全文获取类型
收费全文 | 110588篇 |
免费 | 1906篇 |
国内免费 | 1052篇 |
专业分类
测绘学 | 2477篇 |
大气科学 | 7708篇 |
地球物理 | 21640篇 |
地质学 | 39615篇 |
海洋学 | 10221篇 |
天文学 | 25028篇 |
综合类 | 325篇 |
自然地理 | 6532篇 |
出版年
2022年 | 686篇 |
2021年 | 1181篇 |
2020年 | 1291篇 |
2019年 | 1419篇 |
2018年 | 2975篇 |
2017年 | 2753篇 |
2016年 | 3342篇 |
2015年 | 1795篇 |
2014年 | 3169篇 |
2013年 | 5833篇 |
2012年 | 3533篇 |
2011年 | 4659篇 |
2010年 | 4158篇 |
2009年 | 5401篇 |
2008年 | 4687篇 |
2007年 | 4778篇 |
2006年 | 4401篇 |
2005年 | 3330篇 |
2004年 | 3202篇 |
2003年 | 3036篇 |
2002年 | 2964篇 |
2001年 | 2589篇 |
2000年 | 2562篇 |
1999年 | 2120篇 |
1998年 | 2139篇 |
1997年 | 2027篇 |
1996年 | 1767篇 |
1995年 | 1696篇 |
1994年 | 1447篇 |
1993年 | 1387篇 |
1992年 | 1301篇 |
1991年 | 1331篇 |
1990年 | 1286篇 |
1989年 | 1135篇 |
1988年 | 1068篇 |
1987年 | 1230篇 |
1986年 | 1125篇 |
1985年 | 1354篇 |
1984年 | 1528篇 |
1983年 | 1461篇 |
1982年 | 1357篇 |
1981年 | 1264篇 |
1980年 | 1117篇 |
1979年 | 1064篇 |
1978年 | 1061篇 |
1977年 | 894篇 |
1976年 | 878篇 |
1975年 | 874篇 |
1974年 | 853篇 |
1973年 | 922篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
22.
Abstract— The Vredefort Granophyre represents impact melt that was injected downward into fractures in the floor of the Vredefort impact structure, South Africa. This unit contains inclusions of country rock that were derived from different locations within the impact structure and are predominantly composed of quartzite, feldspathic quartzite, arkose, and granitic material with minor proportions of shale and epidiorite. Two of the least recrystallized inclusions contain quartz with single or multiple sets of planar deformation features. Quartz grains in other inclusions display a vermicular texture, which is reminiscent of checkerboard feldspar. Feldspars range from large, twinned crystals in some inclusions to fine‐grained aggregates that apparently are the product of decomposition of larger primary crystals. In rare inclusions, a mafic mineral, probably biotite or amphibole, has been transformed to very fine‐grained aggregates of secondary phases that include small euhedral crystals of Fe‐rich spinel. These data indicate that inclusions within the Vredefort Granophyre were exposed to shock pressures ranging from <5 to 8–30 GPa. Many of these inclusions contain small, rounded melt pockets composed of a groundmass of devitrified or metamorphosed glass containing microlites of a variety of minerals, including K‐feldspar, quartz, augite, low‐Ca pyroxene, and magnetite. The composition of this devitrified glass varies from inclusion to inclusion, but is generally consistent with a mixture of quartz and feldspar with minor proportions of mafic minerals. In the case of granitoid inclusions, melt pockets commonly occur at the boundaries between feldspar and quartz grains. In metasedimentary inclusions, some of these melt pockets contain remnants of partially melted feldspar grains. These melt pockets may have formed by eutectic melting caused by inclusion of these fragments in the hot (650 to 1610 °C) impact melt that crystallized to form the Vredefort Granophyre. 相似文献
23.
24.
25.
The surface digital photometry for NGC 5253 and NGC 2915 is given. The luminosity profiles and colour gradients are discussed and compared. It is concluded that NGC 2915 differs from NGC 5253, both in the extension and intensity of the star burst event because of the kinematical behaviour of the captured gas.CONICET, Buenos Aires, Visiting Astronomer, Cerro Tololo Inter-American Observatory, La Serena, Chile, operated by NSF 相似文献
26.
J. C. Eichelberger 《Bulletin of Volcanology》1989,51(1):72-75
This work was sponsored at Sandia National Laboratories (contract DE-AC04-76DP00789) by the US Department of Energy, Office of Basic Energy Sciences, as part of the Continental Scientific Drilling Program 相似文献
27.
Measurement of variations in the radial velocities of stars due to the reflex orbital motion of the star around the planetary-system barycenter constitutes a powerful method of searching for substellar or planetary mass companions. After several years of patient data acquisition, radial-velocity searches for planetary systems around other stars are now beginning to bear fruit. In late 1995 and early 1996, three candidate systems were announced with Jovian-mass planets around solar-type stars. The current paradigm for low-mass star formation suggests that planetary systems should be able to form in the circumstellar disks surrounding young stellar objects. These newly discovered systems, and other discoveries which will soon follow them, will test critically our understanding of the processes of star- and planet-formation. We review the techniques used in these radial-velocity searches and their results to date. We then discuss planned improvements in the surveys, and the prospects for the next 20 years. 相似文献
28.
H. A. Harutyunian 《Astrophysics》1996,39(4):370-374
The Voigt function and its derivatives are represented by means of series in Hermite polynomials. The equations obtained can be used both for numerical calculations of these functions and for analytical research.Translated from Astrofizika, Vol. 39, No. 4, pp. 619–625, October–December, 1996. 相似文献
29.
AN ILLUSTRATIVE STUDY ON LOCAL LANDSCAPEAND ITS LONG-TERM CHANGES BASED ON IKONOS AND HISTORICAL AERIAL PHOTO 总被引:2,自引:0,他引:2
RUANRen-zong ErieCELLISt 《中国地理科学(英文版)》2004,14(2):162-169
Nowadays, the research works on landscape at fine scales using high-resolution images are uncommon.This research is based on the analysis of the combination of remote sensing data (1KONOS imagery acquired in 2002 and historical aerial photo taken in 1942). In the paper, the ecotopes in Qiujiadou and Xishao villages in Yixing City of Jiangsu Province in 1942 and 2002 were compared and landscape changes as well as the causes of the considerable changes were analyzed. It was found that the ecotope changes were at greater level in some aspects such as water surface and perennial vegetation coverage etc. This study at fine scale is globally significant for the rural areas, especially for the subsistence agricultural land, which occupies larger percentage in the earth. And it analyzes the structure of landscape based on a new landscape classification system--stratifications method. 相似文献
30.