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   35951篇
  免费   277篇
  国内免费   984篇
测绘学   1644篇
大气科学   2706篇
地球物理   6676篇
地质学   16052篇
海洋学   2179篇
天文学   4079篇
综合类   2207篇
自然地理   1669篇
  2022年   144篇
  2021年   206篇
  2020年   191篇
  2019年   227篇
  2018年   5250篇
  2017年   4431篇
  2016年   3029篇
  2015年   418篇
  2014年   493篇
  2013年   629篇
  2012年   1437篇
  2011年   3260篇
  2010年   2551篇
  2009年   2928篇
  2008年   2445篇
  2007年   2905篇
  2006年   543篇
  2005年   519篇
  2004年   711篇
  2003年   688篇
  2002年   523篇
  2001年   291篇
  2000年   305篇
  1999年   182篇
  1998年   205篇
  1997年   171篇
  1996年   115篇
  1995年   131篇
  1994年   115篇
  1993年   97篇
  1992年   71篇
  1991年   98篇
  1990年   97篇
  1989年   68篇
  1988年   79篇
  1987年   99篇
  1986年   80篇
  1985年   107篇
  1984年   95篇
  1983年   104篇
  1982年   86篇
  1981年   102篇
  1980年   116篇
  1979年   88篇
  1978年   87篇
  1977年   77篇
  1976年   65篇
  1975年   63篇
  1974年   71篇
  1973年   64篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
991.
Astronomy Reports - The concept of a multi-functional astronomical complex as applied to robotic astronomy networks and systems is formulated. The practical realization of this concept in the...  相似文献   
992.
993.
Thermal structure of a fossil subduction wedge in the Western Alps   总被引:1,自引:0,他引:1  
New peak metamorphic temperatures are obtained by Raman spectroscopy of Carbonaceous Material to document the thermal structure of the central Western Alps with high sampling resolution. We show that peak metamorphic T gradually increases eastward from <330 to 350 °C (ultra-Dauphinois to subbriançonnais units), ∼350 to more than 400 °C (Briançonnais domain including the Zone Houillère where metamorphic index minerals are rare) and from 350 to more than 500 °C (Liguro–Piemontese domain). Combined with other constraints on the metamorphic evolution, this dataset reveals a good preservation of the overall thermal structure of the fossil subduction wedge, with no particular thermal overprint during collision. However, local confrontation with P – T estimates and radiometric ages reveals more subtle variations within tectonic units and across the main contacts that are linked to the past activity of the major thrusts and extensional shear zones during subduction and exhumation.  相似文献   
994.
Based on studying the ontogenetic development of Calceola sandalina in the Early Devonian Yukiang Formation from Guangxi Zhuang Autonomous Region, South China, it is for the first time to issue the evidence indicating the existence of sexual dimorphism in Calceola sandalina. The new discovery will add important data on sexual dimorphism throughout the non-colonial fossil metazoan, and it also may throw lights on studying the taxonomy and phylogeny of Calceola sandalina and its relevant taxa.  相似文献   
995.
The methods of anomaly transformations considered are based on a system of combined analysis of the geophysical field and a priori) information on the structure of a geological object. The methods involve calculation of a transformative polynomial (describing geophysical noise) which makes it possible to separate the residual field component related to the geological characteristic under study in a correlatively optimal way. The structure of the transformative polynomial is determined by the nature of the geophysical noise that is eliminated by the field transformation. Various correlation methods of anomaly transformations arise, depending on the structure of the transformative polynomial chosen. By way of example, the correlation method employed for separating the geophysical anomalies is shown to be highly effective in investigating the local geological structure.  相似文献   
996.
The prediction and prevention of floor water inrush is directly related to the safety of the coal mine production. The previous evaluation method of floor water inrush was more one-sided and lacked main control factors related to mining conditions. In order to evaluate the floor water inrush more accurately, under the project background of geological data of Wanglou coal mine, stope width, mining depth, fault scale index, water pressure, water abundance and thickness of aquifer were selected as main controlling factors of floor water inrush. Combined with the subjective weight analytical hierarchy process and the objective weight variation coefficient method, the weight coefficients corresponding to the main controlling factors were obtained respectively. The thematic map of the risk assessment of coal seam floor water inrush was drawn by combining the constructed comprehensive weight vulnerability index model and geographic information system. The results show that: ① according to the actual geological data of mine, two fault related factors were removed. And stope width and mining depth were increased as the main controlling factors to evaluate floor water inrush. It is easier to compare and calculate the weight of evaluation factors. ② The constructed comprehensive weight vulnerability index model can comprehensively evaluate the risk of floor water inrush. And the results of the evaluation are more accurate. ③ The related thematic maps can directly reflect the risk of floor water inrush, which is of guiding significance for the prediction and prevention of coal seam floor water inrush.  相似文献   
997.
998.
In the purple hilly region, erosions and landslides are all serious, and it is of great scientific value and practical significance to study their formation mechanism and distribution features there.In this paper, soil micromorphological methods and techniques were used to study the erosion zonal distribution in the region. The results indicated: (1)According to erosion process, the spacial distribution zones of the erosions and landslides in the purple hilly region with different solums were divided into scouring erosion zone, transport-diffusion zone, rocks and soil turbulence zone and sediment-bury zone; (2) The soil micromorphologic taxonomic feature identifying different erosion-landslide zone were found by studying the soil micromorphology of erosive zone in purple hilly region; (3) As for the erosion-landslide formation in the region, besides the external factors, the internal factors were found more important and favorable for landslide formation through the studies on the micormorphologieal features of slide soil.  相似文献   
999.
A Lagrangian tracer model is set up for Hangzhou Bay based on Coupled Hydrodynamical Ecological model for Regional Shelf Sea (COHERENS). The study area is divided into eight subdomains to identify the dominant physical processes, and the studied periods are March (the dry season) and July (the wet season). The model performance has been first verified by sea-surface elevation and tidal current observations at several stations. Eight tracer experiments are designed and Lagrangian particle tracking is simulated to examine the impact of physical processes (tide, wind and river runoff) on the transport of passive tracer released within the surface layer. Numerical simulations and analysis indicate that: (1) wind does not change the tracer distribution after 30 days except for those released from the south area of the bay during the wet season; (2) the tide and the Qiantang River runoff are important for particle transport in the head area of the bay; (3) the Changjiang River runoff affects the tracer transport at the mouth of the bay, and its impact is smaller in the dry season than in the wet season. Supported by the Natural Science Foundation of China (No.40576080); National High Technology Research and Development Program of China (863 Program, No. 2007AA12Z182)  相似文献   
1000.
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