全文获取类型
收费全文 | 1596篇 |
免费 | 40篇 |
国内免费 | 23篇 |
专业分类
测绘学 | 53篇 |
大气科学 | 159篇 |
地球物理 | 279篇 |
地质学 | 616篇 |
海洋学 | 124篇 |
天文学 | 290篇 |
综合类 | 11篇 |
自然地理 | 127篇 |
出版年
2023年 | 9篇 |
2021年 | 17篇 |
2020年 | 17篇 |
2019年 | 17篇 |
2018年 | 34篇 |
2017年 | 28篇 |
2016年 | 40篇 |
2015年 | 25篇 |
2014年 | 44篇 |
2013年 | 70篇 |
2012年 | 54篇 |
2011年 | 74篇 |
2010年 | 74篇 |
2009年 | 117篇 |
2008年 | 78篇 |
2007年 | 96篇 |
2006年 | 77篇 |
2005年 | 86篇 |
2004年 | 53篇 |
2003年 | 48篇 |
2002年 | 52篇 |
2001年 | 41篇 |
2000年 | 40篇 |
1999年 | 29篇 |
1998年 | 26篇 |
1997年 | 21篇 |
1996年 | 20篇 |
1995年 | 19篇 |
1994年 | 21篇 |
1993年 | 16篇 |
1992年 | 16篇 |
1991年 | 14篇 |
1990年 | 14篇 |
1988年 | 12篇 |
1986年 | 11篇 |
1985年 | 15篇 |
1984年 | 13篇 |
1983年 | 22篇 |
1982年 | 16篇 |
1981年 | 15篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1976年 | 15篇 |
1975年 | 8篇 |
1973年 | 15篇 |
1972年 | 15篇 |
1971年 | 11篇 |
1970年 | 9篇 |
排序方式: 共有1659条查询结果,搜索用时 0 毫秒
1.
Richard T. Jones Jim D. Marshall Stephen F. Crowley Alan Bedford Nigel Richardson Jan Bloemendal Frank Oldfield 《第四纪科学杂志》2002,17(4):329-340
A lacustrine carbonate sequence from Hawes Water, Lancashire, UK, has been studied using stable isotopic, lithological, pollen and mineral magnetic analysis. The data reveal four abrupt climatic oscillations in the Late‐glacial Interstadial leading up to the onset of the Loch Lomond Stadial. The data also point to climatic warming relatively early within the stadial, ca. 12 500 GRIP yr, prior to the onset of the Holocene. The oxygen isotope record is taken as a signature of climate forcing against which the response of the lake‐system can be monitored. By adopting this approach it is revealed that the response of the biological system to the rapid climatic oscillations is non‐linear and primarily a function of the antecedent conditions. A significant end‐Devensian isotopic excursion (A) is matched by only minor changes in the cold‐adapted floras and faunas. During the warmer interstadial, the response of the biological ecosystem (events B–D) is clearly influenced by thresholds: major changes in the catchment vegetation associated with relatively minor oscillations in the isotopic signature. The stratigraphical patterns reveal significant lag effects between the onset of climate deterioration and resulting changes in vegetation. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
2.
3.
4.
This paper introduces a new method for GPS signal acquisition, which is based on the repeatability of successive code phase
measurements and the M-of-N search algorithm. The performance of the proposed method in terms of probability of signal detection
is similar to that of traditional methods, except that the calculation of the probability of detection does not rely on the
noise distribution or the Carrier-to-Noise ratio (C/N0). The code phase repeatability-based method is presented along with equations for probability of detection and probability
of false detection. If the distribution of the noise is known, it also provides an estimate of the C/N0. The proposed method is illustrated for coherent and non-coherent acquisition and C/N0 estimation. 相似文献
5.
