全文获取类型
收费全文 | 891篇 |
免费 | 230篇 |
国内免费 | 156篇 |
专业分类
测绘学 | 97篇 |
大气科学 | 199篇 |
地球物理 | 278篇 |
地质学 | 229篇 |
海洋学 | 237篇 |
天文学 | 8篇 |
综合类 | 45篇 |
自然地理 | 184篇 |
出版年
2024年 | 19篇 |
2023年 | 26篇 |
2022年 | 33篇 |
2021年 | 35篇 |
2020年 | 49篇 |
2019年 | 41篇 |
2018年 | 35篇 |
2017年 | 31篇 |
2016年 | 41篇 |
2015年 | 45篇 |
2014年 | 45篇 |
2013年 | 91篇 |
2012年 | 58篇 |
2011年 | 46篇 |
2010年 | 38篇 |
2009年 | 43篇 |
2008年 | 54篇 |
2007年 | 61篇 |
2006年 | 59篇 |
2005年 | 51篇 |
2004年 | 48篇 |
2003年 | 39篇 |
2002年 | 29篇 |
2001年 | 30篇 |
2000年 | 27篇 |
1999年 | 28篇 |
1998年 | 26篇 |
1997年 | 20篇 |
1996年 | 29篇 |
1995年 | 9篇 |
1994年 | 22篇 |
1993年 | 15篇 |
1992年 | 12篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
排序方式: 共有1277条查询结果,搜索用时 15 毫秒
1.
Cascade model for fluvial geomorphology 总被引:3,自引:0,他引:3
2.
3.
4.
5.
Urban planning construction land standard is the technical specification for scientifically allocating various types of urban construction land, and it is the basis for drawing up and revising the overall urban planning scheme. Considering China's current urban planning construction land standard, many problems exist, such as the gap in the land use control threshold, the lack of regional differences in the climate revision, and failing to consider the topographic factors. To resolve these problems, this study proposed a step-by-step process framework and quantitative calculation method for the establishment and revision of standards in accordance with the principle of Total-Structure control. By setting the conditions, a universal basic standard for construction land was established. Quantitative analysis was then conducted on the relationship between the basic standard and the selected key indicators, such as urban population size, sunshine spacing coefficient, the width of river valleys or inter-montane basins, and terrain slope, among others. Finally, revised standards were formed for climate conditions, topography, and geomorphologic conditions, which were matched with the basic standards. The key results are three-fold:(1) The per capita construction land standard of 95 m~2/person can be used as the total indicator of China's urban planning basic standard, and the corresponding per capita single construction land comprises 32.50% of residential land, 7.42% of public management and public service land, 22.50% of industrial land, 17.50% of transportation facilities, 12.50% of green space, and 7.58% of other land-use types. The results of the revision of the urban population size indicate that the difference in population size has little effect on the total amount of per capita construction land.(2) The climate revision results of per capita residential land and per capita construction land in major cities reveal that the revised climate value varies greatly between north and south China. The revised climate values of the per capita area of construction land vary by latitude as follows: the value at 20°N is 93 m~2/person, the value at 30°N is 97 m~2/person, the value at 40°N is 103 m~2/person, and the value at 50°N is 115 m~2/person. The basic standard land value of 95 m~2/person is generally distributed across the Xiamen-Guilin-Kunming line.(3) The cities located in mountainous areas, hilly valleys, or inter-montane basins can reduce the allocation of community parks and comprehensive parks when the average width of an existing river valley or inter-montane basin is less than 2 km. When the average width of the valley or inter-montane basin is between 2 km to 4 km, the allocation of the comprehensive parks can be reduced. The revised results of per capita sloping construction land reveal that the terrain slope greatly affects the revised value of per capita construction land. Specifically, the revised value at 3° is 3.68% higher than the basic standard value, and the increase rates at 8°, 15°, and 25° are 11.25%, 26.49%, and 68.47%, respectively. 相似文献
6.
前人在讨论水深对内潮能通量影响的时候得出结论:有限深海洋中海面对内潮的反射使得正压潮向内潮的能量转化相比较无限深海的情况显著降低,对于选定的地形,在无限深海假定下得到的能通量是该地形上内潮能通量的上限。鉴于前人所研究的基本上都是平滑的地形,而实际的海洋地形总是比较粗糙的,本文探讨了粗糙地形上内潮能通量随水深的变化。选取了弦函数地形、随机白噪声地形、弦函数地形叠加在高斯地形之上、随机白噪声地形叠加在高斯地形之上和随机白噪声地形与弦函数地形同时叠加在高斯地形之上5种情况进行了研究,发现对于这5种情况,都存在海洋有限深时的能通量大于无限深假定时的能通量,这说明前人得出的"有限深海洋中海面对内潮的反射使得正压潮向内潮的能量转化相比较无限深海的情况显著降低"的结论对于粗糙地形并不适用。 相似文献
7.
Irene Fischer 《Marine Geodesy》2013,36(2):165-175
The current discussion of whether marine geodesy is something entirely new or part of oceanography or geodesy can be clarified by re‐examining our notions about the basic business of geodesy. This paper contends that the same basic geodetic services, which were needed for millenia to chart and control new territory, are being adapted now to the marine environment to suit modern accuracy standards. In a brief historical review it is shown that conceptually, the oceanic regions were always an integral part of geodetic concern. The oceans were certainly part of the world for the ancient map makers and for Pythagoras’ spherical earth model. Notions connected with the marine geoid were implied in ancient speculations. Distances and directions at sea, even depths, were determined to meet the requirements of the times. With the modern sophistication in geodetic theory and measuring techniques, these ideas became more refined and demanding in turn, but they were there all the time. For obvious reasons, land geodesy developed faster; marine geodesy will catch up now, because only now there is the technical capability and also an urgent economic motivation. 相似文献
8.
Abstract: Recent research has indicated river basin outlets draining linear sections of large, uplifting mountain belts often show a regularity of spacing, transverse to the main structural trend. A morphometric analysis of part of the Ruahine Range, on the North Island was undertaken to test whether drainage regularity may exist in smaller, younger mountain ranges. The ratio, R , of the half-width of the mountain belt, W , and the outlet spacing, S , was used to characterize drainage networks on the eastern side of the range. The spacing ratio for the range of 1.31 is lower than R results from studies of larger mountain belts ( R = 1.91–2.23). We suggest the cause of this lower ratio is related to eastward migration of the Ruahine drainage divide. 相似文献
9.
地形与流对水平无旋浅水波的影响 总被引:1,自引:0,他引:1
本文在水平无旋及Boussinesq假设之下,导出了水面变化与水平速度场耦合方程组,以及相应的压力与垂向速度解析表示式。通过数值方法求得水面变化及某一特定水深的水平速度分布之后,压力分布及其余水深的速度分布即可由简单计算得到。由色散关系式可知,不同水深的长波色散关系在O(ε)近似之下是等同的。粘性的存在会使波高随时间的增加而衰减,但粘性与底斜率的耦合又可能使波高增长,形成不稳定;计算及分析说明,当同向流增大时,波速增大,波长增大,波高会增加;而水深减少,使波速减少,波长缩短,振幅增加。 相似文献
10.
使用黄土河谷场地模型对地震动峰值加速度和频谱特征进行研究。结果表明,不同工况下各观测点PGA的放大比呈现出不同的变化规律。分析山顶和山谷各点的傅里叶谱以及谱比发现,在地形和土层共同作用下的放大效应是各自单独作用下放大效应的乘积。 相似文献