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   589篇
  免费   35篇
  国内免费   2篇
测绘学   13篇
大气科学   100篇
地球物理   124篇
地质学   227篇
海洋学   33篇
天文学   112篇
综合类   2篇
自然地理   15篇
  2021年   5篇
  2020年   7篇
  2019年   6篇
  2018年   25篇
  2017年   28篇
  2016年   56篇
  2015年   31篇
  2014年   43篇
  2013年   42篇
  2012年   18篇
  2011年   27篇
  2010年   33篇
  2009年   30篇
  2008年   20篇
  2007年   23篇
  2006年   14篇
  2005年   8篇
  2004年   9篇
  2003年   9篇
  2002年   9篇
  2001年   6篇
  2000年   7篇
  1999年   2篇
  1998年   12篇
  1997年   8篇
  1996年   13篇
  1995年   5篇
  1994年   4篇
  1993年   14篇
  1992年   7篇
  1991年   7篇
  1990年   11篇
  1989年   8篇
  1988年   3篇
  1986年   6篇
  1985年   6篇
  1984年   7篇
  1983年   4篇
  1981年   4篇
  1978年   3篇
  1977年   4篇
  1976年   2篇
  1974年   2篇
  1973年   4篇
  1972年   3篇
  1971年   5篇
  1970年   3篇
  1969年   5篇
  1965年   4篇
  1963年   2篇
排序方式: 共有626条查询结果,搜索用时 31 毫秒
41.
42.
A statistically relevant correlation between the reaction rate coefficient, k OH, for the OH radical reaction with 161 organic compounds in the gas phase at 300 K, and the corresponding vertical ionisation energies E i,v, reveals two classes of compounds: aromatics where –log(k OH/cm3s-1)3/2E i,v(eV)–2 and aliphatics where –log(k OH/cm3s-1)4/5E i,v(eV)+3. The prediction of the rate coefficient, k OH, for the reaction of OH with organic molecules from the above equations has a probability of about 90%. Assuming a global diurnal mean of the OH radical concentration of 5×105 cm3, the upper limit of the tropospheric half-life of organic compounds and their persistence can be estimated.  相似文献   
43.
The lysosomal membrane destabilization and the metallothionein content in the digestive gland cells of mussels (Mytilus galloprovincialis Lam.), collected along the east coast of the North Adriatic (Istrian and Kvarnerine coast, Croatia), were examined over a period of four years (1996–1999). The lysosomal membrane stability, as a biomarker of general stress, showed that the membrane labilization period in mussels from polluted, urban- and industrial-related areas was significantly decreased (p<0.05) when compared to mussels from control, clean sea water sites. In the harbour of Rijeka, the most contaminated site, the lysosomal membrane stability was reduced by more than 70% compared to the control. This method also proved to be a useful biomarker for detection of additional stress caused by short-term hypoxia that occurred once during this study inside the polluted and periodically quite eutrophic Pula Harbour. The concentration of metallothioneins in the mussel digestive gland, as a specific biomarker of exposure to heavy metals, did not reveal significant differences (p<0.05) between sites covered by this study.  相似文献   
44.
45.
The present paper examines magmatic structures in the Jizera and Liberec granites of the Krkonoše–Jizera Plutonic Complex, Bohemian Massif. The magmatic structures are here interpreted to preserve direct field evidence for highly localized magma flow and other processes in crystal-rich mushes, and to capture the evolution of physical processes in an ancient granitic magma chamber. We propose that after chamber-wide mixing and hybridization, as suggested by recent petrological studies, laminar magma flow became highly localized to weaker channel-like domains within the higher-strength crystal framework. Mafic schlieren formed at flow rims, and their formation presumably involved gravitational settling and velocity gradient flow sorting coupled with interstitial melt escape. Local thermal or compositional convection may have resulted in the formation of vertical schlieren tubes and ladder dikes whereas subhorizontal tubes or channels formed during flow driven by lateral gradients in magma pressure. After the cessation or deceleration of channel flow, gravity-driven processes (settling of crystals and enclaves, gravitational differentiation, development of downward dripping instabilities), accompanied by compaction, filter pressing and melt segregation, dominated in the crystal mush within the flow channels. Subsequently, magmatic folds developed in schlieren layers and the magma chamber recorded complex, late magmatic strains at high magma crystallinities. Late-stage magma pulsing into localized submagmatic cracks represents the latest events of magmatic history of the chamber prior to its final crystallization. We emphasize that the most favorable environments for the formation and preservation of magmatic structures, such as those hosted in the Jizera and Liberec granites, are slowly cooling crystal-rich mushes. Therefore, where preserved in plutons, these structures may lend strong support for a “mush model” of magmatic systems.  相似文献   
46.
