全文获取类型
收费全文 | 1538篇 |
免费 | 61篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 20篇 |
大气科学 | 98篇 |
地球物理 | 368篇 |
地质学 | 750篇 |
海洋学 | 124篇 |
天文学 | 178篇 |
综合类 | 5篇 |
自然地理 | 60篇 |
出版年
2024年 | 4篇 |
2023年 | 5篇 |
2022年 | 18篇 |
2021年 | 26篇 |
2020年 | 24篇 |
2019年 | 34篇 |
2018年 | 56篇 |
2017年 | 64篇 |
2016年 | 62篇 |
2015年 | 58篇 |
2014年 | 78篇 |
2013年 | 119篇 |
2012年 | 56篇 |
2011年 | 121篇 |
2010年 | 95篇 |
2009年 | 106篇 |
2008年 | 91篇 |
2007年 | 55篇 |
2006年 | 63篇 |
2005年 | 57篇 |
2004年 | 52篇 |
2003年 | 42篇 |
2002年 | 39篇 |
2001年 | 23篇 |
2000年 | 23篇 |
1999年 | 15篇 |
1998年 | 14篇 |
1997年 | 15篇 |
1996年 | 13篇 |
1995年 | 11篇 |
1994年 | 20篇 |
1993年 | 9篇 |
1992年 | 14篇 |
1991年 | 13篇 |
1990年 | 6篇 |
1989年 | 14篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1977年 | 5篇 |
1975年 | 6篇 |
1974年 | 3篇 |
1973年 | 4篇 |
排序方式: 共有1603条查询结果,搜索用时 0 毫秒
941.
942.
RésuméA Madagascar, les morphologies karstiques et leur activité dépendent de l’interaction entre les facteurs climatiques, lithologi-ques et structuraux, en particulier de l’histoire tectonique récente à actuelle. Le rôle des différents facteurs est analysé et quatre cas-types d’activité karstique sont dégagés en fonction de l’importance, variable dans l’espace et dans le temps, des facteurs tectoniques (fracturation et mouvements verticaux) et climatiques (excédent ou déficit pluviométri-que). 相似文献
943.
Laurent Binet Didier GourierSylvie Derenne François Robert 《Geochimica et cosmochimica acta》2002,66(23):4177-4186
An electron paramagnetic resonance (EPR) investigation was performed on the insoluble organic matter from the Orgueil and Murchison meteorites and on terrestrial coals with similar elemental composition. A complementary electron nuclear double resonance (ENDOR) study was also carried out. The measured g-factors of the observed paramagnetic radicals in the meteoritic organic matter exhibit a similar correlation with the chemical composition as for the type III (i.e., hydrogen-poor) terrestrial coals. The main result, obtained from EPR saturation and 1H ENDOR enhancement measurements, showed that the effective local concentration in radicals of about 3 to 4 × 1019 spin.g−1 in the meteoritic organic matter is much higher than the average concentration, hence the occurrence of radical-rich regions accounting for 5% and 20% of the total volume for Murchison and Orgueil, respectively. This heterogeneity of concentration seems to be unique among natural organic macromolecules. It is proposed that these radical-rich regions correspond to pristine parts of the organic matter synthesized in conditions close to those prevailing in the interstellar medium, and which have survived the hydrothermal process on the parent body. 相似文献
944.
Water-assisted migmatization of metagraywackes in a Variscan shear zone, Aiguilles-Rouges massif, western Alps 总被引:2,自引:0,他引:2
Migmatitic rocks developed in metagraywackes during the Variscan orogeny in the Aiguilles-Rouges Massif (western Alps). Partial melting took place 320 Ma ago in a 500 m-wide vertical shear zone. Three leucosome types have been recognised on the basis of size and morphology: (1) large leucosomes > 2 cm wide and > 40 cm long lacking mafic selvage, but containing cm-scale mafic enclaves; (2) same as 1 but with thick mafic selvage (melanosome); (3) small leucosomes < 2 cm and < 40 cm) with thin dark selvages (stromatic migmatites). Types 1 + 2 have mineralogical and chemical compositions in keeping with partial melting experiments. But Type 3 leucosomes have identical plagioclase composition (An19–28) to neighbouring mesosome, both in terms of major- and trace-elements. Moreover, whole-rock REE concentrations in Type 3 leucosomes are only slightly lower than those in the mesosomes, unlike predicted by partial melting experiments. The main chemical differences between all leucosome types can be related to the coupled effect of melt segregation and late chemical reequilibration.
Mineral assemblages and thermodynamic modelling on bulk-rock composition restrict partial melting to 650 °C at 400 MPa. The large volume of leucosome (20 vol.%) thus generated requires addition of 1 wt.% external water. Restriction of extensive migmatization to the shear zone, without melting of neighbouring metapelites, also points to external fluid circulation within the shear zone as the cause of melting. 相似文献
945.
946.
Azad Sağlam Selçuk M. Korhan Erturaç Serkan Üner Erman Özsayın Edwige Pons-Branchu 《Geodinamica Acta》2017,29(1):1-19
Fissure-ridge travertines (FRTs) are of great importance for the determination and comparison of tectonic deformation in a region. The coeval development of these travertines with active fault zones supplies significant information about regional dynamics in terms of deformation pattern and evolution. In this paper, the characteristics of FRTs of the Ba?kale basin (eastern Turkey) and responsible regional tectonism are discussed for the first time. The Ba?kale basin is located between the Ba?kale Fault Zone (BFZ) characterised by Çaml?k fault and I??kl?–Zirani? fault. It is located between dextral Yüksekova Fault Zone and southern end of dextral Guilato–Siahcheshmeh–Khoy Fault system (Iran). Various morphological features indicating recent activity are exposed along the BFZ, including offsetting rivers, fissure-ridge travertine and fault scarps. The Çaml?k fissure-ridge travertine composing of three different depositions is observed along the eastern edge of the BFZ with approximately parallel orientations. The Çaml?k fissure-ridge travertine has been formed and developed on fault zone related to strike-slip or oblique movements. We explain how kinematic changes of faults can influence the fissure-ridge development. 相似文献
947.
