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31.
The ability of pectins to form gels in the presence of calcium is well-known, and it implies the interaction of carboxylate groups and bivalent ions. However, even when most of the galacturonic units are methyl esterified, pectins are able to form gels but only under certain experimental conditions. In this case, hydrogen bonding and hydrophobic interactions are believed to be responsible for gel formation, and it is likely, as in the other mechanisms of polysaccharide gel formation, that stable junction zones consist of cooperatively ordered chains linked together throughout nonbonded interactions to provide a three-dimensional network. To investigate the junction zones in HM-pectin gels, we investigated, by molecular modeling, all of the ways to associate two, and then three, fully methyl-esterified galacturonic acid chains. Two models are obtained: the first one is based on a packing of parallel chains; it agrees with the hypothetical model derived from fiber diffraction study; the second one displays an antiparallel orientation of the chains; it presents a better arrangement of the chains and, theoretically, a much lower potential energy. In both cases, all of the favorable associations occur within a network of hydrogen bonds and of hydrophobic contacts. 相似文献
32.
The mammalian-type cytochrome c of the basidiomycete Ustilago sphaerogena contains in a single polypeptide chain of 107 residues, two histidine residues located at positions 18 and 33, and one methionine residue situated at position 80 (Bitar et al., 1972). The reaction of Ustilago ferricytochrome c with bromoacetate at neutral pH resulted in the modification of histidine-33, but not of histidine-18 or of the invariant methionine residue. The activities of Ustilago cytochrome c with mitochondrial cytochrome c oxidase and with NADH-cytochrome c reductase were unaltered by the modification. The equilibrium constants for the formation of low-spin complexes of the ferrihaem octapeptide of horse cytochrome c (residues 14-21, including the haem bound covalently to cysteines 14 and 17) with imidazole, N(2)-acetylhistidine and monocarboxymethyl derivatives of N(2)-acetylhistidine were determined spectrophotometrically. Alkylation of the imidazole side-chain group of N(2)-acetylhistidine resulted in a marked decrease in its ability to form low-spin ferrihaem complexes. These results indicate that in Ustilago ferricytochrome c in solution histidine-33 is not involved in the central co-ordination complex. Since side-chain groups of residues other than histidine and methionine do not appear to be involved in the central complexes of other mammalian-type cytochromes c (Hettinger & Harbury, 1964, 1965; Myer & Harbury, 1965) it is likely that in Ustilago ferricytochrome c in solution at neutral pH, the side-chain groups of histidine-18 and methionine-80 are involved in the central co-ordination complex. The latter is stable over the pH range 2.6-8.4. 相似文献
33.
We compare the primary sex ratio (proportion of haploid eggs laid by queens) and the secondary sex ratio (proportion of male pupae produced) in the Argentine ant Iridomyrmex humilis with the aim of investigating whether workers control the secondary sex ratio by selectively eliminating male brood. The proportion of haploid eggs produced by queens was close to 0.5 in late winter, decreased to less than 0.3 in spring and summer, and increased again to a value close to 0.5 in fall. Laboratory experiments indicate that temperture is a proximate factor influencing the primary sex ratio with a higher proportion of haploid eggs being laid at colder temperatures. Production of queen pupae ceased in mid-June, about three weeks before that of male pupae. After this time only worker pupae were produced. During the period of production of sexuals, the proportion of male pupae ranged from 0.30 to 0.38. Outside this period no males were reared although haploid eggs were produced all the year round by queens. Workers thus exert a control on the secondary sex ratio by eliminating a proportion of the male brood during the period of sexual production and eliminating all the males during the remainder of the cycle. These data are consistent with workers preferring a more female-biased sex ratio than queens. The evolutionary significance of the production of male eggs by queens all the year round is as yet unclear. It may be a mechanism allowing queen replacement in the case of the death of the queens in the colony. 相似文献
34.
