全文获取类型
收费全文 | 1426篇 |
免费 | 51篇 |
国内免费 | 3篇 |
学科分类
地球科学 | 1480篇 |
出版年
2021年 | 18篇 |
2020年 | 22篇 |
2019年 | 15篇 |
2018年 | 55篇 |
2017年 | 44篇 |
2016年 | 73篇 |
2015年 | 60篇 |
2014年 | 61篇 |
2013年 | 104篇 |
2012年 | 31篇 |
2011年 | 42篇 |
2010年 | 57篇 |
2009年 | 63篇 |
2008年 | 33篇 |
2007年 | 45篇 |
2006年 | 48篇 |
2005年 | 24篇 |
2004年 | 12篇 |
2003年 | 29篇 |
2002年 | 29篇 |
2001年 | 28篇 |
2000年 | 29篇 |
1999年 | 20篇 |
1998年 | 17篇 |
1997年 | 30篇 |
1996年 | 19篇 |
1995年 | 25篇 |
1994年 | 22篇 |
1993年 | 17篇 |
1991年 | 20篇 |
1990年 | 17篇 |
1988年 | 12篇 |
1987年 | 13篇 |
1984年 | 15篇 |
1983年 | 22篇 |
1982年 | 13篇 |
1980年 | 12篇 |
1979年 | 13篇 |
1978年 | 17篇 |
1977年 | 11篇 |
1976年 | 12篇 |
1975年 | 12篇 |
1974年 | 16篇 |
1973年 | 20篇 |
1972年 | 13篇 |
1971年 | 10篇 |
1970年 | 12篇 |
1969年 | 11篇 |
1968年 | 12篇 |
1965年 | 14篇 |
排序方式: 共有1480条查询结果,搜索用时 15 毫秒
1.
A growing body of evidence implies that the concept of 'treeless tundra' in eastern and northern Europe fails to explain the rapidity of Lateglacial and postglacial tree population dynamics of the region, yet the knowledge of the geographic locations and shifting of tree populations is fragmentary. Pollen, stomata and plant macrofossil stratigraphies from Lake Kurjanovas in the poorly studied eastern Baltic region provide improved knowledge of ranges of north‐eastern European trees during the Lateglacial and subsequent plant population responses to the abrupt climatic changes of the Lateglacial/Holocene transition. The results prove the Lateglacial presence of tree populations (Betula, Pinus and Picea) in the eastern Baltic region. Particularly relevant is the stomatal and plant macrofossil evidence showing the local presence of reproductive Picea populations during the Younger Dryas stadial at 12 900–11 700 cal. a BP, occurring along with Dryas octopetala and arctic herbs, indicating semi‐open vegetation. The spread of Pinus–Betula forest at ca. 14 400 cal. a BP, the rise of Picea at ca. 12 800 cal. a BP and the re‐establishment of Pinus–Betula forest at ca. 11 700 cal. a BP within a span of centuries further suggest strikingly rapid, climate‐driven ecosystem changes rather than gradual plant succession on a newly deglaciated land. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
2.
The theory of collisional systems is generalized for an arbitrary geometry and forces acting in the system, mixtures of different particle types, friction, small deviations from the ideal spherical form, axial rotation, finite size of particles and gravitational interactions. Terms for the formation of new particles and destruction of old ones are also included, and other unspecified parameters can be introduced. Although some approximations are made to simplify the basic equations and to avoid excessive numerical interactions, a comparison with computer simulations shows a good agreement. The tests were continued up to the optical thickness = 5. 相似文献
3.
A smooth surface layer of highly disordered olivine, (Mg, Fe)2SiO4, has been produced by exposure of polished, natural olivine to a dose of 5×1016 cm–2 of 1.5 MeV neon ions from a Van de Graaff accelerator. The dielectric functions of the disordered silicate in the wavelength range from 8 to 30 m have been determined from analysis of specular reflectance data, and extinction for Rayleigh particles of such disordered olivine has been calculated. Extinction measurements for amorphous olivine smoke collected on a substrate are also presented. The small particle extinctions of both kinds of structurally disordered olivine are shown to agree well with the main features of the absorption and emission spectra from interstellar grains in the 10 and 20 m region. 相似文献
4.
Walter J. Heikkila R.J. Pellinen C.-G. Fälthammar L.P. Block 《Planetary and Space Science》1979,27(11):1383-1389
During quiescent auroras the large-scale electric field is essentially irrotational. The volume formed by the plasma sheet and its extension into the auroral oval is connected to an external source by electric currents, which enter and leave the volume at different electric potentials and which supply sufficient energy to support the auroral activity. The location of the actual acceleration of particles depends on the internal distribution of electric fields and currents. One important feature is the energization of the carriers of the cross-tail current and another is the acceleration of electrons precipitated through relatively low-altitude magnetic-field-aligned potential drops.Substorm auroras depend on rapid and (especially initially) localized release of energy that can only be supplied by tapping stored magnetic energy. The energy is transmitted to the charged particle via electric inductive fields.The primary electric field due to changing electric currents is redistributed in a complicated way—but never extinguished—by polarization of charges. As a consequence, any tendency of the plasma to suppress magnetic-field-aligned components of the electric fields leads to a corresponding enhancement of the transverse component. 相似文献
5.
