全文获取类型
收费全文 | 37974篇 |
免费 | 4559篇 |
国内免费 | 2668篇 |
专业分类
测绘学 | 1308篇 |
大气科学 | 1919篇 |
地球物理 | 13462篇 |
地质学 | 7101篇 |
海洋学 | 1115篇 |
天文学 | 16740篇 |
综合类 | 1514篇 |
自然地理 | 2042篇 |
出版年
2024年 | 94篇 |
2023年 | 277篇 |
2022年 | 627篇 |
2021年 | 776篇 |
2020年 | 718篇 |
2019年 | 922篇 |
2018年 | 718篇 |
2017年 | 729篇 |
2016年 | 688篇 |
2015年 | 951篇 |
2014年 | 1098篇 |
2013年 | 1174篇 |
2012年 | 1188篇 |
2011年 | 1278篇 |
2010年 | 1227篇 |
2009年 | 2794篇 |
2008年 | 2533篇 |
2007年 | 2939篇 |
2006年 | 2916篇 |
2005年 | 2682篇 |
2004年 | 2670篇 |
2003年 | 2367篇 |
2002年 | 2067篇 |
2001年 | 1855篇 |
2000年 | 1576篇 |
1999年 | 1528篇 |
1998年 | 1661篇 |
1997年 | 767篇 |
1996年 | 659篇 |
1995年 | 782篇 |
1994年 | 730篇 |
1993年 | 478篇 |
1992年 | 352篇 |
1991年 | 264篇 |
1990年 | 220篇 |
1989年 | 241篇 |
1988年 | 180篇 |
1987年 | 132篇 |
1986年 | 108篇 |
1985年 | 55篇 |
1984年 | 48篇 |
1983年 | 26篇 |
1982年 | 6篇 |
1980年 | 5篇 |
1979年 | 28篇 |
1978年 | 4篇 |
1977年 | 16篇 |
1976年 | 5篇 |
1954年 | 10篇 |
1897年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
11.
12.
Neill Reid 《Monthly notices of the Royal Astronomical Society》2003,342(3):837-850
We present high-resolution echelle spectroscopy of 20 stars in 16 systems catalogued as members of the TW Hydrae association, and 16 stars identified as possible new members. We have calibrated the range of coronal and chromospheric activity expected for such young stars as a function of spectral type by combining our observations with literature data for field and open cluster stars. We also compute space motions for TWA members and candidate members with proper motion measurements, using two techniques to estimate distances to stars lacking direct trigonometric parallax measurements. The mean space motion of the four TWA members with known parallaxes is ( U , V , W : −10.0, −17.8, −4.6) km s−1 . 14 of the candidates have properties inconsistent with cluster membership; the remaining two are potential new members, although further observations are required to confirm this possibility. 相似文献
13.
14.
15.
16.
17.
18.
1 IntroductionAccordingtogeologicalstructure ,theGansu Ningxia Qinghaiareabelongstothenortheastmar ginofQinghai Tibetblock .Thisareahasbeenpaidmuchattentionby geo specialistsinChinaandabroadbecauseofitssignificanttectonicmovement,itsintensiveseismicity ,anditsimportanceinearth quakehazardmitigation .IntheDevelopmentPro gramonNationalKeyBasicResearchesundertheProject“MechanismandPredictionofContinentalStrongEarthquakes”,themechanismsofcontinen talstrongearthquakesarestudied ,usinghypo… 相似文献
19.
FEASIBLE STUDY ON THE INTEGRATION SYSTEM FOR THE SPACE MONITORING OF MAJOR EARTHQUAKES AND VOLCANOES IN TERRESTRIAL LAND 总被引:1,自引:1,他引:0
BOLi-qun 《中国地理科学(英文版)》2002,12(4):350-353
With the rapid development of space technology, earth observation technology and sky observatory technolo-gy, they have played a more and more important part in monitoring and predicting of earthquakes and volcanoes in the terres-trial land. In recent years, the related agencies have done the experiments and researches on monitoring and predicting ofearthquakes and volcanoes in the forewarning period by means of many approaches, such as satellite thermal infrared re-mote sensing (TIRS), Global Positioning System (GPS), differential interferometric synthesis aperture radar (D-INSAR),astronomical time-latitude residual anomaly, and Geographic Information Systems (GIS), etc. A quite large number of re-search foundation has been built in the fundamental theories and application methods. The experiments and researcheshave shown that these technology is efficient methods for high frequency crust movement. If the existed separate scientificforces and results are possibly assembled together to form a more complete integration monitoring system with the combina-tion of space, sky observation, ground, deep geology and macro anomaly, it will come into a new stage of monitoring andpredicting of earthquakes and volcanic eruptions. 相似文献
20.
Roberto F. Viotti Lucio Angelo Antonelli Sonja Rebecchi Corinne Rossi 《Journal of Astrophysics and Astronomy》2002,23(1-2):19-22
We have investigated with BeppoSAX the long term behaviour of the harder X-ray component of the supposed supermassive binary
system η Car along its 5.52 year cycle. We have found that in March 1998 during egress from the last December 1997 eclipse,
this component was the same as outside eclipse, but for a large (×3.5) increase of NH
h
, that can be attributed to the presence or formation of opaque matter in front of the source near periastron. Unexpectedly,
at that time the iron 6.7 keV emission line was 40% stronger. BeppoSAX has for the first time found ahard X-ray tail extending to at least 50 keV, that cannot be adequately fitted with an additional hotter thermal component. The 2–100 keV
spectrum of η Car is instead well fitted with an absorbed powerlaw spectrum with photon index 2.53, suggesting non-thermal
emission as an alternative model for the core source. 相似文献