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   1057篇
  免费   95篇
  国内免费   77篇
测绘学   39篇
大气科学   66篇
地球物理   229篇
地质学   405篇
海洋学   119篇
天文学   81篇
综合类   256篇
自然地理   34篇
  2023年   32篇
  2022年   17篇
  2021年   34篇
  2020年   48篇
  2019年   19篇
  2018年   9篇
  2017年   6篇
  2016年   7篇
  2015年   4篇
  2014年   9篇
  2013年   3篇
  2012年   2篇
  2011年   2篇
  2010年   4篇
  2009年   10篇
  2008年   7篇
  2007年   30篇
  2006年   28篇
  2005年   29篇
  2004年   89篇
  2003年   66篇
  2002年   84篇
  2001年   87篇
  2000年   273篇
  1999年   104篇
  1998年   19篇
  1997年   15篇
  1996年   48篇
  1995年   28篇
  1994年   39篇
  1993年   5篇
  1992年   5篇
  1991年   5篇
  1990年   11篇
  1989年   6篇
  1988年   7篇
  1987年   9篇
  1986年   1篇
  1985年   3篇
  1984年   7篇
  1983年   4篇
  1982年   2篇
  1981年   2篇
  1979年   1篇
  1975年   1篇
  1974年   1篇
  1963年   3篇
  1961年   1篇
  1957年   2篇
  1954年   1篇
排序方式: 共有1229条查询结果,搜索用时 15 毫秒
61.
1INTRODUCTIONGrain production has always been top-priority issue con-cerned by government and people (MA etal., 2002). Af-ter China put household contract responsibility system in force, its domestic issue of grain was basically settled in the mid 1980s (MA and XU, 1999). However, in the days when idea of sustainable development is broadly accepted, efficiency and sustainability of grain produc-tion are now in question, which have prompted interest in reviewing grain production patterns…  相似文献   
62.
1INTRODUCTIONIrrigated ricefieldsarecharacterizedbylargespatialandtemporalvariationsin CH4 emissiontotheatmo-sphere.Accordingly,thereisagreatuncertaintyintheestimate ofCH4 emissionsfromricefields.GreateffortshavebeenmadetoestimatetheCH4 emissionsfromricefieldsandseveralapproacheshavebeendeveloped.TherepresentativemethodsincludetheIPCC(Inter-governmentPanelofClimateChange)region-specificemissionfactormethodandthemodelcalculationmethod.Toimprovethecalculationaccuracy,theIPCCmethodreq…  相似文献   
63.
Songliao Basin is filled predominantly with continental facies sediments including alluvial fan, fluvial plain, fan delta , lacustrine delta, shore ?shallow lacustrine, beach salty flat, semi - deep to deep lacustrine, subaqueous gravity flow, lacustrine swamp and pyroclastic sediments. However, some event units were formed during lake - marine linking periods of the Mid - Cretaceous in the basin, which include black shales with high values for salinity ( Sr/Ba) , alkalinity (Ca Mg)/ (Si Al) , reducibility ( Ni Zn)/Ga and sulfide sulfur as well as heavy isotopes. The Breitenholz ?section to be represen-ted for facies comparison with the Cretaceous evaporitic series in Northeast China is localized in Southwest Germany. Stratig-raphically it belongs to the Crabfeld Formation of Keuper of the Germanic Triassic corresponding to Ladinian - Camian of the international reference scale, and is generally called Lower Gipskeuper. The Germanic Triassic was deposited in the epiconti-nental(cratonic) central Euro  相似文献   
64.
Tanlu Fault Zone (TFZ) is a large NE trending deep fracture system in East China and is about 2500 km long. It extends from the south of Lujiang to Tancheng, and passes through the Bohai Sea and continues to the north, where it branches into Yilan ?Shulan Fault and Dunhua ?Mishan Fault. TFZ is a long lasting huge deep - rooted lithospherical fault system with different characteristics in different parts and at different periods of its evolution. TFZ also controls the distribution and occur-rences of many superlarge, large, middle and small sized gold ore deposits, e. g. Jiapigou, Haigou, Xiaoxihancha and Ciwei-gou gold deposits in Northeast China; Linglong, Jiaojia, Sanshandao, Taishang, Xincheng, Rushan, and Pengjiakuang gold deposits in Jiaodong Peninsula of Shandong Province; and Guilaizhuang and Yinan in Western Shandong Province.  相似文献   
65.
EVALUATION OF ECOLOGICAL SERVICES OF JILIN PROVINCE, NORTHEAST CHINA   总被引:2,自引:1,他引:1  
1INTRODUCTIONEcosystem services can be divided into two major cat-egories, one is system function, and the other is sys-tem services and goods provision, which provide not only materials such as food and medicine, but also support and maintenance of whole system. Ecological services contribute to the whole economic system, both directly and indirectly, and consequently repre-sent parts of the total value of our economy system (COSTANZA etal., 1997; GUO etal., 2001). Sustainable d…  相似文献   
66.
1 IntroductionSiO ,H2 OandOHmaseremissionsarecommonphenomenaassociatedwiththecircumstellarshellsoflatetypestars .SiOmaseremissionshavebeendetectedfromseveralhundredsoflatetypestarsofspectraltypeM 4orlater.SiOmaserisconsideredthemostprevalentmaserinlatetyp…  相似文献   
67.
1 SignificanceofSolarStokesSpectrumObservationDuetothedevelopmentinobservinginstrument,theconceptofsolarspectrumshouldbegeneralized .Inthepast,itisonlyassignedtotheordinaryorunpolarizedspectrumrecordingthewavelength distributedintensityofthecontinuumand…  相似文献   
68.
1 IntroductionCKBoowasdiscoveredandconfirmedtobeacontactbinarybyBond ( 1 975 ) .Afteritsdis coverythesystemisobservedfrequently (e .g .Aslan ,1 978;AslanandDerman ,1 986 :PajdoszandZola ,1 987;Krzesinskietal.,1 991andJiaetal.,1 992 ) .Asreportedbyseveralauthors,thelightcurveofthesy…  相似文献   
69.
70.
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