全文获取类型
收费全文 | 80636篇 |
免费 | 1134篇 |
国内免费 | 938篇 |
专业分类
测绘学 | 2000篇 |
大气科学 | 5878篇 |
地球物理 | 15025篇 |
地质学 | 31211篇 |
海洋学 | 7063篇 |
天文学 | 17233篇 |
综合类 | 317篇 |
自然地理 | 3981篇 |
出版年
2022年 | 378篇 |
2021年 | 643篇 |
2020年 | 738篇 |
2019年 | 787篇 |
2018年 | 4023篇 |
2017年 | 3737篇 |
2016年 | 3201篇 |
2015年 | 1203篇 |
2014年 | 1830篇 |
2013年 | 3410篇 |
2012年 | 2900篇 |
2011年 | 4906篇 |
2010年 | 4315篇 |
2009年 | 5156篇 |
2008年 | 4314篇 |
2007年 | 4840篇 |
2006年 | 2577篇 |
2005年 | 2305篇 |
2004年 | 2083篇 |
2003年 | 2076篇 |
2002年 | 1897篇 |
2001年 | 1522篇 |
2000年 | 1491篇 |
1999年 | 1253篇 |
1998年 | 1224篇 |
1997年 | 1207篇 |
1996年 | 1048篇 |
1995年 | 934篇 |
1994年 | 883篇 |
1993年 | 751篇 |
1992年 | 756篇 |
1991年 | 721篇 |
1990年 | 752篇 |
1989年 | 609篇 |
1988年 | 592篇 |
1987年 | 685篇 |
1986年 | 614篇 |
1985年 | 796篇 |
1984年 | 819篇 |
1983年 | 783篇 |
1982年 | 753篇 |
1981年 | 659篇 |
1980年 | 663篇 |
1979年 | 575篇 |
1978年 | 602篇 |
1977年 | 501篇 |
1976年 | 464篇 |
1975年 | 481篇 |
1974年 | 484篇 |
1973年 | 491篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
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
22.
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
23.
Summary. Four box cores collected from the Ontong—Java plateau during the Eurydice expedition have been used to make relative geomagnetic palaeo-intensity measurements. Rock magnetic measurements on the sediments show that they are characterized by a uniform magnetic mineralogy, and that they are suitable for relative intensity estimates. These are obtained by normalizing the NRM by an ARM imparted in a low DC bias field. the palaeoceanographic event known as the preservation spike is used to establish a crude time-scale for the record so that it may be compared with other data from the same region, and also with global palaeointensity estimates. the marine sediment data are quite similar to Australian intensity data from lake sediments and archaeomagnetic sources, but as might be expected exhibit some obvious differences from the global record. 相似文献
24.
Mallory S. E. Roberts Crystal L. Brogan Bryan M. Gaensler Jason W. T. Hessels C.-Y. Ng Roger W. Romani 《Astrophysics and Space Science》2005,297(1-4):93-100
A remarkable number of pulsar wind nebulae (PWN) are coincident with EGRET γ-ray sources. X-ray and radio imaging studies of unidentified EGRET sources have resulted in the discovery of at least six new pulsar wind nebulae (PWN). Stationary PWN (SPWN) appear to be
associated with steady EGRET sources with hard spectra, typical for γ-ray pulsars. Their toroidal morphologies can help determine the geometry of the
pulsar which is useful for constraining models of pulsed γ-ray emission. Rapidly moving PWN (RPWN) with more cometary morphologies
seem to be associated with variable EGRET sources in regions where the ambient medium is dense compared to what is typical for the ISM. 相似文献
25.
26.
27.
E. C. Hopewell M. J. Barlow J. E. Drew Y. C. Unruh Q. A. Parker M. J. Pierce P. A. Crowther C. Knigge S. Phillipps A. A. Zijlstra 《Monthly notices of the Royal Astronomical Society》2005,363(3):857-866
We report the discovery of five massive Wolf–Rayet (WR) stars resulting from a programme of follow-up spectroscopy of candidate emission-line stars in the Anglo-Australian Observatory United Kingdom Schmidt Telescope (AAO/UKST) Southern Galactic Plane Hα survey. The 6195–6775 Å spectra of the stars are presented and discussed. A WC9 class is assigned to all five stars through comparison of their spectra with those of known late-type WC stars, bringing the known total number of Galactic WC9 stars to 44. Whilst three of the five WC9 stars exhibit near-infrared (NIR) excesses characteristic of hot dust emission (as seen in the great majority of known WC9 stars), we find that two of the stars show no discernible evidence of such excesses. This increases the number of known WC9 stars without NIR excesses to seven. Reddenings and distances for all five stars are estimated. 相似文献
28.
29.
30.
B. A. Ivanov 《Solar System Research》2005,39(5):381-409
Multi-ring impact basins have been found on the surfaces of almost all planetary bodies in the Solar system with solid crusts. The details of their formation mechanism are still unclear. We present results of our numerical modeling of the formation of the largest known terrestrial impact craters. The geological and geophysical data on these structures accumulated over many decades are used to place constraints on the parameters of available numerical models with a dual purpose: (i) to choose parameters in available mechanical models for the crustal response of planetary bodies to a large impact and (ii) to use numerical modeling to refine the possible range of original diameters and the morphology of partially eroded terrestrial craters. We present numerical modeling results for the Vredefort, Sudbury, Chicxulub, and Popigai impact craters and compare these results with available geological and geophysical information. 相似文献