全文获取类型
收费全文 | 97713篇 |
免费 | 1938篇 |
国内免费 | 827篇 |
专业分类
测绘学 | 2285篇 |
大气科学 | 6855篇 |
地球物理 | 19566篇 |
地质学 | 35053篇 |
海洋学 | 8602篇 |
天文学 | 21928篇 |
综合类 | 281篇 |
自然地理 | 5908篇 |
出版年
2022年 | 559篇 |
2021年 | 970篇 |
2020年 | 1094篇 |
2019年 | 1193篇 |
2018年 | 2501篇 |
2017年 | 2392篇 |
2016年 | 2909篇 |
2015年 | 1697篇 |
2014年 | 2861篇 |
2013年 | 5053篇 |
2012年 | 3031篇 |
2011年 | 4155篇 |
2010年 | 3561篇 |
2009年 | 4664篇 |
2008年 | 4254篇 |
2007年 | 4132篇 |
2006年 | 3875篇 |
2005年 | 3017篇 |
2004年 | 2950篇 |
2003年 | 2870篇 |
2002年 | 2610篇 |
2001年 | 2373篇 |
2000年 | 2244篇 |
1999年 | 1851篇 |
1998年 | 1941篇 |
1997年 | 1871篇 |
1996年 | 1546篇 |
1995年 | 1541篇 |
1994年 | 1335篇 |
1993年 | 1213篇 |
1992年 | 1130篇 |
1991年 | 1092篇 |
1990年 | 1184篇 |
1989年 | 1028篇 |
1988年 | 934篇 |
1987年 | 1102篇 |
1986年 | 987篇 |
1985年 | 1242篇 |
1984年 | 1347篇 |
1983年 | 1280篇 |
1982年 | 1229篇 |
1981年 | 1072篇 |
1980年 | 1008篇 |
1979年 | 938篇 |
1978年 | 908篇 |
1977年 | 862篇 |
1976年 | 819篇 |
1975年 | 787篇 |
1974年 | 784篇 |
1973年 | 773篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
781.
The study of granitic plutons of the Baikal Highland and the Tien Shan has made it possible to establish new features of their posthumous (after incorporation into the consolidated Earth’s crust) structural reworking and to understand the implications of the cataclastic flow for the exhumation of the crystalline basement in the studied regions. It is shown that granitic plutons undergo appreciable structural transformation at the stages of tectonic reactivation that is significantly separated in time from the moment of formation of plutons as geological bodies. The 3D cataclastic deformation is the main mode of structural reworking of granitic plutons, while the cataclastic flow is the main form of their mobility. Newly recognized slice structures characterize the volumetric deformation of granites. 相似文献
782.
The lateral variability of structural elements in the collision zone of the Cretaceous-Paleocene Achaivayam-Valagin island arc with the northeastern Asian margin is considered. The similarity and difference of Eocene collision structural elements in the north and the south of Kamchatka are shown. In northern Kamchatka, the continent-arc boundary is traced along the Lesnaya-Vatyn Thrust Fault, which completed its evolution about 45 Ma ago. The thin, near-horizontal allochthon of this thrust, composed of island-arc rocks, overlies the deformed but unmetamorphosed terrigeneous sequences of the Asian margin. The general structure of this suture in the Kamchatka Isthmus and southern Koryakia is comparable with the uppermost subduction zone, where a thin lithospheric wedge overlaps intensely deformed sediments detached from the plunging plate. In southern Kamchatka (Malka Uplift of the Sredinny Range), the arc-continent collision started 55–53 Ma ago with thrusting of island-arc complexes over terrigenous rocks of continental margin. However, the thickness of the allochthon was much greater than in the north. Immediately after this event, both the autochthon and lower part of allochthon were deformed and subsided to a significant depth. This subsidence gave rise to metamorphism of both the autochthon (Kolpakov and Kamchatka groups, Kheivan Formation) and lower allochthon (Andrianovka and Khimka formations). The anomalously fast heating of the crust was most likely related to the ascent of asthenospheric masses due to slab breakoff, when the Eurasian Plate was plunging beneath the Achaivayam-Valagin arc. 相似文献
783.
