全文获取类型
| 收费全文 | 37016篇 |
| 免费 | 6294篇 |
| 国内免费 | 8017篇 |
专业分类
| 测绘学 | 3500篇 |
| 大气科学 | 4975篇 |
| 地球物理 | 6699篇 |
| 地质学 | 20263篇 |
| 海洋学 | 4055篇 |
| 天文学 | 3502篇 |
| 综合类 | 2430篇 |
| 自然地理 | 5903篇 |
出版年
| 2024年 | 173篇 |
| 2023年 | 467篇 |
| 2022年 | 1233篇 |
| 2021年 | 1451篇 |
| 2020年 | 1337篇 |
| 2019年 | 1726篇 |
| 2018年 | 1210篇 |
| 2017年 | 1433篇 |
| 2016年 | 1465篇 |
| 2015年 | 1651篇 |
| 2014年 | 2081篇 |
| 2013年 | 2139篇 |
| 2012年 | 2191篇 |
| 2011年 | 2327篇 |
| 2010年 | 2016篇 |
| 2009年 | 2521篇 |
| 2008年 | 2502篇 |
| 2007年 | 2586篇 |
| 2006年 | 2512篇 |
| 2005年 | 2370篇 |
| 2004年 | 2078篇 |
| 2003年 | 1960篇 |
| 2002年 | 1693篇 |
| 2001年 | 1519篇 |
| 2000年 | 1528篇 |
| 1999年 | 1347篇 |
| 1998年 | 1155篇 |
| 1997年 | 827篇 |
| 1996年 | 707篇 |
| 1995年 | 590篇 |
| 1994年 | 573篇 |
| 1993年 | 467篇 |
| 1992年 | 349篇 |
| 1991年 | 318篇 |
| 1990年 | 210篇 |
| 1989年 | 169篇 |
| 1988年 | 145篇 |
| 1987年 | 73篇 |
| 1986年 | 43篇 |
| 1985年 | 41篇 |
| 1984年 | 23篇 |
| 1983年 | 19篇 |
| 1982年 | 14篇 |
| 1981年 | 16篇 |
| 1980年 | 8篇 |
| 1979年 | 5篇 |
| 1978年 | 16篇 |
| 1977年 | 5篇 |
| 1976年 | 4篇 |
| 1954年 | 7篇 |
排序方式： 共有10000条查询结果，搜索用时 15 毫秒
21.
E.A. Evstigneeva R.R. de Carvalho A.L. Ribeiro H.V. Capelato 《Astrophysics and Space Science》2003,284(2):487-490
We present the preliminary results of a study of how small stellar systems merge to form larger ones. As we display the families
of galaxies in the μe - Re plane (effective surface brightness versus effective radius) we realize that different morphological types occupy different
loci, evidencing the different physical mechanisms operating in each family. As proposed by Capaccioli et al. (1992) this
diagram is the logical equivalent of the HR diagram for stars. Here we take some initial steps in understanding of how we
can establish the evolutionary tracks, solely due to dynamical processes, in the μe - Re plane, ultimately making a dwarf elliptical to turn into a normal elliptical galaxy.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
22.
23.
24.
北部湾北部海上油田的开发工作始于５０年代，６０～７０年代作了大量地质工作。改革开放后，油气勘查取得突破性进展。累计发现油气构造６个，含油面积超过４０ｋｍ２，石油地质储量约４亿ｔ，已开发油田２个，揭开我国南方油气资源开发序幕 相似文献
25.
Zhang Chuanling 《地球科学与环境学报》1997,(1)
文中详细地论述了新疆阿尔泰哈巴河一带古生代火山岩的地质、岩石化学、稀土元素地球化学特征。将其分为三个类型，认为火山岩是在陆缘裂陷槽的区域构造背景下发生和演化的。对各类型火山岩岩浆来源，上升模式也做了初步讨论。 相似文献
26.
概略地叙述了西宁地区的泥石流形成条件和形成机理,并将西宁地区泥石流划分为稀性泥石流类及泥石质泥石流种类。在此基础上提出防治泥石流灾害的意见。 相似文献
27.
C. Dickinson R. D. Davies R. J. Davis 《Monthly notices of the Royal Astronomical Society》2003,341(2):369-384
A full-sky template map of the Galactic free–free foreground emission component is increasingly important for high-sensitivity cosmic microwave background (CMB) experiments. We use the recently published Hα data of both the northern and southern skies as the basis for such a template.
The first step is to correct the Hα maps for dust absorption using the 100-μm dust maps of Schlegel, Finkbeiner & Davis. We show that for a range of longitudes, the Galactic latitude distribution of absorption suggests that it is 33 per cent of the full extragalactic absorption. A reliable absorption-corrected Hα map can be produced for ∼95 per cent of the sky; the area for which a template cannot be recovered is the Galactic plane area | b | < 5°, l = 260°–0°–160° and some isolated dense dust clouds at intermediate latitudes.
The second step is to convert the dust-corrected Hα data into a predicted radio surface brightness. The free–free emission formula is revised to give an accurate expression (1 per cent) for the radio emission covering the frequency range 100 MHz–100 GHz and the electron temperature range 3000–20 000 K. The main uncertainty when applying this expression is the variation of electron temperature across the sky. The emission formula is verified in several extended H ii regions using data in the range 408–2326 MHz.
A full-sky free–free template map is presented at 30 GHz; the scaling to other frequencies is given. The Haslam et al. all-sky 408-MHz map of the sky can be corrected for this free–free component, which amounts to a ≈6 per cent correction at intermediate and high latitudes, to provide a pure synchrotron all-sky template. The implications for CMB experiments are discussed. 相似文献
The first step is to correct the Hα maps for dust absorption using the 100-μm dust maps of Schlegel, Finkbeiner & Davis. We show that for a range of longitudes, the Galactic latitude distribution of absorption suggests that it is 33 per cent of the full extragalactic absorption. A reliable absorption-corrected Hα map can be produced for ∼95 per cent of the sky; the area for which a template cannot be recovered is the Galactic plane area | b | < 5°, l = 260°–0°–160° and some isolated dense dust clouds at intermediate latitudes.
The second step is to convert the dust-corrected Hα data into a predicted radio surface brightness. The free–free emission formula is revised to give an accurate expression (1 per cent) for the radio emission covering the frequency range 100 MHz–100 GHz and the electron temperature range 3000–20 000 K. The main uncertainty when applying this expression is the variation of electron temperature across the sky. The emission formula is verified in several extended H ii regions using data in the range 408–2326 MHz.
A full-sky free–free template map is presented at 30 GHz; the scaling to other frequencies is given. The Haslam et al. all-sky 408-MHz map of the sky can be corrected for this free–free component, which amounts to a ≈6 per cent correction at intermediate and high latitudes, to provide a pure synchrotron all-sky template. The implications for CMB experiments are discussed. 相似文献
28.
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
29.
30.
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