全文获取类型
收费全文 | 2513篇 |
免费 | 402篇 |
国内免费 | 594篇 |
专业分类
测绘学 | 127篇 |
大气科学 | 447篇 |
地球物理 | 710篇 |
地质学 | 1364篇 |
海洋学 | 248篇 |
天文学 | 92篇 |
综合类 | 247篇 |
自然地理 | 274篇 |
出版年
2024年 | 16篇 |
2023年 | 43篇 |
2022年 | 125篇 |
2021年 | 121篇 |
2020年 | 118篇 |
2019年 | 125篇 |
2018年 | 166篇 |
2017年 | 154篇 |
2016年 | 135篇 |
2015年 | 120篇 |
2014年 | 160篇 |
2013年 | 172篇 |
2012年 | 143篇 |
2011年 | 150篇 |
2010年 | 160篇 |
2009年 | 157篇 |
2008年 | 119篇 |
2007年 | 132篇 |
2006年 | 83篇 |
2005年 | 71篇 |
2004年 | 85篇 |
2003年 | 70篇 |
2002年 | 59篇 |
2001年 | 70篇 |
2000年 | 98篇 |
1999年 | 88篇 |
1998年 | 69篇 |
1997年 | 74篇 |
1996年 | 90篇 |
1995年 | 61篇 |
1994年 | 62篇 |
1993年 | 47篇 |
1992年 | 31篇 |
1991年 | 21篇 |
1990年 | 24篇 |
1989年 | 20篇 |
1988年 | 17篇 |
1987年 | 13篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1978年 | 1篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1936年 | 1篇 |
1933年 | 1篇 |
排序方式: 共有3509条查询结果,搜索用时 0 毫秒
71.
台湾以东黑潮的低频变化及机制研究 总被引:1,自引:0,他引:1
本文基于AVISO(Archiving, Validation and Interpretation of Satellite Oceanographic data)1993-2015年间的海表面绝对动力高度数据,研究了台湾以东黑潮的低频变化特征,并探讨了影响其变化的机制。结果表明,台湾以东多年平均的黑潮流幅值约为136 km,表层流量值约为7.75×104 m2/s,对应的标准差分别为28 km和2.14×104 m2/s。台湾以东黑潮不仅具有显著的季节变化特征,还具有显著的年际变化特征。功率谱分析结果表明,台湾以东黑潮表层流量具有1 a和2.8 a的显著周期。空间上,台湾东南部黑潮的年际变化幅度比东北部强烈。相关性及合成分析结果表明,台湾以东黑潮的年际变化与PTO(Philippines-Taiwan Oscillation)之间存在显著的相关性。PTO年际震荡所导致的副热带逆流区反气旋式涡旋与气旋式涡旋的相对强度是影响台湾以东黑潮年际变化的主要动力因素。 相似文献
72.
Xiao-Dong Liu Li-Guang Sun Zhong-Qi Cheng San-Ping Zhao Ke-Xin Liu Xiao-Hong Wu Zhou-Qing Xie Xue-Bin Yin Hong-Hao Luo Xing-Fang Ding Dong-Bo Fu Yu-Hong Wang 《Marine Geology》2008,247(1-2):1-16
The phosphatic cement in the bioclastic sediment sequence on the northeastern shore of Dongdao Island in the South China Sea was studied and its paleoenvironmental implications discussed. Petrological characteristics and major, trace, REE element data unequivocally supported the notion that phosphatization was closely associated with avian guano decomposition and leaching, whereas carbon and oxygen isotope results further revealed that meteoric water were involved in these processes. AMS 14C dates on the brown phosphate cements indicate that they were formed around 5700, 5000–5100 and 2900 yr BP, respectively. The multi-episodes of phosphatization very likely correspond to intermittent seabird occupation on this island — possibly reflecting Holocene sea-level oscillation and/or long term climate changes in the South China Sea that have controlled seabird habitat. The phosphate cementation, which occurs widely in tropical islands, may be another useful monitor for sea-level and/or paleoclimate changes. 相似文献
73.
从1株海绵内生真菌(Alternaria sp.)链格孢菌的发酵液中提取胞外多糖,对其进行Q Sepharose FF离子交换色谱分离纯化,得到2个组分JJY-W和JJY-S。运用各种化学方法及波谱方法对JJY-W和JJY-S的理化性质及结构进行分析,并对多糖清除自由基活性进行了评价。结果表明,JJY-W和JJY-S的分子量分别为1.4KD和1.8KD;JJY-W以半乳糖、葡萄糖为主,含有少量甘露糖,摩尔比为:甘露糖∶葡萄糖∶半乳糖=1∶2.5∶11。JJY-S以甘露糖、葡萄糖为主,含有少量半乳糖,摩尔比为:甘露糖∶葡萄糖∶半乳糖=3∶2∶1。JJY-W总糖含量为46.3%,未检测出糖醛酸,蛋白含量为2%。JJY-S总糖含量为52%,糖醛酸含量为6.1%,蛋白含量为14%。活性分析表明,2种多糖均具有一定的体外抗氧化活性,并随着浓度的增加清除自由基能力均增强,JJY-W清除DPPH自由基的活性要强于JJY-S,而JJY-S清除OH.自由基的活性要强于JJY-W。 相似文献
74.
