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201.
Natural Hazards - Carrying out risk assessments of agricultural drought disasters is helpful to understanding agricultural drought quantitatively and scientifically guiding drought prevention and... 相似文献
202.
古海山是缝合带的关键组成部分,中亚造山带西段的天山造山带内已发现多处古海山,而北山地区却鲜有报道,古海山的发现可以弥补该地区海山研究的不足.通过在北山中部野马泉开展地质调查、测制剖面,发现了一套原始层序完整、以玄武岩、玄武质凝灰岩和大理岩为主的地层,具有火山岩基座和碳酸盐岩顶盖的结构,二者原始接触关系为整合接触,符合海山的沉积特征.依据地层中的岩石组合和沉积构造,确定其形成于海山斜坡相.野马泉古海山残骸呈NWW-SEE向延伸,东南部更接近海山顶.该海山中的玄武岩富集大离子亲石元素、亏损高场强元素,具有岛弧玄武岩的特征.该海山为洋内弧型海山,野马泉一带位于海山斜坡,其被构造肢解后呈NWW-SEE向分布. 相似文献
203.
Clay mineralogy and geochemistry and their palaeoclimatic interpretation of the Pleistocene deposits in the Xuancheng section,southern China 总被引:1,自引:0,他引:1
A red soil profile in Xuancheng, Anhui province, southern China, in the middle to lower reaches of the Yangtze River, was investigated using X‐ray diffraction, X‐ray fluorescence spectrometer, and scanning electron microscopy. The mobile components K2O and Na2O and trace elements Ba and Sr of the Xuancheng section exhibit a general trend of decrease downward along the red soil profile, together with an increase downward of chemical index of alteration (CIA) values, suggesting more intense depletion in the lower portion than in the upper portion. The major components SiO2, Al2O3 and Fe2O3, as well as SiO2/Al2O3, SiO2/Fe2O3 and Al2O3/Fe2O3 ratios, show notable fluctuations along the soil profile, indicating intense climatic oscillations in the area during the Pleistocene age. The clay mineral assemblage of the Xuancheng section can be generally subdivided into three groups, suggesting a general trend of three stages of climate changes. The lower portion of ~10.4–6.3 m depth has a lower illite content and higher abundance of kaolinite and illite–smectite (I/S) clays, indicating that a warm and wet climate prevailed over the episode of ca. 600–350 ka BP. A decrease in abundance of kaolinite and I/S clays and increase in illite content at a depth of ~6.3–2.2 m probably indicate a transition stage of climate change from warm/humid to cool/dry in the period ca. 350–80 ka BP. The higher illite content and lower abundance of kaolinite and I/S clays in the upper portion of ~2.2–0 m depth suggest that a relatively cool and dry climate dominated since ca. 80 ka BP. Based on changes in clay mineralogy and chemical indices of the sediments, seven warm/cold fluctuations were determined in the area since the Middle Pleistocene. Climate changes documented in the Xuancheng section are in agreement with the δ18O records of sediments from the equatorial Pacific Core V28‐238 and the loess–palaeosol sequences in the Loess Plateau of northwestern China. Correlated to the episode of S4 and S5 soil units in the Loess Plateau, the period of ca. 600–350 ka BP in the Xuancheng area was dominated by the particularly strong East Asia summer monsoon, as indicated by its most abundant kaolinite and I/S clays. Fluctuations in clay mineralogy along the Xuancheng soil profile were mainly controlled by both the East Asia summer and winter monsoons in response to the global changes in the Middle–Late Pleistocene. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
204.
