全文获取类型
收费全文 | 834篇 |
免费 | 38篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 36篇 |
大气科学 | 33篇 |
地球物理 | 265篇 |
地质学 | 330篇 |
海洋学 | 49篇 |
天文学 | 121篇 |
综合类 | 7篇 |
自然地理 | 33篇 |
出版年
2023年 | 5篇 |
2022年 | 10篇 |
2021年 | 11篇 |
2020年 | 11篇 |
2019年 | 19篇 |
2018年 | 32篇 |
2017年 | 38篇 |
2016年 | 58篇 |
2015年 | 50篇 |
2014年 | 43篇 |
2013年 | 59篇 |
2012年 | 40篇 |
2011年 | 43篇 |
2010年 | 41篇 |
2009年 | 48篇 |
2008年 | 34篇 |
2007年 | 37篇 |
2006年 | 20篇 |
2005年 | 21篇 |
2004年 | 15篇 |
2003年 | 9篇 |
2002年 | 20篇 |
2001年 | 9篇 |
2000年 | 14篇 |
1999年 | 12篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 10篇 |
1995年 | 5篇 |
1994年 | 10篇 |
1993年 | 5篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1979年 | 3篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1970年 | 3篇 |
排序方式: 共有874条查询结果,搜索用时 890 毫秒
41.
The vermiculite-like minerals show varied relative intensities of basal reflections and do not collapse fully when saturated with K and heated up to 700°C.
Transmission oblique texture X-ray diffraction patterns were used to determine a continuous series of the vermiculite-chlorite intermediate structures. Relative diffraction intensities in the region (060) were correlated with the amount of water released at 500–700°C to show that the investigated samples belong to two structurally distinctive series: vermiculitic and chloritic types. The structural premises indicate that the parent mineral for the chloritic intergrades should be chlorite and that for the vermiculitic series phlogopite. 相似文献
42.
43.
44.
M.A. Gasiński 《Cretaceous Research》1983,4(3):221-249
Eighteen Albian and Cenomanian planktic Foraminiferida from the Pieniny Klippen Belt of Poland are discussed. A local biostratigraphic zonation (six zones) is proposed and certain problems of palaeoecology are reviewed. The lithostratigraphical element is the so-called Trawne Beds, a Cretaceous flysch in the Pieniny Klippen Belt. 相似文献
45.
Effect of agricultural land use on the chemistry of groundwater from basaltic aquifers, Jeju Island, South Korea 总被引:2,自引:0,他引:2
Dong-Chan Koh Kyung-Seok Ko Yongje Kim Seung-Gu Lee Ho-Wan Chang 《Hydrogeology Journal》2007,15(4):727-743
Geochemical processes were identified as controlling factors of groundwater chemistry, including chemical weathering, salinization from seawater and dry sea-salt deposition, nitrate contamination, and rainfall recharge. These geochemical processes were identified using principal component analysis of major element chemistry of groundwater from basaltic aquifers in Jeju Island, South Korea, a volcanic island with intense agricultural activities. The contribution of the geochemical processes to groundwater chemistry was quantified by a simple mass-balance approach. The geochemical effects due to seawater were considered based on Cl contributions, whereas the effects due to natural chemical weathering were based on alkalinity. Nitrogenous fertilizers, and especially the associated nitrification processes, appear to significantly affect groundwater chemistry. A strong correlation was observed between Na, Mg, Ca, SO4 and Cl, and nitrate concentrations in groundwater. Correspondingly, the total major cations, Cl, and SO4 in groundwater were assessed to estimate relative effect of N-fertilizer use on groundwater chemistry. Cl originates more from nitrate sources than from seawater, whereas SO4 originates mostly from rainwater. N-fertilizer use has shown the greatest effect on groundwater chemistry, particularly when nitrate concentrations exceed 6–7 mg/L NO3–N. Nitrate contamination significantly affects groundwater quality and 18% of groundwater samples have contamination-dominated chemistry. 相似文献
46.
47.
Measurements of topsoil magnetic susceptibility are often used for quick assessment of soil contamination of anthropogenic
origin, with heavy metals or other pollutants. However, because of complicated correlations between low-field magnetic susceptibility
(shortened to magnetic susceptibility) of topsoil and soil pollution, the outcome of a field magnetometry survey can not be
related directly to soil pollution. For each case study, the results should be interpreted on their own taking into account
not only the type of pollution but also pedogenic, biogenic and environmental factors. In practice, it is very difficult to
measure and consider all these factors. Here we illustrate the merit of geostatistical methods, which are focused on the spatial
variability of a phenomenon, in the interpretation of soil magnetometry results.
This article presents the analysis of spatial variability of top soil layers magnetic susceptibility-within the Upper Silesia
Industrial Region (USIR)-using semivariance analysis. It also explains how to adjust the sampling density of field magnetometry
measurements to spatial variability of the soil pollution as well as to the spatial scale of the investigated area. For this
purpose, the values of magnetic susceptibility have been measured by using various sampling densities at areas of different
size located within USIR. This enabled to determine the main scales of magnetic susceptibility spatial variability of soils
within USIR using semivariance. A few distinct scales of variability were found from the site scale to a more regional scale.
Variability ranges of 30 km, 12 km, and 5 km refer to the large regional scale, whereas smaller ranges of few hundreds down
to a few tens of meters, can be attributed to the local (site) scale. In addition, the precision of the measuring campaigns,
performed within USIR with different sampling densities, was compared through the analysis of the spatial variability of the
soil magnetic susceptibility signal by using ordinary kriging.
jarek97@yahoo.com, piotr.fabijanczyk@is.pw.edu.pl 相似文献
48.
Alfred Kepiński 《Aquatic Sciences - Research Across Boundaries》1962,24(2):272-290
Ohne Zusammenfassung 相似文献
49.
Kosmochlor (NaCrSi2O6) was synthesized by the flux method from melts along the join Na2O·2 SiO2-Na2O·Cr2O3·4 SiO2 at 1000° C in air, and isolated by dissolving the glassy matrix with hydrofluoric and perchloric acids. The join CaMgSi2O6-NaCrSi2O6 was studied at 1 atmosphere in air by the quenching technique at temperatures between 900° and 1450° C, using mixtures of kosmochlor and diopside crystals or diopside glass as starting materials. The phases are diopside solid solution, kosmochlor, spinel (Mg-chromite), eskolaite (Cr2O3) and glass. The maximum solubility of kosmochlor in diopside is 24 wt percent at 1140° C, while diopside is not soluble at all in kosmochlor, resulting in the existence of a wide range of immiscibility. Petrologic significance of the results is discussed. 相似文献
50.
Zusammenfassung Es wird ein einfaches Modell des zykolnalen Wirbels vorgeschlagen und die Beziehung zwischen seiner Intensität, der Form der Stromlinien und der Deformation der frontalen Grenzoberfläche in seiner Nähe diskutiert. Die Arbeit verfolgt das Ziel, die Kriterien der sogenannten dynamischen Klassifikation der aus den meteorologischen Satelliten photographierten Bewölkung zu finden. 相似文献