全文获取类型
收费全文 | 643篇 |
免费 | 98篇 |
国内免费 | 131篇 |
专业分类
测绘学 | 48篇 |
大气科学 | 112篇 |
地球物理 | 80篇 |
地质学 | 383篇 |
海洋学 | 80篇 |
天文学 | 70篇 |
综合类 | 56篇 |
自然地理 | 43篇 |
出版年
2024年 | 4篇 |
2023年 | 5篇 |
2022年 | 17篇 |
2021年 | 28篇 |
2020年 | 24篇 |
2019年 | 29篇 |
2018年 | 28篇 |
2017年 | 25篇 |
2016年 | 26篇 |
2015年 | 29篇 |
2014年 | 45篇 |
2013年 | 27篇 |
2012年 | 31篇 |
2011年 | 46篇 |
2010年 | 51篇 |
2009年 | 50篇 |
2008年 | 51篇 |
2007年 | 40篇 |
2006年 | 39篇 |
2005年 | 24篇 |
2004年 | 29篇 |
2003年 | 22篇 |
2002年 | 23篇 |
2001年 | 25篇 |
2000年 | 11篇 |
1999年 | 20篇 |
1998年 | 25篇 |
1997年 | 17篇 |
1996年 | 16篇 |
1995年 | 13篇 |
1994年 | 10篇 |
1993年 | 9篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1973年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有872条查询结果,搜索用时 343 毫秒
801.
Wing Yin Mo Zhang Cheng Wai Ming Choi Yu Bon Man Yihui Liu Ming Hung Wong 《Marine pollution bulletin》2014
Food waste was collected from local hotels and fish feed pellets were produced for a 6 months long field feeding trial. Three types of fish feed pellets (control diet: Jinfeng® 613 formulated feed, contains mainly fish meal, plant product and fish oil; Diet A: food waste based diet without meat and 53% cereal; Diet B: food waste based diet with 25% meat and 28% cereal) were used in polyculture fish ponds to investigate the growth of fish (grass carp, bighead and mud carp), changes in water quality and plankton density. No significant differences in the levels of nitrogen and phosphorous compounds of water body were observed between 3 fish ponds after the half-year feeding trial, while pond receiving Diet A had the highest density of plankton. The food waste combination of Diet B seems to be a better formulation in terms of the overall performance on fish growth. 相似文献
802.
Lactococcosis is prevalent on grey mullet (Mugil cephalus) in Hong Kong aquaculture resulting in serious economic loss. A compound formulation of Traditional Chinese Medicines (TCM) (modified Huanglian Jiedu decoction (HLJDD)) comprising Rhizoma coptidis, Radix scutellaria, Cortex phellodendri, Fructus gardeniae, Fructus forsythiae and Flos lonicerae japonicae (in a ratio of 3:2:2:3:3:5) were applied as feed supplements to deal with the disease. The Nitroblue tetrazolium activity in blood, bactericidal activity and total immunoglobulin in plasma were significantly enhanced after feeding 1% of this TCM for 28 days. The disease resistances to Lactococcus garvieae in 1% and 2% TCM feeding groups were significantly enhanced. In the in vitro study, the modified HLJDD also activated the plasma bactericidal activities (p < 0.01). Based on this study, 1% modified HLJDD feeding for 28 days may be an optimal dose to prevent L. garvieae infection and could be used in aquaculture industries. 相似文献
803.
Ruping Mo Paul I. Joe Chris Doyle Paul H. Whitfield 《Pure and Applied Geophysics》2014,171(1-2):323-336
A brief review of the anomalous weather conditions during the Vancouver 2010 Winter Olympic and Paralympic Games and the efforts to predict these anomalies based on some preceding El Niño–Southern Oscillation (ENSO) signals are presented. It is shown that the Olympic Games were held under extraordinarily warm conditions in February 2010, with monthly mean temperature anomalies of +2.2 °C in Vancouver and +2.8 °C in Whistler, ranking respectively as the highest and the second highest in the past 30 years (1981–2010). The warm conditions continued, but became less anomalous, in March 2010 for the Paralympic Games. While the precipitation amounts in the area remained near normal through this winter, the lack of snow due to warm conditions created numerous media headlines and practical problems for the alpine competitions. A statistical model was developed on the premise that February and March temperatures in the Vancouver area could be predicted using an ENSO signal with considerable lead time. This model successfully predicted the warmer-than-normal, lower-snowfall conditions for the Vancouver 2010 Winter Olympics and Paralympics. 相似文献
804.
