全文获取类型
收费全文 | 659篇 |
免费 | 62篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 23篇 |
大气科学 | 58篇 |
地球物理 | 244篇 |
地质学 | 239篇 |
海洋学 | 12篇 |
天文学 | 97篇 |
综合类 | 9篇 |
自然地理 | 42篇 |
出版年
2024年 | 2篇 |
2023年 | 3篇 |
2022年 | 6篇 |
2021年 | 10篇 |
2020年 | 13篇 |
2019年 | 12篇 |
2018年 | 51篇 |
2017年 | 43篇 |
2016年 | 62篇 |
2015年 | 46篇 |
2014年 | 54篇 |
2013年 | 59篇 |
2012年 | 34篇 |
2011年 | 30篇 |
2010年 | 34篇 |
2009年 | 27篇 |
2008年 | 25篇 |
2007年 | 28篇 |
2006年 | 21篇 |
2005年 | 14篇 |
2004年 | 9篇 |
2003年 | 12篇 |
2002年 | 11篇 |
2001年 | 8篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1998年 | 10篇 |
1997年 | 3篇 |
1996年 | 9篇 |
1995年 | 9篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1991年 | 8篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1915年 | 1篇 |
排序方式: 共有724条查询结果,搜索用时 15 毫秒
51.
52.
53.
Tourist farms in Lower Silesia, Poland 总被引:1,自引:0,他引:1
Stanisław Grykień 《GeoJournal》1998,46(3):279-281
In view of the small size of most Polish farms, attempts have been made to encourage diversification into rural tourism. The
paper examines the progress made in Lower Silesia which has good resources for domestic and international tourism. Thanks
to the promotional work of the Agricultural Consultative Centres over a hundred farms are now providing services. They do
not generate a large share of the farm income but business is expanding and some areas are becoming very popular. Thus a base
has been established for future expansion. Further development depends on easier access to credit and government support for
ecological agriculture. Better promotion is also needed to increase interest in rural tourism in Poland and attract more visitors
from abroad.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
54.
Gerhard Bart Mohammed Ikramuddin Michael E. Lipschutz 《Geochimica et cosmochimica acta》1980,44(5):719-730
We report data for Ag, Bi, Cd, Co, Cs, Ga, In, Se, Te, Tl and Zn determined by neutron activation in Allende samples heated for one week at 100° increments in the 1000–1400°C range in a low pressure (initially 10?5atmH2) environment using an apparatus of novel design. In the extremes, concentrations of these trace elements—initially present at ppm-ppb levels—in unheated material are lowered even farther by factors of 10?4–10?5 over a broad temperature span. Loss of some elements above 1000°C extends trends evident below 1000°C; loss of others is even more extreme. On Arrhenius diagrams some elements exhibit but one apparent activation energy over the entire temperature span of loss while others exhibit 2 or 3, each operative in a particular temperature region. These discontinuities seem related to mineralogic/petrologic alteration and probably reflect differences in diffusion mechanism rather than siting differences. The extension of previous experiments into the temperature regime postulated for chondritic differentiation should lead to a better understanding of the evolution of meteoritic parent bodies. 相似文献
55.
Instrumental neutron activation analysis was used for the determination of more than 20 trace and minor elements in water and silt samples (suspended load) of the river Aare. The samples were collected at four different locations along the river between its source and the lake of Bienne. The principal results are: 1. The concentrations of all elements investigated are much lower than WHO-limits for drinking water. 2. Human activities are responsible for an increase of some elements along the river. 3. The concentrations of dissolved trace elements are generally anticorrelated with the water flow rate. 4. The concentrations of the trace elements in particulates (in μg/l) are correlated with the flow rate of water. Except for Ca?Sr there are no significant interelement correlations for all four sampling stations. 相似文献
56.
Invasion of mud filtrate from the borehole into the surrounding formation can significantly alter the response of logging tools.In this paper the neutron tool response was calculated for a gas-bearing rock crossed by the borehole.The invaded zone is characterized by variable fluid and gas saturation and is defined by a specific hyperbolic function. The saturation function is based on the characteristics of Polish Carpathian Foredeep Miocene formations reached in gas-bearing rocks. The whole system including neutron tool equipped with Am-Be neutron source and a set of neutron detectors, borehole, invaded zone, and virgin zone, was numerically modeled and used as the input to the Monte-Carlo neutron transport code. The response of each detector was calculated for different combinations of porosity and saturation of invaded zone and virgin zone. 相似文献
57.
M. Ćwiok W. Dominik K. Małek L. Mankiewicz J. Mrowca-Ciułacz K. Nawrocki L. W. Piotrowski P. Sitek M. Sokołowski G. Wrochna A. F. Żarnecki 《Astrophysics and Space Science》2007,309(1-4):531-535
Experiment “Pi of the Sky” is designed to search for prompt optical emission from GRB sources. 32 CCD cameras covering 2 steradians will monitor the sky continuously. The data will be analysed on-line in search for optical flashes. The prototype with 2 cameras operated at Las Campanas (Chile) since 2004 has recognised several outbursts of flaring stars and has given limits for a few GRB. 相似文献
58.
59.
60.
We present the application of novel diagnostics to the spectroscopic observation of a Coronal Mass Ejection (CME) on disk by the Extreme Ultraviolet Imaging Spectrometer (EIS) on the Hinode spacecraft. We apply a recently developed line profile asymmetry analysis to the spectroscopic observation of NOAA AR 10930 on 14?–?15 December 2006 to three raster observations before and during the eruption of a 1000 km?s?1 halo CME. We see the impact that the observer’s line-of-sight and magnetic field geometry have on the diagnostics used. Further, and more importantly, we identify the on-disk signature of a high-speed outflow behind the CME in the dimming region arising as a result of the eruption. Supported by recent coronal observations of the STEREO spacecraft, we speculate about the momentum flux resulting from this outflow as a secondary momentum source to the CME. The results presented highlight the importance of spectroscopic measurements in relation to CME kinematics, and the need for full-disk synoptic spectroscopic observations of the coronal and chromospheric plasmas to capture the signature of such explosive energy release as a way of providing better constraints of CME propagation times to L1, or any other point of interest in the heliosphere. 相似文献