全文获取类型
收费全文 | 5763篇 |
免费 | 225篇 |
国内免费 | 89篇 |
专业分类
测绘学 | 168篇 |
大气科学 | 546篇 |
地球物理 | 1441篇 |
地质学 | 1997篇 |
海洋学 | 550篇 |
天文学 | 754篇 |
综合类 | 22篇 |
自然地理 | 599篇 |
出版年
2021年 | 60篇 |
2020年 | 64篇 |
2019年 | 86篇 |
2018年 | 124篇 |
2017年 | 116篇 |
2016年 | 156篇 |
2015年 | 144篇 |
2014年 | 202篇 |
2013年 | 323篇 |
2012年 | 242篇 |
2011年 | 263篇 |
2010年 | 191篇 |
2009年 | 307篇 |
2008年 | 285篇 |
2007年 | 262篇 |
2006年 | 220篇 |
2005年 | 188篇 |
2004年 | 196篇 |
2003年 | 189篇 |
2002年 | 181篇 |
2001年 | 133篇 |
2000年 | 136篇 |
1999年 | 115篇 |
1998年 | 107篇 |
1997年 | 91篇 |
1996年 | 84篇 |
1995年 | 85篇 |
1994年 | 75篇 |
1993年 | 63篇 |
1992年 | 65篇 |
1991年 | 69篇 |
1990年 | 66篇 |
1989年 | 59篇 |
1988年 | 58篇 |
1987年 | 65篇 |
1986年 | 43篇 |
1985年 | 73篇 |
1984年 | 80篇 |
1983年 | 72篇 |
1982年 | 65篇 |
1981年 | 76篇 |
1980年 | 63篇 |
1979年 | 57篇 |
1978年 | 38篇 |
1977年 | 54篇 |
1976年 | 63篇 |
1975年 | 46篇 |
1974年 | 56篇 |
1973年 | 47篇 |
1972年 | 25篇 |
排序方式: 共有6077条查询结果,搜索用时 31 毫秒
431.
432.
433.
Peter Bond 《Astronomy& Geophysics》2001,42(3):3.30-3.32
Peter Bond recounts another attempt to visit Mars, yet more data from Galileo and the benefits that result from applying a variety of instruments to a tricky problem. 相似文献
434.
Peter Bond 《Astronomy& Geophysics》2001,42(4):4.24-4.28
The dark universe, in the form of black holes, has been under investigation during recent observations by space-based observatories, reports Peter Bond . 相似文献
435.
Velocity and absorption tomograms are the two most common forms of presentation of radar tomographic data. However, mining personnel, geophysicists included, are often unfamiliar with radar velocity and absorption. In this paper, general formulae are introduced, relating velocity and attenuation coefficient to conductivity and dielectric constant. The formulae are valid for lossy media as well as high-resistivity materials. The transformation of velocity and absorption to conductivity and dielectric constant is illustrated via application of the formulae to radar tomograms from the Hellyer zinc–lead–silver mine, Tasmania, Australia. The resulting conductivity and dielectric constant tomograms constructed at Hellyer demonstrated the potential of radar tomography to delineate sulphide ore zones. 相似文献
436.
Peter Furness 《Journal of Applied Geophysics》2001,48(4)
The general problem of magnetic modelling involves accounting for the effect of both remanent magnetization and the application of an external magnetic field. However, as far as the disturbing field of a magnetic body in a magnetic environment is concerned, there is an equivalence between the effects of these two causations that allows the remanence to be represented in terms of an equivalent primary magnetic H field. Moreover, due to the linearity of the magnetic field in terms of its causations, the general modelling problem involving an applied magnetic field in the presence of remanence can be simply and more efficiently dealt with in terms of an equivalent primary field acting in the absence of any remanent magnetization. 相似文献
437.
Run products from high pressure experiments at 800-1,200 °C and 5-14 GPa (corresponding to depths of 150 to 420 km) on a serpentine bulk composition [close to Mg3Si2O5(OH)4] were analysed by optical microscopy, micro-Raman spectroscopy and electron microprobe. All charges exhibit strong chemical zoning. Fluid, melt and hydrous solids were mostly concentrated at the top, bottom and along the wall of the capsules. The central part of the charge was devoid of H2O. Both fluid and hydrous magnesian phases exhibit a Mg/Si ratio higher than forsterite. In contrast, the centre of the capsule was enriched in SiO2. The observed zoning can neither be explained by gravitational settling nor by a thermal gradient alone. Most likely the fluid was separated from the solids by surface forces and thereby established the chemical gradient by preferentially dissolving MgO. If strong chemical zoning is taken into account, the occurrence of more phases than allowed by the phase rule can be explained by separating the bulk into several domains of different bulk compositions. Results indicate that small amounts of F increase the stability field of clinohumite, Mg9Si4O16(OH,F)2, compared to OH-clinohumite in pure MSH previously reported. Clinohumite coexists with enstatite up to 975 °C at 5 GPa, and up to 1,100 °C at 12 GPa. At 14 GPa (close to the !/#-Mg2SiO4 transition) phase E becomes the most important water carrier. The new results indicate that clinohumite could be an important mantle mineral for transporting water into the Earth's transition zone due to its high thermal stability compared to other important water carriers such as serpentine and phase A. 相似文献
438.
