全文获取类型
收费全文 | 182篇 |
免费 | 1篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 10篇 |
地球物理 | 34篇 |
地质学 | 54篇 |
海洋学 | 18篇 |
天文学 | 54篇 |
综合类 | 1篇 |
自然地理 | 11篇 |
出版年
2024年 | 2篇 |
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 1篇 |
2019年 | 5篇 |
2018年 | 8篇 |
2017年 | 4篇 |
2016年 | 2篇 |
2015年 | 2篇 |
2014年 | 5篇 |
2013年 | 3篇 |
2012年 | 12篇 |
2011年 | 10篇 |
2010年 | 14篇 |
2009年 | 20篇 |
2008年 | 8篇 |
2007年 | 11篇 |
2006年 | 11篇 |
2005年 | 6篇 |
2004年 | 7篇 |
2003年 | 6篇 |
2002年 | 10篇 |
2001年 | 7篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1981年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有186条查询结果,搜索用时 15 毫秒
61.
62.
63.
64.
Carlos Neira Jennifer Cossaboon Guillermo Mendoza Eunha Hoh Lisa A. Levin 《Marine pollution bulletin》2017,114(1):466-479
Polycyclic aromatic hydrocarbons (PAHs) have garnered much attention due to their bioaccumulation, carcinogenic properties, and persistence in the environment. Investigation of the spatial distribution, composition, and sources of PAHs in sediments of three recreational marinas in San Diego Bay, California revealed significant differences among marinas, with concentrations in one site exceeding 16,000 ng g? 1. ‘Hotspots’ of PAH concentration suggest an association with stormwater outfalls draining into the basins. High-molecular weight PAHs (4–6 rings) were dominant (> 86%); the average percentage of potentially carcinogenic PAHs was high in all sites (61.4–70%) but ecotoxicological risks varied among marinas. Highly toxic benzo(a)pyrene (BaP) was the main contributor (> 90%) to the total toxic equivalent quantity (TEQ) in marinas. PAHs in San Diego Bay marina sediments appear to be derived largely from pyrogenic sources, potentially from combustion products that reach the basins by aerial deposition and stormwater drainage from nearby streets and parking lots. 相似文献
65.
66.
67.
Guillermo J. Berri Jorgelina S. Galli Nuin Laura Sraibman German Bertossa 《Boundary-Layer Meteorology》2012,142(2):329-337
Low-level climatological wind fields over the La Plata River region of South America are synthesized with a dry, hydrostatic
mesoscale boundary-layer numerical model. The model is forced at the upper boundary with the 1200 UTC local radiosonde observations
and at the lower boundary with a land-river differential heating function defined from the daily meteorological observations
of the region. The climatological wind field is defined as the mean value of a series of individual daily forecasts, employing
two methods. The simplified method considers a 192-member ensemble (16 wind directions and 12 wind-speed classes at the upper
boundary). Each member has a probability of occurrence that is determined from the 1959–1984 observations; the daily method
uses a total of 3,248 days with available data during the same period. In both methods each realization is a daily forecast
from which the mean wind distributions at 0300, 0900, 1500 and 2100 local standard time are calculated and compared to the
observations of five meteorological stations in the region. The validation of the climatological wind fields for both methods
is evaluated by means of the root-mean-square error of the wind-direction frequency distribution and mean wind speed by wind
sector. The results obtained with the two methods are similar, and the errors in wind speed are always smaller than those
in wind direction. The combined errors of wind direction and wind speed show that the ensemble method is outperformed by the
daily method, on average by meteorological station in only one out of five of them, and on average by the time of the day
in only one out of 4 h. The conclusion of the study is that the ensemble method is an appropriate methodology for determining
high resolution, low-level climatological wind fields, with the boundary-layer model applied to a region with a strong diurnal
cycle of surface thermal contrast. The proposed methodology is of particular utility for synthesizing wind fields over regions
with limited meteorological observations, since the 192-member matrix can be easily defined with few observing points, as
well as in the case of relatively incomplete records. 相似文献
68.
The Mexican coast can be regionalized according to the main economic activities performed in it; for the purpose of this work we are considering five regions: North Pacific, Mar de Cortes, outh Pacific, Gulf of Mexico, and Caribbean. According to the national census, the population of the coastal zone in Mexico is increasing at a higher rate than the national average. The main industries located in the coastal and marine zones are oil and gas, fisheries, aquaculture, tourism, maritime transportation and ports, chemical industries, and minerals. Mexico has developed an environmental legal framework based on the Ley General del Equilibrio Ecologico y la Proteccion al Ambiente (LGEEPA), and the coastal management paradigm is strengthened through several other legal tools developed specifically for this purpose. There are three management strategies identified in this work for the coastal zone in Mexico: (1) Agency Leadership, (2) Protected Areas, and (3) Land Ordinance. Each one of these strategies includes stages for eventually developing an Integrated Coastal Zone Management (ICZM) plan that considers vertical and horizontal integration, scientific research of natural resources and ecosystems, and socioeconomic issues. 相似文献
69.
Adriana?V.?R.?SilvaEmail author Tatiana?F.?Laganá C.?Guillermo?Gimenez?De?Castro Pierre?Kaufmann Joaquim?E.?R.?Costa Hugo?Levato Marta?Rovira 《Solar physics》2005,227(2):265-281
Solar maps at 212 and 405 GHz obtained by the Solar Submillimetric Telescope (SST) show regions of enhanced brightness temperature, which coincide with the location of active regions. A statistical study of the radio emission from these active regions was performed for the first time at such high frequencies during 23 days on June and July 2002, when the atmospheric opacity was low. The brightest regions on the maps were chosen for this study, where the brightness excess observed varies from 3 to 20% above quiet Sun levels (i.e., 200–1000 K) at both wavelengths. Sizes of the regions of enhanced emission calculated at half the maximum value were estimated to be between 2′ and 7′. These sizes agree with observed sizes of active regions at other wavelengths such as Hα and ultraviolet. An important result is that the flux density spectra of all sources increase toward submillimeter frequencies, yielding flux density spectral index with an average value of 2.0. The flux density of the active region sources were complemented with that from maps at 17 and 34 GHz from the Nobeyama Radio Heliograph. The resulting spectra at all four frequencies were fit considering the flux density to be due to thermal bremsstrahlung from the active region. In the calculations, the source radius was assumed to be the mean of the measured values at 212 and 405 K. The effective temperatures of the radio emitting source, assumed homogeneous, obtained from this fit were 0.6–2.9 × 104 K, for source diameters of 2′–7′. 相似文献
70.
The Ba/Ca in the growth bands of Montastraea faveolata from the Veracruz Reef System was used to reconstruct the long-term environmental change associated to anthropogenic activity in the Southern Gulf of Mexico (SGM). The 168-yr coral record shows two periods of distinct Ba concentrations: a pre-industrial period (1835-1965: 7.54 μmol/mol) followed by an industrial one (1966-2000: 8.57 μmol/mol). As human population quadrupoled during the latter, sediment load in the fluvial discharge also increased due to changes in land-use, yielding a 14% increase in the Ba-levels. A remarkable finding is that the periods at which the coral Ba/Ca ratio losses its correlation with fluvial discharge coincide exactly with peak periods of high barite consumption (used for oil drilling) in the Northern Gulf of Mexico, and the onset of oil drilling in the SGM. This finding suggests that barite may be one of the dominant sources for dissolved-Ba in the SGM. 相似文献