全文获取类型
收费全文 | 100445篇 |
免费 | 1556篇 |
国内免费 | 953篇 |
专业分类
测绘学 | 2700篇 |
大气科学 | 7109篇 |
地球物理 | 20526篇 |
地质学 | 34977篇 |
海洋学 | 8647篇 |
天文学 | 22914篇 |
综合类 | 297篇 |
自然地理 | 5784篇 |
出版年
2021年 | 927篇 |
2020年 | 1036篇 |
2019年 | 1128篇 |
2018年 | 2544篇 |
2017年 | 2375篇 |
2016年 | 3018篇 |
2015年 | 1756篇 |
2014年 | 2891篇 |
2013年 | 5210篇 |
2012年 | 3065篇 |
2011年 | 4165篇 |
2010年 | 3581篇 |
2009年 | 4818篇 |
2008年 | 4355篇 |
2007年 | 4228篇 |
2006年 | 3968篇 |
2005年 | 3145篇 |
2004年 | 3085篇 |
2003年 | 2869篇 |
2002年 | 2755篇 |
2001年 | 2523篇 |
2000年 | 2398篇 |
1999年 | 1976篇 |
1998年 | 2072篇 |
1997年 | 2010篇 |
1996年 | 1614篇 |
1995年 | 1613篇 |
1994年 | 1397篇 |
1993年 | 1289篇 |
1992年 | 1190篇 |
1991年 | 1142篇 |
1990年 | 1206篇 |
1989年 | 1099篇 |
1988年 | 988篇 |
1987年 | 1184篇 |
1986年 | 1018篇 |
1985年 | 1264篇 |
1984年 | 1421篇 |
1983年 | 1316篇 |
1982年 | 1271篇 |
1981年 | 1128篇 |
1980年 | 1021篇 |
1979年 | 967篇 |
1978年 | 973篇 |
1977年 | 855篇 |
1976年 | 823篇 |
1975年 | 798篇 |
1974年 | 772篇 |
1973年 | 782篇 |
1972年 | 538篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
902.
903.
This paper reports REE data on resin-asphaltene components of oil from six oil-gas-bearing provinces and on bitumoids from
inferred oil-source rocks (domanikites and bazhenites). It was shown that, regardless of geological-tectonic structure of
the regions, oil composition, depth of reservoirs, and host lithologies, oil exhibits significant REE fractionation, and,
unlike bitumoids, positive Eu anomaly. The (Eu/Sm)n ratio increases from asphaltenes to resins and further to oils. Based on REE distribution in oil, source rocks, and bitumoids,
it was concluded that deep-seated fluids were one of the possible sources that defined the trace element composition of oil. 相似文献
904.
Studies on the water and suspended matter concentration dynamics were performed for the summer and autumn periods in Kruglaya
Bay, Chupa Inlet (Karelian Coast, the White Sea). The tidal cycle appeared as the major factor defining the water salinity,
temperature, and suspended matter concentration. The water temperature and suspended matter concentration increased during
low tide, and the opposite pattern was observed for water salinity; all the processes were true for both surface and bottom
water layers. Therefore, we conclude that major bulk of the allochtonous suspended matter is carried into the sea by the ebb
stream. 相似文献
905.
I. Yu. Melekestseva V. A. Kotlyarov P. V. Khvorov V. N. Ivanov V. E. Beltenev I. G. Dobretsova 《Geology of Ore Deposits》2010,52(8):800-810
The porous fine-grained to microcrystalline copper-zinc ore of the Semenov-2 hydrothermal field, a site in the Semenov hydrothermal
cluster discovered in 2007 (13°31′N, MAR), is anomalously enriched in Au (22–188 ppm) and Ag (127–1787 ppm). Chalcopyrite,
isocubanite, würtzite, and opal are major minerals; sphalerite, marcasite, pyrite, and covellite are auxiliary; and galena,
pyrrhotite, native gold, silver telluride, barite, and aragonite are sporadic. Gold containing 0.31 to 23.07 wt % Ag occurs
as up to 9-μm-sized subhedral, dendritelike, and elongated grains mostly hosted in opal and less frequently in sphalerite
and in pores within isocubanite-chalcopyrite aggregate. An elongated grain (2 × 4 μm in size) of the Ag-Te phase was found
in a pore. So far only basalts have been dredged from the Semenov-2 field, but anomalous gold and silver concentrations suggest
the influence of ultramafic rocks; the latter were found 1.5 km westward, in the Semenov-1 hydrothermal field. Mineral assemblage
and morphology of gold particles indicate its primary origin in contrast to the hydrothermal fields hosted in basalts, where
gold is a product of remobilization. Zonal gold grains, found on oceanic floor for the first time, are characterized by low
Ag content in the cores and high Ag content in the outer rims, reflecting variation in formation conditions. 相似文献
906.
