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101.
Maximum sum-of-splits clustering 总被引:1,自引:1,他引:0
ConsiderN entities to be classified, and a matrix of dissimilarities between pairs of them. The split of a cluster is the smallest dissimilarity between an entity of this cluster and an entity outside it. The single-linkage algorithm provides partitions intoM clusters for which the smallest split is maximum. We study here the average split of the clusters or, equivalently, the sum of splits. A (N
2) algorithm is provided to determine maximum sum-of-splits partitions intoM clusters for allM betweenN – 1 and 2, using the dual graph of the single-linkage dendrogram.
Résumé SoientN objets à classifier et une matrice de dissimilarit és entre paires de ces objets. L'écart d'une classe est la plus petite dissimilarité entre un objet de cette classe et un objet en dehors d'elle. L'algorithme du lien simple fournit des partitions enM classes dont le plus petit écart est maximum. On étudie l'écart moyen des classes, ou, ce qui est équivalent, la somme des écarts. On propose un algorithme en (N 2) pour déterminer des partitions enM classes dont la somme des écarts est maximum pourM allant deN – 1 à 2, basé sur le graphe dual du dendrogramme de la méthode du lien simple.相似文献
102.
Dendrograms are widely used to represent graphically the clusters and partitions obtained with hierarchical clustering schemes. Espaliers are generalized dendrograms in which the length of horizontal lines is used in addition to their level in order to display the values of two characteristics of each cluster (e.g., the split and the diameter) instead of only one. An algorithm is first presented to transform a dendrogram into an espalier without rotation of any part of the former. This is done by stretching some of the horizontal lines to obtain a diagram with vertical and horizontal lines only, the cutting off by diagonal lines the parts of the horizontal lines exceeding their prescribed length. The problem of finding if, allowing rotations, no diagonal lines are needed is solved by anO(N
2) algorithm whereN is the number of entities to be classified. This algorithm is the generalized to obtain espaliers with minimum width and, possibly, some diagonal lines.Work of the first and second authors has been supported by FCAR (Fonds pour la Formation de Chercheurs et l'Aide à la Recherche) grant 92EQ1048, and grant N00014-92-J-1194 from the Office of Naval Research. Work of the first author has also been supported by NSERC (Natural Sciences and Engineering Research Council of Canada) grant to École des Hautes Études Commerciales, Montréal and by NSERC grant GP0105574. Work of the second author has been supported by NSERC grant GP0036426, by FCAR grant 90NC0305, and by an NSF Professorship for Women in Science at Princeton University from September 1990 until December 1991. Work of the third author was done in part during a visit to GERAD, Montréal. 相似文献
103.
Efficient algorithms for divisive hierarchical clustering with the diameter criterion 总被引:1,自引:1,他引:0
Divisive hierarchical clustering algorithms with the diameter criterion proceed by recursively selecting the cluster with
largest diameter and partitioning it into two clusters whose largest diameter is smallest possible. We provide two such algorithms
with complexitiesO(
N
2) andO(N
2logN) respectively, where
denotes the maximum number of clusters in a partition andN the number of entities to be clustered. The former algorithm, an efficient implementation of an algorithm of Hubert, allows
to find all partitions into at most
clusters and is inO(N
2) for fixed
. Moreover, if in each partitioning the size of the largest cluster is bounded byp times the number of entities in the set to be partitioned, with 1/2<=p<1, it provides a complete hierarchy of partitionsO(N
2 logN) time. The latter algorithm, a refinement of an algorithm of Rao allows to build a complete hierarchy of partitions inO(N
2 logN) time without any restriction. Comparative computational experiments with both algorithms and with an agglomerative hierarchical
algorithm of Benzécri are reported.
Résumé Les algorithmes de classification hiérarchique descendante utilisant le critère du diamètre, sélectionnent récursivement la classe de plus grand diamètre et la partitionnent en deux classes, dont le plus grand diamètre est le plus, petit possible. Nous proposons deux tels algorithmes, avec des complexités enO ( N2) etO(N 2 logN) respectivement, où désigne le nombre maximum de classes d'une partition etN le nombre d'objets à classifier. Le premier algorithme, une implantation d'un algorithme de Hubert, permet de construire des partitions avec au plus classes et est enO(N 2) pour fixé. De plus, si dans chaque bipartition le nombre d'objets de la plus grande classe, est borné parp fois le nombre d'objets de l'ensemble à partitionner, où 1/2≤p<1, cet algorithme permet de construire une hiérarchie complète de partitions en tempsO(N 2 logN). Le second algorithme, un raffinement d'un algorithme de Rao, permet de construire une hiérarchie complète de partitions en tempsO(N 2 logN) sans aucune restriction On présente également des résultats de calcul comparatifs pour les deux algorithmes et pour l'algorithme de classification hiérarchique ascendante de Benzécri.相似文献
104.
