全文获取类型
收费全文 | 1097篇 |
免费 | 56篇 |
国内免费 | 84篇 |
专业分类
测绘学 | 33篇 |
大气科学 | 4篇 |
地球物理 | 53篇 |
地质学 | 133篇 |
海洋学 | 357篇 |
天文学 | 1篇 |
综合类 | 152篇 |
自然地理 | 504篇 |
出版年
2024年 | 5篇 |
2023年 | 17篇 |
2022年 | 27篇 |
2021年 | 24篇 |
2020年 | 35篇 |
2019年 | 34篇 |
2018年 | 33篇 |
2017年 | 27篇 |
2016年 | 30篇 |
2015年 | 23篇 |
2014年 | 51篇 |
2013年 | 96篇 |
2012年 | 62篇 |
2011年 | 45篇 |
2010年 | 42篇 |
2009年 | 57篇 |
2008年 | 50篇 |
2007年 | 56篇 |
2006年 | 65篇 |
2005年 | 59篇 |
2004年 | 60篇 |
2003年 | 33篇 |
2002年 | 50篇 |
2001年 | 39篇 |
2000年 | 37篇 |
1999年 | 30篇 |
1998年 | 26篇 |
1997年 | 15篇 |
1996年 | 19篇 |
1995年 | 17篇 |
1994年 | 11篇 |
1993年 | 12篇 |
1992年 | 13篇 |
1991年 | 9篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
排序方式: 共有1237条查询结果,搜索用时 15 毫秒
831.
832.
刘建国 《中国海洋湖沼学报》2002,(2)
INTRODUCTIONSomeω3andω6long chainedpolyunsaturatedfattyacids (PUFAs)havebeenrecognizedasanessentialcomponentsinhumannutrientsduetotheirtherapeuticeffectsandrolesinmaintainingcellmembranesstructure ,fluidityandfunction .AmongthesePUFAs,arachidonicacid (AA ,2 0… 相似文献
833.
在室内水池内以五层笼摞叠养殖方式,试验了入笼时平均壳长21.2 mm(平均体重1.1 7 g)、37.0 mm(平均体重5.43 g)、51.8 mm(平均体重16.08 g)小、中、大3种规格的九孔鲍的不同放养密度对其生长的影响.笼子大小为40 cm×30 cm×12 cm.小规格设每笼放养量为25、30、35、40、45与50只6种密度;中为25、30、35、40、与45只5种密度;大为20、25、30与40只4种密度.经60 d试验,结果表明(1)小个体组以30只/笼生长最快,平均160μm/d,33 mg/d;(2)中个体组以25只/笼生长最快,平均123um/d,62 mg/d;(3)大个体组以20只/笼生长最快,平均95 μm/d,116 mg/d. 相似文献
834.
邵永华 《广东海洋大学学报》2006,26(5):109-111
通过对《源氏物语》文化背景的探讨,论证了其主题并非“物哀”文化所能范围。同时,通过对日本平安文化的代表——物语文化及其特色的考述,指出日本古典文学中《源氏物语》以特有的文学样式集中地表现了“唐风文化”向“国风文化”的转变,并充分反映了日本文化在传承中国文化的同时,所创造出的颇具日本特色的“国风文化”及其派生出来的其它文化。 相似文献
835.
Gender-specific out-migration, deforestation and urbanization in the Ecuadorian Amazon 总被引:4,自引:0,他引:4
The Ecuadorian Amazon, one of the richest reserves of biodiversity in the world, has faced one of the highest rates of deforestation of any Amazonian nation. Most of this forest elimination has been caused by agricultural colonization that followed the discovery of oil fields in 1967. Since the 1990s, an increasing process of urbanization has also engendered new patterns of population mobility within the Amazon, along with traditional ways by which rural settlers make their living. However, while very significant in its effects on deforestation, urbanization and regional development, population mobility within the Amazon has hardly been studied at all, as well as the distinct migration patterns between men and women. This paper uses a longitudinal dataset of 250 farm households in the Northern Ecuadorian Amazon to understand differentials between men and women migrants to urban and rural destinations and between men and women non-migrants. First, we use hazard analysis based on the Kaplan–Meier (KM) estimator to obtain the cumulative probability that an individual living in the study area in 1990 or at time t, will out-migrated at some time, t+n, before 1999. Results indicate that out-migration to other rural areas in the Amazon, especially pristine areas is considerably greater than out-migration to the growing, but still incipient, Amazonian urban areas. Furthermore, men are more likely to out-migrate to rural areas than women, while the reverse occurs for urban areas. Difference-of-means tests were employed to examine potential factors accounting for differentials between male and female out-migration to urban and rural areas. Among the key results, relative to men younger women are more likely to out-migrate to urban areas; more difficult access from farms to towns and roads constrains women's migration; and access to new lands in the Amazon–an important cause of further deforestation–is more associated with male out-migration. Economic factors such as engagement in on-farm work, increasing resource scarcity–measured by higher population density at the farm and reduction in farm land on forest and crops–and increase in pasture land are more associated with male out-migration to rural areas. On the other hand, increasing resource scarcity, higher population density and weaker migration networks are more associated with female out-migration to urban areas. Thus, a “vicious cycle” is created: Pressure over land leads to deforestation in most or all farm forest areas and reduces the possibilities for further agricultural extensification (deforestation); out-migration, especially male out-migration, occurs to other rural or forest areas in the Amazon (with women being more likely to choose urban destinations); and, giving continuing population growth and pressures in the new settled areas, new pressures promote further out-migration to rural destinations and unabated deforestation. 相似文献
836.
