全文获取类型
收费全文 | 64169篇 |
免费 | 542篇 |
国内免费 | 366篇 |
专业分类
测绘学 | 1673篇 |
大气科学 | 4300篇 |
地球物理 | 11907篇 |
地质学 | 25266篇 |
海洋学 | 4971篇 |
天文学 | 13968篇 |
综合类 | 236篇 |
自然地理 | 2756篇 |
出版年
2021年 | 408篇 |
2020年 | 450篇 |
2019年 | 453篇 |
2018年 | 3774篇 |
2017年 | 3521篇 |
2016年 | 2600篇 |
2015年 | 760篇 |
2014年 | 1158篇 |
2013年 | 2170篇 |
2012年 | 2262篇 |
2011年 | 4151篇 |
2010年 | 3744篇 |
2009年 | 4419篇 |
2008年 | 3583篇 |
2007年 | 4154篇 |
2006年 | 1724篇 |
2005年 | 1674篇 |
2004年 | 1584篇 |
2003年 | 1571篇 |
2002年 | 1363篇 |
2001年 | 1032篇 |
2000年 | 989篇 |
1999年 | 826篇 |
1998年 | 846篇 |
1997年 | 816篇 |
1996年 | 691篇 |
1995年 | 702篇 |
1994年 | 623篇 |
1993年 | 536篇 |
1992年 | 501篇 |
1991年 | 509篇 |
1990年 | 581篇 |
1989年 | 498篇 |
1988年 | 457篇 |
1987年 | 584篇 |
1986年 | 484篇 |
1985年 | 610篇 |
1984年 | 690篇 |
1983年 | 656篇 |
1982年 | 573篇 |
1981年 | 615篇 |
1980年 | 515篇 |
1979年 | 472篇 |
1978年 | 476篇 |
1977年 | 434篇 |
1976年 | 424篇 |
1975年 | 417篇 |
1974年 | 396篇 |
1973年 | 426篇 |
1971年 | 260篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
202.
203.
It is pointed out that the total amount of microwave radiation that could possibly be generated by all the graphite needles in space would be considerably smaller than the observed total energy of the cosmic microwave background radiation. The question of relevant optical depth of the cloud containing the needles has been examined. It is found that the optical depth is not sufficiently large for the cloud to radiate like a black body. 相似文献
204.
R. Ostertag G. Amthauer H. Rager H.Y. McSween 《Earth and Planetary Science Letters》1984,67(2):162-166
ALHA 77005, a shocked achondrite of the shergottite group, is unique in containing cumulus olivine crystals which display a brownish color in thin section. Mössbauer, EPR, and optical spectroscopic studies show the presence of Fe3+ in the olivine. Approximately 4.5 wt.% of the total iron in the olivine (24 wt.% as FeO) is in the trivalent state. The Fe3+ ions preferentially occupy M2 lattice positions. Charge transfer between Fe3+ and Fe2+ as well as between Fe3+ and oxygen ligands causes a broad absorption band in the optical spectrum at high energies which is the reason for the olivine color. It is concluded that the color of the ALHA 77005 olivine is preterrestrial and may be the result of shock-induced oxidation of the olivine crystals on the meteorite parent body. 相似文献
205.
Thomas Kenkmann Alex Deutsch Klaus Thoma Matthias Ebert Michael H. Poelchau Elmar Buhl Eva-Regine Carl Andreas N. Danilewsky Georg Dresen Anja Dufresne Nathanaël Durr Lars Ehm Christian Grosse Max Gulde Nicole Güldemeister Christopher Hamann Lutz Hecht Stefan Hiermaier Tobias Hoerth Astrid Kowitz Falko Langenhorst Bernd Lexow Hanns-Peter Liermann Robert Luther Ulrich Mansfeld Dorothee Moser Manuel Raith Wolf Uwe Reimold Martin Sauer Frank Schäfer Ralf Thomas Schmitt Frank Sommer Jakob Wilk Rebecca Winkler Kai Wünnemann 《Meteoritics & planetary science》2018,53(8):1543-1568
This paper reviews major findings of the Multidisciplinary Experimental and Modeling Impact Crater Research Network (MEMIN). MEMIN is a consortium, funded from 2009 till 2017 by the German Research Foundation, and is aimed at investigating impact cratering processes by experimental and modeling approaches. The vision of this network has been to comprehensively quantify impact processes by conducting a strictly controlled experimental campaign at the laboratory scale, together with a multidisciplinary analytical approach. Central to MEMIN has been the use of powerful two-stage light-gas accelerators capable of producing impact craters in the decimeter size range in solid rocks that allowed detailed spatial analyses of petrophysical, structural, and geochemical changes in target rocks and ejecta. In addition, explosive setups, membrane-driven diamond anvil cells, as well as laser irradiation and split Hopkinson pressure bar technologies have been used to study the response of minerals and rocks to shock and dynamic loading as well as high-temperature conditions. We used Seeberger sandstone, Taunus quartzite, Carrara marble, and Weibern tuff as major target rock types. In concert with the experiments we conducted mesoscale numerical simulations of shock wave propagation in heterogeneous rocks resolving the complex response of grains and pores to compressive, shear, and tensile loading and macroscale modeling of crater formation and fracturing. Major results comprise (1) projectile–target interaction, (2) various aspects of shock metamorphism with special focus on low shock pressures and effects of target porosity and water saturation, (3) crater morphologies and cratering efficiencies in various nonporous and porous lithologies, (4) in situ target damage, (5) ejecta dynamics, and (6) geophysical survey of experimental craters. 相似文献
206.
