全文获取类型
收费全文 | 941篇 |
免费 | 39篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 27篇 |
大气科学 | 45篇 |
地球物理 | 174篇 |
地质学 | 312篇 |
海洋学 | 69篇 |
天文学 | 229篇 |
综合类 | 6篇 |
自然地理 | 120篇 |
出版年
2024年 | 9篇 |
2021年 | 11篇 |
2020年 | 14篇 |
2019年 | 13篇 |
2018年 | 10篇 |
2017年 | 22篇 |
2016年 | 22篇 |
2015年 | 10篇 |
2014年 | 29篇 |
2013年 | 26篇 |
2012年 | 24篇 |
2011年 | 27篇 |
2010年 | 37篇 |
2009年 | 40篇 |
2008年 | 45篇 |
2007年 | 43篇 |
2006年 | 35篇 |
2005年 | 30篇 |
2004年 | 31篇 |
2003年 | 38篇 |
2002年 | 35篇 |
2001年 | 19篇 |
2000年 | 24篇 |
1999年 | 29篇 |
1998年 | 29篇 |
1997年 | 13篇 |
1996年 | 24篇 |
1995年 | 12篇 |
1994年 | 14篇 |
1993年 | 6篇 |
1992年 | 13篇 |
1991年 | 7篇 |
1990年 | 10篇 |
1989年 | 9篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 11篇 |
1985年 | 16篇 |
1984年 | 20篇 |
1983年 | 12篇 |
1982年 | 15篇 |
1981年 | 13篇 |
1980年 | 11篇 |
1979年 | 13篇 |
1978年 | 10篇 |
1977年 | 18篇 |
1976年 | 8篇 |
1975年 | 14篇 |
1974年 | 9篇 |
1973年 | 10篇 |
排序方式: 共有982条查询结果,搜索用时 15 毫秒
971.
Effect of remote forcings on the winter precipitation of central southwest Asia part 1: observations
Summary We investigate the effects of the North Atlantic Oscillation (NAO) and the El Nino Southern Oscillation (ENSO) on winter precipitation
in Central Southwest Asia (CSWA) using an analysis of available observed climate data. The analysis is based on correlations,
composites and Singular Value Decomposition (SVD) performed using the gridded dataset of the Climatic Research Unit (CRU)
and station data for the region. We find that both the NAO and ENSO affect climate over the region. In particular a positive
precipitation anomaly is typically found in correspondence of the positive NAO phase and warm ENSO phase over a sub-region
encompassing northern Pakistan, Afghanistan, Tajikistan and southern Uzbekistan. This conclusion is supported by a consistency
across the different analysis methods and observation datasets employed in our study. A physical mechanism for such effect
is proposed, by which western disturbances are intensified over the region as they encounter a low pressure trough, which
is a dominant feature during positive NAO and warm ENSO conditions. Our results give encouraging indications towards the development
of statistically-based prediction tools for winter precipitation over the CSWA region. 相似文献
972.
Quartzofeldspathic rocks of the Gföhl gneiss from the Moldanubian of the Czech Republic span amphibolite-to granulite-facies, and are associated with eclogite. Protomylonitic fabrics related to terminal tectonic emplacement and reworking of the gneiss are common. Some non-mylonitic rocks, however, preserve early, prograde features (e.g., Opx-rimmed Hbl in metabasites), whereas others have characteristics generally associated with near-isothermal decompression (e.g., Pl-Opx moats separating Grt and Qtz in metabasites; Crd ± Spl coronas on Grt and aluminosilicates in metapelites); the unequivocal distinction between prograde and decompressional features in these rocks, however, may not be possible or even justified. For example, some metapelites contain growth-zoned (i.e., rimward increase in XMg) garnets that also record evidence (i.e., rimward decrease in XCa, compensated by the presence of reversely-zoned plagioclase in the same rock) of decompression. In rare instances, eclogitic rocks (P > 11 kbar) interpreted as tectonic enclaves within the gneiss also record mineralogic evidence of decompression (e.g., Crd-Opx-Spr coronas on pyrope). In metapelites, plagioclase-cored coronal garnets with high Prp/Grs ratios (˜ 2.5) record near-isobaric cooling from near the thermal maximum at a relatively shallow but undetermined crustal level.
