全文获取类型
收费全文 | 76507篇 |
免费 | 1036篇 |
国内免费 | 834篇 |
专业分类
测绘学 | 2259篇 |
大气科学 | 5540篇 |
地球物理 | 14564篇 |
地质学 | 27281篇 |
海洋学 | 6669篇 |
天文学 | 18117篇 |
综合类 | 292篇 |
自然地理 | 3655篇 |
出版年
2022年 | 472篇 |
2021年 | 816篇 |
2020年 | 839篇 |
2019年 | 936篇 |
2018年 | 2106篇 |
2017年 | 2019篇 |
2016年 | 2520篇 |
2015年 | 1407篇 |
2014年 | 2419篇 |
2013年 | 4063篇 |
2012年 | 2505篇 |
2011年 | 3250篇 |
2010年 | 2791篇 |
2009年 | 3616篇 |
2008年 | 3116篇 |
2007年 | 3138篇 |
2006年 | 3001篇 |
2005年 | 2265篇 |
2004年 | 2229篇 |
2003年 | 2163篇 |
2002年 | 2072篇 |
2001年 | 1826篇 |
2000年 | 1735篇 |
1999年 | 1463篇 |
1998年 | 1480篇 |
1997年 | 1388篇 |
1996年 | 1234篇 |
1995年 | 1197篇 |
1994年 | 1070篇 |
1993年 | 924篇 |
1992年 | 876篇 |
1991年 | 887篇 |
1990年 | 933篇 |
1989年 | 788篇 |
1988年 | 774篇 |
1987年 | 888篇 |
1986年 | 761篇 |
1985年 | 953篇 |
1984年 | 1043篇 |
1983年 | 957篇 |
1982年 | 915篇 |
1981年 | 789篇 |
1980年 | 759篇 |
1979年 | 712篇 |
1978年 | 704篇 |
1977年 | 618篇 |
1976年 | 556篇 |
1975年 | 552篇 |
1974年 | 548篇 |
1973年 | 600篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
LEIV K. SYDNES 《Polar research》1991,10(2):609-618
The boehaviour and ultimate effect and fate of oil in the marine environment in the polar region depend on a large number of factors. From a chemical point of view the most important ones to consider are the intrinsic chemical properties of the oil, the consequences of oil/water interactions, the influence of ice on physical and chemical processes, and the interactions between oil and light when the influx of solar energy shows great seasonal changes. This paper reviews the main aspects of these issues. 相似文献
102.
The three-dimensional geometry of the heliospheric current sheet seen from fixed points in interplanetary space is constructed for idealized (sinusoidal) magnetic neutral lines (equators) and for an observed magnetic equator on the basis of the “kinematic method” developed by Hakamada and Akasofu (1982). The cross-sections of the wavy current sheet at distances 1, 2 and 5 a.u. are also constructed for the idealized magnetic neutral lines. 相似文献
103.
Radiocaesium isotopes, discharged into the North-east Irish Sea from the Sellafield (formerly Windscale) nuclear fuel reprocessing plant in Cumbria, have been employed as flow monitors to update and extend the record of coastal water movement from the Irish Sea to the Clyde Sea area and, further north, to Loch Etive. The temporal trends in radiocaesium levels have been used to determine the extent of water mixing en route and to define mean advection rates. Flow conditions from the Irish Sea have changed considerably since the mid-1970s, the residence time of northern Irish Sea waters being ~12 months during 1978–1980 inclusive. Average transport times of four and six months are estimated for the Sellafield to Clyde and Sellafield to Etive transects respectively. Sellafield 137Cs levels in seawater were diluted by factors of 27 and 50 respectively during current movement to the Clyde and Etive areas. The decrease in salinity-corrected 137Cs concentrations between the Clyde and Etive suggests that dilution by Atlantic water occurs, the latter mainly entering the Firth of Lorne from the west. The majority (~94%) of the radiocaesium supply to Loch Etive enters the Firth of Lorne via the portion of the coastal current circulating west of Islay, only ~6% arriving via the Sound of Jura. 相似文献
104.
G.C. Sethia G.J. Bailey R.J. Moffett J.K. Hargreaves 《Planetary and Space Science》1985,33(3):321-332
A modelling study of the electron content of the mid-latitude ionosphere and protonosphere has been carried out for solstice conditions using the mathematical model of Bailey (1983). In the model calculations coupled time-dependent O+, H+ continuity and momentum equations and O+, H+ and electron heat balance equations are solved for a magnetic shell extending over both hemispheres. The inclusion of interhemispheric flow of plasma and of heat balance has enabled us to investigate the role of interhemispheric coupling on the electron content and related shape parameters. The computed results are compared with results from slant path observations of the ATS-6 radio beacon made at Lancaster (U.K.) and Boulder, Colorado (U.S.A.).It has been found that the conjugate photoelectron heating has a major effect on the shape of the daily variation of slant slab thickness (τ) and also on the magnitude of the protonospheric content (Np). Some of the main features of τ are closely related to the sunrise and sunset times in the conjugate ionosphere. Also it is found that night-time increases in total electron content (NT) and F2 region peak electron density (Nmax) in winter are natural consequences of ionization loss at low altitudes causing an enhanced downward flow of plasma from the protonosphere which is coupled to the summer hemisphere. One other important consequence of the coupled protonosphere is that the effects on NT of the neutral air wind are not much different in winter from those in summer. 相似文献
105.
106.
An estimate for the anisotropy of the turbulent viscositys is given in a convective layer heated from below and rotating around a vertical axis. In the case of two-dimensional convection,
there is a stationary regime withs⊇2 regardless of the rotation. In the case of three-dimensional convection in a slowly rotating layer (with the Taylor number
equal to 1600), nonstationary turbulent regimes take place withs⊇1.6 forR=2.5×104 (R is the Rayleigh number) ands⊇1.2 forR=104.
The parameters plays an, important role in the theory of differential rotation of the convective solar or stellar envelopes. So far, it
has been evaluated empirically or semi-empirically. Some prospects in the development of the theory of differential rotation
are discussed here in terms of the moment theory of hydrodynamic fields. The relation between this strict approach and an
anisotropic viscosity approximation is considered. 相似文献
107.
108.
109.
During major geomagnetic storms, the interplanetary magnetic field angle φ (phi) changes often abruptly, either from 135° to 315° or 315° to 135°, suggesting that the heliospheric current sheet is pushed upward or downward by disturbed solar wind. The distortion of the heliospheric current sheet by three successive solar flares is simulated to show that such a flapping motion can occur. 相似文献
110.
Summary Two co-existing plutonic rocks (diorite and granodiorite) were studied from an intrusion of Variscan age in the Raztocna Valley
– Nízke Tatry Mountains, Western Carpathians. Geochemical analyses of major and trace elements constrain a volcanic arc as
emplacement environment and give the first hints of a mixture of two magmatic end-members: the so-called Prasivá granodiorite
and the Raztocna diorite. The 87Sr/86Sr(0) ratios vary between 0.7075 and 0.7118, the ε Nd(0) values range from −1.4 to −5.0. Common Pb isotopes reveal a dominant crustal source with minor influences from a mantle and
a lower crustal source.
Modelling based on Sr and Nd isotope data and using three component mixing calculations indicates that mixing of 2/3 of upper
mantle material with 1/3 upper crustal material can produce the isotopic composition of the Raztocna diorite. Very minor amounts
of lower crust were incorporated in the diorite. For the Prasivá granodiorite, the mixing ratio of upper mantle and upper
crust is similar, but a lower crustal reservoir contributed about 5–10% of the source material. 相似文献