Induction of alternative oxidase synthesis by herbicides inhibiting branched-chain amino acid synthesis 总被引:4,自引:0,他引:4
Serge Aubert Richard Bligny David A. Day James Whelan Roland Douce 《The Plant journal : for cell and molecular biology》1997,11(4):649-657
Sycamore suspension cells ( Acer pseudoplatanus L.) were incubated in the presence of sulfonylurea and imidazolinone herbicides. These inhibitors of acetolactate synthase (ALS), a key enzyme of branched-chain amino acid synthesis, triggered a dramatic induction of the alternative oxidase (AOX). AOX activity increased in treated cells, eventually exceeding cytochrome (cyt) pathway activity. This induction of AOX activity was correlated with the accumulation of a 35 kDa AOX protein in isolated mitochondria, detected by Western blotting with a monoclonal antibody against Sauromatum guttatum AOX. It was preceded by the accumulation of putative 1.6 kb AOX mRNA, detected using an Aox cDNA probe from soybean. The metabolic perturbations induced by the herbicides rather than the herbicide molecules themselves were responsible for this induction of AOX. However, α-oxobutyrate (one of the substrates of ALS) and its transamination product, α-aminobutyrate, which accumulated after herbicide treatment, were not involved. The inhibition of branched-chain amino acid synthesis was probably somehow responsible for the AOX induction since: (i) a mixture of those amino acids (leucine, isoleucine, valine) prevented AOX induction by ALS inhibitors; (ii) the herbicide Hoe 704, a potent inhibitor of acetolactate reducto-isomerase (the enzyme following ALS in the branched-chain amino acid pathway), also triggered AOX induction. 相似文献
35.
36.
Kazuhiro A. Fujita Marek Ostaszewski Yukiko Matsuoka Samik Ghosh Enrico Glaab Christophe Trefois Isaac Crespo Thanneer M. Perumal Wiktor Jurkowski Paul M. A. Antony Nico Diederich Manuel Buttini Akihiko Kodama Venkata P. Satagopam Serge Eifes Antonio del Sol Reinhard Schneider Hiroaki Kitano Rudi Balling 《Molecular neurobiology》2014,49(1):88-102
Parkinson's disease (PD) is a major neurodegenerative chronic disease, most likely caused by a complex interplay of genetic and environmental factors. Information on various aspects of PD pathogenesis is rapidly increasing and needs to be efficiently organized, so that the resulting data is available for exploration and analysis. Here we introduce a computationally tractable, comprehensive molecular interaction map of PD. This map integrates pathways implicated in PD pathogenesis such as synaptic and mitochondrial dysfunction, impaired protein degradation, alpha-synuclein pathobiology and neuroinflammation. We also present bioinformatics tools for the analysis, enrichment and annotation of the map, allowing the research community to open new avenues in PD research. The PD map is accessible at http://minerva.uni.lu/pd_map. 相似文献
37.
38.
Dispersal is a crucial ecological process, driving population dynamics and defining the structure and persistence of populations. Measuring demographic connectivity between discreet populations remains a long-standing challenge for most marine organisms because it involves tracking the movement of pelagic larvae. Recent studies demonstrate local connectivity of reef fish populations via the dispersal of planktonic larvae, while biogeography indicates some larvae must disperse 100–1000 s kilometres. To date, empirical measures of long-distance dispersal are lacking and the full scale of dispersal is unknown. Here we provide the first measure of long-distance dispersal in a coral reef fish, the Omani clownfish Amphiprion omanensis, throughout its entire species range. Using genetic assignment tests we demonstrate bidirectional exchange of first generation migrants, with subsequent social and reproductive integration, between two populations separated by over 400 km. Immigration was 5.4% and 0.7% in each region, suggesting a biased southward exchange, and matched predictions from a physically-coupled dispersal model. This rare opportunity to measure long-distance dispersal demonstrates connectivity of isolated marine populations over distances of 100 s of kilometres and provides a unique insight into the processes of biogeography, speciation and adaptation. 相似文献
39.
Chu GH Gu M Cassel JA Belanger S Stabley GJ DeHaven RN Conway-James N Koblish M Little PJ DeHaven-Hudkins DL Dolle RE 《Bioorganic & medicinal chemistry letters》2006,16(3):645-648
A novel series of phenylamino acetamide derivatives was synthesized. These amides were shown to be potent and selective kappa opioid receptor agonists. 相似文献
40.
Human metabolic phenotypes link directly to specific dietary preferences in healthy individuals 总被引:1,自引:0,他引:1
Rezzi S Ramadan Z Martin FP Fay LB van Bladeren P Lindon JC Nicholson JK Kochhar S 《Journal of proteome research》2007,6(11):4469-4477
Individual human health is determined by a complex interplay between genes, environment, diet, lifestyle, and symbiotic gut microbial activity. Here, we demonstrate a new "nutrimetabonomic" approach in which spectroscopically generated metabolic phenotypes are correlated with behavioral/psychological dietary preference, namely, "chocolate desiring" or "chocolate indifferent". Urinary and plasma metabolic phenotypes are characterized by differential metabolic biomarkers, measured using 1H NMR spectroscopy, including the postprandial lipoprotein profile and gut microbial co-metabolism. These data suggest that specific dietary preferences can influence basal metabolic state and gut microbiome activity that in turn may have long-term health consequences to the host. Nutrimetabonomics appears as a promising approach for the classification of dietary responses in populations and personalized nutritional management. 相似文献