全文获取类型
收费全文 | 5618篇 |
免费 | 699篇 |
国内免费 | 724篇 |
专业分类
测绘学 | 1726篇 |
大气科学 | 391篇 |
地球物理 | 1209篇 |
地质学 | 2208篇 |
海洋学 | 347篇 |
天文学 | 51篇 |
综合类 | 369篇 |
自然地理 | 740篇 |
出版年
2024年 | 10篇 |
2023年 | 38篇 |
2022年 | 139篇 |
2021年 | 151篇 |
2020年 | 221篇 |
2019年 | 236篇 |
2018年 | 126篇 |
2017年 | 318篇 |
2016年 | 318篇 |
2015年 | 293篇 |
2014年 | 361篇 |
2013年 | 436篇 |
2012年 | 335篇 |
2011年 | 381篇 |
2010年 | 252篇 |
2009年 | 318篇 |
2008年 | 399篇 |
2007年 | 347篇 |
2006年 | 326篇 |
2005年 | 281篇 |
2004年 | 221篇 |
2003年 | 184篇 |
2002年 | 179篇 |
2001年 | 168篇 |
2000年 | 123篇 |
1999年 | 105篇 |
1998年 | 124篇 |
1997年 | 94篇 |
1996年 | 77篇 |
1995年 | 66篇 |
1994年 | 59篇 |
1993年 | 52篇 |
1992年 | 43篇 |
1991年 | 37篇 |
1990年 | 35篇 |
1989年 | 27篇 |
1988年 | 24篇 |
1987年 | 22篇 |
1986年 | 21篇 |
1985年 | 18篇 |
1984年 | 19篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1973年 | 5篇 |
1972年 | 4篇 |
1971年 | 3篇 |
排序方式: 共有7041条查询结果,搜索用时 15 毫秒
1.
中国1∶100万景观生态制图设计 总被引:5,自引:0,他引:5
中国1∶100万景观生态图系借鉴国内外传统景观制图方法和制图规范,在遥感、地理信息系统先进技术的支持下,设计研制其制图方法、制图内容、样图和技术流程,同时提出初步的景观分类系统,为今后编制中国1∶100万景观生态图奠定基础。 相似文献
2.
A formula for the thickness of a shear band formed in saturated soils under a simple shear or a combined stress state has been proposed. It is shown that the shear band thickness is dependent on the pore pressure properties of the material and the dilatancy rate, but is independent of the details of the combined stress state. This is in accordance with some separate experimental observations. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
3.
This paper describes a wide-field survey made at 34.5 MHz using GEETEE,1 the low frequency telescope at Gauribidanur (latitude
13°36′12′′N). This telescope was used in the transit mode and by per forming 1-D synthesis along the north-south direction
the entire observable sky was mapped in a single day. This minimized the problems that hinder wide-field low-frequency mapping.
This survey covers the declination range of-50° to + 70° (- 33° to +61° without aliasing) and the complete 24 hours of right
ascension. The synthesized beam has a resolution of 26′ x 42′ sec (δ- 14°. 1). The sensitivity of the survey is 5 Jy/beam (1σ). Special care has been taken to ensure that the antenna responds
to all angular scale structures and is suitable for studies of both point sources and extended objects
This telescope is jointly operated by the Indian Institute of Astrophysics, Bangalore and the Roman Research Institute, Bangalore. 相似文献
4.
The SAS® computer software system, widely used and respected for its capabilities in statistical analysis and data base management, now includes a new set of graphic and cartographic procedures called SAS GRAPH?. We have used these cartographic procedures in research on mapping ethno-cultural census data from metropolitan areas in Ontario and in undergraduate and graduate courses in computer cartography. On the basis of that experience, we describe and evaluate SAS/GRAPH'S cartographic capabilities and illustrate with maps drawn by various devices. 相似文献
5.
Non-Newtonian topographic relaxation on Europa 总被引:1,自引:0,他引:1
Models of topographic support on Europa by lateral shell thickness variations have previously assumed a Newtonian ice viscosity. Here I show that using a more realistic stress-dependent viscosity gives relaxation times which can be significantly different. Topography of wavelength 100 km cannot be supported by lateral shell thickness variations for ∼50 Myr, unless the shell thickness is <10 km or the ice grain size >10 mm. Shorter wavelength topography would require even thinner shells, but may be supported elastically. Global-scale variations in shell thickness, however, can be supported for geological timescales if the shell thickness is O(10 km). 相似文献
6.
In order to understand the process of surface erosion and acquire basic data of conditions on hillslope without vege tation, a sprinkling experiment is conducted on a bare slope in Mt. Tanakami in the central part of Japan. Based on the mea surements of runoff, mean soil erosion depth, and sediment yield, etc. , the results suggest the following characteristics in the process of surface erosion in the experimental area. (1) The occurrence of sediment discharge is interrupted; (2) Surface runoff is a saturated overland flow; (3) The mean soil erosion depth is thick compared with other areas in Mt. Tanakami;(4) Sediment discharge process is detachment- limited. 相似文献
7.
Anastassios E. Petropoulos James M. Longuski 《Celestial Mechanics and Dynamical Astronomy》1994,60(4):431-454
An exact analysis of the coverage obtained by spacecraft using cross-track scanning and nadir-centered conical imaging, under imposed viewing obliqueness and resolution requirements, is presented. In addition to exact expressions for the area acquired and the area acquisition rate, envelope theory is introduced to obtain the boundary of the imaged area. These expressions are relatively compact, allowing rapid machine computation. The effects of the sun phase angle, and of imaging system limitations are also examined. The Galileo mission encounter with Callisto is used as a numerical example, from which certain general conclusions are drawn regarding optimal imaging trajectories. 相似文献
8.
吴泽忠 《成都信息工程学院学报》2004,19(2):258-262
在序线性拓扑空间里研究了含有集约束向量极值问题的最优性条件,并建立了充分性和必要性条件. 相似文献
9.
10.
Wang Yanhui 《水文研究》1992,6(2):241-251
Black locust (Robina pseudoacacia) has become one of the most important shelter species in the loess area of northwest China. This paper summarizes recent research concerning its hydrological influence, including canopy interception, litter absorption capacity, its effect on rainfall kinetic energy, infiltration rates, surface runoff, soil moisture, and evapotranspiration, and its role in soil conservation. Several predictive models are listed. on the basis of existing results, optimum characteristics for an effective plantation are defined, and problems requiring further research are identified. 相似文献