全文获取类型
收费全文 | 3382篇 |
免费 | 526篇 |
国内免费 | 694篇 |
专业分类
测绘学 | 405篇 |
大气科学 | 521篇 |
地球物理 | 603篇 |
地质学 | 1684篇 |
海洋学 | 450篇 |
天文学 | 36篇 |
综合类 | 223篇 |
自然地理 | 680篇 |
出版年
2024年 | 17篇 |
2023年 | 50篇 |
2022年 | 134篇 |
2021年 | 147篇 |
2020年 | 146篇 |
2019年 | 167篇 |
2018年 | 149篇 |
2017年 | 156篇 |
2016年 | 149篇 |
2015年 | 163篇 |
2014年 | 207篇 |
2013年 | 220篇 |
2012年 | 188篇 |
2011年 | 228篇 |
2010年 | 197篇 |
2009年 | 219篇 |
2008年 | 192篇 |
2007年 | 213篇 |
2006年 | 242篇 |
2005年 | 178篇 |
2004年 | 167篇 |
2003年 | 172篇 |
2002年 | 132篇 |
2001年 | 105篇 |
2000年 | 96篇 |
1999年 | 95篇 |
1998年 | 62篇 |
1997年 | 56篇 |
1996年 | 44篇 |
1995年 | 43篇 |
1994年 | 39篇 |
1993年 | 40篇 |
1992年 | 28篇 |
1991年 | 10篇 |
1990年 | 17篇 |
1989年 | 11篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 16篇 |
1982年 | 8篇 |
1981年 | 12篇 |
1980年 | 18篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1974年 | 4篇 |
排序方式: 共有4602条查询结果,搜索用时 15 毫秒
1.
In 1903 the Swiss Federal Research Institute WSL started its first forest hydrology measurements with the aim to deliver a sound scientific basis for the implementation of new forest legislation introduced in Switzerland in 1876. This legislation was triggered by several large floods that occurred in Switzerland, for which a major cause was widely seen as the poor condition of forests at that time. Consequently, hydrologic research at WSL first focused on the influence of forests on floods. In the second half of the 20th century, other hydrological issues such as water quality, snow hydrology and sediment transport complemented the hydrologic research at WSL. Some recent results of this work are presented in three papers joining this introductory paper to mark the 100th anniversary of hydrologic research at WSL. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
2.
Gregory P. Marchildon Suren Kulshreshtha Elaine Wheaton Dave Sauchyn 《Natural Hazards》2008,45(3):391-411
Agriculture in the southern Great Plains of Canada has been particularly vulnerable to prolonged episodes of drought. Using
climate data and a precipitation minus potential evapotranspiration index, the extent of the region’s exposure to drought
is examined. Between 1914 and 1917, the Dry Belt was particularly vulnerable to drought, whereas after 1928, a much larger
region known as the Palliser Triangle covering most of southern Alberta and Saskatchewan was much more exposed to drought.
These droughts provoked major institutional adaptation, in particular the establishment of the Special Areas Board by the
Government of Alberta, and the creation of the Prairie Farm Rehabilitation Administration by the Government of Canada. Both
organizations have proved to be relatively permanent public adaptations to the natural hazard of drought in the region. Moreover,
these earlier experiences with prolonged drought as well as institution-building may be of value in helping the residents
of the Palliser Triangle adapt to predicted climate changes in the future as well as anticipate some of the barriers to effective
institutional adaptation. 相似文献
3.
Low-frequency damping of a moored semisubmersible drilling platform was obtained from numerical extinction tests simulated in still water and in regular waves and from mean wave drift forces calculated at zero forward speed. The influence of drag forces was represented by the modified Morison equation. The platform as used for the 18th ITTC Comparative Mooring Study was analyzed in irregular beam waves. The computed time series of sway as well as the corresponding sway response spectrum compared favourably with model test measurements, demonstrating that this procedure to determine low-frequency damping can be effective. 相似文献
4.
5.
A series of transient tests were conducted to determine the seafloor coupling characteristics of a new ocean-bottom seismometer (OBS) developed for the United States Office of Naval Research (ONR). The OBS comprises a large recording package and a separate sensor package that is deployed from the recording package. In addition to the coupling characteristics of both the sensor and the recording packages, the seismic energy radiated from the main recording package as a result of motion of the recording package was measured. The observed vertical coupling resonances of both the recording package and the sensor package are in good agreement with those predicted by a simple model of soil-structure interaction. The most important result of this study is that significant energy is radiated from the recording package in response to horizontal motions of the recording package. When the sensor package is 1 m from the recording package, the amplitude of the recorded signal is similar to that recorded in the recording package. In the field, this effect will result in distortion of seismic signals and increased background noise recorded by the sensor package if the recording package is disturbed by seafloor currents or biological activity. The amplitude of this signal attenuates by approximately a factor of two as sensor/recorder separation is increased from 1 to 6 m, suggesting that an improved response can be achieved by increasing the separation between the recording package and the sensors. This effect is much less severe for vertical disturbances of the recording package. 相似文献
6.
7.
临港新城地质特征及其对新城规划与建设的影响分析 总被引:2,自引:1,他引:1
结合临港新城三维地质调查所取得的成果,分析了该城区地质特征及对新城建设的影响,为新城规划建设提供科学依据和服务。 相似文献
8.
The scope of the present paper is to provide analytic solutions to the problem of the attitude evolution of a symmetric gyrostat about a fixed point in a central Newtonian force field when the potential function isV
(2).We assume that the center of mass and the gyrostatic moment are on the axis of symmetry and that the initial conditions are the following: (t
0)=0, (t
0)=0, (t
0)=(t
0)=0, 1(t
0)=0, 2(t
0)=0 and 3(t
0)=
3
0
.The problem is integrated when the third component of the total angular momentum is different from zero (B
1 0). There now appear equilibrium solutions that did not exist in the caseB
1=0, which can be determined in function of the value ofl
3
r
(the third component of the gyrostatic momentum).The possible types of solutions (elliptic, trigonometric, stationary) depend upon the nature of the roots of the functiong(u). The solutions for Euler angles are given in terms of functions of the timet. If we cancel the third component of the gyrostatic momentum (l
3
r
=0), the obtained solutions are valid for rigid bodies. 相似文献
9.
10.
异常形态、分布严格受推覆断裂控制,范围大、浓集中心明显,浓度变化及因子载荷表明。区内找Ag、Pb有利,而Sb又为其最佳指示元素。 相似文献