全文获取类型
收费全文 | 337篇 |
免费 | 82篇 |
国内免费 | 172篇 |
专业分类
测绘学 | 33篇 |
大气科学 | 413篇 |
地球物理 | 55篇 |
地质学 | 25篇 |
海洋学 | 7篇 |
天文学 | 38篇 |
综合类 | 12篇 |
自然地理 | 8篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 9篇 |
2021年 | 17篇 |
2020年 | 15篇 |
2019年 | 27篇 |
2018年 | 21篇 |
2017年 | 14篇 |
2016年 | 14篇 |
2015年 | 23篇 |
2014年 | 25篇 |
2013年 | 20篇 |
2012年 | 29篇 |
2011年 | 25篇 |
2010年 | 16篇 |
2009年 | 36篇 |
2008年 | 15篇 |
2007年 | 29篇 |
2006年 | 26篇 |
2005年 | 25篇 |
2004年 | 21篇 |
2003年 | 17篇 |
2002年 | 27篇 |
2001年 | 14篇 |
2000年 | 10篇 |
1999年 | 16篇 |
1998年 | 21篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 9篇 |
1994年 | 9篇 |
1993年 | 3篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 4篇 |
排序方式: 共有591条查询结果,搜索用时 328 毫秒
381.
本文利用美国科罗拉多州立大学95年完成的RAMS(Regional atmosphere Modeling system)3B版模式,通过冷、暖云两种方案,以常规报文资料为初值对1998年7月20-21日发生在湖北地区的特大暴雨过程进行了模拟分析,初步试验表明模式具有模拟此次强暴雨过程的能力,20日20时至21日20时24小时降水分别为304mm和206mm,最大雨强分别为48mm/hr和31mm/hr,降水中位于鄂东地区,与实况基本吻合。进一步分析表明聚合体粒子在此次降水中占有主要地位,冰相粒子的加入对降水有重要的增幅作用。 相似文献
382.
Robert A. Dull 《Quaternary Research》2004,61(2):159-167
An ∼8000-cal-yr stratigraphic record of vegetation change from the Sierra de Apaneca, El Salvador, documents a mid-Holocene warm phase, followed by late Holocene cooling. Pollen evidence reveals that during the mid-Holocene (∼8000-5500 cal yr B.P.) lowland tropical plant taxa were growing at elevations ∼200-250 m higher than at present, suggesting conditions about 1.0°C warmer than those prevailing today. Cloud forest genera (Liquidambar, Juglans, Alnus, Ulmus) were also more abundant in the mid-Holocene, indicating greater cloud cover during the dry season. A gradual cooling and drying trend began by ∼5500 cal yr B.P., culminating in the modern forest composition by ∼3500 cal yr B.P. A rise in pollen from weedy plant taxa associated with agriculture occurred ∼5000 cal yr B.P., and pollen from Zea first appeared in the record at ∼4440 cal yr B.P. Human impacts on local vegetation remained high throughout the late Holocene, but decreased abruptly following the Tierra Blanca Joven (TBJ) eruption of Volcán Ilopango at ∼1520 cal yr B.P. The past 1500 years are marked by higher lake levels and periodic depositions of exogenous inorganic sediments, perhaps indicating increased climatic variability. 相似文献
383.
1998年6月28日~7月2日淮河流域暴雨分析 总被引:4,自引:3,他引:4
文中对比分析了 1998年 6月 2 8~ 2 9日和 7月 1~ 2日淮河水循环试验期间两次特大暴雨过程的天气形势、红外卫星云图上降水云系的特征及其水汽来源。结果表明 :(1) 6月底的暴雨是一次东移的西南低涡引发的暖性切变线降水 ,β中尺度对流系统起主要作用。 7月初的暴雨过程是一次移动缓慢的锋面降水 ,锋面上有中尺度的云团活动 ,这是一次大中尺度系统相互作用的结果。 (2 )两场特大暴雨的水汽源地都为中国南海北部地区 ,而强度达到18~ 2 2m/s的西南低空急流是水汽的输送带。 相似文献
384.
385.
386.
Man–computer interactive method on cloud classification based on bispectral satellite imagery 总被引:5,自引:0,他引:5
A bispectral cloud classification method based on man-computer interactive way, i.e. a unit feature space clasification method (UFSCM), has been presented in this paper. Apart from land and water, six types of clouds including cumulonimbus, multilayer cloud system, thin / think cirrus, middle and low level clouds are recognized. The method has been tested by using more than two hundred samples, with total accuracy reaching 87.1%. 相似文献
387.
本文根据地物光谱特性和卫星的信号接收原理,提出了一种利用气象卫星识别水体的简单而有效的方法,使得薄云覆盖下的水体和云影中的水体得到较好的识别效果。在洪水监测中使用该方法,可以充分利用气象卫星数据获取丰富的洪水动态信息.并以1991年江淮洪涝灾害为背景,对试验结果进行了分析. 相似文献
388.
A numerical evaluation of the complete Navier-Stokes equations of motion for steady-state, incompressible flow past an infinite circular cylinder is given in terms of the stream function, vorticity, and pressure distribution past such bodies. A method is described which allows use of these flow characteristics: (1) to approximate the characteristics of air flow past hexagonal columnar ice crystals falling under gravity at terminal velocity in air, (2) to compute the trajectory of supercooled cloud drops relative to such ice crystals, and (3) to determine the efficiency with which short columnar ice crystals and needle shaped ice crystals collide with supercooled cloud drops. It is found that for all columnar type ice crystals riming is negligible if the cloud drop size is less than 5 m, and that for riming to commence short columnar crystals must have diameters larger than 50 m, while needle crystals must have diameters larger than 40 m. It is further shown that the collision efficiency cut-offs at the small drop radius and at the large drop radius end of the collision efficiency diagram can be explained on the basis of the cloud drop trajectories for these drop size ranges. 相似文献
389.
390.
Paul S. K. Pillai A. G. Selvam A. M. Murty A. S. R. 《Pure and Applied Geophysics》1985,123(6):930-940
Characteristics of cloud drop spectra were studied using 400 samples obtained from 120 warm cumulus clouds formed during the summer monsoon season.The total concentration of cloud drops (N
T) varied from 384 to 884 cm–3 and the maximum concentration was observed in the layer below the cloud-top. The width of the drop spectrum was broader in the cloud-base region and in the region below the cloud-top. The spectrum was multimodal at all levels except in the cloud-top region where it was unimodal. The concentration of drops with diameter greater than 50 m (N
L) varied from 0.0 to 0.674 cm–3.N
L was larger in the cloud-base region.N
L decreased with height up to the middle level and thereafter showed an increase. In the cloud-top region no large drops were present. The computed values of the liquid water varied between 0.132 and 0.536 g m–3 and the mean volume diameter (MVD) varied between 8.1 and 12.0 m. The LWC and MVD showed a decrease with height except in the middle region of the cloud where the values were higher than the adjacent levels. The dispersion of the cloud drops was lower (0.65) in the cloud-top region and higher (1.01) in the cloud-base region.The observed cloud microphysical characteristics were attributed to vertical mixing in clouds induced by the cloud-top gravity oscillations (buoyancy oscillations) generated by the intensification of turbulent eddies due to the buoyant production of energy by the microscale-fractional-condensation (MFC) in turbulent eddies. 相似文献