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   613篇
  免费   29篇
  国内免费   5篇
测绘学   17篇
大气科学   45篇
地球物理   149篇
地质学   211篇
海洋学   76篇
天文学   81篇
综合类   7篇
自然地理   61篇
  2021年   10篇
  2020年   7篇
  2019年   14篇
  2018年   14篇
  2017年   11篇
  2016年   21篇
  2015年   12篇
  2014年   13篇
  2013年   38篇
  2012年   21篇
  2011年   34篇
  2010年   29篇
  2009年   36篇
  2008年   19篇
  2007年   29篇
  2006年   28篇
  2005年   17篇
  2004年   14篇
  2003年   14篇
  2002年   10篇
  2001年   13篇
  2000年   8篇
  1999年   11篇
  1998年   14篇
  1997年   4篇
  1996年   4篇
  1995年   9篇
  1994年   3篇
  1993年   8篇
  1992年   8篇
  1991年   4篇
  1990年   5篇
  1989年   4篇
  1988年   11篇
  1987年   10篇
  1986年   5篇
  1985年   11篇
  1984年   12篇
  1983年   13篇
  1982年   8篇
  1981年   10篇
  1980年   6篇
  1978年   10篇
  1977年   8篇
  1976年   7篇
  1975年   12篇
  1974年   6篇
  1973年   8篇
  1969年   3篇
  1965年   2篇
排序方式: 共有647条查询结果,搜索用时 15 毫秒
131.
Previous climate risk assessments provide important methodological insights into how to derive tractable research questions and the appropriate use of data under uncertainty, as well as identifying steps that benefit from stakeholder involvement. Here we propose the use of a framework for the systematic and objective exploration of climate risk assessments. The matrix facilitates a breakdown of information about aim and context, main results, methodological choices, stakeholder involvement, sources and characteristics of uncertainties and overall weaknesses. We then apply the matrix to three risk assessments in the water sector to explore some methodological strengths and weaknesses of approaches strongly linked to climate model outputs (top-down) versus those that originate from local knowledge of climate exposures (bottom-up), and demonstrate that closer integration with social and physical sciences is more likely to yield robust climate risk assessments.  相似文献   
132.
The prevalence of dermal neoplasia among neotenic tiger salamanders (Ambystoma tigrinum) collected from the Reese Air Force Base sewage lagoon far exceeded that among salamanders from nearby uncontaminated lagoons. Perylene was the predominant pglycyclic aromatic hydrocarbon contaminant in this lagoon. Perylene was shown to be a substrate for monooxygenases in skin and liver homogenates and formed DNA-binding metabolites. Perylene exposure appeared to augment subsequent perylene metabolism by dermal enzymes but it was not a strong inducer of hepatic monooxygenases. Aroclor 1254 induced benzo(a)pyrene and perylene metabolism by both skin and liver enzymes. However, perylene apparently was not activated by salamander enzymes, as suggested by its lack of in vitro mutagenicity and failure to induce tumors.  相似文献   
133.
134.
A section near the Kilgen Lake (Adana Province) has yielded a fauna of rugose and tabulate corals including Disphyllum cf. rugosum (Wedekind, 1922), D. cf. curtum Hill, 1954, Wapitiphyllum sp., Thamnopora sp., and Alveolites sp. This coral assemblage is consistent with the previous Frasnian age assigned to the limestones of the Gümü?ali Formation. The rather well-preserved material provides new data on the structure and microstructure of Disphyllum and allows to describe in Thamnopora unusual calicinal morphology (septal ridges, median teeth, and pseudopercula) as well as new structures linked to the lateral increase (basal low wall, apical cul-de-sac).  相似文献   
135.
It is expected that an average protostar will undergo at least one impulsive interaction with a neighbouring protostar whilst a large fraction of its mass is still in a massive, extended disc. Such interactions must have a significant impact upon the evolution of the protostars and their discs.   We have carried out a series of simulations of coplanar encounters between two stars, each possessing a massive circumstellar disc, using an SPH code that models gravitational, hydrodynamic and viscous forces. We find that during a coplanar encounter, disc material is swept up into a shock layer between the two interacting stars, and the layer then fragments to produce new protostellar condensations. The truncated remains of the discs may subsequently fragment; and the outer regions of the discs may be thrown off to form circumbinary disc-like structures around the stars. Thus coplanar disc–disc encounters lead efficiently to the formation of multiple star systems and small- N clusters, including substellar objects.  相似文献   
136.
Introduction     
Francis Owusu 《GeoJournal》2005,62(1):115-116
  相似文献   
137.
138.
In this technical note we compare silica gel grains and quartz sand as sediment media for vegetation root growth in laboratory experiments for ecohydrology and ecohydraulics. Silica gel grains become quite transparent when saturated with water. This would be useful in order to non-invasively observe the rate of growth of plant roots and plan parallel laboratory experiments made in more typical sand sediments. In this work, we compare the results of preliminary tests conducted using quartz sand with the same grain size distribution of silica gel grains. We show that the complex microstructure of silica gel grains seems to influence the evaporation and, in turn, plant growth dynamics. The potential and limitations of the use of silica grains are accordingly discussed in light of more detailed experiments.  相似文献   
139.
The ocean bottom seismograph described in this paper has been developed primarily for recording earthquakes on the mid-oceanic ridges. The instrument is suitable for dropping onto the most rugged areas of the ocean floor. Acoustic tracking with the ship's precision echo sounder enables it to be located there relative to both the topography of the sea bed and the ship. The outputs of a 3-component seismometer and a hydrophone are recorded in FM form on a low-power magnetic tape recorder designed specifically for the instrument.  相似文献   
140.
This review is intended to summarize the current observations of reduced carbon in Martian meteorites, differentiating between terrestrial contamination and carbon that is indigenous to Mars. Indeed, the identification of Martian organic matter is among the highest priority targets for robotic spacecraft missions in the next decade, including the Mars Science Laboratory and Mars 2020. Organic carbon compounds are essential building blocks of terrestrial life, so the occurrence and origin (biotic or abiotic) of organic compounds on Mars is of great significance; however, not all forms of reduced carbon are conducive to biological systems. This paper discusses the significance of reduced organic carbon (including methane) in Martian geological and astrobiological systems. Specifically, it summarizes current thinking on the nature, sources, and sinks of Martian organic carbon, a key component to Martian habitability. Based on this compilation, reduced organic carbon on Mars, including detections of methane in the Martian atmosphere, is best described through a combination of abiotic organic synthesis on Mars and infall of extraterrestrial carbonaceous material. Although conclusive signs of Martian life have yet to be revealed, we have developed a strategy for life detection on Mars that can be utilized in future life‐detection studies.  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