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271.
272.
Anson W. Mackay George E. A. Swann Melanie J. Leng David W. Morley Natalia Piotrowska Patrick Rioual Dustin White 《第四纪科学杂志》2011,26(6):627-634
We present a new palaeoenvironmental record of hydrological variability in Lake Baikal, based on re‐modelled δ18Odiatom values of diatom silica (δ18Omodelled), where the residual contaminants are identified and compensated for using electron optical imaging and whole‐sample geochemistry. δ18Omodelled interpretations are based on the balance between rivers with high δ18O values and rivers with low δ18O values. Isotopic variability is related to latitudinal differences in precipitation which feed these rivers. The δ18Omodelled record suggests that rather moist conditions prevailed in the Lake Baikal region during the latter stages of the Younger Dryas. Throughout the Holocene, episodes of low δ18Omodelled values are, in general, in good agreement with increases in percentage haematite‐stained grains in North Atlantic sediments (indicative of ice‐rafted debris events). Rivers with southerly catchments dominate fluvial input especially between c. 3.3 and 2 cal ka BP, concurrent with high precipitation in the Lake Baikal region. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
273.
典型城市区与森林区空气负氧离子特征比较分析 总被引:1,自引:0,他引:1
利用连续15个月逐小时对比观测资料,分析比较了典型城市区和森林区负氧离子特征,结果显示:1城市区负氧离子平均浓度为240个/cm3、森林区为1470个/cm3,森林区明显高于城市区5~6倍;森林区负氧离子中"小离子"约占8成、"中离子"约占2成,而城区"中离子"几乎为零。2城市区和森林区负氧离子浓度日变化趋势大体一致,夜间高于白天,午夜到早晨为高浓度时段,峰值出现在凌晨04:00—5:00;低浓度时段在中午到傍晚前后,最低值均出现在13:00。3负氧离子浓度在季节分布上,森林区以春季和冬季较高,城市区以秋季较高。城市区秋季较高可能与当年秋季雨水异常偏多有关。4大老岭林区负氧离子浓度有缓慢下降趋势,而城市区有缓慢上升趋势。5负氧离子日平均浓度,城市区以雾天和雨天较高,雷雨天、阴天次之,晴天较低;森林区以晴天和雷雨天气较高,阴天次之,而雨天和雾天反而较低,与城市区相反。 相似文献
274.
275.
The lake groups in the Songnen Plain are low plain lake groups, which are located in the temperate semihumid area in China.
They are characterized by small area, shallow basin, thick density and various types. In the try for classifying comprehensively
the lake groups, a classification system is developed based on three main factors, i.e. forming cause, water quantity and
water quality. The most internal character can be concisely grasped through three principal indexes and three auxiliary indexes
of three main factors. A sample of complicated changeable path is put forward for further analyzing and outlining these basic
types, in the meantime, it’s linking up easily with the classification system of the single factor. According to the regional
environment, the regional differences of the type composition and the principal types, the lake groups in the Songnen Plain
can be divided into 6 sub-regions.
Foundation item: Under the auspices of the National Natural Science Foundation of China(49671077).
Biography: LU Jin-fu (1938–), male, professor. His research interest includes paleo-environment in the Quaternary. 相似文献
276.
Angela L. Lamb Tim S. Brewer Melanie J. Leng Hilary J. Sloane Henry F. Lamb 《Journal of Paleolimnology》2007,37(4):499-516
The analysis of oxygen isotope ratios (δ18O) in biogenic silica (e.g. diatoms, sponge spicules, phytoliths) is an increasingly utilised palaeoclimatic proxy for lakes
and oceans, providing an alternative to carbonate δ18O. Currently, the problems associated with the cleaning and extraction of pure diatom silica, especially from lake sediments,
may compromise the precision associated with δ18Odiatom records. This is because, despite improvements in cleaning techniques, it is still difficult to remove silica-containing
contaminants (e.g. tephra, silts and clays) from biogenic silica. Where it has proved difficult to remove all the silica bearing
contaminants from a sample, mass balance calculations involving point counting have been used, but these are inherently inaccurate
as they only consider the surface area of the contaminant, rather than volume. The new method described here assesses the
volume of contamination in each sample of biogenic silica by using major and trace element geochemistry, allowing the δ18O of the contamination to be removed from the biogenic silica δ18O value by linear mass balance. In this case, diatom silica was contaminated with tephra, however the method should also be
applicable to other contaminants such as silts and clays. 相似文献
277.
278.
随着人类社会对稀土资源的需求日益增加,资源量丰富的深海稀土逐渐引起各国的关注。深海稀土是近年来发现的一种富集中-重稀土的新型海洋矿产资源,具有重要的价值并可能成为最先开发的深海矿产资源之一。目前,深海稀土矿产资源的调查研究工作才开展十余年,对深海稀土元素的来源富集、分布规律、成矿机理等方向做了较多基础研究工作,但由于开采设备、环境保护、市场收益等环节还存在诸多技术难题和未知因素,尚不能实现商业化的开发利用。本文分析了深海稀土矿产资源的研究现状以及存在的关键问题,重点剖析了中国超前布局其产业化的前景和可行性,提出未来产业化开发利用的相关对策与建议。今后需继续加大深海稀土开发利用技术的研发力度,升级改造中国稀土全产业链布局和融合发展,推广深海绿色采矿新概念,提高中国在国际深海资源勘探开发的话语权。 相似文献
279.
本文提出,在玉米籽粒生长发育过程中,于物质累积呈逻辑斯蒂模型。模型的参数主要受生育期平均气温制约。在成熟期,籽粒干重不仅与籽粒发育期间的平均气温有关,还与籽粒发育所经历的天数有关。 相似文献
280.