As seedling culture is a crucial factor for successful cultivation ofGelidium, the authors researched tissue culture technology for producing seedlings. The morphogeny and experimental ecology were observed
and studied fully in 2–5 mm isolated tissue fragments. Regeneration, appearance of branching creepers and attaching structure
and new erect seedlings production and development were studied. Fragments were sown on bamboo slice and vinylon rope. The
seedlings were cultured 20–30 days indoor, then cultured in the sea, where the density of erect seedlings was 3–19 seedlings/cm2, growth rate was 3.84% day. The frond arising from seedlings directly was up to 10 cm per year. The ecological conditions
for regenerated seedlings are similar to the natural ones. The regenerated seedlings are suitable for raft culture in various
sea areas. 相似文献
837.
地质文化村建设是积极响应“乡村振兴”等国家战略的地质实践,其理论体系构建与实践模式探索具有重要意义。本文基于乡村振兴视角,以“生态振兴”、“文化振兴”、“产业振兴”、“人才振兴”和“组织振兴”五个方面为总纲,以“两山理论”、“乡村治理理论”等为指导,提出地质文化村建设应以“地质保护优先”+“科学合理利用”为核心宗旨,以“讲好地质故事”+“传承乡村文化”为发展动力,以“产业体系构建”+“村民增收致富”为重点内容,以“人才队伍建设”+“共建共享共赢”为建设方式,以“地质价值认同”+“基层组织建设”为根本保证,形成地质文化村的理论框架体系。在实践模式方面,体现了“三生一体”、“近景、近园”、“多元融合发展”、“村支两委+村民”主导等模式。在未来发展中,应大力开展全国创建试点,加大地质文化村理论研究的广度和深度,构建服务地方工作机制。 相似文献
838.
Dewayany Sutrisno Suzan Novtalia Gill Suseno Suseno 《International Journal of Digital Earth》2018,11(9):863-879
A major problem associated with marine spatial planning (MSP) involves the difficult and time-consuming practice of creating a scenario that encompasses complex datasets in near real time via the use of a simple spatial analysis method. Moreover, decision-makers require a reliable, user-friendly system to quickly and accessibly acquire accurate spatial planning information. The development of national spatial data infrastructure (NSDI), which links the spatial data of a nation’s many diverse institutions, may pave the way for the development of a tool that can better utilize spatial datasets, such as a spatial decision support system (SDSS). Thus, this project aimed to develop an SDSS for MSP and to evaluate the feasibility of its integration within the NSDI framework. The seaweed culture was selected as an example due to its economic and technological acceptance by traditional fishers. Additionally, a multi-criteria analysis was used to develop the tool. Furthermore, a feasibility evaluation of its implementation within the NSDI framework was conducted based on the Delphi method. The results of the assessment indicated that the SDSS can be incorporated into the NSDI framework by addressing the policy issue – one map policy, updating custodians’ decree and data, and improve the standard and protocol. 相似文献
839.
流动人口城市间流动的时空结构特征及其性别差异:基于福建省的实证研究 总被引:4,自引:3,他引:1
基于福建省流动人口问卷调查数据,使用多种流动指标分析和生存分析方法,探讨不同性别流动人口城市间流动的时空特征和规律。研究发现:流动人口的城市间流动是一种常见的现象,在空间特征上,遵循随着流动次数的增加在距离上由近及远、在城市等级上由小到大的规律,且流动距离相对于初次流动趋于缩小,流动的就近性特征显著;在时间特征上,大多数城市间流动发生在流动生涯的前期,随着流动时间的延长,流动状态趋于稳定;在性别差异上,女性城市间流动的强度大于男性,地域选择具有明显的大城市导向,而男性的流动空间活动范围大,地域选择则是大城市和小城市同时兼顾并重。 相似文献
840.
Stable carbon and nitrogen isotopes were used to investigate nutrient pathways and trophic relationships from the rice-crab system in Panjin,Liaoning Province,China. Values of δ 13 C ranged from-27.38‰±0.44‰ to-18.34‰±0.26‰ and δ 15 N ranged from 1.10‰±0.88‰ to 9.33‰±0.57‰. Pseudorasbora parva(Stone moroko) had the highest δ 13 C and δ 15 N values. The lowest δ 13 C values were obtained for the macrophytes and the lowest δ 15 N value was found in sediments. Stable carbon and nitrogen isotopes were used to determine the contribution of different food items to the diets of crabs. The δ 13 C results indicated that the P seudorasbora parva made the greatest contribution to the diet of E riocheir sinensis(Chinese mitten crab),while the δ 15 N results indicated that most food items contributed more than 10% to the diet of the crab. There were three trophic levels identified in the system(Levels 0–2). The crab Eriocheir sinensis,fish Pseudorasbora parva and Misgurnus anguillicaudatus(Oriental weatherfish),and the oligochaete L imnodrilus hoffmeisteri(Limnodrilus worm),were at the second level,zooplankton were at the first level and suspended particulate matter and macrophytes were at trophic position 0. 相似文献