全文获取类型
收费全文 | 2773篇 |
免费 | 471篇 |
国内免费 | 478篇 |
专业分类
测绘学 | 773篇 |
大气科学 | 484篇 |
地球物理 | 748篇 |
地质学 | 837篇 |
海洋学 | 434篇 |
天文学 | 136篇 |
综合类 | 201篇 |
自然地理 | 109篇 |
出版年
2024年 | 15篇 |
2023年 | 47篇 |
2022年 | 94篇 |
2021年 | 97篇 |
2020年 | 125篇 |
2019年 | 149篇 |
2018年 | 89篇 |
2017年 | 143篇 |
2016年 | 121篇 |
2015年 | 145篇 |
2014年 | 165篇 |
2013年 | 174篇 |
2012年 | 172篇 |
2011年 | 154篇 |
2010年 | 135篇 |
2009年 | 167篇 |
2008年 | 160篇 |
2007年 | 195篇 |
2006年 | 158篇 |
2005年 | 164篇 |
2004年 | 133篇 |
2003年 | 106篇 |
2002年 | 88篇 |
2001年 | 78篇 |
2000年 | 79篇 |
1999年 | 62篇 |
1998年 | 70篇 |
1997年 | 60篇 |
1996年 | 58篇 |
1995年 | 44篇 |
1994年 | 53篇 |
1993年 | 50篇 |
1992年 | 30篇 |
1991年 | 25篇 |
1990年 | 35篇 |
1989年 | 18篇 |
1988年 | 23篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有3722条查询结果,搜索用时 203 毫秒
31.
32.
33.
34.
35.
The ionospheric eclipse factor method (IEFM) and its application to determining the ionospheric delay for GPS 总被引:4,自引:1,他引:3
A new method for modeling the ionospheric delay using global positioning system (GPS) data is proposed, called the ionospheric
eclipse factor method (IEFM). It is based on establishing a concept referred to as the ionospheric eclipse factor (IEF) λ
of the ionospheric pierce point (IPP) and the IEF’s influence factor (IFF) . The IEF can be used to make a relatively precise distinction between ionospheric daytime and nighttime, whereas the IFF
is advantageous for describing the IEF’s variations with day, month, season and year, associated with seasonal variations
of total electron content (TEC) of the ionosphere. By combining λ and with the local time t of IPP, the IEFM has the ability to precisely distinguish between ionospheric daytime and nighttime, as well as efficiently
combine them during different seasons or months over a year at the IPP. The IEFM-based ionospheric delay estimates are validated
by combining an absolute positioning mode with several ionospheric delay correction models or algorithms, using GPS data at
an international Global Navigation Satellite System (GNSS) service (IGS) station (WTZR). Our results indicate that the IEFM
may further improve ionospheric delay modeling using GPS data. 相似文献
36.
37.
38.
An important task in modern geostatistics is the assessment and quantification of resource and reserve uncertainty. This uncertainty
is valuable support information for many management decisions. Uncertainty at specific locations and uncertainty in the global
resource is of interest. There are many different methods to build models of uncertainty, including Kriging, Cokriging, and
Inverse Distance. Each method leads to different results. A method is proposed to combine local uncertainties predicted by
different models to obtain a combined measure of uncertainty that combines good features of each alternative. The new estimator
is the overlap of alternate conditional distributions. 相似文献
39.
以国家重大产业技术开发专项“西部煤炭资源高精度三维地震勘探技术”项目的由来、意义和总体研究目标为引,概括的介绍了项目依托工程中各个专项技术研究完成情况,并对非均匀介质成像技术、高精度三维地震静校正技术、高密度采集技术、特观技术、岩性反演技术、属性体解释技术等六项重大关键技术取得的突破性进展进行了重点说明。指出随着我国煤炭生产重点的逐步西移,应加强诸如叠前、叠后深度偏移技术的研究,以解决复杂山区三维地震面元内地震反射波散射问题,提高其三维地震勘探精度,为西部煤炭工业做出新贡献! 相似文献
40.
R. M. Kippen J. Ryan A. Connors M. McConnell C. Winkler L. O. Hanlon V. Schönfelder J. Greiner M. Varendorff W. Collmar W. Hermsen L. Kuiper 《Astrophysics and Space Science》1995,231(1-2):231-234
In its first three years of operation, the COMPTEL instrument on theCompton Gamma-Ray Observatory has measured the locations (mean accuracy 1°) and spectra (0.75-30 MeV) of 18 gamma-ray bursts and continues to observe new events at a rate of 1/month. With good angular resolution and sensitivity at MeV energies, the growing COMPTEL burst catalog is an important new piece of evidence in the on-going GRB mystery. The COMPTEL burst locations are consistent with an isotropic distribution of sources, yet the spatial coincidence of two of the bursts indicates the possibility of repetition. The COMPTEL burst spectra are in most cases consistent with a single power law model with spectral index in the range 2–3. However, two bursts show evidence of a spectral break in the MeV range. Measurement of rapid variability at MeV energies in the stronger bursts provides evidence that either the sources are nearby (within the Galaxy) or the gamma-ray emission is relativistically beamed. We present an overview of analysis results obtained from the COMPTEL burst catalog concentrating on the search for burst repetition and the implications of highly variable MeV emission. 相似文献