全文获取类型
收费全文 | 1691篇 |
免费 | 319篇 |
国内免费 | 366篇 |
专业分类
测绘学 | 89篇 |
大气科学 | 334篇 |
地球物理 | 457篇 |
地质学 | 789篇 |
海洋学 | 243篇 |
天文学 | 83篇 |
综合类 | 163篇 |
自然地理 | 218篇 |
出版年
2024年 | 11篇 |
2023年 | 33篇 |
2022年 | 94篇 |
2021年 | 108篇 |
2020年 | 99篇 |
2019年 | 95篇 |
2018年 | 95篇 |
2017年 | 112篇 |
2016年 | 122篇 |
2015年 | 101篇 |
2014年 | 113篇 |
2013年 | 120篇 |
2012年 | 100篇 |
2011年 | 123篇 |
2010年 | 82篇 |
2009年 | 105篇 |
2008年 | 91篇 |
2007年 | 85篇 |
2006年 | 74篇 |
2005年 | 56篇 |
2004年 | 42篇 |
2003年 | 47篇 |
2002年 | 39篇 |
2001年 | 36篇 |
2000年 | 32篇 |
1999年 | 63篇 |
1998年 | 43篇 |
1997年 | 51篇 |
1996年 | 25篇 |
1995年 | 26篇 |
1994年 | 24篇 |
1993年 | 20篇 |
1992年 | 29篇 |
1991年 | 21篇 |
1990年 | 11篇 |
1989年 | 13篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 7篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1971年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有2376条查询结果,搜索用时 265 毫秒
151.
152.
晋豫间黄河峡谷黄土状沙丘的光释光年代学探讨 总被引:6,自引:6,他引:0
通过对风陵渡-三门峡晋豫间黄河峡谷的地貌考察和1:50000 地形图(1970年)的分析,初步查明了黄河南岸黄土状沙丘的分布特征.选取河南省灵宝市豫灵镇阌底约75m高的黄土状沙丘剖面进行了观测和取样.根据该剖面的粒度分布特点,选取中颗粒(40~90μm)石英进行了光释光(OSL)测年研究.采用简化SAR法测量样品的等效剂量(De),其中5个样品与SAR法测量的De值对比,结果在误差范围内一致.对阌底剖面自上而下19个样品运用简化SAR法做了OSL年龄测定,其中8个还进行了4~11μm细颗粒石英简易多测片再生法(SMAR)OSL测年,两个粒级石英的OSL年龄测定值在测量误差范围内一致.初步结果表明,晋豫间黄河峡谷阌底黄土状沙丘发育不晚于距今约5.5万年前,并延续到全新世初期,风沙堆积速率在3.2万年前后曾出现显著变化. 相似文献
153.
154.
Hongyuan Wang Zhenyao Shen Xuejun Guo Junfeng Niu Bin Kang 《Environmental Earth Sciences》2010,60(8):1653-1660
The influences of suspended particles (SPs) on NH4
+ adsorption and nitritation occurring in the water system of the Three Gorges Reservoir (TGR) were evaluated in this study.
The results indicated that the adsorption of NH4
+ was significantly affected by the SPs concentration under the conditions typically present in the TGR. The amount of ammonia
adsorbed per unit weight of suspended particles was inverse proportional to the concentration of suspended particles. However,
the influences of the particle size and the organic matter concentration existing in SPs were insignificant under the experimental
conditions. The effects of suspended particles on nitritation were determined by the use of ammonia-oxidizing bacteria (AOB)
strain SW16, identified as Nitrosomonas nitrosa, which was isolated from sediment samples of the TGR. Suspended particle concentration in water–sediment solution played
an important role in the nitritation process. The rate of nitritation enhanced with the increase of the suspended particle
concentration. It was found that the critical factor controlling ammonia oxidizing rate was the AOB biomass resulting from
the AOB growth rate. Moreover, results demonstrated that both particle size and organic matter content showed little effect
on the nitritation process under the experimental conditions. 相似文献
155.
