全文获取类型
收费全文 | 8348篇 |
免费 | 348篇 |
国内免费 | 94篇 |
专业分类
测绘学 | 200篇 |
大气科学 | 576篇 |
地球物理 | 1965篇 |
地质学 | 2992篇 |
海洋学 | 768篇 |
天文学 | 1257篇 |
综合类 | 20篇 |
自然地理 | 1012篇 |
出版年
2021年 | 88篇 |
2020年 | 114篇 |
2019年 | 116篇 |
2018年 | 169篇 |
2017年 | 162篇 |
2016年 | 227篇 |
2015年 | 201篇 |
2014年 | 200篇 |
2013年 | 476篇 |
2012年 | 250篇 |
2011年 | 317篇 |
2010年 | 290篇 |
2009年 | 353篇 |
2008年 | 329篇 |
2007年 | 287篇 |
2006年 | 324篇 |
2005年 | 243篇 |
2004年 | 298篇 |
2003年 | 268篇 |
2002年 | 270篇 |
2001年 | 177篇 |
2000年 | 174篇 |
1999年 | 146篇 |
1998年 | 145篇 |
1997年 | 108篇 |
1996年 | 117篇 |
1995年 | 122篇 |
1994年 | 131篇 |
1993年 | 112篇 |
1992年 | 113篇 |
1991年 | 107篇 |
1990年 | 103篇 |
1989年 | 86篇 |
1988年 | 85篇 |
1987年 | 115篇 |
1986年 | 98篇 |
1985年 | 165篇 |
1984年 | 192篇 |
1983年 | 145篇 |
1982年 | 127篇 |
1981年 | 129篇 |
1980年 | 108篇 |
1979年 | 127篇 |
1978年 | 119篇 |
1977年 | 104篇 |
1976年 | 99篇 |
1975年 | 92篇 |
1974年 | 68篇 |
1973年 | 85篇 |
1972年 | 51篇 |
排序方式: 共有8790条查询结果,搜索用时 31 毫秒
991.
Linda Sedlacek David Thistle Kevin R. Carman John W. Fleeger James P. Barry 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(6):1018-1025
As part of the evaluation of the environmental impact of sequestering carbon dioxide in the deep ocean, we exposed the sediment-dwelling fauna at a station in Monterey Submarine Canyon (36.378°N, 122.676°W, 3262 m) to carbon dioxide-rich seawater and found that most of the harpacticoid copepods were killed. In an expanded, follow-on experiment on the continental rise nearby (36.709°N, 123.523°W, 3607 m), not only did harpacticoids survive exposure to carbon dioxide-rich seawater, but we found no evidence from seven additional metrics that the harpacticoids had been affected. We infer that during the second experiment the harpacticoids were not exposed to a stressful dose. During the second experiment, carbon dioxide-rich seawater appears to have been produced more slowly than in the first, probably because of differences in the near-bottom flow regimes. We conclude that local physical circumstances can substantially influence the results of experiments of this type and will complicate the evaluation of the environmental consequences of deep-ocean carbon dioxide sequestration. 相似文献
992.
The California Current System (CCS) is forced by the distribution of atmospheric pressure and associated winds in relation to the west coast of North America. In this paper, we begin with a simplified case of winds and a linear coast, then consider variability characteristic of the CCS, and conclude by considering future change. The CCS extends from the North Pacific Current (~50°N) to off Baja California, Mexico (~15–25°N) with a major discontinuity at Point Conception (34.5°N). Variation in atmospheric pressure affects winds and thus upwelling. Coastal, wind-driven upwelling results in nutrification and biological production and a southward coastal jet. Offshore, curl-driven upwelling results in a spatially large, productive habitat. The California Current flows equatorward and derives from the North Pacific Current and the coastal jet. Dominant modes of spatial and temporal variability in physical processes and biological responses are discussed. High surface production results in deep and bottom waters depleted in oxygen and enriched in carbon dioxide. Fishing has depleted demersal stocks more than pelagic stocks, and marine mammals, including whales, are recovering. Krill, squid, and micronekton are poorly known and merit study. Future climate change will differ from past change and thus prediction of the CCS requires an understanding of its dynamics. Of particular concern are changes in winds, stratification, and ocean chemistry. 相似文献
993.
Earth, Moon, and Planets - 相似文献
994.
Through a combination of aerobraking (drag deceleration) and ablation, meteoroids which enter planetary atmospheres may be slowed sufficiently to soft-land as meteorites. Results of an earlier study suggest that the current 6 mbar atmosphere of Mars is sufficient to aerobrake significant numbers of small (<10 kg) asteroidal-type meteoroids into survivable, low-velocity (<500 m s−1) impacts with the planet's surface. Since rates of meteorite production depend upon the density of Mars's atmosphere, they must also change as the martian climate changes. However, to date, martian meteorite production has received relatively little attention in the literature Here we expand upon our previous work to study martian meteorite production rates and how they depend upon variations of the martian atmosphere, and to estimate the ranges of mass, velocity and entry-angle that produce meteorites. We find that even the current atmosphere of Mars is sufficient to soft-land significant fractions of incident stony and iron objects, and that these fractions increase dramatically for denser martian atmospheres. Therefore, like impact cratering, meteorite populations may preserve evidence of past martian climates. 相似文献
995.
John D. Bunton 《Experimental Astronomy》2004,17(1-3):251-259
When the SKA was proposed, a major technical obstacle to its feasibility was the cost of the correlator. Significant advances made in correlator design since then are described. These advances have made SKA correlator possible within reasonable cost constrains. At the same time performance issues with the proposed FX architecture have been addressed. 相似文献
996.
A set of well-measured, {low-z}, type Ia supernovae from the Calán/Tololo SNe data sets is used to determine benchmark parameters
in our hydrodynamics-based, light-curve model. The light-curve data fit fairly well in B, V, and R passbands but not as well
in the I passband. The fitting procedure, extracted best-fit model parameters, and their connection to type Ia SN parameters
are presented. Our benchmarked light-curve model represents an alternative to empirical template methods for the analysis
of light-curve data. 相似文献
997.
998.
999.
1000.