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   687篇
  免费   39篇
  国内免费   2篇
测绘学   47篇
大气科学   24篇
地球物理   185篇
地质学   219篇
海洋学   19篇
天文学   198篇
综合类   6篇
自然地理   30篇
  2023年   4篇
  2022年   8篇
  2021年   7篇
  2020年   12篇
  2019年   16篇
  2018年   30篇
  2017年   36篇
  2016年   50篇
  2015年   43篇
  2014年   39篇
  2013年   39篇
  2012年   33篇
  2011年   21篇
  2010年   27篇
  2009年   38篇
  2008年   31篇
  2007年   32篇
  2006年   22篇
  2005年   21篇
  2004年   14篇
  2003年   19篇
  2002年   23篇
  2001年   6篇
  2000年   18篇
  1999年   10篇
  1998年   12篇
  1997年   3篇
  1996年   12篇
  1995年   7篇
  1994年   6篇
  1993年   3篇
  1992年   5篇
  1991年   12篇
  1990年   7篇
  1989年   9篇
  1987年   3篇
  1986年   5篇
  1985年   3篇
  1984年   4篇
  1983年   3篇
  1981年   2篇
  1979年   2篇
  1978年   4篇
  1977年   3篇
  1976年   3篇
  1975年   2篇
  1974年   3篇
  1973年   2篇
  1970年   2篇
  1968年   2篇
排序方式: 共有728条查询结果,搜索用时 93 毫秒
681.
682.
Study on contamination of tsunami sediments deposited on 26 December 2004 conducted shortly after the tsunami in coastal zone of Thailand revealed elevated contents of salts in water-soluble and some heavy metals and arsenic in bioavailable fractions (Szczuciński et al. in Env Geol 49:321–331, 2005). Few months later rainy season started and effected in total rainfall of over 3,300 mm. This paper presents results of survey repeated 1 year after the tsunami. To assess the effects of rainy season on mobilization of previously determined potential contaminants, the same locations were sampled again and analysed with the same methods. The tsunami deposit layer was well preserved but in many locations the sediments were coarser than just after tsunami due to washing out of finer fractions. The water-soluble salts contents were strongly reduced after the rainy season. However, the concentrations of acid leachable heavy metals and metalloids were still elevated in comparison to reference sample from an area not impacted by tsunami. It is possible that the metals and metalloids are successively moved to more bioavailable fraction from forms which were more resistant to mobilization.  相似文献   
683.
The spread of a passive contaminant in an open-channel reach is considered with use of a two-dimensional advection-diffusion equation with the included off-diagonal dispersion coefficients. This paper presents the calculation of truncation errors, namely numerical diffusion and numerical dispersion for various finite difference schemes. The accuracy of the considered finite-difference approximations is analysed by deriving and studying the relevant modified partial differential equation.  相似文献   
684.
The quantity and quality of lignin phenols (Σ8, Λ, S/V, C/V and (Ad/Al)v) in the sediments of three small Lobelia lakes with neither inlets nor outlets were investigated and compared with palynological data and lithology of the profiles. The method of alkaline CuO oxidation was used. Substantial differences with respect to sedimentary lignin concentration and provenance recorded along the profiles and among the sites are in good agreement with pollen data describing the dominant type of vegetation and with indices of soil erosion in the lakes’ catchments. This relation shows that the compositions of lignin degradation products in these lakes are closely related to the local environmental conditions. In all the lakes gymnosperm wood is the main source of lignin products; however, each lake is characterized by different S/V index values. Especially good correlations were obtained between pine pollen proportions in sediments and the S/V index. The correlation between the C/V and (Ad/Al)v indices indicates a higher degradation of organic matter when non-woody tissue is more abundant. This pilot study illustrates the usefulness and potential for a wider application of lignin oxidation products in palaeoecological reconstructions. This kind of data would be of special importance when investigating local presence/absence of woody plants and the role of angiosperms/gymnosperms in local vegetation. Estimates of lignin biodegradation levels, as well as the data on diagenetic processes, may afford supplementary information on possible disturbances in sedimentation.  相似文献   
685.
The amplitude of the ellipsoidal variability, the mass function and the evolutionary limits on the component masses have been used to constrain the binary system parameters of T Coronae Borealis. Contrary to all previous studies, our analysis shows that the mass ratio of T CrB is q ≡ M g/ M h≈0.6, which implies a low-mass binary system, with the stellar masses M g∼0.7 M⊙ for the red giant and M h∼1.2 M⊙ for the hot companion. This result strongly supports the thermonuclear runaway model for this recurrent nova, and solves all controversies about the nature of the hot component and the physical causes of its eruptions.  相似文献   
686.
We describe the possible measurable difference in the Cherenkov light component of EAS induced by an electromagnetic particle (i.e., e+, e or γ) and induced by a hadron (i.e., proton or heavier nuclei) in the TeV range. The method can be applied in experiments which use wave front sampling method of EAS Cherenkov light detection (e.g., THEMISTOCLE, ASGAT).  相似文献   
687.
The interaction between the atmosphere and the underlying solid mantle is oneof the most important sources of changes in all three components of theEarth's rotation vector on different time scales. In this paper the NCEP/NCARreanalysis time series of four times daily atmospheric effective angularmomentum (EAM) estimates is used to investigate some selected aspects of theatmospheric influence on Earth rotation. Emphasis is placed on thecontroversial features which were difficult or impossible to study using theoperational EAM data, such as excitation of the free oscillations in polarmotion, the Chandler wobble (CW) and the free core nutation (FCN), or theroles of diurnal and semidiurnal atmospheric tides and atmospheric normalmodes in the rotational dynamics of the Earth.  相似文献   
688.
Long‐term studies were conducted on the polymictic Siemianówka reservoir (SR), situated in a seminatural forest‐peat catchment in NE Poland. The studies were started on the second year of the reservoir's existence. The records showed dissolved organic carbon (DOC) concentrations gradually increasing up to 25…30 mg/L. The largest DOC pool in the reservoir comes from the spring load input, supplemented by the excessive development of phytoplankton with cyanobacteria dominance. The DOC limited the range of the photic zone, eliminated the occurrence of aquatic plants, and was a significant carrier of nutrients, which were gradually released to water, bringing about the “humoeutrophication” of the reservoir.  相似文献   
689.
The occurrence of redeposited sediments and foraminiferids within the Upper Senonian deposits of the Silesian Unit (Northern Carpathians) have allowed a reconstruction of a part of the southern slope of the Silesian Basin. Three main zones have been established with specific sediments and associations of foraminiferids; basin plain, slope and upper slope-shelf which correspond to part of the “Recurvoides” and “Marssonella” associations sensu Haig (1979). Nine species of Foraminiferida from the uppermost associations are described.  相似文献   
690.
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