Unlike Gföhl gneisses elsewhere (e.g., in Austria), the rocks described here do not preserve evidence of extreme metamorphic conditions. Texturally stable Grt-Bt pairs in non-mylonitic samples give Tmax < 750 °C. Pmax is not known, but prograde metamorphism apparently progressed from the kyanite to sillimanite fields, implying P ˜ 8 kbar at the maximum Grt-Bt temperature. At these conditions, dehydration of mafic gneiss occurred in the presence of a CO2-rich (XCO2 ˜ 0.85) pore fluid 相似文献
973.
Geochemistry of lamprophyres from the Western Alps,Italy: implications for the origin of an enriched isotopic component in the Italian mantle 总被引:3,自引:0,他引:3
Jennifer Paige Owen 《Contributions to Mineralogy and Petrology》2008,155(3):341-362
Cenozoic lamprophyres (minettes, spessartites, kersantite) from the Western Alps, northern Italy, represent small volume,
mafic melts with high Mg#s and high Ni and Cr contents. All the lamprophyres show light REE enrichment, high incompatible
element contents, and Ta, Ti and Nb troughs on chondrite-normalized diagrams. Age-corrected 87Sr/86Sr isotopic ratios (assuming t = 30 Ma) are highly variable and range from 0.70590 to 0.71884; 143Nd/144Nd ratios range from 0.51203 to 0.51242. Pb isotopic ratios are: 206Pb/204Pb = 18.669–18.895, 207Pb/204Pb = 15.605–15.689 and 208Pb/204Pb = 38.224–39.134. 87Sr/86Sr ratios show a negative correlation with 143Nd/144Nd, and a positive correlation with K, Ba, and Rb as well as with Ti, Th, Ta, Nb and Zr abundances. The primitive nature of
the lamprophyres, coupled with their enriched incompatible trace element and isotopic signatures, suggest derivation from
a metasomatized upper mantle source. Linear arrays in isotope space and elemental data plots suggest mixing between two distinct
end-members in the Italian mantle; an enriched end-member that is isotopically similar to pelagic sediments, and a significantly
less enriched end-member that approaches Bulk Earth values. New isotopic data indicate that the mantle source(s) of the lamprophyres
from the Western Alps contain a very high proportion of the enriched end-member. The geochemical signature of the enriched
end-member is attributed to fluids or melts derived from pelagic sediments subducted during the closure of the Tethyan Ocean
in the late Cretaceous to early Tertiary. 相似文献
974.
Sediment cores were taken at three locations in Narragansett Bay, Rhode Island, USA in 1997 and analyzed for a variety of organic contaminants including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), chlordanes, linear alkyl benzenes (LABs), benzotriazoles (BZTs) and dichlorodiphenyltrichloroethanes (DDTs) and metabolites. The distributions of these chemicals at Apponaug Cove and in the Seekonk River indicate that there was a disturbance in the depositional environment relative to cores collected at these locations in 1986 demonstrating the potential for buried contaminants to be remobilized in the environment even after a period of burial. Sharp breaks in the concentration of several organic markers with known dates of introduction were successfully used to determine the sedimentation rate at Quonset Point. Both the Quonset Point and Seekonk River cores had subsurface maximums for DDTs, PCBs, PAHs and BZTs, which are consistent with expected inputs to the environment. The Apponaug Cove core showed an increase of most contaminants at the surface indicating a recent event in which more contaminated sediments were deposited at that location. 相似文献
975.
R. F. King 《Geological Journal》1966,5(1):43-66
Magnetic anisotropy measurements have been made on fifty-four oriented samples from the Carna and Screeb areas of the Galway Granite, and from the Ardara pluton and the Main Granite (including the Trawenagh Bay Granite) in Donegal. The origin of magnetic anisotropy in plutonic magnetic rocks is discussed, and it is concluded that it is probably due to grain alignment of inequant magnetite, which may occur either as free grains or as secondary inclusions in ferromagnesian minerals. The grain alignment may occur either whilst the magma is essentially fluid, giving a magnetic lineation transverse to the flow, or at a much later stage of consolidation during plastic deformation, in which case the magnetic lineation parallels the direction of greatest elongation. The results of the measurements are consistent with macroscopic foliations and lineations where these have been observed, but also indicate the existence of fabrics too weak to observe by conventional methods. This is because the magnetic method assesses the alignment of a very large number of grains, and is therefore much more sensitive than conventional fabric analysis. The weak fabrics can be qualitatively explained in terms consistent with other evidence relating to the emplacement of the granites, and experimental work now in progress may make possible a more quantitative interpretation. 相似文献
976.
