全文获取类型
收费全文 | 3462篇 |
免费 | 312篇 |
国内免费 | 383篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 286篇 |
地球物理 | 1080篇 |
地质学 | 306篇 |
海洋学 | 1056篇 |
天文学 | 692篇 |
综合类 | 63篇 |
自然地理 | 664篇 |
出版年
2024年 | 9篇 |
2023年 | 23篇 |
2022年 | 36篇 |
2021年 | 31篇 |
2020年 | 51篇 |
2019年 | 85篇 |
2018年 | 61篇 |
2017年 | 72篇 |
2016年 | 68篇 |
2015年 | 81篇 |
2014年 | 100篇 |
2013年 | 187篇 |
2012年 | 47篇 |
2011年 | 119篇 |
2010年 | 114篇 |
2009年 | 215篇 |
2008年 | 262篇 |
2007年 | 307篇 |
2006年 | 231篇 |
2005年 | 176篇 |
2004年 | 188篇 |
2003年 | 206篇 |
2002年 | 172篇 |
2001年 | 121篇 |
2000年 | 144篇 |
1999年 | 161篇 |
1998年 | 151篇 |
1997年 | 73篇 |
1996年 | 103篇 |
1995年 | 77篇 |
1994年 | 74篇 |
1993年 | 69篇 |
1992年 | 60篇 |
1991年 | 53篇 |
1990年 | 48篇 |
1989年 | 40篇 |
1988年 | 26篇 |
1987年 | 25篇 |
1986年 | 18篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 19篇 |
1979年 | 3篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1954年 | 4篇 |
排序方式: 共有4157条查询结果,搜索用时 125 毫秒
921.
INTRODUCFIONlt is well known that the stability and interaction of nonlinear waves lead to modulations ofwavenumber and frequency, as well as arnplitude, with the frequency dePendent on bothwavenumber and arnplitude (Witham, l974; Philips, l98l ). These medulations are not justtheoretical curiossities but have important conSequences in oceanography and meteorology, aswell as naval architecture and ocean engineering (honguer-Higgins, l980).By means of Hilbert transfOrm technique, Melvill… 相似文献
922.
基于Longuet-Higgins提出的非线性随机海浪模型,在二阶近似下通过直接计算联合分布的各阶矩,导出了非线性海浪波面高度和波面垂直速度的联合分布。该分布为非正态,其形式为截断的级数,而非由累积矩母函数方法可能得到的渐近无穷级数。由于非线性的影响,波面高度与波面垂直速度不再相互独立。 相似文献
923.
Miao Guoping Liu Yingzhong
Professor Dept. of Naval Architecture Ocean Engineering Shanghai Jiao Tong University Shanghai 《中国海洋工程》1991,(1)
The analytical study is made by using the method of matched asymptotic expansions on the transmission and reflection of solitary waves and cnoidal waves on two-dimensional floating bodies. The solutions give explicitly the variation pattern of the transmitted waves and the characteristics of the reflected waves, including the wave profile, amplitude, phase shift and evolution. The effects of the gap between the body and the sea bottom on the transmission and reflection of those waves are also discussed. 相似文献
924.
A numerical model is presented to predict the interaction of multidirectional random surface waves with one or more rectangular submarine pits. The water depth is assumed uniform and the method involves the superposition of diffraction solutions based on linearized shallow water wave theory obtained by a two-dimensional boundary integral approach. The incident wave conditions are specified using a discrete form of the Mitsuyasu directional spectrum. The present numerical model has been validated through comparisons with previous theoretical results for regular waves. Good agreement was obtained in all cases. Based on these comparisons it is concluded that the present numerical model is an accurate and efficient tool to predict the wave field around multiple submarine pits and navigation channels in many practical situations. 相似文献
925.
An analytical solution using homotopy analysis method is developed to describe the nonlinear progressive waves in water of finite depth. The velocity potential of the wave is expressed by Fourier series and the nonlinear free surface boundary conditions are satisfied by continuous mapping. Unlike the perturbation method, the present approach is not dependent on small parameters. Thus solutions are possible for steep waves. Furthermore, a significant improvement of the convergence rate and region is achieved by applying Homotopy-Padé Approximants. The calculated wave characteristics of the present solution agree well with previous numerical and experimental results. 相似文献
926.
