首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   880篇
  免费   33篇
  国内免费   21篇
测绘学   8篇
大气科学   121篇
地球物理   191篇
地质学   365篇
海洋学   30篇
天文学   191篇
综合类   4篇
自然地理   24篇
  2021年   13篇
  2020年   13篇
  2019年   11篇
  2018年   13篇
  2017年   13篇
  2016年   23篇
  2015年   27篇
  2014年   28篇
  2013年   43篇
  2012年   41篇
  2011年   42篇
  2010年   34篇
  2009年   40篇
  2008年   47篇
  2007年   31篇
  2006年   33篇
  2005年   36篇
  2004年   31篇
  2003年   23篇
  2002年   28篇
  2001年   20篇
  2000年   22篇
  1999年   19篇
  1998年   15篇
  1997年   7篇
  1996年   13篇
  1995年   11篇
  1994年   14篇
  1993年   10篇
  1992年   8篇
  1991年   17篇
  1990年   9篇
  1989年   6篇
  1988年   11篇
  1987年   8篇
  1986年   7篇
  1985年   8篇
  1984年   12篇
  1983年   13篇
  1981年   16篇
  1980年   12篇
  1979年   7篇
  1978年   12篇
  1977年   8篇
  1976年   13篇
  1975年   8篇
  1974年   6篇
  1973年   10篇
  1972年   6篇
  1960年   4篇
排序方式: 共有934条查询结果,搜索用时 78 毫秒
421.
In the final decades of the last century, an increasing number of strandings of male sperm whales (Physeter macrocephalus) around the North Sea led to an increase in public interest. Anthropogenic influences (such as contaminants or intensive sound disturbances) are supposed to be the main causes, but natural environmental effects may also explain the disorientation of the animals. We compared the documented sperm whale strandings in the period from 1712 to 2003 with solar activity, especially with sun spot number periodicity and found that 90% of 97 sperm whale stranding events around the North Sea took place when the smoothed sun spot period length was below the mean value of 11 years, while only 10% happened during periods of longer sun spot cycles. The relation becomes even more pronounced (94% to 6%, n = 70) if a smaller time window from November to March is used (which seems to be the main southward migration period of male sperm whales). Adequate chi-square tests of the data give a significance of 1% error probability that sperm whale strandings can depend on solar activity. As an alternative explanation, we suggest that variations of the earth's magnetic field, due to variable energy fluxes from the sun to the earth, may cause a temporary disorientation of migrating animals.  相似文献   
422.
The concept of Volunteered Geographic Information (VGI) has progressed from being an exotic prospect to making a profound impact on GIScience and geography in general, as initially anticipated. However, while massive and manifold data is continuously produced voluntarily and applications are built for information and knowledge extraction, the initially introduced concept of VGI lacks certain methodological perspectives in this regard which have not been fully elaborated. In this article we highlight and discuss an important gap in this concept, i.e. the lack of formal acknowledgment of temporal aspects. By coining the proposed advanced framework ‘Volunteered Geo‐Dynamic Information’ (VGDI), we attempt to lay the ground for full conceptual and applied spatio‐temporal integration. To illustrate that integrative approach of VGDI and its benefits, we describe the potential impact on the field of dynamic population distribution modeling. While traditional approaches in that domain rely on survey‐based data and statistics as well as static geographic information, the use of VGDI enables a dynamic setup. Foursquare venue and user check‐in data are presented for a test site in Lisbon, Portugal. Two core modules of spatio‐temporal population assessment are thereby addressed, namely time use profiling and target zone characterization, motivated by the potential integration in existing population dynamics frameworks such as the DynaPop model.  相似文献   
423.
424.
Sedimentary processes and structures across the continental rise in the western Weddell Sea have been investigated using sediment acoustic and multichannel seismic data, integrated with multibeam depth sounding and core investigations. The results show that a network of channels with associated along-channel ridges covers the upper continental slope. The seismic profiles reveal that the channels initially developed as erosive turbidite channels with associated levees on their northern side due to Coriolis force. Later they were partly or fully infilled, probably as a result of decreasing turbidite activity. Now the larger ones exist as erosive turbidite channels of reduced size, whereas the smaller ones are non-erosive channels, their shape being maintained by contour current activity. Drift bodies only developed where slumps caused a distinctive break in slope inclination on the upper continental rise, which served to initiate the growth of a drift body fed by contour currents or by the combined action of turbidites and contourites. The history of sedimentation can be reconstructed tentatively by correlation of seismo-stratigraphic units with the stages of evolution of the drifts on the western side of the Antarctic Peninsula. Three stages can be distinguished in the western Weddell Sea after a pre-drift stage, which is delimited by an erosional unconformity at the top: (1) a growth stage, dominated by turbidites, with occasional occurrence of slumps during its initial phase; (2) during a maintenance stage turbiditiy-current intensity (and presumably sedimentation rate also) decreased, probably as a result of the ice masses retreating from the shelf edge, and sedimentation became increasingly dominated by contour current activity; and (3) a phase of sheeted-sequence formation. A southward decrease in sediment thickness shows that the Larsen Ice Shelf plays an important role in sediment delivery to the western Weddell Sea. This study shows that the western Weddell Sea has some characteristics in common with the southern as well as the northwestern Weddell Sea: contour currents off the Larsen Ice Shelf have been present for a long time, probably since the late Miocene, but during times of high sediment input from the shelves as a result of advancing ice masses a channel-levee system developed and dominated over the contour-current transport of sediment. At times of relatively low sediment input the contour-current transport dominated, leading to the formation of drift deposits on the upper continental rise. Seaward of areas without shelf ice masses the continental rise mainly shows a rough topography with small channels and underdeveloped levees. The results demonstrate that sediment supply is an important, maybe the controlling factor of drift development on the Antarctic continental rise.  相似文献   
425.
