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151.
White steenbras Lithognathus lithognathus (Teleostei: Sparidae) is an overexploited marine fish species endemic to South Africa. Overexploitation in recreational, subsistence and commercial fisheries has resulted in stock collapse and the need for improved management of the species. Adults are thought to undertake large-scale annual spawning migrations, yet studies of their movement indicate low levels of connectivity among coastal regions. To address this, mitochondrial DNA sequencing and genotyping of microsatellite loci in the nuclear genome were conducted to determine the genetic stock structure and level of gene flow in this species. Genetic diversity was high throughout the species’ core distribution, with no evidence of isolation by way of distance or localised spawning. Low, non-significant pairwise fixation indices (FST, RST and Jost’s Dest) indicated low genetic differentiation and high levels of gene flow. The observed results, and agreement between mitochondrial and microsatellite DNA, confirm that white steenbras exists as a single genetic stock with high levels of gene flow throughout its distribution. 相似文献
152.
利用实测干叶片生化组分和高光谱反射率数据,提出了基于面积归一化的高光谱位置变量一阶导数极值法提取生化组分的新思路。结果表明:该方法能较好地提取叶片全氮、纤维素、木质素和淀粉含量,尤其是对纤维素、木质素和淀粉含量的反演精度有了提高。研究还表明:该方法在提取全氮、纤维素、木质素含量时,能有效剔除土壤影响,但是在提取淀粉含量时,效果不够理想。 相似文献
153.
154.
155.
The genetic diversity of Artemisia halodendron(Asteraceae), a constructive and dominant species in Horqin Sandy Land,was investigated to examine the genetic relationships with different hydrothermal regions in Horqin Sandy Land. We sequenced chloroplast DNA(cp DNA) fragments(trn L–F) of 243 plants from 10 populations across the Horqin Sandy Land.The analyses of cp DNA variation identified seven haplotypes. A low level of haplotype diversity(H_d=0.706) and nucleotide diversity(π=0.0013) was detected. Haplotypes clustered into two tentative clades. Low genetic differentiation among regions was consistently indicated by hierarchical analyses of molecular variance(AMOVA). Across the sampled populations, the haplotype distributions were differentiated with hydrothermal gradients. 相似文献
156.
Marthasterias glacialis are found in the cool-temperate waters of the north-eastern Atlantic Ocean, in the subtropical waters of the Mediterranean Sea and along the south-western tip of Africa. The South African Marthasterias population includes two morphotypes, a smooth, spineless rarispina form and a spiny africana form, that have been described as separate species, subspecies, or forma by various authors over the past century. To test whether these two morphotypes represent separate species, and whether either, or both, are conspecific with the North-East Atlantic species, 78 Marthasterias were collected from the Cape Peninsula of South Africa. Morphological comparisons between individuals of the two forms showed no significant clustering of samples, indicating that there is no morphological separation of the two South African forms into distinct groupings. The africana and rarispina forms were also shown to be genetically indistinguishable, using a fragment of the mitochondrial cytochrome c oxidase subunit I (COI) gene and the nuclear internal transcribed spacer 1 (ITS1). In addition, the COI sequences were also compared to those from European specimens, and phylogenetic reconstruction and intra- and interspecific levels of divergence suggested that the South African specimens form a single group that is genetically distinct from the European M. glacialis. Although the allopatric distribution, high genetic divergence (more than 3% for the COI fragment) and morphological differences suggest that the South African form should be raised to species status under the name Marthasterias africana, further work must assess an independent genetic marker (nuclear) to support raising the COI clade to species level. True M. glacialis have a spine-armament pattern of a series of three or more regular spine rows down the length of each arm, whereas M. africana are either covered in many irregularly spaced spines, or have an extraordinarily bare surface with only two spine rows per arm. Marthasterias africana may also have an actinal spine simulating the presence of a third inferomarginal spine. This work tentatively resolves the taxonomic dispute, elucidates the separation and amalgamation of the two African forms and suggests a single, uniquely South African Marthasterias species that might be distinct from the north Atlantic M. glacialis, although further analyses to test reproductive isolation between the North-East Atlantic and South African forms are required. 相似文献
157.
M. Luczynski R. Rösch J. A. Vuorinen P. Brzuzan 《Aquatic Sciences - Research Across Boundaries》1995,57(2):136-143
Ripe females of whitefish (Coregonus lavaretus) of Lake Constance were caught at spawning time on their known spawning sites. Fish were examined for their size, gill-raker number, and for their egg dry weight. On the basis of their spawning sites as well as on correlation between body weight and egg weight, fish were allocated at one of the two sympatric populations: nearshore spawning Gangfisch or pelagic spawning Blaufelchen. The two fish samples were examined electrophoretically for the enzyme products of 37 genetic loci. Blaufelchen and Gangfisch were genetically identical (Nei's unbiased genetic distance D = 0.000) when all fish samples were included into the analysis. However, some genetic differentiation (D = 0.001) was evident after excluding the fish whose data points on body weight versus egg weight overlapped. Additional enzyme systems or some other genetic methodology should be used to provide more information on the genetic status of the two whitefish forms in Lake Constance.Contribution No. 8 in the Program of Joint Investigation of Holarctic Fishes among the Russia, Canada, Finland, and Poland 相似文献
158.
Sinking particulate material collected from Nansha Yongshu reef lagoon and the continental shelf of the East China Sea by
sediment traps has been analyzed and studied for the first time using organic geochemical method. The results show that about
half of the sinking particulate organic matter in the two study areas are consumed before reaching the depth of 5 m to the
sea floor and the degree of this consumption in Yongshu reef lagoon is larger than that in the continental shelf of the East
China Sea. The distributions of hydrocarbons and fatty acids indicate that the minor difference of biological sources of sinking
particulate organic matter exists between Yongshu reef lagoon and the continental shelf of the East China Sea, but they mainly
come from marine plankton. Stronger biological and biochemical transformations of sinking particulate organic matter are also
observed and the intensity of this transformation in Yongshu reef lagoon is greater than that in the continental shelf of
the East China Sea. It is found that the occurrence of C25 highly branched isoprenoid (HBI) diene may be related to the composition of diatom species. 相似文献
159.
用淀粉凝胶电泳检测和比较了加利福尼亚湾拉巴斯和马萨特兰两海区巴拿马珠母贝Pinctada mazatlanica的28个基因座位的生化遗传变异。结果发现,两群体的平均杂合度分别为0.153和0.124,与已报道的珠母贝属的其他种很接近。说明这种珠母贝的遗传变异相当丰富,未受40多年前过度采捕所引起的群体数量大幅度起伏的影响。两群体的遗传距D=0.012,预示两地间有相当强的基因流。 相似文献