全文获取类型
收费全文 | 14061篇 |
免费 | 1555篇 |
国内免费 | 2956篇 |
专业分类
测绘学 | 992篇 |
大气科学 | 1071篇 |
地球物理 | 2341篇 |
地质学 | 5602篇 |
海洋学 | 1560篇 |
天文学 | 5114篇 |
综合类 | 745篇 |
自然地理 | 1147篇 |
出版年
2024年 | 47篇 |
2023年 | 115篇 |
2022年 | 346篇 |
2021年 | 399篇 |
2020年 | 486篇 |
2019年 | 580篇 |
2018年 | 454篇 |
2017年 | 416篇 |
2016年 | 494篇 |
2015年 | 564篇 |
2014年 | 799篇 |
2013年 | 816篇 |
2012年 | 918篇 |
2011年 | 1030篇 |
2010年 | 1037篇 |
2009年 | 1322篇 |
2008年 | 1199篇 |
2007年 | 1087篇 |
2006年 | 1063篇 |
2005年 | 917篇 |
2004年 | 834篇 |
2003年 | 672篇 |
2002年 | 525篇 |
2001年 | 472篇 |
2000年 | 392篇 |
1999年 | 372篇 |
1998年 | 273篇 |
1997年 | 144篇 |
1996年 | 130篇 |
1995年 | 109篇 |
1994年 | 90篇 |
1993年 | 112篇 |
1992年 | 50篇 |
1991年 | 45篇 |
1990年 | 38篇 |
1989年 | 35篇 |
1988年 | 28篇 |
1987年 | 14篇 |
1986年 | 18篇 |
1985年 | 26篇 |
1984年 | 22篇 |
1983年 | 17篇 |
1982年 | 16篇 |
1981年 | 6篇 |
1980年 | 12篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 15篇 |
1877年 | 1篇 |
1875年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 672 毫秒
931.
Shift-share Analysis on International Tourism Competitiveness - A Case of Jiangsu Province 总被引:5,自引:0,他引:5
SHI Chunyun ZHANG Jie YANG Yang ZHOU Zhang 《中国地理科学(英文版)》2007,17(2):173-178
Shift-share analysis has been confirmed a useful approach in the study of regional economics and many kinds of extended shift-share models have been advanced and put into practice in economic studies, but few have hitherto been introduced and applied to the tourism research in China. Moreover understanding the spatially competitive relationship is of paramount importance for marketers, developers, and planners involved in tourism strategy development. Based on international tourism receipts from 1995 to 2004, this study aims at probing into the spatial competitiveness of interna- tional tourism in Jiangsu Province in comparison with its neighbors by applying a spatially extended shift-share model and a modified dynamic shift-share model. The empirical results illustrate that exceptional years may exist in the ap- plication of dynamic shift-share models. To solve this issue, modifications to dynamic shift-share model are put forward. The analytical results are not only presented but also explained by the comparison of background conditions of tourism development between Jiangsu and its key competitors. The conclusions can be drawn that the growth of international tourism receipts in Jiangsu mainly attributes to the national component and the competitive component and Zhejiang is the most important rival to Jiangsu during the period of 1995-2004. In order to upgrade the tourism competitiveness, it is indispensable for Jiangsu to take proper positioning, promoting and marketing strategies and to cooperate and integrate with its main rivals. 相似文献
932.
R. Cornelisse R. Wijnands J. Homan 《Monthly notices of the Royal Astronomical Society》2007,380(4):1637-1641
We observed the neutron star X-ray transient 2S 1803−245 in quiescence with the X-ray satellite XMM–Newton , but did not detect it. An analysis of the X-ray bursts observed during the 1998 outburst of 2S 1803−245 gives an upper limit to the distance of ≤7.3 kpc, leading to an upper limit on the quiescent 0.5–10 keV X-ray luminosity of ≤2.8 × 1032 erg s−1 (3σ). Since the expected orbital period of 2S 1803−245 is several hours, this limit is not much higher than those observed for the quiescent black hole transients with similar orbital periods. 相似文献
933.
What is the origin of the soft excess in active galactic nuclei? 总被引:1,自引:0,他引:1
Magorzata A. Sobolewska Chris Done 《Monthly notices of the Royal Astronomical Society》2007,374(1):150-158
934.
Li-Xin Li 《Monthly notices of the Royal Astronomical Society》2007,375(1):240-256
Recently, a soft blackbody component was observed in the early X-ray afterglow of GRB 060218, which was interpreted as shock breakout from the thick wind of the progenitor Wolf–Rayet (WR) star of the underlying Type Ic supernova 2006aj. In this paper, we present a simple model for computing the characteristic quantities (including energy, temperature and time duration) for the transient event from the shock breakout in Type Ibc supernovae produced by the core-collapse of WR stars surrounded by dense winds. In contrast to the case of a star without a strong wind, the shock breakout occurs in the wind region rather than inside the star, caused by the large optical depth in the wind. We find that, for the case of a WR star with a dense wind, the total energy of the radiation generated by the supernova shock breakout is larger than that in the case of the same star without a wind by a factor of >10. The temperature can be either hotter or colder, depending on the wind parameters. The time duration is larger caused by the increase in the effective radius of the star due to the presence of a thick wind. Then, we apply the model to GRB 060218/SN 2006aj. We show that, to explain both the temperature and the total energy of the blackbody component observed in GRB 060218 by the shock breakout, the progenitor WR star has to have an unrealistically large core radius (the radius at optical depth of 20), larger than 100 R⊙ . In spite of this disappointing result, our model is expected to have important applications to the observations on Type Ibc supernovae in which the detection of shock breakout will provide important clues to the progenitors of Type Ibc supernovae. 相似文献
935.
936.
937.
938.
939.
940.