全文获取类型
收费全文 | 8016篇 |
免费 | 435篇 |
国内免费 | 275篇 |
专业分类
测绘学 | 239篇 |
大气科学 | 964篇 |
地球物理 | 2116篇 |
地质学 | 3163篇 |
海洋学 | 528篇 |
天文学 | 1214篇 |
综合类 | 92篇 |
自然地理 | 410篇 |
出版年
2024年 | 29篇 |
2023年 | 49篇 |
2022年 | 101篇 |
2021年 | 201篇 |
2020年 | 194篇 |
2019年 | 156篇 |
2018年 | 379篇 |
2017年 | 387篇 |
2016年 | 526篇 |
2015年 | 388篇 |
2014年 | 464篇 |
2013年 | 614篇 |
2012年 | 484篇 |
2011年 | 453篇 |
2010年 | 425篇 |
2009年 | 441篇 |
2008年 | 334篇 |
2007年 | 259篇 |
2006年 | 253篇 |
2005年 | 194篇 |
2004年 | 206篇 |
2003年 | 166篇 |
2002年 | 167篇 |
2001年 | 132篇 |
2000年 | 139篇 |
1999年 | 119篇 |
1998年 | 115篇 |
1997年 | 127篇 |
1996年 | 78篇 |
1995年 | 96篇 |
1994年 | 98篇 |
1993年 | 53篇 |
1992年 | 42篇 |
1991年 | 54篇 |
1990年 | 86篇 |
1989年 | 40篇 |
1988年 | 35篇 |
1987年 | 49篇 |
1986年 | 36篇 |
1985年 | 35篇 |
1984年 | 42篇 |
1983年 | 37篇 |
1982年 | 39篇 |
1981年 | 41篇 |
1980年 | 23篇 |
1979年 | 28篇 |
1978年 | 22篇 |
1977年 | 23篇 |
1974年 | 21篇 |
1973年 | 24篇 |
排序方式: 共有8726条查询结果,搜索用时 15 毫秒
61.
Octopus (Octopus vulgaris, Mollusca, Cephalopoda) is an important and valuable fishery resource on the eastern and southern coasts of Tunisia, but its landings are highly variable. This paper explores the effect of environment on octopus catch per unit effort (CPUE) during a 12‐year period, through correlation analyses and the incorporation into surplus production models of sea surface temperature (SST) and rainfall data collected during cold (January–May) and hot (August–October) seasons. CLIMPROD software was used to select the appropriate model and fit it to the fishery and environment data. In both seasons, SST significantly contributed to CPUE variability; fishery production was influenced positively by cold season SST but negatively by hot season SST. Due to a poor fit with cold season data, the impact of rainfall was analysed only for the hot season, during which it has a positive effect on production. Results are discussed in view of the life‐cycle of octopus and the dynamics of the Tunisian fishery. This first study of octopus variability in Tunisia highlights the necessity to incorporate environmental influence into stock assessment and management advice. 相似文献
62.
63.
Algal humic-like substances were oxidized with KMnO4. The oxidation products were analyzed by GC-MS. Normal and branched fatty acids, dicarboxylic and benzene carboxylic acids were identified. Aliphatic acids were by far the most prominent compounds. Similarities between humic and fulvic acids of both Fucus and Laminaria algae were apparent. Fucus humic acids, however, showed a more aromatic structure than their Laminaria counterpart. The contribution of algae to marine sedimentary humus is discussed. 相似文献
64.
人工神经网络与分析测试技术的研究与发展 总被引:8,自引:0,他引:8
回顾了人工神经网络研究的发展历程,简要介绍了神经网络模型与算法,对分析测试技术和相关学科中的人工神经网络研究及在流程控制、错误诊断、参数估计、传感器模型、模式识别与分类、环境监测与治理及光谱与化学分析中的应用等作了评述。引用参考文献113篇。 相似文献
65.
K. Andrée 《International Journal of Earth Sciences》1916,6(7-8):351-397
Ohne Zusammenfassung 相似文献
66.
Discontinuous Galerkin numerical simulations of single phase flow problem are described in this paper. The simulations show the advantages of using discontinuous approximation spaces. hp convergence results are obtained for smooth solutions. Unstructured meshes and unsmooth solutions are also considered. 相似文献
67.