Establishing the petrogenesis of volcanic and plutonic rocksis a key issue in unraveling the evolution of distinct subduction-relatedtectonic phases occurring along the South American margin. Thisis particularly true for Cenozoic times when large volumes ofmagma were produced in the Andean belt. In this study we havefocused on Oligo-Miocene magmatism in central Chile at 33°S.Our data include field and petrographic observations, whole-rockmajor and trace element analyses, U–Pb zircon dating,and Pb, Sr, and Hf isotope analyses of plagioclase, clinopyroxene,and zircon mineral separates. Combined with earlier dating resultsthe new zircon ages define a 28·8–5·2 Maperiod of plutonic and volcanic activity that ceased as a consequenceof flattening subduction of the Nazca–Farallon plate.Rare earth elements patterns are variable, with up to 92 timeschondrite concentrations for light rare earth elements yielding(La/Yb)N between 3·6 and 7·0, and an absence ofEu anomalies. Initial Pb isotope signatures are in the rangeof 18·358–19·023 for 206Pb/ 204Pb, 15·567–15·700for 207Pb/ 204Pb and 38·249–39·084 for 208Pb/204Pb. Initial 87Sr/ 86Sr are mostly in the range of 0·70369–0·70505,with two more radiogenic values at 0·7066. Initial Hfisotopic compositions of zircons yield exclusively positiveHfi ranging between + 6·9 and + 9·6. The newlydetermined initial isotope characteristics of the Oligo-Miocenemagmas suggest that the mantle source lithologies are differentfrom both those of Pacific mid-ocean ridge basalt and oceanisland basalt, plotting in the field of reference values forsubcontinental lithospheric mantle, characterized by moderatelarge ion lithophile element–high field strengh elementdepletion and high 238U/ 204Pb. A Hf model age of 2 Ga is estimatedfor the formation of the subcontinental mantle–continentalcrust assemblage in the region, suggesting that the initialSr and Pb isotope ratios inferred for the source of the Oligo-Mioceneparental magmas are the result of later Rb and U enrichmentcaused by mantle metasomatism. A time-integrated model Rb/Srof 0·039 and µ 16 are estimated for the sourceof the parental magmas, consistent with ratios measured in peridotitexenoliths from continental areas. Evolution from predominant(>90%) basaltic–gabbroic to andesitic–dioriticmagmas seems to involve a combination of (1) original traceelement differences in the metasomatized subcontinental mantle,(2) different degrees of partial melting and (3) fractionalcrystallization in the garnet- and spinel-peridotite stabilityfields. The genesis of more differentiated magmas reaching rhyolitic–graniticcompositions most probably also includes additional crystalfractionation at both shallow mantle depths and within the crust,possibly leading to some very minor assimilation of crustalmaterial. KEY WORDS: calc-alkaline magmatism; Oligo-Miocene; U–Pb dating; Sr–Pb–Hf isotopes; central Chile 相似文献
784.
The petroleum resource potential is considered for the Atlantic, West Pacific, and East Pacific types of deepwater continental margins. The most considerable energy resources are concentrated at the Atlantic-type passive margins in the zone transitional to the ocean. The less studied continental slope of backarc seas of the generally active margins of the West Pacific type is currently not so rich in discoveries as the Atlantic-type margin, but is not devoid of certain expectations. In some of their parameters, the margins bounded by continental slopes may be regarded as analogs of classical passive margins. At the margins of the East Pacific type, the petroleum potential is solely confined to transform segments. In the shelf-continental-slope basins of the rift and pull-apart nature, petroleum fields occur largely in the upper fan complex, and to a lesser extent in the lower graben (rift) complex. In light of world experience, the shelf-continental-slope basins of the Arctic and Pacific margins of Russia are evaluated as highly promising. 相似文献
785.
M. G. Leonov 《Geotectonics》2008,42(5):327-356
The factual material and modeling results concerning the geology of specific structural elements defined as lateral protrusions, or flowing layers, are considered. The formation of such structural elements is a fundamental phenomenon that controls many features of the structural evolution and geodynamics of platform basement and foldbelts. A lateral protrusion, or flowing layer, is a spatially constrained, nearly horizontal geological body with attributes of 3D tectonic flow (rheid deformation) and lateral transport of rock masses. Flowing layers are large lateral protrusions that play important role in the structure of the continental and oceanic lithosphere. They embody the internal mobility of huge rock bodies and confirm the possibility of their lateral redistribution at different depths of the continental lithosphere. The lateral displacement of rocks within such assemblies may occur in the regime of cold deformation, heating, metamorphism, and ductile flow of rocks under subsolidus conditions or in the process of their partial melting. 相似文献
786.
Klauea historical summit lavas have a wide range in matrix 18OVSMOWvalues (4·9–5·6) with lower values in rockserupted following a major summit collapse or eruptive hiatus.In contrast, 18O values for olivines in most of these lavasare nearly constant (5·1 ± 0·1). The disequilibriumbetween matrix and olivine 18O values in many samples indicatesthat the lower matrix values were acquired by the magma afterolivine growth, probably just before or during eruption. BothMauna Loa and Klauea basement rocks are the likely sources ofthe contamination, based on O, Pb and Sr isotope data. However,the extent of crustal contamination of Klauea historical magmasis probably minor (< 12%, depending on the assumed contaminant)and it is superimposed on a longer-term, cyclic geochemicalvariation that reflects source heterogeneity. Klauea's heterogeneoussource, which is well represented by the historical summit lavas,probably has magma 18O values within the normal mid-ocean ridgebasalt mantle range (5·4–5·8) based on thenew olivine 18O values. KEY WORDS: Hawaii; Klauea; basalt; oxygen isotopes; crustal contamination 相似文献
787.