Partly laminated sediments were sampled from the brine-filled, anoxic Shaban Deep basin in the northern Red Sea. At about 4200 cal yr BP more than two millennia of anoxic sedimentation is replaced by a sub-oxic facies strongly suggesting the episodic absence of the brine. At the same time stable oxygen isotopes from surface dwelling foraminifera show a sharp increase (within less than 100 yr) pointing to a strong positive salinity anomaly at the sea surface. This major evaporation event significantly enhanced the renewal of deep water and the subsequent ventilation of the small Shaban Deep basin. The timing and strength of the reconstructed environmental changes around 4200 cal yr BP suggest that this event is the regional expression of a major drought event, which is widely observed in the neighboring regions, and which strongly affected Middle East agricultural civilizations. 相似文献
6.
7.
A Reflection on Mg, Cd, Ca, Li and Si Isotopic Measurements and Related Reference Materials 总被引:6,自引:1,他引:6
Jean Carignan Damien Cardinal Anton Eisenhauer Albert Galy Mark Rehkamper Frank Wombacher Nathalie Vigier 《Geostandards and Geoanalytical Research》2004,28(1):139-148
This contribution aims to report the reflections we had with the scientific community during two international workshops on reference materials for stable isotopes in Davos (2002) and Nice (2003). After evaluating the isotopic homogeneity of some existing reference materials, based on either certificates, literature data or specific inter-laboratory rounds, we confirm these as primary reference materials or propose new ones relative to which stable isotope compositions should be reported. We propose DSM-3 for Mg, NIST SRM 915a for Ca, L-SVEC for Li and NBS28 for Si. Cadmium does not yet have a well identified delta zero material, although three commercial mono-elemental Cd solutions have yielded the same isotopic composition relative to one another. In order to scale the linearity of any mass spectrometer, some secondary reference materials are also proposed: Cambridge-1 solution for Mg, the "Münster-Cd" and JEPPIM Cd solutions for Cd and the "Big Batch" silicate for Si. The team from Nancy propose to prepare a mixed spike solution for Li isotopes. Well-characterised natural samples such as ocean or continental waters, diatoms, sponges, rocks and minerals are needed to validate the entire analytical procedure, particularly to take into account the effect of sample mineralisation and of chemical manipulations for elemental separation prior to analysis. 相似文献
8.
Frank A. Podosek 《Geochimica et cosmochimica acta》2005,69(21):5147-5148
9.
10.
A space-time envelope of minor seismicity related to major shallow earthquakes is identified from observations of the long-term Precursory Scale Increase () phenomenon, which quantifies the three-stage faulting model of seismogenesis. The envelope, which includes the source area of the major earthquake, is here demarcated for 47 earthquakes from four regions, with tectonic regimes ranging from subduction to continental collision and continental transform. The earthquakes range in magnitude from 5.8 to 8.2, and include the 24 most recent mainshocks of magnitude 6.4 and larger in the San Andreas system of California, the Hellenic Arc region of Greece, and the New Zealand region, together with the six most recent mainshocks of magnitude 7.4 and larger in the Pacific Arc region of Japan. Also included are the destructive earthquakes that occurred at Kobe, Japan (1995, magnitude 7.2), Izmit, Turkey (1999, magnitude 7.4), and W.Tottori, Japan (2000, magnitude 7.3). The space (A
P
) in the space-time envelope is optimised with respect to the scale increase, while the time (T
P
) is the interval between the onset of the scale increase and the occurrence of the earthquake. A strong correlation is found between the envelope A
P
T
P
and the magnitude of the earthquake; hence the conclusion that the set of precursory earthquakes contained in the envelope is intrinsic to the seismogenic process. Yet A
P
and T
P
are correlated only weakly with each other, suggesting that A
P
is affected by differences in statical conditions, such as geological structure and lithology, and T
P
by differences in dynamical conditions, such as plate velocity. Among other scaling relations, predictive regressions are found between, on the one hand, the magnitude level of the precursory seismicity, and on the other hand, both T
P
and the major earthquake magnitude. Hence the method, as here applied to retrospective analysis, is potentially adaptable to long-range forecasting of the place, time and magnitude of major earthquakes. 相似文献