全文获取类型
收费全文 | 84855篇 |
免费 | 769篇 |
国内免费 | 1383篇 |
专业分类
测绘学 | 2601篇 |
大气科学 | 5571篇 |
地球物理 | 16273篇 |
地质学 | 34107篇 |
海洋学 | 6472篇 |
天文学 | 15649篇 |
综合类 | 2340篇 |
自然地理 | 3994篇 |
出版年
2022年 | 592篇 |
2021年 | 860篇 |
2020年 | 958篇 |
2019年 | 1036篇 |
2018年 | 6693篇 |
2017年 | 5804篇 |
2016年 | 4695篇 |
2015年 | 1295篇 |
2014年 | 2110篇 |
2013年 | 3233篇 |
2012年 | 3287篇 |
2011年 | 5396篇 |
2010年 | 4549篇 |
2009年 | 5289篇 |
2008年 | 4506篇 |
2007年 | 5205篇 |
2006年 | 2668篇 |
2005年 | 1875篇 |
2004年 | 1987篇 |
2003年 | 1917篇 |
2002年 | 1653篇 |
2001年 | 1436篇 |
2000年 | 1272篇 |
1999年 | 966篇 |
1998年 | 992篇 |
1997年 | 1008篇 |
1996年 | 757篇 |
1995年 | 751篇 |
1994年 | 687篇 |
1993年 | 595篇 |
1992年 | 577篇 |
1991年 | 559篇 |
1990年 | 611篇 |
1989年 | 533篇 |
1988年 | 483篇 |
1987年 | 565篇 |
1986年 | 434篇 |
1985年 | 635篇 |
1984年 | 674篇 |
1983年 | 643篇 |
1982年 | 597篇 |
1981年 | 570篇 |
1980年 | 564篇 |
1979年 | 473篇 |
1978年 | 544篇 |
1977年 | 453篇 |
1976年 | 426篇 |
1975年 | 443篇 |
1974年 | 396篇 |
1973年 | 426篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
271.
Summary This paper concerns the use of airborne or ground-based Doppler radars to observe precipitating systems over complex orography.
As nearly all of the previous experiments involving Doppler radars were conducted over flat surfaces over the continents or
the oceans, new techniques are needed firstly to separate ground clutter from meteorological signal and, in the case of airborne
Doppler observations, to deduce navigational errors. Secondly, it is necessary to take the atmospheric circulation induced
by orography into account in the three-dimensional wind field analysis. Variational techniques are presented to solve these
problems.
The proposed methods are tested with simulated ground-based and airborne Doppler radar observations for analytic flows over
analytic terrains and for numerically simulated wind and reflectivity fields for the Brig event (22 September 1993) of heavy
precipitation over the southern flank of the Alps (Cosma and Richard, 1998), and with actual airborne Doppler data relative
to weak snow showers over the Rocky Mountains on 12 March 1995.
Received March 22, 1999/Revised June 1, 1999 相似文献
272.
273.
Natural Hazards - The article was published with the citation “Worni et al. (2012)”. The author group of the article would like readers to know that this information should instead... 相似文献
274.
This paper presents an integrated measurement technique based on DC methods (vertical electrical sounding, electrical resistivity tomography) which was used to identify faults and determine their geoelectric parameters in the western part of the Chuya basin. New information on the structure of the Chagan River valley located in the zone of the disastrous 27 September 2003 Chuya earthquake has been obtained from the results of these methods. Geoelectric cross-sections of the sedimentary sequence and the upper part of the basement were obtained from VES data, showing the block structure of the study area. Electrical resistivity tomography sections confirm the presence of a major fault between basement blocks of different heights and indicate the presence of faults bounding the valley on its right side and in the southwestern part. 相似文献
275.
An ecotoxicological assessment is given to the state of small lakes in specially protected natural areas in Northwestern and Central European Russia, which suffer from aerotechnogenic acidification. The toxicity of water and bottom sediments is shown to increase with decreasing water pH. The most sensitive characteristics of aquatic organisms in different trophic groups are chosen, allowing the state of lakes to be monitored. 相似文献
276.
