全文获取类型
收费全文 | 353篇 |
免费 | 16篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 13篇 |
大气科学 | 65篇 |
地球物理 | 84篇 |
地质学 | 114篇 |
海洋学 | 18篇 |
天文学 | 43篇 |
综合类 | 2篇 |
自然地理 | 31篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 1篇 |
2021年 | 10篇 |
2020年 | 7篇 |
2019年 | 9篇 |
2018年 | 13篇 |
2017年 | 13篇 |
2016年 | 22篇 |
2015年 | 6篇 |
2014年 | 21篇 |
2013年 | 31篇 |
2012年 | 14篇 |
2011年 | 16篇 |
2010年 | 17篇 |
2009年 | 23篇 |
2008年 | 12篇 |
2007年 | 14篇 |
2006年 | 12篇 |
2005年 | 17篇 |
2004年 | 13篇 |
2003年 | 5篇 |
2002年 | 2篇 |
2001年 | 11篇 |
2000年 | 8篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1975年 | 2篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有370条查询结果,搜索用时 15 毫秒
81.
S. Jacob A. D. Chintagunta R. Banerjee 《International Journal of Environmental Science and Technology》2016,13(10):2363-2374
Potato being the staple vegetable in India is widely cultivated and processed for different value additions. During processing of potato, a huge amount of waste is generated in the form of peel and meat (mash). These wastes constitute a potential feedstock for biogas generation. The present study is focused on mitigation of acidogenesis that occurs during early stages of anaerobic digestion (AD) of potato waste which eventually inhibits the process of methanogenesis. A novel strategy of selective digestion was adopted in which the leachate and solid slurry resulting from the first stage digestion were further subjected to second stage by separating the solid and liquid phases. The obtained results indicated that stepwise digestion enhanced biomethane yield with an increase in methane percent from 46.47 to 60.4 % and reduction in total COD to about 94 %. Another novel strategy adopted in this study was the use of specifically developed microbial consortia for AD of potato wastes instead of conventional inoculum for production of biogas. The obtained yield is at par with the conventional inoculums which suggests that the developed consortia could act as potential substitute. The present study paves the way for sustainable utilization of industrial potato wastes for bioenergy production by overcoming the problems associated with conventional processes. 相似文献
82.
This article explored the relationship between the local food environment and walkability in the socioeconomically diverse, inner-ring suburbs of metropolitan Detroit. The availability and cost differentials of food were surveyed using a modified version of the Nutrition Environment Measures Survey for Stores (NEMS–S), and a geographic information system–based method was designed to map walkability relative to licensed food retail establishments. Results showed that minority communities lack access to fresh produce and nutritionally adequate foods, which is compounded by limited mobility. By incorporating local-based economic incentives, low-income communities can better align neighborhood goals of obtaining nutritionally adequate food (and other services) with economic opportunity. 相似文献
83.
84.
The 5ν1 absorption band of NH3 is displayed from 6418 to 6550 Å. The total band intensity has been measured: SB = 0.66 cm?1m?1amagat?1. Line intensities and self-broadening coefficients have been measured for some of the prominent lines. Our line intensities are in good agreement with those of Rank et al. (1966), but are about 2 times greater than those of Mason (1970). The spectrum displayed was obtained photoelectrically at a pressure of 0.061 atm, and shows many more lines than the spectrum obtained by McBride and Nicholls (1972a) at a pressure of 0.39 atm. Therefore, our new measurements can provide the basis for making a more complete rotational analysis than those of McBride and Nicholls (1972a).Since the total band absorption has previously been measured by others on moderate resolution photoelectric scans of the spectra of Jupiter and Saturn, we can use the band intensity to derive the NH3 abundance in the atmospheres of these two planets. The NH3 abundances in a single vertical path obtained by this method are about 10m amagat for Jupiter and 2m amagat for Saturn. These results are in agreement with previous results obtained from higher resolution photographic spectra. 相似文献
85.
David H. Roberts Jacob C. Yde N. Tvis Knudsen Antony J. Long Jerry M. Lloyd 《Quaternary Science Reviews》2009,28(3-4):209-222
The Kuannersuit Glacier surged 11 km between 1995 and 1998. The surge resulted in the formation of an ice cored thrust moraine complex constructed by subglacial and proglacial glaciotectonic processes. Four main thrust zones are evident in the glacier snout area with phases of compressional folding and thrusting followed by hydrofracture in response to the build-up of compressional stresses and the aquicludal nature of submarginal permafrost and naled. Various types of stratified debris-rich ice facies occur within the marginal zone: The first (Facies I) comprises laterally continuous strata of ice with sorted sediment accumulations, and is reworked and thrust naled ice. The second is laterally discontinuous stratified debris-rich ice with distinct tectonic structures, and is derived through subglacial extensional deformation and localised regelation (Facies II), whilst the third type is characterised by reworked and brecciated ice associated with the reworking and entrainment of meteoric ice (Facies III). Hydrofracture dykes and sills (Facies IV) cross-cut the marginal ice cored thrust moraines, with their sub-vertically frozen internal contact boundaries and sedimentary structures, suggesting supercooling operated as high-pressure evacuation of water occurred during thrusting, but this is not related to the formation of basal stratified debris-rich ice. Linear distributions of sorted fines transverse to ice flow, and small stratified sediment ridges that vertically cross-cut the ice surface up-ice of the thrust zone relate to sediment migration along crevasse traces and fluvial infilling of crevasses. From a palaeoglaciological viewpoint, marginal glacier tectonics, ice sediment content and sediment delivery mechanisms combine to control the development of this polythermal surge valley landsystem. The bulldozing of proglacial sediments and the folding and thrusting of naled leads to the initial development of the outer zone of the moraine complex. This becomes buried in bulldozed outwash sediment and well-sorted fines through surface ablation of naled. Up-ice of this, the heavily thrust margin becomes buried in sediment melted out from basal debris-rich ice and subglacial diamicts routed along thrusts. These mechanisms combine to deliver sediment to supraglacial localities, and promote the initial preservation of structurally controlled moraines through insulation, and the later development of kettled dead ice terrain. 相似文献
86.
