全文获取类型
收费全文 | 2293篇 |
免费 | 550篇 |
国内免费 | 349篇 |
专业分类
测绘学 | 136篇 |
大气科学 | 703篇 |
地球物理 | 765篇 |
地质学 | 890篇 |
海洋学 | 134篇 |
天文学 | 5篇 |
综合类 | 129篇 |
自然地理 | 430篇 |
出版年
2024年 | 15篇 |
2023年 | 35篇 |
2022年 | 46篇 |
2021年 | 99篇 |
2020年 | 121篇 |
2019年 | 114篇 |
2018年 | 83篇 |
2017年 | 100篇 |
2016年 | 113篇 |
2015年 | 106篇 |
2014年 | 131篇 |
2013年 | 239篇 |
2012年 | 120篇 |
2011年 | 110篇 |
2010年 | 101篇 |
2009年 | 108篇 |
2008年 | 108篇 |
2007年 | 160篇 |
2006年 | 146篇 |
2005年 | 129篇 |
2004年 | 143篇 |
2003年 | 142篇 |
2002年 | 93篇 |
2001年 | 99篇 |
2000年 | 87篇 |
1999年 | 80篇 |
1998年 | 68篇 |
1997年 | 65篇 |
1996年 | 59篇 |
1995年 | 35篇 |
1994年 | 34篇 |
1993年 | 29篇 |
1992年 | 21篇 |
1991年 | 5篇 |
1990年 | 22篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1987年 | 2篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有3192条查询结果,搜索用时 15 毫秒
951.
952.
953.
GIS和SDSS在高速公路选线之中的应用 总被引:6,自引:1,他引:6
以地理信息系统(GIS)和空间决策支持系统(SDSS)技术为基础,以地理信息系统工具CITYSTAR为平台,以VB为开发工具,在高速公路选线理论的指导下并考虑选线工作中的实际问题,对如何把GIS和SDSS应用到高速公路选线中进行了探讨,并以青岛、黄岛、灵山卫、南岭等环胶州湾地区为研究对象,初步设计出了高速公路选线决策支持系统。 相似文献
954.
文章分析了1998年夏季我国长江、嫩江、珠江流域发生的严重洪涝灾害的气象、水文特征及其成因。6月中、下旬珠江、长江、嫩江流域出现了持续性强降水, 局部地区下了大暴雨; 7月下旬长江流域出现了“二度梅”, 湖南、湖北和江西省普降暴雨; 8月上半月嫩江流域再次出现持续性强降水。频繁的强降水使长江、嫩江、华南西江等干、支流水位迅猛上涨, 支流河水不断涌入干流, 使得干流洪峰迭起。雨水和洪峰迭加, 引发了百年一遇的大洪水。1998年7月副热带高压南落是造成长江流域“二度梅”的主要原因。副热带高压、南海季风涌、中高纬冷空气和从青藏高原东移的中尺度对流系统 (MCS) 等4个因子的最佳组配, 有利于长江流域出现持续性强降水。 相似文献
955.
956.
Chen Hao 《地理学报(英文版)》2001,11(1):71-79
From a long-term point of view, the balance between erosion and sediment yield in a drainage system can basically realize,
i.e., the delivery ratio can be close to 1. However, substantial variations among individual rainfall events or between annual
delivery ratio exist, causing frequent sediment retaining or re-erosion and re-delivery of the retained sediments in a short
period of time. Thus the delivery ratio will be < 1 or > 1. The sediment delivery ratio is closely related to the spatial
distribution of rainfall and magnitude of rise and fall of peak flood and that of runoff depth in the drainage system. Delivery
ratio of single event in a drainage system and changes of delivery capacity of silt-laden runoff in various classes of gullies
can be expressed by transformation mechanism of shear force of a single rainstorm event with flood resulting from increase
and decrease of peak flood per unit area. 相似文献
957.
S. N. Rajaguru Avijit Gupta V. S. Kale Sheila Mishra R. K. Ganjoo L. L. Ely Yahouda Enzel V. R. Baker 《地球表面变化过程与地形》1995,20(5):407-421
The 1300 km long Narmada River flows along a structural lineament, alternating between constricting rocky gorges and rapids, and meandering wide alluvial reaches. Channel forms and processes were studied in a 120 km long section of an alluvial reach. Channel size, shape and bedforms in the Narmada River are related to very large floods which have occurred three times in this century. During such floods the entire 400 m wide channel is utilized and 10–15 m high cliffs on both sides operate as riverbanks. Normally, even the high flows of the south-western monsoon are insufficient to fill the whole channel, and hence their effects are limited to building of discontinuous floodplains between the cliffs and modifying bedforms and bars. A channel-in-channel topography is thus created. The very large floods are also responsible for erosion of the rocky stretches and building of point bars. The river meanders, but its movement is restricted because of (1) rocky gorges and scablands operating as anchor points at intervals, and (2) the presence of high alluvial cliffs which are topped on extremely rare occasions. In spite of being located in a tectonically active zone in a monsoon setting, it is the exceptional high-magnitude floods at irregular intervals which control the form and behaviour of the Narmada River. 相似文献
958.
J. R. Stedinger L. -H. Lu 《Stochastic Environmental Research and Risk Assessment (SERRA)》1995,9(1):49-75
Our results illustrate the performance of at-site and regional GEV/PWM flood quantile estimators in regions with different coefficients of variation, degrees of regional heterogeneity, record lengths, and number of sites. Analytic approximations of bias and variance are employed. For realistic GEV distributions and short records, the index-flood quantile estimator performs better than a 2-parameter GEV/PWM quantile estimator with a regional shape parameter, or a 3-parameter at-site GEV/PWM quantile estimator, in both humid and especially in arid regions, as long as the degree of regional heterogeneity is moderate. As regional heterogeneity or record lengths increases, 2-parameter estimators quickly dominate. Flood frequency models that assign probabilities larger than 2% to negative flows are unrealistic; experiments employing such distributions provide questionable results. This appraisal generally demonstrates the value of regionalizing estimators of the shape of a flood distribution, and sometimes the coefficient of variation. 相似文献
959.
塔里木河1994年大洪水及其相关问题分析 总被引:4,自引:1,他引:4
塔里木河阿拉尔站1994年7月发生了有记载以来的第二位最大洪峰流量,时段最大洪量。超过了以往的记录,在分析塔里木河洪水成因的基础上,对1994年洪水的形成,特性,沿程耗损作了剖析;回顾了1956年以来干流上,中,下游段耗用水比的变迁,并对其后果进行了分析。 相似文献
960.