全文获取类型
收费全文 | 6819篇 |
免费 | 1614篇 |
国内免费 | 2570篇 |
专业分类
测绘学 | 248篇 |
大气科学 | 1421篇 |
地球物理 | 2172篇 |
地质学 | 4579篇 |
海洋学 | 809篇 |
天文学 | 253篇 |
综合类 | 803篇 |
自然地理 | 718篇 |
出版年
2024年 | 17篇 |
2023年 | 67篇 |
2022年 | 198篇 |
2021年 | 254篇 |
2020年 | 166篇 |
2019年 | 249篇 |
2018年 | 280篇 |
2017年 | 239篇 |
2016年 | 287篇 |
2015年 | 247篇 |
2014年 | 325篇 |
2013年 | 279篇 |
2012年 | 299篇 |
2011年 | 504篇 |
2010年 | 419篇 |
2009年 | 452篇 |
2008年 | 323篇 |
2007年 | 384篇 |
2006年 | 474篇 |
2005年 | 475篇 |
2004年 | 728篇 |
2003年 | 555篇 |
2002年 | 446篇 |
2001年 | 356篇 |
2000年 | 292篇 |
1999年 | 298篇 |
1998年 | 313篇 |
1997年 | 323篇 |
1996年 | 234篇 |
1995年 | 223篇 |
1994年 | 182篇 |
1993年 | 292篇 |
1992年 | 269篇 |
1991年 | 137篇 |
1990年 | 61篇 |
1989年 | 94篇 |
1988年 | 50篇 |
1987年 | 79篇 |
1986年 | 44篇 |
1985年 | 12篇 |
1984年 | 14篇 |
1983年 | 8篇 |
1982年 | 12篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1976年 | 3篇 |
1958年 | 4篇 |
1937年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
上元-坑园牡蛎礁位于高潮位以下3m,主要成分为长牡蛎和近江牡蛎,其~(14)C年龄为3043±82a,B.P.。据此推算出罗源湾一带海岸处于缓慢上升状态,速率为1.15mm/a。根据上元-坑园牡蛎礁的上述特征,并结合断块差异升降运动的表现,作者认为这一地区中、晚全新世以来以“陆动型”海平面变化占主导地位。 相似文献
92.
93.
Total of 33 species of dinoflagellate cysts were discovered from surface sediment in the searegion of Guangxi, among them 12 cyst types (Diplopsalopsis sp.1, D. sp. 2, D. sp. 3, Cochlodinium sp., Protoperidinium sp. 1, P. sp. 2, P. compressum , Scrippsiella sp. 1, S. sp. 2, Alexandrium sp. 1, A. sp. 2, A. sp. 3) were first reported from the South China Sea. And one cyst type (Cochlodinium sp.) was first reported in the world. Scrippsiella trochoidea is the dominant species in this area, accounting for 45% of all the cysts. There are 2 cysts of toxic dinoflagellate (Alexandrium tamarensis and Gymnodinium catenatum). But there is no relationship between cyst number and grain size distribution. 相似文献
94.
Yang Zhengji Zuo Qihua
Senior Engineer River Harbour Department Nanjing Hydraulic Research Institute Nanjing Engineer River Harbour Department Nanjing Hydraulic Research Institute Nanjing 《中国海洋工程》1991,(2)
The wave forces on 1, 2 and 4 vertical circular piles under the action of several wave trains of the same wave parameters, such as Hs,Tp and Mo, but different wave group factor GF are measured in the laboratory. After comparing these forces, it may be concluded that the mean and significant wave forces are almost of no difference for the wave trains with different GF. When GF is larger, the one-tenth of the wave froce extreme is slightly increased and the maximum wave force is much larger than the ones with smaller GF, to which attention must be paid in engineering practice. 相似文献
95.
The phase one project of the twin jetties at the Tao-er Estuary yields no effect on the flow, and there is a large area of deposition. A numerical model is employed to simulate the flow field, and the scouring and silting in the channel be-tween the two jetties are analyzed. The results show that the effective tidal flux between the two jetties is reduced due to the notch located at the heel of the east jetty, and the effect of contraction-flush is not obvious. As for the regulation of this kind of estuary under the tide action, the capability of tidal flux should be fully used. 相似文献
96.
作者使用 NCEP/ NCAR再分析资料 ,在热带 30°S~ 30°N纬带用谐波分析方法分离出超长波之后 ,再采用环流诊断方法 ,发现南海季风区存在地域性环流系统。文中给出冬、夏季风期该系统的三维空间结构和相应的热源分布 ,讨论了该地域性环流系统对南海季风气候及其异常的作用 ,并探讨夏季风爆发北部先于南部的一种可能的气候原因。 相似文献
97.
In this paper, the characteristics of different forms of mild slope equations for non-linear wave are analyzed, and new non-linear theoretic models for wave propagation are presented, with non-linear terms added to the mild slope equations for non-stationary linear waves and dissipative effects considered. Numerical simulation models are developed of non-linear wave propagation for waters of mildly varying topography with complicated boundary, and the effects are studied of different non-linear corrections on calculation results of extended mild slope equations. Systematical numerical simulation tests show that the present models can effectively reflect non-linear effects. 相似文献
98.
99.
Benthic nutrient fluxes in the intertidal flat within the Changjiang (Yangtze River) Estuary 总被引:1,自引:0,他引:1
GAO Lei LI Daoji WANG Yanming YU Lihua KONG Dingjiang LI Mei LI Yun and FANG Tao State Key Laboratory of Marine Geology Tongji University Shanghai China State Key Laboratory of Estuarine Coastal Research East China Normal University Shanghai China 《中国地球化学学报》2008,27(1):58-71
In an annual cycle from March 2005 to February 2006, benthic nutrient fluxes were measured monthly in the Dongtan intertidal flat within the Changjiang (Yangtze River) Estuary. Except for NH4^+, there always showed high fluxes from overlying water into sediment for other four nutrients. Sediments in the high and middle marshes, covered with halophyte and consisting of macrofauna, demonstrated more capabilities of assimilating nutrients from overlying water than the low marsh. Sampling seasons and nutrient concentrations in the overlying water could both exert significant effects on these fluxes. Additionally, according to the model provided by previous study, denitrification rates, that utilizing NO3- transported from overlying water (Dw) in Dongtan sediments, were estimated to be from -16 to 193 μmol·h^-1·m^-2 with an average value of 63 μmol·h^-1·m^-2 (n=18). These estimated values are still underestimates of the in-situ rates owing to the lack of consideration of DN, i.e., denitrification supported by the local NO3^- production via nitrification. 相似文献
100.