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991.
Siri Malmgren David G. Nicholls Jalal Taneera Karl Bacos Thomas Koeck Ashkan Tamaddon Rolf Wibom Leif Groop Charlotte Ling Hindrik Mulder Vladimir V. Sharoyko 《The Journal of biological chemistry》2009,284(47):32395-32404
The biochemical mechanisms underlying glucose-stimulated insulin secretion from pancreatic β-cells are not completely understood. To identify metabolic disturbances in β-cells that impair glucose-stimulated insulin secretion, we compared two INS-1-derived clonal β-cell lines, which are glucose-responsive (832/13 cells) or glucose-unresponsive (832/2 cells). To this end, we analyzed a number of parameters in glycolytic and mitochondrial metabolism, including mRNA expression of genes involved in cellular energy metabolism. We found that despite a marked impairment of glucose-stimulated insulin secretion, 832/2 cells exhibited a higher rate of glycolysis. Still, no glucose-induced increases in respiratory rate, ATP production, or respiratory chain complex I, III, and IV activities were seen in the 832/2 cells. Instead, 832/2 cells, which expressed lactate dehydrogenase A, released lactate regardless of ambient glucose concentrations. In contrast, the glucose-responsive 832/13 line lacked lactate dehydrogenase and did not produce lactate. Accordingly, in 832/2 cells mRNA expression of genes for glycolytic enzymes were up-regulated, whereas mitochondria-related genes were down-regulated. This could account for a Warburg-like effect in the 832/2 cell clone, lacking in 832/13 cells as well as primary β-cells. In human islets, mRNA expression of genes such as lactate dehydrogenase A and hexokinase I correlated positively with HbA1c levels, reflecting perturbed long term glucose homeostasis, whereas that of Slc2a2 (glucose transporter 2) correlated negatively with HbA1c and thus better metabolic control. We conclude that tight metabolic regulation enhancing mitochondrial metabolism and restricting glycolysis in 832/13 cells is required for clonal β-cells to secrete insulin robustly in response to glucose. Moreover, a similar expression pattern of genes controlling glycolytic and mitochondrial metabolism in clonal β-cells and human islets was observed, suggesting that a similar prioritization of mitochondrial metabolism is required in healthy human β-cells. The 832 β-cell lines may be helpful tools to resolve metabolic perturbations occurring in Type 2 diabetes. 相似文献
992.
993.
In vitro cultures of prothoracic glands of larvae of Periplaneta americana and of some Lepidoptera as biological tests are described. Incorporation of 3H-5-uridine in the RNA of the prothoracic glands represented the measure of the cellular activity of the glands.Activation factor I separated from extracts of corpora cardiaca of the cockroach Periplaneta americana by means of gel filtration techniques caused significant stimulation of RNA synthesis of the glands. 相似文献
994.
Proline residues in the maturation and degradation of peptide hormones and neuropeptides 总被引:8,自引:0,他引:8
R Mentlein 《FEBS letters》1988,234(2):251-256
The proteases involved in the maturation of regulatory peptides like those of broader specificity normally fail to cleave peptide bonds linked to the cyclic amino acid proline. This generates several mature peptides with N-terminal X-Pro-sequences. However, in certain non-mammalian tissues repetitive pre-sequences of this type are removed by specialized dipeptidyl (amino)peptidases during maturation. In mammals, proline-specific proteases are not involved in the biosynthesis of regulatory peptides, but due to their unique specificity they could play an important role in the degradation of them. Evidence exists that dipeptidyl (amino)peptidase IV at the cell surface of endothelial cells sequesters circulating peptide hormones which are then susceptible to broader aminopeptidase attack. The cleavage of several neuropeptides by prolyl endopeptidase has been demonstrated in vitro, but its role in the brain is questionable since the precise localization of the protease is not clarified. 相似文献
995.
996.
Fragmentation and destruction of natural habitats is currently considered to be the major threat to wildlife populations.
We here perform a comprehensive analysis of the demographic effects of habitat fragmentation and destruction on 14 populations
of the root vole. The experiment was divided into two consecutive periods. During the first period, we contrasted populations
with the same initial size and structure in continuous and fragmented habitat. During the second period, we fragmented the
continuous habitat into the same configuration as the permanently fragmented habitat so that the effect of habitat destruction
could be evaluated. We estimated survival and fecundity parameters and combined them into population projection matrices to
evaluate their relative impact on population growth. In the first period of the experiment there was no difference in population
growth rate between fragmented and continuous populations, although litter size was significantly higher in the continuous
populations. In the second period, we found higher population growth rates in populations that had experienced habitat destruction.
By applying the transition matrix model to empirical estimates of demographic parameters, we demonstrate that the difference
in population growth rate in the second period of the experiment was the result of a nonsignificant difference in adult survival.
Movements out of the habitat patches were significantly lower in populations that had experienced habitat destruction. We
conclude that predator-caused mortality of animals moving out of the habitat patches was the main determinant of demographic
variation in this system.
Received: January 31, 2002 / Accepted: March 25, 2003 相似文献
997.
998.
Halicryptus spinulosus (Priapulida) is extraordinarily resistant to hydrogen sulfide. As described previously, the body wall of specimens from oxic and from hydrogen sulfide-contaminated habitats differs strikingly in colour. In the present paper the ultrastructure of the body wall of specimens kept under oxic conditions is described. These findings serve as a reference for changes induced by exposure to hydrogen sulfide. There are marked ultrastructural differences between epidermal and muscular mitochondria exposed to hydrogen sulfide. Epidermal mitochondria of individuals subjected to hydrogen sulfide are often associated with dense granules of unknown composition. Findings are compared with those from other taxa which may encounter hydrogen sulfide in their environment.Contribution No. 386 of the Alfred-Wegener-Institut für Polar- and Meeresforschung (Awl Bremerhaven). 相似文献
999.
Rolf Nöhring 《Journal of Ornithology》1971,112(2):244-245
Ohne Zusammenfassung 相似文献
1000.