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   350篇
  免费   8篇
  国内免费   7篇
测绘学   6篇
大气科学   12篇
地球物理   107篇
地质学   108篇
海洋学   22篇
天文学   57篇
综合类   3篇
自然地理   50篇
  2021年   3篇
  2020年   3篇
  2019年   3篇
  2018年   5篇
  2017年   2篇
  2016年   8篇
  2015年   5篇
  2014年   11篇
  2013年   11篇
  2012年   9篇
  2011年   11篇
  2010年   12篇
  2009年   12篇
  2008年   11篇
  2007年   20篇
  2006年   10篇
  2005年   20篇
  2004年   7篇
  2003年   12篇
  2002年   13篇
  2001年   7篇
  2000年   4篇
  1999年   6篇
  1998年   7篇
  1997年   8篇
  1996年   10篇
  1995年   7篇
  1994年   9篇
  1993年   7篇
  1992年   3篇
  1991年   8篇
  1990年   2篇
  1989年   2篇
  1988年   3篇
  1987年   5篇
  1986年   4篇
  1985年   3篇
  1984年   15篇
  1983年   10篇
  1982年   5篇
  1981年   10篇
  1980年   5篇
  1979年   6篇
  1978年   7篇
  1977年   4篇
  1976年   6篇
  1975年   2篇
  1973年   5篇
  1972年   2篇
  1968年   3篇
排序方式: 共有365条查询结果,搜索用时 78 毫秒
31.
The effect of recent drilling operations (fluid and well cuttings) on polychaete feeding guilds from the continental shelf off Atlantic City, New Jersey, was examined. Although there were some adverse effects on macrobenthos from 2160 metric tons of cuttings and mud solids discharged into the marine environment, the composition of polychaete feeding guilds remained essentially unchanged. This key trophic relationship between polychaetes and the changing environment due to the drilling operation was apparently uninterrupted. This relationship remains to be examined in other natural and perturbed habitats.  相似文献   
32.
33.
34.
The electronic absorption spectra of Fe2+ in non-chromium beryls are examined. Fe2+ in the Al-rich six-coordinate site produces absorption bands at about 820 nm and 970 nm polarizedEc. Fe2+ in the channel produces bands at 820 nm (⊥c) and 2100 nm (‖c). Some blue beryls which are more intensely colored than most aquamarines, have an absorption band at ~700 nm (‖c) which is suggested to arise from an Fe2+/Fe3+ intervalence interaction. Fe2+ in both the six-coordinate site and the channel is identified in the Mössbauer spectra. The Mössbauer spectra of deep blue beryls are unusual and have not been satisfactorily explained. Color changes which accompany heating and irradiation are strongly influenced by the channel iron.  相似文献   
35.
Molecular hydrogen (H(2)) is an important intermediate product and electron donor in microbial metabolism. Concentrations of dissolved H(2) are often diagnostic of the predominant terminal electron-accepting processes in ground water systems or aquatic sediments. H(2) concentrations are routinely measured in ground water monitoring wells but are rarely measured in saturated aquatic sediments due to a lack of simple and practical sampling methods. This report describes the design and development (including laboratory and field testing) of a simple, syringe-based H(2) sampler in (1) saturated, riparian sediments, (2) surface water bed sediments, and (3) packed intervals of a fractured bedrock borehole that are inaccessible by standard pumped methods.  相似文献   
36.
We report here on the observation and offline detection of the meteotsunami off the New Jersey coast on June 13, 2013, using coastal radar systems and tide gauges. This work extends the previous observations of tsunamis originating in Japan and Indonesia. The radars observed the meteotsunami 23 km offshore, 47 min before it arrived at the coast. Subsequent observations showed it moving onshore. The neighboring tide gauge height reading provides confirmation of the radar observations near the shore.  相似文献   
37.
