全文获取类型
收费全文 | 4233篇 |
免费 | 915篇 |
国内免费 | 803篇 |
专业分类
测绘学 | 195篇 |
大气科学 | 322篇 |
地球物理 | 1329篇 |
地质学 | 2420篇 |
海洋学 | 757篇 |
天文学 | 25篇 |
综合类 | 185篇 |
自然地理 | 718篇 |
出版年
2024年 | 17篇 |
2023年 | 69篇 |
2022年 | 157篇 |
2021年 | 184篇 |
2020年 | 205篇 |
2019年 | 236篇 |
2018年 | 192篇 |
2017年 | 194篇 |
2016年 | 209篇 |
2015年 | 219篇 |
2014年 | 287篇 |
2013年 | 321篇 |
2012年 | 245篇 |
2011年 | 269篇 |
2010年 | 229篇 |
2009年 | 251篇 |
2008年 | 255篇 |
2007年 | 282篇 |
2006年 | 250篇 |
2005年 | 195篇 |
2004年 | 219篇 |
2003年 | 177篇 |
2002年 | 152篇 |
2001年 | 122篇 |
2000年 | 144篇 |
1999年 | 92篇 |
1998年 | 112篇 |
1997年 | 104篇 |
1996年 | 103篇 |
1995年 | 95篇 |
1994年 | 77篇 |
1993年 | 61篇 |
1992年 | 48篇 |
1991年 | 33篇 |
1990年 | 19篇 |
1989年 | 34篇 |
1988年 | 28篇 |
1987年 | 15篇 |
1986年 | 9篇 |
1985年 | 12篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1971年 | 2篇 |
1954年 | 5篇 |
排序方式: 共有5951条查询结果,搜索用时 203 毫秒
51.
52.
53.
54.
55.
At hatching the larvae of flatfish closely resemble the bilateral symmetric larvae of other teleosts, especially perciforms. Literature data show that transformation to asymmetric benthic juveniles normally occurs at body lengths between 10 and 25 mm. Unexpectedly, minimal size at its completion (including eye migration) can be 4.1 mm SL and maximal size is over 72 mm. In this paper we consider the functional requirements for a successful switch from a symmetric pelagic larva to a typical asymmetric juvenile benthic flatfish partly based on evidence from other teleosts. The unfavourable period of eye migration and transition to a benthic habitat requires some food reserves and rewiring and/or recalibration of vision and gravity-associated structures utilised previously by the still symmetric larvae for e.g. food detection. Binocular fixation of the prey probably occurs in that stage. Critical or sensitive periods occurring during development of fish larvae suggest that a completely functional symmetric stage of development must precede transformation. The normal size range in flatfish larvae at transformation seems to confirm our considerations. Recent data on temperature effects during development provide an explanation for metamorphosis at the minimal size. Some evidence for paedomorphic heterochrony in flatfish larvae is presented. 相似文献
56.
57.
58.
This paper presents a potential based boundary element method for solving a nonlinear free surface flow problem for a ship moving with a uniform speed in finite depth of water. The free surface boundary condition is linearized by the systematic method of perturbation in terms of a small parameter up to third order. The surfaces are discretized into flat quadrilateral elements and the influence coefficients are calculated by Morino's analytical formula. Dawson's upstream finite difference operator is used in order to satisfy the radiation condition. The second order solution gives better result than the first or third order solution. So the present method with the second order solution can be adopted as a powerful tool for the hydrodynamic analysis of the thin ship in finite depth of water. 相似文献
59.
The steady response of the ventilated thermocline to an increase in Ekman pumping is investigated, focusing on the effect
of the mixed layer depth distribution on the subsurface density anomaly. We consider only the subtropical gyre, and the mixed
layer is assumed to be deep in the northwest and shallow elsewhere with a narrow transition zone separating the deep and shallow
mixed layer regions. At the intersection of this narrow transition zone and the outcrop line, low potential vorticity fluid
is subducted into and ventilates the thermocline. In such a situation, an enhancement of the Ekman pumping confined to the
northern subtropical gyre leads to pronounced subsurface cold anomalies in the southern subtropics, which is free of anomalous
forcing. These density anomalies are much greater than those that occur when either the mixed layer depth is zonally uniform
or the Ekman pumping is enhanced in the whole subtropical gyre. They are caused by anomalous changes in the trajectory of
the low potential vorticity fluid in response to anomalous Sverdrup flow.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
60.
- The spectral form of wind waves is investigated based on the ocean wave data observed at three nearshore stations of Taiwan. In this study, the generalized forms of Pierson-Moskowitz spectrum and JONSWAP spectrum are used to describe the local wave spectrum by selecting suitable spectral form parameters. It is shown that, at a specific site, the similarity of wave spectral form exists. Thus it is possible to use a representative spectral form for a given nearshore region to describe the wave spectrum at this nearshore. On the other hand, the effects of relative water depth on spectral form are examined. The feasibility of two spectral models in finite water depth is evaluated by using the same field wave data. 相似文献