研究南极树粉孢属(Oidiodendron truncatum)真菌所产胞外多糖的理化性质和结构特征。采用阴离子交换柱层析和凝胶柱层析对南极树粉孢属(Oidiodendron truncatum)真菌胞外多糖进行了系统的分离纯化,从中得到4个均一的组分(AFW1,AFW2,AFS1和AFS2),并结合红外、气质及核磁等技术对它们的结构进行了解析。结果表明:AFW1和AFW2为中性多糖,AFS1和AFS2中含有少量的蛋白;AFW1和AFS1是由甘露糖、葡萄糖和半乳糖3种单糖组成的结构复杂的杂多糖;AFW2和AFS2则仅由葡萄糖组成,其中AFW2属线性(-1,6-葡聚糖,而AFS2属于C-3位有分支的α-1,6-葡聚糖。 相似文献
75.
The system with one floating rectangular body on the free surface and one submerged rectangular body has been applied to a wave energy conversion device in water of finite depth. The radiation problem by this device on a plane incident wave is solved by the use of an eigenfunction expansion method, and a new analytical expression for the radiation velocity potential is obtained. The wave excitation force is calculated via the known incident wave potential and the radiation potential with a theorem of Haskind employed. To verify the correctness of this method, an example is computed respectively through the bound element method and analytical method. Results show that two numerical methods. are in good agreement, which shows that the present method is applicable. In addition, the trends of hydrodynamic coefficients and wave force are analyzed under different conditions by use of the present analytical method. 相似文献
76.
77.
Experimental Study on Sloshing Characteristics in the Elastic Tank Based on Morlet Wavelet Transform
Mei-rong Jiang Wen-jun Zhong Jian-xing Yu Pei-lin Liu Han-jun Yin Shou-dong Wang Yu-xiang Ma 《中国海洋工程》2018,32(4):400-412
Hydroelastic effect of sloshing is studied through an experimental investigation. Different excitation frequencies are considered with low-fill-depth and large amplitude. Morlet wavelet transform is introduced to analyze the free surface elevations and sloshing pressures. It focuses on variations and distributions of the wavelet energy in elastic tanks. The evolutions of theoretical and experimental wavelet spectra are discussed and the corresponding Fourier spectrums are compared. Afterwards, average values of the wavelet spectra are extracted to do a quantitative study at various points. From the wavelet analysis, sloshing energies are mainly distributed around the external excitation frequency and expanded to high frequencies under violent condition. In resonance, experimental wavelet energy of the elevation in elastic tanks is obviously less than that in the rigid one; for sloshing pressures, the elastic wavelet energy close to the rigid one and conspicuous impulse is observed. It recommends engineers to concern the primary natural frequency and impulsive peak pressures. 相似文献
78.
2013年青岛输油管道爆炸,大量石油污染了附近海岸。课题组采集了污染的沉积物样品,以原油为唯一碳源和能源,富集了四个石油降解菌群。生物多样性和群落分析表明,Luteibacter、Parvibaculum 和属于食烷菌科的一个属是降解菌群的主要优势菌,都属于变形菌门。从石油降解菌群中分离筛选,获得了9株具有不同16S rRNA基因序列的降解菌,分别属于8个属。重量法测定降解菌的石油降解率,其中5株的石油降解率大于30%。GC-MS分析结果表明,石油降解菌多倾向于降解烷烃,对多环芳烃的降解能力较差,其中5株细菌的烷烃降解率较大,仅1株菌D2对多环芳烃的降解率较大,其降解率在34.9%到77.5%。通过对高通量数据的分析,表明食烷菌属是菌群A和菌群E的主要降解菌群,其中筛选获得的菌株E4可能是菌群E的一株优势降解菌。本研究所筛选菌株证明了其石油降解潜力,为油污染海滩生物修复提供了菌株资源。 相似文献
79.
Spatial and temporal variations of mesozooplankton in the Pearl River estuary, China 总被引:10,自引:0,他引:10
This paper examines spatial and temporal variations of mesozooplankton abundance, biomass and community structure during three cruises of July 2002 (summer), January 2003 (winter), and April 2003 (spring) in the Pearl River estuary, China. Zooplankton abundance and biomass fluctuated widely and showed distinct heterogeneity in the Pearl River estuary. A total of 154 species were identified during three surveys. The number of zooplankton species richness was strongly linked to salinity. Hierarchical cluster analysis identified three zooplankton groups during this study. Estuarine, neritic and pelagic groups corresponded to the upper, middle and lower reaches in the Pearl River estuary. The difference among groups could be mainly ascribed to changes in the relative contributions of the dominant species. The fluctuations in the zooplankton abundance, biomass and community structure were determined by the interactive effects of freshwater inflow, tidal and coastal currents, chlorophyll a, salinity and temperature. Significant spatial variability in the distribution of zooplankton species, abundance and biomass can be ascribed to the virtual presence of a horizontal gradient in salinity. 相似文献
80.
曹妃甸填海工程初期规划有明显缺陷,填海面积过大,尤其是阻断了浅滩潮道(纳潮河),对海洋环境、老龙沟港口潜力区有明显损害。作者的积极建议和相关论文的发表促成了2007年曹妃甸新填海规划的出台,其中保留浅滩潮道(即开通纳潮河)和在老龙沟上游修建大港池是新规划的主要改进内容。阻断浅滩潮道后曹妃甸区域的地形地貌及水动力变化证实了作者观点的正确性。纳潮河于2016年8月开通。纳潮河的开通,可大大提升曹妃甸景观,增加约40 km不淤积的优良海岸线,部分恢复原海洋潮流系统和保护海洋环境,促进海水的循环,并使曹妃甸的几个港池不再淤积或淤积变轻。 相似文献