全文获取类型
收费全文 | 748篇 |
免费 | 22篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 29篇 |
大气科学 | 38篇 |
地球物理 | 165篇 |
地质学 | 287篇 |
海洋学 | 32篇 |
天文学 | 147篇 |
综合类 | 4篇 |
自然地理 | 71篇 |
出版年
2019年 | 14篇 |
2018年 | 24篇 |
2017年 | 10篇 |
2016年 | 22篇 |
2015年 | 10篇 |
2014年 | 24篇 |
2013年 | 34篇 |
2012年 | 30篇 |
2011年 | 28篇 |
2010年 | 29篇 |
2009年 | 43篇 |
2008年 | 29篇 |
2007年 | 29篇 |
2006年 | 36篇 |
2005年 | 24篇 |
2004年 | 23篇 |
2003年 | 21篇 |
2002年 | 29篇 |
2001年 | 11篇 |
2000年 | 15篇 |
1999年 | 22篇 |
1998年 | 16篇 |
1997年 | 9篇 |
1996年 | 15篇 |
1995年 | 12篇 |
1994年 | 11篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 15篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1985年 | 12篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 9篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1973年 | 8篇 |
1971年 | 5篇 |
1955年 | 5篇 |
1950年 | 4篇 |
1949年 | 5篇 |
排序方式: 共有773条查询结果,搜索用时 312 毫秒
571.
572.
Hermann L. F. Meyer 《International Journal of Earth Sciences》1912,3(5-6):434-436
573.
574.
Boron-isotope fractionation between tourmaline and fluid: an experimental re-investigation 总被引:2,自引:1,他引:1
Christian Meyer Bernd Wunder Anette Meixner Rolf L. Romer Wilhelm Heinrich 《Contributions to Mineralogy and Petrology》2008,156(2):259-267
The fractionation of boron isotopes between synthetic dravitic tourmaline and fluid was determined by hydrothermal experiments
between 400 and 700°C at 200 MPa and at 500°C, 500 MPa. Tourmaline was crystallized from an oxide mix in presence of water
that contained boron in excess. In one series of experiments, [B]fluid/[B]tour was 9 after the run; in another series it was 0.1. All experiments produced tourmaline as the sole boron-bearing solid, along
with traces of quartz and talc. Powder XRD and Rietveld refinements revealed no significant amounts of tetrahedrally coordinated
boron in tourmaline. 11B always preferentially fractionated into the fluid. For experiments where [B]fluid/[B]tour was 9, a consistent temperature-dependent boron isotope fractionation curve resulted, approximated by Δ11B(tour–fluid) = −4.20 · [1,000/T (K)] + 3.52; R
2 = 0.77, and valid from 400 to 700°C. No pressure dependence was observed. The fractionation (−2.7 ± 0.5‰ at 400°C; and −0.8 ± 0.5‰
at 700°C) is much lower than that previously presented by Palmer et al. (1992). Experiments where [B]fluid/[B]tour was 0.1 showed a significant larger apparent fractionation of up to −4.7‰. In one of these runs, the isotopic composition
of handpicked tourmaline crystals of different size varied by 1.3‰. This is interpreted as resulting from fractional crystallization
of boron isotopes during tourmaline growth due to the small boron reservoir of the fluid relative to tourmaline, thus indicating
larger fractionation than observed at equilibrium. The effect is eliminated or minimized in experiments with very high boron
excess in the fluid. We therefore suggest that values given by the above relation represent the true equilibrium fractionations. 相似文献
575.
Susceptibility analysis for slides and rockfall: an example from the Northern Calcareous Alps (Vorarlberg, Austria) 总被引:2,自引:0,他引:2
In this paper a tool for semi-quantitative susceptibility assessment at a regional scale is presented which is applicable
at areas with complex geological setting. At a study area within the Northern Calcareous Alps geotechnical mappings were implemented
into a Geographical Information System and analysed as grid data with a cell size of 25 m. The susceptibility to sliding and
falling processes was considered according to five classes (very low, low, medium, high, very high). Susceptibility to sliding
was analysed using an index method. The layers of lithology, bedding conditions, tectonic faults, slope angle, slope aspect,
vegetation and erosion were combined iteratively. Dropout zones of rockfall material were determined with help of a Digital
Elevation Model. The movement of rolling rock samples was modelled by a cost analysis of all potential rockfall trajectories.
These trajectories were also divided into five susceptibility classes. The susceptibility maps are presented in a general
way to be used by communities and spatial planners. Conflict areas of susceptibility and landuse were located and can be presented
destinctively. 相似文献
576.
