全文获取类型
收费全文 | 451篇 |
免费 | 24篇 |
专业分类
测绘学 | 11篇 |
大气科学 | 36篇 |
地球物理 | 120篇 |
地质学 | 185篇 |
海洋学 | 24篇 |
天文学 | 69篇 |
自然地理 | 30篇 |
出版年
2022年 | 2篇 |
2021年 | 7篇 |
2020年 | 9篇 |
2019年 | 5篇 |
2018年 | 14篇 |
2017年 | 11篇 |
2016年 | 19篇 |
2015年 | 15篇 |
2014年 | 15篇 |
2013年 | 22篇 |
2012年 | 15篇 |
2011年 | 21篇 |
2010年 | 33篇 |
2009年 | 21篇 |
2008年 | 19篇 |
2007年 | 14篇 |
2006年 | 20篇 |
2005年 | 21篇 |
2004年 | 24篇 |
2003年 | 14篇 |
2002年 | 13篇 |
2001年 | 8篇 |
2000年 | 12篇 |
1999年 | 11篇 |
1998年 | 8篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1974年 | 4篇 |
1931年 | 1篇 |
1926年 | 1篇 |
1924年 | 1篇 |
排序方式: 共有475条查询结果,搜索用时 406 毫秒
81.
The Lippmann diagram for the system(Ba, Sr)SO4-H2O was computed at 25 °Cby determining the solid-phase activity coefficientsfrom first principles calculations. Directcalculations of the mixing properties of thebarite-celestite series indicate this solid solutionbehaves as non-ideal and non-regular. At 25 °C,the enthalpy of mixing shows a minimum around 50 mole% SrSO4 due to an ordering tendency. Thefree energy of mixing shows two minima that delimit awide and symmetric miscibility gap (from 2.1 to 97.9 mole% SrSO4) at this temperature. The excessfree energy of mixing requires a Guggenheim expansionseries of 5 terms to be described, where the termswith odd exponents are null as a consequence of thesymmetric distribution of the mixing properties withcomposition. The Lippmann diagram shows a peritecticpoint that corresponds to the composition of an aqueoussolution which is simultaneously at equilibrium withthe two extremes of the miscibility gap. The largedifference between the solubility products of theendmembers involves a strong preferential partitioningof the less soluble endmember towards the solid phase,which explains the extremely Ba-poor composition ofthe aqueous solution (aqueous activity fraction forBa2+ = 0.000446 ) at the peritectic point. 相似文献
82.
The Ardara pluton as part of the Donegal batholith was intruded into Neoproterozoic metasediments and metadolerites at mid-crustal
levels. The emplacement mechanism of the Ardara granite is very controversial, and mechanisms ranging from diapirism, ballooning
and stoping followed by nested diapirism have been proposed. Magnetic fabrics, rock fabrics and K/Ar dating of micas are used
here to constrain the emplacement history. The compositional zoning of the Ardara pluton is clearly reflected in the different
bulk magnetic susceptibilities between the outer quartz monzodiorite and the central granodiorite, whereas the intervening
tonalite is of intermediate nature. The magnetic carriers are characterized by the anisotropy of the magnetic susceptibility
(AMS), thermomagnetic measurements and through high field analyses (HFA). The separation of the ferrimagnetic and paramagnetic
contributions revealed that biotite and magnetite control the AMS in the quartz monzodiorite. Both minerals are oriented in
such a way that their summed contribution is constructive and originates from the shape fabric of magnetite and the texture
of biotite. Biotite is responsible mainly for the AMS in the tonalite and granodiorite. The magnetic foliation can be directly
related to the macroscopic foliation and also to the D4 structures in the country rocks. The foliation is consistent with
the geometry of the roughly circular shape and has a mostly steep to vertical dip. Towards the central granodiorite the magnetic
foliation dies out, although plagioclase texture measurements indicate a weak magmatic shape fabric. With the exception of
the tail, the Kmax axes (magnetic lineation) vary from steeply to gently plunging. The so-called lineation factor is approximately 1.01 and
therefore points to a less significant axial symmetry. These observations coincide with strain estimates on mafic enclaves
that show a very consistent pattern of K ∼0 flattening strain. Texture analyses of biotite and quartz additionally support
the observations made by the strain analyses and the magnetic fabric data. Microstructural investigations give evidence that
the fabrics are associated with the emplacement over a range of temperatures from truly magmatic to high-temperature solid-state
conditions. The age of the intrusion is still under discussion, but a new cooling age was determined by K/Ar dating of biotite
at 403.7±8 Ma corresponding to a temperature range between 450 and 300°C. For a mylonite along the southern contact between
the Ardara pluton and the country rock a K/Ar muscovite age of 378.8±7 Ma indicates a minimum age for the shear zone when
the Ardara pluton must have already been cooled down below 350±50°C.
