全文获取类型
收费全文 | 37115篇 |
免费 | 293篇 |
国内免费 | 212篇 |
专业分类
测绘学 | 721篇 |
大气科学 | 1705篇 |
地球物理 | 7045篇 |
地质学 | 14625篇 |
海洋学 | 3529篇 |
天文学 | 8801篇 |
综合类 | 98篇 |
自然地理 | 1096篇 |
出版年
2022年 | 487篇 |
2021年 | 705篇 |
2020年 | 754篇 |
2019年 | 826篇 |
2018年 | 1696篇 |
2017年 | 1544篇 |
2016年 | 1637篇 |
2015年 | 614篇 |
2014年 | 1414篇 |
2013年 | 2035篇 |
2012年 | 1619篇 |
2011年 | 1900篇 |
2010年 | 1790篇 |
2009年 | 1986篇 |
2008年 | 1765篇 |
2007年 | 1978篇 |
2006年 | 1736篇 |
2005年 | 899篇 |
2004年 | 815篇 |
2003年 | 809篇 |
2002年 | 741篇 |
2001年 | 764篇 |
2000年 | 630篇 |
1999年 | 416篇 |
1998年 | 436篇 |
1997年 | 475篇 |
1996年 | 336篇 |
1995年 | 357篇 |
1994年 | 335篇 |
1993年 | 282篇 |
1992年 | 284篇 |
1991年 | 290篇 |
1990年 | 337篇 |
1989年 | 272篇 |
1988年 | 258篇 |
1987年 | 260篇 |
1986年 | 191篇 |
1985年 | 301篇 |
1984年 | 302篇 |
1983年 | 295篇 |
1982年 | 274篇 |
1981年 | 248篇 |
1980年 | 266篇 |
1979年 | 203篇 |
1978年 | 242篇 |
1977年 | 204篇 |
1976年 | 178篇 |
1975年 | 184篇 |
1974年 | 171篇 |
1973年 | 206篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
861.
862.
V. E. Strikha 《Geochemistry International》2006,44(8):791-807
Geochemical and isotopic data were used for a comparative analysis of Late Mesozoic (150–120 Ma) granitoids in various geological
structures of the upper Amur area. The granitoids are metaluminous high-potassic I-type rocks of the magnetite series. They
have variable alkalinity and consist of the monzonite-granite and granosyenite-granite associations. The monzonite-granite
association consists of calc-alkaline granitoids of normal alkalinity belonging to the Umlekan-Ogodzhinskaya volcanic-plutonic
zone and the Tynda-Bakaran Complex of the Stanovoy terrane. The rocks are characterized by negative anomalies of U, Ta, Nd,
Hf, and Ti (in patterns normalized to the primitive mantle), with Eu anomalies pronounced weakly in the granodiorites and
quartz and monzodiorites and more clearly in the granites: Eu/Eu* = 0.37–0.95, and (La/Yb)n = 7–24, Tbn/Ybn = 1.4–3.2. The granosyenite-granite association comprises of moderately alkaline rocks, which are subdivided into three groups
according to their geochemistry. The first group consists of phase-I granosyenites of the Uskalinskii Massif of the Umlekan-Ogodzhinskaya
zone with the highest concentrations of Sc, V, Cr, Co, Ni, Cu, Cs, Rb, Sr, Y, Zr, Yb, and Th; negative anomalies at Ba, Ta,
Sr, and Hf; Eu/Eu* = 0.50–0.58, (La/Yb)n = 15–16, and Tbn/Ybn = 1.8. The second group comprises of moderately alkaline granitoids of the Umlekan-Ogodzhinskaya zone and the Khaiktinskii
Complex of the Baikal-Vitim superterrane. Geochemically, the granitoids of this group are generally similar to the monzodiorite-granite
association and differ from it in having lower concentrations of REE and Y, Eu/Eu* = 6.2–1.0, (La/Yb)n = 28–63, and Tbn/Ybn = 2.1–4.5. The third group consists of granitoids of the Chubachinskii Complex of the Stanovoi terrane, which typically show
negative Cs, Rb, Th, U, Ta, Hf, and Ti anomalies; the lowest concentrations of V, Cr, Co, and Ni; and the highest contents
of Sr. The granosyenites of the first phase display clearly pronounced negative Eu anomalies (Eu/Eu* = 0.53–0.68), (La/Yb)n = 7–24, and Tbn/Ybn = 0.8–2.0. The granitoids of the second phase have (La/Yb)n = 51–84, no Eu anomalies, or very weak Eu anomalies (Eu/Eu* = 0.97–1.23). The silica-oversaturated leucogranites of the third
phase are characterized by elevated concentrations of REE, clearly pronounced Eu anomalies (Eu/Eu* = 0.48), and flat REE patterns
(Tbn/Ybn = 1.3). The diversity of the granitoids is demonstrated to have been caused largely by the composition of the Precambrian
source, which was isotopically heterogeneous. The rocks of the monzodiorite-granite association and first-group granosyenites
of the granosyenite-granite association of the Tynda-Bakaran Complex were supposedly derived from garnet-bearing biotite amphibolites.
