全文获取类型
收费全文 | 1001篇 |
免费 | 40篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 41篇 |
大气科学 | 84篇 |
地球物理 | 218篇 |
地质学 | 343篇 |
海洋学 | 75篇 |
天文学 | 159篇 |
综合类 | 13篇 |
自然地理 | 113篇 |
出版年
2022年 | 7篇 |
2021年 | 15篇 |
2020年 | 14篇 |
2019年 | 22篇 |
2018年 | 35篇 |
2017年 | 20篇 |
2016年 | 33篇 |
2015年 | 23篇 |
2014年 | 38篇 |
2013年 | 74篇 |
2012年 | 37篇 |
2011年 | 44篇 |
2010年 | 41篇 |
2009年 | 63篇 |
2008年 | 66篇 |
2007年 | 50篇 |
2006年 | 38篇 |
2005年 | 35篇 |
2004年 | 32篇 |
2003年 | 39篇 |
2002年 | 31篇 |
2001年 | 27篇 |
2000年 | 13篇 |
1999年 | 17篇 |
1998年 | 14篇 |
1997年 | 14篇 |
1996年 | 16篇 |
1995年 | 12篇 |
1994年 | 7篇 |
1993年 | 10篇 |
1992年 | 4篇 |
1991年 | 9篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 12篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 15篇 |
1982年 | 12篇 |
1981年 | 5篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 5篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1974年 | 4篇 |
1972年 | 3篇 |
1969年 | 3篇 |
排序方式: 共有1046条查询结果,搜索用时 31 毫秒
101.
Yves Grosdidier Anthony F.J. Moffat Agnès Acker 《Astrophysics and Space Science》1998,260(1-2):181-184
We present HST-WFPC2/Hα deep images of the ejected nebula M1-67. Our data suggest that M1-67 is the imprint of a previous,
slow LBV wind ejected from the central star WR124, now a WN8 star. We find evidence that the LBV wind is highly variableand anisotropic. Some dense, persisting clumps have possibly been ejected directly from the stellar surface.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
102.
Anthony B. Kaye & Klaus G. Strassmeier 《Monthly notices of the Royal Astronomical Society》1998,294(2):L35-L39
In an investigation of the starspot hypothesis as it applies to the 'slowly variable' F-type dwarfs, we spectroscopically observed eight promising γ Doradus candidates to search for Ca ii H&K emission. We found that there are no significant emission reversals in the cores of these resonance lines. Based on the ceiling flux calculations of the Ca ii K line and on calculations of the Rossby number, we conclude that there is no support for the presence of strong magnetic activity and the starspot hypothesis in these objects. 相似文献
103.
Anthony J. Crawford 《Contributions to Mineralogy and Petrology》1981,75(4):353-367
The Howqua Olivine Pyroxenite of eastern Victoria, Australia, intrudes a metamorphosed sequence of Cambrian high-Mg lavas. It crystallized an unusual mineral assemblage: Cr-rich magnesiochromite, olivine (Fo94), and protoenstatite (now inverted to polysynthetically-twinned clinoenstatite). Residual liquid crystallized strongly-zoned interstitial pyroxenes followed by pargasite. Pargasite, often showing quench habit, crystallized in interstitial glass which is now altered to serpentine.The extremely refractory nature of the cumulus phases indicates a very high temperature of crystallization for liquidus olivine and chromite from a high-MgO, low-Al2O3 parent liquid similar in some respects to Archaean peridotitic komatiites. The suggested origin by hydrous melting of depleted mantle peridotite, plus other compositional and mineralogical similarities (especially the olivine-liquid reaction producing protoenstatite) indicate that the parent magma of the Howqua Olivine Pyroxenite had many features in common with the high-SiO2, high-MgO clinoenstatite-bearing boninitic lavas of the Western Pacific. It is interpreted as a more extreme melt with affinities to boninite and it demonstrates that ultramafic magmas existed in the Cambrian. 相似文献
104.
Subsolidus and melting relations for the CaCO3-MgCO3 join at 30 kb have been determined using piston-cylinder apparatus. Data are also presented for the melting curve of CaCO3 to 30 kb, the decomposition and melting curves of MgCO3 to 36 kb, and the calcite-aragonite transition at 800°C, 950°C and 1100°C. At 30kb, the melting loop for the CaCO3-MgCO3 join extends from 1610°C (CaCO3) to 1585°C (MgCO3) through a liquidus minimum at 1290°C (near 42 mole% MgCO3). The dolomite-magnesite solvus barely intersects the 30 kb melting loop to produce a peritectic reaction at 1385°C. Integration of the new experimental data with other published data permits construction of a complete P-T projection and a sequence of isobars for the CaCO3-MgCO3 join for pressures between 5 and 30 kb. The phase relations for this join provide part of the essential framework of the model peridotite system CaO-MgO-SiO8-CO2-H2O, which has particular application to the origin of carbonatitic and kimberlitic magmas. In light of the accumulating evidence for CO2 in various forms within the upper mantle and of its effect on magmatic processes, analysis of the melting relations in this system is of considerable importance. 相似文献
105.
