全文获取类型
收费全文 | 482篇 |
免费 | 9篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 17篇 |
大气科学 | 49篇 |
地球物理 | 91篇 |
地质学 | 221篇 |
海洋学 | 13篇 |
天文学 | 47篇 |
综合类 | 5篇 |
自然地理 | 53篇 |
出版年
2022年 | 3篇 |
2021年 | 7篇 |
2020年 | 7篇 |
2019年 | 5篇 |
2018年 | 15篇 |
2017年 | 14篇 |
2016年 | 14篇 |
2015年 | 16篇 |
2014年 | 19篇 |
2013年 | 25篇 |
2012年 | 23篇 |
2011年 | 25篇 |
2010年 | 19篇 |
2009年 | 18篇 |
2008年 | 20篇 |
2007年 | 24篇 |
2006年 | 21篇 |
2005年 | 13篇 |
2004年 | 19篇 |
2003年 | 16篇 |
2002年 | 10篇 |
2001年 | 10篇 |
2000年 | 11篇 |
1999年 | 8篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 5篇 |
1995年 | 15篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 6篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1970年 | 2篇 |
1967年 | 2篇 |
1966年 | 4篇 |
排序方式: 共有496条查询结果,搜索用时 15 毫秒
341.
342.
343.
344.
Use of coprostanol as a specific allochthonous fecal indicator in surface sediment of the Lake of Neuchâtel 总被引:1,自引:0,他引:1
André Pittet Roland Stettler Bernard Kuebler 《Aquatic Sciences - Research Across Boundaries》1990,52(2):130-143
Coprostanol has been proven to be a good specific allochthonous fecal indicator in sedimentary surface samples of the lake of Neuchâtel (Switzerland). Its concentration is slightly affected in surface sediment by the microbial reduction of cholesterol to cholestanol and coprostanol. 相似文献
345.
Roland R. Draxler 《Boundary-Layer Meteorology》1988,42(1-2):43-53
Experimental studies have shown that tracers injected over short time intervals can often be measured downwind near the ground for a much longer time than would be expected considering the duration of the release and the wind speed. A two-dimensional advection-diffusion model was used in a numerical study to investigate this effect. The results from the numerical study showed that the rate of decrease in concentrations downwind at a receptor after a source has stopped emitting was more sensitive to magnitude of the wind speed and alongwind mixing coefficient than the rate of increase in concentrations when the source first starts emitting. The lower the wind speed or the greater the mixing, the more slowly the concentration decreased as the region upwind of the receptor continued to contribute tracer until it was depleted by advection and vertical diffusion. These atmospheric processes are able, qualitatively, to account for the slowly decreasing air concentrations. 相似文献
346.
R. Zander G. Roland L. Delbouille A. Sauval C. B. Farmer R. H. Norton 《Journal of Atmospheric Chemistry》1987,5(4):385-394
The amount of hydrogen fluoride (HF) above the International Scientific Station of the Jungfraujoch (Switzerland) has been monitored during the last 8 years. The results deduced spectro-scopically from solar IR absorption measurements near 2.48 m indicate a cumulative trend equivalent to (8.5±1)% increase per year, as well as short-term variability which appears to be strongly correlated with meridional circulation patterns during the February–April months. Based on intensified measurements made over the last three years, it is found that the integrated content of HF undergoes a seasonal change with a minimum occurring in the fall. The HF/HCl ratio derived from simultaneous HF and HCl measurements was found equal to 0.15 during the period 1977–79, and 0.24 for the 1983–85 timespan. 相似文献
347.
