全文获取类型
收费全文 | 68425篇 |
免费 | 2640篇 |
国内免费 | 3612篇 |
专业分类
测绘学 | 2351篇 |
大气科学 | 6192篇 |
地球物理 | 12927篇 |
地质学 | 26556篇 |
海洋学 | 7041篇 |
天文学 | 14362篇 |
综合类 | 1184篇 |
自然地理 | 4064篇 |
出版年
2023年 | 402篇 |
2022年 | 1062篇 |
2021年 | 1500篇 |
2020年 | 1416篇 |
2019年 | 1509篇 |
2018年 | 2526篇 |
2017年 | 2386篇 |
2016年 | 2770篇 |
2015年 | 1719篇 |
2014年 | 2630篇 |
2013年 | 3763篇 |
2012年 | 2746篇 |
2011年 | 3357篇 |
2010年 | 2925篇 |
2009年 | 3498篇 |
2008年 | 3073篇 |
2007年 | 3114篇 |
2006年 | 2906篇 |
2005年 | 2014篇 |
2004年 | 1996篇 |
2003年 | 1954篇 |
2002年 | 1947篇 |
2001年 | 1735篇 |
2000年 | 1534篇 |
1999年 | 1352篇 |
1998年 | 1309篇 |
1997年 | 1245篇 |
1996年 | 1061篇 |
1995年 | 1031篇 |
1994年 | 910篇 |
1993年 | 781篇 |
1992年 | 755篇 |
1991年 | 698篇 |
1990年 | 705篇 |
1989年 | 599篇 |
1988年 | 574篇 |
1987年 | 588篇 |
1986年 | 537篇 |
1985年 | 651篇 |
1984年 | 710篇 |
1983年 | 625篇 |
1982年 | 598篇 |
1981年 | 522篇 |
1980年 | 490篇 |
1979年 | 500篇 |
1978年 | 473篇 |
1977年 | 382篇 |
1976年 | 357篇 |
1975年 | 375篇 |
1973年 | 355篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
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
63.
64.
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
65.
The paper provides a new stereo‐analytical method, which is a combination of the stereographic method and analytical methods, to separate finite removable blocks from the infinite and tapered blocks in discontinuous rock masses. The methodology has applicability to both convex and concave blocks. Application of the methodology is illustrated through examples. Addition of this method to the existing block theory procedures available in the literature improves the capability of block theory in solving practical problems in rock engineering. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
66.
67.
68.
S. A. Petrova 《Monthly notices of the Royal Astronomical Society》2006,368(4):1764-1772
Pulsar radio emission is modelled as a sum of two completely polarized non-orthogonal modes with the randomly varying Stokes parameters and intensity ratio. The modes are the result of polarization evolution of the original natural waves in the hot, magnetized, weakly inhomogeneous plasma of the pulsar magnetosphere. In the course of the wavemode coupling, the linearly polarized natural waves acquire purely orthogonal elliptical polarizations. Further on, as the waves pass through the cyclotron resonance, they become non-orthogonal. The pulse-to-pulse fluctuations of the final polarization characteristics and the intensity ratio of the modes are attributed to the temporal fluctuations in the plasma flow.
The model suggested allows one to reproduce the basic features of the one-dimensional distributions of the individual-pulse polarization characteristics. Besides that, the propagation origin of the pulsar polarization implies a certain correlation between the mode ellipticity and position angle. On a qualitative level, for different sets of parameters, the expected correlations appear compatible with the observed ones. Further theoretical studies are necessary to establish the quantitative correspondence of the model to the observational results and to develop a technique of diagnostics of the pulsar plasma on this basis. 相似文献
The model suggested allows one to reproduce the basic features of the one-dimensional distributions of the individual-pulse polarization characteristics. Besides that, the propagation origin of the pulsar polarization implies a certain correlation between the mode ellipticity and position angle. On a qualitative level, for different sets of parameters, the expected correlations appear compatible with the observed ones. Further theoretical studies are necessary to establish the quantitative correspondence of the model to the observational results and to develop a technique of diagnostics of the pulsar plasma on this basis. 相似文献
69.
70.