In contrast to these rocks, the source of the second-group granites of the granosyenite-granite association was of mixed amphibolite-metagraywacke
composition. The third-group of granitoids were melted out of Early Proterozoic crustal feldspar-rich granulites of variable
basicity, with minor amounts of Archean crustal material. The granitoids were emplaced in a collisional environment, perhaps,
during the collision of the Amur superterrane and Siberian craton. This makes it possible to consider these rocks as components
of a single continental volcanic-plutonic belt.
Original Russian Text ? V.E. Strikha, 2006, published in Geokhimiya, 2006, No. 8, pp. 855–872. 相似文献
863.
V. I. Vinogradov G. A. Belenitskaya M. I. Bujakaite V. N. Kuleshov M. A. Minaeva B. G. Pokrovskii 《Lithology and Mineral Resources》2006,41(1):85-97
New isotope data on Lower Cambrian rocks of the Irkutsk amphitheater are reported in three communications. The first communication
is devoted to the sulfur isotopic composition, which is most sensitive to ostsedimentary geochemical transformations of sulfate
rocks in saliferous formations. It is shown that δ34S values in Bel’sk and Zhigalovo boreholes are within 22–35‰ The lowest values are close to the sulfur isotopic composition
of a halogenic basin, while the highest values are related to epigenetic sulfate reduction. This process was responsible for
the elimination of 100 m of anhydrites from the Lower Cambrian section. 相似文献
864.
The aim of this work is the joint application and integration of non-invasive geoelectrical methods for studying the landfill of Savoia di Lucania (Southern Italy). This landfill for its engineering features and small dimensions (70 m × 30 m × 6 m) represents an optimal test site to assess a geophysical survey protocol for municipal solid waste landfills investigation and monitoring. The landfill of Savoia di Lucania has been built with a reinforced concrete material and coated with a high-density polyethylene (HDPE) liner. Three electrical resistivity tomographies (ERT), two self-potential (SP) map surveys and one induced polarization (IP) section have been performed, both in the surrounding area and inside the waste landfill. The geophysical investigations have well defined some buried boundaries of the landfill basin and localized the leachate accumulation zones inside the dumpsite. Comparison of our results with other engineering and geological investigations could be the key for evaluating the integrity of the HDPE liner. Finally, the joint use of the ERT, IP and SP methods seems to be a promising tool for studying and designing new monitoring systems able to perform a time-lapse analysis of waste landfill geometry and integrity. 相似文献
865.
866.
The bimodal volcanoplutonic (basalt-peralkaline rhyolite with peralkaline granites) association of the Noen and Tost ranges was formed 318 Ma ago in the Gobi-Tien Shan rift zone of the Late Paleozoic-Early Mesozoic central Asian rift system, the development of which was related to the movement of the continental lithosphere over a mantle hot spot. A specific feature of the Late Paleozoic rifting was that it occurred within the Middle-Late Paleozoic active continental margin of the northern Asian paleocontinent. Continental margin magmatism was followed after a short time delay by the magmatism of the Gobi-Tien Shan rift zone, which was located directly in the margin of the paleocontinent. Such a geodynamic setting of the rift zone was reflected in the geochemical characteristics of rift-related rocks. The distribution of major elements and compatible trace elements in the rift-related basic and intermediate rocks corresponds to a crystallization differentiation series. The distribution of incompatible trace elements suggests contributions from several sources. This is also supported by the heterogeneity of Sr and Nd isotopic compositions of the rift-related basaltoids: εNd(T) ranges from 4.4 to 6.7, and (87Sr/86Sr)0, from 0.70360 to 0.70427. The geochemical characteristics of the rift-related basaltoids of the Noen and Tost ranges are not typical of rift settings (negative anomalies in Nb and Ta and positive anomalies in K and Pb) and suggest a significant role of the rocks of a metasomatized mantle wedge in their source. In addition, there are high-titanium rocks among the rift-related basaltoids, whose geochemical characteristics approach those of the basalts of mid-ocean ridges and ocean islands. This allowed us to conclude that the compositional variations of the rift-related basaltoids of the Noen and Tost ranges were controlled by three magma sources: the enriched mantle, depleted mantle (high-titanium basaltoids), and metasomatized mantle wedge (medium-Ti basaltoids). The medium-titanium basaltoids were formed in equilibrium with spinel peridotites, whereas the high-titanium magmas were formed at deeper levels both in the spinel and garnet zones. It terms of geodynamics, the occurrence of three sources of the rift-related basaltoids of the Noen and Tost ranges was related to the ascent of a mantle plume with enriched geochemical characteristics beneath a continental margin, where its influence caused melting in the overlying depleted mantle and the metasomatized mantle wedge. The formation of rift-related andesites in the Noen and Tost ranges was explained by the contamination of mantle-derived basaltoid melts with sialic (mainly sedimentary) continental crustal materials or the assimilation of anatectic granitoid melts. 相似文献
867.
