全文获取类型
收费全文 | 18039篇 |
免费 | 4685篇 |
国内免费 | 5149篇 |
专业分类
测绘学 | 2080篇 |
大气科学 | 2655篇 |
地球物理 | 5205篇 |
地质学 | 10875篇 |
海洋学 | 2507篇 |
天文学 | 787篇 |
综合类 | 1507篇 |
自然地理 | 2257篇 |
出版年
2024年 | 99篇 |
2023年 | 293篇 |
2022年 | 863篇 |
2021年 | 1024篇 |
2020年 | 832篇 |
2019年 | 1209篇 |
2018年 | 1146篇 |
2017年 | 1146篇 |
2016年 | 1282篇 |
2015年 | 1252篇 |
2014年 | 1342篇 |
2013年 | 1552篇 |
2012年 | 1466篇 |
2011年 | 1488篇 |
2010年 | 1426篇 |
2009年 | 1316篇 |
2008年 | 1275篇 |
2007年 | 1295篇 |
2006年 | 1065篇 |
2005年 | 904篇 |
2004年 | 748篇 |
2003年 | 593篇 |
2002年 | 664篇 |
2001年 | 671篇 |
2000年 | 558篇 |
1999年 | 396篇 |
1998年 | 297篇 |
1997年 | 263篇 |
1996年 | 217篇 |
1995年 | 189篇 |
1994年 | 177篇 |
1993年 | 152篇 |
1992年 | 148篇 |
1991年 | 101篇 |
1990年 | 85篇 |
1989年 | 67篇 |
1988年 | 61篇 |
1987年 | 38篇 |
1986年 | 26篇 |
1985年 | 23篇 |
1984年 | 24篇 |
1983年 | 20篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 5篇 |
1979年 | 9篇 |
1978年 | 5篇 |
1958年 | 8篇 |
1957年 | 4篇 |
1954年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
81.
82.
83.
研究了风浪频谱JONSWAP谱的峰度因子γ、尖度因子Pj和N谱尖度因子PN,参变量p,q间的关系;并在此关系上给出了由这两种谱计算的几个对应参量间的关系,在使用不同的谱形进行特征量的计算时,应注意不同频谱间的成长因子致性,以免引起计算结果的错误。 相似文献
84.
继“西沙、中沙群岛附近海域浮游硅藻类分类的研究”之后,作者又对西沙群岛所属岛、礁附近海域的羽纹硅藻进行了初步整理,共鉴定出羽纹硅藻11属27种及其变种(其中8种是我国首次记录)。本文对首次记录的种类进行了比较详细的说明和绘图。某些在我国其他海域已有报道的种类,如光辉针杆藻、串珠梯楔形藻、海生斑条藻、琴状舟形藻、流苏胸隔藻、双标胸隔藻、钝端双眉藻、细纹斜盘藻等,以往的描述较简单,并且与西沙群岛标本的形态也不完全雷同,为了便于应用和比较,本文根据西沙群岛的标本,又进行了较详细的描述或补充说明。对有图而无说明,或仅有名录的种类的国内资料,在地理分布内注明。为了保持西沙群岛所属海城硅藻分类研究的连续性,本文仍采用 Hendey 提出的分类系统排列。
为便于读者査找,每一种名下列出其同物异名。
标本多用小型浮游生物网采得,有些则取自珊瑚表面。插图均用描图仪描绘。 相似文献
85.
A one-dimentional three-layer model for the thermal structure in the Huanghai Sea is presented in this study, me model consists of the upper mixed layer caused by heating and wind mixing, the lower mixed layer driven by tidal mixing, and the thermocline with certain thickness. The entrainment velocities of the upper and lower layers are obtained respectively. The results show that the model is capable of describing the development and decline processes of the seasonal thermocline in the Huanghai Sea, simulating successfully the Huanghai Sea Cold Water Mass, the nearshore front and surface cold water off North Jiangsu and explaining reasonably their formation mechanisms as well as the strong thermocline off Qingdao. It is suggested that the tidal mixing plays key role in the formation of the nearshore front off North Jiangsu and the strong thermocline off Qingdao. The wind mixing and the tidal mixing make the lower layer water with high nutrients go up to the upper layer. This physical process may be sig 相似文献
86.
Wen Shengchang 《海洋学报(英文版)》1988,7(3):325-343
The method developed by Wen et al. (1988 a) for deriving theoretical wind wave frequency spectrum in deep water is extended to the case of water of finite depth, in which a parameter η=H/d is introduced, where H and d represent the average wave height and water depth respectively. The derived spectra reduce to those in deep water when η=0. The case of η=1/2 corresponds to waves impending to break because of the effect of the bottom. Simplified forms of spectra are given. The theoretical results agree with the observed spectra well. 相似文献
87.
Sea ice characteristics between the middle Weddell Sea and the Prydz Bay, Antarctica during the austral summer of 2003 总被引:1,自引:0,他引:1
The antarctic sea ice was investigated upon five occasions between January 4 and February 15, 2003. The investigations included: (1) estimation of sea ice distribution by ship-based observations between the middle Weddell Sea and the Prydz Bay; (2) estimation of sea ice distribution by aerial photography in the Prydz Bay; (3) direct measurements of fast ice thickness and snow cover, as well as ice core sampling in Nella Fjord; (4) estimation of melting sea ice distribution near the Zhongshan Station; and (5) observation of sea ice early freeze near the Zhongshan Station. On average, sea ice covered 14.4% of the study area. The highest sea ice concentration (80%) was observed in the Weddell Sea. First-year ice was dominant (99.7%-99.8%). Sea ice distributions in the Prydz Bay were more variable due to complex inshore topography, proximity of the Larsemann Hills, and/or grounded icebergs. The average thickness of landfast ice in NeUa Fjord was 169.5 cm. Wind-blown snow redistribution plays an important role in affecting the ice thickness in Nella Fjord. Preliminary freezing of sea ice near the Zhongshan Station follows the first two phases of the pancake cycle. 相似文献
88.
阐明了东山湾重矿物组合规律,物质来源,自生黄铁矿的富集与形成环境。研究表明,湾内重矿物含量<1%,来自漳江及周边水系。东山湾西部的沉积环境有利于自生黄铁矿的形成。 相似文献
89.
在流星分析和t-S点聚分析的基础上,在台湾东北部IS断面和东海中部PN断面上选取适当的纵剖面作为分界面,将以面分成东、西两侧,计算了界面两侧的海水交换星。结果表明:1.东海陆架区海水交换可归纳为两种类型,即“穿插型”和“进退型”。2.参与分界面处海水交换总量的年平均是夏季最大,春、秋季次之,冬季最小。黑潮水向陆架区输运量为0.58×106m3/s,陆架水向黑潮刚输运量为0.84×106m3/s;参与交换的总量为1.42×106m3/s.3.相对输运量计算结果表明;黑潮水对陆架区水文状况的影响是冬季最强,秋、春季次之,夏季最弱,而陆架水对黑潮区水文状况的影响是夏季最大,秋季次之,春季和冬季最小。 相似文献
90.
A vertical two-dimensional turbulence numerical model for the interaction of waves and currents is developed in the paper based on the nonlinear two-equation k-ε model with the VOF method.The one-dimensional equivalent advection velocity and equivalent mixing coefficient are defined and the solving process is introduced:The pollutant concentration field,generated by an instant source in waves and currents,is calculated with the model,and then the equivalent advection velocity and equivalent mixing coefficient are obtained by calculating the time derivative of the mean and variance of pollutant concentration probability distribution.The effects of wave period and wave height on the equivalent mixing coefficient for waves and wave-currents are also investigated. 相似文献