Climate evolution associated with the uplift in Gyirong, southern margin of the Tibetan plateau, was investigated based on
the clay mineralogy of the Gyirong sediments, using X-ray diffraction and scanning electron microscopy methods. The (chlorite + illite)/(kaolinite + smectite)
ratio and the illite crystallinity index suggest the trend of paleoclimate evolution in Gyirong basin during ~7–1.7 Ma BP,
with a warm and humid climate in ~7.0–5.8 Ma, a relative cool and dry climate in ~5.8–5.5 Ma, a relative warm and humid climate
in ~5.5–2.5 Ma, and a much warmer climate in ~2.5–1.7 Ma, respectively. The fluctuating kaolinite/smectite index and calcite
content and the frequent occurrence of gypsum in the episode of ~6.7–5.5 Ma suggest intense climatic fluctuations between
humid and more seasonal humid conditions. Five peaks exhibit at 5.8, 4.9, 4.3, 3.6, and 2.5 Ma in the curves of illite and
chlorite content and illite crystallinity. The intense uplift and tectonic-forced cooling at ~5.8 and 4.3 Ma were indicated
by the high-illite crystallinity index and illite and chlorite content. A remarkable increase in illite and chlorite content
associated with only little increase in illite crystallinity at ~3.6 Ma indicates a rapid uplift, but no significant climate
change. And a sharp increase in illite crystallinity, while small change in illite and chlorite content at ~2.5 Ma suggests
that no remarkable relief was produced by the uplift, which may take place in the whole south Tibet plateau, while cooling
at 4.9 Ma is probably a record of the global climate cooling. 相似文献
205.
湛江东海岛二月海陆风环流特征研究 总被引:1,自引:0,他引:1
利用2011年2月湛江东海岛风廓线雷达资料,系统分析了湛江东海岛2月平均风场特征及海陆风特征,结果表明:2月湛江东海岛150 m高度处以东偏北出现频率最大,在E、ENE和NE三个方位的风向出现频率之和为66.6%,偏西七个方位的风向出现频率之和仅为1%。以SSW方位为界,偏东风与偏西风的出现频率差异明显。各整点的月平均风速1:00—15:00变化较小,均在1 m/s左右波动;15:00—20:00风速及风速波动都较大,最大值出现在16:00时,为2.1 m/s。2011年2月中只有2日与14日两日符合海陆风日条件,两日共同海风时段为13:00—20:00,持续7 h;陆风时段为2:00—7:00,持续5 h。海风平均风速为2.1 m/s,陆风平均风速为0.8 m/s,海风平均风速明显大于陆风风速。海风与陆风环流垂直高度相差甚小,约1.2 km,风速随高度变化趋势均为先增后减;海风最大风速出现在750 m高度处,陆风出现在500 m高度处,500~750 m高度区间海风环流强度明显强于陆风环流。2 km之上为均匀一致的系统性西风环流。 相似文献
206.
207.
大同5.5级地震前的电磁前兆信号 总被引:6,自引:0,他引:6
1976年唐山地震皮后,上地震引起的电磁信号异常现象开始引起人们的极大关注,我国相继建立了200多个地震电磁波观测台,并且积累了许多震例资料。同时在国外也发表了一些相关的文章,但大多数文章仅涉及到震前一个台的异常信号或某个频段上的异常信号。 相似文献
208.
209.
New paleontological evidence on time determination of the east part of the Eastern Kunlun Mélange and its tectonic significance 总被引:2,自引:2,他引:2
ZHANG Kexin LIN Qixiang ZHU Yunhai YIN Hongfu LUO Mansheng CHEN Nengsong & WANG Guocan Faculty of Earth Science China University of Geosciences Wuhan China 《中国科学D辑(英文版)》2004,(10)
The area studied is located in the middle ofQinghai Province, at the south end of Qaidam Basinand the eastern part of the Eastern Kunlun Mountainsin Dulan County, Haixi Prefecture and Madoi County,Golog Tibetan Autonomous Prefecture, Qinghai Prov-ince (fig. 1). The area is situated tectonically in theeast of the Eastern Kunlun Mountains at the junctionof the Eastern Kunlun Orogenic Belt with the WesternQingling which is also the junction of the QaidamPlate with the South China Plat… 相似文献
210.