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51.
After a marked decline at the beginning of the 1900s, the arctic fox Alopex lagopus population in Fennoscandia has remained at a very low level. We suggest that the main cause for the population crash was
winter starvation caused by (1) over-hunting of reindeer Rangifer tarandus populations, and thus reduced carcass availability in the mountains, and (2) increased interspecific competition for these
carcasses because of increased invasion of red foxes Vulpes vulpes from lower altitudes. The failure of arctic fox populations to recover, despite increasing reindeer populations in the mid
1900s, can be explained by a concurrent strong increase in red fox numbers. Analyses of countywide hunting statistics from
Norway 1891–1920 suggest that there actually was an increase in red fox numbers in the period of arctic fox decline, and that
the increase in reindeer populations from the 1920s to the 1950s was accompanied by a new increase in red fox numbers. We
conclude that restoring arctic fox populations most likely will require a substantial and lasting reduction of red fox populations. 相似文献
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Caitlin R Ross Dominick S DeFelice Greg J Hunt Kate E Ihle Gro V Amdam Olav Rueppell 《BMC genomics》2015,16(1)
Background
Meiotic recombination has traditionally been explained based on the structural requirement to stabilize homologous chromosome pairs to ensure their proper meiotic segregation. Competing hypotheses seek to explain the emerging findings of significant heterogeneity in recombination rates within and between genomes, but intraspecific comparisons of genome-wide recombination patterns are rare. The honey bee (Apis mellifera) exhibits the highest rate of genomic recombination among multicellular animals with about five cross-over events per chromatid.Results
Here, we present a comparative analysis of recombination rates across eight genetic linkage maps of the honey bee genome to investigate which genomic sequence features are correlated with recombination rate and with its variation across the eight data sets, ranging in average marker spacing ranging from 1 Mbp to 120 kbp. Overall, we found that GC content explained best the variation in local recombination rate along chromosomes at the analyzed 100 kbp scale. In contrast, variation among the different maps was correlated to the abundance of microsatellites and several specific tri- and tetra-nucleotides.Conclusions
The combined evidence from eight medium-scale recombination maps of the honey bee genome suggests that recombination rate variation in this highly recombining genome might be due to the DNA configuration instead of distinct sequence motifs. However, more fine-scale analyses are needed. The empirical basis of eight differing genetic maps allowed for robust conclusions about the correlates of the local recombination rates and enabled the study of the relation between DNA features and variability in local recombination rates, which is particularly relevant in the honey bee genome with its exceptionally high recombination rate.Electronic supplementary material
The online version of this article (doi:10.1186/s12864-015-1281-2) contains supplementary material, which is available to authorized users. 相似文献56.
Vidar Selås Geir A. Sonerud Olav Hjeljord Lars Erik Gangsei Helge B. Pedersen Erik Framstad Tor Kristian Spidsø Øystein Wiig 《European Journal of Wildlife Research》2011,57(3):523-535
The plant stress hypothesis states that plant stress factors other than herbivory improve herbivore performance due to changes
in the content of nutritive or defensive compounds in the plants. In Norway, the bilberry (Vaccinium myrtillus) is important forage for the bank vole (Myodes glareolus) in winter and for the moose (Alces alces) in summer and autumn. The observed peaks in bank vole numbers after years with high production of bilberries are suggested
to be caused by increased winter survival of bank voles due to improved forage quality. High production of bilberries should
also lead to higher recruitment rates in moose in the following year. We predict, however, that there is an increasing tendency
for a 1-year delay of moose indices relative to vole indices with decreasing summer temperatures, because low temperatures
prolong the period needed by plants to recover in the vole peak year, and thus positively affect moose reproduction also in
the succeeding year. In eight out of nine counties in south-eastern Norway, there was a positive relationship between the
number of calves observed per female moose during hunting and a bilberry seed production index or an autumn bank vole population
index. When dividing the study area into regions, there was a negative relationship between a moose-vole time-lag index and
the mean summer temperature of the region. These patterns suggest that annual fluctuations in the production of bilberries
affect forage quality, but that the effect on moose reproduction also depends on summer temperatures. 相似文献
57.
Koji Murashita Ann-Elise Olderbakk Jordal Tom Ole Nilsen Sigurd Olav Stefansson Tadahide Kurokawa Björn Thrandur Björnsson Anne-Grethe Gamst Moen Ivar Rønnestad 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2011,158(1):79-86
Leptin (Lep) is a key factor for the energy homeostasis in mammals, but the available data of its role in teleosts are not conclusive. There are large sequence differences among mammalian and teleost Lep, both at the gene and protein level. Therefore, in order to characterize Lep function in fish, the use of species-specific Lep is crucial. In this study, the cDNA sequence of salmon leptin a1 (lepa1) was used to establish a production protocol for recombinant salmon LepA1 (rsLepA1) in Escherichia coli, that enabled a final yield of 1.7 mg pure protein L?1 culture. The effects of 20-day administration of rsLepA1 on growth and brain neuroendocrine peptide gene expression [npy, cart, agrp (-1 and -2), pomc (-a1, -a2, -a2s, and -b)] were studied in juvenile, immature Atlantic salmon (96.5 ± 2.1 g) fed a commercial diet to satiation. Intraperitoneal osmotic pumps were used to deliver rsLepA1 at four different concentrations (calculated pumping rates were 0, 0.1, 1.0 and 10 ng g?1 h?1). In the highest dosage group (10 ng g?1 h?1), the growth rate was significantly reduced, and pomc-a1 gene expression was higher than in controls. The results support the lipostatic hypothesis and suggest that sLepA1 reduces growth in Atlantic salmon by affecting food intake through the central pro-opiomelanocortin pathway. 相似文献
58.
