全文获取类型
收费全文 | 1401篇 |
免费 | 259篇 |
国内免费 | 511篇 |
专业分类
测绘学 | 35篇 |
大气科学 | 163篇 |
地球物理 | 436篇 |
地质学 | 1003篇 |
海洋学 | 178篇 |
天文学 | 62篇 |
综合类 | 119篇 |
自然地理 | 175篇 |
出版年
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 5篇 |
2016年 | 8篇 |
2015年 | 16篇 |
2014年 | 9篇 |
2013年 | 24篇 |
2012年 | 16篇 |
2011年 | 141篇 |
2010年 | 96篇 |
2009年 | 100篇 |
2008年 | 40篇 |
2007年 | 72篇 |
2006年 | 116篇 |
2005年 | 134篇 |
2004年 | 263篇 |
2003年 | 160篇 |
2002年 | 129篇 |
2001年 | 90篇 |
2000年 | 76篇 |
1999年 | 56篇 |
1998年 | 52篇 |
1997年 | 85篇 |
1996年 | 56篇 |
1995年 | 40篇 |
1994年 | 24篇 |
1993年 | 57篇 |
1992年 | 59篇 |
1991年 | 56篇 |
1990年 | 21篇 |
1989年 | 26篇 |
1988年 | 19篇 |
1987年 | 17篇 |
1986年 | 14篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 11篇 |
1976年 | 13篇 |
1970年 | 2篇 |
1968年 | 3篇 |
1965年 | 3篇 |
1950年 | 2篇 |
1940年 | 2篇 |
1937年 | 6篇 |
1934年 | 5篇 |
排序方式: 共有2171条查询结果,搜索用时 15 毫秒
81.
Adjoint Matching Condition for Parameterized Discontinuities—A Derivation Using Lagrangian-form Costfunction 总被引:1,自引:0,他引:1
AdjointMatchingConditionforParameterizedDiscontinuities—ADerivationUsingLagrangian-formCostfunctionXuQin(许秦)CooperativeInstit... 相似文献
82.
Sarbari Ghosh Utpal Kumar De Atmospheric Science Research Department of Physics Jadavpur University Calcutta India Received April revised July 《大气科学进展》1997,(1)
AComparativeStudyoftheAtmosphericLayersbelowFirstLiftingCondensationLevelforInstantaneousPre-MonsoonThunderstormOcurenceatAga... 相似文献
83.
AnalysisandstudyofthelargeearthquakeriskinYanqingHuailaibasinCHANGQUANLIU(刘昌铨)SHIXUJIA(嘉世旭)MINGJUNLIU(刘明军)CHANGFALI(李长发... 相似文献
84.
WANG Tiefeng Northeast Investigation Design Research Institute China ZHANG Zhi Northeast Investigation Design Research Institute China YI Yue Northeast Investigation. Design Research Institute China 《国际泥沙研究》1997,(3)
I.INTRODUCTIONThePtlmped-storagepoll,erprojectofPushiriverisconsistedofupperreservoir,lobal-erreset'oir.watertransmissionSystemandpotvergeneratingsystem.ThelowerreservoirIviththecatchmentbasinareaof1141kmZisthewatersupplierl-c'hichislocatedonthedownstreamofthePushiriverinthesouthernpactofNortheastChina.Theupperreservoirisabout300-400metershigherthanthelowerresen!oirattheleftsideoftheriverwithcatchmentbasinareaof1.12km2.Thecharacteristicsoftheprojectandreservoirareshottviintablel-l.Ino… 相似文献
85.
XU Guobin Senior Research Engineer Tianjin Institute of Hydroelectric Investigation Design Research Ministry of Water Resources. Dongting Road Hexi District Tianjin P R. China. BAI Shilu Senior Research Engineer Tianjin Institute o 《国际泥沙研究》1997,(3)
I.INTRODUCTIONReseri,oirsonoverloadedriverswillreachthestateofrelativeequilibriumwithcontinuousdevelopmentofsedimentation.Insuchcase,thereisdePOsitinfrontofthedam.Thereforethesiltpressureonthedambodyisconsiderablylarge.Sedimentationelevationinfrontofthedamisoneofthefactorsofcalculatingthesiltpressure.Inaddition,tokeeplong-termworkingstorageinreservoif,itisnecessarytoinstallbottomoutlets.Asthereisapressureconduitinfrontoftheoperatinggateofthebottomoutlet,thesedimelltenteredtheconduitwill… 相似文献
86.
