全文获取类型
收费全文 | 8786篇 |
免费 | 1883篇 |
国内免费 | 2062篇 |
专业分类
测绘学 | 258篇 |
大气科学 | 1288篇 |
地球物理 | 1746篇 |
地质学 | 2790篇 |
海洋学 | 5075篇 |
天文学 | 215篇 |
综合类 | 521篇 |
自然地理 | 838篇 |
出版年
2024年 | 85篇 |
2023年 | 253篇 |
2022年 | 390篇 |
2021年 | 443篇 |
2020年 | 482篇 |
2019年 | 516篇 |
2018年 | 377篇 |
2017年 | 407篇 |
2016年 | 438篇 |
2015年 | 447篇 |
2014年 | 602篇 |
2013年 | 624篇 |
2012年 | 554篇 |
2011年 | 592篇 |
2010年 | 519篇 |
2009年 | 583篇 |
2008年 | 483篇 |
2007年 | 554篇 |
2006年 | 516篇 |
2005年 | 459篇 |
2004年 | 411篇 |
2003年 | 372篇 |
2002年 | 385篇 |
2001年 | 269篇 |
2000年 | 275篇 |
1999年 | 257篇 |
1998年 | 215篇 |
1997年 | 181篇 |
1996年 | 176篇 |
1995年 | 131篇 |
1994年 | 139篇 |
1993年 | 113篇 |
1992年 | 104篇 |
1991年 | 87篇 |
1990年 | 61篇 |
1989年 | 50篇 |
1988年 | 37篇 |
1987年 | 21篇 |
1986年 | 18篇 |
1985年 | 21篇 |
1984年 | 18篇 |
1983年 | 16篇 |
1982年 | 20篇 |
1981年 | 10篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1973年 | 1篇 |
1954年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The characteristics of rain and point charges based on routine measurements extending over four rainy seasons are presented. An average rain current density of (1.0±0.1)×10–10 A m–2 and charge per unit volume of rain water of (0.43±0.02)×10–4 C m–3 for the locality are obtained, which are compared with data obtained elsewhere by other workers. The point-discharge current measurements lead to a revised estimate of (0.86±0.08)×10–9 A m–2 for the average point discharge current below storm clouds. 相似文献
992.
993.
994.
995.
996.
997.
The balance conditions of relative angular momentum and time-mean kinetic energy and their annual variations are studied for the Northern Hemisphere tropical belt. The belt is divided into two roughly equal size parts, the monsoon and the extramonsoon regions. The data used consist of all available daily rawinsonde reports from the world areological network for the two 5-year periods 1958–63 and 1968–73.In winter, the trade winds in the monsoon and extramonsoon regions are both sources of westerly relative angular momentum for the middle latitude circulation. However, it is found that the angular momentum gained in the extramonsoon region of the Tropics is mostly destroyed by a net southward flow of mass in that region, and becomes regenerated in the monsoon region by a net northward flow of mass there. This excess of angular momentum together with the angular momentum picked up locally in the monsoon region is almost all exported across its northern boundary. It is further found that in winter the Tropics are also an important source of mean kinetic energy for middle latitudes. Again almost all export of kinetic energy was found to take place across the northern boundary of the monsoon sector. Most of this energy must be generated through the pressure gradient term inside the monsoon region itself, the transformation from transient eddy kinetic energy being very small. The proper evaluation of the pressure gradient appears to be the main stumbling block in the present study, preventing us from estimating the generation and thereby, as a residual, the frictional dissipation in the two regions.In summer, the extramonsoon region remains a source of angular momentum, but the monsoon region with its surface westerlies acts as a sink, leading to a sharp reduction (and even a midsummer reversal) of the export into middle latitudes. Also the export of mean kinetic energy almost vanishes in summer, except for a small southward transfer across the equator. The calculations for two 5-year periods give very similar estimates and thereby show the reliability of the results.Parts of this paper were presented at the International Symposium on Monsoons, March 7–12, 1977 in New Delhi, India. 相似文献
998.
An Arctic Ocean eddy in sub-surface layer is analyzed in this paper by use of temperature,salinity and current profiles data obtained at an ice camp in the Canada Basin during the second Chinese Arctic Expedition in summer of 2003.In the vertical temperature section,the eddy shows itself as an isolated cold water block at depth of 60 m with a minimum temperature of-1.5℃,about 0.5℃ colder than the ambient water.Isopycnals in the eddy form a pattern of convex,which indicates the eddy is anticyclonic.Although maximum velocity near 0.4 m s-1 occurs in the current records observed synchronously,the current pattern is far away from a typical eddy.By further analysis,inertial frequency oscillations with amplitudes comparable with the eddy velocity are found in the sub-surface layer currents.After filter the inertial current and mean current,an axisymmetric current pattern of an eddy with maximum velocity radius of 5 km is obtained.The analysis of the T-S characteristics of the eddy core water and its ambient waters supports the conclusion that the eddy was formed on the Chukchi Shelf and migrated northeastward into the northern Canada Basin. 相似文献
999.
This paper, the first of two, hypothesizes that: (1) the temporal variation of stream power of a river channel at a given station with varying discharge is accomplished by the temporal variation in channel form (flow depth and channel width) and hydraulic variables, including energy slope, flow velocity and friction; (2) the change in stream power is distributed among the changes in flow depth, channel width, flow velocity, slope, and friction, depending on the boundary conditions that the channels has to satisfy. The second hypothesis is a result of the principle of maximum entropy and the theory of minimum energy dissipation or its simplified minimum stream power. These two hypotheses lead to families of at‐a‐station hydraulic geometry relations. The conditions under which these families of relations can occur in the field are discussed. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
1000.
本文用平均风速和最大风速法对若尔盖等三地的韦伯分布参数k、c进行估算,并用韦伯分布计算风能的指标。计算表明:若尔盖、红原属风能可利用区,用风力发电是有利用价值的;阿坝属风能贫乏地区。 相似文献