全文获取类型
收费全文 | 79930篇 |
免费 | 4501篇 |
国内免费 | 5397篇 |
专业分类
测绘学 | 2545篇 |
大气科学 | 8765篇 |
地球物理 | 16314篇 |
地质学 | 33557篇 |
海洋学 | 7218篇 |
天文学 | 13215篇 |
综合类 | 2664篇 |
自然地理 | 5550篇 |
出版年
2023年 | 350篇 |
2022年 | 958篇 |
2021年 | 1193篇 |
2020年 | 1096篇 |
2019年 | 1211篇 |
2018年 | 4748篇 |
2017年 | 4483篇 |
2016年 | 3666篇 |
2015年 | 1656篇 |
2014年 | 2069篇 |
2013年 | 3071篇 |
2012年 | 3243篇 |
2011年 | 5334篇 |
2010年 | 4903篇 |
2009年 | 5484篇 |
2008年 | 4573篇 |
2007年 | 5132篇 |
2006年 | 2193篇 |
2005年 | 2603篇 |
2004年 | 2129篇 |
2003年 | 2201篇 |
2002年 | 1921篇 |
2001年 | 1563篇 |
2000年 | 1671篇 |
1999年 | 1915篇 |
1998年 | 1631篇 |
1997年 | 1708篇 |
1996年 | 1524篇 |
1995年 | 1320篇 |
1994年 | 1117篇 |
1993年 | 1016篇 |
1992年 | 897篇 |
1991年 | 761篇 |
1990年 | 701篇 |
1989年 | 591篇 |
1988年 | 572篇 |
1987年 | 570篇 |
1986年 | 536篇 |
1985年 | 588篇 |
1984年 | 630篇 |
1983年 | 597篇 |
1982年 | 555篇 |
1981年 | 501篇 |
1980年 | 486篇 |
1979年 | 423篇 |
1978年 | 427篇 |
1977年 | 368篇 |
1975年 | 349篇 |
1974年 | 340篇 |
1973年 | 341篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
利用“地震预报计算机专家系统”的思想对大同 -阳高 Ms6 .1地震前每一前兆异常事件进行综合评估 ,以每一异常的最可能发震时间来计算发震概率 ,利用地震前兆综合加权信息熵研究了系统熵值与地震的关系。对华北地区的地震前兆综合加权信息熵研究表明 ,在大同 -阳高 Ms6 .1地震前 ,信息熵出现了明显的减熵有序变化 相似文献
22.
23.
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
24.
本文针对低纬度地区频率域化磁极存在的问题,在频谱分析的基础上,提出了一种新的滤波方法即振幅滤波法。该方法能将低纬度地区化极磁场的频谱恢复到垂直磁化磁场的频谱,大大提高了低纬度地区化磁极的精度。 相似文献
25.
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
26.
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
27.
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
28.
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
29.