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   314篇
  免费   22篇
  国内免费   4篇
测绘学   16篇
大气科学   15篇
地球物理   113篇
地质学   90篇
海洋学   31篇
天文学   54篇
综合类   2篇
自然地理   19篇
  2024年   1篇
  2021年   11篇
  2020年   9篇
  2019年   7篇
  2018年   11篇
  2017年   15篇
  2016年   26篇
  2015年   14篇
  2014年   17篇
  2013年   21篇
  2012年   24篇
  2011年   23篇
  2010年   22篇
  2009年   26篇
  2008年   15篇
  2007年   14篇
  2006年   11篇
  2005年   18篇
  2004年   11篇
  2003年   10篇
  2002年   6篇
  2001年   5篇
  2000年   7篇
  1999年   3篇
  1998年   2篇
  1997年   3篇
  1996年   2篇
  1995年   1篇
  1994年   2篇
  1988年   2篇
  1983年   1篇
排序方式: 共有340条查询结果,搜索用时 250 毫秒
31.
32.
We present preliminary results obtained from integral-field (IFU) data of the giant extragalactic Hii region NGC5461, located in a spiral arm (RA=14h03m41.4s, dec=+54°19′05″) of M101. The spatial and spectral information obtained with IFUs allows us to decompose the Hii region and analyze it at high resolution.  相似文献   
33.
We investigate the properties of optically passive spirals and dusty red galaxies in the A901/2 cluster complex at redshift ∼0.17 using rest-frame near-ultraviolet–optical spectral energy distributions, 24-μm infrared data and Hubble Space Telescope morphologies from the STAGES data set. The cluster sample is based on COMBO-17 redshifts with an rms precision of  σ cz ≈ 2000 km s−1  . We find that 'dusty red galaxies' and 'optically passive spirals' in A901/2 are largely the same phenomenon, and that they form stars at a substantial rate, which is only four times lower than that in blue spirals at fixed mass. This star formation is more obscured than in blue galaxies and its optical signatures are weak. They appear predominantly in the stellar mass range of  log  M */M=[10, 11]  where they constitute over half of the star-forming galaxies in the cluster; they are thus a vital ingredient for understanding the overall picture of star formation quenching in clusters. We find that the mean specific star formation rate (SFR) of star-forming galaxies in the cluster is clearly lower than in the field, in contrast to the specific SFR properties of blue galaxies alone, which appear similar in cluster and field. Such a rich red spiral population is best explained if quenching is a slow process and morphological transformation is delayed even more. At  log  M */M < 10  , such galaxies are rare, suggesting that their quenching is fast and accompanied by morphological change. We note that edge-on spirals play a minor role; despite being dust reddened they form only a small fraction of spirals independent of environment.  相似文献   
34.
Fabio Noviello   《New Astronomy》2009,14(8):659-665
Phase transitions taking place during the inflationary epoch give rise to bubbles of true vacuum embedded in the false vacuum. These bubbles can imprint a distinctive signal on the Cosmic Microwave Background (CMB). We evaluate the feasibility of detecting these signatures with wavelets in CMB maps, such as those that will be made available by the European Space Agency’s (ESA) Planck mission.  相似文献   
35.
Journal of Seismology - A three-dimensional tomographic image of the seismic velocity structure in the crust and upper mantle of northwestern Nicaragua was performed using the back-projection...  相似文献   
36.
The present work investigates the time oscillations of the temperature at several depths of a Martian soil analogue made of two layers of different physical properties. The maximum temperature-time oscillation inside the Martian soil analogue, DT, and its derivative with depth, d(DT)/dz or DDT, can be analysed to understand the presence of a boundary between dry and frozen soil. The maximum temperature-time oscillation, DT, reduces by about one order of magnitude at the boundary between dry and frozen soil if a frozen layer is present. The reduction of DT at the boundary between two dry soils with different porosity is much smaller. DDT decreases by more than one order of magnitude at the boundary between dry and frozen soil if a frozen layer is present. The reduction of DDT at the boundary between two dry soils with different porosity is much smaller.  相似文献   
37.
