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121.
122.
洞穴碳酸盐微层研究及其发展方向 总被引:4,自引:0,他引:4
近几年,在分辨率气候-环境变化研究中,洞穴碳酸盐微层逐渐受到人们重视。洞穴碳酸盐微层的类型较多,主要为年层。微层是在沉积条件发生高频率的周期性改变时形成的,要受到供水条件和碳酸钙浓度等多因素的控制。洞穴碳酸盐微层的稳定同位素组成,生长速率,微层结构与物质组分,微层厚度与灰度和光学特征等可以反映降水,温度,土壤成分及植被变化等信息。 相似文献
123.
Low-Temperature Oxidation of Magnetite in Loess-Paleosol Sequences: a Correction of Rock Magnetic Parameters 总被引:4,自引:0,他引:4
Low-temperature oxidation under atmospheric conditions affects the magnetic properties of magnetite in natural rocks: the coercivities of magnetite grains increase and other parameters change accordingly. It was recently shown that heating to 150°C largely removes the effects of low-temperature oxidation (van Velzen and Zijderveld, 1995). Heating may therefore serve as a detection tool for the presence of the effect of low-temperature oxidation.
In the present study, a collection of loess and paleosol samples from various loess regions of the world is examined for the influence of low-temperature oxidation. In all samples of the collection a decrease of coercivities was found after heating to 150°C. Generally loess samples were affected to a larger extent than paleosol samples. The original range of remanent coercivities(B
cr)of 21-58 mT changed to 20-42 mT after heating. The IRM capacity of the samples decreased from 0 up to 25%. ARM showed changes between a decrease of 10% and an increase of 15%. The grain-size indicative parameter IRM/ARM is considerably influenced by the heating and therefore by low-temperature oxidation. The changes in susceptibility are limited and will not influence the interpretation of large-scale features of the susceptibility record as a paleoclimate proxy. Small variations, however, may be obscured by the varying influence of oxidation in the outcrop, which can significantly modify the rock-magnetic record.
Rock-magnetic parameters used to determine magnetic mineral content and grain sizes should be corrected for the effect of low-temperature oxidation. To this end heating to 150°C is recommended. The occurrence of the changes is in itself already an indication for the presence of magnetite. Low-temperature oxidation will not only be due to recent weathering in the outcrop, but also to earlier oxidation processes in the source area, during transport and deposition of the loess and during pedogenesis. Truly fresh sediment samples are only influenced by this earlier oxidation. In that case heating will reveal the degree of ancient low-temperature oxidation, which may be related to climate at the time of deposition and pedogenesis. 相似文献
124.
中原新石器文化与古气候的关系 总被引:13,自引:1,他引:12
讨论了中原新石器时代文化遗址^14C年代序列的代表性;分析了新石器古文化与古气候描淡写焦;根据陕西扶风案板遗址(傍龙寺)的孢粉资料,结合冰川前进、冰缘现象等因素,重建了代表中原地区的12 ̄3kaB.P.的古年均气温和古年降水量曲线; 相似文献
125.
太白盆地黄土地层厚16m左右.发育有两层红褐色古土壤。化学分析与微结构鉴定表明该盆地黄土中的古土壤为FeO3与Al2O3迁移深度大但无聚集的棕壤.并已成为明显的风化无,发育时的年平均降水量在1000mm以上.太白盆地黄土中CaCO3含量少,发育有淀积型的光性定向粘土.表明黄土地层发育时的降水量也在600mm以上。该盆地黄土地层发育在距今约20多万年前.指示从这一时期开始,中国黄土搬运高度已超过2000m。微结构的观察还表明,光性定向粘土不仅可用于降水量的研究,也可用于指示温度的相对高低. 相似文献
126.
