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241.
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Liquidus relations in the four-component system Na2OAl2O3SiO2F2O1were studied at 0· 1 and 100 MPa to define the locationof fluoridesilicate liquid immiscibility and outlinedifferentiation paths of fluorine-bearing silicic magmas. Thefluoridesilicate liquid immiscibility spans the silicaalbitecryoliteand silicatopazcryolite ternaries and the haplogranite-cryolitebinary at greater than 960°C and 0· 1100 MPa.With increasing Al2O3 in the system and increasing aluminum/alkalication ratio, the two-liquid gap contracts and migrates fromthe silica liquidus to the cryolite liquidus. The gap does notextend to subaluminous and peraluminous melt compositions. Forall alkali feldsparquartz-bearing systems, the miscibilitygap remains located on the cryolite liquidus and is thus inaccessibleto differentiating granitic and rhyolitic melts. In peralkalinesystems, the magmatic differentiation is terminated at the albitequartzcryoliteeutectic at 770°C, 100 MPa, 5 wt % F and cation Al/Na =0· 75. The addition of topaz, however, significantlylowers melting temperatures and allows strong fluorine enrichmentin subaluminous compositions. At 100 MPa, the binary topazcryoliteeutectic is located at 770°C, 39 wt % F, cation Al/Na 0·95, and the ternary quartztopazcryolite eutecticis found at 740°C, 32 wt % F, 30 wt % SiO2 and cation Al/Na 0· 95. Such location of both eutectics enables fractionationpaths of subaluminous quartz-saturated systems to produce fluorine-rich,SiO2-depleted and nepheline-normative residual liquids. KEY WORDS: silicate melt; granite; rhyolite; fluorine; liquid immiscibility 相似文献
243.
为了研究川西卡拉地区晚古生代沉积环境特征,以该地区下石炭统邛依组和上二叠统卡翁沟组中广泛分布的硅质岩为研究对象,开展了岩石学、地球化学特征等研究。结果表明: 研究区古生代硅质岩属纯硅质岩范畴,在沉积过程中有持续的陆源物质供给; Al/(Al+Fe+Mn)平均值0.62,结合Al-Fe-Mn三角图解,显示它们为生物成因硅质岩; Al2O3/(Al2O3+Fe2O3)、Th/U、Th/Sc、(La/Ce)N、(La/Yb)N等特征比值以及构造环境判别图,反映出硅质岩沉积环境为大陆边缘的浅海-斜坡; Ceanom值为-0.04~0.07,从石炭纪—二叠纪逐渐增大,指示水体为缺氧环境,且还原性逐渐增强。结合区域地质演化,认为甘孜理塘洋在石炭纪时期已经打开,并在二叠纪时期持续扩张,区内沉积盆地的海水逐渐变深。 相似文献
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江西金山含金黄铁矿的稀土元素赋存状态研究 总被引:4,自引:1,他引:3
稀土元素在地质领域得到广泛的应用,查明稀土元素在地质体中的赋存状态,对应用稀土元素解决地学问题非常有意义。本文利用分步溶样ICP-MS测试方法对江西金山金矿含金黄铁矿中稀土元素作了详细的研究,试图弄清黄铁矿中稀土元素的赋存状态。实验表明,金山金矿与金成矿关系密切的黄铁矿的流体包裹体中稀土元素的含量很低;而具有高稀土元素含量的硫化物中的稀土元素主要赋存在硫化物所包含的富Zr微矿物中,如锆石、金红石、尖晶石、钛铁矿等。这些微矿物究竟是以包裹体子晶的形式存在,还是以捕虏晶的形式存在尚有待进一步研究。黄铁矿中包含的硅酸盐相对黄铁矿稀土元素含量及特征的影响很大,直接制约了黄铁矿的稀土元素组成。黄铁矿流体包裹体与黄铁矿矿物的稀土元素组成虽然在含量上有差异,但其配分形式相似,所以黄铁矿的稀土元素组成可以代表黄铁矿中液体包裹体的稀土元素组成,通过分析黄铁矿的稀土元素特征,可以示踪成矿流体的来源与性质,前提是实验中不要将黄铁矿样品全部溶掉,以保证黄铁矿中所包裹的硅酸盐相不参与黄铁矿REE组成的测量。 相似文献
248.
This research evaluates the economics of cost-sharing improved irrigation technologies to reduce agricultural, nonpoint-source
contamination. Irrigation and fertilization inefficiencies are modeled within a nonjoint production process to evaluate both
private and public costs of technology adoption and its effect on groundwater nitrate-contamination levels. A central Nebraska
application indicates that even without a current government subsidy, a farmer is economically better off switching from gravity-flow
to surge-flow irrigation rather than a center-pivot system. An annual government subsidy of $22.50 (US$) per hectare per year
is required over the life of a center-pivot system to make the farmer financially indifferent. However, cost-sharing center-pivot
adoption improves the groundwater contamination level, while other irrigation systems result in continued deterioration of
groundwater quality.
Received: 3 November 1998 · Accepted: 15 February 1999 相似文献
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H. Kagi J. B. Parise H. Cho G. R. Rossman J. S. Loveday 《Physics and Chemistry of Minerals》2000,27(4):225-233
Neutron powder diffraction data of phase A (Mg7Si2O8(OH)6) were collected at ambient pressure and 3.2?GPa (calculated from the compressibility of phase A) from the deuterated compound, and the structure was refined using the Rietveld method. The derived crystal structure implies that hydrogen atoms occupy two distinct sites in phase A, both forming hydrogen bonds of different lengths with the same oxygen atom. This picture is supported by IR spectra, which exhibit two absorption bands at 3400 and 3513?cm?1 corresponding to OH stretching vibrations, and proton NMR spectra, which display two peaks with equal intensities and isotropic chemical shifts of 3.7 and 5?ppm. The D-D distance [D(1)-D(2) distance] at ambient pressure was found to be 2.09?±?0.02?Å from the neutron diffraction data and 2.09?±?0.05?Å from the NMR spectra. At 3.2?GPa, there is no statistically significant increase in the O-D interatomic distance while the hydrogen bonding interaction D···O appears to increase for one of the hydrogen sites, D(1), which has the stronger hydrogen bonding interaction compared with the other hydrogen, D(2), at ambient pressure. The O-D bond valences, determined indirectly from the D···O distances were 0.86 and 0.91 at ambient pressure, and 0.83 and 0.90?at 3.2?GPa, for D(1) and D(2), respectively. 相似文献