全文获取类型
收费全文 | 5871篇 |
免费 | 1219篇 |
国内免费 | 1588篇 |
专业分类
测绘学 | 327篇 |
大气科学 | 1961篇 |
地球物理 | 1456篇 |
地质学 | 2803篇 |
海洋学 | 947篇 |
天文学 | 408篇 |
综合类 | 290篇 |
自然地理 | 486篇 |
出版年
2024年 | 19篇 |
2023年 | 40篇 |
2022年 | 150篇 |
2021年 | 174篇 |
2020年 | 196篇 |
2019年 | 250篇 |
2018年 | 187篇 |
2017年 | 239篇 |
2016年 | 222篇 |
2015年 | 272篇 |
2014年 | 329篇 |
2013年 | 343篇 |
2012年 | 291篇 |
2011年 | 354篇 |
2010年 | 328篇 |
2009年 | 458篇 |
2008年 | 445篇 |
2007年 | 493篇 |
2006年 | 438篇 |
2005年 | 422篇 |
2004年 | 364篇 |
2003年 | 298篇 |
2002年 | 293篇 |
2001年 | 231篇 |
2000年 | 241篇 |
1999年 | 226篇 |
1998年 | 200篇 |
1997年 | 187篇 |
1996年 | 201篇 |
1995年 | 129篇 |
1994年 | 151篇 |
1993年 | 111篇 |
1992年 | 101篇 |
1991年 | 86篇 |
1990年 | 51篇 |
1989年 | 33篇 |
1988年 | 46篇 |
1987年 | 21篇 |
1986年 | 10篇 |
1985年 | 9篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 15篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1971年 | 1篇 |
排序方式: 共有8678条查询结果,搜索用时 718 毫秒
51.
A surface panel method treating a boundary-value problem of the Dirichlet type with the free surface is presented to design a three-dimensional body corresponding to a prescribed pressure distribution. The free surface boundary condition is linearized with respect to the oncoming flow, and computed by four-point finite difference scheme. Sample designs for submerged spheroids and Wigley hull are carried out to demonstrate the stable convergence, the effectiveness and the robustness of the method. The design of a 5500TEU container carrier is performed with respect to reduction of the wave resistance. To reduce the wave resistance, calculated pressure on the hull surface is modified to have the lower fluctuation, and is applied as a Dirichlet type dynamic boundary condition on the hull surface. The designed hull form is verified to have the lower wave resistance than the initial one not only by computation but also by experiment. 相似文献
52.
53.
本文根据CTD观测资料,分析了研究海区的温、盐、密度跃层的分布与变化,讨论了逆温逆盐层的分布区域,并从跃层角度出发,分析了深层水的涌升,黄海冷水团的上边界以及台湾暖流在东海北部的影响范围。 相似文献
54.
张若君 《中国海洋大学学报(自然科学版)》2002,32(5):848-852
本文考虑四阶奇异边值问题x( 4 ) =λa(t) f (t,x(t) ) ,0 相似文献
55.
Temperature data at different layers of the past 45 years were studied and we found adiploe mode in the thermocline layer (DMT): anomalously cold sea temperature off the coast of Sumatra and warm sea temperature in the western Indian Ocean. First, we analyzed the temperature and the temperature anomaly (TA) along the equatorial Indian Ocean in different layers. This shows that stronger cold and warm TA signals appeared at subsurface than at the surface in the tropical Indian O-cean. This result shows that there may be a strong dipole mode pattern in the subsurface tropical Indian Ocean. Secondly we used Empirical Orthogonal Functions (EOF) to analyze the TA at thermocline layer. The first EOF pattern was a dipole mode pattern. Finally we analyzed the correlations between DMT and surface tropical dipole mode (SDM), DMT and Nino 3 SSTA, etc. and these correlations are strong. 相似文献
56.
The effect of the cone spacing of a conieal structure on the ice force is studied by model experiments. The ice force reduction coefficient presented in this paper expresses the relationship between the ice force and the arrangement of cones. The experiments prove that the mode of the ice failure before the boundary of upward-downward bending cone (UDBC) is crushing. A conclusion can also be drawn from the experiments that the ice force on the boundary of UDBC is by far less than that on a vertical pile with the same diameter. Moreover, the ice force frequencies on upright and inve-rted cones are obtained under the field condition of the platform JZ20-2, respectively. The results show that the alterna-tion of the ice force on UDBC can hardly induce resonance of platform JZ20-2. 相似文献
57.
利用TRMM资料对热带气旋“威马逊”结构及其降水特征的研究 总被引:6,自引:2,他引:6
利用NASA提供的热带测雨卫星(TRMM)资料和NCEP/AVN模式的实况分析场研究了热带气旋“威马逊”(2002)的演变过程、结构和降水特征.对要素场及倾斜对流有效位能诊断分析发现,降水的分布和强度对热带气旋的发展有很好的指示作用.针对MM5的几种积云参数化方案进行了数值试验,初步研究了各方案在热带气旋定量降水预报(QPF)中的作用. 相似文献
58.
A study of sea surface wave propagation and its energy deformation was carried out using field observations and numerical experiments over a region spanning the midshelf of the South Atlantic Bight (SAB) to the Altamaha River Estuary, GA. Wave heights on the shelf region correlate with the wind observations and directional observations show that most of the wave energy is incident from the easterly direction. Comparing midshelf and inner shelf wave heights during a time when there was no wind and hence no wave development led to an estimation of wave energy dissipation due to bottom friction with corresponding wave dissipation factor of 0.07 for the gently sloping continental shelf of the SAB. After interacting with the shoaling region of the Altamaha River, the wave energy within the estuary becomes periodic in time showing wave energy during flood to high water phase of the tide and very little wave energy during ebb to low water. This periodic modulation inside the estuary is a direct result of enhanced depth and current-induced wave breaking that occurs at the ebb shoaling region surrounding the Altamaha River mouth at longitude 81.23°W. Modelling results with STWAVE showed that depth-induced wave breaking is more important during the low water phase of the tide than current-induced wave breaking during the ebb phase of the tide. During the flood to high water phase of the tide, wave energy propagates into the estuary. Measurements of the significant wave height within the estuary showed a maximum wave height difference of 0.4 m between the slack high water (SHW) and slack low water (SLW). In this shallow environment these wave–current interactions lead to an apparent bottom roughness that is increased from typical hydraulic roughness values, leading to an enhanced bottom friction coefficient. 相似文献
59.
60.
1 .IntroductionUnder the influence of surface waves ,sandripples often appear on beaches . Whenthe amplitudeof water oscillationis sufficientlylarge ,vortices are formed onthe lee of every sand ripple crest . A-mongthese vortices ,the most important are t… 相似文献