全文获取类型
收费全文 | 310篇 |
免费 | 10篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 24篇 |
大气科学 | 25篇 |
地球物理 | 140篇 |
地质学 | 70篇 |
海洋学 | 20篇 |
天文学 | 27篇 |
自然地理 | 15篇 |
出版年
2021年 | 2篇 |
2018年 | 5篇 |
2017年 | 2篇 |
2016年 | 10篇 |
2015年 | 6篇 |
2014年 | 3篇 |
2013年 | 13篇 |
2012年 | 7篇 |
2011年 | 9篇 |
2010年 | 11篇 |
2009年 | 16篇 |
2008年 | 8篇 |
2007年 | 16篇 |
2006年 | 8篇 |
2005年 | 4篇 |
2004年 | 11篇 |
2003年 | 5篇 |
2002年 | 7篇 |
2001年 | 5篇 |
2000年 | 8篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 13篇 |
1984年 | 11篇 |
1983年 | 11篇 |
1982年 | 18篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 13篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1972年 | 2篇 |
1970年 | 2篇 |
1953年 | 1篇 |
1952年 | 1篇 |
1936年 | 1篇 |
1928年 | 1篇 |
排序方式: 共有321条查询结果,搜索用时 515 毫秒
21.
22.
Modern methods of analyses of environment yield multivariate data sets of measured objects which are used as the basis of the evaluation and interpretation of substances, differentiated effects, but also of samples or processes. The integrated evaluation and assessment of such multivariate data requires the application of mathematical-statistical methods, the method of pattern recognition being particularly suitable. Pattern recognition program systems constitute a compilation of different methods, as e.g. the multivariate linear regression, classification methods (discriminant analysis, multivariate variance analysis), cluster algorithms, multidimensional scaling, factorial analysis. A few possibilities of such pattern comparisons and identifications are represented by the example of gas chromatography and of the structure/effect analysis for the mutagenity to be expected of 117 substances. 相似文献
23.
24.
25.
26.
R. Koch 《洁净——土壤、空气、水》1983,11(5):511-522
The molecular connectivity index developed by Randic as a numerical expression characterizes the position and bond of atoms in the molecular structure. Since significant correlations between the molar refraction as well as electron polarizability and ecotoxicologically relevant parameters of substances were determined in the preceding investigations, such connections are investigated also for this index and sorption coefficients, bioconcentration factors and toxicity data. By the example of 56 differentiated organic substances, significant regression relations are demonstrated between bioconcentration factors, sorption coefficients and toxicity data as well as the valency molecular connectivity indices. By these regressions it is possible to determine essential distribution and action parameters of chemical substances from the structure for assesing an ecotoxicological risk. The possibilities resulting from this for predicting ecotoxicologically relevant parameters of substances are discussed. 相似文献
27.
Fredric L. Prikle Thomas R. Bement Jo Ann Howell Charles D. Koch Newton K. Stablein Richard J. Beckman Gary L. Tietjen 《Journal of Geochemical Exploration》1983,18(3):175-187
Throughout the aerial radiometric reconnaissance survey portion of the U.S. Department of Energy's National Uranium Resource Evaluation (NURE) program, the identification of outliers (anomalies) was an important approach to locating regions with radio-element concentrations that are either higher or lower than expected. The method introduced herein to locate such regions involves three steps: selection of a high (or low) threshold for the variate of interest; use of the sample percentile to identify all points of interest; and movement of a window over the selected data to locate significant clusters of observations. These steps, applied to aerial radiometric 214Bi (equivalent uranium) data collected over the Copper Mountain area in Wyoming, resulted in the identification of areas enriched in that variate. 相似文献
28.
Tom Koch Kenneth Denike 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(5):523-531
The problem is not uncertainty—proposed here as an inevitable condition—but the chimera of certainty asserted by most contemporary
researchers. Problems of data definition, collection, and their use are reviewed in terms of spatial epidemiology and health
data with examples drawn from several areas of contemporary health research. The argument is that preconceptions limit data
modeled in a manner assuming its completeness. The result, as the West Nile Virus example seeks to demonstrate, may obscure
other patterns and limit avenues of research. 相似文献
29.
The impacts of military activities in peacetime, military action and territorial changes on greenhouse gas emission commitments of nations under the Kyoto Protocol are analysed. We propose rules and institutional responsibilities to deal with the repercussions of such changes on markets in emission permits and national commitments aiming at prevention of serious distortions. 相似文献
30.
M. Tichomirowa H.-J. Berger E.A. Koch B.V. Belyatski J. Gtze U. Kempe L. Nasdala U. Schaltegger 《Lithos》2001,56(4):303-332
This study is an attempt to unravel the tectono-metamorphic history of high-grade metamorphic rocks in the Eastern Erzgebirge region. Metamorphism has strongly disturbed the primary petrological genetic characteristics of the rocks. We compare geological, geochemical, and petrological data, and zircon populations as well as isotope and geochronological data for the major gneiss units of the Eastern Erzgebirge; (1) coarse- to medium-grained “Inner Grey Gneiss”, (2) fine-grained “Outer Grey Gneiss”, and (3) “Red Gneiss”. The Inner and Outer Grey Gneiss units (MP–MT overprinted) have very similar geochemical and mineralogical compositions, but they contain different zircon populations. The Inner Grey Gneiss is found to be of primary igneous origin as documented by the presence of long-prismatic, oscillatory zoned zircons (540 Ma) and relics of granitic textures. Geochemical and isotope data classify the igneous precursor as a S-type granite. In contrast, Outer Grey Gneiss samples are free of long-prismatic zircons and contain zircons with signs of mechanical rounding through sedimentary transport. Geochemical data indicate greywackes as main previous precursor. The most euhedral zircons are zoned and document Neoproterozoic (ca. 575 Ma) source rocks eroded to form these greywackes. U–Pb-SHRIMP measurements revealed three further ancient sources, which zircons survived in both the Inner and Outer Grey Gneiss: Neoproterozoic (600–700 Ma), Paleoproterozoic (2100–2200 Ma), and Archaean (2700–2800 Ma). These results point to absence of Grenvillian type sources and derivation of the crust from the West African Craton. The granite magma of the Inner Grey Gneiss was probably derived through in situ melting of the Outer Grey Gneiss sedimentary protolith as indicated by geological relationships, similar geochemical composition, similar Nd model ages, and inherited zircon ages. Red Gneiss occurs as separate bodies within fine- and medium-grained grey gneisses of the gneiss–eclogite zone (HP–HT overprinted). In comparison to Grey Gneisses, the Red Gneiss clearly differs in geochemical composition by lower contents of refractory elements. Rocks contain long-prismatic zircons (480–500 Ma) with oscillatory zonation indicating an igneous precursor for Red Gneiss protoliths. Geochemical data display obvious characteristics of S-type granites derived through partial melting from deeper crustal source rocks. The obtained time marks of magmatic activity (ca. 575 Ma, ca. 540 Ma, ca. 500–480 Ma) of the Eastern Erzgebirge are compared with adjacent units of the Saxothuringian zone. In all these units, similar time marks and geochemical pattern of igneous rocks prove a similar tectono-metamorphic evolution during Neoproterozoic–Ordovician time. 相似文献