收费全文 | 2382篇 |
免费 | 420篇 |
国内免费 | 694篇 |
测绘学 | 14篇 |
大气科学 | 33篇 |
地球物理 | 717篇 |
地质学 | 1983篇 |
海洋学 | 161篇 |
天文学 | 13篇 |
综合类 | 66篇 |
自然地理 | 509篇 |
2024年 | 9篇 |
2023年 | 28篇 |
2022年 | 52篇 |
2021年 | 61篇 |
2020年 | 69篇 |
2019年 | 68篇 |
2018年 | 54篇 |
2017年 | 55篇 |
2016年 | 60篇 |
2015年 | 64篇 |
2014年 | 72篇 |
2013年 | 97篇 |
2012年 | 139篇 |
2011年 | 105篇 |
2010年 | 82篇 |
2009年 | 123篇 |
2008年 | 170篇 |
2007年 | 217篇 |
2006年 | 214篇 |
2005年 | 181篇 |
2004年 | 201篇 |
2003年 | 152篇 |
2002年 | 136篇 |
2001年 | 125篇 |
2000年 | 110篇 |
1999年 | 128篇 |
1998年 | 116篇 |
1997年 | 103篇 |
1996年 | 91篇 |
1995年 | 65篇 |
1994年 | 63篇 |
1993年 | 73篇 |
1992年 | 34篇 |
1991年 | 39篇 |
1990年 | 30篇 |
1989年 | 21篇 |
1988年 | 28篇 |
1987年 | 30篇 |
1986年 | 17篇 |
1985年 | 6篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1954年 | 2篇 |
相似文献
965.
Thomas Stachel Sonja Aulbach Gerhard P. Brey Jeff W. Harris Ingrid Leost Ralf Tappert K.S. Viljoen 《Lithos》2004,77(1-4):1-19
On a global scale, peridotitic garnet inclusions in diamonds from the subcratonic lithosphere indicate an evolution from strongly sinusoidal REEN, typical for harzburgitic garnets, to mildly sinusoidal or “normal” patterns (positive slope from LREEN to MREEN, fairly flat MREEN–HREEN), typical for lherzolitic garnets. Using the Cr-number of garnet as a proxy for the bulk rock major element composition it becomes apparent that strong LREE enrichment in garnet is restricted to highly depleted lithologies, whereas flat or positive LREE–MREE slopes are limited to less depleted rocks. For lherzolitic garnet inclusions, there is a positive relation between equilibration temperature, enrichment in MREE, HREE and other HFSE (Ti, Zr, Y), and decreasing depletion in major elements. For harzburgitic garnets, relations are not linear, but it appears that lherzolite style enrichment in MREE–HREE only occurs at temperatures above 1150–1200 °C, whereas strong enrichment in Sr is absent at these high temperatures. These observations suggest a transition from melt metasomatism (typical for the lherzolitic sources) characterized by fairly unfractionated trace and major element compositions to metasomatism by CHO fluids carrying primarily incompatible trace elements. Melt and fluid metasomatism are viewed as a compositional continuum, with residual CHO fluids resulting from primary silicate or carbonate melts in the course of fractional crystallization and equilibration with lithospheric host rocks.
Eclogitic garnet inclusions show “normal” REEN patterns, with LREE at about 1× and HREE at about 30× chondritic abundance. Clinopyroxenes approximately mirror the garnet patterns, being enriched in LREE and having chondritic HREE abundances. Positive and negative Eu anomalies are observed for both garnet and clinopyroxene inclusions. Such anomalies are strong evidence for crustal precursors for the eclogitic diamond sources. The trace element composition of an “average eclogitic diamond source” based on garnet and clinopyroxene inclusions is consistent with derivation from former oceanic crust that lost about 10% of a partial melt in the garnet stability field and that subsequently experienced only minor reenrichment in the most incompatible trace elements. Based on individual diamonds, this simplistic picture becomes more complex, with evidence for both strong enrichment and depletion in LREE. Trace element data for sublithospheric inclusions in diamonds are less abundant. REE in majoritic garnets indicate source compositions that range from being similar to lithospheric eclogitic sources to strongly LREE enriched. Lower mantle sources, assessed based on CaSi–perovskite as the principal host for REE, are not primitive in composition but show moderate to strong LREE enrichment. The bulk rock LREEN–HREEN slope cannot be determined from CaSi–perovskites alone, as garnet may be present in these shallow lower mantle sources and then would act as an important host for HREE. Positive and negative Eu anomalies are widespread in CaSi–perovskites and negative anomalies have also been observed for a majoritic garnet and a coexisting clinopyroxene inclusion. This suggests that sublithospheric diamond sources may be linked to old oceanic slabs, possibly because only former crustal rocks can provide the redox gradients necessary for diamond precipitation in an otherwise reduced sublithospheric mantle. 相似文献 966.