A. V. Mityukov A. M. Nikishin O. A. Almendinger S. N. Bolotov V. A. Lavrishchev N. K. Myasoedov E. V. Rubtsova 《Moscow University Geology Bulletin》2012,67(2):81-92
This work is based on the results of 2-D and 3-D surveys in the Tuapse Basin and field works in the Crimea-Caucasus region. Seven zones were outlined in the model of sedimentation starting from the eroded mountain structure of the Greater Caucasus down to deep water sediments of the Tuapse Basin. The slope and deep-water sediments of channels and fan complexes are characterized. Volume models of the sedimentation system in the Black Sea are shown for the first time. 相似文献
277.
Identification of the “source” and “sink” patterns influencing non-point source pollution in the Three Gorges Reservoir Area 总被引:6,自引:0,他引:6
Non-point source pollution is one of the primarily ecological issues affecting the Three Gorges Reservoir Area. In this paper, landscape resistance and motivation coefficient, which integrated various landscape elements, such as land use, soil, hydrology, topography, and vegetation, was established based on the effects of large-scale resistance and motivation on the formation of non-point source pollution. In addition, cost models of the landscape resistance and motivation coefficients were constructed based on the distances from the landscape units to the sub-basin outlets in order to identify the “source” and “sink” patterns affecting the formation of non-point source pollution. The results indicated that the changes in the landscape resistance and motivation coefficients of the 16 sub-basins exhibited inverse relationships to their spatial distributions. The landscape resistance and motivation cost curves were more volatile than the landscape resistance and motivation coefficient curves. The landscape resistance and motivation cost trends of the 16 sub-basins became increasingly apparent along the flow of the Yangtze River. The landscape resistance and motivation cost models proposed in this paper could be used to identify large-scale non-point source pollution “source” and “sink” patterns. Moreover, the proposed model could be used to describe the large-scale spatial characteristics of non-point source pollution formation based on “source” and “sink” landscape pattern indices, spatial localization, and landscape resistance and motivation coefficients. 相似文献
278.
279.
Marina Hruška William Corea Donald Seeburger William Schweller William H. Crane 《Mathematical Geosciences》2009,41(6):703-716
We describe a wavelet-transform-based method for automated segmentation of resistivity image logs that takes into account
the apparent dip in the data and addresses the problem of discriminating lithofacies boundaries from noise and intrafacies
variations. Our method can be applied to borehole measurements in general, but might have an advantage when applied to resistivity
image logs as it addresses explicitly the large variability in facies segments recorded with a high-resolution multiple-sensor
tool. We have developed an algorithm based on this method that might outperform other existing segmentation methods in the
cases of low to moderate dip. We made a detailed comparison of the segmentation from our method with the one done by a geologist
to delineate different lithofacies blocks in a well drilled in a deepwater depositional environment. Our results show considerable
success rates in reproducing the geologically defined lithofacies boundaries, and the generality of our procedure suggests
it could also be applied to other depositional environments. 相似文献
280.
Geocentre motion from the DORIS space system and laser data to the Lageos satellites: comparison with surface loading data 总被引:3,自引:0,他引:3
F. Bouillé A. Cazenave J. M. Lemoine J. F. Crétaux 《Geophysical Journal International》2000,143(1):71-82
Surface mass redistribution within the Earth system, especially in the atmosphere, oceans, continents and ice sheets, causes the position of the centre of mass to vary in a reference frame attached to the solid Earth. Space techniques are now precise enough to measure the centre of mass motion. Here we present a determination of the centre of mass coordinates at regular monthly intervals using DORIS data on SPOT‐2, SPOT‐3 and Topex–Poseidon (1993–1997) and laser data on Lageos‐1 and Lageos‐2 (1993–1996). The amplitude and phase of the space‐geodesy‐derived annual cycle for each coordinate are further compared to estimates based on surface mass redistribution at the Earth surface derived from various climatic data sources: surface pressure, soil moisture, snow depth and ocean mass variations. 相似文献