Low-velocity structure beneath Africa from forward modeling   总被引:1,自引:0,他引:1  
Seismic waveforms observed in South Africa containing the first arrival crossover of S to SKS (70° to 110°) are analyzed. The data consist of analog records from the World Wide Seismographic Station Network (WWSSN) of deep events beneath South America. The S-waves arrive 2 to 3 s early relative to PREM at ranges from 70° to 95° and then become increasingly delayed, becoming 5 to 6 s late at 110°. The SKS phase is late by 3 to 5 s over the entire range. This pushes crossover between S and SKS, normally observed at about 81°, out about 2° to 3°, which is the most anomalous shift ever reported. To model such features, we modified Grand's tomography model [Grand et al., GSA Today 7 (1997) 1–7], and generated 2D synthetics to match the data. The overall shape and position of the lower mantle low-velocity anomaly proposed by Grand predicts good results if lower mantle anomalies are enhanced to a level of about 4%. This results in a complex tabular structure extending upward from the core–mantle boundary about 1500 km into the mantle. These features appear to be consistent with a large young plume which is erupting off the CMB.  相似文献   
38.
Following the statistical analyses of long‐term rainfall‐runoff records from research basins in humid temperate latitudes, Hewlett and co‐workers extended the global challenge to disprove their findings that rainfall intensity was non‐significant. This paper responds to Hewlett's challenge as no preceding analyses have involved forested basins in a tropical cyclone‐prone area. Based on a 7 year rainfall‐runoff record, quickflow (QF), peak flow (QP) and quickflow response ratios (QRR) were regressed as dependent variables against rainfall parameters (intensity, Pi, amount, P), storm duration, D and antecedent flow, I. These data sets were categorised into total streamflow (Q) classes and stratified into three seasons, (monsoon, post‐monsoon and dry) for forested and cleared catchments. Where rainfall variable collinearity met acceptable levels, the addition of Pi to regression models including P, D, I contributed up to 9% and 66% of the respective variations in quickflow and peak flow. For the highest Q storm classes (monsoon), Pi alone accounted for up to 67% and 91% of the variation in QF and QP respectively and was the dominant influence on QP for all seasons. The very high rainfall intensities experienced in the monsoon season is a causal factor why these results differ from those of other research drainage basins. Surprisingly, Pi continued to have a significant influence on QF for dry season classes when less‐intense rainfall occurs. Further the results were similar for both catchments across all seasons. P was the dominant independent variable affecting QF above a threshold Q of 50 mm (monsoon), as rainfall contributes directly to saturation overland flow and return flow under saturated conditions. Further although QRR increased with increasing Q for each season, the regression results for that parameter were poor possibly due to the non‐linearity of the rainfall‐runoff relationship. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   
39.
We present photoelectric photometry of λ And never before published, obtained between February 1982 and December 1990 at 29 different observatories. Then we combine it with all other photometry available to us (previously published, contained in the I.A.U. Commission 27 Archives, and obtained with the Vanderbilt 16-inch automatic telescope but not yet published), to yield a 14.8-year data base. Analysis reveals a long-term cycle in mean brightness, with a full range of 0m.15 and a period of 11.4 ± 0.4 years. Because most of our new photometry was concentrated in the 1983-84 observing season, we analyze that one well-defined light curve with a two-spot model. Spot A keeps a 0m.04 amplitude throughout four rotation cycles whereas the amplitude of spot B diminishes from 0m.09 down almost to 0m.03. The spot rotation periods were 55d.9 ± 0d.6 and 520d.8 ± 1d.0, respectively.  相似文献   
40.
Don Hallett 《Geology Today》2002,18(5):182-185
Just a few kilometres south of Cracow, in southern Poland, the scenery changes abruptly from the fluvial plain of the Vistula river, mantled by tills and loess deposits of the Pleistocene glaciation, to a boldly undulating topography representing the outermost thrust sheet of the Carpathian mountains. These northern foothills of the Carpathians are known in Poland as the Beskid Mountains. The Carpathian thrust front can be traced from Upper Silesia through Cracow and Przemysl in southern Poland as far as the Ukraine and Romania. At several places along the thrust front, salt deposits have been found, which have been mined over many centuries. One of the best known mines is located at Wieliczka, 15 km south-east of Cracow. The mine is a popular tourist location, but it also illustrates some spectacular geological features.  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