Reports
Regional Seas and Sustainable Development Results of an International Workshop 相似文献68.
Márton Pécsi 《GeoJournal》1995,36(2-3):117-131
In the process of loessification, the development of loess fabric, the role of zonal, regional and partly of local environmental factors is regarded decisive. In the loess sequences various genetic types of loess pockets and paleosols occur and reflect different climatic and paleogeographical conditions.As a consequence, even within a single profile the colour, grain size and mineral composition, CaCO3 content, degree of weathering and fabric of loess may vary. Zonal, regional or even local variations in such loess properties may equally derive from syngenetic or postgenetic processes. For similar reasons, spatially and temporally different forms, types and subtypes of paleosol also developed.This way, loess and soil formation resulted in various spatial types in the same glacial, interstadial or interglacial phase in the various geographical zones and regions. Although there exist major loess regions where the interglacial soils (eg brown forest soils) are markedly distinct from interstadial steppe soils or from other types of humic soils, continental loess areas can also be observed where the paleosols developed under interglacial and interstadial conditions (eg steppe or forest steppe soils) cannot be referred into different genetic types. In such cases the changes in paleoenvironments are difficult and uncertain to reconstruct.The interregional correlation of paleosols is occasionally hindered by the various terminologies applied to denote them. In addition, there are uncertainties concerning the dating and identification of paleoenvironments of polygenetic soils and of soil complexes consisting of paleosol units: how many soil formation phases they represent and how long erosional gaps can be reckoned with between these phases. 相似文献
69.
Due to its physical and chemical properties, areas with a loess mantle of proper thickness favour arable farming. Loess as a parent material promotes the formation of soils of good structure, nutrient supply and water budget. The ongoing land evaluation project places particular emphasis on the consideration of parent material in its scoring system as soil and climatic parameters are assessed in conjunction with the grain size composition of subsurface material and soil texture.A test area most suitable for the presentation of the method seems to be a sandy alluvial fan with loess mantle and this circumstance allows the contrasting of the agroecological potentials of soils developed on the two parent materials of different nature.The favourable water storage properties of loess make this deposit particularly valuable under the conditions of climatic aridification. The geographical information system applied here is capable of simulating the agroecological potential changes caused by reduced precipitation, increased evaporation and dropping groundwater levels.The research for this paper was carried out as part of the MEDALUS II (Mediterranean Desertification and Land Use) collaborative research project. MEDALUS II was funded by the EC under its Environment Progamme, contract no. EV5V 0128/0166. A grant was also provided by the OTKA (Hungarian National Science Foundation), project no 1278. The support is gratefully acknowledged. 相似文献
70.
P. Schmidt-Thomé 《International Journal of Earth Sciences》1954,42(2):172-187
Zusammenfassung Klufttektonische Untersuchungen in den Alpen sind spärlich. Nur die Arbeiten aus den bayerischen Kalkalpen lohnen eine vergleichende Betrachtung. Die in nichtalpinen Gebirgen zu Beginn der Faltung auftretenden kubischen Zerrungs-Kluftsysteme lassen sich in den nördlichen Kalkalpen nicht erkennen. Dort treten statt dessen Scherkluftsysteme auf, teils als gekreuzte Systeme, teils als Begleitklüfte streichender Störungen. Unbeeinflußt ziehen sie über Falten- und Deckenstrukturen hinweg, sind also jünger als diese. Das Diagonalkluftsystem geht auf seitliche Spannungen infolge Horizontalbeanspruchung zurück, die gegen Norden gerichtet war. Die Schernatur kommt in der vorwiegend horizontalen Striemung zum Ausdruck. Ein Vergleich mit den offenbar aus Scherklüften hervorgegangenen Diagonalstörungen, die mit den Klüften annähernd gleich alt sind, macht es wahrscheinlich, daß in Südbayern die Einbeziehung der Molasse in den Faltenbau jünger ist als die Diagonalstörungen. Scherkluftsystem und Diagonal-Blattverschiebungen sind für die nördlichen Kalkalpen mit ihrem flachen, nordvergenten Deckenbau besonders bezeichnend und scheinen in zentralen oder westlicheren Alpengebieten zurückzutreten oder ganz zu fehlen. 相似文献