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   252933篇
  免费   5295篇
  国内免费   3283篇
测绘学   6956篇
大气科学   19098篇
地球物理   53102篇
地质学   87337篇
海洋学   21351篇
天文学   54623篇
综合类   1009篇
自然地理   18035篇
  2021年   2189篇
  2020年   2598篇
  2019年   2837篇
  2018年   3298篇
  2017年   2985篇
  2016年   5610篇
  2015年   4235篇
  2014年   6938篇
  2013年   14259篇
  2012年   6447篇
  2011年   7774篇
  2010年   6683篇
  2009年   9406篇
  2008年   8326篇
  2007年   7705篇
  2006年   9714篇
  2005年   7721篇
  2004年   7661篇
  2003年   7162篇
  2002年   6763篇
  2001年   6042篇
  2000年   5923篇
  1999年   4819篇
  1998年   4853篇
  1997年   4652篇
  1996年   4228篇
  1995年   4328篇
  1994年   4013篇
  1993年   3767篇
  1992年   3524篇
  1991年   3529篇
  1990年   3635篇
  1989年   3337篇
  1988年   3167篇
  1987年   3729篇
  1986年   3250篇
  1985年   4137篇
  1984年   4645篇
  1983年   4314篇
  1982年   4238篇
  1981年   3857篇
  1980年   3600篇
  1979年   3435篇
  1978年   3431篇
  1977年   3221篇
  1976年   2967篇
  1975年   2905篇
  1974年   2871篇
  1973年   3066篇
  1972年   1995篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Wuyep  E. O.  Oluyemi  G. F.  Yates  K.  Akisanya  A. R. 《Natural Resources Research》2020,29(2):1239-1258
Natural Resources Research - Sand failure and production occurs when the formation stress exceeds the strength of the formation, which is derived majorly from the natural material that cements the...  相似文献   
22.

The use of spontaneous potential (SP) anomalies is well known in the geophysical literatures because of its effectiveness and significance in solving many complex problems in mineral exploration. The inverse problem of self-potential data interpretation is generally ill-posed and nonlinear. Methods based on derivative analysis usually fail to reach the optimal solution (global minimum) and trapped in a local minimum. A new simple heuristic solution to SP anomalies due to 2D inclined sheet of infinite horizontal length is investigated in this study to solve these problems. This method is based on utilizing whale optimization algorithm (WOA) as an effective heuristic solution to the inverse problem of self-potential field due to a 2D inclined sheet. In this context, the WOA was applied first to synthetic example, where the effect of the random noise was examined and the method revealed good results using proper MATLAB code. The technique was then applied on several real field profiles from different localities aiming to determine the parameters of mineralized zones or the associated shear zones. The inversion parameters revealed that WOA detected accurately the unknown parameters and showed a good validation when compared with the published inversion methods.

  相似文献   
23.
Natural Resources Research - In the present study, ground subsidence in the Aliabad plain (central Iran) was investigated using differential synthetic aperture radar interferometry. The data used...  相似文献   
24.
Natural Resources Research - Identification of geochemical anomalies is of particular importance for tracing the footprints of anomalies. This can be implemented by advanced techniques of...  相似文献   
25.
Gomo  M. 《Natural Resources Research》2020,29(3):2227-2235
Natural Resources Research - Single-borehole tracer dilution tests are used to estimate the Darcy velocity (vd) which is important for investigating contaminant transport and distribution within...  相似文献   
26.
Natural Resources Research - The physical and chemical characteristics of mined phosphate rock will vary temporally as the location and nature of the ore body changes and as the type of equipment...  相似文献   
27.
Ali  Moamen  Abdelmaksoud  Ahmed  Essa  M. A.  Abdelhady  A.  Darwish  M. 《Natural Resources Research》2020,29(4):2575-2597
Natural Resources Research - Two main reservoirs are producing in Komombo Basin: the first one belongs to the C Member of the Six Hills Formation, and the second belongs to the Albian/Cenomanian...  相似文献   
28.
Natural Resources Research - Borehole-controlled one-dimensional geo-electric data were integrated with water samples obtained from boreholes drilled near the vertical electrical sounding at 12...  相似文献   
29.
Yanchi County is located in the agro-pastoral ecotone and belongs to the ecologically fragile area of Northwest China.It is important to study the evolution of landscape pattern to curb its environmental degradation.In order to intuitively show how the landscape pattern of the study area changes over time,Landsat Thematic Mappers(TM)and Landsat Operational Land Imager(OLI)data of 1991,2000,2010 and 2017 were used.This paper attempts to apply niche theories and methods into landscape ecology,and constructs a niche model of landscape components by using"n-dimentional hypervolume niche theory"and landscape pattern indices.By evaluating the spatial and temporal evolution of niche from the perspective of two-dimensional space to reflect the changes of landscape pattern in the study area over the past 26 years,new theories and methods were introduced for the characterization of landscape pattern.The results indicate that:1)The larger the attribute and dominance value of landscape components,the higher the ecological niche and the stronger the control effect on the overall landscape.2)The ecological niche of each landscape component was significantly different,just as its control effect on the overall landscape.3)The dynamic change of the ecological niche of each landscape component was different,with grassland,unused land and arable land always in a high dominant position,although the ecological niche of construction land and water area was always low.In general,the introduction of niche theory into the landscape ecology provided a new method to study the changes in regional landscape pattern.  相似文献   
30.
Low‐pressure and high‐temperature (LP–HT) metamorphism of basaltic rocks, which occurs globally and throughout geological time, is rarely constrained by forward phase equilibrium modelling, yet such calculations provide valuable supplementary thermometric information and constraints on anatexis that are not possible to obtain from conventional thermometry. Metabasalts along the southern margin of the Sudbury Igneous Complex (SIC) record evidence of high‐grade contact metamorphism involving partial melting and melt segregation. Peak metamorphic temperatures reached at least ~925°C at ~1–3 kbar near the SIC contact. Preservation of the peak mineral assemblage indicates that most of the generated melt escaped from these rocks leaving a residuum characterized by a plagioclase–orthopyroxene–clinopyroxene–ilmenite‐magnetite±melt assemblage. Peak temperatures reached ~875°C up to 500 m from the SIC lower contact, which marks the transition to metabasalts that only experienced incipient partial melting without melt loss. Metabasalts ~500 to 750 m from the SIC contact are characterized by a similar two‐pyroxene mineral assemblage, but typically contain abundant hornblende that overgrew clino‐ and orthopyroxene along an isobaric cooling path. Metabasalts ~750 to 1,000 m from the SIC contact are characterized by a hornblende–plagioclase–quartz–ilmenite assemblage indicating temperatures up to ~680°C. Mass balance and phase equilibria calculations indicate that anatexis resulted in 10–20% melt generation in the inner ~500 m of the aureole, with even higher degrees of melting towards the contact. Comparison of multiple models, experiments, and natural samples indicates that modelling in the Na2O–CaO–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O2 (NCFMASHTO) system results in the most reliable predictions for the temperature of the solidus. Incorporation of K2O in the most recent amphibole solution model now successfully predicts dehydration melting by the coexistence of high‐Ca amphibole and silicate melt at relatively low pressures (~1.5 kbar). However, inclusion of K2O as a system component results in prediction of the solidus at too low a temperature. Although there are discrepancies between modelling predictions and experimental results, this study demonstrates that the pseudosection approach to mafic rocks is an invaluable tool to constrain metamorphic processes at LP–HT conditions.  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