全文获取类型
收费全文 | 3621篇 |
免费 | 731篇 |
国内免费 | 880篇 |
专业分类
测绘学 | 967篇 |
大气科学 | 717篇 |
地球物理 | 876篇 |
地质学 | 1387篇 |
海洋学 | 550篇 |
天文学 | 42篇 |
综合类 | 353篇 |
自然地理 | 340篇 |
出版年
2024年 | 27篇 |
2023年 | 93篇 |
2022年 | 142篇 |
2021年 | 182篇 |
2020年 | 207篇 |
2019年 | 229篇 |
2018年 | 151篇 |
2017年 | 207篇 |
2016年 | 211篇 |
2015年 | 216篇 |
2014年 | 288篇 |
2013年 | 267篇 |
2012年 | 276篇 |
2011年 | 267篇 |
2010年 | 205篇 |
2009年 | 225篇 |
2008年 | 233篇 |
2007年 | 283篇 |
2006年 | 210篇 |
2005年 | 176篇 |
2004年 | 168篇 |
2003年 | 145篇 |
2002年 | 109篇 |
2001年 | 99篇 |
2000年 | 86篇 |
1999年 | 67篇 |
1998年 | 89篇 |
1997年 | 62篇 |
1996年 | 56篇 |
1995年 | 34篇 |
1994年 | 41篇 |
1993年 | 52篇 |
1992年 | 26篇 |
1991年 | 23篇 |
1990年 | 26篇 |
1989年 | 18篇 |
1988年 | 17篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有5232条查询结果,搜索用时 15 毫秒
41.
电子地图在走向产业化、实用化的过程中,人们越来越感到电子地图的显示所产生的问题不能被忽视。目前,对电子地图显示缺少系统的研究,特别是从理论、技术和实际应用层面相结合的研究还比较少见。因此,在分析基础电子地图显示存在问题的基础上,以地图制图理论为指导,研究了基础电子地图的显示特点,提出了基础电子地图显示研究的理论框架,并针对基础电子地图自适应变焦显示、可视化表达以及显示风格转换系统的研制等关键问题进行了探讨和实践。 相似文献
42.
43.
Xin Li Dongliang Wang Baoquan Liu Chunling Ren Jianying Guo Xuefeng Su Jian Wang 《中国地球化学学报》2008,27(4):412-419
The northern margin of the Qaidam Basin is one of the main oil-gas exploration areas in western China, where source rocks are composed mostly of Middle and Lower Jurassic dark mud shale, carbargillite and coal. A large number of subsurface and outcrop samples differing in lithology with different types of organic matter were selected for resource evaluation, research and calculation. And among them, 13 samples were used for simulation experiment on hydrocarbon generating potential of various source rocks. At first, two kinds of heating modes were compared through simulation experiment, including single temperature-step heating and continual heating. Perhaps, the process of hydrocarbon generation and expulsion occurred naturally between a close system and an open system. In addition, the first heating mode was convenient, and all its reaction products were involved in the whole thermal evolution, and the final simulation experimental results were basically in consistency with the natural evolution trend Therefore, the first heating mode was adopted and the hydrocarbon yield of every sample was worked out. According to the type and lithology of organic matter and the hydrocarbon yield of samples for simulation experiment, hydrocarbon generation and expulsion mode with three kinds of lithology and five types of source rock has been established to provide the basis for hydrocarbon generation evaluation, research and resource calculation. 相似文献
44.
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
45.
46.
47.
48.
49.
50.
GIS正在从传统意义上的地理信息系统向地理信息服务偏移,地理信息服务已成为信息服务业中重要组成部分之一.文中归纳总结了地理信息服务概念、技术体系、服务模式以及我国地理信息服务发展的差距、对策与建议. 相似文献