全文获取类型
收费全文 | 76104篇 |
免费 | 922篇 |
国内免费 | 1159篇 |
专业分类
测绘学 | 2407篇 |
大气科学 | 5356篇 |
地球物理 | 14336篇 |
地质学 | 31513篇 |
海洋学 | 5567篇 |
天文学 | 12988篇 |
综合类 | 2251篇 |
自然地理 | 3767篇 |
出版年
2022年 | 259篇 |
2021年 | 439篇 |
2020年 | 512篇 |
2019年 | 585篇 |
2018年 | 7247篇 |
2017年 | 6511篇 |
2016年 | 4486篇 |
2015年 | 859篇 |
2014年 | 1130篇 |
2013年 | 1883篇 |
2012年 | 2816篇 |
2011年 | 5825篇 |
2010年 | 5029篇 |
2009年 | 5617篇 |
2008年 | 4673篇 |
2007年 | 5593篇 |
2006年 | 1655篇 |
2005年 | 1660篇 |
2004年 | 1747篇 |
2003年 | 1827篇 |
2002年 | 1421篇 |
2001年 | 930篇 |
2000年 | 875篇 |
1999年 | 736篇 |
1998年 | 737篇 |
1997年 | 724篇 |
1996年 | 588篇 |
1995年 | 572篇 |
1994年 | 499篇 |
1993年 | 453篇 |
1992年 | 408篇 |
1991年 | 423篇 |
1990年 | 437篇 |
1989年 | 390篇 |
1988年 | 369篇 |
1987年 | 398篇 |
1986年 | 415篇 |
1985年 | 508篇 |
1984年 | 545篇 |
1983年 | 542篇 |
1982年 | 496篇 |
1981年 | 472篇 |
1980年 | 453篇 |
1979年 | 408篇 |
1978年 | 375篇 |
1977年 | 384篇 |
1976年 | 350篇 |
1975年 | 353篇 |
1974年 | 340篇 |
1973年 | 370篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
241.
Abstract— The 50,000 year old, 1.8 km diameter Lonar crater is one of only two known terrestrial craters to be emplaced in basaltic target rock (the 65 million year old Deccan Traps). The composition of the Lonar basalts is similar to martian basaltic meteorites, which establishes Lonar as an excellent analogue for similarly sized craters on the surface of Mars. Samples from cores drilled into the Lonar crater floor show that there are basaltic impact breccias that have been altered by post‐impact hydrothermal processes to produce an assemblage of secondary alteration minerals. Microprobe data and X‐ray diffraction analyses show that the alteration mineral assemblage consists primarily of saponite, with minor celadonite, and carbonate. Thermodynamic modeling and terrestrial volcanic analogues were used to demonstrate that these clay minerals formed at temperatures between 130°C and 200°C. By comparing the Lonar alteration assemblage with alteration at other terrestrial craters, we conclude that the Lonar crater represents a lower size limit for impact‐induced hydrothermal activity. Based on these results, we suggest that similarly sized craters on Mars have the potential to form hydrothermal systems, as long as liquid water was present on or near the martian surface. Furthermore, the Fe‐rich alteration minerals produced by post‐impact hydrothermal processes could contribute to the minor iron enrichment associated with the formation of the martian soil. 相似文献
242.
Ulrich Hopp Regina E. Schulte-Ladbeck Jürgen Kerp 《Astrophysics and Space Science》2003,284(2):647-650
We are investigating the hypothesis that Compact High-Velocity Clouds (CHVCs) are the left-over building blocks of Local Group
galaxies. To this end, we are searching for their embedded stellar populations using FORS at the VLT. The search is done with
single-star photometry in V and I bands, which is sensitive to both, young and old, stellar populations. Five CHVCs of our
sample have been observed so far down to I=24. We pointed the VLT towards the highest HI column density regions, as determined
in Effelsberg radio data. In an alternate approach, we searched 2MASS public data towards those 5 CHVCs down to K=16. While
the VLT data probe the central regions out to distance moduli of about 27, the 2MASS data are sensitive to a population of
red giant stars to distance moduli of about 20. The 2MASS data, on the other hand, cover a much wider field of view than the
VLT data (radius of 1 degree versus FORS field of 6.8 arcmin). We did not find a stellar population intrinsic to the CHVCs
in either data. In this paper, we illustrate our search methods.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
243.
244.
245.
246.
247.
248.
WANGWei-wu ZHULi-zhong WANGRen-chao SHIYong-jung 《中国地理科学(英文版)》2003,13(1):39-47
Urban heat environmental quality(UHEQ) is affected by the interacting of weather condition and underlying surface framework of urban area .In the last two decades,many researchers from domestic and overseas have studied many problems at the aspect of urban heat environment such as urban heat islands ,urban air temperature and their rela-tion with urban land cover,city population,air pollution etc,In the recent years,Hangzhou,acting as a center city of Zhejiang Province in China,its urbanization quantum and quantity have both changed greatly,in particular ,representing as business affairs building,resident real property and all kins of specialty market having arisen in built-up zone,Based on Landsat TM images data in 1991 and 1999,urban underlying surface temperature value and Normalized Difference Vegetation Index (NDVI) were calculated using image interpreting and supervised classification technique by remote sensing software ERDAS image 8.4,The relation model between urban underlying surface temperature (UUST )and urban air temperature was setup according to the certain correlation patten .Reference to the relational standard of assessing human comfort and other meteorology data of Hangzhou City in summer,the spatial distribution characteristic and the spatial varia-tion degree of human comfort of heat environmental quality are estimated and mapped on a middle scale,that is ,in six districts of Hangzhou City .Then the paper reveals the main characteristic of spatial variation from 1991 to 1999.Lastly,the change mechanism is analyzed and discussed from the viewpoint of city planning,construction and environmental protec-tion. 相似文献
249.
250.