全文获取类型
收费全文 | 1361篇 |
免费 | 50篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 21篇 |
大气科学 | 94篇 |
地球物理 | 372篇 |
地质学 | 360篇 |
海洋学 | 101篇 |
天文学 | 287篇 |
综合类 | 12篇 |
自然地理 | 169篇 |
出版年
2021年 | 15篇 |
2020年 | 12篇 |
2019年 | 11篇 |
2018年 | 26篇 |
2017年 | 28篇 |
2016年 | 20篇 |
2015年 | 25篇 |
2014年 | 31篇 |
2013年 | 104篇 |
2012年 | 43篇 |
2011年 | 44篇 |
2010年 | 51篇 |
2009年 | 55篇 |
2008年 | 56篇 |
2007年 | 57篇 |
2006年 | 54篇 |
2005年 | 67篇 |
2004年 | 47篇 |
2003年 | 35篇 |
2002年 | 29篇 |
2001年 | 32篇 |
2000年 | 37篇 |
1999年 | 31篇 |
1998年 | 36篇 |
1997年 | 36篇 |
1996年 | 18篇 |
1995年 | 24篇 |
1994年 | 26篇 |
1993年 | 19篇 |
1992年 | 17篇 |
1991年 | 17篇 |
1990年 | 20篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 25篇 |
1986年 | 11篇 |
1985年 | 20篇 |
1984年 | 16篇 |
1983年 | 16篇 |
1982年 | 27篇 |
1981年 | 18篇 |
1980年 | 13篇 |
1979年 | 16篇 |
1978年 | 11篇 |
1977年 | 15篇 |
1976年 | 11篇 |
1975年 | 13篇 |
1974年 | 15篇 |
1973年 | 16篇 |
1972年 | 7篇 |
排序方式: 共有1416条查询结果,搜索用时 250 毫秒
891.
Tangential discontinuities and the optical analogy for stationary fields IV. High speed fluid sheets
E. N. Parker 《地球物理与天体物理流体动力学》2013,107(4):229-247
Abstract It was shown in the previous paper that a sufficiently strong pressure maximum applied to an equilibrium flux surface, by the fields on either side of the surface, produces a gap in the flux surface. The fields on either side make contact through the gap to produce a surface of tangential discontinuity (current sheet). It is shown in the present paper that there is a high speed sheet of fluid and field sliding over the surface of discontinuity when the applied pressure moves slowly across the flux surface. Conditions in the active X-ray corona of the sun suggest that such sheets are generally present, with velocities of the order of 102 km/sec, but with thicknesses too small to be observed. More substantial high speed sheets of fluid may occur in solar flares. 相似文献
892.
J. Vaughn Barrie Kim W. Conway Kim Picard H. Gary Greene 《Continental Shelf Research》2009,29(5-6):796-806
The Pacific margin of Canada has been subjected to tectonism, dramatic sea level change and vigorous storm and tidal energy since glacial times resulting in a complex seafloor. Extensive multibeam mapping of this shelf has provided an opportunity to understand how these processes have impacted sedimentology and morphology. Bathymetric restriction of the tidally dominated flow between the inland seas and the open Pacific has resulted in the development of very large subaqueous dune fields and terrace moats. For example, in the southern Strait of Georgia nearly symmetrical dunes with wavelengths between 100 and 300 m, dune heights up to 28 m, cover the seafloor in 170–210 m water depth. In northern Hecate Strait a 72 km2 area of large 2D dunes occurs at the transition with Dixon Entrance which opens to the Pacific Ocean and steep (>10°) wave-cut terraces and drowned spits, a result of sea level changes during the Holocene, are now being undercut to generate moats 7 m deep, in a narrowing shelf trough. Currents, with velocities ranging between 0.2 and 2.2 m s?1, are dominated by semi-diurnal tidal streams that are continually modified by wind and estuarine circulation. There appears to be a clear association of grain size, water depth and flow velocity controlling the size of the subaqueous dunes. 相似文献
893.
894.
895.
Martin Cohen Jessica M. Chapman Rachel M. Deacon † Robert J. Sault Quentin A. Parker Anne J. Green 《Monthly notices of the Royal Astronomical Society》2006,369(1):189-196
We present radio observations of the unique, recently formed, planetary nebula (PN) associated with a very long-period OH/IR variable star V1018 Sco that is unequivocally still in its asymptotic giant branch phase. Two regions within the optical nebula are clearly detected in non-thermal radio continuum emission, with radio spectral indices comparable to those seen in colliding-wind Wolf–Rayet binaries. We suggest that these represent shocked interactions between the hot, fast stellar wind and the cold nebular shell that represents the PN's slow wind moving away from the central star. This same interface produces both synchrotron radio continuum and the optical PN emission. The fast wind is neither spherical in geometry nor aligned with any obvious optical or radio axis. We also report the detection of transient H2 O maser emission in this nebula. 相似文献
896.
