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   659篇
  免费   34篇
  国内免费   4篇
测绘学   13篇
大气科学   27篇
地球物理   175篇
地质学   302篇
海洋学   30篇
天文学   127篇
综合类   4篇
自然地理   19篇
  2022年   7篇
  2021年   14篇
  2020年   12篇
  2019年   17篇
  2018年   36篇
  2017年   22篇
  2016年   47篇
  2015年   32篇
  2014年   52篇
  2013年   90篇
  2012年   30篇
  2011年   38篇
  2010年   44篇
  2009年   33篇
  2008年   28篇
  2007年   8篇
  2006年   19篇
  2005年   10篇
  2004年   7篇
  2003年   9篇
  2002年   5篇
  2001年   7篇
  2000年   8篇
  1999年   8篇
  1998年   7篇
  1997年   11篇
  1996年   5篇
  1994年   3篇
  1993年   2篇
  1992年   2篇
  1991年   2篇
  1990年   5篇
  1989年   9篇
  1988年   5篇
  1987年   5篇
  1986年   3篇
  1985年   3篇
  1984年   3篇
  1983年   3篇
  1982年   7篇
  1981年   4篇
  1980年   3篇
  1978年   5篇
  1974年   3篇
  1973年   7篇
  1972年   3篇
  1970年   2篇
  1969年   2篇
  1968年   2篇
  1935年   1篇
排序方式: 共有697条查询结果,搜索用时 31 毫秒
21.
22.
Volcanism along the northwest boundary of the Arabian Plate found in the Gaziantep Basin, southeast Turkey, is of Miocene age and is of alkaline and calc-alkaline basic composition. The rare earth element data for both compositional series indicates spinel–peridotite source areas. The rare earth and trace elements of the alkaline lavas originate from a highly primitive and slightly contaminated asthenospheric mantle; those of the calc-alkaline lavas originate from a highly heterogeneous, asthenospheric, and lithospheric mantle source. Partial melting and magmatic differentiation processes played a role in the formation of the petrological features of these volcanics. These rocks form two groups on the basis of their ~(87) Sr/~(86) Sr and ~(143) Nd/~(144) Nd isotopic compositions in addition to their classifications based on their chemical compositions(alkaline and calc-alkaline). These isotopic differences indicate a dissimilar parental magma. Therefore, high Nd isotope samples imply a previously formed and highly primitive mantle whereas low Nd isotope samples may indicate comparable partial melting of an enriched heterogeneous shallow mantle. Other isotopic changes that do not conform to the chemical features of these lavas are partly related to the various tectonic events of the region, such as the Dead Sea Fault System and the Bitlis Suture Zone.  相似文献   
23.
International Journal of Earth Sciences - This study reports on spectacular deformation structures, including arrays of striated thrusts, discovered by excavation work in Holocene deposits in...  相似文献   
24.
Novel map projections can be derived by solving one of the two primary problems in mathematical cartography: direct and inverse. The combination of the equations of existing projections is a method that belongs to the direct problem category in mathematical cartography. As projections of different types, different classes, and different aspects can be combined, a considerable number of projections can be obtained by using this method. This paper aims to develop a novel projection by combining two conformal cylindrical projections with different aspects, namely normal and transverse, to reduce the distortions in map projection. It is observed that the resulting projection exhibits less distortion than those in normal and transverse cylindrical projections. Furthermore, the developed projection preserves conformality.  相似文献   
25.
This study attempted to examine the effects of biochar amendment together with bio-fertilizer on soybean yield and its qualitative properties, as well as a few chemical properties of soil through a factorial randomized complete block design at three replications in east of Golestan Province (Iran) during 2014. The two factors under study included the following: (1) biochar amendment (in four levels of 0, 2.5, 8, and 16 tons per hectare), (2) bio-fertilizer containing phosphorus and sulfur growth-promoting rhizobacteria (in two levels of inoculation and non-inoculation) applied through foliar feeding. The results of analysis of variance indicated that interactions of biochar amendment and bio-fertilizer on harvest index and grain yield were significant (p ≤?0.01). According to the results of this study, the highest harvest index and oil content were 56.9, and 17.7%, respectively, in the treatment of 8 tons per hectare biochar and inoculation with bio-fertilizer. The lowest harvest index and the lowest oil content were in the control treatment. The interaction of biochar and bio-fertilizer on bulk density and cation exchange capacity was significant (p ≤?0.01). The results of this study demonstrated that biochar affected the amount of residual nitrogen in the soil after harvest, cation exchange capacity (CEC), acidity (pH), and electrical conductivity (EC). The highest grain yield (3440 kg/ha) was in the 8-ton biochar treatment with inoculated bio-fertilizer. Our study concludes that the biochar and bio-fertilizers can improve grain yield of soybean till 51% relative to the control.  相似文献   
26.
Natural Hazards - The seismically induced ground failure is defined as any earthquake-generated process that leads to deformations within a soil medium, which in turn results in permanent...  相似文献   
27.

A 6.8-magnitude earthquake that occurred on January 24, 2020, has been effective in Turkey’s eastern regions. The earthquake, with recorded peak ground acceleration (PGA) value of 0.292 g, caused the destruction or heavy damage of buildings, especially in the city center of Elaz?? province. The purpose of this paper was to share the results of detailed investigation in the earthquake-stricken area. Additionally, the causes of damages and failures observed in the buildings were compared to those that had occurred in previous earthquakes in Turkey. In this study, the damages observed in especially RC buildings as well as in masonry and rural buildings were summarized, the lessons learned were evaluated, and the results were interpreted with reference to Turkish earthquake codes. In the study, it was particularly emphasized why the building stock underwent such damage even though the buildings were exposed to earthquake acceleration well below the design acceleration values.

  相似文献   
28.
Geotechnical and Geological Engineering - The physical and chemical characteristics of water critically influence the mechanical and chemical breakdown of rocks. The physical properties of rocks,...  相似文献   
29.
30.
Journal of Oceanology and Limnology - The aim of this study was to determine the species composition, biodiversity and, relative abundance of epiphytic algae and their relationship with...  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