全文获取类型
收费全文 | 112755篇 |
免费 | 1490篇 |
国内免费 | 1504篇 |
专业分类
测绘学 | 3271篇 |
大气科学 | 7851篇 |
地球物理 | 21699篇 |
地质学 | 42737篇 |
海洋学 | 9259篇 |
天文学 | 22173篇 |
综合类 | 2367篇 |
自然地理 | 6392篇 |
出版年
2022年 | 645篇 |
2021年 | 1109篇 |
2020年 | 1184篇 |
2019年 | 1341篇 |
2018年 | 7054篇 |
2017年 | 6165篇 |
2016年 | 5269篇 |
2015年 | 1704篇 |
2014年 | 2845篇 |
2013年 | 4869篇 |
2012年 | 3932篇 |
2011年 | 6359篇 |
2010年 | 5436篇 |
2009年 | 6633篇 |
2008年 | 5692篇 |
2007年 | 6171篇 |
2006年 | 3814篇 |
2005年 | 2914篇 |
2004年 | 3036篇 |
2003年 | 2820篇 |
2002年 | 2668篇 |
2001年 | 2114篇 |
2000年 | 2123篇 |
1999年 | 1631篇 |
1998年 | 1712篇 |
1997年 | 1533篇 |
1996年 | 1319篇 |
1995年 | 1313篇 |
1994年 | 1122篇 |
1993年 | 1070篇 |
1992年 | 1012篇 |
1991年 | 1017篇 |
1990年 | 980篇 |
1989年 | 859篇 |
1988年 | 797篇 |
1987年 | 925篇 |
1986年 | 818篇 |
1985年 | 996篇 |
1984年 | 1119篇 |
1983年 | 1095篇 |
1982年 | 1001篇 |
1981年 | 961篇 |
1980年 | 858篇 |
1979年 | 803篇 |
1978年 | 771篇 |
1977年 | 647篇 |
1976年 | 658篇 |
1975年 | 635篇 |
1974年 | 609篇 |
1973年 | 680篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
401.
402.
403.
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
404.
405.
406.
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
407.
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
408.
The specific features of the generation and intensification of internal gravity wave structures in different atmospheric-ionospheric regions, caused by zonal local nonuniform winds (shear flows), are studied. The model of the medium has been explained and an initial closed system of equations has been obtained in order to study the linear and nonlinear dynamics of internal gravity waves (IGWs) when they interact with the geomagnetic field in a dissipative ionosphere (for the D, E, and F regions). 相似文献
409.
The geomorphological environment is one of the most fundamental variables af-fecting the development of human society.The mission of geomorphological environment research is to explore the most basic environment and features of our Earth’s surface mor-phology.The results can be applied to resource evaluation,environmental protection and reducing and preventing geological disasters.Thus,it can serve to help achieve sustainable development.This paper examines the Shenzhen east coastal zone as a case strongly in-fluenced by urban expansion.We use modern geomorphological theory and methods,along with GIS and RS techniques,to reveal key characteristics of the geomorphological environ-ment and landform classification.Furthermore,coastal ecosystem evaluation and regional resources sustainable utilization should be considered relative to the corresponding geo-morphological environment.Based on this study,we conclude that modern geomorphological theory and methods,supported by "3S" techniques including GIS,RS and GPS,can play an important role in resolving the environment,resources and population problems as well as sustainable development challenges facing humankind at present. 相似文献
410.