全文获取类型
收费全文 | 6849篇 |
免费 | 126篇 |
国内免费 | 222篇 |
专业分类
测绘学 | 94篇 |
大气科学 | 80篇 |
地球物理 | 151篇 |
地质学 | 646篇 |
海洋学 | 132篇 |
天文学 | 5988篇 |
综合类 | 28篇 |
自然地理 | 78篇 |
出版年
2024年 | 14篇 |
2023年 | 29篇 |
2022年 | 48篇 |
2021年 | 48篇 |
2020年 | 52篇 |
2019年 | 79篇 |
2018年 | 29篇 |
2017年 | 42篇 |
2016年 | 56篇 |
2015年 | 96篇 |
2014年 | 104篇 |
2013年 | 97篇 |
2012年 | 109篇 |
2011年 | 98篇 |
2010年 | 148篇 |
2009年 | 497篇 |
2008年 | 413篇 |
2007年 | 577篇 |
2006年 | 570篇 |
2005年 | 641篇 |
2004年 | 535篇 |
2003年 | 528篇 |
2002年 | 483篇 |
2001年 | 370篇 |
2000年 | 329篇 |
1999年 | 311篇 |
1998年 | 392篇 |
1997年 | 51篇 |
1996年 | 45篇 |
1995年 | 103篇 |
1994年 | 56篇 |
1993年 | 25篇 |
1992年 | 17篇 |
1991年 | 27篇 |
1990年 | 35篇 |
1989年 | 32篇 |
1988年 | 28篇 |
1987年 | 23篇 |
1986年 | 9篇 |
1985年 | 11篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1976年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有7197条查询结果,搜索用时 15 毫秒
1.
Monitoring of the fluctuations of groundwater storage is particularly important in arid and semi-arid regions where water scarcity brings about various challenges. Remote sensing data and techniques play a preponderant role in developing solutions to environmental problems. The launch of Gravity Recovery and Climate Experiment (GRACE) satellites has eased the remote monitoring and evaluation of groundwater resources with an unprecedented precision over large scales. Within the scope of the current study, the latest release (RL06) of GRACE mass concentrations (Mascons) from Jet Propulsion Laboratory (JPL) dataset as well as Global Land Data Assimilation System (GLDAS) models of Noah and Catchment Land Surface Model (CLSM) were used to provide Groundwater Storage Anomalies (GWSA) over Turkey. The temporal interactions of the estimated GWSA with the climatic variables of precipitation and temperature (derived from the reanalysis datasets of CHELSA [Climatologies at High resolution for the Earth's Land Surface Areas] and FLDAS [the Famine Early Warning Systems Network Land Data Assimilation System], respectively) were investigated statistically. The results suggest that there is a descending trend (from 2003 to 2016) for Terrestrial Water Storage Anomalies (TWSA) and GWSA over Turkey with a total loss of 11 and 6 cm of water, respectively. The statistical analysis results also indicate that the monthly variations of GWSA over Turkey are highly correlated with precipitation and temperature at 2-month lag. The analysis of the climatology (long-term) values of monthly GWSA, precipitation and temperature also revealed high agreement between the variables. 相似文献
2.
3.
4.
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
5.
6.
7.
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
8.
9.
A wide-field time-series CCD photometric survey of variable stars in the field of the open cluster NGC 2168 was carried out using the BATC Schmidt telescope. In total 13 new variable stars are discovered with three W UMa systems, one EA type and two EB type eclipsing binaries (one of them could be a W UMa system), and seven pulsating stars including three candidates of δScuti stars. 相似文献
10.
Xue-Fei Chen Zhan-Wen HanNational Astronomical Observatories Yunnan Observatory Chinese Academy of Sciences. Kunming Graduate School of the Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2005,5(1):65-76
We have studied the influence of different choices of core-envelope transition point on the final merger of contact binaries with two main-sequence components. A binary of 1.00 + 0.90M⊙ with an initial orbital period of 0.35d is examined. The mass fraction of the primary mixed with the matter of the secondary, qmix, determined by the chosen core-envelope transition point, ranges from 0.04 to 1.00 in our analysis. If as qmix< 0.8, none of the 相似文献