全文获取类型
收费全文 | 574篇 |
免费 | 61篇 |
国内免费 | 142篇 |
专业分类
测绘学 | 16篇 |
大气科学 | 47篇 |
地球物理 | 91篇 |
地质学 | 90篇 |
海洋学 | 361篇 |
综合类 | 97篇 |
自然地理 | 75篇 |
出版年
2024年 | 6篇 |
2023年 | 20篇 |
2022年 | 30篇 |
2021年 | 15篇 |
2020年 | 20篇 |
2019年 | 20篇 |
2018年 | 13篇 |
2017年 | 6篇 |
2016年 | 21篇 |
2015年 | 19篇 |
2014年 | 27篇 |
2013年 | 22篇 |
2012年 | 19篇 |
2011年 | 26篇 |
2010年 | 27篇 |
2009年 | 30篇 |
2008年 | 41篇 |
2007年 | 32篇 |
2006年 | 43篇 |
2005年 | 55篇 |
2004年 | 44篇 |
2003年 | 30篇 |
2002年 | 25篇 |
2001年 | 36篇 |
2000年 | 23篇 |
1999年 | 22篇 |
1998年 | 16篇 |
1997年 | 14篇 |
1996年 | 16篇 |
1995年 | 9篇 |
1994年 | 18篇 |
1993年 | 8篇 |
1992年 | 7篇 |
1991年 | 2篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有777条查询结果,搜索用时 15 毫秒
21.
眼斑拟石首鱼的营养需求及环境因子对生长的影响 总被引:3,自引:1,他引:3
综述发眼斑拟石首鱼对饵料营养的需求量,以及环境因子如水浊,盐度,溶解氧,氮化物,总硬度,氯化物等对其生长,生存的影响。 相似文献
22.
23.
Yuchun WANG Jun ZHU Congqiang LIU 《中国地球化学学报》2006,25(B08):161-162
Damming is a common anthropogenic intervention along the course of rivers, which is defined as "artificial-lake effect", both in China and across the world. Today as many as 48000 dams and/or reservoirs are in operation in the Changjiang River (Yangtze River) drainage area, and more are being constructed. While damming is well known to affect riverbome nutrient loads, and thus the riverine ecosystems owing to removal of carbon fixation, and removal of particles in reservoir sediments, there is limited information on the detailed early diagenesis of sediments in reservoirs including the regeneration processes of nutrients deposited in sediments and exchange flux across the sediment-water interface, which is important for mass balance of riverbome nutrients. In the present study, two large-size reservoirs, Wujiangdu Reservoir (WJDR) and Dongfeng Reservoir (DFR), located on the main steam of the Wujiang River and with uniformity hydrography and discrepancy biogeochemical activity (e. g. primary production), were selected for a comparative study on the detailed processes of nutrient regeneration. Water, pore water and sediment were sampled from these two reservoirs and dissolved organic carbon (DOC), NH4^+, NO3^-, PO4^3-, dissolved silica (DSi) in the overlying water and pore water, and total organic matter in sediments were determined. The results of correlation analysis suggested that in these two reservoirs, processes of nutrient regeneration near the sediment-water interface were significantly different. As a result of rapid decomposition of algae-derived "labile" organic matter in upper sediments, nutrient regeneration processes and upward fluxes in WJDR are dramatically stronger than those of DFR. NH4^+ upward flux from sediment in WJDR was about 17 times higher than that in DFR. PO4^3- flux in WJDR is about 13 times above that in DFR. DOC flux in WJDR is larger that in DFR by 5 times, and DSi by 1 time. 相似文献
24.
Weihong WANG Min JI Yuwei XUE 《中国地球化学学报》2006,25(B08):167-168
In recent years, reclaimed wastewater as a water source for urban artificial landscape rivers is being rapidly developed in some coastal cities with limited water resource available in China. However, eutrophication occurs more often in the landscape waterbody with reclaimed wastewater than in natural rivers and lakes. The study of restoration and reconstruction of macrophytes, especially the submerged aquatic vegetation, is essential to inhibit eutrophication of reclaimed wastewater. This study investigated the seasonal variation of biomass of Ruppia maritima in the artificial landscape river using reclaimed wastewater as the only water source in Tianjin, China. It was found that there were two seasonal growth peaks of Ruppia maritima each year in the coastal reclaimedwastewater. The contents of nitrogen and phosphorus of Ruppia maritima varied with the season. 相似文献
25.
26.
27.
两个相连湖泊的微生态系统——云南高原湖泊中浅水的星云湖和深水的抚仙湖研究 总被引:4,自引:0,他引:4
抚仙湖是中国云南省的一个深水湖,连接着富营养化的浅水湖--星云湖,星云湖排放含绿藻的水进入抚仙湖。两湖位于省会昆明附近,由于地方文化、集约化农业、以及旅游业的发展,两湖已经富营养化。因为湖泊体积容量的级别差异,深水湖的富营养化几乎没被注意,抚仙湖秋季下层滞水带缺氧已经关注了20年,似乎下层滞水带是深水湖富营养化的指标或趋势。抚仙湖看起来目前情况尚好,可以说寡营养,然而,外界负荷是潜在的,且是以稳定的加速度进行的。在此对浅水湖富营养化的原因进行了讨论,包括在其它云南湖泊观察到富营养化的过程,再者,对两个连相湖的藻和蓝藻碎片的大小构成进行比照。为了与深水的抚仙湖状况进行比较,简略介绍了一个日本的深湖及其径流系统。其中,涡流和它的微生态系统,在两者中相关性很好。对于以涡流生态系统的见解判断微生态系统的深水湖富营养化问题将给予概括。 相似文献
28.
泥炭藓是贫营养泥炭类型中的建群植物,由于生态水环境主要靠大气降水补给,少受其他水源的污染,可自然反映古降水、古湿度的情况,所以是古气候研究最理想的纤维素同位素测试材料之一。因此,弄清我国贫营养泥炭沉积的物质组成及水化学环境特征,具有重要意义。笔根据多年来的国内外野外调查,结合收集到的资料,以东北大小兴安岭山地的泥炭辞贫营养泥炭地为基础,与美国、加拿大以及俄罗斯等国家的同类泥炭地相比较,对我国贫营养泥炭沉积的物质组成、理化特性及水化学环境做了系统的分析研究,并就此讨论了湿地保护中的一些实际问题,以及相应的对策。 相似文献
29.
Multi-parameter studies (stable isotopes in carbonate and organic matter, pigment,organic carbon and nitrogen contents) from a 660-yr continuous sediment core from Lake Cheng-hai, a closed, eutropic lake in southern China, provide information on lake historical eutrophi-cation. During the last 660 years, great changes have taken place in productivity and eutrophi-cation of Lake Chenghai in response to human activities. In 1690, the productivity of the lakebegan to increase as Lake Chenghai became closed from agriculture in the lake‘‘ s watershed. In 1942, Lake Chenghai evolved to eutrophic state, marked by an increase in organic carbon, ni-trogen, CaC03, pigment contents and obvious negative values of stable isotopes, which is more or less simultaneous with the large-scale population immigration during the period. In 1984, in-tensive human activities induced modern lacustrine productivity and eutrophic level. Human-in-duced trophic changes during the past few decades have affected the Lake Chenghai ecosystem tosuch an extent that it has never experienced before in the last 660 years. 相似文献
30.