Kristin Tøndel Ulf G Indahl Arne B Gjuvsland Jon Olav Vik Peter Hunter Stig W Omholt Harald Martens 《BMC systems biology》2011,5(1):1-17
Background
Network inference methods reconstruct mathematical models of molecular or genetic networks directly from experimental data sets. We have previously reported a mathematical method which is exclusively data-driven, does not involve any heuristic decisions within the reconstruction process, and deliveres all possible alternative minimal networks in terms of simple place/transition Petri nets that are consistent with a given discrete time series data set.Results
We fundamentally extended the previously published algorithm to consider catalysis and inhibition of the reactions that occur in the underlying network. The results of the reconstruction algorithm are encoded in the form of an extended Petri net involving control arcs. This allows the consideration of processes involving mass flow and/or regulatory interactions. As a non-trivial test case, the phosphate regulatory network of enterobacteria was reconstructed using in silico-generated time-series data sets on wild-type and in silico mutants.Conclusions
The new exact algorithm reconstructs extended Petri nets from time series data sets by finding all alternative minimal networks that are consistent with the data. It suggested alternative molecular mechanisms for certain reactions in the network. The algorithm is useful to combine data from wild-type and mutant cells and may potentially integrate physiological, biochemical, pharmacological, and genetic data in the form of a single model. 相似文献59.
Gerard C. Van Stein Gerard Van Koten Hans Passenier Olav Steinebach Kees Vrieze 《Inorganica chimica acta》1984,89(2):79-87
The reactions of the dianionic [(pyrrole-2-CHN)2R]2? ligands [(N′2N2)2?] (R = (R)(S)-1,2-cyclohexane or 1,2-ethane) with Zn(II) yield neutral dimeric [Zn2(N′2N2)2] complexes. The dimeric nature of the complexes was established by field-desorption mass spectrometry. 1H NMR studies show that these complexes have dimeric structures in solution in which the (N′2N2)2? ligands act as di-bidentates.The metal centres have tetrahedral geometries and bot have Δ or Λ configurations. The complex with the (R)(S)-1,2-cyclohexanediyl bridges has a rigid structure in solution. Neither intermolecular nor intramolecular exchange processes are observed The 1H NMR spectrum of the complex with the 1,2-ethanediyl bridging groups shows that at 213 K in CDCl3 a fast conformational movement is already taking place between two identical structures of the complex. It is not possible to determine whether in this complex intermolecular exchange processes are also taking place.The reactions of the anionic [pyrrole-2-CHNR′]? ligands [(N′N)?] (R′ = t-Bu, i-Pr, (S)-CHMePh or 2,6-xylyl) with Zn(II) yield the neutral Zn(N′N)2 complexes. These complexes were synthesized to study the coordination properties of the [pyrrole-2-CHNR′]? moieties with Zn(II). A 1H NMR study established that the zinc centres in the complexes containing the prochiral i-Pr or chiral (S)-CHMePh substituents have tetrahedral geometries with Δ or Λ configurations in CDCl3 at 213 K. These complexes undergo an intramolecular exchange process at higher temperatures (above 260 K when R′ = i-Pr) which involves inversion of the configuration of the zinc centre. A mechanism for this exchange process is proposed. 相似文献
60.
Vesali RF Klaude M Rooyackers O Wernerman J 《American journal of physiology. Endocrinology and metabolism》2005,288(2):E360-E364
Decreased plasma amino acid concentrations and increased net release of amino acids from skeletal muscle, especially for glutamine, are common features in critically ill patients. A low dose of endotoxin administered to healthy volunteers was used as a human model for the initial phase of sepsis to study the early metabolic response to sepsis. Six healthy male volunteers were studied in the postabsorptive state. Blood samples from the forearm artery and femoral vein were taken during 4 h before and 4 h after an intravenous endotoxin injection (4 ng/kg body wt). In addition, muscle biopsies from the leg muscle were taken. Plasma concentration of the total sum of amino acids decreased by 19% (P = 0.001) and of glutamine by 25% (P = 0.004) the 3rd h after endotoxin administration. At the same time, muscle concentrations of the sum of amino acids and glutamine decreased by 11% (P = 0.05) and 9% (P = 0.09), respectively. In parallel, the efflux from the leg increased by 35% (P = 0.004) for the total sum of amino acids and by 43% (P = 0.05) for glutamine. In conclusion, intravenous endotoxin administration to healthy volunteers, used as a model for the initial phase of sepsis, resulted in a decrease in plasma amino acid concentrations. At the same time, amino acid concentrations in muscle tissue decreased, whereas the efflux of amino acids from leg skeletal muscle increased. 相似文献