Received: 28 January 1999 / Accepted: 28 December 1999 相似文献
83.
Sylvain Orseau Nicolas Huybrechts Pablo Tassi Damien Pham Van Bang Fabrice Klein 《国际泥沙研究》2021,36(6):736-746
In order to optimize ship navigation in the macrotidal Gironde Estuary, a recent project funded by the port of Bordeaux aims at better understand and forecast hydrodynamic and fine sediment transport within the estuary. In the framework of this project, a two-dimensional hydro-sedimentary model is built. The model includes hydrodynamic forcings, mixed-sediment transport, and consolidation processes. The harmonic analysis of the astronomical tides reveals a strong distortion of the tidal wave inducing the growth of overtide constituents and the non-significant effect of tide-surge interactions in annual-scale prediction. Depending on hydrological conditions, river discharge can considerably alter the model accuracy due to the migration of the turbidity maximum zone modifying the bottom roughness. Comparison with measurements shows the ability of the model to reproduce suspended-sediment concentrations in the central Estuary. Sensitivity of the model to sediment features has also been discussed in regard of suspended-sediment concentrations and fluid mud deposits. The model will be further coupled with ship squat predictions and a morphodynamic model. 相似文献
84.
S. Siegesmund H. Jelsma J. Becker G. Davies P. Layer E. van Dijk L. Kater M. Vinyu 《International Journal of Earth Sciences》2002,91(1):20-34
In order to constrain the temporal relationship between granite (sensu lato) emplacement and metamorphism, isotope work was carried out on the minerals zircon and apatite (U-Pb), garnet (Pb-Pb) and hornblende (Ar-Ar) from wall rock samples in the Shamva area in Zimbabwe. The area, encompassing parts of the Chinamora and Murehwa batholiths and a wedge-shaped greenstone belt segment in between, is commonly quoted in the literature as an example illustrating pluton emplacement processes and deformational models for the Archean. New U-Pb dating of apatite from a boudinaged pegmatite within mafic schists in the batholith-greenstone contact zone has yielded an age of 2619 +28/-24 Ma. This age is interpreted as the best estimation of the intrusion age of this unit, depending on the assumed closure temperature, and provides an upper age limit for the syntectonic emplacement of the now gneissic granites. Pb-Pb dating of late kinematic garnets in cordierite-bearing rocks within the greenstone belt wall rocks gives an age of 2623NJ Ma. Together, this timing of relatively late, syntectonic plutonism and metamorphic mineral growth at ca. 2.62 Ga compares well with existing zircon crystallization ages for felsic volcanics (2645dž Ma, 2643NJ Ma) and post-tectonic porphyritic monzogranites (2601ᆢ Ma). Ar-Ar hornblende ages for mafic schists from different areas within the greenstone belt wall rocks range between 2621 and 2498 Ma and have been interpreted to indicate mixing between metamorphic ages and cooling ages. The data support a geological model whereby volcanism and sedimentation are associated with an early phase of regional deformation at ca. 2.64 Ga, which may have started earlier and lasted longer, and evolves into the voluminous emplacement of granites (now gneissic granites) in the batholiths at approximately 2.62 Ga. Emplacement of post-tectonic tabular monzogranites takes place at ca. 2.60 Ga. 相似文献
85.
