全文获取类型
收费全文 | 5740篇 |
免费 | 11篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 27篇 |
大气科学 | 1033篇 |
地球物理 | 1322篇 |
地质学 | 3192篇 |
海洋学 | 52篇 |
天文学 | 71篇 |
综合类 | 4篇 |
自然地理 | 55篇 |
出版年
2013年 | 70篇 |
2009年 | 33篇 |
1997年 | 40篇 |
1996年 | 78篇 |
1995年 | 48篇 |
1994年 | 44篇 |
1993年 | 67篇 |
1992年 | 156篇 |
1991年 | 154篇 |
1990年 | 144篇 |
1989年 | 142篇 |
1988年 | 138篇 |
1987年 | 176篇 |
1986年 | 132篇 |
1985年 | 119篇 |
1984年 | 162篇 |
1983年 | 173篇 |
1982年 | 189篇 |
1981年 | 189篇 |
1980年 | 164篇 |
1979年 | 192篇 |
1978年 | 167篇 |
1977年 | 154篇 |
1976年 | 120篇 |
1975年 | 145篇 |
1974年 | 125篇 |
1973年 | 142篇 |
1972年 | 131篇 |
1971年 | 141篇 |
1970年 | 148篇 |
1969年 | 103篇 |
1968年 | 134篇 |
1967年 | 125篇 |
1966年 | 86篇 |
1965年 | 98篇 |
1964年 | 101篇 |
1963年 | 44篇 |
1962年 | 93篇 |
1960年 | 106篇 |
1959年 | 35篇 |
1957年 | 41篇 |
1956年 | 37篇 |
1955年 | 40篇 |
1954年 | 68篇 |
1953年 | 39篇 |
1952年 | 49篇 |
1951年 | 38篇 |
1950年 | 61篇 |
1949年 | 44篇 |
1948年 | 36篇 |
排序方式: 共有5756条查询结果,搜索用时 593 毫秒
1.
2.
Transport by southeastern rivers has insignificant influence on the lead concentration of southeastern shelf waters. If the rate of mobilization and transport of lead by these rivers is representative of uncontaminated fluvial transport during the Pleistocene, only about 5% of the prehistoric output of lead to the North Atlantic can be accounted for by river input.Lead concentrations in southeastern shelf waters are similar to those of North Atlantic Water from the upper 1000 m, which is probably similar to the intrusion source water for the shelf. Atmospheric inputs to the shelf of the same magnitude as observed for the Western North Atlantic are difficult to reconcile given the residence time of shelf waters and their lead concentration unless the rate of loss of lead to shelf sediments is about the same as the atmospheric flux. 相似文献
3.
4.
5.
6.
7.
8.
Dr M. J. Wooller D. L. Swain K. J. Ficken A. D. Q. Agnew F. A. Street-Perrott G. Eglinton 《第四纪科学杂志》2003,18(1):3-15
Woody, subalpine shrubs and grasses currently surround Lake Rutundu, Mount Kenya. Multiple proxies, including carbon isotopes, pollen and grass cuticles, from a 755‐cm‐long core were used to reconstruct the vegetation over the past 38 300 calendar years. Stable carbon‐isotope ratios of total organic carbon and terrestrial biomarkers from the lake sediments imply that the proportion of terrestrial plants using the C4 photosynthetic pathway was greater during the Late Pleistocene than in the Holocene. Pollen data show that grasses were a major constituent of the vegetation throughout the Late Pleistocene and Holocene. The proportion of grass pollen relative to the pollen from other plants was greatest at the last glacial maximum (LGM). Grass cuticles confirm evidence that C4 grass taxa were present at the LGM and that the majority followed the cold‐tolerant NADP‐MEC4 subpathway. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
9.
Abstract— We report the results of dynamic crystallization experiments that were specifically designed to study the dependence of Ca and Al partitioning between forsterite and melt in rapidly cooling Caand Al‐rich melts. The partitioning of Ca between olivine and silicate melt is found to be independent of the cooling rate within the range of 1.5 to 1000°C/hr and at CaO contents of up to 25 wt%. Within analytical uncertainty, our data plot on the equilibrium partitioning curve obtained by Libourel (1999). The partitioning behavior of Al at high cooling rates is more complex. Aluminum is much more heterogenously distributed in the olivine and the co‐existing melt than Ca. But, no systematic trend of Al partition coefficient with cooling rate is observed. We apply the results of the experiments to the formation of meteoritic forsterites with relatively high contents of Ca and Al. Although these forsterites are found frequently inside chondrules, the Ca contents of their host chondrules are far too low to crystallize these high Ca‐forsterites. This is also true for very rapid cooling of chondrule melts. The parental melt of these forsterites requires CaO contents above 20 wt%. 相似文献
10.
Wolfram Neutsch Herbert Kalisch Horst Fichtner S. Ranga Sreenivasan Maurice Shevalier 《Astrophysics and Space Science》2003,288(3):391-408
The study of the expansion of the solar wind out of a system of coronal holes is continued. To this end, we consider the numerical
integration of partial differential equations for problems with icosahedral symmetry, in general. First, employing Weyl theory,
orbifold coordinates are introduced. Second, the icosahedral coordinates are discussed in detail. Third, following an analysis
of the properties of these coordinates and the derivation of a few expressions useful for grid construction, various alternatives
for the distribution of lattice points required for numerical integration are considered. A comparison of these numerical
grids motivates the choice of a specific grid optimized for the numerical integration carried out in the accompanying paper
by Kalish et al.(2002).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献