N. V. Chalapathi Rao 《Journal of Earth System Science》2006,115(1):161-183
Amongst all the perceptible igneous manifestations (volcanic tuffs and agglomerates, minor rhyolitic flows and andesites,
dolerite dykes and sills near the basin margins, etc.) in the Vindhyan basin, the two Mesoproterozoic diamondiferous ultramafic
pipes intruding the Kaimur Group of sediments at Majhgawan and Hinota in the Panna area are not only the most conspicuous
but also well-known and have relatively deeper mantle origin. Hence, these pipes constitute the only yet available ‘direct’
mantle samples from this region and their petrology, geochemistry and isotope systematics are of profound significance in
understanding the nature of the sub-continental lithospheric mantle beneath the Vindhyan basin. Their emplacement age (∼ 1100
Ma) also constitutes the only reliable minimum age constrain on the Lower Vindhyan Group of rocks. The Majhgawan and Hinota
pipes share the petrological, geochemical and isotope characteristics of kimberlite, orangeite (Group II kimberlite) and lamproite
and hence are recognised as belonging to a ‘transitional kimberlite-orangeite-lamproite’ rock type. The namemajhagwanite has been proposed by this author to distinguish them from other primary diamond source rocks. The parent magma of the Majhgawan
and Hinota pipes is envisaged to have been derived by very small (<1%) degrees of partial melting of a phlogopite-garnet lherzolite
source (rich in titanium and barium) that has been previously subjected to an episode of initial depletion (extensive melting
during continent formation) and subsequent metasomatism (enrichment). There is absence of any subduction-related characteristics,
such as large negative anomalies at Ta and Nb, and therefore, the source enrichment (metasomatism) of both these pipes is
attributed to the volatile- and K-rich, extremely low-viscosity melts that leak continuously to semi-continuously from the
asthenosphere and accumulate in the overlying lithosphere. Lithospheric/crustal extension, rather than decompression melting
induced by a mantle plume, is favoured as the cause of melting of the source regions of Majhgawan and Hinota pipes. This paper
is a review of the critical evaluation of the published work on these pipes based on contemporary knowledge derived from similar
occurrences elsewhere. 相似文献
868.
A. M. Larin E. B. Sal’nikova A. B. Kotov L. B. Makar’ev S. Z. Yakovleva V. P. Kovach 《Stratigraphy and Geological Correlation》2006,14(5):463-474
Early Proterozoic granitoids are of a limited occurrence in the Baikal fold area being confined here exclusively to an arcuate belt delineating the outer contour of Baikalides, where rocks of the Early Precambrian basement are exposed. Geochronological and geochemical study of the Kevakta granite massif and Nichatka complex showed that their origin was related with different stages of geological evolution of the Baikal fold area that progressed in diverse geodynamic environments. The Nichatka complex of syncollision granites was emplaced 1908 ± 5 Ma ago, when the Aldan-Olekma microplate collided with the Nechera terrane. Granites of the Kevakta massif (1846 ± 8 Ma) belong to the South Siberian postcollision magmatic belt that developed since ~1.9 Ga during successive accretion of microplates, continental blocks and island arcs to the Siberian craton. In age and other characteristics, these granites sharply differ from granitoids of the Chuya complex they have been formerly attributed to. Accordingly, it is suggested to divide the former association of granitoids into the Chuya complex proper of diorite-granodiorite association ~2.02 Ga old (Neymark et al., 1998) with geochemical characteristics of island-arc granitoids and the Chuya-Kodar complex of postcollision S-type granitoids 1.85 Ga old. The Early Proterozoic evolution of the Baikal fold area and junction zone with Aldan shield lasted about 170 m.y. that is comparable with development periods of analogous structures in other regions of the world. 相似文献
869.
870.
Paleoproterozoic accretion in the Northeast Siberian craton: Isotopic dating of the Anabar collision system 总被引:1,自引:0,他引:1
O. M. Rosen L. K. Levskii D. Z. Zhuravlev A. Ya. Rotman Z. V. Spetsius A. F. Makeev N. N. Zinchuk A. V. Manakov V. P. Serenko 《Stratigraphy and Geological Correlation》2006,14(6):581-601
Geochronological database considered in the work and characterizing the Anabar collision system in the Northeast Siberian craton includes coordinated results of Sm-Nd and Rb-Sr dating of samples from crustal xenoliths in kimberlites, deep drill holes, and bedrock outcrops. As is inferred, collision developed in three stages dated at 2200–2100, 1940–1760, and 1710–1630 Ma. The age of 2000–1960 Ma is established for substratum of mafic rocks, which probably originated during the lower crust interaction with asthenosphere due to the local collapse of the collision prism. Comparison of Sm-Nd and Rb-Sr isochron dates shows that the system cooling from ≈700 to ≈300°C lasted approximately 300 m.y. with a substantial lag relative to collision metamorphism and granite formation. It is assumed that accretion of the Siberian craton resulted in formation of a giant collision mountainous structure of the Himalayan type that was eroded by 1.65 Ga ago, when accumulation of gently dipping Meso-to Neoproterozoic (Riphean) platform cover commenced. 相似文献