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   147篇
  免费   4篇
  国内免费   10篇
测绘学   2篇
大气科学   12篇
地球物理   45篇
地质学   36篇
海洋学   23篇
天文学   28篇
综合类   11篇
自然地理   4篇
  2021年   2篇
  2020年   3篇
  2019年   1篇
  2018年   2篇
  2017年   2篇
  2016年   10篇
  2015年   3篇
  2014年   3篇
  2013年   6篇
  2012年   9篇
  2011年   9篇
  2010年   2篇
  2009年   7篇
  2008年   8篇
  2007年   6篇
  2006年   3篇
  2005年   8篇
  2004年   4篇
  2003年   4篇
  2002年   3篇
  2001年   4篇
  2000年   8篇
  1999年   4篇
  1998年   3篇
  1997年   1篇
  1996年   5篇
  1995年   2篇
  1994年   1篇
  1993年   1篇
  1990年   1篇
  1989年   2篇
  1987年   4篇
  1986年   1篇
  1985年   4篇
  1984年   1篇
  1983年   1篇
  1982年   4篇
  1981年   2篇
  1980年   2篇
  1978年   2篇
  1977年   1篇
  1976年   3篇
  1975年   3篇
  1974年   1篇
  1973年   2篇
  1971年   2篇
  1965年   1篇
排序方式: 共有161条查询结果,搜索用时 15 毫秒
71.
It is well known that sea-salt aerosols in particulate matter (PM) react with acids such as H2SO4 and HNO3 during transportation and thereby lose chloride ions (Cl-loss). The PM and fog were sampled concurrently at different altitudes in the Hachimantai mountain range, northern Japan. The PM and fog sampled at different altitudes had nearly identical properties for the ion components. However, the PM was in a Cl-depleted state (more than 80% of all samples), but the fog water was not in so Cl-depleted state (less than 29%). As a result, it could be explained that this phenomenon caused because the fog droplets took up the gaseous state HCl other than sea-salt PM. After all Cl- in the fog water recovered and was rather rich compared with the sea-salt or the PM by the uptake of the gaseous state HCl. Moreover, it was found that for PMcoarse(2.5 < D < 10), 86% of the acid (H2SO4 and HNO3) was consumed for Cl-loss reactions and/or for dissolution of Ca and Mg in soil particles.  相似文献   
72.
The -ray and white-light flare of 13 May, 1981 is used for a study of spatial distributions of energetic electrons and high-temperature plasma.  相似文献   
73.
A model for diurnal variations of neutral and ionic nitrogen compounds in the thermosphere is reconstructed on the basis of a new photochemical aspect on N(2D), together with new observations of the NO density. The NO density so far measured must be reduced by a factor 2, due to a revision of the fluorescence coefficient for the NO γ-band airglow. Incorporating the quenching reaction of N(2D) with O in the model calculation results in a reduction of the NO density at heights as low as 100 km. These two effects are combined to lead to an evaluation that the N(2D) quantum yield for various possible reactions is as large as 0.9. A smaller rate coefficient for the quenching reaction than that measured in the laboratory, i.e. 1.0 × 10?12cm3sec?1 is favourable for the recent NO observation in the early morning, as well as the observed emission rates of the 5200 A airglow from N(2D) The present model predicts a significant day-to-night variation of N and NO densities at heights above 100 km. Below 100 km, the NO density is fairly stable because of its long chemical time constant. Since the rate coefficient for the conversion of N(4S) to NO is highly temperature dependent, the relative population of N(4S) and NO is very sensitive to the thermospheric temperature variation. Large variations of both N(4S) and NO densities due to the temperature change could occur especially at night. The model is in good agreement with the NO observations so far available in low and middle latitudes, as well as the N observation by the use of a rocket in the twilight.  相似文献   
74.
The intensity ratios of the 1304 Å triplet airglow of atomic oxygen observed by Fastie and Crosswhite (1964) are interpreted on the basis of the radiative transfer formulation for a model with complete frequency redistribution in a Voigt line profile. A model for the fine structure levels O(3Pj) in local thermodynamic equilibrium is favorable to the observed intensity ratios, as far as a Voigt profile is applicable. In view of large cross sections as calculated theoretically by Allison and Burke (1969), the mutual relaxation among the 3Pj levels should occur rapidly enough to allow the population in the 3Pj levels to be in thermodynamic equilibrium with the ambient neutral gases.  相似文献   
75.
1 Introduction Ultravioletradiationisahighlyactivecomponentofsolarspectrum .Ultravioletradiationhasdetrimentaleffectsonlivingthingsexposedtosunlight ,includingthedestructionofDNA ,proteinsandothermolecules(Harm ,1980 ) ,inhibitionofphotosynthesisandgrow…  相似文献   
76.
