全文获取类型
收费全文 | 1390篇 |
免费 | 65篇 |
国内免费 | 114篇 |
专业分类
测绘学 | 63篇 |
大气科学 | 54篇 |
地球物理 | 100篇 |
地质学 | 140篇 |
海洋学 | 146篇 |
天文学 | 958篇 |
综合类 | 45篇 |
自然地理 | 63篇 |
出版年
2024年 | 3篇 |
2023年 | 8篇 |
2022年 | 16篇 |
2021年 | 19篇 |
2020年 | 23篇 |
2019年 | 28篇 |
2018年 | 20篇 |
2017年 | 23篇 |
2016年 | 21篇 |
2015年 | 43篇 |
2014年 | 41篇 |
2013年 | 61篇 |
2012年 | 37篇 |
2011年 | 30篇 |
2010年 | 41篇 |
2009年 | 84篇 |
2008年 | 56篇 |
2007年 | 97篇 |
2006年 | 91篇 |
2005年 | 110篇 |
2004年 | 102篇 |
2003年 | 94篇 |
2002年 | 89篇 |
2001年 | 70篇 |
2000年 | 68篇 |
1999年 | 70篇 |
1998年 | 93篇 |
1997年 | 10篇 |
1996年 | 10篇 |
1995年 | 21篇 |
1994年 | 15篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 10篇 |
1990年 | 12篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1976年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1569条查询结果,搜索用时 31 毫秒
321.
322.
Osman Demircan 《Astrophysics and Space Science》2005,296(1-4):209-220
An analytically tractable method of transforming the problem of light curve analysis of eclipsing binaries from the time domain
into the frequency domain was introduced by Kopal (1975, 1979, 1990). This method uses a new general formulation of eclipse
functions α, the so-called moments A
2m
, and their combinations as g
2m
= A
2m+2/(A
2m
A
2m+4) functions for the basic spherical model. In this paper, I will review the use of these functions in the light curve analysis
of eclipsing binaries. 相似文献
323.
H. L. Worters S. P. S. Eyres G. E. Bromage J. P. Osborne 《Monthly notices of the Royal Astronomical Society》2007,379(4):1557-1561
The latest outburst of the recurrent nova RS Oph occurred in 2006 February. Photometric data presented here show evidence of the resumption of optical flickering, indicating re-establishment of accretion by day 241 of the outburst. Magnitude variations of up to 0.32 mag in V band and 0.14 mag in B band on time-scales of 600–7000 s are detected. Over the two-week observational period, we also detect a 0.5 mag decline in the mean brightness, from V ≈ 11.4 to 11.9, and record B ≈ 12.9 mag . Limits on the mass accretion rate of are calculated, which span the range of accretion rates modelled for direct wind accretion and Roche lobe overflow mechanisms. The current accretion rates make it difficult for thermonuclear runaway models to explain the observed recurrence interval, and this implies average accretion rates are typically higher than seen immediately post-outburst. 相似文献
324.
325.
Period–luminosity sequences have been shown to exist among the semiregular variables (SRVs) in the Magellanic Clouds, the bulge of the Milky Way galaxy and elsewhere. Using modern-period and revised Hipparcos parallax data, this paper demonstrates that they also appear among the M giant SRVs of the solar neighbourhood. Their distribution in the K , log P diagram resembles that of Bulge stars more closely than those in the Magellanic Clouds. The prevalence of mass-loss among local M-type SRVs and its dependence on period and spectral subtype are also discussed. K −[12] , a measure of circumstellar dust emission, increases clearly with V amplitude, M giant subtype and log P . 相似文献
326.
327.
Abstract This study quantifies global changes in irrigation requirements for areas presently equipped for irrigation of major crop types, using climate projections from 19 GCMs up to the 2080s. Analysis is based on results from the global eco-hydrological model LPJmL that simulates the complex and dynamic interplay of direct and indirect climate change effects upon irrigation requirements. We find a decrease in global irrigation demand by ~17% in the ensemble median, due to a combination of beneficial CO2 effects on plants, shorter growing periods and regional precipitation increases. In contrast, increases of >20% are projected with a high likelihood (i.e. in more than two thirds of the climate change scenarios) for some regions, including southern Europe, and, with a lower likelihood, for parts of Asia and North America as well. If CO2 effects were not accounted for, however, global irrigation demand would hardly change, and increases would prevail in most regions except for southern Asia (where higher precipitation is projected). We stress that the CO2 effects may not be realized everywhere, that irrigation requirements will probably increase further due to growing global food demand (not considered here), and that a significant amount of water to meet future irrigation requirements will have to be taken from fossil groundwater, environmental flow reserves or diverted rivers. Editor D. Koutsoyiannis; Associate editor A. Montanari Citation Konzmann, M., Gerten, D., and Heinke, J., 2013. Climate impacts on global irrigation requirements under 19 GCMs, simulated with a vegetation and hydrology model. Hydrological Sciences Journal, 58 (1), 1–18. 相似文献
328.
Recruitment of early life stages into estuaries is an integral part of the life cycle of many marine fish species. Although estuaries are naturally environmentally dynamic, they also are subject to anthropogenic disturbances, including land use and climate change, which may affect recruitment. Rhabdosargus holubi is an endemic marine-spawning species predominantly associated with freshwater-rich estuaries which serve as nursery areas for postflexion larvae and juveniles. This study assessed the effect of environmental variables on the dynamics of recruitment of R. holubi larvae and juveniles into the Swartkops and Sundays estuaries, South Africa. Over a period of two years, fyke nets were set at each estuary mouth to monitor movement into the estuaries at each tidal phase over a 24 h cycle during two sampling sessions per season. Rhabdosargus holubi larvae recruited into estuaries primarily in summer and autumn and during the ebb tide at night, while juvenile movements showed no pattern. Salinity, turbidity and temperature were significantly important factors affecting R. holubi recruitment, with pH having no significant effect. Turbidity and salinity are affected by rainfall and freshwater abstraction which may thus influence recruitment. Rhabdosargus holubi is dependent on estuaries, so a combination of future changes in turbidity, salinity and temperature due to predicted climate change may place populations at risk. 相似文献
329.
330.
R. Zamanov S. Boeva G. Latev K. A. Stoyanov S. V. Tsvetkova 《Astronomische Nachrichten》2015,336(2):189-195
We performed simultaneous observations in 3 bands (U BV) of the flickering variability of the recurrent novae RS Oph and T CrB at quiescence. Using new and published data, we compare the colours of the flickering in cataclysmic variables and symbiotic recurrent novae. We find a difference between the colours of the flickering source in these two types of accreting white dwarfs. The detected difference is highly significant with p ‐values ≈2 x 10–6 for the distributions of (U – B)0 colour and p ≈ 3 x 10–5 on an (U – B) versus (B – V) diagram. The possible physical reasons are briefly discussed. The data are available upon request from the authors. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献