Baohong Chen Kaiwen Zhou Kang Wang Jigang Wang Sumin Wang Xiuwu Sun Jinmin Chen Cai Lin Hui Lin 《海洋学报(英文版)》2022,41(1):1-2
This research investigated eight stations in Clarion-Clipperton Fracture Zone(CCFZ) in the eastern tropical Pacific in 2017 to study the spatial distribution characteristics of nutrients and chlorophyll a(Chl a) concentration,and compared nutrient concentrations and molar ratios with those of other investigations 20 years ago in the same area. The study found that dissolved inorganic nutrient(N, P and Si) concentrations were lowest in the upper layer, and increased from surface to some depths, t... 相似文献
156.
Gaoge Wang Xiaojiao Wei Limei Shuai Bojun Lu Shasha Wang Dongdong Kang 《中国海洋大学学报(英文版)》2014,13(4):677-682
Silvetia babingtonii is a potentially economic brown alga for sources of food and high-value added utilization. So far, sporeling nursery and field cultivation has not been successful. The lack of knowledge on development and life cycle of this alga hinder the development of techniques for the sporeings and cultivation. In this study, internal structure of oogonium and antherium of S. babingtonii was observed with hematoxylin and eosin staining and through microscope. Meanwhile, early development from zygotes to juvenile sporelings was studied at 20℃ under 60–100 μmol photons m-2 s-1. Zygotes germinated and divided into thallus and rhizoid cells. The larger thallus cells further divided and developed into juvenile sporelings; while the smaller rhizoid cells divided and elongated into rhizoid hairs. These findings documented the life cycle of S. babingtonii and provided fundamental knowledge for sporeling nursery in the near future. 相似文献
157.
Present studies on the coupling relationship and hydrology mechanism between basin ecosystem and hydrological process has become an international research frontier in hydrology. This paper investigates this coupling relationship, and also summarizes research and presents a method of combining isotopic technology with hydro-chemical methods, for the study of eco-hydrological process and function in different landscape zones. We then examine research trends for future direction and development of this field. 相似文献
158.
Surface melt has great impacts on the Greenland Ice Sheet (GrlS) mass balance and thereby has become the focus of significant GrlS research in recent years. The production, transport, and release processes of surface meltwater are the keys to understanding the poten- tial impacts of the GrlS surface melt. These hydrological processes can elucidate the following scientific questions: How much melt- water is produced atop the GrlS? What are the characteristics of the meltwater-formed supraglacial hydrological system? How does the meltwater influence the GrlS motion? The GrlS supraglacial hydrology has a number of key roles and yet continues to be poorly understood or documented. This paper summarizes the current understanding of the GrlS surface melt, emphasizing the three essential supraglacial hydrological processes: (1) meltwater production: surface melt modeling is an important approach to acquire surface melt information, and areas, depths, and volumes of supraglacial lakes extracted from remotely sensed imagery can also provide surface melt information; (2) meltwater transport: the spatial distributions of supraglacial lakes, supraglacial sarams, moulins, and crevasses demonstrate the characteristics of the supraglacial hydrological system, revealing the meltwater transport process; and (3) meltwater release: the release of meltwater into the englacial and the subglacial ice sheet has important but undetermined impacts on the GrlS motion. The correlation between surface runoff and the GrlS motion speed is employed to understand these influences. 相似文献
159.
160.
城市道路交通状态具有空间自相关特征。某一道路交通状态的变化会对其周边道路产生影响,故把握道路交通状态的空间自相关性是提高交通规划、交通预测水平的基础。然而,城市道路交通状态又具有空间异质性,即道路交通状态的影响扩散并非各向同性,其使得道路交通状态空间自相关性的度量更为复杂,因此仅从地理空间下道路之间的邻近关系出发进行分析有失偏颇。同时,城市道路具有拓扑结构特征和几何形态特征,二者对于交通状态自相关性的影响和制约,却未引起足够重视。本文从城市道路的拓扑结构特征和几何形态特征出发,提出了一种新的交通状态空间自相关路段识别规则,即基于交通状态变化的路段空间识别规则,通过拓扑社区发现方法刻画路段在空间上的聚集特征,同时,基于Stroke跟踪的几何形态概化来描述道路交通状态变化影响的空间异质性。结果表明,利用本文提出的识别规则产生的交通状态自相关路段集合,较仅考虑地理空间邻近或拓扑结构的识别规则更为合理,更好地揭示了城市道路交通状态的空间自相关特征。 相似文献