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   1388篇
  免费   31篇
  国内免费   15篇
测绘学   16篇
大气科学   136篇
地球物理   370篇
地质学   582篇
海洋学   111篇
天文学   159篇
综合类   3篇
自然地理   57篇
  2021年   12篇
  2018年   26篇
  2017年   14篇
  2016年   25篇
  2015年   19篇
  2014年   34篇
  2013年   41篇
  2012年   35篇
  2011年   55篇
  2010年   38篇
  2009年   50篇
  2008年   56篇
  2007年   37篇
  2006年   50篇
  2005年   41篇
  2004年   35篇
  2003年   32篇
  2002年   48篇
  2001年   20篇
  2000年   20篇
  1999年   18篇
  1998年   27篇
  1997年   18篇
  1996年   19篇
  1995年   23篇
  1994年   13篇
  1993年   19篇
  1991年   12篇
  1990年   17篇
  1989年   14篇
  1987年   15篇
  1986年   12篇
  1985年   25篇
  1984年   21篇
  1983年   27篇
  1982年   18篇
  1981年   17篇
  1980年   14篇
  1979年   21篇
  1978年   18篇
  1977年   17篇
  1976年   15篇
  1975年   11篇
  1974年   11篇
  1973年   17篇
  1970年   11篇
  1959年   15篇
  1956年   11篇
  1954年   12篇
  1948年   13篇
排序方式: 共有1434条查询结果,搜索用时 15 毫秒
831.
We carried out experiments with various concentrations of Trichoderma harzianum YC459 in different soil types (forest soil, mixed soil, merchantable soil, and leaf mold soil) to evaluate its effect on seed germination and seedling establishment of four species (Festuca arundinacea Schreb., Dianthus barbatus var. asiaticus Nakai, Lespedeza cyrtobotrya Miq., and Parthenocissus tricuspidata Planch) for rock slope restoration. We also investigated the use of drilled slanted holes on the rock slopes for seedling establishment. The results showed that T. harzianum concentration had significant effects on seed germination, seedling growth, and seedling survival for all the species with different soil types. Seed germination and survival rates peaked at 5% T. harzianum concentration with leaf mold soil and decreased as T. harzianum concentration increased from 5% to 10%. Seedling survival rates of all four species were generally lowest at 0% T. harzianum concentration in all soil types. The height of F. arundinacea and L. cyrtobotrya peaked at 5% T. harzianum concentration whereas that of D. barbatus and P. tricuspidata peaked at 10% T. harzianum concentration. We concluded that 5% T. harzianum concentration with leaf mold soil is appropriate for seed germination and seedling survival rates of most species, thus enhancing seedling establishment. Practical application of the findings of this study will contribute in the vegetation restoration of steep rocks in mountain environments  相似文献   
832.
833.
834.
835.
836.
837.
838.
Hans Brix   《Limnologica》1999,29(1):5-10
Reeds (Phragmites australis (Cav.) Trin. ex Steudel) are dying back at a fast rate in sizeable areas of Europe, with significant impacts on important wetland functions (biodiversity, stability of river and lake margins, water quality) and local economy. EUREED is a European strategic fundamental research initiative that aims at analyzing the mechanisms which control the growth dynamics and stability of reed-dominated ecosystems, at modelling and predicting how the ecosystem is disturbed by human activities and climate change, and at developing remedial management options. Expected achievements include (i) assessment of the functional role of reed-dominated ecotones as nutrient accumulators and transformers and as sources for atmospheric greenhouse gases, (ii) an ecosystem model capable of predicting future changes in ecosystem functioning in relation to climatic conditions, trophic status and water table management, (iii) assessment of genetic diversity of reed populations and its relation to die-back, and (iv) development of management tools, including preventative and restorative measures in relation to die-back. The project is carried out by research groups with complimentary skills and expertise from nine European countries. A reference study site is selected in each country as the basis for the field studies. The reference sites cover boreal-mediterranean and oceanic-continental climatic gradients, and the observational and experimental studies at these sites will permit interpolation between sites and extrapolation of results to the European scale.  相似文献   
839.
The North Penninic basin was a subbasin in the northern part of the Mesozoic Tethys ocean. Its significance within the framework of this ocean is controversial because it is not clear whether it was underlain by thinned continental or oceanic crust. Remnants of the eastern North Penninic basin are preserved in the Alps of eastern Switzerland (Grisons) as low metamorphic "Bündnerschiefer" sediments and associated basaltic rocks which formed approximately 140–170 Ma ago (Misox Bündnerschiefer zone, Middle Jurassic to Early Cretaceous). Nb/U, Zr/Nb, and Y/Nb ratios, as well as Nd–Sr isotopic and REE data of most of the metabasalts point to a depleted MORB-type mantle origin. They have been contaminated by magmatic assimilation of Bündnerschiefer sediments and by exchange with seawater, but do not prove the existence of a subcontinental lithospheric mantle or continental crust beneath the North Penninic basin. This suggests that the studied part of the North Penninic realm was underlain by oceanic crust. Only the metabasalts from two melange zones (Vals and Grava melanges) show a more important contamination by crustal material. Since this type of contamination cannot be observed in the other tectonic units, we suggest that its occurrence is related to melange formation during the subduction of the North Penninic basin in the Tertiary. The North Penninic basin was probably, despite the occurrence of oceanic crust, smaller than the South Penninic ocean where the presence of oceanic crust is well established. Modern analogues for the North Penninic basin could be the transitional zone of the Red Sea or the pull-apart basins of the southernmost Gulf of California where local patches of oceanic crust with effusive volcanism have been described.  相似文献   
840.
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