全文获取类型
收费全文 | 51331篇 |
免费 | 21432篇 |
国内免费 | 46995篇 |
专业分类
测绘学 | 6470篇 |
大气科学 | 22822篇 |
地球物理 | 15452篇 |
地质学 | 44512篇 |
海洋学 | 18784篇 |
天文学 | 1076篇 |
综合类 | 5644篇 |
自然地理 | 4998篇 |
出版年
2024年 | 432篇 |
2023年 | 1015篇 |
2022年 | 1850篇 |
2021年 | 2472篇 |
2020年 | 3100篇 |
2019年 | 6319篇 |
2018年 | 6368篇 |
2017年 | 6087篇 |
2016年 | 6151篇 |
2015年 | 5840篇 |
2014年 | 5218篇 |
2013年 | 6020篇 |
2012年 | 6003篇 |
2011年 | 5744篇 |
2010年 | 5699篇 |
2009年 | 4949篇 |
2008年 | 4408篇 |
2007年 | 4272篇 |
2006年 | 3957篇 |
2005年 | 3487篇 |
2004年 | 3506篇 |
2003年 | 2963篇 |
2002年 | 2729篇 |
2001年 | 2491篇 |
2000年 | 2040篇 |
1999年 | 1805篇 |
1998年 | 1743篇 |
1997年 | 1788篇 |
1996年 | 1404篇 |
1995年 | 1343篇 |
1994年 | 1207篇 |
1993年 | 1165篇 |
1992年 | 1012篇 |
1991年 | 752篇 |
1990年 | 719篇 |
1989年 | 602篇 |
1988年 | 509篇 |
1987年 | 402篇 |
1986年 | 319篇 |
1985年 | 261篇 |
1984年 | 281篇 |
1983年 | 180篇 |
1982年 | 212篇 |
1981年 | 149篇 |
1980年 | 111篇 |
1979年 | 113篇 |
1978年 | 52篇 |
1977年 | 46篇 |
1971年 | 53篇 |
1970年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
982.
983.
984.
Nannorrhops ritchiana (Mazari Palm) is a distinctive flora growing in the Saharo-Sindian region. It is well distributed on the ultramafic soil,
derived from the Bela Ophiolite in the Khuzdar District, Balochistan, Pakistan. Quantitative estimation of Ca, Mg, Fe and
Ni in soil and plant ash has been carried out. The constituents of plant ash have been discussed in relation to soil chemistry,
pH, climate, mobility, average abundance in plant ash and exclusion mechanism of the flora. Relationship among Ca, Mg, Fe
and Ni has been established using scattergrams to evaluate the biogeochemistry of the plant. High contents of Mg and high
coefficient of biological absorption allow it to be classed as Mg-flora. Both Ca and Fe appeared to be antagonistic to Mg.
The metal assemblage ofN. ritchiana nicely reflected the nature of the bed rock as being serpentinized ultramafic, and its corresponding soils. Good exclusion
mechanism ofN. ritchiana did not allow it to absorb high Ni from the soil. Relatively high concentrations of Ni inN. ritchiana from the Baran Lak area can be used to localize Ni-mineralization in the study area.
Statistical analyses, such as minimum, maximum, mean, mode, median, standard deviations, and coefficient of correlation, were
also made to improve raw geochemical data and interpretations. 相似文献
985.
986.
987.
988.
989.
The phase relations of quaternary systems are generally represented by projections onto ternary compositional planes. Such
projections often obscure relationships that would only be evident in a three-dimensional tetrahedral plot. The tetrahedral
plot requires that compositions of the minerals and melts be transformed into Cartesian coordinates. It is shown here how
this transformation is carried out. The application is demonstrated by tetrahedral plots of experimental melt compositions
of partially molten lherzolite. Furthermore, the plot can be used to evaluate whether or not a particular basaltic composition
represents a primary melt. The methods are applicable to any four-component system. 相似文献
990.