全文获取类型
收费全文 | 450篇 |
免费 | 25篇 |
国内免费 | 12篇 |
专业分类
测绘学 | 7篇 |
大气科学 | 50篇 |
地球物理 | 125篇 |
地质学 | 164篇 |
海洋学 | 80篇 |
天文学 | 31篇 |
综合类 | 4篇 |
自然地理 | 26篇 |
出版年
2024年 | 3篇 |
2023年 | 7篇 |
2022年 | 7篇 |
2021年 | 15篇 |
2020年 | 21篇 |
2019年 | 9篇 |
2018年 | 29篇 |
2017年 | 15篇 |
2016年 | 11篇 |
2015年 | 23篇 |
2014年 | 13篇 |
2013年 | 25篇 |
2012年 | 25篇 |
2011年 | 38篇 |
2010年 | 22篇 |
2009年 | 27篇 |
2008年 | 28篇 |
2007年 | 25篇 |
2006年 | 14篇 |
2005年 | 21篇 |
2004年 | 15篇 |
2003年 | 15篇 |
2002年 | 11篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 8篇 |
1998年 | 3篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1995年 | 7篇 |
1994年 | 3篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 2篇 |
排序方式: 共有487条查询结果,搜索用时 312 毫秒
421.
Ricardo?A.?OleaEmail author N.?Janardhana?Raju Juan?José?Egozcue Vera?Pawlowsky-Glahn Shubhra?Singh 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(1):241-259
The area east of Varanasi is one of numerous places along the watershed of the Ganges River with groundwater concentrations of arsenic surpassing the maximum value of 10 parts per billion (ppb) recommended by the World Health Organization in drinking water. Here we apply geostatistics and compositional data analysis for the mapping of arsenic and iron to help in understanding the conditions leading to the occurrence of elevated level of arsenic in groundwater. The methodology allows for displaying concentrations of arsenic and iron as maps consistent with the limited information from 95 water wells across an area of approximately 210 km2; visualization of the uncertainty associated with the sampling; and summary of the findings in the form of probability maps. For thousands of years, Varanasi has been on the erosional side in a meander of the river that is free of arsenic values above 10 ppb. Maps reveal two anomalies of high arsenic concentrations on the depositional side of the valley, which has started seeing urban development. The methodology using geostatistics combined with compositional data analysis is completely general, so this study could be used as a prototype for hydrochemistry mapping in other areas. 相似文献
422.
423.
An extension to the existing SAC/FEMA expressions to estimate mean annual frequency of exceedance (MAFE) for a given limit state is described. In specific, this study pertains to structural systems whose demand versus seismic intensity relationship cannot be reasonably represented by a linear fit in logspace, but rather a bilinear fit over the entire range of structural response. Using a predefined limiting intensity, the median demand is separated into two distinct zones of response. These expressions are derived using a second-order polynomial hazard model fit and can be considered a further extension of the closed-form expressions available in the literature. The steps in the derivation are described along with an example application of the proposed expressions. Comparing different models shows that the MAFE can be significantly misrepresented when using a linear demand-intensity model for systems whose behaviour deviates from this assumption in logspace. Similarly, a logarithmic function demand-intensity fit is examined and seen not to be suitable in the specific situations focused on here. Furthermore, significant underestimation or overestimation is observed when using local fits in the vicinity of the behaviour transition point, which highlights the need for such a bilinear model when assessing the structural performance at the transition point's vicinity. Adopting a bilinear model is shown to better represent structural systems with complex response characteristics, also allowing the use of a single demand model for the entire range of response. This is at the same time still compatible with the existing framework for performance-based seismic design and assessment. 相似文献
424.
The effectiveness of Tuned Mass Dampers (TMD) on buildings subjected to moderate and high-intensity motions is analysed. First, the response of a 22-storey four-bay reinforced concrete non-linear frame with a TMD is studied for motions with different intensities. Several values of the relevant parameters are assumed in the analyses. Then, equivalent single-degree-of-freedom systems with TMDs and without them are defined and analysed under the action of ground motions with intensities associated with different return intervals at the site where the structures are located. Vulnerability curves for the systems are obtained based on the probabilities of reaching two different performance limit states. The expected annual rate of exceedance of each limit state is calculated. The results show that the effectiveness of TMDs is higher for systems with small non-linearity produced by small and moderate earthquakes, than for systems with high non-linear behaviour, generally associated with high-intensity motions. Some recommendations about the applicability of TMD are given. Copyright © 1999 John Wiley & Sons Ltd. 相似文献
425.