利用β平面上大气斜压强迫模式,探讨了局地海表温度异常所造成的非绝热加热影响的赤道小振幅“拦截波”的稳定性。指出当加热函数是半余弦形式时,在加热区大气的反应是局地性的,但这个加热函数的小扰动能产生非局地性的大尺度反应。平均海表温度降低了赤道波动的稳定性。当稍超过临界值时,小尺度海表温度异常有可能使波动不稳定。 相似文献
927.
The probability distribution of the height of global maximum for a Gaussian random field evolving in time is studied. In particular, the effect of spreading is studied and the role of the wave kinematics is discussed. It is observed that taking into account time dynamics of spatial characteristics results in distributions different from those obtained for the static case. The results are illustrated by computing the derived distribution for different Gaussian seas for three distinct sampling schemes. The resulting distributions are also used to compute return periods for rogue waves. 相似文献
928.
A numerical wave model based on the modified four-order nonlinear Schoedinger (NKS) equation in deep water is developed to simulate freak waves. A standard split-step, pseudo-spectral method is used to solve NLS equation. The validation of the model is firstly verified, and then the simulation of freak waves is perforated by changing sideband condi- tions. Results show that freak waves entirely consistent with the definition in the evolution of wave trains are obtained. The possible occurrence mechanism of freak waves is discussed and the relevant characteristics are also analyzed. 相似文献
929.
Warren B. White Kathryn A. Gloersen Francis Marsac Yves M. Tourre 《Journal of Oceanography》2004,60(3):531-541
Interannual coupled Rossby waves in the extratropical Indian Ocean propagate westward in covarying pycnocline depth, sea surface
temperature, and meridional surface wind anomalies from the west coast of Australia between 15°S and 35°S, taking 3–4 years
to transit the interior ocean to Madagascar. In the interior subtropical gyre, where the tuna longline catch (TLC) mainly
concerns two species (albacore and bigeye), these waves have been observed to affect year-to-year changes in catch, with wave
crests (troughs) in the main pycnocline associated with high (low) TLC anomalies. This suggested that tuna longline catch
is associated with the entrainment of nutrient-rich pycnocline water into the photic zone and a subsequent increase in primary
productivity there. Here, this hypothesis is examined within the context of SeaWiFS chlorophyll concentration (CC). We find
the situation the opposite of that expected, with wave crests (troughs) in the main pycnocline associated with low (high)
CC anomalies averaged over the photic zone. These results are shown to be consistent with a model relating the anomalous CC
tendency to upper-layer divergence in the wave, not unlike that relating surface slicks to upper-layer divergence in internal
gravity waves. Thus, the connection between interannual coupled Rossby waves and TLC in the interior subtropical gyre does
not appear to derive from wave-induced modulation of the pelagic food web.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
930.
Dune erosion is shown to occur at the embayment of beach mega-cusps O(200 m alongshore) that are associated with rip currents. The beach is the narrowest at the embayment of the mega-cusps allowing the swash of large storm waves coincident with high tides to reach the toe of the dune, to undercut the dune and to cause dune erosion. Field measurements of dune, beach, and rip current morphology are acquired along an 18 km shoreline in southern Monterey Bay, California. This section of the bay consists of a sandy shoreline backed by extensive dunes, rising to heights exceeding 40 m. There is a large increase in wave height going from small wave heights in the shadow of a headland, to the center of the bay where convergence of waves owing to refraction over the Monterey Bay submarine canyon results in larger wave heights. The large alongshore gradient in wave height results in a concomitant alongshore gradient in morphodynamic scale. The strongly refracted waves and narrow bay aperture result in near normal wave incidence, resulting in well-developed, persistent rip currents along the entire shoreline.
The alongshore variations of the cuspate shoreline are found significantly correlated with the alongshore variations in rip spacing at 95% confidence. The alongshore variations of the volume of dune erosion are found significantly correlated with alongshore variations of the cuspate shoreline at 95% confidence. Therefore, it is concluded the mega-cusps are associated with rip currents and that the location of dune erosion is associated with the embayment of the mega-cusp. 相似文献