全文获取类型
收费全文 | 8946篇 |
免费 | 1601篇 |
国内免费 | 2160篇 |
专业分类
测绘学 | 471篇 |
大气科学 | 1310篇 |
地球物理 | 2627篇 |
地质学 | 4727篇 |
海洋学 | 977篇 |
天文学 | 1111篇 |
综合类 | 497篇 |
自然地理 | 987篇 |
出版年
2024年 | 82篇 |
2023年 | 220篇 |
2022年 | 392篇 |
2021年 | 452篇 |
2020年 | 415篇 |
2019年 | 446篇 |
2018年 | 377篇 |
2017年 | 393篇 |
2016年 | 416篇 |
2015年 | 451篇 |
2014年 | 501篇 |
2013年 | 485篇 |
2012年 | 549篇 |
2011年 | 542篇 |
2010年 | 437篇 |
2009年 | 555篇 |
2008年 | 530篇 |
2007年 | 560篇 |
2006年 | 568篇 |
2005年 | 486篇 |
2004年 | 466篇 |
2003年 | 404篇 |
2002年 | 354篇 |
2001年 | 294篇 |
2000年 | 342篇 |
1999年 | 254篇 |
1998年 | 302篇 |
1997年 | 269篇 |
1996年 | 211篇 |
1995年 | 171篇 |
1994年 | 177篇 |
1993年 | 115篇 |
1992年 | 119篇 |
1991年 | 76篇 |
1990年 | 74篇 |
1989年 | 63篇 |
1988年 | 54篇 |
1987年 | 25篇 |
1986年 | 32篇 |
1985年 | 15篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 1篇 |
1980年 | 5篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1971年 | 1篇 |
1954年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Summary. Four box cores collected from the Ontong—Java plateau during the Eurydice expedition have been used to make relative geomagnetic palaeo-intensity measurements. Rock magnetic measurements on the sediments show that they are characterized by a uniform magnetic mineralogy, and that they are suitable for relative intensity estimates. These are obtained by normalizing the NRM by an ARM imparted in a low DC bias field. the palaeoceanographic event known as the preservation spike is used to establish a crude time-scale for the record so that it may be compared with other data from the same region, and also with global palaeointensity estimates. the marine sediment data are quite similar to Australian intensity data from lake sediments and archaeomagnetic sources, but as might be expected exhibit some obvious differences from the global record. 相似文献
2.
中国古生教授学会微体古生物学分会举行代表大会和学术年会中国古竽物学会微体古物学分会第五次会员代表大分暨第六次不术年会于1996年1月24日到30日在福州市召开。来自全国地质、石油、煤炭的和产、科研和大学的100多位代表参加了这次大会和学术研讨。大会共... 相似文献
3.
4.
5.
Harker David E. Woodward Charles E. McMURTRY Craig W. Goetz J. A. Pipher J. L. Forrest W. J. 《Earth, Moon, and Planets》1997,78(1-3):259-264
We present 1- to 5-μm broadband and CVF images of comet Hale-Bopp taken 1997 February 10.5 UT, 50 days before perihelion.
All the images exhibit a nonspherical coma with a bright “ridge” in the direction of the dust tail approximately 10″ from
the coma. Synthetic aperture spectrophotometry implies that the optically important grains are of a radius ≤0.4 μm; smallest
radius for any comet seen to date. The variation of the integrated surface brightness with radial distance from the coma (ρ)
in all the images closely follows the “steady state” ρ−1 model for comet dust ablation (Gehrz and Ney, 1992). The near-infrared colors taken along the dust tail are not constant
implying the dust grain properties vary with coma distance.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
J. M. De Buizer 《Monthly notices of the Royal Astronomical Society》2003,341(1):277-298
The results of a survey searching for outflows using near-infrared imaging are presented. Targets were chosen from a compiled list of massive young stellar objects associated with methanol masers in linear distributions. Presently, it is a widely held belief that these methanol masers are found in (and delineate) circumstellar accretion discs around massive stars. If this scenario is correct, one way to test the disc hypothesis is to search for outflows perpendicular to the methanol maser distributions. The main objective of the survey was to obtain wide-field near-infrared images of the sites of linearly distributed methanol masers using a narrow-band 2.12-μm filter. This filter is centred on the H2 v = 1–0 S(1) line; a shock diagnostic that has been shown to successfully trace CO outflows from young stellar objects. 28 sources in total were imaged of which 18 sources display H2 emission. Of these, only two sources showed emission found to be dominantly perpendicular to the methanol maser distribution. Surprisingly, the H2 emission in these fields is not distributed randomly, but instead the majority of sources are found to have H2 emission dominantly parallel to their distribution of methanol masers. These results seriously question the hypothesis that methanol masers exist in circumstellar discs. The possibility that linearly distributed methanol masers are instead directly associated with outflows is discussed. 相似文献
7.
8.
Flavio Scappini Cesare Cecchi-Pestellini Harvey Smith William Klemperer Alexander Dalgarno 《Monthly notices of the Royal Astronomical Society》2003,341(2):657-661
We consider sulphur depletion in dense molecular clouds, and suggest hydrated sulphuric acid, H2 SO4 · n H2 O, as a component of interstellar dust in icy mantles. We discuss the formation of hydrated sulphuric acid in collapsing clouds and its instability in heated regions in terms of the existing hot core models and observations. We also show that some features of the infrared spectrum of hydrated sulphuric acid have correspondence in the observed spectra of young stellar objects. 相似文献
9.
10.