全文获取类型
收费全文 | 29073篇 |
免费 | 5244篇 |
国内免费 | 7268篇 |
专业分类
测绘学 | 4518篇 |
大气科学 | 5225篇 |
地球物理 | 6899篇 |
地质学 | 12024篇 |
海洋学 | 5873篇 |
天文学 | 287篇 |
综合类 | 2324篇 |
自然地理 | 4435篇 |
出版年
2024年 | 110篇 |
2023年 | 351篇 |
2022年 | 981篇 |
2021年 | 1200篇 |
2020年 | 1333篇 |
2019年 | 1558篇 |
2018年 | 1288篇 |
2017年 | 1561篇 |
2016年 | 1559篇 |
2015年 | 1734篇 |
2014年 | 1880篇 |
2013年 | 2045篇 |
2012年 | 1910篇 |
2011年 | 2049篇 |
2010年 | 1603篇 |
2009年 | 1856篇 |
2008年 | 1863篇 |
2007年 | 1967篇 |
2006年 | 1868篇 |
2005年 | 1665篇 |
2004年 | 1461篇 |
2003年 | 1284篇 |
2002年 | 1178篇 |
2001年 | 961篇 |
2000年 | 936篇 |
1999年 | 835篇 |
1998年 | 759篇 |
1997年 | 670篇 |
1996年 | 581篇 |
1995年 | 536篇 |
1994年 | 479篇 |
1993年 | 434篇 |
1992年 | 243篇 |
1991年 | 226篇 |
1990年 | 145篇 |
1989年 | 105篇 |
1988年 | 105篇 |
1987年 | 64篇 |
1986年 | 38篇 |
1985年 | 43篇 |
1984年 | 25篇 |
1983年 | 9篇 |
1982年 | 15篇 |
1981年 | 20篇 |
1980年 | 12篇 |
1979年 | 11篇 |
1978年 | 11篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1954年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
191.
热带印度洋偶极子发生和演变机制的数值研究 总被引:5,自引:0,他引:5
对中国科学院大气物理研究所(IAP)大气科学和地球流体力学数值模拟国家重点实验室(LASG)发展的第三代海洋模式(L30T63 OGCM)进行了改进。分析了该模式1959年1月—1998年12月的40a积分结果,以此研究热带印度洋偶极子发生、发展和消亡的物理机制。对数值模拟结果的分析表明,赤道印度洋表面异常东风引起的异常环流结构是偶极子发生、发展的主要动力学原因,其表面异常东风转换为异常西风所引起的异常环流结构调整是偶极子消亡的主要动力学原因;海气界面热通量异常的交换对热带印度洋海表温度距平偶极子模态的形成和演变起着重要的作用;垂直输送作用是热带印度洋次表层海温偶极子模态发生和演变的主要物理机制。 相似文献
192.
通过对目前生态动力学模型的总结和综合,以生态系统中氮、磷营养盐循环为主线,建立了适用于海洋围隔浮游生态系统的多变量的营养盐迁移-转化动力学模型.该模型包括浮游植物、浮游动物、溶解无机态营养盐、溶解有机态营养盐和生物碎屑5个模块,涉及溶解无机氮、磷酸盐、溶解有机氮、溶解有机磷、浮游植物、浮游动物和生物碎屑7个状态变量.分别利用1999年秋季和2000年夏季胶州湾围隔生态实验数据进行了模型和验证工作,成功地模拟了富加营养盐条件下围隔浮游生态系统中氮、磷营养盐生物化学迁移-转化过程,并确定了20余个参数的量值. 相似文献
193.
Ocean surface waves are strongly forced by high wind conditions associated with winter storms in the Sea of Japan. They are also modulated by tides and storm surges. The effects of the variability in surface wind forcing, tides and storm surges on the waves are investigated using a wave model, a high-resolution atmospheric mesoscale model and a hydrodynamic ocean circulation model. Five month-long wave model simulations are inducted to examine the sensitivity of ocean waves to various wind forcing fields, tides and storm surges during January 1997. Compared with observed mean wave parameters, results indicate that the high frequency variability in the surface wind filed has very great effect on wave simulation. Tides and storm surges have a significant impact on the waves in nearshores of the Tsushima-kaihyō, but not for other regions in the Sea of Japan. High spatial and temporal resolution and good quality surface wind products will be crucial for the prediction of surface waves in the JES and other marginal seas, especially near the coastal regions. 相似文献
194.
195.
