全文获取类型
收费全文 | 12404篇 |
免费 | 1125篇 |
国内免费 | 2316篇 |
专业分类
测绘学 | 296篇 |
大气科学 | 393篇 |
地球物理 | 1099篇 |
地质学 | 4224篇 |
海洋学 | 3319篇 |
天文学 | 5096篇 |
综合类 | 573篇 |
自然地理 | 845篇 |
出版年
2024年 | 41篇 |
2023年 | 104篇 |
2022年 | 315篇 |
2021年 | 313篇 |
2020年 | 353篇 |
2019年 | 440篇 |
2018年 | 339篇 |
2017年 | 306篇 |
2016年 | 364篇 |
2015年 | 374篇 |
2014年 | 659篇 |
2013年 | 697篇 |
2012年 | 681篇 |
2011年 | 857篇 |
2010年 | 873篇 |
2009年 | 1166篇 |
2008年 | 1122篇 |
2007年 | 1034篇 |
2006年 | 945篇 |
2005年 | 815篇 |
2004年 | 685篇 |
2003年 | 575篇 |
2002年 | 482篇 |
2001年 | 427篇 |
2000年 | 365篇 |
1999年 | 351篇 |
1998年 | 241篇 |
1997年 | 108篇 |
1996年 | 110篇 |
1995年 | 83篇 |
1994年 | 95篇 |
1993年 | 119篇 |
1992年 | 67篇 |
1991年 | 47篇 |
1990年 | 38篇 |
1989年 | 22篇 |
1988年 | 24篇 |
1987年 | 14篇 |
1986年 | 18篇 |
1985年 | 39篇 |
1984年 | 31篇 |
1983年 | 28篇 |
1982年 | 23篇 |
1981年 | 14篇 |
1980年 | 12篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 15篇 |
1877年 | 1篇 |
1875年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
R. F. Griffin 《Journal of Astrophysics and Astronomy》1990,11(4):533-540
Photoelectric radial-velocity measurements show that HD 118670 is a double-lined spectroscopic binary in an orbit which is
not quite circular and whose period is about 48 days. Spectral types of K0 V and K7 V would satisfy the photometry and the
mass ratio; the mass function would then suggest the possibility of eclipses. However, actual spectral classification indicates
a luminosity somewhat above the main sequence 相似文献
82.
Autotrophic biomass and productivity as well as nutrient distributions and phytoplankton cell populations in the James River estuary, Virginia, were quantified both spatially and temporally over a 17-month period. Emphasis was placed on the very low salinity region of the estuary in order to gain information on the fate of freshwater phytoplankters. Differing amounts of freshwater plant biomass are advected into the estuary as living material, DOC or POC and the demonstrated variability of this input must play an important role in marine biogeochemical cycling.Late summer and fall maxima in both chlorophyll a and the photosynthetic production of particulate organic carbon in very low salinity regions were inversely correlated with river discharge.During periods of low river discharge greater than 50% of the chlorophyll a biomass measured at 0‰ disappeared within a narrow range of salinity (0–2‰). Cell enumeration data suggest that species introduced from the freshwater end-member tend to comprise the bulk of the biomass removed. Confounding factors, which may contribute to the regulation of both the abundance and species of phytoplankters mid-river, include the flocculation of colloidal material with phytoplankton cells, the presence of the turbidity maximum and the growth of endemic phytoplankton populations.An inverse relationship exists between the phytoplankton abundance in very low salinity waters and the abundance of biomass measured in the lower portion of the river (estuary). Thus, autotrophic production in the fresh and very low salinity areas may indirectly regulate the onset on the spring bloom in the estuary by controlling the amount of nutrients available. 相似文献
83.
84.
85.
86.
87.
88.
M. R. Bate S. H. Lubow G. I. Ogilvie K. A. Miller 《Monthly notices of the Royal Astronomical Society》2003,341(1):213-229
We analyse the non-linear, three-dimensional response of a gaseous, viscous protoplanetary disc to the presence of a planet of mass ranging from 1 Earth mass (1 M⊕ ) to 1 Jupiter mass (1 MJ ) by using the zeus hydrodynamics code. We determine the gas flow pattern, and the accretion and migration rates of the planet. The planet is assumed to be in a fixed circular orbit about the central star. It is also assumed to be able to accrete gas without expansion on the scale of its Roche radius. Only planets with masses M p ≳ 0.1 MJ produce significant perturbations in the surface density of the disc. The flow within the Roche lobe of the planet is fully three-dimensional. Gas streams generally enter the Roche lobe close to the disc mid-plane, but produce much weaker shocks than the streams in two-dimensional models. The streams supply material to a circumplanetary disc that rotates in the same sense as the orbit of the planet. Much of the mass supply to the circumplanetary disc comes from non-coplanar flow. The accretion rate peaks with a planet mass of approximately 0.1 MJ and is highly efficient, occurring at the local viscous rate. The migration time-scales for planets of mass less than 0.1 MJ , based on torques from disc material outside the Roche lobes of the planets, are in excellent agreement with the linear theory of type I (non-gap) migration for three-dimensional discs. The transition from type I to type II (gap) migration is smooth, with changes in migration times of about a factor of 2. Starting with a core which can undergo runaway growth, a planet can gain up to a few MJ with little migration. Planets with final masses of the order of 10 MJ would undergo large migration, which makes formation and survival difficult. 相似文献
89.
90.