全文获取类型
收费全文 | 670篇 |
免费 | 21篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 43篇 |
大气科学 | 26篇 |
地球物理 | 165篇 |
地质学 | 249篇 |
海洋学 | 16篇 |
天文学 | 169篇 |
综合类 | 9篇 |
自然地理 | 22篇 |
出版年
2022年 | 17篇 |
2021年 | 17篇 |
2020年 | 19篇 |
2019年 | 17篇 |
2018年 | 40篇 |
2017年 | 35篇 |
2016年 | 33篇 |
2015年 | 37篇 |
2014年 | 42篇 |
2013年 | 37篇 |
2012年 | 40篇 |
2011年 | 28篇 |
2010年 | 27篇 |
2009年 | 27篇 |
2008年 | 19篇 |
2007年 | 19篇 |
2006年 | 21篇 |
2005年 | 5篇 |
2004年 | 9篇 |
2003年 | 7篇 |
2002年 | 9篇 |
2001年 | 6篇 |
2000年 | 12篇 |
1999年 | 6篇 |
1998年 | 4篇 |
1997年 | 5篇 |
1996年 | 9篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1989年 | 3篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 6篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1971年 | 7篇 |
1970年 | 4篇 |
排序方式: 共有699条查询结果,搜索用时 406 毫秒
571.
572.
Optimal mitigation strategies with negative emission technologies and carbon sinks under uncertainty
Sabine Fuss Wolf Heinrich Reuter Jana Szolgayová Michael Obersteiner 《Climatic change》2013,118(1):73-87
In recent years a body of literature has arisen on the topic of how to compose the optimal portfolio of mitigation options. The focus has been mainly on options involving shifts from high- to low- or even negative-carbon technologies. Natural sinks play an important role in any attempt to stabilize atmospheric CO2 and usually enter as a constant term in the overall carbon budget. In this paper, we introduce natural sinks to the carbon management problem and analyze the implications for negative emission technology deployment and the overall mitigation strategy. Amongst other sensitivity analyses, we also investigate the impact of uncertainty in the carbon sink, which we find to raise the importance of negative emissions in the mitigation portfolio significantly lowering the cost of the policy mix. 相似文献
573.
Environmental, biological, socio-cultural and economic status variation existing in the Central Himalaya have led to the evolution
of diverse and unique traditional agroecosystems, crop species and livestock, which facilitate the traditional mountain farming
societies to sustain themselves. Indigenous agroecosystems are highly site specific and differ from place to place, as they
have evolved along divergent lines. For maintenance of traditional agrodiversity management the farmers of the Central Himalaya
have evolved various types of crop rotations in consonance with the varied environmental conditions and agronomic requirements.
In irrigated flat lands two crops are harvested in a year with negligible fallow period but in rainfed conditions if a cropping
sequence is presumed to be starting after winter fallow phase then four major cropping seasons can be identified namely first
kharif season (first crop season), first rabi season (second crop season), second kharif season (third crop season) and second
rabi season (fourth crop season). Highest crop diversity is present in kharif season in comparison to rabi season. Traditionally
the fields are left fallow after harvest of the second kharif season crop. Important characteristics of agrodiversity management
are the use of bullocks for draught power, human energy as labour, crop residues as animal feed and animal waste mixed with
forest litter as organic input to restore soil fertility levels. Women provide most of the human labour except for ploughing
and threshing grain. The present study deals with assessment of traditional agrodiversity management such as (i) crop diversity,
(ii) realized yield under the traditional practices and (iii) assess the differences of realized yields under sole and mixed
cropping systems. It indicated that crop rotation is an important feature of the Central Himalayan village ecosystem which
helps to continue the diversity of species grown, as are the distribution of crops in the growing period and the management
of soil fertility. The cropping diversity existing and the sequences practiced by the traditional farmers seems to have achieved
high degree of specialization and thus even when the yield/biomass variations are about 60%, the farmers continue to practice
these sequences as they need to maintain diversity and synergistic relationships of crops in addition to manage the food and
labour requirements for crop husbandry. Crop yields are generally higher in irrigated systems than rainfed systems and in
sole cropping as compared with mixed cropping. However, gross biological and economic yields are higher in mixed cropping
than sole cropping systems. 相似文献
574.
575.
Water and surface sediment samples were analyzed for butyltins (TBT, DBT, MBT) from various ports along the east and west coast of India. The total butyltin (TB) in water samples varied between ∼1.7 and 342 ng Sn l−1, whereas for sediments it varied between below detection limit to 14861 ng Sn g−1 dry weight of sediment. On an average Chennai port recorded the highest level of butyltins in the sediments while Paradip recorded the highest level of butylins in the waters. A fairly good relationship between the TB in the sediment and overlying water samples, as well as between organic carbon and TB, implicates the importance of adsorption/desorption process in controlling the levels of TBT in these port areas. In India the data on organotin pollution is very sparse; most of the port areas have been surveyed for butyltins for the first time during this study. 相似文献
576.