Pressures at which partial crystallization occurs for mid-oceanridge basalts (MORB) have been examined by a new petrologicalmethod that is based on a parameterization of experimental datain the form of projections. Application to a global MORB glassdatabase shows that partial crystallization of olivine + plagioclase+ augite ranges from 1 atm to 1·0 GPa, in good agreementwith previous determinations, and that there are regional variationsthat generally correlate with spreading rate. MORB from fast-spreadingcenters display partial crystallization in the crust at ridgesegment centers and in both mantle and crust at ridge terminations.Fracture zones are likely to be regions where magma chambersare absent and where there is enhanced conductive cooling ofthe lithosphere at depth. MORB from slow-spreading centers displayprominent partial crystallization in the mantle, consistentwith models of enhanced conductive cooling of the lithosphereand the greater abundance of fracture zones through which theypass. In general, magmas that move through cold mantle experiencesome partial crystallization, whereas magmas that pass throughhot mantle may be comparatively unaffected. Estimated pressuresof partial crystallization indicate that the top of the partialmelting region is deeper than about 2035 km below slow-spreadingcenters and some ridge segment terminations at fast-spreadingcenters. KEY WORDS: MORB; olivine gabbro; partial crystallization; partial melting; ridge segmentation; fracture zones; crust; mantle; lithosphere 相似文献
967.
Rheological Properties of Partially Molten Lherzolite 总被引:2,自引:1,他引:2
Lherzolite samples synthesized from fine-grained powders preparedfrom a natural xenolith were deformed at P = 300 MPa and 1373 相似文献
968.
BRUECKNER HANNES K.; VAN ROERMUND HERMAN L. M.; PEARSON NORMAN J. 《Journal of Petrology》2004,45(2):415-437
Mineralogical, isotopic, geochemical and geochronological evidencedemonstrates that the Friningen body, a garnet peridotite bodycontaining garnet pyroxenite layers in the Seve Nappe Complex(SNC) of Northern Jämtland, Sweden, represents old, certainlyProterozoic and possibly Archean, lithosphere that became incorporatedinto the Caledonian tectonic edifice during crustal subductioninto the mantle at c. 450 Ma. Both garnet peridotite and pyroxenitecontain two (M1 and M2) generations of garnet-bearing assemblagesseparated by the formation of two-pyroxene, spinel symplectitearound the M1 garnet and the crystallization of low-Cr spinel1Cin the matrix. These textures suggest initial high-pressure(HP) crystallization of garnet peridotite and pyroxenite succeededby decompression into the spinel stability field, followed byrecompression into the garnet peridotite facies. Some pyroxenitelayers appear to be characterized solely by M2 assemblages withstretched garnet as large as several centimeters. Laser ablationmicroprobeinductively coupled plasma mass spectrometryReOs analyses of single sulfide grains generally definemeaningless model ages suggesting more than one episode of Reand/or Os addition and/or loss to the body. Pentlandite grainsfrom a single polished slab of one garnet peridotite, however,define a linear array on an ReOs isochron diagram that,if interpreted as an errorchron, suggests an Archean melt extractionevent that left behind the depleted dunite and harzburgite bodiesthat characterize the SNC. Refertilization of this mantle bymelts associated with the development of the pyroxenite layersis indicated by enriched clinopyroxene SrNd isotope ratios,and by parallel large ion lithophile-enriched trace elementpatterns in clinopyroxene from pyroxenite and the immediatelyadjacent peridotite. Clinopyroxene and whole-rock model SmNdages (TDM = 1·12·2 Ga) indicate that fertilizationtook place in Proterozoic times. SmNd garnet2clinopyroxene2wholerock ± orthopyroxene2 mineral isochrons from three pyroxenitelayers define overlapping ages of 452·1 ± 7·5and 448 ± 13 Ma and 451 ± 43 Ma (2 相似文献
969.
WILLIAMS H. M.; TURNER S. P.; PEARCE J. A.; KELLEY S. P.; HARRIS N. B. W. 《Journal of Petrology》2004,45(3):555-607
Neogene potassic lavas in northern and southern Tibet have differentisotopic ( 相似文献
970.
鄂东南铜山口、殷祖埃达克质(adakitic)侵入岩的地球化学特征对比:(拆沉)下地壳熔融与斑岩铜矿的成因 总被引:29,自引:22,他引:29
鄂东南地区铜山口花岗闪长斑岩体是与斑岩铜钼矿床共生的岩体,但殷祖花岗闪长岩体是与金属成矿无关的岩体。铜山口和殷祖侵入岩的元素地球化学特征与埃达克岩的地球化学特征非常类似,如高Al2O3、Sr含量与La/Yb、Sr/Y比值,富Na2O(Na2O/K2O>1.0),亏损Y与Yb,极弱负Eu异常-正Eu异常以及正Sr异常等。但是铜山口和殷祖侵入岩也存在 明显的差别:前者比后者更偏酸性,但具有较高的K2O,MgO,Cr,Ni和Sr含量,较低的Y和Yb含量,轻重稀土元素分异更明显,并主要显示出正铕异常,区别于后者的极弱负Eu异常-不明显Eu异常。这表明铜山口埃达克质侵入岩的岩浆来源可能比殷祖埃达克质侵入岩的岩浆来源更深:前者可能由拆沉的下地壳熔融形成,残留物主要含石榴子石;而后者可能由增厚的下地壳熔融形成,残留物可能为石榴子石±斜长石±角闪石。另外,热的地幔上涌,底辟(diapir)进入下地壳,导致含角闪石的榴辉岩发生熔融也可形成铜山口埃达克质岩浆。铜山口埃达克质岩浆在穿过地幔的过程中,将会与地幔橄榄岩发生交换反应:一方面由于受橄榄岩的混染而使得岩浆的MgO,Cr和Ni增高;另一方面岩浆中的Fe2O3不断加入到地幔中,导致地幔的氧逸度(fo2)增高,地幔中金属硫化物被氧化并进入岩浆中,富含Cu-Mo等成矿物质的岩浆上升很容易形成斑岩铜钼矿 相似文献
|