Based on a large data set from the national Danish monitoring program, spatial and temporal variability in total algal cover and in the fraction of opportunistic macroalgae was analysed in relation to environmental variables. Variations in water clarity and salinity combined with information on geographical location of sampling areas were found to explain almost 80% of the large-scale variation in algal cover between areas. As water clarity was largely regulated by concentrations of total-nitrogen (TN), and TN-concentrations by TN-input from land, total algal cover at given water depths was partly related to TN-input from land. The fraction of opportunistic algae responded predominantly to differences in salinity, the highest fractions being found in the most brackish areas. Temporal variability in algal cover and fraction of opportunists over the 14-year investigation period was much smaller than the variability between areas and could not be predicted from variations in environmental variables. In order for macroalgal cover to become a more sensitive indicator of water quality it would be necessary to either increase the sensitivity of the method or identify and include supplementary regulating factors in the model. 相似文献
87.
Carstensen J 《Marine pollution bulletin》2007,55(1-6):3-15
Bias, precision and confidence of the classification framework are crucial elements for decisions to invest large sums to improve the ecological quality. In this study, the statistical principles for classification in relation to WFD are outlined and exemplified. Indicator adjustment to seasonal variation and other significant covariates reduces bias and improves precision. Precision is generally improved using annual means with seasonal adjustment instead of seasonal means. For classification I argue that the balance between costs of monitoring and reduction measures is only fully maintained by the fail-safe approach. The required monitoring efforts to ensure a precise classification are substantially higher than envisaged in WFD, for nutrients and phytoplankton measurements as high as 500 observations to characterise a water body. It must be ensured that sufficient monitoring data become available for classification, while indicator bias and precision is improved through modelling and further development of measurement techniques. 相似文献
88.
The forthcoming GRAV-D gravimetric geoid model over the United States is to be updated regularly to account for changes in
geoid height. Its baseline precision is to be at the 10–20 mm level over non-mountainous regions. The aim of this study is
to provide an estimate of the magnitude, time scale, and spatial footprint of geoid height change over North America, from
mass redistribution processes of hydrologic, cryospheric and solid Earth nature. Geoid height changes from continental water
storage changes over the past 50 years and predicted over the next century are evaluated and are highly dependent on the used
model. Groundwater depletion from anthropogenic pumping in regional scale aquifers may lead to geoid changes of 10 mm magnitude
every 50–100 years. The GRACE time varying gravity fields are used to (i) assess the errors in a glacial isostatic adjustment
model, which, if used to correct the GRAV-D model, may induce errors at the 10 mm geoid height level after ~20 years, (ii),
evaluate geoid height change over ice mass loss regions of North America, which, if they remain unchanged in the future, may
lead to geoid height changes at the 10 mm level in under a decade and (iii), compute sea level rise and its effect on the
geoid, which is found to be negligible. Coseismic gravitational changes from past North American earthquakes are evaluated,
and lead to geoid change at the 10-mm level for only the largest thrust earthquakes. Finally, geoid change from volcanic processes
are assessed and found to be significant with respect to the GRAV-D geoid model baseline precision for cataclysmic events,
such as that of the 1980 Mt. St. Helens eruption. Recommendations on how to best monitor geoid change in the future are given. 相似文献
89.
90.
This article takes its point of departure in the assumption that values shape planning practices and that alternatively one can reconstruct such values from the way planning interventions are argued and evaluated. We contend that planners’ discourses involve implicit value commitments that are observable in their representations of public space and implicated in the results of public-space planning. The paper builds an empirical case from representations of public space elaborated in planning documents developed by planners in four medium-sized Nordic cities. We show how these planning representations form four thematic value clusters concerning urban public space, namely leisure-play, identity-unity, power-organization and unruliness-change. Together these clusters constitute a value framework which reveals a number of central tensions relating to the way that planners seek to balance order and spontaneity in public space. The paper concludes by outlining and discussing these values and the tensions they represent. 相似文献