A. van Geen K. Radloff Z. Aziz Z. Cheng M.R. Huq K.M. Ahmed B. Weinman S. Goodbred H.B. Jung Y. Zheng M. Berg P.T.K. Trang L. Charlet J. Metral D. Tisserand S. Guillot S. Chakraborty A.P. Gajurel B.N. Upreti 《Applied Geochemistry》2008
One of the reasons the processes resulting in As release to groundwater in southern Asia remain poorly understood is the high degree of spatial variability of physical and chemical properties in shallow aquifers. In an attempt to overcome this difficulty, a simple device that collects groundwater and sediment as a slurry from precisely the same interval was developed in Bangladesh. Recently published results from Bangladesh and India relying on the needle-sampler are augmented here with new data from 37 intervals of grey aquifer material of likely Holocene age in Vietnam and Nepal. A total of 145 samples of filtered groundwater ranging in depth from 3 to 36 m that were analyzed for As (1–1000 μg/L), Fe (0.01–40 mg/L), Mn (0.2–4 mg/L) and S (0.04–14 mg/L) are compared. The P-extractable (0.01–36 mg/kg) and HCl-extractable As (0.04–36 mg/kg) content of the particulate phase was determined in the same suite of samples, in addition to Fe(II)/Fe ratios (0.2–1.0) in the acid-leachable fraction of the particulate phase. Needle-sampler data from Bangladesh indicated a relationship between dissolved As in groundwater and P-extractable As in the particulate phase that was interpreted as an indication of adsorptive equilibrium, under sufficiently reducing conditions, across 3 orders of magnitude in concentrations according to a distribution coefficient of 4 mL/g. The more recent observations from India, Vietnam and Nepal show groundwater As concentrations that are often an order of magnitude lower at a given level of P-extractable As compared to Bangladesh, even if only the subset of particularly reducing intervals characterized by leachable Fe(II)/Fe >0.5 and dissolved Fe >0.2 mg/L are considered. Without attempting to explain why As appears to be particularly mobile in reducing aquifers of Bangladesh compared to the other regions, the consequences of increasing the distribution coefficient for As between the particulate and dissolved phase to 40 mL/g for the flushing of shallow aquifers of their initial As content are explored. 相似文献
788.
T. N. Palechek E. P. Terekhov A. V. Mozherovskii 《Stratigraphy and Geological Correlation》2008,16(6):650-663
The results of radiolarian analysis confirm the Campanian-Maastrichtian age of the Malokuril’skaya Formation in the Shikotan Island. The Campanian-Maastrichtian age of the formation is implied simultaneously by radiolarians and inoceramids. The studied Campanian and Campanian-Maastrichtian radiolarian assemblages include abundant specimens representing genus Prunobrachium, characteristic of which was bipolar distribution in cold-water to temperate basins. The new occurrence site of prunobrachids is established at the latitude of 43°N, the Far East of Russia. 相似文献
789.
M. P. Chekhovskaya I. A. Basov A. G. Matul T. A. Khusid S. A. Gorbarenko 《Stratigraphy and Geological Correlation》2008,16(3):328-342
Taxonomic composition and distribution of planktonic foraminifers are studied in section of Core GC-11 that penetrated through Upper Quaternary sediments of the Bowers Ridge western slope, the southern Bering Sea. As is shown, structure of foraminiferal assemblage and productivity have varied substantially during the last 32000 calendar years in response to changes in surface water temperatures and water mass circulation in the northern part of the Pacific, the Bering Sea included. The productivity was maximal during deglaciation epoch, being notably lower in the Holocene and minimal at the glaciation time. 相似文献
790.
The described fusulinids of the Moscovian Stage are found in the Asad-Abad section of the Sanandaj-Sirjan tectonic zone of Iran. Five successive fusulinid assemblages are distinguished. Three lower of them belong to the Kashirian Substage, the other two to the Podolskian Substage. The section studied is correlated with most complete sections of the Moscovian Stage in the western Tethys. Two new species Fusulinella (Moellerites) pygmea and Putrella primaris are identified; in addition to nominative taxon, the latter includes new subspecies P. primaris compacta. 相似文献