全文获取类型
收费全文 | 115篇 |
免费 | 0篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 3篇 |
地球物理 | 4篇 |
地质学 | 23篇 |
海洋学 | 4篇 |
天文学 | 71篇 |
自然地理 | 2篇 |
出版年
2022年 | 1篇 |
2020年 | 1篇 |
2018年 | 5篇 |
2017年 | 8篇 |
2016年 | 8篇 |
2015年 | 6篇 |
2014年 | 3篇 |
2013年 | 5篇 |
2012年 | 4篇 |
2011年 | 10篇 |
2010年 | 8篇 |
2009年 | 5篇 |
2008年 | 2篇 |
2007年 | 3篇 |
2006年 | 5篇 |
2005年 | 7篇 |
2004年 | 3篇 |
2003年 | 1篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1982年 | 2篇 |
1977年 | 1篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有117条查询结果,搜索用时 15 毫秒
81.
IUE observations of the hydrogen-deficient irregular variable star MV Sgr obtained in 1980 June-October and also in 1979 November
are discussed. These observations show a prominent λ 2200 absorption feature. A value ofE(B — V) = 0.55 is deduced from the strength of λ 2200 band assuming that this absorption is caused by interstellar medium. The dereddened
continuum obtained at different times can be fitted to a theoretical energy distribution of a helium star model with Teff = 18000 K and log g = 2.5, similar to that of BD + 10‡ 2179. This theoretical energy distribution, after applying interstellar extinction, givesV = 12.7 mag, agreeing with the observed visual magnitude of ≃ 13 in 1979 November and 1980 June-October. Even though there
was no change in the continuum flux, the ultraviolet line-spectrum shows variations. The IUE spectra of 1980 October show
enhanced (circumstellar) absorption lines of Fe II, Si II, O I, C I and others along with the absorption lines of a B star.
In view of the similarity of the spectroscopic phenomena of MV Sgr with that of α Sco system, a model is proposed in which
a cool companion star, surrounded by dust, occasionally blows gas towards the hotter hydrogen-poor B star. This model explains
the irregular light variations and the spectroscopic phenomena.
Based on observations obtained with IUE satellite at the Villafranca Satellite Tracking Station of the European Space Agency. 相似文献
82.
Mountaintop trace-gas mixing ratios are often assumed to represent free atmospheric values, but are affected by valley planetary boundary-layer (PBL) air at certain times. We hypothesize that the afternoon valley–PBL height relative to the ridgetop is important in the diurnal cycle of mountaintop trace-gas mixing ratios. To investigate this, we use, (1) 4-years (1 January 2009–31 December 2012) of CO and \(\hbox {CO}_{2}\) mixing-ratio measurements and supporting meteorological observations from Pinnacles (\(38.61^{\circ }\hbox {N}\), \(78.35^{\circ }\hbox {W}\), 1017 m a.s.l.), which is a monitoring site in the Appalachian Mountains, (2) regional \(\hbox {O}_{3}\) mixing-ratio measurements, and (3) PBL heights determined from a nearby sounding station. Results reveal that the amplitudes of the diurnal cycles of CO and \(\hbox {CO}_{2}\) mixing ratios vary as a function of the daytime maximum valley–PBL height relative to the ridgetop. The mean diurnal cycle for the subset of days when the afternoon valley–PBL height is at least 400 m below the ridgetop shows a daytime CO mixing-ratio increase, implying the transport of PBL air from the valley to the mountaintop. During the daytime, on days when the PBL heights exceed the mountaintop, PBL dilution and entrainment cause CO mixing ratios to decrease. This decrease in CO mixing ratio, especially on days when PBL heights are at least 400 m above the ridgetop, suggests that measurements from these days can be used as with afternoon measurements from flat terrain in applications requiring regionally-representative measurements. 相似文献
83.
Mitali Dey Chumki Chowdhury Asim A. Pattnaik Dipnarayan Ganguly Sandip K. Mukhopadhyay Tarun K. De Tapan K. Jana 《Marine Ecology》2013,34(1):14-29
Ongoing climate change and anthropogenic activities are introducing stressors that affect the structure and function of coastal ecosystems. This paper focuses on the fluvial fluxes and estuarine transport of nutrients from a tropical river (Mahanadi River) in Northeastern India and compares select nutrient and water quality parameters between 1983 and 2008. This estuary acts as a perennial source of CO2 with a net annual flux to the atmosphere of about 135 tons. The non‐conservative fluxes showed a net annual removal of 650 and 140 tons of phosphorus and nitrogen from the water column, respectively. Negative biogeochemical feedbacks that decreased the availability of N and P in 2008 relative to 1983 levels indicate major changes in biogeochemical responses towards fluvial fluxes of nutrient. 相似文献
84.
85.
86.
We self-consistently obtain shock locations in an accretion flow by using an analytical method. One can obtain the spectral
properties, quasi-periodic oscillation frequencies and the outflow rates when the inflow parameters are known. Since temperature
of the CENBOL decides the spectral states of the black hole, and also the outflow rate, the outflow rate is directly related
to the spectral states. 相似文献
87.
88.
Sourav Palit Sandip Kumar Chakrabarti Dipak Debnath A. R. Rao Anuj Nandi Vipin K. Yadav V. Girish 《Experimental Astronomy》2009,27(1-2):77-93
We present the results of simulations of shadows cast by a zone plate telescope which may have one to four pairs of zone plates. From the shadows we reconstruct the images under various circumstances. We discuss physical basis of the resolution of the telescope and demonstrate this by our simulations. We allow the source to be at a finite distance (diverging beam) as well as at an infinite distance (parallel beam) and show that the resolution is worsened when the source is nearby. By reconstructing the zone plates in a way that both the zone plates subtend the same solid angles at the source, we obtain back high resolution even for sources at a finite distance. We present simulated results for the observation of the galactic center and show that the sources of varying intensities may be reconstructed with accuracy. Results of these simulations would be of immense use in interpreting the X-ray images from recently launched CORONAS-PHOTON satellite. 相似文献
89.
90.
Abstract As the sun evolves, a sharp compositional peak of He 3 builds up in the core. Nuclear reactions involving He 3 are very temperature sensitive, as a result, this He 3 layer is susceptible to thermal instability. The small horizontal wavenumber g-modes have large time scales, comparable to the thermal time scale. Using a two-layer model, we find that such “shellular modes” are the most unstable. As a result of nuclear heating, these modes may be excited in the solar core in a shallow layer confined to the He 3 zone. A possible effect of such shellular convection on the solar neutrino problem is discussed. In this paper we discuss the linear theory; the nonlinear effects will be treated in a subsequent paper. 相似文献