川东南隔挡式构造区隧道空间展布影响下岩溶涌突水特征简析 总被引:2,自引:2,他引:0
隔挡式构造区隧道工程涌水特征研究多局限于某个具体隧道工程及对应的特定岩溶水系统,缺乏关于隧道空间展布影响下涌突水问题的系统研究。文章提出以隧道穿越区岩溶发育及岩溶水水平与垂直分带差异作为隧道空间布置类型划分的主要标准,将隧道空间展布区的岩溶水文地质特征分为七类,对不同类型中岩溶含水介质空间结构特征、岩溶发育差异以及岩溶水在此区域流动的特点进行分析,并对八种类型的隧道涌突水的特征进行比较。据此,结合研究区拟建渝万客专铜锣山隧道和明月山隧道案例,分析此两隧道展布区域的岩溶水文地质特征,分别属于补给-垂直入渗型类型及补给径流-水平径流型类型。进一步对此两隧道可能遭遇的岩溶涌突水进行定性评价和涌水量计算,认为铜锣山隧道主要出现雨季涌水现象,水量大小受降雨强度控制,而明月山隧道涌水量较大。 相似文献
805.
姑咱台观测的汶川地震应变异常变得越来越显著.同时,在龙门山断裂带的另一端,原来不好判别的宁陕台钻孔体应变观测异常也逐渐清晰起来.利用小波分解和改进的超限率分析方法,可以将细微的地震异常变化精细地提取出来.一般地,小波分解得到的某个带通信号,可以分为正常背景和异常"坏点"两部分.通过对这两部分界线划分的研究,找到了客观、惟一确定超限率分析的阈值的方法.分析结果表明:沿整个汶川地震发震构造带,应变异常影响范围比我们以前知道的大很多;特别是,这种异常变化明显受固体潮影响,这对进一步揭示其机制提供了新的重要线索. 相似文献
806.
807.
为了丰富和发展天然气水合物的定性识别方法和定量解释技术,研究试验了由测井资料计算孔隙水的氯离子质量浓度并确定水合物饱和度的方法。根据南海某海域水合物储层的测井特征和孔隙水氯离子质量浓度化验结果,证实了氯离子质量浓度与水合物饱和度有密切关系。利用孔隙度测井和电阻率测井资料,计算了孔隙水的氯离子质量浓度,由此确定了天然气水合物的饱和度。为了提高测井解释的可靠性,用回归方法建立了储层的孔隙度解释公式,确定了相应的阿尔奇参数m和a,用滤波和插值的方法得到了目的层的氯离子质量浓度的背景值。初步应用表明,由测井解释氯离子质量浓度计算的水合物饱和度与化验结果的平均值和分布范围都有较好的匹配。 相似文献
808.
武汉黏土Duncan本构模型参数研究 总被引:1,自引:1,他引:0
通过常规三轴压缩排水试验,确定了武汉正常固结黏土的Duncan Et-?t模型、Et-Bt模型及常值?t模型参数;通过三轴试样的有限元变形分析,验证了模型参数的合理性与有效性,为武汉地区Duncan本构模型的应用提供了参考。针对Duncan Et-?t模型基于?1-?3曲线为双曲线关系假设,而实际试验曲线常常偏离理想的双曲线关系,造成?t参数拟合的困难,提出利用通过应力水平为70 %与95 %对应点的直线拟合?3 /?1与?3之间线性关系从而确定?t模型参数的改进方法,并将该模型参数用于三轴试样的体积变形预测,经与Duncan Et-Bt、Duncan Et和常值?t模型参数预测结果的对比,发现该方法与试验结果有更好的一致性,并具有简单方便的优点。 相似文献
809.
810.
CAO Taotao LIU Guangxiang LIU Hu DENG Mo HAN Yuanhong HUANG Yanran Andrew S. HURSTHOUSE 《《地质学报》英文版》2019,93(4):1025-1046
Nanoscale pore characteristics of the Upper Permian Longtan transitional mudrocks and their equivalent strata Wujiaping Formation marine mudrocks in and around the eastern Sichuan Basin was investigated using field emission scanning electron microscopy (FE-SEM) and low-pressure N2 adsorption experiments. The results indicate that the Upper Permian mudrock is at a mature stage with total organic carbon (TOC) values ranging between 0.47% and 12.3%. The Longtan mudrocks mainly contain vitrinite, and their mineral composition is primarily clay. In contrast, the Wujiaping mudrocks are dominated by sapropelinite and solid bitumen, and their mineral compositions are mainly quartz and a notably high amount of pyrite. The FE-SEM reveals that clay mineral pores and microcracks are the common pore types in the Longtan mudrocks. The specific surface area and pore volume depend on the clay content but are negatively correlated with the TOC. The generation of nanometer pores in the Longtan mudrocks is caused by high clay mineral contents. Meanwhile, the Wujiaping mudrock mainly contains OM pores, and the pore parameters are positively correlated with the TOC. The OM pore development exhibits remarkable differences in the Longtan and Wujiaping mudrocks, which might be related to their sedimentary facies and maceral fractions. Vitrinite and inertinite appear as discrete particles in these mudrocks and cannot generate pores during thermal maturation. Sapropelinite often contains many secondary pores, and solid bitumen with large particles, usually with several pores, is not the major contributor to the pore system of the investigated mudrock. 相似文献