907.
M. A. Akhmet’ev N. I. Zaporozhets A. I. Iakovleva G. N. Aleksandrova V. N. Beniamovsky T. V. Oreshkina Z. N. Gnibidenko Zh. A. Dolya 《Stratigraphy and Geological Correlation》2010,18(6):635-659
The analysis of the main biospheric events that took place in West Siberia and the Arctic region during the Early Paleogene
revealed the paleogeographic and paleobiogeographic unity of marine sedimentation basins and close biogeographic relations
between their separate parts. Most biotic and abiotic events of the first half of the Paleogene in the Arctic region and West
Siberia were synchronous, unidirectional, and interrelated. Shelf settings, sedimentation breaks, and microfaunal assemblages
characteristic of these basins during the Paleogene are compared. The comparative analysis primarily concerned events of the
Paleocene-Eocene thermal maximum (PETM) and beds with Azolla (aquatic fern). The formation of the Eocene Azolla Beds in the Arctic region and West Siberia was asynchronous, although it proceeded in line with a common scenario related
to the development of a system of estuarine-type currents in a sea basin partly isolated from the World Ocean. 相似文献
908.
C. Labaune M. Tesson B. Gensous O. Parize P. Imbert V. Delhaye-Prat 《Sedimentary Geology》2010,223(3-4):360-379
Quaternary incised valley systems are usually characterized by the preservation of a single valley-fill attributed to the last post-glacial period. Moreover, there are very few cases of correlation between incised valley system developed on inner shelf and sedimentary units observed on the mid to outer shelf, mainly forced regressive wedges. The Roussillon shelf, in the western part of the Gulf of Lion, is a particular example of preserved Quaternary compound incised valley system also characterized by a direct correlation with the forced regressive lowstand wedges on the mid-outer shelf. High-resolution seismic data and a borehole, 60 m deep, located on the beach barrier permit an accurate study of the geometry and lithology of the system. Six imbricated and more or less preserved incised valleys and valley-fills are observed up to the inner to mid-shelf. The key surfaces associated to the incised valleys are correlated to the boundaries of the forced regressive wedges. They are assumed to be reworked surfaces. At the borehole location, only few thin layers, less than 1 m thick, of coarse grain and/or floating pebbles, are observed and should correspond to preserved fluvial lowstand deposits reworked under marine influence. The valley fills are mainly composed of estuarine muddy silts. From AMS 14C age dating it is inferred that the uppermost incised valley system is younger than 45 ky cal BP. Based on those observations, the six preserved incised valley systems are assumed to be controlled by the last six 4th order sea-level cycles — 100 ky — of the middle to late Quaternary. The paleo-topography of the underlying Plio-Quaternary deposits controls the compound incised valley system location. The deep topography of the Messinian Erosionnal Surface is a controlling factor at a lower degree. The partial preservation of the successive valley fill is attributed not only to the differential subsidence but also to the lateral migration of each incision and to the hydrodynamic regime. 相似文献
909.
J. M. Charnock C. M. B. Henderson J. F. W. Mosselmans R. A. D. Pattrick 《Physics and Chemistry of Minerals》1996,23(7):403-408
The X-ray absorption spectra of the transition metal L3,2-edges of the dichalcogenides FeS2 (pyrite), FeSe2, FeTe2, CoS2, CoSe2, CoTe2, NiS2, NiSe2 and NiTe2 have been studied. These spectra are compared with theoretical simulations make using the atomic multiplet approach assuming on octahedral site for the metal atoms. The Ni spectra can be closely simulated using this approach but the Fe and Co spectra show less good fits to the experimental data. The reasons for this and its implications for the use of L-edge spectra in the study of such minerals are discussed in terms of the covalency and the ground states of the compounds; these results indicate the mixing of the ground states increases in the order Ni<Co<Fe. 相似文献
910.