全文获取类型
收费全文 | 18471篇 |
免费 | 2139篇 |
国内免费 | 2687篇 |
专业分类
测绘学 | 5571篇 |
大气科学 | 2535篇 |
地球物理 | 2952篇 |
地质学 | 4899篇 |
海洋学 | 1611篇 |
天文学 | 2307篇 |
综合类 | 1647篇 |
自然地理 | 1775篇 |
出版年
2024年 | 89篇 |
2023年 | 200篇 |
2022年 | 566篇 |
2021年 | 740篇 |
2020年 | 727篇 |
2019年 | 856篇 |
2018年 | 585篇 |
2017年 | 897篇 |
2016年 | 847篇 |
2015年 | 870篇 |
2014年 | 1007篇 |
2013年 | 1211篇 |
2012年 | 1093篇 |
2011年 | 1007篇 |
2010年 | 817篇 |
2009年 | 1049篇 |
2008年 | 1096篇 |
2007年 | 1267篇 |
2006年 | 1168篇 |
2005年 | 997篇 |
2004年 | 960篇 |
2003年 | 777篇 |
2002年 | 675篇 |
2001年 | 582篇 |
2000年 | 533篇 |
1999年 | 483篇 |
1998年 | 404篇 |
1997年 | 266篇 |
1996年 | 261篇 |
1995年 | 230篇 |
1994年 | 208篇 |
1993年 | 169篇 |
1992年 | 130篇 |
1991年 | 112篇 |
1990年 | 84篇 |
1989年 | 68篇 |
1988年 | 68篇 |
1987年 | 34篇 |
1986年 | 33篇 |
1985年 | 25篇 |
1984年 | 20篇 |
1983年 | 5篇 |
1982年 | 16篇 |
1981年 | 8篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1977年 | 11篇 |
1972年 | 4篇 |
1971年 | 6篇 |
1954年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
63.
Starting with analysis on the evolving course of oasis and the characteristics and evolution of transitional zone between oasis and desert, in consideration of ecological elements including plant stomata resistance, area covered by vegetation, and physical elements including albedo of vegetation and bare soil, atmosphere temperature, and humidity, under the condition of the balance among net radiation flux, latent heat flux, and sensible heat flux, the following are calculated: temperatures of vegetation and bare soil in different conditions, as well as the evapotranspiration rate of ecosystem. Analysis on evapotranspiration rate indicates that it depends on both the climate of environment and the physiological and ecological conditions of plants. On certain conditions, the evapotranspiration rate of transitional zone between oasis and desert (i.e. area covered by vegetation less than 20%), in some parameter domains, appears in bifurcation or multiequilibrium state. Meanwhile, in such area, ecosystem is extremely unstable. Any minor change to the balance will cause either increase or reduction of area covered by vegetation in ecosystem, on the basis of discussion on the emergency of these phenomena. This paper is attempting to propose an effective way of destruction and rebuilt ecosystem in transitional zone. The way is to control the evaporation of plant through selecting anti-drought country plant with big stomata resistance, and modify the roughness of the underlying surface in ecosystem by establishing rational interspace structure of plant community, so as to put the degenerative ecosystem into the natural succession track. This primary theory is being verified through observation and analysis on historical data. 相似文献
64.
65.
66.
67.
O. J. Bennett A. S. Dickinson T. Leininger F. X. Gadéa 《Monthly notices of the Royal Astronomical Society》2003,341(1):361-368
The role in radiative association of narrow resonances arising from quasi-bound levels is examined. For the rate coefficient the contribution from such levels is readily calculated in terms of the Einstein A -coefficient from bound rovibrational levels generated using a suitable alternative boundary condition. By locating systematically all the quasi-bound levels, an enhancement by more than an order of magnitude of the rate coefficient for Li(2s) + H(1s) association above about 600 K is obtained. The effect on the LiH abundance in the early Universe is no more than an increase of a factor of 3 for limited ranges of values of the redshift. For the Li(2p) state the effect of narrow resonances appears to have been taken into account in previous calculations. 相似文献
68.
区域GPS网实时计算可降水量的若干问题 总被引:1,自引:0,他引:1
SONG Shuli ZHU Wenyao 《中国科学院上海天文台年刊》2003,(1)
目前地基GPS气象学测得的可降水量 (PWV )精度好于 2mm ,但在利用区域GPS网实时计算每个测站上空的PWV时 ,要涉及到很多常规GPS资料处理时所忽略的问题 ,如需考虑数据处理软件和计算方式的选择、站坐标的确定和约束、轨道的使用方法、网外辅助站最佳数量的确定、海潮对实时计算PWV的影响以及实时应用于气象服务时的端部效应等问题。利用上海GPS综合应用网获取的 2 0 0 2年 6、7月份长江三角洲地区入梅前后的数据 ,分析了利用区域性的GPS网实时计算高精度的PWV时要解决的各种问题 ,探讨了其数据处理方案 相似文献
69.
Dong-Mei Qin Ping Guo Zhan-Yi Hu Yong-Heng ZhaoNational Laboratory of Pattern Recognition Laboratory Institute of Automation Chinese Academy of Sciences Beijing dmqin@nlpr.ia.ac.cnDepartment of Computer Sciences Beijing Normal University Beijing National Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2003,3(3)
For LAMOST, the largest sky survey program in China, the solution of the problem of automatic discrimination of stars from galaxies by spectra has shown that the results of the PSF test can be significantly refined. However, the problem is made worse when the redshifts of galaxies are not available. We present a new automatic method of star/(normal) galaxy separation, which is based on Statistical Mixture Modeling with Radial Basis Function Neural Networks (SMM-RBFNN). This work is a continuation of our previous one, where active and non-active celestial objects were successfully segregated. By combining the method in this paper and the previous one, stars can now be effectively separated from galaxies and AGNs by their spectra-a major goal of LAMOST, and an indispensable step in any automatic spectrum classification system. In our work, the training set includes standard stellar spectra from Jacoby's spectrum library and simulated galaxy spectra of EO, SO, Sa, Sb types with redshift ranging from 0 to 1 相似文献
70.