The permeability and structure of four fine-grained soils were observed to be changed by freezing and thawing. In all cases freezing and thawing caused a reduction in void ratio and an increase in vertical permeability. The increase in permeability is attributed to the formation of polygonal shrinkage cracks and/or to the reduction of the volume of fines in the pores of the coarse fraction, the mechanism controlling the process depending on material type. No definite relationships are established; however, it appears that the largest increase in permeability occurs for the soil of highest plasticity. 相似文献
106.
Victor C. Farmer Anthony R. Fraser J.Mervyn Tait 《Geochimica et cosmochimica acta》1979,43(9):1417-1420
Infrared spectra in the 300–1400 cm?1 region indicate that the non-crystalline products of interaction between hydroxyaluminium species and orthosilicic acid in dilute aqueous solutions of pH < 5 differ markedly in structure from those formed in near-neutral and alkaline solutions of pH > 6. The compound formed in acid solution has an infrared spectrum similar to imogolite, and is termed proto-imogolite; like imogolite, it contains orthosilicate groups and 6-coordinated aluminium, and has an ideal Si:Al ratio of around 0.5, but it can incorporate some excess alumina or silica and it does not have the regular tubular structure of imogolite. Compounds formed in alkaline solutions that are not too dilute have infrared spectra resembling the feldspathoid group of minerals and are termed hydrous feldspathoids. They incorporate a condensed tetrahedral framework with an Si:Al ratio greater than one, but can also contain 6-coordinated aluminium.Natural allophanes of the proto-imogolite and hydrous feldspathoid types exist. The allophane of weathered pumice, however, contains a condensed silicate anion that incorporates little tetrahedral aluminium. Proto-imogolite forms stable sols at pH < 5 and must play an important role in the transport of aluminium in acidic natural waters containing dissolved silica. 相似文献
107.
Statistical methods are available which predict the maximum response of simple oscillators given the peak acceleration (Ap), peak velocity (Vp) or peak displacement (Dp) of seismic ground motions. An alternative parameter, namely an ordinate (or ordinates) of the Fourier amplitude spectrum of ground motion acceleration, FS(f), may in fact be a preferred predictor of peak response, especially in a frequency range close to f. Other statistical methods (attenuation laws) use distance R and other parameters such as magnitude (M), Modified Mercalli epicentral Intensity (Io) and Modified Mercalli site Intensity (MMI or Is) to predict spectral velocity (Sv(f)), etc. In using such approaches, it is most desirable to know the total uncertainty in the predicted peak response of the system given the starting parameter values. An extensive strong motion data set is used to study these questions, The most direct prediction models are found to be preferable (have lower prediction dispersion) but data may not be available in all regions to permit their use. 相似文献
108.
Veli-Matti Kerminen Risto E. Hillamo Anthony S. Wexler 《Journal of Atmospheric Chemistry》1998,30(3):345-370
A box model was constructed to investigate connections between the particulate MSA to non-sea-salt sulfate ratio, R, and DMS chemistry in a clean marine boundary layer. The simulations demonstrated that R varies widely with particle size, which must be taken into account when interpreting field measurements or comparing them with each other. In addition to DMS gas-phase chemistry, R in the submicron size range was shown to be sensitive to the factors dictating sulfate production via cloud processing, to the removal of SO2 from the boundary layer by dry deposition and sea-salt oxidation, to the entrainment of SO2 from the free troposphere, to the relative concentration of sub- and supermicron particles, and to meteorology. Three potential explanations for the increase of R toward high-latitudes during the summer were found: larger MSA yields from DMS oxidation at high latitudes, larger DMSO yields from DMS oxidation followed by the conversion of DMSO to MSA at high latitudes, or lower ambient H2O2 concentrations at high latitudes leading to less efficient sulfate production in clouds. Possible reasons for the large seasonal amplitude of R at mid and high latitudes include seasonal changes in the partitioning of DMS oxidation to the OH and NO3 initiated pathways, seasonal changes in the concentration of species participating the DMS-OH reaction pathway, or the existence of a SO2 source other than DMS oxidation in the marine boundary layer. Even small anthropogenic perturbations were shown to have a potential to alter the MSA to non-sea-salt sulfate ratio. 相似文献
109.
The second order theory of elasticity, in which terms to second order in strain are retained in calculating atomic bond length changes and elastic moduli, is extended to describe thermal vibration of a face-centred cubic crystal. Coupled with equations relating the pressure dependences of elastic constants, this yields a new formulation of the thermal Grüneisen parameter γ in terms of pressure P, incompressibility K and rigidity, μ where f = 24 (3 K ? 2 P)/(3 K + 115 μ + 90 P). The factor f arises from bond interactions and the case f = 1, representing independent bonds (no interactions), yields the free-volume γ- Since we have shown earlier that the second order elasticity theory provides a convincing explanation of the elasticity of the inner core, we believe that the new formula is appropriate for the inner core. It is, however, inadequate to describe the lower mantle γ, in which atomic bond angle rigidity, not considered here, may be appreciable. 相似文献
110.
Latin America: Contesting extraction, producing geographies 总被引:3,自引:3,他引:0
Anthony Bebbington 《Singapore journal of tropical geography》2009,30(1):7-12