Jussi Kääriäinen 《Journal of Geodesy》1992,66(3):281-283
Two water tube clinometers are installed in a deep mine in Lohja, Finland. One, lying in an E-W direction, is 177 m long and the other, lying in a N-S direction, is 62 m long. These instruments are used for tidal records and research. Because the station was on the zone of totality of the 1990 solar eclipse, the instruments offered a suitable tool for investigating whether there was any shielding effect on the direction of the vertical. During the eclipse, the resolution of the instruments was increased to 0.00001 and 0.00004, respectively. p ]Recordings and data evaluation are discussed, and the results obtained show that no gravitational shielding was found at the level of the above accuracy. 相似文献
6.
7.
8.
Meso-gamma scale forecasts using the nonhydrostatic model LM 总被引:10,自引:0,他引:10
J. Steppeler G. Doms U. Schättler H. W. Bitzer A. Gassmann U. Damrath G. Gregoric 《Meteorology and Atmospheric Physics》2003,82(1-4):75-96
Summary ?The nonhydrostatic model LM was developed for small scale operational predictions. Advances in computer development will
give the possibility of operational models of a rather fine scale, which will cover the meso-gamma scale. The LM is currently
applied at a scale of 7 km and an increase of the operational resolution to 2.5 km is planned for the next few years. Predictions
of such high resolution require to abandon the hydrostatic assumption, which is used with most current operational weather
prediction models. The LM was designed to cover all resolutions from 50 m to 50 km with an efficiency making it suitable for
operational use. It is a fully elastic model, using second order centred finite differences. The time integration is done
using the Klemp–Wilhelmson method, treating the slow modes by a larger time step than the fast modes. The vertical propagation
of the fast waves is done implicitly.
After describing the design of the LM, this paper gives examples of model predictions at the meso-γ scale. Some results of
the current operational application at the resolution 7 km are presented. Deficiencies in the localisation of model generated
precipitation are investigated using an idealised bell shaped mountain and applying different resolutions. In this way the
convergence to the correct solution can be investigated. From these results it is concluded, that orographic filtering is
necessary and the effect of such filtering on precipitation forecasts is investigated. Finally, the prediction of a squall
line over northern Germany is shown in order to demonstrate the potential of the model in forecasting the meso-γ scale.
Received May 15, 2001; revised September 21, 2001 相似文献
9.
A. L. Läufer W. Frisch G. Steinitz J. Loeschke 《International Journal of Earth Sciences》1997,86(3):612-626
The Eder unit in the Carnic Alps, which is situated immediately south of the Periadriatic lineament (PL), represents a fault-bounded block consisting of a low-grade (up to 400?°C, indicated by epizonal illite “crystallinity” values, recrystallized quartz, and non-recrystallized white mica) metamorphic Paleozoic metasedimentary sequence. Until now, it has been assumed to represent a separate Variscan nappe. The rocks of the Eder unit show a strong E- to W-oriented stretching lineation on steep foliation planes (D1) subparallel to the PL. D1 structures originated near the temperature peak of metamorphism, and shear sense indicators show dextral ductile shear parallel to the PL. Tight mesoscale D2 folds formed on the cooling path. K–Ar and Ar–Ar ages from newly formed white mica cluster around 32–28 and 18–13 Ma and suggest a two-stage Tertiary history of the Eder unit. We interpret the Eder unit as a fault-bounded block formed during Oligocene large-scale dextral shearing along the PL (near Tmax) and exhumed in mid-Miocene times during another phase of activity along the PL. Its nature as a separate Variscan nappe is questioned. 相似文献
10.
Chr Samtleben A. Munnecke T. Bickert J. Pätzold 《International Journal of Earth Sciences》1996,85(2):278-292
The Silurian of Gotland, Sweden, consists of 440 m of carbonate deposits. Repeatedly, uniform sequences of micritic limestones
and marls are interrupted by complex-structured reefs and by adjacent platform sediments. Generally, the alteration of facies
is interpreted as the result of sea-level fluctuations caused by a gradual regression with superimposed minor transgressive
pulses. The purpose of this study is a facies interpretation based on both field observations and stable isotope measurements
of brachiopod shells. Approximately 700 samples from stratigraphically arranged localities in different facies areas have
been investigated. The carbon and oxygen isotopes show principally parallel curves and a close relationship to the stratigraphic
sequence. Lower values occur in periods dominated by deposition of marly sequences. Higher values are observed in periods
dominated by reefs and extended carbonate platforms. The oxygen isotope ratios are interpreted to reflect paleosalinity changes
due to varying freshwater input, rather than to paleotemperature. Carbon isotope ratios are believed to have been connected
to global changes in the burial of organic carbon in black shales during periods of euxinic deep water conditions. Consequently,
the facies succession on Gotland results from global paleoclimatic conditions. Changes in terrigenous input due to different
rates of weathering and freshwater runoff, rather than sea-level fluctuations, control the carbonate formation of the Silurian
on Gotland. 相似文献