Iron isotope fractionation in subduction-related high-pressure metabasites (Ile de Groix,France) 总被引:1,自引:0,他引:1
Afifé?El KorhEmail author Béatrice?Luais Etienne?Deloule Damien?Cividini 《Contributions to Mineralogy and Petrology》2017,172(6):41
Characterisation of mass transfer during subduction is fundamental to understand the origin of compositional heterogeneities in the upper mantle. Fe isotopes were measured in high-pressure/low-temperature metabasites (blueschists, eclogites and retrograde greenschists) from the Ile de Groix (France), a Variscan high-pressure terrane, to determine if the subducted oceanic crust contributes to mantle Fe isotope heterogeneities. The metabasites have δ56Fe values of +0.16 to +0.33‰, which are heavier than typical values of MORB and OIB, indicating that their basaltic protolith derives from a heavy-Fe mantle source. The δ56Fe correlates well with Y/Nb and (La/Sm)PM ratios, which commonly fractionate during magmatic processes, highlighting variations in the magmatic protolith composition. In addition, the shift of δ56Fe by +0.06 to 0.10‰ compared to basalts may reflect hydrothermal alteration prior to subduction. The δ56Fe decrease from blueschists (+0.19 ± 0.03 to +0.33 ± 0.01‰) to eclogites (+0.16 ± 0.02 to +0.18 ± 0.03‰) reflects small variations in the protolith composition, rather than Fe fractionation during metamorphism: newly-formed Fe-rich minerals allowed preserving bulk rock Fe compositions during metamorphic reactions and hampered any Fe isotope fractionation. Greenschists have δ56Fe values (+0.17 ± 0.01 to +0.27 ± 0.02‰) similar to high-pressure rocks. Hence, metasomatism related to fluids derived from the subducted hydrothermally altered metabasites might only have a limited effect on mantle Fe isotope composition under subsolidus conditions, owing to the large stability of Fe-rich minerals and low mobility of Fe. Subsequent melting of the heavy-Fe metabasites at deeper levels is expected to generate mantle Fe isotope heterogeneities. 相似文献
86.
Molybdenum disulfide (MoS2), a layered transition-metal dichalcogenide, has been of special importance to the research community of geochemistry, materials
and environmental chemistry, and geotechnical engineering. Understanding the oxidation behavior and charge-transfer mechanisms
in MoS2 is important to gain better insight into the degradation of this mineral in the environment. In addition, understanding the
insertion of metals into molybdenite and evaluation of charge-transfer mechanism and dynamics is important to utilize these
minerals in technological applications. Furthermore, a detailed investigation of thermal oxidation behavior and metal-insertion
will provide a basis to further explore and model the mechanism of adsorption of metal ions onto geomedia. 相似文献
87.
Emmanuel Damien Rivière Michel Pirre Gwenaël Berthet Jean-Baptiste Renard Franck Lefèvre 《Journal of Atmospheric Chemistry》2004,48(3):261-282
Two cases of simultaneous nighttime measurements of NO2 and OClO in the winter polar stratosphere are analyzed in order to test our present knowledge of halogen chemistry in the presence of high amount of NO2 at low temperature. Comparisons with Lagrangian model calculations using several hypotheses are performed. First simulations, using the admitted constant rates of chemical reaction, strongly underestimate the measured OClO while the NO2 profiles are correctly reproduced. If uncertainties in actinic fluxes calculations are taken into account, simulation results do not show a significant reduction of the underestimation. A better agreement can be achieved if the formation of unstable isomers of ClONO2 and of BrONO2 occurs in the cold conditions of the polar stratosphere. An approximate value of the branching ratios of the channels leading to ClONO2 and ClOONO, and to BrONO2 and BrOONO, necessary to reproduce both OClO and NO2 is given and discussed. 相似文献
88.
Summary Monthly precipitation trends of 160 stations in China from 1951–2002 have been analysed and interpolated. The Mann-Kendall trend test was applied to examine the monthly precipitation data. Significant positive and negative trends at the 90, 95, and 99 percent confidence levels were detected for numerous stations. The number, distribution, and direction of the trends varied from month to month.The detected trends were spatially interpolated by applying the Inverse Distance Weighted (IDW) interpolation method. The spatial presentation of the detected precipitation trends gives a better understanding of climatic changes or variations in China during the last 50 years. This is especially the case for highlighting the spatial structure of precipitation trends.A clustering of trends is observed in certain months, including distinct trend belts especially in east and north-east China. Nevertheless, positive as well as negative monthly trends can be noted simultaneously in different areas. The spatial interpolation of precipitation trend analysis results is a useful approach to give further understanding of the regional pattern of precipitation trends in China. 相似文献
89.
90.