全文获取类型
收费全文 | 7770篇 |
免费 | 152篇 |
国内免费 | 314篇 |
专业分类
测绘学 | 212篇 |
大气科学 | 604篇 |
地球物理 | 1609篇 |
地质学 | 2880篇 |
海洋学 | 636篇 |
天文学 | 1849篇 |
综合类 | 29篇 |
自然地理 | 417篇 |
出版年
2023年 | 45篇 |
2022年 | 52篇 |
2021年 | 58篇 |
2020年 | 66篇 |
2019年 | 81篇 |
2018年 | 234篇 |
2017年 | 190篇 |
2016年 | 274篇 |
2015年 | 161篇 |
2014年 | 261篇 |
2013年 | 412篇 |
2012年 | 237篇 |
2011年 | 404篇 |
2010年 | 287篇 |
2009年 | 456篇 |
2008年 | 357篇 |
2007年 | 323篇 |
2006年 | 335篇 |
2005年 | 305篇 |
2004年 | 289篇 |
2003年 | 272篇 |
2002年 | 250篇 |
2001年 | 218篇 |
2000年 | 205篇 |
1999年 | 178篇 |
1998年 | 168篇 |
1997年 | 161篇 |
1996年 | 154篇 |
1995年 | 136篇 |
1994年 | 114篇 |
1993年 | 92篇 |
1992年 | 78篇 |
1991年 | 87篇 |
1990年 | 78篇 |
1989年 | 83篇 |
1988年 | 59篇 |
1987年 | 101篇 |
1986年 | 64篇 |
1985年 | 64篇 |
1984年 | 69篇 |
1983年 | 71篇 |
1982年 | 72篇 |
1981年 | 68篇 |
1980年 | 54篇 |
1979年 | 51篇 |
1977年 | 48篇 |
1976年 | 47篇 |
1975年 | 35篇 |
1974年 | 30篇 |
1973年 | 41篇 |
排序方式: 共有8236条查询结果,搜索用时 15 毫秒
991.
K. F. Tiampo W. Klein H.-C. Li A. Mignan Y. Toya S. Z. L. Kohen-Kadosh J. B. Rundle C.-C. Chen 《Pure and Applied Geophysics》2010,167(6-7):763-782
Recently the equilibrium property of ergodicity was identified in an earthquake fault system (Tiampo et al., Phys. Rev. Lett. 91, 238501, 2003; Phys. Rev. E 75, 066107, 2007). Ergodicity in this context not only requires that the system is stationary for these networks at the applicable spatial and temporal scales, but also implies that they are in a state of metastable equilibrium, one in which the ensemble averages can be substituted for temporal averages when studying their behavior in space and time. In this work we show that this property can be used to identify those regions of parameter space which are stationary when applied to the seismicity of two naturally-occurring earthquake fault networks. We apply this measure to one particular seismicity-based forecasting tool, the Pattern Informatics index (Tiampo et al., Europhys. Lett. 60, 481–487, 2002; Rundle et al., Proc. National Acad. Sci., U.S.A., Suppl. 1, 99, 2463, 2002), in order to test the hypothesis that the identification of ergodic regions can be used to improve and optimize forecasts that rely on historic seismicity catalogs. We also apply the same measure to synthetic catalogs in order to better understand the physical process that affects this accuracy. We show that, in particular, ergodic regions defined by magnitude and time period provide more reliable forecasts of future events in both natural and synthetic catalogs, and that these improvements can be directly related to specific features or properties of the catalogs that impact the behavior of their spatial and temporal statistics. 相似文献
992.
Electrical imaging provides important subsurface information for the construction of hypervelocity impact models. We here provide an overview and evaluation of the current electrical imaging methods used in impact cratering studies. Although apparent resistivity models are commonly used in the geoelectrical imaging of impact structures, the reliability of these models has not hitherto been determined. In order to assess these imaging approaches in impact cratering, we investigate for the first time the discrepancies between the apparent resistivity and true resistivity models of an impact structure. To this end, we present (1) a new true resistivity model of the Araguainha impact structure in central Brazil by applying L2-norm inversion to previously published data, (2) apparent resistivity model of the impact structure, and (3) models obtained from different stages of the iterative tomographic inversions. Our results show that changes in vertical resistivity gradient are significantly better defined in the true resistivity models than in the apparent resistivity model. On the basis of these results, we outline a new approach that true resistivity models can be effectively assessed by applying both L1- and L2-norm inversion schemes together with the monitoring of intermediate models from iterative inversion. The results of our study highlight the importance of tomographic inversion of resistivity data in impact cratering studies, and they provide a data modeling framework and foundation for cost-effective subsurface imaging of impact structures in the future. 相似文献
993.
994.
Geomagnetism and Aeronomy - The solar influence on long-term climatic processes of Earth has been studied with the use of long-term series of historical reconstructions of Total Solar Irradiation... 相似文献
995.