George W. Roland 《Mineralium Deposita》1968,3(3):249-260
Silica-tube quenching experiments and gold-tube pressure experiments were used to study phase relations in the PbS-rich portion of the system Pb-As-S. Emphasis was placed on determining the P-T-X stability relations of jordanite, the most Pb-rich of the synthetic Pb-As-S compounds. Jordanite, Pb9As4S15, is stable below 549 ± 3° C, at which temperature it melts to galena, liquid, and a sulfur-rich vapor phase. Confining pressures of up to 2 Kb do not measurably change this reaction temperature. Density measurements on synthetic material show that the jordanite cell contains 3 (Pb9As4S15); space group P21/m requires that the cell content be expressed as either Pb28–xAs12S46–x or Pb26+xAs12S44+x, with the former much more probable from a structural point of view. In both cases 0.8 < x < 1.4 and the situation is thus quite different from the usual case of defect structures, such as pyrrhotite, Fe1–xS, which shows considerable range of solid solution. Heating experiments on natural gratonite (Pb9As4S15) show that this mineral is most probably a low-temperature dimorph of jordanite, the inversion occurring below 250° C. Experiments have also confirmed the extensive substitution of Sb for As in jordanite, as suspected from chemical analyses of the isostructural mineral geocronite (Pb28–x(As,Sb)12S46–x).
Zusammenfassung Durch Abschreckversuche mit Hilfe von Quarz- und Gold-Druckampullen wurden die Phasenbeziehungen im PbS-reichen Teil des Pb-As-S-Systems studiert. Besonderer Wert wurde auf die Feststellung der P-T-X-Stabilitätsverhältnisse des Jordanits, des Pb-reichsten Phase der synthetischen Pb-As-S-Reihe, gelegt. Jordanit (Pb9As4S15) ist unterhalb 549 ± 3° C stabil, wo er sich semikongruent zu PbS, einer Schmelze und einer schwefelreichen Dampfphase zersetzt. Drucke bis zu 2 kb ergaben keine meßbaren Änderungen dieser Reaktionstemperatur. Dichtemessungen am synthetischen Material weisen darauf hin, daß die Jordanitzelle 3 × (Pb9As4S15) enthält. Die Raumgruppe P21/m fordert entweder die Formel Pb28–xAs12S46–x oder Pb26+xAs12S44+x, wobei die erstere Form strukturell wahrscheinlicher zu sein scheint. In beiden Fällen ist 0.8 < x < 1.4 und weicht vom gebräuchlichen Begriff der Defektstrukturen, wie z.B. beim Pyrrhotin (Fe1–xS) ab, wie das bemerkenswerte Mischkristallfeld zeigt. Erhitzen von natürlichem Gratonit (Pb9As4S15) zeigt, daß dieses Mineral sehr wahrscheinlich eine dimorphe Tieftemperaturphase des Jordanits ist. Die Umwandlung erfolgt unterhalb 250° C. Außerdem wurde eine umfangreichere Substitution von As durch Sb im Jordanit festgestellt, was nach den chemischen Analysen des isostrukturellen Geochronits Pb28–x(As,Sb)12S46–x) zu erwarten war.相似文献
348.
349.
The imaging of a multichannel seismic record was improved by reprocessing using pre-stack techniques. The reprocessed record shows structures that indicate tectonic erosion and gravity collapse at the front of the Japan Trench margin. Much of the lower slope appears to be underlain by a detached, coherent block of continental crust. The lower slope has failed by mass wasting and the resulting apron of slump debris at the base of the slope has become involved in thrust faulting at the front of the subduction zone. Slumping continues as long as debris is removed from the front of the margin by subduction, and the apron cannot build up sufficiently to stabilize the failing lower slope. Truncated beds at the base of the upper plate indicate subcrustal erosion as well, this probably being the main cause of massive subsidence of the margin. Subsidence was the cause of oversteepening, destabilization and subsequent gravity collapse of the leading edge of the upper plate. 相似文献
350.
On the basis of a seven-point isochron, the RbSr whole-rock age of the Hästefjorden granite in southwestern Sweden is 1240 ± 30 Ma using a decay constant of 1.39·10?11 yr?1. The initial 87Sr/86Sr ratio is 0.712. This dating sets a lower limit for the beginning of the Dalslandian (Dal sequence) sedimentation and supports suggestions of a chronological diversity of the so-called Gothian Åmål—Kroppefjäll granite complex in western Sweden. It also invalidates correlation of the Åmål—Kroppefjäll complex as a whole with the Småland plutonics of southeastern Sweden. This proves that rocks previously considered as being formed during the “Gothian Cycle” are very different in age. 相似文献