全文获取类型
收费全文 | 52568篇 |
免费 | 922篇 |
国内免费 | 329篇 |
专业分类
测绘学 | 1487篇 |
大气科学 | 4306篇 |
地球物理 | 10073篇 |
地质学 | 17650篇 |
海洋学 | 4310篇 |
天文学 | 12559篇 |
综合类 | 122篇 |
自然地理 | 3312篇 |
出版年
2020年 | 391篇 |
2019年 | 372篇 |
2018年 | 937篇 |
2017年 | 937篇 |
2016年 | 1231篇 |
2015年 | 806篇 |
2014年 | 1320篇 |
2013年 | 2641篇 |
2012年 | 1181篇 |
2011年 | 1674篇 |
2010年 | 1569篇 |
2009年 | 2093篇 |
2008年 | 1889篇 |
2007年 | 1862篇 |
2006年 | 1757篇 |
2005年 | 1606篇 |
2004年 | 1548篇 |
2003年 | 1463篇 |
2002年 | 1418篇 |
2001年 | 1292篇 |
2000年 | 1205篇 |
1999年 | 1163篇 |
1998年 | 1111篇 |
1997年 | 1110篇 |
1996年 | 882篇 |
1995年 | 885篇 |
1994年 | 854篇 |
1993年 | 764篇 |
1992年 | 734篇 |
1991年 | 706篇 |
1990年 | 808篇 |
1989年 | 704篇 |
1988年 | 673篇 |
1987年 | 764篇 |
1986年 | 637篇 |
1985年 | 861篇 |
1984年 | 987篇 |
1983年 | 954篇 |
1982年 | 896篇 |
1981年 | 856篇 |
1980年 | 757篇 |
1979年 | 717篇 |
1978年 | 736篇 |
1977年 | 649篇 |
1976年 | 620篇 |
1975年 | 551篇 |
1974年 | 642篇 |
1973年 | 629篇 |
1972年 | 382篇 |
1971年 | 351篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
281.
282.
G.C. Sethia G.J. Bailey R.J. Moffett J.K. Hargreaves 《Planetary and Space Science》1985,33(3):321-332
A modelling study of the electron content of the mid-latitude ionosphere and protonosphere has been carried out for solstice conditions using the mathematical model of Bailey (1983). In the model calculations coupled time-dependent O+, H+ continuity and momentum equations and O+, H+ and electron heat balance equations are solved for a magnetic shell extending over both hemispheres. The inclusion of interhemispheric flow of plasma and of heat balance has enabled us to investigate the role of interhemispheric coupling on the electron content and related shape parameters. The computed results are compared with results from slant path observations of the ATS-6 radio beacon made at Lancaster (U.K.) and Boulder, Colorado (U.S.A.).It has been found that the conjugate photoelectron heating has a major effect on the shape of the daily variation of slant slab thickness (τ) and also on the magnitude of the protonospheric content (Np). Some of the main features of τ are closely related to the sunrise and sunset times in the conjugate ionosphere. Also it is found that night-time increases in total electron content (NT) and F2 region peak electron density (Nmax) in winter are natural consequences of ionization loss at low altitudes causing an enhanced downward flow of plasma from the protonosphere which is coupled to the summer hemisphere. One other important consequence of the coupled protonosphere is that the effects on NT of the neutral air wind are not much different in winter from those in summer. 相似文献
283.
Luigi R. Bedin † Santi Cassisi Fiorella Castelli Giampaolo Piotto Jay Anderson Maurizio Salaris Yazan Momany Adriano Pietrinferni 《Monthly notices of the Royal Astronomical Society》2005,357(3):1038-1048
We propose a zero-point photometric calibration of the data from the Advanced Camera for Surveys (ACS) Wide Field Channel (WFC) on board the Hubble Space Telescope , based on a spectrum of Vega and the most up-to-date in-flight transmission curves of the camera. This calibration is accurate at the level of a few hundredths of a magnitude. The main purpose of this effort is to transform the entire set of evolutionary models into a simple observational photometric system for ACS/WFC data, and to make them available to the astronomical community. We provide the zero-points for the most used ACS/WFC bands, and give basic recipes for calibrating both the observed data and the models. We also present the colour–magnitude diagram from ACS data of five Galactic globular clusters, spanning the metallicity range −2.2 <[Fe/H] < −0.04 , and we provide fiducial points representing their sequences from several magnitudes below the turn-off to the red giant branch tip. The observed sequences are compared with the models in the newly defined photometric system. 相似文献
284.
285.
286.
287.
288.
289.
290.
In this paper, the currently accepted correlation of the Early Pleistocene Ludhamian stage of England with the Tiglian‐A sub‐stage of the Netherlands is challenged. Recent investigations of Early Pleistocene marine North Sea deposits from a borehole near Noordwijk (the Netherlands) yielded evidence from molluscs, dinoflagellate cysts and sporomorphs for an alternation of warm‐temperate and arctic intervals within the Praetiglian and Tiglian stages. Marine equivalents of the terrestrial‐based pollen sub‐stages Tiglian A and B have been recognised in the upper part of the sequence. A Praetiglian age can be assigned to the lower part of the sequence on the basis of mollusc analysis. Within the Praetiglian, an alternation of warm and cold phases has been recognised from both the dinoflagellate cyst and molluscan records. Three cold phases within the Praetiglian are tentatively correlated with marine isotope stages (MIS) 96–100. The molluscan assemblages provide evidence for climate forcing of the sea level: highest sea levels are reached in the warm‐temperate intervals. Within the Praetiglian, an interval with an acme zone of the dinoflagellate cyst Impagidinium multiplexum, is correlated with the Ludhamian and tentatively linked to MIS 97 and/or MIS 96. The cold molluscan assemblages from the Noordwijk borehole include an acme zone of Megayoldia thraciaeformis, the first and only occurrence of this North Pacific bivalve in the North Sea Basin. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献