全文获取类型
收费全文 | 2576篇 |
免费 | 497篇 |
国内免费 | 679篇 |
专业分类
测绘学 | 178篇 |
大气科学 | 491篇 |
地球物理 | 622篇 |
地质学 | 1247篇 |
海洋学 | 444篇 |
天文学 | 93篇 |
综合类 | 304篇 |
自然地理 | 373篇 |
出版年
2024年 | 19篇 |
2023年 | 64篇 |
2022年 | 140篇 |
2021年 | 197篇 |
2020年 | 171篇 |
2019年 | 169篇 |
2018年 | 184篇 |
2017年 | 157篇 |
2016年 | 177篇 |
2015年 | 134篇 |
2014年 | 184篇 |
2013年 | 147篇 |
2012年 | 117篇 |
2011年 | 152篇 |
2010年 | 137篇 |
2009年 | 173篇 |
2008年 | 148篇 |
2007年 | 113篇 |
2006年 | 94篇 |
2005年 | 78篇 |
2004年 | 71篇 |
2003年 | 90篇 |
2002年 | 74篇 |
2001年 | 80篇 |
2000年 | 86篇 |
1999年 | 87篇 |
1998年 | 79篇 |
1997年 | 69篇 |
1996年 | 56篇 |
1995年 | 55篇 |
1994年 | 45篇 |
1993年 | 43篇 |
1992年 | 38篇 |
1991年 | 30篇 |
1990年 | 17篇 |
1989年 | 18篇 |
1988年 | 15篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1962年 | 1篇 |
1958年 | 5篇 |
1957年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有3752条查询结果,搜索用时 31 毫秒
41.
Xueying Jia Zhijie Tian Lei Qin Linlin Zhang Yuanchun Zou Ming Jiang Xianguo Lyu 《中国地理科学(英文版)》2018,28(2):337-352
Iron-rich groundwater flowing into wetlands is a worldwide environmental pollution phenomenon that is closely associated with the stability of wetland ecosystems. Combined with high phosphorus(P) loading from agricultural runoff, the prediction of the evolution of wetland vegetation affected by compound contamination is particularly urgent. We tested the effects of anaerobic iron-rich groundwater discharge in a freshwater marsh by simulating the effect of three levels of eutrophic water on native plants(Glyceria spiculosa(Fr. Schmidt.) Rosh.). The management of wetland vegetation with 1–20 mg/L Fe input is an efficient method to promote the growth of plants, which showed an optimum response under a 0.10 mg/L P surface water environment. Iron-rich groundwater strongly affects the changes in ecological niches of some wetland plant species and the dominant species. In addition, when the P concentration in a natural body of water is too high, the governance effect of eutrophication might not be as expected. Under iron-rich groundwater conditions, the δ~(13)C values of organs were more depleted, which can partially explain the differences in δ~(13)C in the soil profile. Conversely, the carbon isotope composition of soil organic carbon is indicative of past changes in vegetation. The results of our experiments confirm that iron-rich groundwater discharge has the potential to affect vegetation composition through toxicity modification in eutrophic environments. 相似文献
42.
Guidong Miao Ying Xu Di Wang Songlin Chen Tingjun Fan Yongsheng Tian 《中国海洋大学学报(英文版)》2011,10(3):241-245
Half-smooth tongue sole (Cynoglossus semilaevis) is a promising species for aquaculture in China.The wild population of C. semilaevis is under threat from environmental factors. Microsatellite markers are very suitable for assessing genetic diversity. Four microsatellite-enriched libraries of half smooth tongue sole (Cynoglossus semilaevis) were constructed,from which 57 polymorphic microsatellites were isolated and characterized.The polymorphism of these microsatellites was assessed by genotyping in 30 ind... 相似文献
43.
Huahua Lü 《世界地质(英文版)》2006,9(1)
In order to make use of ocean clay reasonably and excavate its potential applications the properties of ocean clay in Chinese investigating area of the East Pacific have been tested with the chemical analysis, XRFS, ICP/MAS, granulometry and SSA, etc. The results show that the clay sediments of this area are rich in clay minerals, fine granularity, bigger SSA, bigger water absorbability and lower ion changing ability etc. To improve the adaptability of ocean clay and macromolecule materials, using the dry milling method with silane, aluminate, stearic acid coupling agents etc the properties of ocean clay are improved. The effect has been evaluated by testing the water absorbing of the modified ocean clay and their dispersing in paraffin liquid. The result is that KH550 is better than any other active reagents, and the best activation technics is that 1.5% (volume) of KH550 quantity, 20min of milling time. The DTA, XRD, SEM and IR analyses and SSA testing show that the organic activation can not change the mineral structure but can densify the structure of clay, and activation mechanism is chemical covered mainly and chemical combined secondly. 相似文献
44.