The spectra of two roAp stars have been analyzed as part of a project to study lithium in magnetic Ap stars. Variability of the Li I 6708 Å resonance doublet and rare-earth lines was detected, which can be explained using an oblique rotator model with the lithium spots located at the magnetic poles. Synthetic spectra obtained at different rotational phases have yielded the first data on the atmospheric chemical compositions of these spotted stars. Using refined atomic data and the most complete line lists has enabled a detailed study of the spectra near the Li I 6708 Å line and computation of the Li I line profile taking into account the spotted distribution of the lithium over the stellar surfaces. The positions of two lithium spots and lithium abundances for each of the spots have been determined.  相似文献   
47.
Electron transport properties of single crystal and polycrystalline natural mineral galena (PbS) samples from the Trep?a mine, Yugoslavia, were determined using the photoacoustic frequency transmission technique. Their thermal diffusivity (D T≈0.16 × 10?5 m2 s?1), the coefficient of diffusion (D between 0.15×10?2 0.16×10?2 m2 s?1) and lifetime of the excess carrier (τ≈35 μs and the front and rear recombination velocity (s g≈65.5 m s?1 and s b≈66.4 m s?1, respectively), were calculated by comparing the experimental results and the theoretical photoacoustic amplitude and phase signals. The lattice parameter obtained by X-ray work was a?=5.936?Å. The free carrier concentration of these single-crystal samples was measured using the Hall method (N?=?3×1018 cm?3). Measurements of the optical reflectivity of the same samples, as a function of wavelength, in the infrared and far infrared ranges, were performed. In the far infrared range a free electron plasma frequency was observed and numerically analyzed, using the least-squares fitting procedure. The values of optical parameters were calculated and the value of the free carrier concentration obtained by the Hall method was confirmed.  相似文献   
48.
Summary A numerical model for the quantitative precipitation forecasting has been formulated. In this model precipitation is computed as a function of the vertical velocity and humidity distribution in the atmosphere. The orographic influence on the vertical velocity was taken into consideration. Further, the relation between vertical velocity and static stability of the atmosphere has been considered and, as an important factor in the condensation process, was introduced into the equation of the model. This numerical model for the precipitation forecasting has been applied in the North Adriactic Sea region, which is characterized by a strong vertical gradient of the specific humidity and pronounced orographic influence. The results achieved show that this model could successfully be used as an objective method in the routine forecasting of the amount of precipitation.  相似文献   
49.
Zusammenfassung In der Umgebung der Stadt Prilep in Mazedonien kommen an mehreren Stellen in einer hochmetamorphen, aus Glimmerschiefern und Amphiboliten bestehenden Zone Calcit- und Dolomitmarmore vor. In den letzterwähnten wurden bisher Dolomit, Calcit, Korund, Diaspor, -Zoisit, Rutil, Fluorit, Achroit, Pyrit, Muskovit, Illit, Margarit und Chlorit (vonErdmannnsdörfer auch Kossmatit) festgestellt. Diese Paragenese ist regionalmetamorph entstanden.
Dolomite-marble in the surroundings of the town prilep, macedonia, and its minerals
Summary Calcite- and dolomite-marbles occur in a highly metamorphic series together with micaschists and amphibolites at several localities in the surroundings of Prilep, Macedonia. In the dolomite-marbles, dolomite, calcite, corundum, diaspore, -zoisite, rutile, fluorite, achroite pyrite, muscovite, illite, margarite, chlorite, and kossmatite (the last only byErdmannsdörffer) have been found. The paragenesis is of regional metamorphic origin.


Mit 1 Abbildung  相似文献   
50.
ABSTRACT

Climate change projections of precipitation and temperature suggest that Serbia could be one of the most affected regions in southeastern Europe. To prepare adaptation measures, the impact of climate changes on water resources needs to be assessed. Pilot research is carried out for the Lim River basin, in southeastern Europe, to predict monthly flows under different climate scenarios. For estimation of future water availability, an alternative approach of developing a deterministic-stochastic time series model is chosen. The proposed two-stage time series model consists of several components: trend, long-term periodicity, seasonality and the stochastic component. The latter is based on a transfer function model with two input variables, precipitation and temperature, as climatic drivers. The Nash-Sutcliffe model efficiency for the observed period 1950–2012 is 0.829. The model is applied for the long-term hydrological prediction under the representative concentration pathway (RCP) emissions scenarios for the future time frame 2013–2070.  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