The first geodetic experiment tying Europe, Africa and South-America was realized in July 1985 by Very Long Baseline Interferometry
with a network of 5 radiotelescopes. TheVLBI technique and data analysis are presented, with special emphasis on the ionosphere modeling because of its importance in
this particular experiment. Comparisons of the results with other geodetic information confirm the achievement of decimetric
accuracy. 相似文献
948.
Monomeric palladium(II) chloro aqua complexes of the form PdClr(H2O)4-r2-r (r = [0,4]) were studied both experimentally and theoretically to gain insight on both the stabilities and the nature of palladium-chloride interactions.The thermodynamic stabilities of these complexes were studied in aqueous solutions from 5 to 125°C with UV-vis spectrophotometry using a quartz flow-through cell. Tentative measurements up to 200°C were also carried out in pressurised titanium and gold-lined optical cells but revealed important losses in soluble palladium. The strong ligand-to-metal charge transfer bands of the palladium complexes below 350 nm were used to constrain the stepwise thermodynamic formation constants at each temperature, using results of singular value decompositions of the spectra over a broad range of palladium:chloride ratios and wavelengths. The temperature-dependent constants were used to obtain changes in enthalpy and in entropy for each reaction. The thermodynamic stabilities of PdCl(H2O)3+, PdCl2(H2O)20, and PdCl3(H2O)- are larger at higher temperatures, whilst the one of PdCl42- is smaller. All changes in entropies are positive for the former three species, but negative for the latter, presumably due to a larger solvent reorganisation around the doubly charged PdCl42- species. The room temperature thermodynamic values derived from this study are also in agreement with previously published calorimetric data.Theoretical calculations on the intramolecular distributions of electrons in the different palladium(II) chloro aqua complexes, using the methods of atoms in molecules and of the electron localisation function, showed Pd-Cl and Pd-OH2 interactions to be of largely closed-shell/ionic nature. These interactions induce an important distortion of the outer core shell electrons of Pd, as well as stable accumulations of electrons between adjacent Pd-Cl and Pd-OH2 bonds known as ligand opposed core charge concentrations. 相似文献
949.
Gündüz Horasan Aysun Boztepe Güney Ayşegül Küsmezer Feyza Bekler Zafer Öğütçü Nebiye Musaoğlu 《Journal of Asian Earth Sciences》2009,34(1):90-99
Scientists have proposed two fault systems of different ages in the Sea of Marmara: the Thrace-Eski?ehir Fault Zone of Early Miocene–Early Pliocene age and the North Anatolian Fault Zone of Late Pliocene–Recent age. Different seismicity rates and extensions of these faults onto land near ?stanbul have been suggested. One of the reasons for these differences is the contamination of seismicity catalogs by seismic events from quarries operated in ?stanbul and its vicinity, including Gaziosmanpa?a (Cebeci and Kemerburgaz), Çatalca, Ömerli, Gebze, and Hereke.In this study, we investigated waveforms of 179 seismic events (1.8 < Md < 3.0) from the KOERI, NEMC digital database. We determined differences between earthquakes and quarry blasts based on time- and frequency-domain analyses of their seismograms (amplitude peak ratio, power ratio, and spectral amplitude ratio) and used these differences as discriminants. The results of this study indicate that 15% and 85% of the investigated seismic events are earthquakes and quarry blasts, respectively. 相似文献
950.
The aim of this experimental study was to determine the solubility of cassiterite in natural topaz- and cassiterite-bearing granite melts at temperatures close to the solidus. Profiles of Sn concentrations at glass–crystal (SnO2) interface were determined following the method of (Harrison, T.M., Watson, E.B., 1983. Kinetics of zircon dissolution and zirconium diffusion in granitic melts of variable water content. Contributions to Mineralogy and Petrology 84, 66–72). The cassiterite concentration calculated at the SnO2–glass interface is the SnO2 solubility. Experiments were performed at 700–850 °C and 2 kbar using a natural F-bearing peraluminous granitic melt with 2.8 wt.% normative corundum. Slightly H2O-undersaturated to H2O-saturated melt compositions were chosen in order to minimize the loss of Sn to the noble element capsule walls. At the nickel–nickel oxide assemblage (Ni–NiO) oxygen fugacity buffer, the solubility of cassiterite in melts containing 1.12 wt.% F increases from 0.32 to 1.20 wt.% SnO2 with an increasing temperature from 700 to 850 °C. At the Ni–NiO buffer and a given corundum content, SnO2 solubility increases by 10% to 20% relative to an increase of F from 0 to 1.12 wt.%. SnO2 solubility increases by 20% relative to increasing Cl content from 0 to 0.37 wt.% in synthetic granitic melts at 850 °C. We show that Cl is at least as important as F in controlling SnO2 solubility in evolved peraluminous melts at oxygen fugacities close to the Ni–NiO buffer. In addition to the strong effects of temperature and fO2 on SnO2 solubility, an additional controlling parameter is the amount of excess Al (corundum content). At Ni–NiO and 850 °C, SnO2 solubility increases from 0.47 to 1.10 wt.% SnO2 as the normative corundum content increases from 0.1 to 2.8 wt.%. At oxidizing conditions (Ni–NiO +2 to +3), Sn is mainly incorporated as Sn4+ and the effect of excess Al seems to be significantly weaker than at reducing conditions. 相似文献