We present the results of our systematic study of the long-period orbital evolution of all of the outer Saturnian, Uranian, and Neptunian satellites known to date. The plots of the orbital elements against time give a clear idea of the pattern of the orbital evolution of each satellite. The tabular data allow us to estimate the basic parameters of the evolving orbits, including the ranges of variation in the semimajor axes, eccentricities, and ecliptical inclinations as well as the variation periods and mean motions of the arguments of pericenters and the longitudes of the nodes. We compare the results obtained by numerically integrating the rigorous equations of the perturbed motion of the satellites with the analytical and numerical-analytical results. The satellite orbits with a librational pattern of variation in the arguments of pericenters are set apart. 相似文献
207.
The thermal stability of stars with a condensed core and an extended convective envelope (red giants) is discussed. It is shown that the thernal stability is determined by the way the opacity of the photosphere depends on density and temperature. In particular, the H? opacity in red giants' photospheres ensures their stability. 相似文献
208.
P. P. Malovichko 《Kinematics and Physics of Celestial Bodies》2007,23(5):185-190
Current instability of Alfvén waves in coronal loops is considered. Such a mechanism of Alfvén wave generation is shown to be very efficient, and it can give rise to low-frequency perturbations even in the case of very weak currents, thus fostering the reconnection of magnetic fields and development of a flare. The low-frequency turbulence which arises in the process can be favorable to the heating and acceleration of particles. 相似文献
209.
Impact of Sea-level Rise and Storm Surges on a Coastal Community 总被引:7,自引:7,他引:7
A technique to evaluate the risk of storm tides (the combination of a storm surge and tide) under present and enhanced greenhouse conditions has been applied to Cairns on the north-eastern Australian coast. The technique combines a statistical model for cyclone occurrence with a state-of-the-art storm surge inundation model and involves the random generation of a large number of storm tide simulations. The set of simulations constitutes a synthetic record of extreme sea-level events that can be analysed to produce storm tide return periods. The use of a dynamic storm surge model with overland flooding capability means that the spatial extent of flooding is also implicitly modelled. The technique has the advantage that it can readily be modified to include projected changes to cyclone behaviour due to the enhanced greenhouse effect. Sea-level heights in the current climate for return periods of 50, 100, 500 and 1000 years have been determined to be 2.0 m, 2.3 m, 3.0 m and 3.4 m respectively. In an enhanced greenhouse climate (around 2050), projected increases in cyclone intensity and mean sea-level see these heights increase to 2.4 m, 2.8 m, 3.8 m and 4.2 m respectively. The average area inundated by events with a return period greater than 100 years is found to more than double under enhanced greenhouse conditions. 相似文献
210.
U-Pb (SHRIMP-II) isotopic dating has been conducted for zircons of the ash sediments of the Ust’-Suifun Suite, which was the
final stage of Late Cenozoic explosive volcanism in Southwest Primorskii krai. These pyroclastic units are widespread within
sediments that fill in Cenozoic depressions including large coalfields. The concordant dates (23.7–24.6 Ma) are in line with
the results of the K-Ar determinations for volcanic tephra (23.6–27.1 Ma) and correspond to the beginning of the active phase
of spreading and taphrogenesis in the neighboring Trench of the Sea of Japan. These processes started as early as the Eocene
and are reflected in the continental vicinity with the formation of riftogenic depressions and the occurrence of a peculiar
gas volcanism. 相似文献