全文获取类型
收费全文 | 665篇 |
免费 | 34篇 |
国内免费 | 149篇 |
专业分类
测绘学 | 48篇 |
大气科学 | 45篇 |
地球物理 | 384篇 |
地质学 | 196篇 |
海洋学 | 83篇 |
天文学 | 29篇 |
综合类 | 20篇 |
自然地理 | 43篇 |
出版年
2023年 | 17篇 |
2022年 | 8篇 |
2021年 | 7篇 |
2020年 | 23篇 |
2019年 | 17篇 |
2018年 | 16篇 |
2017年 | 4篇 |
2016年 | 8篇 |
2015年 | 11篇 |
2014年 | 18篇 |
2013年 | 14篇 |
2012年 | 48篇 |
2011年 | 74篇 |
2010年 | 7篇 |
2009年 | 14篇 |
2008年 | 47篇 |
2007年 | 32篇 |
2006年 | 42篇 |
2005年 | 36篇 |
2004年 | 41篇 |
2003年 | 33篇 |
2002年 | 28篇 |
2001年 | 22篇 |
2000年 | 17篇 |
1999年 | 28篇 |
1998年 | 17篇 |
1997年 | 10篇 |
1996年 | 13篇 |
1995年 | 10篇 |
1994年 | 13篇 |
1993年 | 24篇 |
1992年 | 19篇 |
1991年 | 7篇 |
1990年 | 14篇 |
1989年 | 13篇 |
1988年 | 5篇 |
1987年 | 8篇 |
1986年 | 3篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1980年 | 3篇 |
1948年 | 3篇 |
1947年 | 3篇 |
1943年 | 3篇 |
1942年 | 3篇 |
1937年 | 3篇 |
1935年 | 12篇 |
1934年 | 4篇 |
1925年 | 7篇 |
1923年 | 5篇 |
排序方式: 共有848条查询结果,搜索用时 15 毫秒
811.
812.
The significance of the volcanic and the volcano-sedimentary processes inthe formation of mineral deposits has, as a rule, not yet been sufficiently recog-nized by geologists. Intensive studies carried out recently by the Soviet geologistsin the Altai and Ural regions have furnished more and more informations 相似文献
813.
814.
The interpretation of mid-UV albedo spectra of planetary atmospheres, especially that of Titan, is the main goal of the SIPAT (Spectroscopie uv d'Interet Prebiologique dans l'Atmosphere de Titan) research program. This laboratory experiment has been developed in order to systematically determine the absorption coefficients of molecular compounds which are potential absorbers of scattered sunlight in planetary atmospheres, with high spectral resolution, and at various temperatures below room temperature. From photochemical modelling and experimental simulations, we may expect triacetylene (C6H2) to be present in the atmosphere of Titan, even though it has not yet been detected. We present here the first determination of the absolute absorption coefficient of that compound in the 200-300 nm range and at two temperatures (296 K and 233 K). The temperature dependence of the C6H2 absorption coefficient in that wavelength range is compared to that previously observed in the case of cyanoacetylene (HC3N). We then discuss the implications of the present results for the interpretation of Titan UV spectra, where it appears that large uncertainities can be introduced either by the presence of trace impurities in laboratory samples or by the variations of absorption coefficients with temperature. 相似文献
815.
Liu W Hu J. Y. Beijing Astronomical Observatory National Astronomical Observatories The Chinese Academy of Sciences Beijing China Email: liuwu@class. bao. ac. cn 《天文研究与技术》1999,(Z1)
1 IntroductionInourspectroscopicobservationoftheopticalidentificationofROSATX raysourcesinthehighgalacticlatitude ,8newcataclysmicvariableswerediscoveredbasedontheirspectralnature.PreliminarydiscusshadbeenreportedbyHuetal ( 1 998) .WehavemadeCCDtime resolvedp… 相似文献
816.
梁静 《地震地磁观测与研究》1990,(3)
以国家地震局科技监测司副司长孙其政为团长的中国数字地震台网考察团,一行10人,于1989年10月13日,赴泰国进行了为期8天的地震考察。在此期间,我们对不久前在泰缅边界发生的6.4级破坏性地震现场进行了考察,以及位于泰国西北部距曼谷近300公里的2个水库大坝和电站。两国地震工作者就如何利用强震仪监测库区水位变化,如何研究强地面运动对水坝的影响等多项内容进行了讨论;两国台站的工 相似文献
817.
The extensive deterioration of coral reefs worldwide highlights the importance of creating efficient monitoring methods to best assess their state of health. At present, several suggested parameters serve such indicators. None of these, however, is well accepted as reliably representing reef community health. In the present study we examine a new approach based on the ratio between mortality and recruitment rates of branching corals, which we term 'Deterioration Index' (DI). It aims at providing a quantitative indication of the state of health of reef-building coral communities. The method was developed and tested on 16 coral communities on artificially laid rocks along the coast of Eilat, Red Sea (Gulf of Aqaba). In contrast to frequently used indices (i.e. mortality rate, abundance and species richness), which did not demonstrate a consistent result in comparing disturbed vs. undisturbed coral communities, the DI revealed significant differences between these communities. Our results suggest that the use of the DI may enable the detection of disturbed coral communities in one instance monitoring, where the other parameters had failed. The DI, therefore, may provide a comparable quantitative assessment of the deterioration process and its intensity in a coral community. We propose the DI approach as an efficient and applicable tool for coral reef monitoring. 相似文献
818.
819.
The late tail of the breakthrough curve (BTC) of a conservative tracer in a regional-scale alluvial system is explored using Monte Carlo simulations. The ensemble numerical BTC, for an instantaneous point source injected into the mobile domain, has a heavy late tail transforming from power law to exponential due to a maximum thickness of clayey material. Haggerty et al.'s (2000) multiple-rate mass transfer (MRMT) method is used to predict the numerical late-time BTCs for solutes in the mobile phase. We use a simple analysis of the thicknesses of fine-grained units noted in boring logs to construct the memory function that describes the slow decline of concentrations at very late time. The good fit between the predictions and the numerical results indicates that the late-time BTC can be approximated by a summation of a small number of exponential functions, and its shape depends primarily on the thicknesses and the associated volume fractions of immobile water in "blocks" of fine-grained material. The prediction of the late-time BTC using the MRMT method relies on an estimate of the average advective residence time, t(ad). The predictions are not sensitive to estimation errors in t(ad), which can be approximated by L/v , where v is the arithmetic mean ground water velocity and L is the transport distance. This is the first example of deriving an analytical MRMT model from measured hydrofacies properties to predict the late-time BTC. The parsimonious model directly and quantitatively relates the observable subsurface heterogeneity to nonlocal transport parameters. 相似文献
820.
Profiles of nonylphenol isomers in surface waters from Sri Lanka 总被引:1,自引:0,他引:1
Isomer-specific concentrations of nonylphenol (NP) and their predicted estrogenic potency were investigated in Sri Lankan waters for the first time. The total concentration of 13 NP isomers ranged from 90 to 1835 ng/L, while the predicted estrogenic equivalent concentration ranged from 0.072 to 1.38 ng 17β-estradiol (E2)/L. Bire Lake, located in the central area of the commercial capital, Colombo, had the highest contamination among the studied locations. These data show that NP levels in Sri Lankan waters are well within the recently reported concentrations in other regions of the world. The spatial differences in NP concentrations suggest that NP contamination in Sri Lanka may be widespread, and comprehensive study is vital. 相似文献