全文获取类型
收费全文 | 23968篇 |
免费 | 3931篇 |
国内免费 | 5183篇 |
专业分类
测绘学 | 5254篇 |
大气科学 | 1463篇 |
地球物理 | 2826篇 |
地质学 | 16054篇 |
海洋学 | 2110篇 |
天文学 | 412篇 |
综合类 | 2147篇 |
自然地理 | 2816篇 |
出版年
2024年 | 91篇 |
2023年 | 284篇 |
2022年 | 891篇 |
2021年 | 1024篇 |
2020年 | 1054篇 |
2019年 | 1192篇 |
2018年 | 905篇 |
2017年 | 1110篇 |
2016年 | 1214篇 |
2015年 | 1303篇 |
2014年 | 1591篇 |
2013年 | 1678篇 |
2012年 | 1633篇 |
2011年 | 1654篇 |
2010年 | 1451篇 |
2009年 | 1579篇 |
2008年 | 1542篇 |
2007年 | 1711篇 |
2006年 | 1599篇 |
2005年 | 1337篇 |
2004年 | 1248篇 |
2003年 | 1046篇 |
2002年 | 896篇 |
2001年 | 796篇 |
2000年 | 700篇 |
1999年 | 654篇 |
1998年 | 554篇 |
1997年 | 514篇 |
1996年 | 366篇 |
1995年 | 292篇 |
1994年 | 255篇 |
1993年 | 198篇 |
1992年 | 190篇 |
1991年 | 152篇 |
1990年 | 89篇 |
1989年 | 73篇 |
1988年 | 49篇 |
1987年 | 46篇 |
1986年 | 31篇 |
1985年 | 23篇 |
1984年 | 21篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1972年 | 1篇 |
1954年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 826 毫秒
141.
142.
Ching-Piao Tsai Hong-Bin Chen Hwung-Hweng Hwung Ming-Jen Huang 《Ocean Engineering》2005,32(3-4):469-483
Estimation of the wave height transformation of shoaling and breaking is essential for the nearshore hydrodynamics and the design of coastal structures. Many empirical formulas have been well recognized to the wave height transformation, but most of them were only applicable for gentle slopes. This paper reports the experimental results of wave shoaling and breaking over the steep slopes to examine the applicability of the previous empirical formulas. Two steep bottom slopes of 1/3 and 1/5, and one gentle slope of 1/10 were conducted in the present experiments. Experimental results show that the shoaling distance of steep slopes become short and the surface waves may be partially reflected from the steep bottom, thus the estimation of wave shoaling using the well-known previous formula did not conform completely to the experimental results. The previous empirical formulas for the wave breaking criteria were also examined, and the modified equations to the steep beaches were proposed in this work. A numerical model was finally adopted to calculate the wave height transformation in the surf zone by introducing the modified breaking index. 相似文献
143.
Shinya Magome Tomohiro Yamashita Takeshi Kohama Atsushi Kaneda Yuichi Hayami Satoru Takahashi Hidetaka Takeoka 《Journal of Oceanography》2007,63(5):761-773
Jellyfish patch formation is investigated by conducting a drifter experiment combined with aerial photography of a sustained
patch of the moon jellyfish in Hokezu Bay, Japan. Jellyfish patches are aggregations of individuals that are caused by a combination
of swimming (active influence) and advection by currents (passive influence). The drifter experiment involved the injection
of 49 drifters around a distinct surface patch of jellyfish within an area of approximately 300 m × 300 m. The drifters’ motion,
caused only by the passive influence, was recorded in a series of 38 aerial photographs taken over approximately 1 h. The
ambient uniform current field larger than the patch scale was estimated from the movement of the centroid position of drifters,
while the distribution of horizontal divergence and relative vorticity around the patch was estimated from the time-derivative
in areas of triangles formed by the drifters. The centroid positions of both drifters and patches moved stably toward the
bay head at different speeds. The difference vector between the patch and drifter centroids was directed to the sun, and was
opposite to the ambient current. The distributions of vorticity and divergence around patches exhibited inhomogeneity within
the patch scale, and the drifters in this nonuniform current field aggregated near the convergence area within 1 h. The results
suggest that horizontal patch formation is predominantly influenced by passive factors at the surface of Hokezu Bay. Furthermore,
the upward swimming against downwelling may make sustained patch in surface layer. 相似文献
144.
Anna Badosa Dani Boix Sandra Brucet Rocío Lpez-Flores Xavier D. Quintana 《Estuarine, Coastal and Shelf Science》2006,66(3-4):513-522
The role of the hydrological regime in the nutrients and zooplankton composition and dynamics has been analysed in five lagoons of La Pletera salt marshes (NE Iberian Peninsula) during a complete hydrological cycle (2002–2003). Two of the lagoons have their origin in the old river mouths while the other three were recently created in the framework of a Life Restoration project. This fact has also allowed us to study the effect of the lagoon age on nutrient and zooplankton composition and dynamics. The salt marsh hydrology is determined by a prolonged period of confinement without water inputs, irregularly interrupted by sudden water inputs due to flooding events (sea storms or intense rainfalls). While the dynamics of oxidized nitrogen compounds in the lagoons depends on the water inputs variability within each hydrological cycle, the internal load of phosphorus, total nitrogen and organic matter is related more to the cumulative mechanisms during the confinement periods. Accumulation processes may be easily related to lagoon age, since old lagoons have higher content of nutrients and organic matter, suggesting that these lagoons progressively accumulate nutrients during the successive confinement events. This is the usual case for most Mediterranean salt marshes without an artificially manipulated water regime. The zooplankton community in La Pletera integrates the effects of both the hydrological regime and the lagoon age since the former determines the temporal pattern of the main zooplankton species and the latter explains differences in composition and structure between old and new lagoons. 相似文献
145.
146.
147.
海中悬移质是决定海洋光学性质、海洋水质,河口海岸带演变动力过程的重要环境参数。本文利用模拟遥感反射比数据集建立人工神经网络反演悬移质浓度,并利用东中国海现场同步数据对该算法进行验证。 相似文献
148.
149.
山东全新世滨海软土与工程地质灾害的研究 总被引:2,自引:0,他引:2
吴建政 《海洋地质与第四纪地质》1995,15(3):43-54
山东全新世滨海软土分布在海湾、泻湖、河口区,厚度1-10m。海湾、泻湖软土为淤泥、淤泥质土,陆源物质供应丰富的浅水区,软土颗粒偏粗,强度相对较高,触变性对建筑物危害性大,陆源物质供应少的深水区,软土颗粒偏细,低强度、高压缩性、沉降变形大和蠕变性是危及建筑物稳定的主要因素。海湾、泻湖软土位于地下水位下,具低透水性,掩埋后短期不易排水固结,软土下为强度较高的冲积物,对一般建筑物,利用强夯、粉喷搅拌桩、 相似文献
150.
Most of the existing relevant materials have been obtained from experiments, in which evaluating the added mass at the resonant frequency corresponding to the peak of a frequency-response curve obtained from the “forced” vibration analysis is the most popular technique. In this paper, a simple experimental method was presented where the “free” vibration responses instead of the “forced” ones were used to determine the values of mah and Iap. The main part of the experimental system is composed of a floating body (model) and a spring–shaft shaker. The “free” vibration of this main part was induced by imposing on it an initial displacement (and/or an initial velocity), and from the time histories of displacements information such as the “damped” natural frequencies, damping ratios, sectional added mass coefficients (CV and CP) were obtained. Since the displacements of the spring–shaft shaker are “translational” and those of the floating body due to pitch motions are “angular”, a technique for the transformation between the associated parameters of the two components of the main part was presented. 相似文献