全文获取类型
收费全文 | 23964篇 |
免费 | 4278篇 |
国内免费 | 6357篇 |
专业分类
测绘学 | 4518篇 |
大气科学 | 4667篇 |
地球物理 | 5697篇 |
地质学 | 10596篇 |
海洋学 | 3481篇 |
天文学 | 231篇 |
综合类 | 1940篇 |
自然地理 | 3469篇 |
出版年
2024年 | 158篇 |
2023年 | 422篇 |
2022年 | 881篇 |
2021年 | 1054篇 |
2020年 | 1215篇 |
2019年 | 1334篇 |
2018年 | 1118篇 |
2017年 | 1282篇 |
2016年 | 1407篇 |
2015年 | 1505篇 |
2014年 | 1581篇 |
2013年 | 1794篇 |
2012年 | 1643篇 |
2011年 | 1659篇 |
2010年 | 1347篇 |
2009年 | 1502篇 |
2008年 | 1509篇 |
2007年 | 1566篇 |
2006年 | 1487篇 |
2005年 | 1317篇 |
2004年 | 1167篇 |
2003年 | 1000篇 |
2002年 | 939篇 |
2001年 | 781篇 |
2000年 | 728篇 |
1999年 | 649篇 |
1998年 | 602篇 |
1997年 | 523篇 |
1996年 | 462篇 |
1995年 | 426篇 |
1994年 | 380篇 |
1993年 | 319篇 |
1992年 | 192篇 |
1991年 | 173篇 |
1990年 | 113篇 |
1989年 | 85篇 |
1988年 | 88篇 |
1987年 | 58篇 |
1986年 | 27篇 |
1985年 | 29篇 |
1984年 | 15篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1972年 | 1篇 |
1954年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Several large deployments of neutrally buoyant floats took place within the Antarctic Intermediate (AAIW), North Atlantic Deep Water (NADW), and the Antarctic Bottom Water (AABW) of the South Atlantic in the 1990s and a number of hydrographic sections were occupied as well. Here we use the spatially and temporally averaged velocities measured by these floats, combined with the hydrographic section data and various estimates of regional current transports from moored current meter arrays, to determine the circulation of the three major subthermocline water masses in a zonal strip across the South Atlantic between the latitudes of 19°S and 30°S. We concentrate on this region because the historical literature suggests that it is where the Deep Western Boundary Current containing NADW bifurcates. In support of this notion, we find that a net of about 5 Sv. of the 15–20 Sv that crosses 19°S does continue zonally eastward at least as far as the Mid-Atlantic Ridge. Once across the ridge it takes a circuit to the north along the ridge flanks before returning to the south in the eastern half of the Angola Basin. The data suggest that the NADW then continues on into the Indian Ocean. This scheme is discussed in the context of distributions of dissolved oxygen, silicate and salinity. In spite of the many float-years of data that were collected in the region a surprising result is that their impact on the computed solutions is quite modest. Although the focus is on the NADW we also discuss the circulation for the AAIW and AABW layers. 相似文献
132.
An Ecosystem Model Coupled with Nitrogen-Silicon-Carbon Cycles Applied to Station A7 in the Northwestern Pacific 总被引:1,自引:0,他引:1
Yasuhiro Yamanaka Naoki Yoshie Masahiko Fujii Maki N. Aita Michio J. Kishi 《Journal of Oceanography》2004,60(2):227-241
A model based on that of Kishi et al. (2001) has been extended to 15 compartments including silicon and carbon cycles. This model was applied to Station A7 off
Hokkaido, Japan, in the Northwestern Pacific. The model successfully simulated the observations of: 1. a spring bloom of diatoms;
2. large seasonal variations of nitrate and silicate concentrations in the surface water; and 3. large inter-annual variations
in chlorophyll-a. It also reproduced the observed features of the seasonal variations of carbon dioxide partial pressure (pCO2)—a peak in pCO2 in winter resulting from deep winter convection, a rapid decrease in pCO2 as a result of the spring bloom, and an almost constant pCO2 from summer through fall (when the effect of increasing temperature cancels the effect of biological production). A comparison
of cases with and without silicate limitation shows that including silicate limitation in the model results in: 1. decreased
production by diatoms during summer; and 2. a transition in the dominant phytoplankton species, from diatoms to other species
that do not take up silicate. Both of these phenomena are observed at Station A7, and our results support the hypothesis that
they are caused by silicate limitation of diatom growth.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
133.
134.
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
135.
136.
137.
砂质海岸岸滩侵蚀演变模式探讨——以山东南部海岸侵蚀岸段的岸滩演变为例 总被引:5,自引:0,他引:5
在分析山东南部海岸几十年来的地形观测资料的基础上,运用砂质海岸等深线变化预测理论,建立该区的岸滩侵蚀演变预测模型,研究了该区域岸滩演变规律。实测资料验证表明:预测结果合理,基本反映了本区岸滩演变的特征。 相似文献
138.
139.
140.
波浪作用下海床的有效应力分析 总被引:4,自引:0,他引:4
波浪作用下海床的稳定性分析是海洋工程地质评价的重要内容。海床的稳定性可通过计算分析其随时间变化的有效应力场来评估。本文建议了一个周期荷载作用下土体的本构模型 ,并用于计算波浪作用下海床的应力与变形。采用Biot固结理论和有限单元法 ,分析了海床的动态应力场与孔隙水压力场。波浪作用下两种渗透系数时有效应力的动态变化过程结果对比 ,反映了渗透消散作用对海床有效应力变化的影响 相似文献