We use a synthetic data experiment to assess the accuracy of ocean tides estimated from satellite altimetry data, with emphasis on the impact of the phase-locked internal tide, which has a surface expression of several centimeters near its sites of genesis. Previous tidal estimates have regarded this signal as a random measurement error; however, it is deterministic and not scale-separated from the barotropic (surface) tide around complex bathymetric features. The synthetic data experiments show that the internal tide has a negligible impact on the barotropic tidal fields inferred under these circumstances, and the barotropic dissipation (a quadratic functional of the tidal fields) is in good agreement with the energetics of the three-dimensional regional primitive equations model which is the source of the synthetic data. 相似文献
196.
回顾了近年来国内外河口、近岸海域三维斜压水流数值模式研究的进展,着重讨论了不同垂向坐标下三维水流模式的发展状况以及存在的问题。地形拟合坐标(σ坐标)模式可以很好地拟合床面地形和自由面,已在物理海洋学中被广泛使用。但在地形变化剧烈,尤其在密度层结效应明显的海域,σ坐标模式中的水平压强梯度力误差会引起伪密度流。寻求高精度的数值模式以及更加有效的拟合坐标变换将是值得努力的方向。 相似文献
197.
198.
Sebastiano Calvo Gianfranco Lovison Maria Pirrotta Germana Di Maida Agostino Tomasello & Mariangela Sciandra 《Marine Ecology》2006,27(4):361-371
The relationship between flowering and growth performance of Posidonia oceanica (L.) Delile in meadows distributed along the south‐eastern coast of Sicily (Italy) was investigated by means of a statistical model (generalized linear mixed model) combined with the lepidochronological analysis. Over a 28‐year period, 67 floral stalk remains were observed. The highest flowering index was recorded in lepidochronological year 1998 (10.1%) and the Inflorescence Frequency per age showed a clear decrease corresponding to 15‐year‐old shoots. The sexual reproductive event had positive effects on rhizome elongation (cm year?1) and leaf production (no. leaves year?1) in the same flowering year, whilst no effect on the rhizome production (mg year?1) was observed. Rhizome growth variables showed significant negative lagged responses in the two years following flowering. On the whole, we calculated that the effect exerted by flowering, in terms of loss on rhizome elongation and production, was about 27% and 38%, respectively. Although it has been demonstrated that recovery from the stress induced by sexual reproduction is limited to the two years after flowering, the magnitude of the reproductive cost may become quite considerable especially in comparison with the whole lifespan of individual shoots. 相似文献
199.
Dissolved and particulate samples were collected to study the distribution of thorium isotopes (234Th, 232Th and 230Th) in the water column of the Indian sector of the Southern Ocean (from 42°S to 47°S and from 60°E to 66°E, north of the Polar Front) during Austral summer 1999. Vertical profiles of excess 230Th (230Thxs) increases linearly with depth in surface water (0–100 m) and a model was applied to estimate a residence time relative to the thorium scavenging (τscav). Low τscav in the Polar Front Zone (PFZ) are found, compared to those estimated in the Subtropical Front Zone (STZ). Changes in particle composition between the PFZ and STZ could influence the 230Thxs scavenging efficiency and explain this difference. An innovative coupling between 234Th and 230Thxs was then used to simultaneously constrain the settling velocities of small (0.6–60 μm) and large (above 60 μm) particles. Although the different hydrological and biogeochemical regimes visited during the ANTARES IV cruise did not explain the spatial variation of sinking velocity estimates, our results indicate that less particles may reach the seafloor north (60 ± 2 m d− 1, station 8) than south of the Agulhas Return Current (119 ± 23 and 130 ± 5 m d− 1 at stations 3 and 7, respectively). This information is essential for understanding particle transport and by extension, carbon export. In the deep water column, the 230Thxs concentrations did not increase linearly with depth, probably due to lateral transport of North Atlantic Deep Water (NADW) from the Atlantic to the Indian sector, which renews the deep waters and decreases the 230Thxs concentrations. A specific 230Thxs transport model is applied in the deep water column and allows us to assess a “travel time” of NADW ranging from 2 to 15 years. 相似文献
200.
An optimization mathematical model of the pile forces for piled breasting dolphins in the open sea under various loading conditions is presented. The optimum layout with the well distributed pile forces and the least number of piles is achieved by the multiplier penalty function method. Several engineering cases have been calculated and compared with the result of the conventional design method. It is shown that the number of piles can be reduced at least by 10%—20% and the piles‘ bearing state is improved greatly. 相似文献