We present a high-resolution dark matter reconstruction of the   z = 0.165  Abell 901/902 supercluster from a weak lensing analysis of the Hubble Space Telescope STAGES survey. We detect the four main structures of the supercluster at high significance, resolving substructure within and between the clusters. We find that the distribution of dark matter is well traced by the cluster galaxies, with the brightest cluster galaxies marking out the strongest peaks in the dark matter distribution. We also find a significant extension of the dark matter distribution of Abell 901a in the direction of an infalling X-ray group Abell 901α. We present mass, mass-to-light and mass-to-stellar mass ratio measurements of the structures and substructures that we detect. We find no evidence for variation of the mass-to-light and mass-to-stellar mass ratio between the different clusters. We compare our space-based lensing analysis with an earlier ground-based lensing analysis of the supercluster to demonstrate the importance of space-based imaging for future weak lensing dark matter 'observations'.  相似文献   
38.
Reale  Fabio 《Solar physics》1999,190(1-2):139-144
A TRACE field of view well inside the solar disk shows very well defined large loops, likely to be very inclined to the solar surface. On the other hand there is little evidence of large loops perpendicular to the solar surface. We show that this does not mean that most large loops have such large inclination but that perpendicular loops are much less visible to TRACE, because of density stratification. We quantitatively evaluate this effect by modeling in detail loops with different inclinations.  相似文献   
39.
Daily rainfall is a complex signal exhibiting alternation of dry and wet states, seasonal fluctuations and an irregular behavior at multiple scales that cannot be preserved by stationary stochastic simulation models. In this paper, we try to investigate some of the strategies devoted to preserve these features by comparing two recent algorithms for stochastic rainfall simulation: the first one is the modified Markov model, belonging to the family of Markov-chain based techniques, which introduces non-stationarity in the chain parameters to preserve the long-term behavior of rainfall. The second technique is direct sampling, based on multiple-point statistics, which aims at simulating a complex statistical structure by reproducing the same data patterns found in a training data set. The two techniques are compared by first simulating a synthetic daily rainfall time-series showing a highly irregular alternation of two regimes and then a real rainfall data set. This comparison allows analyzing the efficiency of different elements characterizing the two techniques, such as the application of a variable time dependence, the adaptive kernel smoothing or the use of low-frequency rainfall covariates. The results suggest, under different data availability scenarios, which of these elements are more appropriate to represent the rainfall amount probability distribution at different scales, the annual seasonality, the dry-wet temporal pattern, and the persistence of the rainfall events.  相似文献   
40.
The organic composition and organic‐inorganic interaction in paper mill sludge (PS) solvent extracts (hexane, ethyl acetate, acetone and ethanol) and humic fractions, humic acid (HA) and humin (HU) were studied by electron paramagnetic resonance spectroscopy (EPR), proton and carbon‐13 nuclear magnetic resonance spectroscopy (1H NMR; 13C NMR), Fourier‐transformed infrared spectroscopy (FTIR), and ultraviolet‐visible spectroscopy (UV‐vis). The strategy of fractionating the PS, sequentially, with organic solvents of increasing polarity is a reliable analytical procedure for humic substance sample separation because it results in more purified fractions. FTIR, 1H NMR and 13C NMR results showed that hexane extract consisted mainly of aliphatic hydrocarbon structures. Their contents in the extracts decreased as the polarity of the extracting solvent increased and the content of oxygen functional groups increased. Carboxylic and carboxylate functional groups were found in the acetone extract, and ester and ether functions were predominantly found in the ethanol extract. EPR spectra revealed some Fe3+ complexes with rhombic structure (g1 = 4.3; g2 = 9.0) in the humic fractions and in all solvent extracts, except hexane. Quasi‐octahedral Fe3+ complexes (g = 2.3; ΔHpp ≤ 400 G) were found in the HU fraction and in the acetone extract. The organic free radical content in the HA fraction was higher than the non‐fractionated PS sample and HU fraction.  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