Pirin Erdodu Ofer Lahav John P. Huchra † Matthew Colless Roc M. Cutri Emilio Falco † Teddy George Thomas Jarrett D. Heath Jones Lucas M. Macri Jeff Mader Nathalie Martimbeau Michael A. Pahre Quentin A. Parker Anaïs Rassat Will Saunders 《Monthly notices of the Royal Astronomical Society》2006,373(1):45-64
897.
898.
E.N. Parker 《Astrophysics and Space Science》2001,277(1-2):1-11
The Sun and the heliosphere form a single dynamical system, driven by the convection in the Sun and the magnetic fields generated
by that convection. The magnetic fields are the primary channel for producing the high temperatures and high velocities that
extend outward to form the heliosphere. The essential point is that, while the general picture seems to be reasonable, several
important steps in the process are not understood, and several concepts commonly employed in explanation are false physics.
These scientific gaps should not be forgotten in the rush to pursue new and exotic discoveries.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
899.
Abstract— High-purity separates of presolar diamond were prepared from 14 primitive chondrites from 7 compositional groups. Their noble gases were measured using stepped pyrolysis. Three distinct noble gas components are present in diamonds, HL, P3, and P6, each of which is found to consist of five noble gases. P3 , released between 200 °C and 900 °C, has a “planetary” elemental abundance pattern and roughly “normal” isotopic ratios. HL , consisting of isotopically anomalous Xe-HL and Kr-H, Ar with high 38Ar/36Ar, and most of the gas making up Ne-A2 and He-A, is released between 1100 °C and 1600 °C. HL has “planetary” elemental ratios, except that it has much more He and Ne than other known “planetary” components. HL gases are carried in the bulk diamonds, not in some trace phase. P6 has a slightly higher median release temperature than HL and is not cleanly separated from HL by stepped pyrolysis. Our data suggest that P6 has roughly “normal” isotopic compositions and “planetary” elemental ratios. Both P3 and P6 seem to be isotopically distinct from P1, the dominant “planetary” noble-gas component in primitive chondrites. Release characteristics suggest that HL and P6 are sited in different carriers within the diamond fractions, while P3 may be sited near the surfaces of the diamonds. We find no evidence of separability of Xe-H and Xe-L or other isotopic variations in the HL component. However, because ~1010 diamonds are required to measure a Xe composition, a lack of isotopic variability does not constrain diamonds to come from a single source. In fact, the high abundance of diamonds in primitive chondrites and the presence of at least three distinct noble-gas components strongly suggest that diamonds originated in many sources. Relative abundances of noble-gas components in diamonds correlate with degree of thermal processing (see companion paper), indicating that all meteorites sampled essentially the same mixture of diamonds. That mixture was probably inherited from the Sun's parent molecular cloud. 相似文献
900.
Yanhong Zhang Shaoxiong Huang Diann Schneider Paul H. Benoit John M. DeHart Gary E. Lofgren Derek W. G. Sears 《Meteoritics & planetary science》1996,31(1):87-96
Abstract— In order to explore the thermal history of enstatite chondrites, we examined the cathodoluminescence (CL) and thermoluminescence (TL) properties of 15 EH chondrites and 21 EL chondrites, including all available petrographic types, both textural types 3–6 and mineralogical types α–δ. The CL properties of EL3α and EH3α chondrites are similar. Enstatite grains high in Mn and other transition metals display red CL, while enstatite with low concentrations of these elements show blue CL. A few enstatite grains with >5 wt% FeO display no CL. In contrast, the luminescent properties of the metamorphosed EH chondrites are very different from those of metamorphosed EL chondrites. While the enstatites in metamorphosed EH chondrites display predominantly blue CL, the enstatites in metamorphosed EL chondrites display a distinctive magenta CL with blue and red peaks of approximately equal intensity in their spectra. The TL sensitivities of the enstatite chondrites correlate with the intensity of the blue CL and, unlike other meteorite classes, are not simply related to metamorphism. The different luminescent properties of metamorphosed EH and EL chondrites cannot readily be attributed to compositional differences. But x-ray diffraction data suggests that the enstatite in EH5γ,δ chondrites is predominantly disordered orthopyroxene, while enstatite in EL6β chondrites is predominantly ordered orthopyroxene. The difference in thermal history of metamorphosed EL and EH chondrites is so marked that the use of single “petrographic” types is misleading, and separate textural and mineralogical types are preferable. Our data confirm earlier suggestions that metamorphosed EH chondrites underwent relatively rapid cooling, and the metamorphosed EL chondrites cooled more slowly and experienced prolonged heating in the orthopyroxene field. 相似文献