Dr. A. P. Hansen B. Rerkasem S. Lordkaew 《Cellular and molecular life sciences : CMLS》1995,51(11):1085-1089
The question of whether ammonium uptake influences the occurrence of ureides in legumes has been addressed in this study by investigating threeP. vulgaris genotypes as well as one cultivar ofGlycine max. All plants were raised in sand culture during the dry season in northern Thailand and irrigated daily with nitrogen-free nutrient solution, or the same solution containing 12 mol m–3 nitrogen in the form of (NH4)2SO4 or KNO3, each treatment consisting of different proportions of either compound. Regression analyses of xylem sap composition relative to ammonium vs. nitrate supply of plants harvested at V4, R1 and R6 indicated close positive correlations of xylem amino nitrogen content and negative correlations with xylem nitrate content and ammonium supply. Statistically significant correlations between relative xylem ureide content and ammonium availability could be established for theP. vulgaris cultivar Brilliant up to stage R1, but not for the other plants investigated. It was concluded that at least for some genotypes of common bean a relationship exists between ureide production and ammonium uptake by the root system. Since the extent to which ureide production is stimulated remains quite small, its relevance to the xylem solute technique for measurement of N2 fixation may be limited. Nevertheless, due to the possibility of large genotypic differences in the impact of ammonium on ureide production, this factor must be considered in calculations if N2 fixation is to be determined in soils containing significant amounts of ammonium, e.g. in paddy fields. 相似文献
105.
Li Y Vinckenbosch N Tian G Huerta-Sanchez E Jiang T Jiang H Albrechtsen A Andersen G Cao H Korneliussen T Grarup N Guo Y Hellman I Jin X Li Q Liu J Liu X Sparsø T Tang M Wu H Wu R Yu C Zheng H Astrup A Bolund L Holmkvist J Jørgensen T Kristiansen K Schmitz O Schwartz TW Zhang X Li R Yang H Wang J Hansen T Pedersen O Nielsen R Wang J 《Nature genetics》2010,42(11):969-972
Targeted capture combined with massively parallel exome sequencing is a promising approach to identify genetic variants implicated in human traits. We report exome sequencing of 200 individuals from Denmark with targeted capture of 18,654 coding genes and sequence coverage of each individual exome at an average depth of 12-fold. On average, about 95% of the target regions were covered by at least one read. We identified 121,870 SNPs in the sample population, including 53,081 coding SNPs (cSNPs). Using a statistical method for SNP calling and an estimation of allelic frequencies based on our population data, we derived the allele frequency spectrum of cSNPs with a minor allele frequency greater than 0.02. We identified a 1.8-fold excess of deleterious, non-syonomyous cSNPs over synonymous cSNPs in the low-frequency range (minor allele frequencies between 2% and 5%). This excess was more pronounced for X-linked SNPs, suggesting that deleterious substitutions are primarily recessive. 相似文献
106.
107.
Steinthorsdottir V Thorleifsson G Reynisdottir I Benediktsson R Jonsdottir T Walters GB Styrkarsdottir U Gretarsdottir S Emilsson V Ghosh S Baker A Snorradottir S Bjarnason H Ng MC Hansen T Bagger Y Wilensky RL Reilly MP Adeyemo A Chen Y Zhou J Gudnason V Chen G Huang H Lashley K Doumatey A So WY Ma RC Andersen G Borch-Johnsen K Jorgensen T van Vliet-Ostaptchouk JV Hofker MH Wijmenga C Christiansen C Rader DJ Rotimi C Gurney M Chan JC Pedersen O Sigurdsson G Gulcher JR Thorsteinsdottir U Kong A 《Nature genetics》2007,39(6):770-775
108.
