates) and spring (diatoms). Typical seasonal peak concentrations were achieved at discharges as high as 970 m3 s?1, but sustained discharges greater than 1,100 m3 s?1 retarded development. Optimum growth conditions occurred following runoff events of 10 to 15 d duration which produced transit times to the transition zone of 7 to 10 d. Wet years with numerous moderate-sized runoff events, such as 1980, tend to produce greater biomass in the transition zone and estuary than do dry years such as 1981. 相似文献
30.
Summary This work presents a statistical study of the wind power potential of three stations in the Catalonia area (Spain) over the 1973–1982 period. These stations correspond to three airports (Barcelona, Palma de Mallorca and Girona), which obviously do not present a high wind power potential and are not the suitable locations for wind power utilization, but which have been chosen for the long record of data stored (10 years). The aim of this work is to provide a model of wind potential in terms of the speed and wind direction, which may be applied to other sites. The wind speed has been modelled by a Weibull distribution function and the wind direction by a normal two-dimensional function. A spectral analysis of both variables has also been carried out. The present study provides an evaluation of the local wind power in the geographic area of Catalonia.With 10 Figures 相似文献