全文获取类型
收费全文 | 645篇 |
免费 | 32篇 |
国内免费 | 7篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 69篇 |
地球物理 | 186篇 |
地质学 | 220篇 |
海洋学 | 36篇 |
天文学 | 106篇 |
综合类 | 1篇 |
自然地理 | 61篇 |
出版年
2022年 | 7篇 |
2021年 | 7篇 |
2020年 | 9篇 |
2019年 | 13篇 |
2018年 | 13篇 |
2017年 | 14篇 |
2016年 | 18篇 |
2015年 | 13篇 |
2014年 | 18篇 |
2013年 | 37篇 |
2012年 | 21篇 |
2011年 | 24篇 |
2010年 | 18篇 |
2009年 | 25篇 |
2008年 | 24篇 |
2007年 | 21篇 |
2006年 | 25篇 |
2005年 | 22篇 |
2004年 | 26篇 |
2003年 | 26篇 |
2002年 | 18篇 |
2001年 | 17篇 |
2000年 | 13篇 |
1999年 | 13篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 12篇 |
1995年 | 14篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1988年 | 5篇 |
1987年 | 8篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1983年 | 11篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1975年 | 10篇 |
1974年 | 11篇 |
1973年 | 13篇 |
1972年 | 4篇 |
1970年 | 4篇 |
排序方式: 共有684条查询结果,搜索用时 15 毫秒
31.
Hui Wang Scott R. Stephenson Shijin Qu 《International journal of geographical information science》2019,33(7):1313-1334
Simulating land use/cover change (LUCC) and determining its transition rules have been a focus of research for several decades. Previous studies used ordinary logistic regression (OLR) to determine transition rules in cellular automata (CA) modeling of LUCC, which often neglected the spatially non-stationary relationships between driving factors and land use/cover categories. We use an integrated geographically weighted logistic regression (GWLR) CA-Markov method to simulate LUCC from 2001–2011 over 29 towns in the Connecticut River Basin. Results are compared with those obtained from the OLR-CA-Markov method, and the sensitivity of LUCC simulated by the GWLR-CA-Markov method to the spatial non-stationarity-based suitability map is investigated. Analysis of residuals indicates better goodness of fit in model calibration for geographically weighted regression (GWR) than OLR. Coefficients of driving factors indicate that GWLR outperforms OLR in depicting the local suitability of land use/cover categories. Kappa statistics of the simulated maps indicate high agreement with observed land use/cover for both OLR-CA-Markov and GWLR-CA-Markov methods. Similarity in simulation accuracy between the methods suggests that the sensitivity of simulated LUCC to suitability inputs is low with respect to spatial non-stationarity. Therefore, this study provides critical insight on the role of spatial non-stationarity throughout the process of LUCC simulation. 相似文献
32.
No meteorites from Mercury and Venus have been conclusively identified so far. In this study, we develop an original approach based on extensive Monte Carlo simulations and diffusion models to explore the radiogenic argon (40Ar*) and helium (4He*) loss behavior and the range of 40Ar/39Ar and (U‐Th)/He age signatures expected for a range of crystals if meteorites from these planets were ever to be found. We show that we can accurately date the crystallization age of a meteorite from both Mercury and Venus using the 40Ar/39Ar technique on clinopyroxene (± orthopyroxene) and that its 40Ar/39Ar age should match the Pb‐Pb age. At the surface of Mercury, phases like albite and anorthite will exhibit a complete range of 40Ar* loss ranging from 0% to 100%, whereas merrillite and apatite will show 100% 4He* loss. By measuring the crystal size and diffusion parameters of a series of plagioclase crystals, one can inverse the 40Ar* loss value to estimate the maximum temperature experienced by a rock, and narrow down the possible pre‐ejection location of the meteorite at the surface of Mercury. At the surface of Venus, plagioclase and phosphate phases will only record the age of ejection. The (U‐Th)/He systematics of merrillite and apatite will be, respectively, moderately and strongly affected by 4He* loss during the transit of the meteorite from its host planet to Earth. Finally, meteorites from Mercury or Venus will each have their own 40Ar/39Ar and (U‐Th)/He isotopic age and 38Arc cosmic ray exposure age signatures over a series of different crystal types, allowing to unambiguously recognize a meteorite for any of these two planets using radiogenic and cosmogenic noble gases. 相似文献
33.
34.
Occultations and eclipses from ancient times down to the present are analysed to determine changes in the length of the day. By subtracting the expected tidal contribution from the observed changes, the non-tidal variations are obtained. The non-tidal varations are shown to occur on time-scales of decades and millennia. 相似文献
35.
36.
37.
38.
39.
Patrick G. Hatcher Bernd R.T. Simoneit Fred T. Mackenzie A.Conrad Neumann Donald C. Thorstenson Sol M. Gerchakov 《Organic Geochemistry》1982,4(2):93-112
Mangrove Lake, Bermuda, is a small coastal, brackish-water lake that has accumulated 14 m of banded, gelatinous, sapropelic sediments in less than 104 yr. Stratigraphic evidence indicates that Mangrove Lake's sedimentary environment has undergone three major depositional changes (peat, freshwater gel, brackish-water gel) as a result of sea level changes. The deposits were examined geochemically in an effort to delineate sedimentological and diagenetic changes. Gas and pore water studies include measurements of sulfides, ammonia, methane, nitrogen gas, calcium, magnesium, chloride, alkalinity, and pH. Results indicate that sulfate reduction is complete, and some evidence is presented for bacterial denitrification and metal sulfide precipitation. The organic-rich sapropel is predominantly algal in origin, composed mostly of carbohydrates and insoluble macromolecular organic matter called humin with minor amounts of proteins, lipids, and humic acids. Carbohydrates and proteins undergo hydrolysis with depth in the marine sapropel but tend to be preserved in the freshwater sapropel. The humin, which has a predominantly aliphatic structure, increases linearly with depth and composes the greatest fraction of the organic matter. Humic acids are minor components and are more like polysaccharides than typical marine humic acids. Fatty acid distributions reveal that the lipids are of an algal and/or terrestrial plant source. Normal alkanes with a total concentration of 75 ppm exhibit two distribution maxima. One is centered about n-C22 with no odd/even predominance, suggestive of a degraded algal source. The other is centered at n-C31 with a distinct odd/even predominance indicative of a vascular plant origin. Stratigraphic changes in the sediment correlate to observed changes in the gas and pore water chemistry and the organic geochemistry. 相似文献
40.