77.
Consumption of silicate and nitrate (Si:N molar ratio) in the upper layer of the pelagic subarctic Pacific in summer was evaluated by a regression analysis of silicate vs. nitrate concentrations at the upper 100 m depth. Based on data of three cruises, the pelagic subarctic Pacific can be classified into two groups. First group is characterized by roughly 1:1 consumption of silicate and nitrate, and occupies rather larger area of subarcfic Pacific, i.e., the Gulf of Alaska and the Western Subarctic gyre (averaged slope of Si:N linear regression: 1.21, n = 10 and 1.45, n = 9, respectively). Second group is the regions of the Bering Sea basin and the Oyashio region, and showed higher silicate consumption compared to that of nitrate (averaged slope of Si:N linear regression: 2.14, n = 9 and 2.36, n = 3, respectively). The Si:N difference observed is possibly attributed to relative contribution of diatoms production among the phytoplankton assemblages in the regions, i.e., dominance of diatoms production in the regions of the second group. Higher accumulation of ammonium at the bottom of euphotic layer in the summer Bering Sea basin would also contribute to increase consumption ratio of Si:N amounts.  相似文献   
78.
Some experiments were carried out to explain thein situ phenomena that the number of coliform organisms decreased rapidly from estuaries to offshore, and also at deeper layer, and that the appearance of coliform types varied.In natural seawater, experimental results did not show thatEscherichia coli was extinct by self-purification or anti-biosis action of seawater, but it showed that this organism decreased mainly because of their starvation caused by lack of nourishment. Although the decreasing rate of bacterial density was delayed in enriched seawater, addition of nutrient even at the time of bacterial extinction promoted the appearance of variated form of this bacteria with floc formation.Flocculation of bacterial cells was influenced by quality and quantity of added nutrients. Temperature was shown to have an effect on the floc formation, but appearance of variated form in flocculated cells ofE. coli was not affected by temperature. Flocculated particles of coliform bacteria were adsorbed on suspended particles in seawater and precipitated rapidly. This phenomenon seems to be a cause of the rapid disappearance of coliform bacteria in coastal waters.In bottom deposits the coliform bacteria probably survive longer as physiologically variated forms when suitable nutrients were supplied.  相似文献   
79.
The concentrations of dissolved organic carbon and nitrogen (DOC and DON, respectively) were measured in Shiraho fringing reef (Japan), using a high-temperature catalytic-oxidation method. When the seawater on the reef flat (shallow lagoon) was isolated from the surrounding ocean due to the low tide, the concentrations of DOC and DON on the reef flat were 66–75 and 4.8–5.7 μmol l−1, respectively. The DOC and DON concentrations were higher than those of the adjacent outer ocean (57–58 and 3.8 μmol l−1, respectively), suggesting that the coral reef functioned as a net source of dissolved organic matter for the surrounding ocean. In order to investigate long-term bacterial decomposition of the reef-derived DOC (RF-DOC), the seawater samples collected on the reef flat and at the adjacent ocean were incubated in the dark for 1 year. Regression analysis using an exponential curve that considered two degradability pools (labile and refractory) fitted the mineralization of the RF-DOC very well (r 2 > 0.89). According to the regression analysis, the DOC produced on the reef flat was composed of the labile fraction of 63–94% (average 77%) and the refractory fraction of 6–37% (average 23%). It was concluded that some of the DOC that was produced in the coral reef ecosystem was exported to the surrounding ocean if the reef flat had a water residence time less than several months. The exported organic matter may support microbial communities in the ocean as an energy source.  相似文献   
80.
An instrumented field study of the across-shore evolution of wave characteristics was conducted under wind-wave and swell-wave conditions on a sloping type B shore platform along the mesotidal, fetch-limited coast of Auckland, New Zealand, based on spectral analysis of hydrodynamic data recorded in pressure-sensor time series during a 24-h deployment on 24–25 November 2008. The results highlight the ability of the shore platform in dissipating wave energy reaching the cliff toe under wind-wave and swell-wave conditions, and the spectral redistribution of wave energy. As waves propagated onto the platform surface and towards the cliff toe, infragravity-wave energy became progressively more dominant, while gravity waves were dissipated. Wave height and period in the central sector of the platform and at the cliff toe were not markedly affected by differences in incident-wave conditions observed during the survey. The findings confirm the importance of platform morphology in modulating wave-energy delivery to the cliff toe. In contrast to previous studies, infragravity-wave height at the cliff toe did not appear to be correlated to incident-wave conditions.  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