全文获取类型
收费全文 | 1039篇 |
免费 | 135篇 |
国内免费 | 150篇 |
专业分类
测绘学 | 103篇 |
大气科学 | 131篇 |
地球物理 | 325篇 |
地质学 | 125篇 |
海洋学 | 168篇 |
天文学 | 198篇 |
综合类 | 29篇 |
自然地理 | 245篇 |
出版年
2024年 | 2篇 |
2023年 | 5篇 |
2022年 | 11篇 |
2021年 | 22篇 |
2020年 | 26篇 |
2019年 | 28篇 |
2018年 | 12篇 |
2017年 | 25篇 |
2016年 | 26篇 |
2015年 | 30篇 |
2014年 | 41篇 |
2013年 | 52篇 |
2012年 | 32篇 |
2011年 | 50篇 |
2010年 | 51篇 |
2009年 | 56篇 |
2008年 | 69篇 |
2007年 | 61篇 |
2006年 | 96篇 |
2005年 | 72篇 |
2004年 | 56篇 |
2003年 | 40篇 |
2002年 | 46篇 |
2001年 | 53篇 |
2000年 | 42篇 |
1999年 | 42篇 |
1998年 | 33篇 |
1997年 | 19篇 |
1996年 | 37篇 |
1995年 | 24篇 |
1994年 | 27篇 |
1993年 | 26篇 |
1992年 | 19篇 |
1991年 | 13篇 |
1990年 | 17篇 |
1989年 | 15篇 |
1988年 | 20篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1324条查询结果,搜索用时 265 毫秒
41.
42.
Scattering Properties of Atmospheric Aerosols over Lanzhou City and Applications Using an Integrating Nephelometer 总被引:2,自引:0,他引:2
The data, measured by a three-wavelength Integrating Nephelometer over Lanzhou City during the winters of 2001/2002 and 2002/2003 respectively, have been analyzed for investigating the scattering properties of atmospheric aerosols and exploring their relationship and the status of air pollution. The aerosol particle volume distribution is inverted with the measured spectral scattering coefficients. The results show that the daily variation of the aerosol scattering coefficients is in a tri-peak shape. The average ratio of backscattering coefficient to total scattering coefficient at 550 nm is 0.158; there exists an excellent correlation between the scattering coefficients and the concentration of PM10. The average ratio of the concentration of PM10 to the scattering coefficients is 0.37 g m-2, which is contingent on the optical parameters of aerosol particles such as the size distribution, etc.; an algorithm is developed for inverting the volume distribution of aerosol particles by using the histogram and Monte-Carlo techniques, and the test results show that the inversion is reasonable. 相似文献
43.
借助辅助函数的思想, 采用波函数展开法给出了圆弧形凸起地形中隧洞对入射平面SH波影响问题的一个解析解.数值结果表明,凸起地形中隧洞的存在以及隧洞大小,对凸起地形表面运动,以及凸起地形中的隧洞的动应力集中均具有显著影响. 相似文献
44.
Imaging the Dead Sea Transform with scattered seismic waves 总被引:2,自引:0,他引:2
45.
46.
Green''''s functions for uniformly distributed loads acting on an inclined line in a poroelastic layered site 总被引:4,自引:0,他引:4
Based on one type of practical Biot's equation and the dynamic-stiffness matrices of a poroelastic soil layer and half-space, Green's functions were derived for uniformly distributed loads acting on an inclined line in a poroelastic layered site. This analysis overcomes significant problems in wave scattering due to local soil conditions and dynamic soil-structure interaction. The Green's functions can be reduced to the case of an elastic layered site developed by Wolf in 1985. Parametric studies are then carried out through two example problems. 相似文献
47.
On the basis of Biot dynamic theory, an analytic solution of two-dimensional scattering and diffraction of plane SV waves by circular cylindrical canyons in a half space of saturated porous media is presented in this paper for the first time. The solution is obtained by employing the Fourier–Bessel series expansion technique. Parametric studies had been carried out, which includes: the angle of incidence, the frequency of the incident SV wave, the porosity of saturated porous medium and the stiffness and Poisson's ratio of the solid-skeleton. All the outcomes are useful for the seismic analysis of the surface topography conditions. 相似文献
48.
49.
The impact of shade on establishment of shrubs adapted to the high light irradiation of semi-arid environments 总被引:1,自引:0,他引:1
Light may be an important limiting resource that influences community structure of chenopod shrublands. As part of a larger study that aimed to determine the factors that influence chenopod community structure, the focus of this study was the influence of plant canopy on the growth and establishment of smaller plants. We therefore measured the height and cover of three chenopods (Enchylaena tomentosa, Maireana brevifolia and Maireana georgei) when growing within and outside of the canopy of Atriplex bunburyana under field conditions. All three chenopods had lower cover and E. tomentosa was taller when growing within the canopy of A. bunburyana in comparison to those growing outside of the canopy. The chenopods were then grown under three artificial shade regimes. Plant height, cover, biomass, relative leaf area and photosynthetic surface area measurements showed that each species responded differently to shade. E. tomentosa biomass was facilitated by shade. This was inferred by an increase in total plant biomass. M. brevifolia, in contrast, tolerated shade by increasing above-ground biomass allocation. M. georgei was adversely affected by the shade regimes: root biomass decreased in response to shade. Competition for light is, therefore, likely to influence chenopod community structure of semi-arid and arid environments. 相似文献
50.
Sensitivity kernels for finite-frequency surface waves 总被引:1,自引:1,他引:1