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151.
The vertical and seasonal distributions of the phytoflagellate Cryptomonas spp., and its most common, the planktonic ciliate predators (Oligotrichida, Scuticociliatida, Hypotrichida and Prostomatida) were investigated in chemocline region of small saline, meromictic lake Shunet (Siberia, Russia) during 2003 and 2005. The
lake has a pronounced chemocline, with abundance of purple and green sulphur bacteria. Vertical distribution of the Cryptomonas populations near the oxic/anoxic boundary layer was studied at close intervals in water sampled using a hydraulically operated
thin-layer sampler. In both summer and winter, Cryptomonas peaked in water stratum 5–10 cm above anoxic zone or in the anoxic zone water column in the chemocline (about 5 m). Ciliate
densities and biomass were also much higher in chemocline than in mixolimnion. The range of diurnal migration of Cryptomonas population was not very wide, and it was restricted to layers with high light intensity. The ciliates were sometimes detected
above the upper border of the anoxic zone but also several centimetres below this zone. 相似文献
152.
The species diversity of planktonic diatoms in thanatocenoses of bottom sediments in Lake Bol’shoe Miassovo (Southern Urals) has been studied and a reconstruction of the thermal regime of the lake for the last 1000 years is made. It is established that the restructuring of the diatom assemblage and decrease in species diversity in thanatocenoses are caused by rapid climate warming that began in the 19th century in the Southern Urals. 相似文献
153.
The t complex in the proximal part of chromosome 17 is one of the most thoroughly studied regions of the mouse genome. We determined the sequence of Tu80, a molecular clone derived from microdissected fragments of chromosome 17. The sequence data demonstrated that the total length being 324 bp, Tu80 contains an open-reading frame (ORF) of 204 bp. Two fragments were detected within the ORF, one homologous to the LINE1-element, the other to the first intron of the C epsilon gene of mouse immunoglobin. A sequence designated NOV1 was isolated from the genomic library of mouse chromosome 17. NOV1 was found to contain a B2 insert, making in structurally different from Tu80. The sequences of Tu80 and NOV1 were compared with those of LINE1 and the first intron of the C epsilon gene. The results suggested that the ancestor of the Tu80-like sequence might have arisen through illegitimate recombination between the fragments of LINE1 and the C epsilon gene. It is concluded that Tu80 and NOV1 might have resulted from duplication of the ancestral sequence and following divergence. The comparative analysis also demonstrated high degree of conservation of the LINE1 fragments in Tu80 and NOV1, as well as in the LINE1 in a number of mammalian species. Based on the structure of human, rat, rabbit and mouse LINE1 fragments, and also on that of NOV1 and Tu80, phylogenetic tree has been constructed. Its topology is consistent with the accepted phylogenetic relationships among the species studied. The data available tend to support the assumption that the ancestor for the Tu80-like sequence might have arisen not later than 27-33 million years ago. 相似文献
154.
Genome trees constructed using five different approaches suggest new major bacterial clades 总被引:1,自引:0,他引:1
Yuri I Wolf Igor B Rogozin Nick V Grishin Roman L Tatusov Eugene V Koonin 《BMC evolutionary biology》2001,1(1):8-22
Background
The availability of multiple complete genome sequences from diverse taxa prompts the development of new phylogenetic approaches, which attempt to incorporate information derived from comparative analysis of complete gene sets or large subsets thereof. Such attempts are particularly relevant because of the major role of horizontal gene transfer and lineage-specific gene loss, at least in the evolution of prokaryotes. 相似文献155.
156.
A. G. Rogozin 《Inland Water Biology》2013,6(2):106-113
The Argazi reservoir on the Miass River, the oldest reservoir in the Southern Urals, has been investigated. In total 49 species and forms of zooplankton are identified, including new and rare species for the fauna of the Urals. Throughout the reservoir zooplankton has high species diversity and considerable biomass (up to 11 g/m3). Rotifers are the leading group in the plankton of the reservoir. Compared to the early 1960s, the abundance and biomass of zooplankton has increased by 5–10 times. The disappearance of some plankton forms and the emergence of new ones, as well as an increased number of rotifers and some crustaceans by 1–2 orders of magnitude, are noted. The influence of three main factors that could lead to long-term changes in zooplankton—eutrophication, heavy metals pollution, and global warming—are considered. The last factor seems to be the most important. 相似文献
157.
158.
159.
We present here a new algorithm for functional site analysis. It is based on four main assumptions: each variation of nucleotide
composition makes a different contribution to the overall binding free energy of interaction between a functional site and
another molecule; nonfunctioning site-like regions (pseudosites) are absent or rare in genomes; there may be errors in the
sample of sites; and nucleotides of different site positions are considered to be mutually dependent. In this algorithm, the
site set is divided into subsets, each described by a certain consensus. Donor splice sites of the human protein-coding genes
were analyzed. Comparing the results with other methods of donor splice site prediction has demonstrated a more accurate prediction
of consensus sequences AG/GU(A,G), G/GUnAG, /GU(A,G)AG, /GU(A,G)nGU, and G/GUA than is achieved by weight matrix and consensus
(A,C)AG/GU(A,G)AGU with mismatches. The probability of the first type error, E1, for the obtained consensus set was about
0.05, and the probability of the second type error, E2, was 0.15. The analysis demonstrated that accuracy of the functional
site prediction could be improved if one takes into account correlations between the site positions. The accuracy of prediction
by using human consensus sequences was tested on sequences from different organisms. Some differences in consensus sequences
for the plant Arabidopsis sp., the invertebrate Caenorhabditis sp., and the fungus Aspergillus sp. were revealed. For the yeast Saccharomyces sp. only one conservative consensus, /GUA(U,A,C)G(U,A,C), was revealed (E1 = 0.03, E2 = 0.03). Yeast is a very interesting
model to use for analysis of molecular mechanisms of splicing.
Received: 14 October 1996 / Accepted: 30 January 1997 相似文献