Ricardo Sousa Joana Vasconcelos Rodrigo Riera Joo Delgado Jos A. Gonzlez Mafalda Freitas Paulo Henriques 《Marine Ecology》2019,40(2)
Harvesting of intertidal grazers such as topshells is known to affect negatively the exploited populations by altering population structure and decreasing abundance. Phorcus sauciatus has a wide geographic distribution in the North‐eastern Atlantic Ocean and is subject to increasing levels of harvesting pressure due to the expansion of human population on coastal areas. The effect of proximity to human settlements and coastal accessibility on the size structure and abundance of P. sauciatus populations was examined in Madeira archipelago. Mean size, proportion of reproductive individuals, and abundance of this species were generally smaller in areas closer to human settlements and in more accessible coastal areas. Marine protected areas returned the highest mean sizes evidencing their effectiveness in preserving the size structure of this species. The results highlight the necessity to regulate the harvest of P. sauciatus in Madeira archipelago, as well as the implementation of management measures aiming at the sustainable exploitation and conservation of this species, exploited in this region since the early 15th century. 相似文献
426.
Erten Oktay Pardo-Igúzquiza Eulogio Olea Ricardo A. 《Natural Resources Research》2020,29(2):1087-1099
Natural Resources Research - The semivariogram, which measures the spatial variability between experimental data, is generally used as a structural input in all two-point geostatistical procedures.... 相似文献
427.
The reproductive biology and population dynamics of the cirolanid isopod Excirolana armata (Dana, 1853) were analysed through monthly samples from December 2003 to November 2005 on Una beach, São Paulo state (24° S), in Southeastern Brazil. Sampling was performed along three transects established from the base of foredunes to the waterline. On Una beach, E. armata showed continuous reproduction with higher abundances of ovigerous females in winter and spring (July–November) with a higher peak of juveniles in spring (November 2004). The fecundity ranged from 2 to 18 eggs/embryos per female, depending on the female length. The incubation period was estimated as 2 months. The life span of males and females was nearly 1 year. The short life span and the high energetic expenditure inherent to reproduction with maternal care, probably kept females from producing more than one brood in their lifetime. When comparing the population of E. armata on Una beach (24° S) with populations in Southern Brazil (32° S), Uruguay (34° S) and Argentina (36° S), it was verified that several biological population traits (length of the smallest juvenile, length of the largest individual, length of the smallest and largest ovigerous females, range of fecundity and life span) tended to increase at higher latitudes, whereas other traits (instantaneous rate of mortality and the curvature parameter of von Bertalanffy growth function) tended to decrease. However, comparing E. armata on Una beach (24° S) with a population situated at a close latitude (25° S), unexpected differences in relation to population structure and to growth demonstrated and reinforced the importance of density‐dependent factors over life history traits of E. armata on dissipative beaches. 相似文献
428.
We evaluated the applicability of Rapoport’s Rule (RR) to the marine bony fishes of the world. The biogeographical pattern predicted by RR has been the subject of a large number of studies, some supporting it and some not. In this exercise, we attempted to generate results free of biases from taxonomy or geographic scale. The study area encompassed all world oceans. Our analysis was based on secondary data. We tested the relationship of the geographic range and the bathymetric range to the latitude gradient, using the method of Stevens (American Naturalist 1989, 133 , 240–256) . We compared all known species of marine bony fishes together, and performed a second analysis limited to the non‐pelagic species. Our results were generated from a databank including 13,957 species. The results indicated that RR (latitudinal range) is valid for 11 regions. However, there were exceptions for the northern part of the Eastern Atlantic and Pacific, the northern part of the Western Indian, and the Arctic Oceans. The analyses of RR (bathymetric range) were supported for 13 regions. We found only one exception, for the northern part of the Western Indian Ocean. The applicability of RR and its relationship to energy supply, represented here by the temperature variability of the marine water masses, was clear. The exceptions appeared when some feature associated with the distribution of water masses was superposed on the latitudinal gradient, or when some life trait characteristic of a taxon, for instance body size, was confounded with the effect of climate variability. 相似文献
429.
Marangoni Gazineu Marinho Pinto Paula Martins Campos Ricardo Gallo Marcos Nicolas Parente Ribeiro Carlos Eduardo 《Ocean Dynamics》2023,73(6):303-315
Ocean Dynamics - Accurate simulations of significant wave height (Hs) are extremely important for the safety of navigation, port operations, and oil and gas exploration. Thus, accurate forecasts of... 相似文献
430.