全文获取类型
收费全文 | 58900篇 |
免费 | 761篇 |
国内免费 | 1366篇 |
专业分类
测绘学 | 2616篇 |
大气科学 | 4790篇 |
地球物理 | 11698篇 |
地质学 | 23674篇 |
海洋学 | 3639篇 |
天文学 | 9547篇 |
综合类 | 2341篇 |
自然地理 | 2722篇 |
出版年
2021年 | 359篇 |
2020年 | 345篇 |
2019年 | 366篇 |
2018年 | 5414篇 |
2017年 | 4682篇 |
2016年 | 3675篇 |
2015年 | 955篇 |
2014年 | 1255篇 |
2013年 | 1963篇 |
2012年 | 2151篇 |
2011年 | 3927篇 |
2010年 | 3143篇 |
2009年 | 3709篇 |
2008年 | 3112篇 |
2007年 | 3471篇 |
2006年 | 1334篇 |
2005年 | 1271篇 |
2004年 | 1333篇 |
2003年 | 1307篇 |
2002年 | 1158篇 |
2001年 | 892篇 |
2000年 | 860篇 |
1999年 | 746篇 |
1998年 | 718篇 |
1997年 | 682篇 |
1996年 | 635篇 |
1995年 | 583篇 |
1994年 | 561篇 |
1993年 | 465篇 |
1992年 | 414篇 |
1991年 | 442篇 |
1990年 | 443篇 |
1989年 | 422篇 |
1988年 | 384篇 |
1987年 | 466篇 |
1986年 | 393篇 |
1985年 | 475篇 |
1984年 | 516篇 |
1983年 | 509篇 |
1982年 | 479篇 |
1981年 | 412篇 |
1980年 | 414篇 |
1979年 | 349篇 |
1978年 | 344篇 |
1977年 | 329篇 |
1976年 | 290篇 |
1975年 | 294篇 |
1974年 | 316篇 |
1973年 | 343篇 |
1972年 | 218篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
A general method for representing the flow properties in the three-dimensional boundary layers around ship hulls of arbitrary shape is described. It makes use of an efficient two-point finite-diffirence schem to solve the boundary-layer equations and includes an algebraic eddy-viscosity representaion of the Reynolds-stress ternsor. The numericzal method contains novel and desirable features and allows the calculation of flows in which the circumferential velocity component contains regions of flow reversal across the boundary layer. The inviscid pressure distribution is determined with the Douglas-Neumann method which, if necessary, can conveniently allow for the boundary-layer displacement surface. To allow its application to ships, and particularly to those with double-elliptic and flat-bottomed hulls, a non-orthogonal coordinate system has been developed and is shown to be economical, precise and comparatively easy to use. Present calculations relate to zero Froude number but they can be extended to include the effects of a water wave and local regions of flow separation which may stem from bulbous-bow geometries. 相似文献
102.
Formation of pockmarks by pore-water escape 总被引:1,自引:1,他引:1
P. K. Harrington 《Geo-Marine Letters》1985,5(3):193-197
During the course of a North Sea rig site investigation, a number of seabed depressions were observed on side-scan sonar records, some of which may be identified as pockmarks. Others are described as pits. A pockmark evolutionary series is proposed on the basis of all these features with a suggested mechanism which would favor release of pore water, but does not exclude gas escape. Acoustic voids are considered to be a related phenomenon. 相似文献
103.
Growth rate of Raia clavata in the Northeast Irish Sea 总被引:1,自引:0,他引:1
104.
105.
106.
107.
M. Tiwari R. Ramesh B. L. K. Somayajulu A. J. T. Jull G. S. Burr 《Geo-Marine Letters》2006,26(1):23-30
Rapid shifts in past climate recorded in polar ice sheets have elicited various explanations relating to either thermohaline
circulation changes by ice-rafting or natural greenhouse gas concentrations modulated by climatic conditions in the tropics.
To compare the tropical paleoclimate record with the polar record, one must choose sediment cores from highly productive ocean
regions. Necessarily, such regions reflect the wind records in the tropics, because high productivity is associated with upwelling
driven by winds. Comparing tropical precipitation records with high-latitude records is, however, a more difficult task because
sediments recording paleoprecipitation usually have low sedimentation rates, and offer coarser resolution relative to polar
ice cores. Here, we present δ
18O data of three planktonic species of Foraminifera (a proxy for precipitation) from such a sediment core, spanning the past
35 ka for the equatorial Indian Ocean, which falls under the southwest monsoon (SWM) realm. Results show that minimum SWM
precipitation occurred at the Last Glacial Maximum, with a subsequent increase at Termination IA. During the Holocene, SWM
precipitation intensified uniformly up to the core top (∼2.2 ka b.p.), as revealed by generally decreasing δ
18O values. Variations in precipitation are consistent with climate changes recorded in polar ice sheets. Although the different resolutions of the two records preclude
a rigorous comparison, abrupt cooling/warming events appear to be accompanied by sudden reduction/enhancement in (SWM) rainfall.
Thus, mechanisms with time scales much shorter than a millennium, such as natural greenhouse warming (e.g., CH4 concentration), controlled by emissions from the tropics, could have played a major role in high-latitude climate change. 相似文献
108.
109.
Data on the Tsushima Current and its neighboring coastal current are analyzed to examine short-term variability of the currents and storm events due to typhoons. A three current-meter array was deployed in a strong current region of the east Tsushima channel during summer in 1983 and 1984, and other two current-meter arrays in the eastern coastal area of the channel (the Sea of Genkai) in the summer and autumn in 1983. The observations of coastal current show that the kinetic energy of the subtidal current component was larger in summer than in autumn by a factor of about 2. A comparison of the wind stresses and the estimated values of mixed layer depth in the summer and autumn season suggest that this seasonal change is closely associated with that of the mixed layer depth rather than with that of the wind stress. The Tsushima Current was greatly influenced by two storm events: its speed increased by a factor of 2 in one event and decreased to nearly zero in the other. Such a large variation of mean current during the storm was observed only for the Tsushima Current and not for the coastal current, suggesting that the Tsushima Current may temporarily change its regular course as a result of a storm. 相似文献
110.