Zusammenfassung Es wird eine Anordnung zur genauen und zuverlässigen Messung des Emanationsgehaltes von Luft und Wasser beschrieben. Die Entemanierung geschieht dabei ohne Benutzung einer mechanischen Pumpe; die Emanation kommt nur mit Glas und mit der zu untersuchenden Flüssigkeit in Berührung. Radonbestimmungen an See- und Quellwasser im oberbayrischen Raum lassen wichtige Gesetzmäßigkeiten geologischer und geophysikalischer Art für den Emanationsgehalt erkennen.
Summary A device for exact and reliable measurements of the emanation content of air and water is described. The disemanation is effected without a mechanical pump; the emanation comes into contact only with glass and with the fluid to be investigated. Radon determinations of water from lakes and springs in the region of Upper Bavaria show important relations of the emanation content to geological and geophysical conditions.

Résumé On décrit un procédé pour la mesure exacte et sûre de l'émanation dans l'air et dans l'eau. La séparation du gaz s'y fait sans intervention d'une pompe mécanique. L'émanation n'entre ainsi en contact qu'avec du verre et le liquide à analyser. Des déterminations de radon faites dans l'eau de lacs et de sources de Haute Bavière permettent d'établir des rapports étroits entre les quantités d'émanation recueillies et les conditions géologiques et géophysiques.


Mit 3 Textabbildungen  相似文献   
426.
In this paper we describe a flux‐free fusion technique for the highly precise LA‐ICP‐MS bulk analysis of geological samples. For this purpose we have developed an automated iridium‐strip heater with temperature and melt time control. To optimise the homogeneity of the fused glasses and to reduce possible depletion of volatile elements during melting, we undertook experiments with basaltic rock and glass powders using different melting temperatures (1300–1700 °C) and melting times (5‐80 s). Major and trace element microanalysis was performed using EPMA and LA‐ICP‐MS. Homogeneous glasses were obtained for temperatures ≥ 1500 °C and melting times ≥ 10 s. High loss (20‐90%) of highly volatile elements (e.g., Cs, Ge, Sn, Pb) was observed for high melting temperatures (≥ 1600 °C) and long melting times (80 s). Standard melting conditions (1600 °C, 10 s) represent a compromise, as the glasses were homogeneous with respect to major and trace elements and, at the same time, were not depleted in elements with condensation temperatures (at a pressure of 10?4 bar) higher than about 900 K (e.g., Zr, Hf, Ba, Sr, REE, U, Mo, Ni, Rb, Ga). Several international geological reference materials with SiO2 ranging between 47% m/m and 59% m/m were prepared using our standard melting conditions (1600 °C, 10 s) and subsequently analysed by LA‐ICP‐MS. These samples also include the new Brazilian basaltic reference material BRP‐1. Matrix‐matched calibration of the LA‐ICP‐MS data was performed using the basaltic reference glasses KL2‐G, ML3B‐G, BCR‐2G and BHVO‐2G. Most analytical data agreed within uncertainty at the 95% confidence level with the GeoReM preferred values published in the GeoReM database for reference materials of geological and environmental interest. To demonstrate routine bulk LA‐ICP‐MS analyses of geochemical and cosmochemical samples using the whole rock fusion technique, we also present trace element data for ocean island basalts from Lanai (Hawaii) and of Martian meteorites.  相似文献   
427.
In 2005 the Geostandards and Geoanalytical Research editorial team, in the true spirit of scientific endeavour, embarked on an experiment of our own. We decided to trial a new kind of review, somewhat different from those more typically observed in journals, and one that would provide readers with a summary of analytical developments across a broad range of topics appropriate to the Earth sciences. The first contribution of this kind appeared in 2005, and reported on developments in 2003 (Hergt et al. 2005). The second, this time a biennial review, was published in 2006 and reported on highlights of the 2004 and 2005 literature (Hergt et al. 2006). Based on reprint requests, positive remarks at conferences and strong citations we consider the experiment a resounding success and proudly present here the third in this series. This comprises six individual review sections that cover the main analytical technologies and topical application fields in geoanalysis and geochemistry, including geological and environmental reference materials, ICP‐thermal and secondary ionisation‐mass spectrometry, as well as neutron activation analysis, X‐ray fluorescence and atomic absorption spectrometry.  相似文献   
428.
429.
430.
This paper presents a new methodology for estimating the expected energies and first impact distances at the base of a rock cliff, subject to the geometry and properties of the cliff and the representative block being known. The method is based on a sensitivity analysis, conducted by means of kinematic simulations and carried out for a large range of input parameters and their combinations, taking into account the uncertainty associated with their estimate. The proposed approach is validated by comparing predictions to experimental data and shows great potential for a quick qualitative hazard assessment.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号