William E. Scott William D. McCoy Ralph R. Shroba Meyer Rubin 《Quaternary Research》1983,20(3):261-285
A substantially modified history of the last two cycles of Lake Bonneville is proposed. The Bonneville lake cycle began prior to 26,000 yr B.P.; the lake reached the Bonneville shoreline about 16,000 yr B.P. Poor dating control limits our knowledge of the timing of subsequent events. Lake level was maintained at the Bonneville shoreline until about 15,000 yr B.P., or somewhat later, when catastrophic downcutting of the outlet caused a rapid drop of 100 m. The Provo shoreline was formed as rates of isostatic uplift due to this unloading slowed. By 13,000 yr B.P., the lake had fallen below the Provo level and reached one close to that of Great Salt Lake by 11,000 yr B.P. Deposits of the Little Valley lake cycle are identified by their position below a marked unconformity and by amino acid ratios of their fossil gastropods. The maximum level of the Little Valley lake was well below the Bonneville shoreline. Based on degree of soil development and other evidence, the Little Valley lake cycle may be equivalent in age to marine oxygenisotope stage 6. The proposed lake history has climatic implications for the region. First, because the fluctuations of Lake Bonneville and Lake Lahontan during the last cycle of each were apparently out of phase, there may have been significant local differences in the timing and character of late Pleistocene climate changes in the Great Basin. Second, although the Bonneville and Little Valley lake cycles were broadly synchronous with maximum episodes of glaciation, environmental conditions necessary to generate large lakes did not exist during early Wisconsin time. 相似文献
577.
A study of the available gravity, magnetic and geoelectrical data for the Proterozoic Namaqua-Natal Belt of South Africa shows that the boundaries of this tectonic province have distinct geophysical signatures. The southern boundary is marked by a large static field magnetic anomaly and a transition from electrically resistive to conductive crust. The northern margin of the belt is associated with a distinctive gravity signature. These geophysical signatures proved ideal to extrapolate and interpolate the boundaries of the Namaqua-Natal Belt, especially through areas where the transition is covered by Phanerozoic sediments. Numeraial modelling of the gravity data shows that a simple model of uplift in the Namaqua-Natal Belt associated with differential movement along a faulted transition to the older provinces can explain the gravity signature. This model is consistent with the development of the Namaqua-Natal Belt in its final stages as part of an Andean mountain belt with northward subduction and the associated trench south of the southern boundary of the belt. The Andean model of crustal development for this Proterozoic province is consistent with features such as the large quantity of calcalkaline magmatism, the low-pressure, high-temperature metamorphism, the metamorphic zonation and differential uplift along the northern margin, the major mantle derived contribution to the crust between 1300 and 1200 Ma ago and the deformational history. 相似文献
578.
This paper describes relations between the degree of complexation calculated with a mathematical model (FISCHER and REISSIG, 1984) and the ion-exchange and migration behaviour of iron(II, III)-compounds in a simulated aquifer. In general, the bonding of the complexes to the soil matrix becomes stronger with increasing positive charge. Negatively charged or neutral complex compounds do not show any, or show only slight interactions with the soil matrix. By complexation it is possible to achieve great differences in the migration behaviour of a particular metal. In the course of migration in the deposit there was found a separation of the complex mixture in accordance with charge. The break-through curves are characterized by a stepped shape, for this case. If weak acids or weak bases act as complex-forming ligands, the pH-dependent dissociation of the complexing species has to be taken into account in the complex calculation; this is represented by the example of the iron(III)-citrate system in this paper. Moreover, experimental results concerning the migration behaviour of iron(II, III)-fulvic acid complexes are given 相似文献
579.
Jaroslava Plomerová Libuše Ruprechtová Bernd Tittel Joachim Weyrauch Kurt Wylegalla Reviewer A. Zátopek 《Studia Geophysica et Geodaetica》1979,23(2):189-196
n¶rt; auau uu ¶rt; mnu¶rt; n, n, g, Sg, m anmam anauu ¶rt; numa amu 2.6° ¶rt; 4.7° m aa amu uu (mau). aa, m m auum Sg(D) mam mua ¶rt; m n¶rt;u aum¶rt; uma a uu mu. 相似文献
580.
Dr. M. Behrens Dr. K. Krumsiek Dr. D. E. Meyer Dr. Essen A. Schäfer Prof. Dr. A. Siehl Dr. J. Stets Dr. J. Thein Prof. Dr. P. Wurster 《International Journal of Earth Sciences》1978,67(2):424-453
The Geological Institute of Bonn University since 1975 investigates in connection with DSDP/IPOD the Cretaceous of the Atlantic coastal basin in south-western Morocco. 30 main stratigraphic sections and numerous auxiliary ones were taken along several traverses, running along distances of 150 to 200 km in west-east direction. The recognized epicontinental facies-pattern along the traverse of the southern High Atlas mountain range depicts clearly, that we cut here the critical region of intertonguing marine, fine-clastic-carbonaceous sediments and continental detritic deposits. The littoral zone successively progrades with three major transgressions (Neocomian, Upper Aptian, Turonian) towards the African Continent. Sedimentation processes, stratigraphy, paleomagnetics, geochemistry, sedimentology and paleogeography are investigated, taking selected horizons on one hand and complete stratigraphic columns on the other. A new sedimentation model reflecting transgression and regression events in the Cretaceous “Atlas Gulf” show some probabilities of eustatic sea-level changes. There are similarities between the Atlas Gulf and other coastal basins on both sides of the Atlantic Ocean. There are certain relations between the sedimentary record of the proand regrading littoral zone on the continent and in the nearby deep sea deposits. There is an exciting coincidence between the stratigraphie succession of the downwarping Atlas Gulf and the sedimentary cover of the interior of Africa, especially the Mesozoic Sahara Basin. 相似文献