D. E. Owen 《Geological Journal》1966,5(1):135-148
The highly fossiliferous fore-reef limestones of B2 age from near Castleton, Derbyshire are rich in Polyzoa. Ten species are described, six of them new. 相似文献
977.
Tomasz Sapota Ala Aldahan Göran Possnert John Peck John King Alexander Prokopenko Mikhail Kuzmin 《Journal of Paleolimnology》2004,32(4):341-349
The sedimentary record from Lake Baikal (Siberia, Russia) has been an important source of information about paleoclimatic variability in the northern hemisphere and dynamics of continental rift development. A lack of reliable chronology has, however, been a major obstacle to fully utilizing the Baikal archive for time scales beyond about 4-5 Myr. In this paper we use the distribution of 10Be to establish a new chronology for the longest core drilled in Lake Baikal so far. The 10Be-based chronology spans the last 8 Myr and provides better constraints on sedimentation rates and consequently on an east-west tectonic extension in the lake, which has been apparently coeval with other rifts in Asia that are related to the Tibetan plateau uplift. Our data also show higher 10Be flux in the sediment section older then 5 Myr compared with the younger period. This can be explained partly by warm and humid climatic conditions of the Miocene and partly by a high cosmic ray flux to the Earth resulting from possible low geomagnetic field intensity during that time. 相似文献
978.
979.
D. E. Owen 《Geological Journal》1973,8(2):297-306
Six species of Bryozoa, three new, of Upper Visean age are described from Tullaghoge, County Tyrone, Ireland. The assemblage suggests shallow water conditions subject to wave action. The new species are Dyscritella tyronei, Stenophragmidium incrustans, and Sulcoretepora? ramosa. 相似文献
980.
J. Victor Owen 《Geoarchaeology》2001,16(7):785-802
The major element compositions of 15 ceramic sherds from the Bonnin and Morris factory site were determined by electron microprobe. Thirteen samples are phosphatic; the others consist of (a) “soapstone” (magnesian/plombian) and (b) true porcelain, and are interpreted as exotic artifacts, as is one compositionally distinct (relatively SiO2‐poor, P2O5+CaO‐rich) phosphatic sample. Although long considered to be virtually indistinguishable from Bow porcelain (London: ca. 1747–1776), the phosphatic Philadelphia wares have a relatively low mean CaO/P2O5 ratio (3.3 versus 3.8; molecular proportions) and high alumina content (6.6 versus 5.4 wt % Al2O3). Furthermore, unlike Bow, the Bonnin and Morris samples contain calcic plagioclase (bytownite), and in some instances, an orthoclase‐rich ternary feldspar. The preservation of calcic plagioclase indicates that Philadelphia porcelain was fired at (rather than above) the thermal minimum in the An‐SiO2‐C3P system, although the presence of Na (and other fluxes) in these wares precludes the exact determination of the maximum firing temperature from this phase diagram. These wares are also distinctive insofar as the phosphate and melt phases can contain small amounts of lead; they have bulk lead contents of approximately 0.1–1.2 wt % PbO. This component has not been detected in the body of Bow or other contemporary British phosphatic porcelains. Their principal similarity lies in the fact that both wares contain sulfate. In addition, the glazes on Bonnin and Morris porcelain (e.g., PbO ∼ 35–50 wt %; SnO2 ∼ 1–2%) compositionally resemble those used at Bow. If feldspar is formed at all, then Al‐poor phosphatic porcelain (or those with low CaO/P2O5 ratios) will have comparatively low modal calcic plagioclase contents, thereby allowing the rapid depletion of this mineral via resorption by the melt phase during vitrification. Such appears to have been the case for analyzed Bow porcelain, which is therefore interpreted to have been overfired (sensu lato) relative to its Philadelphia counterpart. Conceivably, calcic plagioclase could be preserved in low‐Al wares that were fired only briefly at vitrification temperatures. Given the role of firing history in governing the mineralogy of porcelain, compositional criteria are more reliable for distinguishing these wares. © 2001 John Wiley & Sons, Inc. 相似文献