全文获取类型
收费全文 | 783篇 |
免费 | 44篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 14篇 |
大气科学 | 53篇 |
地球物理 | 210篇 |
地质学 | 336篇 |
海洋学 | 83篇 |
天文学 | 71篇 |
自然地理 | 64篇 |
出版年
2021年 | 14篇 |
2020年 | 10篇 |
2019年 | 11篇 |
2018年 | 19篇 |
2017年 | 22篇 |
2016年 | 28篇 |
2015年 | 32篇 |
2014年 | 23篇 |
2013年 | 45篇 |
2012年 | 40篇 |
2011年 | 57篇 |
2010年 | 34篇 |
2009年 | 56篇 |
2008年 | 38篇 |
2007年 | 44篇 |
2006年 | 34篇 |
2005年 | 37篇 |
2004年 | 22篇 |
2003年 | 25篇 |
2002年 | 26篇 |
2001年 | 21篇 |
2000年 | 10篇 |
1999年 | 12篇 |
1998年 | 11篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1995年 | 5篇 |
1994年 | 11篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 6篇 |
1973年 | 8篇 |
1970年 | 4篇 |
1862年 | 2篇 |
排序方式: 共有831条查询结果,搜索用时 15 毫秒
101.
102.
103.
The fourth-order integral form of Clairaut theory have been derived in terms of Hansen-Tisserand (H-T) polynomials. 相似文献
104.
ThierryContini Marie A.Treyer MarkSullivan Richard S.Ellis 《Monthly notices of the Royal Astronomical Society》2002,330(1):75-91
We discuss the chemical properties of a sample of UV-selected intermediate-redshift (0≲z≲0.4) galaxies in the context of their physical nature and star-formation history. This work represents an extension of our previous studies of the rest-frame UV-luminosity function (Treyer et al.) and the star-formation properties of the same sample (Sullivan et al.) . We revisit the optical spectra of these galaxies and perform further emission-line measurements restricting the analysis to those spectra with the full set of emission lines required to derive chemical abundances. Our final sample consists of 68 galaxies with heavy-element abundance ratios and both UV and CCD B -band photometry. Diagnostics based on emission-line ratios show that all but one of the galaxies in our sample are powered by hot, young stars rather than by an AGN. Oxygen-to-hydrogen (O/H) and nitrogen-to-oxygen (N/O) abundance ratios are compared with those of various local and intermediate-redshift samples. Our UV-selected galaxies span a wide range of oxygen abundances, from ∼0.1 to 1 Z⊙ , intermediate between low-mass H ii galaxies and massive starburst nuclei. For a given oxygen abundance, most have strikingly low N/O values. Moreover, UV-selected and H ii galaxies systematically deviate from the usual metallicity–luminosity relation in the sense of being more luminous by 2–3 mag . Adopting the 'delayed-release' chemical evolution model, we propose our UV-selected sources are observed at a special stage in their evolution, following a powerful starburst that enriched their ISM in oxygen and temporarily lowered their mass-to-light ratios. We discuss briefly the implications of our conclusions on the nature of similarly selected high-redshift galaxies. 相似文献
105.
Equivalent width calculations for some electronic and vibration-rotation transitions of the molecules PO, PH, MgH+f, and CN have been carried out for a few umbral, photospheric, and facular model atmospheres. It appears that a few weak lines of these molecules might show up in the umbral spectrum. Le Blanc bands of CN are too weak for detection in the solar spectrum. 相似文献
106.
107.
108.
An H solar prominence with the characteristics of a spray was ejected in association with a bright limb flare. Knots of material were observed to a distance of more than one solar radius above the west limb of the Sun. The optical event was followed by 80 MHz emission from a type IV source which was observed moving out through several solar radii.Coronagraph observations have been used to determine the trajectories and velocities of the knots in directions perpendicular to the line of sight. After some early deceleration velocities increase to 300–500 km/sec and slowly decline with variations depending on the initial direction of outflow. We suggest that the magnetic field over the spot group is deformed by the energy of the mass motions of material fragments, some of which then continue to move outward from the Sun. 相似文献
109.
Pores present in ices in the solar system do not remain unchanged. In isothermal conditions they shrink while in a thermal gradient they migrate towards the higher temperature and escape so that the ice densifies. This motion has been investigated for pure H2O- and CO2-ices in a very simple one-dimensional model assuming uniform thermal conductivity and temperature gradient. The results indicate that the densification of H2O-ice is so slow that it could be significant only for icy satellites having an internal heat source. On the other hand, CO2-ice densifies orders of magnitude faster and the effect should be important for the CO2 component of cometary nuclei. No effect is expected for icy planetary rings. 相似文献
110.
A proposal for a new scenario framework to support research and assessment in different climate research communities 总被引:1,自引:0,他引:1
Detlef P. van Vuuren Keywan Riahi Richard Moss Jae Edmonds Allison Thomson Nebojsa Nakicenovic Tom Kram Frans Berkhout Rob Swart Anthony Janetos Steven K. Rose Nigel Arnell 《Global Environmental Change》2012,22(1):21-35
In this paper, we propose a scenario framework that could provide a scenario “thread” through the different climate research communities (climate change – vulnerability, impact, and adaptation - and mitigation) in order to support assessment of mitigation and adaptation strategies and climate impacts. The scenario framework is organized around a matrix with two main axes: radiative forcing levels and socio-economic conditions. The radiative forcing levels (and the associated climate signal) are described by the new Representative Concentration Pathways. The second axis, socio-economic developments comprises elements that affect the capacity for mitigation and adaptation, as well as the exposure to climate impacts. The proposed scenarios derived from this framework are limited in number, allow for comparison across various mitigation and adaptation levels, address a range of vulnerability characteristics, provide information across climate forcing and vulnerability states and span a full century time scale. Assessments based on the proposed scenario framework would strengthen cooperation between integrated-assessment modelers, climate modelers and vulnerability, impact and adaptation researchers, and most importantly, facilitate the development of more consistent and comparable research within and across these research communities. 相似文献