Larry A. Mayer Cyril Gobrecht Nicklas G. Pisias 《International Journal of Earth Sciences》1996,85(3):505-512
Recent developments in continuous core-logging techniques now permit us to recover the high-resolution time series necessary
for the detailed spectral analyses of paleoclimatic proxy records. When applied to long records recovered by scientific drilling
(5–10 Ma) they enable us to look at the long-term history and evolution of the ocean's response to orbital forcing. A serious
limitation in these studies is the need to display the complex, multidimensional spatial and temporal interactions of the
ocean-climate system in an easily comprehensible manner. We have addressed this issue by developing a series 3D visualization
tools which permit visualization of the role of the orbital parameters in determining the latitudinal variation of insolation
as well as the interactive exploration of multidimensional data sets. The ORBITS tool allows us to visualize the effect of
orbital eccentricity, precession, and tilt on the latitudinal distribution of insolation on the earth at the solstices and
the equinoxes for any time over the past 5 Ma (for Berger's orbital model) or 10 Ma (for Laskar's orbital model). The effect
of the orbital parameters on insolation can be viewed individually, in pairs, or all three together. By moving the model steadily
through time, the rate at which orbitally induced changes in insolation occur can also be visualized. To look at the ocean's
response to orbital forcing we take the long time series generated from our paleoclimatic proxies and calculate their spectrum
over a fixed, but sliding, time window. To view the complex multidimensional relationships found in these evolutionary spectral
analyses, we use another interactive 3D data exploration tool developed at the University of New Brunswick (Canada). This
tool (FLEDERMAUS) uses a six-degrees-of-freedom input device (BAT) and a series of software modules for color coding, shading,
and rendering complex data sets, to allow the user to interactively "fly" through the multidimensional data. Through the use
of color, texture, and 3D position, as many as six or seven variables can be explored in a simple and intuitive manner. With
special liquid-crystal-display glasses, the scene can be viewed in true "stereo." We use these tools to explore the relationship
between orbital forcing and the response of the benthic isotope and calcium carbonate record at ODP Site 846 (90°W and 5°S)
This analysis shows an equatorial Pacific carbonate record which has a large component of linear response to tilt, but little
linear response to precession. There is a major shift in response, from a carbonate-dominated response to an isotope (ice
volume)-dominated response at approximately 4.5 Ma, and as expected, there is a large nonlinear response at the lower frequencies
(400 and 100 kyr) during the past 800 kyr to 1 Ma
Received: 22 June 1995 / Accepted: 29 January 1996 相似文献
127.
黄土高原中部的陕西泾阳、旬邑黄土剖面具有高分辨率气候记录,记录了130ka 以来的气候波动,一些细微的气候波动也被记录下来。位于大陆的黄土磁化率气候记录可以与南极冰芯气候记录对比。结果表明:Lorius 与 Jouzel 等将冰芯同位素曲线划分为 A、B、C、D、E、F、G、H 冷暖阶段,可与黄土磁化率气候曲线划分的1、2、3、4、(5、6、7)、8,9、10冷暖阶段对比。其中冰芯记录所反映的 A、C、E、G(或黄土记录反映的1、3、5、6、7、9)为暖阶段:B、D、F、H(2、4、8、10)为冷阶段。总之,黄土磁化率记录曲线与冰芯气候记录曲线的形态极为相似,指示了黄土高原地区的大陆气候变化与极地气候变化同受全球变化的影响。这证明了极地冰量变化与东亚大陆冬、夏季风强弱变化,是全球气候变化在极地与大陆的两种表现形式。黄土记录的气候变化时间滞后于冰芯记录,可能暗示着大陆气候变化滞后于极地气候变化。 相似文献
128.
由于自然档案中稳定同位素组成对气候变化的有效指示作用,环境地球化学研究对古全球变化研究起着十分重要的作用,长期以来被看成古全球变化科学的基石。本文从时间尺度、空间尺度和气候驱动因素等方面的环境地球化学研究,论述了近年来取得的一些新进展。 相似文献
129.
中国近20万年以来古气候研究概况及其发展方向 总被引:2,自引:0,他引:2
全球变化是当今人们所面临的重大问题之一,而对过去全球变化的认识,尤其对近20万年以来的古气候变化的认识是预测未来全球变化的关键。我国对黄土、湖泊沉积物、冰心、海洋沉积物等信息载体的研究已取得了大量的成果,但仍存在分辨率不高、研究区域分布不均、系统研究不够等问题。因此,应针对这些不足,并结合我国的特殊地域优势和气候形成机制,对一些重点地段和时间段加强研究,以便加深对青藏高原抬升对东亚气候的影响和东亚季风的演化规律等问题的认识。 相似文献
130.
冕宁冶勒地区新生代孢粉组合特征 总被引:2,自引:0,他引:2
冕宁冶勒地区,分布着较大面积的新生代地层,通过野外填图、实测剖面,以及采获的孢粉化石,划分出了昔格达组及Ⅰ~Ⅴ级阶地,并建立了冶勒地区四个孢粉组合带。结合同位素地质年龄,区域对比分析,确认昔格达组属上新世至早更新世沉积。区内Ⅱ~Ⅴ级阶地为更新世堆积,Ⅰ级阶地为全新世堆积,并对古气候进行了初步分析 相似文献