PAUL C. ADAMS 《Geographical review》1997,87(2):155-171
ABSTRACT. Computer networks are often described in terms that imply a virtual space or place: electronic frontier, cyberspace, and information superhighway have been used to indicate computer networks as a whole; cafés, dungeons, and virtual offices are some of the “places” people refer to as being in or on networks. The use of this language, which I collectively call “virtual-place metaphors,” indicates three broad metaphorical themes: virtual architecture, electronic frontier, and cyberspace. The metaphors encourage control, surveillance, and capitalist expansion through computer technologies—and also evasion and resistance through computer technologies. 相似文献
87.
Oxygen Isotope Exchange Kinetics Between Coexisting Minerals and Water in the Aral Granite Pluton of the Altay Mountains, Northern Xinjiang 总被引:2,自引:0,他引:2
Liu Wei Research Center of Mineral Resources Exploration Chinese Academy of Sciences Chinese Academy of Sciences BeijingHe Baichu Changsha Institute of Geotectonics Chinese Academy of Sciences Changsh Hunanand Chen ZhenshengYichang Institute of Geology Mineral Resources Chinese Academy of GeologicalSciences Yichang Hubei 《《地质学报》英文版》1996,70(4)
Coexisting quartz, feldspar and biotite vary widely in their δ18O values and display a remarkable 18O/16O disequilibrium relation; especially, a quartz-feldspar reversal (△ 18OQUartz_feldspar< 0) exsists in the Aral granite pluton of the Altay Mountains, northern Xinjiang. The 18O / 16O exchange reaction definitely occurred between granite and water. Initial δ18O values of the granite and exotic fluid are evaluated by the mass balance consideration. The conventional method of discrimination between various magma derivations simply with δ18O values of either whole rock or separate minerals is misleading and unreliable. Experiments carried out by the authors show that the 18O / 16O exchange reaction is not accompanied by what geologists describe as petrological and mineralogical alteration effect. This decoupling relation implies that exchange reaction occurs at a relatively high temperature during subsolidus-postmagmatic cooling of magmas. The exchange mechanism is mainly diffusion-controlled. It is 相似文献
88.
Coeval stratigraphic units of similar petrology occur throughout the northern Bahamas islands. The petrographic composition of these limestones provides clues about regional sea level and climate changes during the late Quaternary. At least eight fossil shoreline units, which are linked to transgressive episodes between the middle Pleistocene and the late Holocene, are recognized in the Bahamas. The petrographic composition of these units is either dominated by ooids and peloids or by bioclasts. Sedimentological observations demonstrate that oolitic-peloidal units were formed when sea level was higher than today, whereas skeletal units were deposited at or below modern ordnance datum. Skeletal units may reflect times of partial, or modest platform flooding, when the bulk of sediments brought to islands originates from bank-margin reefs. In contrast, oolitic-peloidal units correspond to major flooding events and active water circulation on the bank top. Cement fabrics further show that the early diagenesis of oolitic units took place during warm and humid climatic conditions, whereas skeletal rock bodies underwent subaerial diagenesis during drier climatic conditions characterized by marked seasonal changes. This example from the Bahamas suggests that compositional analysis of limestone from fossil carbonate platforms could be used for resolving ancient climate and sea-level changes. 相似文献
89.
90.
In this paper,the Gutenberg-Richter model is used to generate seismic events.The events that satisfy the random distribution are also generated.With those events,the natural probability distribution of Load and Unload Response Ratio(LURR),which measures quantitatively the degree of instability of a nonlinear system,is discussed.The study is based on stress energy release,which is chosen as the response of nonlinear system F3.The comparative results from the observation catalogue and generating data are also studied.It is revealed that the natural probability of LURR is mostly stable when the sample number is sufficient.The lower the natural probability of LURR,the more the precursory is information it may contain.The influence of Y3 resulting from the sample number and the magnitude range of events is also discussed. 相似文献