全文获取类型
收费全文 | 71861篇 |
免费 | 1006篇 |
国内免费 | 638篇 |
专业分类
测绘学 | 2005篇 |
大气科学 | 5178篇 |
地球物理 | 14793篇 |
地质学 | 25010篇 |
海洋学 | 6240篇 |
天文学 | 16092篇 |
综合类 | 192篇 |
自然地理 | 3995篇 |
出版年
2021年 | 593篇 |
2020年 | 633篇 |
2019年 | 741篇 |
2018年 | 1619篇 |
2017年 | 1451篇 |
2016年 | 1878篇 |
2015年 | 1061篇 |
2014年 | 1784篇 |
2013年 | 3473篇 |
2012年 | 1996篇 |
2011年 | 2701篇 |
2010年 | 2408篇 |
2009年 | 3219篇 |
2008年 | 2879篇 |
2007年 | 2831篇 |
2006年 | 2664篇 |
2005年 | 2094篇 |
2004年 | 2116篇 |
2003年 | 1973篇 |
2002年 | 1995篇 |
2001年 | 1729篇 |
2000年 | 1667篇 |
1999年 | 1469篇 |
1998年 | 1460篇 |
1997年 | 1454篇 |
1996年 | 1176篇 |
1995年 | 1162篇 |
1994年 | 1080篇 |
1993年 | 969篇 |
1992年 | 865篇 |
1991年 | 838篇 |
1990年 | 865篇 |
1989年 | 791篇 |
1988年 | 794篇 |
1987年 | 902篇 |
1986年 | 795篇 |
1985年 | 1030篇 |
1984年 | 1161篇 |
1983年 | 1108篇 |
1982年 | 995篇 |
1981年 | 922篇 |
1980年 | 883篇 |
1979年 | 832篇 |
1978年 | 854篇 |
1977年 | 742篇 |
1976年 | 721篇 |
1975年 | 702篇 |
1974年 | 714篇 |
1973年 | 738篇 |
1972年 | 500篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
891.
Martin P. Kirkbride Margaret A. Bradshaw Fraka J. Harmsen 《Meteoritics & planetary science》1991,26(3):213-216
Abstract— Nine additional iron meteorite fragments weighing a total of 72 kg were recovered from the Derrick Peak area by a Canterbury Museum geological party in late 1988. One iron was located in the Onnum Valley, 6 km south of the previous finds. Geochemical analysis indicates that all irons belong to a single meteorite shower, greatly increasing the known extent of the fall zone. Kamp and Lowe (1982) have previously estimated the terrestrial age of the meteorite from glacial geological evidence. The location of the 1988 finds supports Kamp and Lowe's interpretation that the meteorites lie in situ, but recent revisions of the chronology of Cenozoic glacial history of the region reduce the interpreted terrestrial age. An age of between Oxygen Isotope stages 6 and 2 is probable (190–125 to 35–12 ka BP). This conflicts with a terrestrial age estimate of 1.0 ± 0.1 Ma BP from cosmogenic radionuclides. 相似文献
892.
From reflection and refraction data a crustal model of the Concepcion Bank NE of Lanzarote Island has been calculated. It is interpreted as a tectonic unit of volcanic origin. Its evolution history of mainly Tertiary age does not depend on sea floor spreading. The Bank is built of intruded basaltic layers over material with a reduced mantle p-velocity. 相似文献
893.
894.
895.
896.
897.
Europa is bombarded by intense radiation that erodes the surface, launching molecules into a thin “atmosphere” representative of surface composition. In addition to atoms and molecules created in the mostly water ice surface such as H2O, O2, H2, the atmosphere is known to have species representative of trace surface materials. These trace species are carried off with the 10-104 H2O molecules ejected by each energetic heavy ion, a process we have simulated using molecular dynamics. Using the results of those simulations, we found that a neutral mass spectrometer orbiting ∼100 km above the surface could detect species with surface concentrations above ∼0.03%. We have also modeled the atmospheric spatial structure of the volatile species CO2 and SO2 under a variety of assumptions. Detections of these species with moderate time and space resolution would allow us to constrain surface composition, chemistry and to study space weathering processes. 相似文献
898.
We have investigated the role of group velocity in the calculation of pitch-angle diffusion coefficients by electron cyclotron harmonic (ECH) waves in planetary magnetospheres. The assumption which is generally made that the parallel group velocity can be neglected in comparison with particle parallel velocity is examined in detail. It is found that for lowest harmonic band this assumption is quite good. It is found that in general it is not possible to ignore the parallel group velocity. However, for lowest harmonic band this assumption is quite good at low electron temperatures. 相似文献
899.
900.
In this paper we have studied the possible proton collisions in cosmic ray sources. On the basis of our calculations of background temperature, the operational domains of various proton collisions are suggested. The energy rate loss through the photo-neutrino processes on protons is computed and we have discussed the energy distribution of the secondary particles in various collisions. 相似文献