全文获取类型
收费全文 | 7502篇 |
免费 | 1761篇 |
国内免费 | 2636篇 |
专业分类
测绘学 | 1298篇 |
大气科学 | 1063篇 |
地球物理 | 1507篇 |
地质学 | 4818篇 |
海洋学 | 1326篇 |
天文学 | 157篇 |
综合类 | 688篇 |
自然地理 | 1042篇 |
出版年
2024年 | 62篇 |
2023年 | 172篇 |
2022年 | 413篇 |
2021年 | 528篇 |
2020年 | 413篇 |
2019年 | 492篇 |
2018年 | 482篇 |
2017年 | 433篇 |
2016年 | 431篇 |
2015年 | 531篇 |
2014年 | 489篇 |
2013年 | 580篇 |
2012年 | 696篇 |
2011年 | 663篇 |
2010年 | 656篇 |
2009年 | 640篇 |
2008年 | 649篇 |
2007年 | 582篇 |
2006年 | 565篇 |
2005年 | 448篇 |
2004年 | 360篇 |
2003年 | 287篇 |
2002年 | 337篇 |
2001年 | 309篇 |
2000年 | 250篇 |
1999年 | 142篇 |
1998年 | 71篇 |
1997年 | 38篇 |
1996年 | 38篇 |
1995年 | 24篇 |
1994年 | 18篇 |
1993年 | 16篇 |
1992年 | 11篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1979年 | 5篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1966年 | 2篇 |
1962年 | 1篇 |
1957年 | 5篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
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
92.
FANG Tao LI Daoji YU Lihua LI Yun 《中国地球化学学报》2008,27(2):161-170
We conducted ship-board incubation experiments to investigate changes in nutrient uptake of phytoplankton under different phosphate concentrations and irradiances in the Changjiang River Estuary and its adjacent waters in China. Under 100% natural irradiance the uptake rates of phosphate, silicate, and nitrate were accelerated at high phosphate levels (1.84 μM), while under low irradiance (about 50% natural irradiance) their uptake rates were restrained at the high but stimulated greatly at the intermediate phosphate concentrations (1.26 μM), as the growth of phytoplankton, changes in nitrite and ammonium uptake didn't follow an obvious pattern. Our results also showed that there were linear relationships between nitrate, silicate and phosphate uptake at different phosphate concentrations under low and high irradiances, and the growth period of phytoplankton was prolonged both at the high phosphate concentrations under high irradiance and at the intermediate concentrations under low irradiance, suggesting that the limitation of phytoplankton growth mainly reflected changes in its growth period, and because no such environment (low irradiance and low phosphate concentrations) actually existed in a high turbidity zone, phytoplankton blooms hardly occurred there. In the absence of irradiance, denitrification occurred readily and phytoplankton was kept decreasing, which resulted in phosphate regeneration. 相似文献
93.
Palygorskite is a typical indicator mineral of the arid and strong evaporation environment. Distribution of palygorskite in loess-red clay sequences may act as an important indicator for reconstruction of the paleoenvironment and paleoclimate. In this paper, field emission scanning electron microscope and high-resolution transmission electron microscope observations on the red clay-loess-paleosol of the Renjiapo profile at Lingtai, Gansu Province indicate that palygorskite occurs widely in red clay sequences formed before 3.6 Ma, but no occurrence has been found in eolian sediments since 3.2 Ma. Micromorphological features and microstructure of palygorskite show that it is an autogenic mineral formed during pedogenesis, and transformed from iilite-montmorilionite under the pore water action. In the Lingtai profile, the disappearance horizon of palygorskite is consistent with those of increasing magnetic susceptibility, dust flux and depositional rate. The distribution of palygorskite in the profile indicates that the interval of around 3.6 Ma was an important transformation period of the East Asian paleomonsoon, when changes took place in the East Asia paleoclimate pattern, i.e. a high-frequency strong fluctuation alternative evolution of the environment. Therefore, palygorskite is a key indicator mineral of the East Asian paleomonsoon evolution of that time. 相似文献
94.
95.
96.
97.
98.
99.
100.
基于倒频谱的运动模糊图像PSF参数估计 总被引:7,自引:0,他引:7
针对任意方向的直线运动模糊图像,说明只能直接在运动方向上得到运动参数,从而设置二维点扩展函数(point spread function,PSF).在此基础上,应用倒频谱分析法给出了PSF参数估计的方法.实验表明,该方法在模糊为任意方向且模糊范围介于5~55像素时对参数的估计误差较小,能保证较好的恢复质量;当模糊范围超出该范围时,估计误差急剧加大,估计值不可信,无法保证恢复质量. 相似文献