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   119109篇
  免费   1588篇
  国内免费   798篇
测绘学   2776篇
大气科学   8210篇
地球物理   22946篇
地质学   42091篇
海洋学   10687篇
天文学   27322篇
综合类   310篇
自然地理   7153篇
  2022年   700篇
  2021年   1203篇
  2020年   1328篇
  2019年   1451篇
  2018年   3043篇
  2017年   2840篇
  2016年   3397篇
  2015年   1799篇
  2014年   3355篇
  2013年   6115篇
  2012年   3552篇
  2011年   4660篇
  2010年   4278篇
  2009年   5453篇
  2008年   4815篇
  2007年   4938篇
  2006年   4589篇
  2005年   3491篇
  2004年   3410篇
  2003年   3196篇
  2002年   3096篇
  2001年   2746篇
  2000年   2686篇
  1999年   2279篇
  1998年   2283篇
  1997年   2158篇
  1996年   1847篇
  1995年   1823篇
  1994年   1614篇
  1993年   1533篇
  1992年   1425篇
  1991年   1456篇
  1990年   1500篇
  1989年   1318篇
  1988年   1246篇
  1987年   1442篇
  1986年   1253篇
  1985年   1591篇
  1984年   1820篇
  1983年   1734篇
  1982年   1628篇
  1981年   1525篇
  1980年   1338篇
  1979年   1298篇
  1978年   1262篇
  1977年   1130篇
  1976年   1093篇
  1975年   1026篇
  1974年   1075篇
  1973年   1111篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
We report the results of new observations of three anomalous X-ray pulsars: 1E 2259+586, 4U 0142+61, and XTE J1810-197. The observations were carried out on high-sensitivity radio telescopes of the Pushchino Radio Astronomy Observatory: the Large Phased Array at 111MHz and the DKR-1000 at 62 MHz. New, digital, multi-channel receivers designed for pulsar observations were used. Pulse profiles and dynamical spectra for the three pulsars are presented. The mean flux density for XTE J1810-197 is estimated to be ∼160 mJy at 62 MHz. An estimated spectral index for this pulsar is also presented.  相似文献   
983.
984.
985.
The results of comprehensive geological and metallogenic studies of the Greater Altai are presented. This project has been carried out since 1997 under the guidance of Academician G.N. Shcherba. The importance of these investigations is determined by the need to enhance and further develop mineral resources of nonferrous, noble, rare, and other metals for operating mining and metallurgical enterprises of Kazakhstan. The great body of information on the geology, geophysics, and metallogeny of the region obtained over many years has been integrated on the basis of new global tectonics. The Greater Altai embraces the Hercynides of the Rudny Altai, Qalba-Narym, West Qalba, Zharma-Saur, and the adjacent territories of Russia and China. The present-day tectonic units are considered to be detached blocks of ancient continental massifs that drifted in the Paleoasian ocean and then amalgamated into the structure of the Greater Altai during the Hercynian collision. The tectonic and metallogenic demarcation of the studied territory made possible the recognition of the Rudny Altai, Qalba-Narym, West Qalba, and Zharma-Saur ore belts, different in geology, geodynamic evolution, and metallogeny. The formation conditions and localization of volcanic-hosted massive sulfide, gold, and rare-metal deposits pertaining to certain ore-bearing geochronological levels were specified, and the potential of the region for various mineral resources was estimated.  相似文献   
986.
Weathering of pyrite in the core recovered from black shales of the Bazhenovo Formation (Upper Jurassic-Lower Cretaceous) in the West Siberian marine basin promoted the successive formation of melanterite (FeSO4 · 7H2O) and szomolnokite (FeSO4 · H2O). Szomolnokite was detected in West Siberia for the first time.  相似文献   
987.
Outcrops of the Early Jurassic Navajo Sandstone in southern Utah and northern Arizona, south-western USA are being actively eroded by sand-laden, south-westerly winds. Small-scale stepped topography with risers facing into the wind develops even on steep canyon walls when wind-swept grains strike the rock at a low angle. Photosynthetic, endolithic microbes directly underlie most outcrop surfaces; the crusts formed by these organisms are essential to formation of the small-scale steps. Wind erosion of highlands also forms troughs and pits that are tens of metres across. The pits have deeply scalloped, overhanging walls, and contain central domes surrounded by 'moats' filled with dune sand. Wind erosion of aeolian sandstone is favoured by a positive feedback mechanism in which grains that are liberated from outcrops by impacting particles become a fresh supply of pre-sorted abrasive particles for further attack.  相似文献   
988.
Sedimentologic analysis of cores from wells sunk in the Vankor petroleum field allowed refinement of the accumulation conditions producing the sandy strata of the Nizhnyaya Kheta River (Nizhnekhetsky) Formation accumulated in the coastal marine zone and of the Yakovlevo (Yakovlevsky) Formation accumulated under alluvial-deltaic conditions. Petrographic examination of the sandstones added information on the sources, transport, and accumulation conditions of the terrigenous material in the northeastern marginal part of the West Siberian sedimentation basin.  相似文献   
989.
Application and development of municipal solid waste treatment technology depends on various socio-economic and environmental factors. All those factors are work as development drivers for waste management systems. The study aims to identify key drivers from case studies of waste management development trend in Sweden. Social, economic and environmental drivers are identified and presented in this study. The study identifies personal behaviour, local waste management practice, consumption and generation of waste as the key social drivers. Resource value of waste, economic benefit from waste treatment facilities and landfill tax have been acknowledged as economic drivers for developing waste treatment technology. Moreover, global climate change, environmental movement and awareness have been working as environmental drivers for developing various waste treatment methods in Sweden. In addition, the study aims to analyse emerging waste treatment technologies based on a number of literature review and questionnaire survey. Dry composting, pyrolysis-gasification, plasma arc, and anaerobic digestion have been identified as potential emerging technologies for waste management systems in Sweden.  相似文献   
990.
Division of sedimentary strata according to groundwater chemistry is discussed with implications for petroleum reservoir potential. It is suggested to process multiparametric water chemistry data from West Siberia using formalized clustering techniques. The efficiency of this approach has been tested for Neocomian clinoform reservoirs with reference to regional-scale appraisal and subregional petroleum division.  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