全文获取类型
收费全文 | 13113篇 |
免费 | 509篇 |
国内免费 | 172篇 |
专业分类
测绘学 | 260篇 |
大气科学 | 1091篇 |
地球物理 | 3168篇 |
地质学 | 4565篇 |
海洋学 | 1232篇 |
天文学 | 1912篇 |
综合类 | 54篇 |
自然地理 | 1512篇 |
出版年
2022年 | 54篇 |
2021年 | 173篇 |
2020年 | 211篇 |
2019年 | 221篇 |
2018年 | 285篇 |
2017年 | 270篇 |
2016年 | 363篇 |
2015年 | 321篇 |
2014年 | 380篇 |
2013年 | 690篇 |
2012年 | 427篇 |
2011年 | 627篇 |
2010年 | 535篇 |
2009年 | 702篇 |
2008年 | 597篇 |
2007年 | 590篇 |
2006年 | 532篇 |
2005年 | 458篇 |
2004年 | 436篇 |
2003年 | 434篇 |
2002年 | 380篇 |
2001年 | 268篇 |
2000年 | 310篇 |
1999年 | 243篇 |
1998年 | 228篇 |
1997年 | 194篇 |
1996年 | 203篇 |
1995年 | 211篇 |
1994年 | 201篇 |
1993年 | 161篇 |
1992年 | 160篇 |
1991年 | 116篇 |
1990年 | 162篇 |
1989年 | 137篇 |
1988年 | 143篇 |
1987年 | 153篇 |
1986年 | 141篇 |
1985年 | 178篇 |
1984年 | 215篇 |
1983年 | 192篇 |
1982年 | 173篇 |
1981年 | 130篇 |
1980年 | 124篇 |
1979年 | 122篇 |
1978年 | 119篇 |
1977年 | 99篇 |
1976年 | 109篇 |
1975年 | 117篇 |
1974年 | 94篇 |
1973年 | 115篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
James Binney 《Journal of Astrophysics and Astronomy》1996,17(3-4):81-93
52.
This paper considers the problem of estimatingm, the number of components in a finite mixture of distributions from a parametric family. A step-up procedure using the bootstrap method is proposed. Some properties of the procedure are illustrated with simulation studies. An example of the method, applied to orientation of beach clasts, is given. 相似文献
53.
Andrew J. L. Harris Anna L. Butterworth Richard W. Carlton Ian Downey Peter Miller Pedro Navarro David A. Rothery 《Bulletin of Volcanology》1997,59(1):49-64
Satellite data offer a means of supplementing ground-based monitoring during volcanic eruptions, especially at times or locations
where ground-based monitoring is difficult. Being directly and freely available several times a day, data from the advanced
very high resolution radiometer (AVHRR) offers great potential for near real-time monitoring of all volcanoes across large
(3000×3000 km) areas. Herein we describe techniques to detect and locate activity; estimate lava area, thermal flux, effusion
rates and cumulative volume; and distinguish types of activity. Application is demonstrated using data for active lavas at
Krafla, Etna, Fogo, Cerro Negro and Erebus; a pyroclastic flow at Lascar; and open vent systems at Etna and Stromboli. Automated
near real-time analysis of AVHRR data could be achieved at existing, or cheap to install, receiving stations, offering a supplement
to conventional monitoring methods.
Received: 21 January 1997 / Accepted: 3 April 1997 相似文献
54.
We report on a year's study of spatial and seasonal patterns of zooplankton abundance in Port Phillip and Westernport Bays, July 1982 to August 1983. These two bays, closely adjacent on the southern coast of Victoria, Australia, differ in several respects: Port Phillip is a nearly landlocked bay with a broad basin, while Westernport is an open tidal embayment with extensive mud and seagrass banks. Both bays have a resident zooplankton fauna distinct from that of Bass Strait. Although these resident communities have many species in common, patterns of abundance and dominance are quite different. We found that the holoplankton of Port Phillip was about half copepods, mostly Paracalanus indicus, with 23% Caldocera and 21% larvaceans. Westernport Bay zooplankton was dominated by Acartia tranteri, with no resident cladoceran fauna. Bass Strait species were more often found in Westernport than in Port Phillip Bay, but the resident community of Port Phillip Bay was more similar to that of Bass Strait than to that of Westernport.Although this study was undertaken in an exceptionally dry year, the available historical data show that the overall patterns found in 1982–1983 are typical for these bays. The differences in community composition probably relate to differences in depth profile, predator abundance, and suspended matter between the bays. 相似文献
55.
Sunetra Giridhar N. Kameswara Rao David L. Lambert 《Journal of Astrophysics and Astronomy》1996,17(1-2):23-40
Two high resolution spectra of the hot RCrB star DY Cen in the red region are compared. The photospheric absorption lines
show a radial velocity variation of 12 kms-1 between 1989 July and 1992 May. Emission components to some CII lines present
in 1989 are almost entirely absent in 1992. Nebular forbidden lines of [OI], [NII] and [SII] appear unchanged from 1989 to
1992 相似文献
56.
57.
58.
Jeremy Allington-Smith Graham Murray Robert Content George Dodsworth Bryan W. Miller James Turner Inger Jorgensen Isobel Hook 《Experimental Astronomy》2002,13(1):1-37
We describe the integral field unit (IFU) which converts the Gemini Multiobject Spectrograph (GMOS) installed on the Gemini-North telescope to an integral field spectrograph,which produces spectra over a contiguous field of view of 7 × 5 arcsec with spatial sampling of 0.2 arcsecover the wavelength range 0.4-1.0 μm.GMOS is converted to this mode by the remote insertion of the IFU into thebeam in place of the masks used for the multiobject mode. A separate fieldof half the area of the main field, but otherwise identical, is alsoprovided to improve background subtraction. The IFU contains 1500lenslet-coupled fibres and was the first facility of any type for integralfield spectroscopy employed on an 8/10 m telescope.We describe the design, construction and testing of the GMOS IFU and present measurements of the throughput both in the laboratory and at the telescope. We compare these with a theoretical prediction made before construction started. All are in good agreement with each other, with the on-telescope throughput exceeding 60% (averaged over wavelength). Finallywe show an example of data obtained during commissioning to illustrate the power of the device. 相似文献
59.
Antony J. Long Sarah A. Woodroffe Sue Dawson David H. Roberts Charlotte L. Bryant 《第四纪科学杂志》2009,24(4):345-359
In West Greenland, early and mid Holocene relative sea level (RSL) fall was replaced by late Holocene RSL rise during the Neoglacial, after 4–3 cal. ka BP (thousand calibrated years before present). Here we present the results of an isolation basin RSL study completed near to the coastal town of Sisimiut, in central West Greenland. RSL fell from 14 m above sea level at 5.7 cal. ka BP to reach a lowstand of ?4.0 m at 2.3–1.2 cal. ka BP, before rising by an equivalent amount to present. Differences in the timing and magnitude of the RSL lowstand between this and other sites in West and South Greenland record the varied interplay of local and non‐Greenland RSL processes, notably the reloading of the Earth's crust caused by a Neoglacial expansion of the Greenland Ice Sheet (GIS) and the subsidence associated with the collapse of the Laurentide Ice Sheet forebulge. This means that the timing of the sea level lowstand cannot be used to infer directly when the GIS advanced during the Neoglacial. The rise in Late Holocene RSL is contrary to recently reported bedrock uplift in the Sisimiut area, based on repeat GPS surveys. This indicates that a belt of peripheral subsidence around the current ice sheet margin was more extensive in the late Holocene, and that there has been a switch from subsidence to uplift at some point in the last thousand years or so. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
60.