Othmar Müntener Peter B. Kelemen Timothy L. Grove 《Contributions to Mineralogy and Petrology》2001,141(6):643-658
Exposed, subduction-related magmatic arcs commonly include sections of ultramafic plutonic rocks that are composed of dunite, wehrlite, and pyroxenite. In this experimental study we examined the effects of variable H2O concentration on the phase proportions and compositions of igneous pyroxenites and related ultramafic plutonic rocks. Igneous crystallization experiments simulated natural, arc magma compositions at 1.2 GPa, corresponding to conditions of the arc lower crust. Increasing H2O concentration in the liquid changes the crystallization sequence. Low H2O concentration in the liquid stabilizes plagioclase earlier than garnet and amphibole while derivative liquids remain quartz normative. Higher H2O contents (>3%) suppress plagioclase and lead to crystallization of amphibole and garnet thereby producing derivative corundum normative andesite liquids. The experiments show that alumina in the liquid correlates positively with Al in pyroxene, as long as no major aluminous phase crystallizes. Extrapolation of this correlation to natural pyroxenites in the Talkeetna and Kohistan arc sections indicates that clinopyroxenes with low Ca-Tschermaks component represent near-liquidus phases of primitive, Si-rich hydrous magmas. Density calculations on the residual solid assemblages indicate that ultramafic plutonic rocks are always denser than upper mantle rocks in the order of 0.05 to 0.20 g/cm3. The combination of high pressure and high H2O concentration in the liquid suppresses plagioclase crystallization, so that ultramafic plutonic rocks form over a significant proportion of the crystallization interval (up to 50% crystallization of ultramafic rocks from initial, mantle-derived liquids). This suggests that in subduction-related magmatic arcs the seismic Moho might be shallower than the petrologic crust/mantle transition. It is therefore possible that calculations based on seismic data have overestimated the normative plagioclase content (e.g., SiO2, Al2O3) of igneous crust in arcs. 相似文献
439.
Peter J. Pollard 《Mineralium Deposita》2001,36(1):93-100
Iron-oxide–Cu–Au deposits, particularly those formed in deeper level (plutonic) environments, are commonly characterized
by regional scale sodic(–calcic) alteration, which typically formed pre- or syn-Cu–Au mineralization. The sodic(–calcic) assemblages
include albite, scapolite, pyroxene, actinolite, apatite, titanite, epidote and calcite. The consistent presence of coexisting
hypersaline aqueous and CO2-rich fluids in minerals from sodic(–calcic) alteration and associated Fe-oxide–Cu–Au deposits is the result of unmixing of
H2O–CO2–NaCl ± CaCl2–KCl magmatic fluids. Experimental evidence indicates that the Na/(Na + K) ratio of fluids in equilibrium with two alkali
feldspars in CO3
2−-bearing parent fluids would be significantly higher than in unmixed chloride-bearing aqueous fluids. Therefore, fluid unmixing
caused by decreases in temperature and/or pressure, will result in albitization of wall rocks, as is observed in most deeper
level Fe-oxide–Cu–Au deposits. This alteration style may be succeeded by K-feldspathization with decreasing temperature because
of the increase in equilibrium Na/(Na + K) in chloride-bearing fluids buffered by alkali feldspars.
Received: 26 May 1999 / Accepted: 8 June 2000 相似文献
440.
Su Young Lee Masatsugu Ohnishi Yasuhiro Shibata Makoto Wwatanabe Kenichi Hoshino Mayumi Jige Xiangping Gu Hitoshi Chiba Tamotsu Oomori Kantaro Fujioka Peter A. Rona 《Resource Geology》2001,51(1):63-68
Abstract: Pyrite rich in Zn, up to 3.1 wt%, was found in the TAG active mound of the TAG hydrothermal field, the slow-spreading Mid-Atlantic Ridge at 26°08'N and 44°49'W. The Zn-rich pyrite is characterized by an optical homogeneity, a homogeneous distribution of Zn in the back-scattered electron images, both at a magnification of about 500, a negative correlation between Fe and Zn contents of the pyrite and a rather small unit cell edge (a0 = 5.4117 ± 0.0008Å), strongly indicating that the detected Zn is present in the pyrite in solid solution. Such Zn concentrations are observed exclusively in dendritic pyrite, suggesting that the Znrich pyrite grew from hydrothermal fluids of a high degree of supersaturation due to quenching on the seafloor. 相似文献