全文获取类型
收费全文 | 101508篇 |
免费 | 1438篇 |
国内免费 | 811篇 |
专业分类
测绘学 | 2180篇 |
大气科学 | 6680篇 |
地球物理 | 19393篇 |
地质学 | 36662篇 |
海洋学 | 9355篇 |
天文学 | 23643篇 |
综合类 | 273篇 |
自然地理 | 5571篇 |
出版年
2022年 | 723篇 |
2021年 | 1222篇 |
2020年 | 1340篇 |
2019年 | 1459篇 |
2018年 | 2992篇 |
2017年 | 2790篇 |
2016年 | 3258篇 |
2015年 | 1672篇 |
2014年 | 3129篇 |
2013年 | 5401篇 |
2012年 | 3394篇 |
2011年 | 4394篇 |
2010年 | 3974篇 |
2009年 | 5017篇 |
2008年 | 4390篇 |
2007年 | 4488篇 |
2006年 | 4176篇 |
2005年 | 2962篇 |
2004年 | 2868篇 |
2003年 | 2684篇 |
2002年 | 2664篇 |
2001年 | 2328篇 |
2000年 | 2277篇 |
1999年 | 1819篇 |
1998年 | 1893篇 |
1997年 | 1750篇 |
1996年 | 1500篇 |
1995年 | 1486篇 |
1994年 | 1314篇 |
1993年 | 1202篇 |
1992年 | 1144篇 |
1991年 | 1158篇 |
1990年 | 1163篇 |
1989年 | 982篇 |
1988年 | 923篇 |
1987年 | 1095篇 |
1986年 | 929篇 |
1985年 | 1186篇 |
1984年 | 1283篇 |
1983年 | 1231篇 |
1982年 | 1142篇 |
1981年 | 1040篇 |
1980年 | 976篇 |
1979年 | 890篇 |
1978年 | 886篇 |
1977年 | 746篇 |
1976年 | 753篇 |
1975年 | 730篇 |
1974年 | 709篇 |
1973年 | 785篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
A. S. Trew 《Astrophysics and Space Science》1982,82(1):223-228
The possible correlation noted between the intrinsic quasar luminosity and the absorption line expulsion velocity is re-examined using homogeneous data sets for metal and L only line systems. The method of analysis is chosen to enable any reasonable form of correlation to be found. No correlation is detected at a confidence level >10%. 相似文献
132.
133.
The spreading angle of a number of light and dark Martian streaks is determined from selected Mariner 9 images. The resulting frequency distributions of spreading half-angles have maxima at ~5° for light, and ~7° for dark streaks; however the dark streaks have a secondary maximum spreading angle at ~14°. The smaller values, which include most streaks, are interpreted as crater-wake spreading phenomena. The larger value, found in only a few dark streaks or “tails,” may result from atmospheric diffusion and subsequent deposition of material from isolated sources such as vents or blowouts. An atmospheric diffusion-deposition analysis is presented, assuming this streak origin, from which it is possible to deduce the eddy diffusivity, K, in Mars' boudary layer. Calculated K values are found to agree with various theoretical estimates. They lie in the range 107 and 109 cm2 sec?1 and exhibit the proper scale dependence. Thus it appears that, in addition to streak-derived wind direction patterns and speed information, it is possible in a few cases to derive information on Mars' boundary-layer turbulence from streak-spreading measurements. 相似文献
134.
135.
136.
137.
138.
The problem of the diversity of the geochemical types of carbon dioxide waters (CDW) in petrografically and mineralogically uniform crystalline rock masses is solved with allowance made for the effect of different boundary conditions (physicochemical parameters) on the geochemical effect of interaction in the rock–water system. The formation of the entire geochemical spectrum of CDW in crystalline rock masses is shown to be explicable on the basis of a model of interaction in granite–water systems at different mass ratios of reacting rock (S) and water (L), different temperatures T, and equilibrium concentrations of dissolved CO2 (P
CO2). 相似文献
139.
Global assessment of the potential impacts of anthropogenically-induced climate change on vector-borne diseases suggests an increase in extent of the geographical areas susceptible to transmission of malarial Plasmodium parasites, dengue Flavivirus and Schistosoma worms. The transmission potential of the three associated vector-borne diseases studied is highly sensitive to climate changes on the periphery of the currently endemic areas and at higher altitudes within such areas. Our findings vis-à-vis the present endemic areas indicate that the increase in the epidemic potential of malaria and dengue transmission may be estimated at 12–27% and 31–47%, respectively, while in contrast, schistosomiasis transmission potential may be expected to exhibit a 11–17% decrease. 相似文献
140.
Late Cretaceous rift-related upwelling and melting of the Trindade starting mantle plume head beneath western Brazil 总被引:1,自引:0,他引:1
S. A. Gibson R. N. Thompson R. K. Weska A. P. Dickin O. H. Leonardos 《Contributions to Mineralogy and Petrology》1997,126(3):303-314
High mantle potential temperatures and local extension, associated with the Late-Cretaceous impact of the Trindade mantle plume, produced substantial widespread and voluminous magmatism around the northern half of the Paraná sedimentary basin. Our previous studies have shown that, above the central and eastern portions of the postulated impact zone where lithosphere extension is minimal, heat conducted by the plume caused large-scale melting of the more fusible parts of the subcontinental lithospheric mantle beneath the margin of the São Francisco craton and the surrounding Brasilía mobile belt. Here we combine geochemical data and field evidence from the Poxoreu Igneous Province, western Brazil to show how more intense lithospheric extension above the western margin of the postulated impact zone permitted greater upwelling and melting of the Trindade plume than further east. Laser 40Ar/39Ar age determinations indicate that rift-related basaltic magmas of the Poxoreu Igneous Province were emplaced at ? 84 Ma. Our detailed geochemical study of the mafic magmas shows that the parental melts underwent polybaric crystal fractionation within the crust prior to final emplacement. Furthermore, some magmas (quartz-normative) appear to have assimilated upper crust whereas others (nepheline- and hypersthene-normative) appear to have been unaffected by open-system crustal magma chamber processes. Incompatible trace element ratios (e.g. chondrite-normalised La/Nb?=?1) and isotopic ratios (87Sr/86Sr?=?0.704 and 143Nd/144Nd?=?0.51274) of the Hy-normative basalts resemble those of oceanic islands (OIB). We therefore propose that these “OIB-like” magmas were predominantly derived from convecting-mantle-source melts (i.e. Trindade mantle plume). Inverse modelling of rare-earth element (REE) abundances suggests that the initial melts were predominantly generated within the depth range of ?80–100 km, in mantle with a potential temperature of ?1500 °C. 相似文献