All recent available data sets containing traveltimes of Pg and Sg phases for the Moravo-Silesian region were collected. These
data come from several experiments designed mostly in 2D (in-line) configurations. Simultaneous processing of all data is
possible only considering the true 3D measurement geometry. The goal of this work is to establish the representative 3D seismic
model by means of seismic tomography. The resulting minimum-structure model is presented in a simple and easy to use form
on the Internet. The amount of processed data is relatively low but repeating the computations with new experimental data
included would be very easy. Important material related to this paper is placed on web pages. 相似文献
577.
Robert Barouki Manolis Kogevinas Karine Audouze Kristine Belesova Ake Bergman Linda Birnbaum Sandra Boekhold Sebastien Denys Celine Desseille Elina Drakvik Howard Frumkin Jeanne Garric Delphine Destoumieux-Garzon Andrew Haines Anke Huss Genon Jensen Spyros Karakitsios Jana Klanova Iida-Maria Koskela Francine Laden Paolo Vineis 《Chemie der Erde / Geochemistry》2011
The outbreak of COVID-19 raised numerous questions on the interactions between the occurrence of new infections, the environment, climate and health. The European Union requested the H2020 HERA project which aims at setting priorities in research on environment, climate and health, to identify relevant research needs regarding Covid-19. The emergence and spread of SARS-CoV-2 appears to be related to urbanization, habitat destruction, live animal trade, intensive livestock farming and global travel. The contribution of climate and air pollution requires additional studies. Importantly, the severity of COVID-19 depends on the interactions between the viral infection, ageing and chronic diseases such as metabolic, respiratory and cardiovascular diseases and obesity which are themselves influenced by environmental stressors. The mechanisms of these interactions deserve additional scrutiny. Both the pandemic and the social response to the disease have elicited an array of behavioural and societal changes that may remain long after the pandemic and that may have long term health effects including on mental health. Recovery plans are currently being discussed or implemented and the environmental and health impacts of those plans are not clearly foreseen. Clearly, COVID-19 will have a long-lasting impact on the environmental health field and will open new research perspectives and policy needs. 相似文献
578.
Distillery and tanneries are major source of heavy metals pollution in natural wetland sites in India. Present study deals
with the heavy metals accumulation potential of Typha angustifolia and Cyperus esculentus growing in distillery and tannery effluent polluted wetland sites. The metal accumulation pattern in both macrophytes showed
direct correlation with the metal content in sediments. Both macrophytes were observed root accumulator for Fe, Cr, Pb, Cu,
and Cd. The metal accumulation in T. angustifolia was found higher than C. esculentus, and accumulation pattern was Fe > Mn > Cr > Zn > Pb > Cu > Ni > Cd. Simultaneously, chlorophyll, protein, cysteine, and
ascorbic acid were also induced in T. angustifolia than C. esculentus. In addition, formation of multinucleolus in shoot of T. angustifolia was found an evidence of extra protein synthesis for tolerance under stress conditions. Hence, C. esculentus was observed potential but less tolerance for metals than T. angustifolia. Therefore, these wetland plants could be used for phytoremediation of heavy metals from wastewater. 相似文献
579.
Approximate analytical solution of the coupled momentum and heat transfer equations are obtained, using an integral method, for natural convection boundary layers which are produced by a step change of surface temperature. The accuracy of the laminar solution is shown to be good, especially at high Prandtl Number (Pr). The corresponding solutions for the turbulent fluid yield a model of a boundary layer in which the horizontal flow strengthens downstream and is fed by downward motion from above. We call this system, which could possibly simulate the initiation of a sea breeze circulation, a subsidence front. Interesting properties of the solution include the control of the boundary-layer development by the product (PrS), whereS is the slope of the boundary layer, and also the generation of log-linear velocity and temperature profiles by heat flux divergence. 相似文献
580.
C. Jeganathan S. A. Khan Ramesh Chandra H. Singh V. Srivastava P. L. N. Raju 《Journal of the Indian Society of Remote Sensing》2001,29(1-2):31-36
As per the World Health Organisation, about 260 million people worldwide are infected with malaria and 1.5 to 2.7 million patients die annually due to this most significant infectious parasite. In this study two important species,Anopheles dints andAnopheles minimus, have been studied in North Lakhimpur and Dibrugarh districts of Assam in the North-Eastern India. Remote sensing has certainly provided a clue in identifying the symptoms of mosquito habitat and Geographical Information System (GIS) has helped us to analyse and identify two species with several environmental parameters. Remote sensing inputs have made a difference in understanding the presence of these species in two districts which are having similar meteorological conditions. It has been found that the nature of the breeding ground for mosquitoes and their spreading patterns are not so complex as generally expected. 相似文献