996.
997.
The temporal variability of 210Po and 210Pb was examined in the overlying water of the Zhubi Coral Reef flat to detect nutrient-like behavior of 210Po. Different mechanisms influencing their geochemical behaviors were observed. Excess 210Po relative to 210Pb revealed an additional input of 210Po other than in situ production from 210Pb. The 210Po input comes from the reef flat sediment through diffusion. The diffusion contributes 62% of the total 210Po. This diffusion of 210Po directly highlights its nutrient-like behavior. No input, but the slight removal, of 210Pb was observed. Fractionation factors indicate that particulate matter prefers to adsorb 210Po rather than 210Pb. In combination with particulate composition, 210Po diffusion was closely related to organic matter. These results reveal that 210Po might be a potential tracer for quantifying nutrient recycling in the Coral Reef system. 相似文献
998.
S. Wang G. H. Huang H. W. Lu Y. P. Li 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(2):211-222
In this study, an interval-valued fuzzy linear programming with infinite α-cuts (IVFLP-I) method is developed for municipal
solid waste (MSW) management under uncertainty. IVFLP-I can not only tackle uncertainties expressed as intervals and interval-valued
fuzzy sets, but also take all fuzzy information into account by discretizing infinite α-cut levels to the interval-valued
fuzzy membership functions. Through adoption of the interval-valued fuzzy sets, IVFLP-I can directly communicate information
of waste managers’ confidence levels over various subjective judgments into the optimization process. Compared to the existing
methods in which only finite α-cut levels exist, IVFLP-I would have enhanced the robustness in the optimization efforts. A
MSW management problem is studied to illustrate the applicability of the proposed method. Four groups of optimal solutions
can be obtained through assigning different intervals of α-cut levels. The results indicate that wider intervals of α-cut
levels could lead to a lower risk level of constraint violation associated with a higher system cost; contrarily, narrower
intervals of α-cut levels could lead to a lower cost with a higher risk of violating the constraints. The solutions under
different intervals of α-cut levels can support in-depth analyses of tradeoffs between system costs and constraint-violation
risks. 相似文献
999.
Comparison of SDSM and LARS-WG for simulation and downscaling of extreme precipitation events in a watershed 总被引:6,自引:6,他引:6
Muhammad Zia Hashmi Asaad Y. Shamseldin Bruce W. Melville 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(4):475-484
Future climate projections of Global Climate Models (GCMs) under different emission scenarios are usually used for developing
climate change mitigation and adaptation strategies. However, the existing GCMs have only limited ability to simulate the
complex and local climate features, such as precipitation. Furthermore, the outputs provided by GCMs are too coarse to be
useful in hydrologic impact assessment models, as these models require information at much finer scales. Therefore, downscaling
of GCM outputs is usually employed to provide fine-resolution information required for impact models. Among the downscaling
techniques based on statistical principles, multiple regression and weather generator are considered to be more popular, as
they are computationally less demanding than the other downscaling techniques. In the present study, the performances of a
multiple regression model (called SDSM) and a weather generator (called LARS-WG) are evaluated in terms of their ability to
simulate the frequency of extreme precipitation events of current climate and downscaling of future extreme events. Areal
average daily precipitation data of the Clutha watershed located in South Island, New Zealand, are used as baseline data in
the analysis. Precipitation frequency analysis is performed by fitting the Generalized Extreme Value (GEV) distribution to
the observed, the SDSM simulated/downscaled, and the LARS-WG simulated/downscaled annual maximum (AM) series. The computations
are performed for five return periods: 10-, 20-, 40-, 50- and 100-year. The present results illustrate that both models have
similar and good ability to simulate the extreme precipitation events and, thus, can be adopted with confidence for climate
change impact studies of this nature. 相似文献
1000.
Formation of iron plaque on mangrove roots receiving wastewater and its role in immobilization of wastewater-borne pollutants 总被引:2,自引:0,他引:2
Iron (Fe) plaque formed on mangrove root increased with wastewater discharge, but the extent was species-specific. For Bruguiera gymnorrhiza, Fe plaque concentration was 0.80 mg g(-1) root d.wt at Day 0 and increased to 4.59, 6.84 and 7.52 mg g(-1) at Day 75 in the fresh water control (FW), synthetic wastewater with pollutant concentrations five times of municipal sewage (5SW) and double of 5SW (10SW) treatments, respectively; the respective increases in Excoecaria agallocha were from 0.70 to 2.37, 10.73 and 13.21 mg g(-1). For Acanthus ilicifolius, similar increase was found in 5SW, but all of the plants were dead in 10SW at Day 75. The concentrations of heavy metals and phosphorus immobilized were positively correlated with the amounts of Fe plaque formed, but the regression coefficients varied among species. The performance of mangrove plants in wastewater treatments was related to the Fe plaque formed and its immobilized wastewater-borne pollutants. 相似文献