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   56928篇
  免费   817篇
  国内免费   577篇
测绘学   1424篇
大气科学   4733篇
地球物理   11505篇
地质学   20455篇
海洋学   4626篇
天文学   12073篇
综合类   129篇
自然地理   3377篇
  2021年   400篇
  2020年   462篇
  2019年   486篇
  2018年   1154篇
  2017年   1143篇
  2016年   1458篇
  2015年   855篇
  2014年   1396篇
  2013年   2802篇
  2012年   1552篇
  2011年   2096篇
  2010年   1809篇
  2009年   2423篇
  2008年   2091篇
  2007年   1973篇
  2006年   2037篇
  2005年   1590篇
  2004年   1571篇
  2003年   1518篇
  2002年   1513篇
  2001年   1359篇
  2000年   1372篇
  1999年   1119篇
  1998年   1082篇
  1997年   1158篇
  1996年   974篇
  1995年   929篇
  1994年   891篇
  1993年   743篇
  1992年   763篇
  1991年   730篇
  1990年   745篇
  1989年   706篇
  1988年   683篇
  1987年   779篇
  1986年   716篇
  1985年   842篇
  1984年   926篇
  1983年   959篇
  1982年   867篇
  1981年   807篇
  1980年   797篇
  1979年   725篇
  1978年   720篇
  1977年   663篇
  1976年   594篇
  1975年   587篇
  1974年   641篇
  1973年   614篇
  1972年   390篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
SENSITIVITY OF MALARIA, SCHISTOSOMIASIS AND DENGUE TO GLOBAL WARMING   总被引:5,自引:0,他引:5  
Global assessment of the potential impacts of anthropogenically-induced climate change on vector-borne diseases suggests an increase in extent of the geographical areas susceptible to transmission of malarial Plasmodium parasites, dengue Flavivirus and Schistosoma worms. The transmission potential of the three associated vector-borne diseases studied is highly sensitive to climate changes on the periphery of the currently endemic areas and at higher altitudes within such areas. Our findings vis-à-vis the present endemic areas indicate that the increase in the epidemic potential of malaria and dengue transmission may be estimated at 12–27% and 31–47%, respectively, while in contrast, schistosomiasis transmission potential may be expected to exhibit a 11–17% decrease.  相似文献   
92.
93.
94.
95.
The theoretical accuracy of photographically determined star positions is studied, based on the assumption that the whole sphere is covered by a net of fields, 4 plates each, and that all the plates are adjusted simultaneously in a closed block. The influence of the number of fields on the accuracy is estimated by computing schematized spheric blocks containing only a few reference stars. If the plates are taken with a focal length of 2 meters, the block will consist of 2500 fields, and a mean accuracy of star position of 0.1 can be expected.  相似文献   
96.
97.
A Model of Magmatic Crystallization   总被引:2,自引:0,他引:2  
A computer model simulating fractional crystallization at oneatmosphere pressure incorporates nine broadly-defined minerals—magnetite,olivine, hypersthene, augite, quartz, plagioclase, orthoclase,leucite, and nepheline. The crystallization temperature of eachmineral is considered to be a smooth function of the compositionof the magmatic liquid. These mineral temperature equationsare obtained by multiple linear regression analysis of informationfrom published silicate systems and rock melting experiments.The nine equations are solved for any primary liquid, withinthe broad range of common magma types, to select the crystallizingmineral or minerals. Partition ratios from published experimentsand analyses of lavas and phenocrysts permit calculation ofthe composition of the crystallizing mineral assemblage. Subtractionof a small amount of that composition from the primary liquidyields a new liquid, which may be recycled to yield a sequenceof liquids during fractional crystallization. The crystallizationmodel handles assemblages of co-precipitating minerals, andcan trace progressive saturation in new minerals, substitutionof a new mineral for an old mineral, and cessation of crystallizationof a mineral. The sequences of minerals and liquids derivedfrom a broad set of primary liquids are geologically realistic,so the model is useful in predicting phenocrysts in volcanicrocks and events during crystallization of shallow intrusions.  相似文献   
98.
The physical-synoptic principles of the automated method of summer precipitation forecasting introduced into operational prognostic practice in 2006 by the decree of the Central Methodical Commission of the Federal Service for Hydrometeorology and Environmental Monitoring (Roshydromet) are presented. Beside that, improved modifications of this method, which are automatically updated, are shown. Validation of those updates based on observational data collected in 2004 has shown improvement of all major criteria of forecasts efficiency. The performed improvement is based on the more detailed quantitative realization of mechanism of various showers formation (including heavy rainfalls).  相似文献   
99.
With the aid of a statistical approach regarding only the nearest optical object to a given radio position we have found identification rates of nearly 30 per cent up to the blue and red limits of the Palomar Sky Survey prints covering the region of the 5C4 radio survey. Roughly 60 per cent of these identifications are blue starlike objects and therefore possible quasar candidates. The remainig identifications are galaxies. Probabilities for the first neighbours to be an optical counterpart and finding charts for highly reliable objects are given.  相似文献   
100.
The structural relationships of several intrusive sheets belonging to the extensive metadolerite suite of the Appin (lower) Dalradian rocks of the Creeslough area, northwest Donegal, Ireland have been examined. It is concluded that, relative to the regional chronology of deformation of the enclosing metasediments, sheet emplacement has occurred: pre-D2; syn-D2; between D2 and D3; and syn-D3. The height of activity came in the post-D2, pre-D3 interval and coincided with the peak of regional metamorphism in the area. These relationships in Donegal are compared with those of the pretectonic basic rocks of the southwest Highlands and models are discussed.  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