Buchhave LA Latham DW Johansen A Bizzarro M Torres G Rowe JF Batalha NM Borucki WJ Brugamyer E Caldwell C Bryson ST Ciardi DR Cochran WD Endl M Esquerdo GA Ford EB Geary JC Gilliland RL Hansen T Isaacson H Laird JB Lucas PW Marcy GW Morse JA Robertson P Shporer A Stefanik RP Still M Quinn SN 《Nature》2012,486(7403):375-377
The abundance of heavy elements (metallicity) in the photospheres of stars similar to the Sun provides a 'fossil' record of the chemical composition of the initial protoplanetary disk. Metal-rich stars are much more likely to harbour gas giant planets, supporting the model that planets form by accumulation of dust and ice particles. Recent ground-based surveys suggest that this correlation is weakened for Neptunian-sized planets. However, how the relationship between size and metallicity extends into the regime of terrestrial-sized exoplanets is unknown. Here we report spectroscopic metallicities of the host stars of 226 small exoplanet candidates discovered by NASA's Kepler mission, including objects that are comparable in size to the terrestrial planets in the Solar System. We find that planets with radii less than four Earth radii form around host stars with a wide range of metallicities (but on average a metallicity close to that of the Sun), whereas large planets preferentially form around stars with higher metallicities. This observation suggests that terrestrial planets may be widespread in the disk of the Galaxy, with no special requirement of enhanced metallicity for their formation. 相似文献
109.
Cheatgrass ( Bromus tectorum L.) is a dominant weed that has increased the frequency of wildfire in the Great Basin since its introduction about 100 yr ago. This study examines characteristics of respiratory metabolism in several different populations. Seeds from 6 populations were germinated and metabolic heat rates (q) and dark respiration rates (R co2 ) of all seedlings were measured calorimetrically at 15° and 25° C or (for 3 populations) at 5° intervals from 5° to 35° C. Growth rates, substrate carbon conversion efficiencies, and Arrhenius temperature coefficients were calculated from the data. Results show that cheatgrass metabolism is most efficient at temperatures near 0° C; at temperatures above 20-25° C, efficiency goes to zero. Cheatgrass populations differ in their temperature dependencies of substrate carbon conversion efficiency and predicted growth rate. Measurements of respiratory heat and CO 2 rates as functions of temperature can be made relatively quickly and used to aid understanding of metabolic adaptation by invasive and native species to the environment. 相似文献
110.
Caitlin Collin Frank Hauser Ernesto Gonzalez de Valdivia Shizhong Li Julia Reisenberger Eva M. M. Carlsen Zaid Khan Niels Ø. Hansen Florian Puhm Leif Søndergaard Justyna Niemiec Magdalena Heninger Guilin R. Ren Cornelis J. P. Grimmelikhuijzen 《Cellular and molecular life sciences : CMLS》2013,70(17):3231-3242
Muscarinic acetylcholine receptors (mAChRs) play a central role in the mammalian nervous system. These receptors are G protein-coupled receptors (GPCRs), which are activated by the agonists acetylcholine and muscarine, and blocked by a variety of antagonists. Mammals have five mAChRs (m1–m5). In this study, we cloned two structurally related GPCRs from the fruit fly Drosophila melanogaster, which, after expression in Chinese hamster ovary cells, proved to be muscarinic acetylcholine receptors. One mAChR (the A-type; encoded by gene CG4356) is activated by acetylcholine (EC50, 5 × 10?8 M) and muscarine (EC50, 6 × 10?8 M) and blocked by the classical mAChR antagonists atropine, scopolamine, and 3-quinuclidinyl-benzilate (QNB), while the other (the B-type; encoded by gene CG7918) is also activated by acetylcholine, but has a 1,000-fold lower sensitivity to muscarine, and is not blocked by the antagonists. A- and B-type mAChRs were also cloned and functionally characterized from the red flour beetle Tribolium castaneum. Recently, Haga et al. (Nature 2012, 482: 547–551) published the crystal structure of the human m2 mAChR, revealing 14 amino acid residues forming the binding pocket for QNB. These residues are identical between the human m2 and the D. melanogaster and T. castaneum A-type mAChRs, while many of them are different between the human m2 and the B-type receptors. Using bioinformatics, one orthologue of the A-type and one of the B-type mAChRs could also be found in all other arthropods with a sequenced genome. Protostomes, such as arthropods, and deuterostomes, such as mammals and other vertebrates, belong to two evolutionarily distinct lineages of animal evolution that split about 700 million years ago. We found that animals that originated before this split, such as cnidarians (Hydra), had two A-type mAChRs. From these data we propose a model for the evolution of mAChRs. 相似文献