GPU accelerated marine data visualization method 总被引:1,自引:0,他引:1
The study of marine data visualization is of great value. Marine data, due to its large scale, random variation and multiresolution in nature, are hard to be visualized and analyzed. Nowadays, constructing an ocean model and visualizing model results have become some of the most important research topics of ‘Digital Ocean'. In this paper, a spherical ray casting method is developed to improve the traditional ray-casting algorithm and to make efficient use of GPUs. Aiming at the ocean current data, a 3D view-dependent line integral convolution method is used, in which the spatial frequency is adapted according to the distance from a camera. The study is based on a 3D virtual reality and visualization engine, namely the VV-Ocean. Some interactive operations are also provided to highlight the interesting structures and the characteristics of volumetric data. Finally, the marine data gathered in the East China Sea are displayed and analyzed. The results show that the method meets the requirements of real-time and interactive rendering. 相似文献
45.
A new moored microstructure recorder (MMR) is designed, developed, tested, and evaluated. The MMR directly measures the high-frequency shear of velocity fluctuations, with which we can estimate the dissipation rate of turbulent kinetic energy. We summarize and discuss methods for estimating the turbulent kinetic energy dissipation rate. Instrument body vibrations contaminate the shear signal in an ocean field experiment, and a compensating correction successfully removes this contamination. In both tank test and ocean field experiment, the dissipation rate measured with the MMR agreed well with that measured using other instruments. 相似文献
46.
As an effective livelihood approach to alleviate poverty without rural population migration, ethnic tourism has become the primary choice of economic development in ethnic areas worldwide in addition to traditional livelihood approaches. This article applies the theories of livelihood to study the community evolution driven by tourism livelihood and examine three mountainous tourism communities in different stages of tourist area life cycle. Drawing on the methods of GIS spatial analysis, semi-structured interviews and questionnaires, this article proposes a sustainable livelihood framework for ethnic tourism to explore the evolution of ethnic tourism communities by identifying changes in livelihood assets (natural, financial, social, cultural and human capitals) in the process of tourism development. The results show that the development of ethnic tourism has led to changes in the increase of building land, and the diversification of land use functions with a trend of shifting from meeting local villagers' living needs to satisfying tourists, income composition and uneven distribution of tourism income spatially. Ethnic tourism also led to the deterioration of traditional social management structure, collapse of neighboring relationship, the over- commercialization and staged authenticity of ethnic culture, as well as the gradual vanish of agricultural knowledge with a trend of increasing modern business knowledge and higher education. In addition, these changes, involving livelihood assets from natural, economic, human, social and cultural aspects are interrelated and interactive, which form new evolution characters of ethnic community. This study reveals the conflicts over livelihood approaches which have formed new vulnerabilities to impact on sustainable evolution of ethnic communities. This research provides implications for achieving the sustainable development of ethnic communities with the driving force of tourism livelihood. 相似文献
47.
空间同位模式分析是数据挖掘中一种常见的方法,可有效挖掘城市设施在空间位置上的关联特征,进而发现城市设施的分布规律.本文基于POI数据同位模式挖掘用来获取城市服务业空间关联结构:首先,通过邻近实例获取、同位候选模式存储与筛选,得到城市服务业二阶同位模式;然后,据此构造产业空间关联图,得到产业间的关联结构;最后,分别构造了... 相似文献
48.
49.
The morphology and toxicity ofPseudo-nitzschia strain PP0201-01, isolated near the estuary of Changjiang (Yangtze) River in Year 2002 and tentatively identified asPseudo-nitzschia pungens, were studied. The strain was identified morphologically asP. pungens using scanning electronic microscope (SEM). The analytical results of LC-PDA (liquid chromatography with photodiode array
detector), LC-MS (liquid chromatography with mass detector), and the toxicity data from mouse bioassay, showed that no domoic
acid was produced by the strain. However, the mechanism of domoic acid production byPseudo-nitzschia species is complicated. More works are needed to assess the toxic species and to evaluate the potential risk of amnesic shellfish
poisoning (ASP) in China.
Supported by the projects of Ministry of Science and Technology (No. 2001CB409704 and No. 2001BA804A20), and the innovation
project of the Institute of Oceanology, CAS (No. 200223107). 相似文献
50.
Advances in the Study on Nutrient Requirements of Grouper(Epinephelus sp. ):a Review 总被引:1,自引:0,他引:1
LUOZhi LIUYongjian MAIKangsen TIANLixia 《中国海洋大学学报(英文版)》2005,4(2):93-98
The paper reviews the recent advances in studying grouper nutrition requirement for the development of cost-effective and environmentally friendly artificial diets. It consists of seven parts: protein and amino acid, lipid and essential fatty acid, carbohydrate, vitamin, mineral, alternative protein source, broodstock and larval nutrition. The review provides some basic information for further investigation of nutrient requirements of groupers. 相似文献