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191.
Neural stem cells confer unique pinwheel architecture to the ventricular surface in neurogenic regions of the adult brain 总被引:5,自引:0,他引:5
Mirzadeh Z Merkle FT Soriano-Navarro M Garcia-Verdugo JM Alvarez-Buylla A 《Cell Stem Cell》2008,3(3):265-278
Neural stem cells (NSCs, B1 cells) are retained in the walls of the adult lateral ventricles but, unlike embryonic NSCs, are displaced from the ventricular zone (VZ) into the subventricular zone (SVZ) by ependymal cells. Apical and basal compartments, which in embryonic NSCs play essential roles in self-renewal and differentiation, are not evident in adult NSCs. Here we show that SVZ B1 cells in adult mice extend a minute apical ending to directly contact the ventricle and a long basal process ending on blood vessels. A closer look at the ventricular surface reveals a striking pinwheel organization specific to regions of adult neurogenesis. The pinwheel's core contains the apical endings of B1 cells and in its periphery two types of ependymal cells: multiciliated (E1) and a type (E2) characterized by only two cilia and extraordinarily complex basal bodies. These results reveal that adult NSCs retain fundamental epithelial properties, including apical and basal compartmentalization, significantly reshaping our understanding of this adult neurogenic niche. 相似文献
192.
Carvalho JE Gomes FR Navas CA 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2008,178(4):447-456
Anuran amphibians exhibit different patterns of energy substrate utilization that correlate with the intensity of vocal and
locomotor activities. Given the remarkable differences among species in breeding and feeding strategies, and the different
ways energy is used in the whole animal, the suggested correlations between calling and locomotor behavior and the level of
energy substrates in the muscles responsible for such activities are more complex than previously reported. We explored the
relationships between calling and locomotor behavior and energy supply to trunk and hindlimb muscles, respectively, within
the ecologically diverse tree-frog genus Scinax. Specifically, we measured the relative amount of carbohydrates and lipids in these two groups of muscles, and in the liver
of three species of Scinax that differ in vocal and locomotor performance, and compared our results with those of two other species for which comparable
data are available. We also compared the contents of lipids and carbohydrates of conspecific males collected at the beginning
and after 4 h of calling activity. The stomach content to potential feeding opportunities across species was also assessed
in both groups of males. Scinax hiemalis and S. rizibilis exhibit comparatively low and episodic calling during long periods of activity whereas S. crospedospilus calls at higher rates over shorter periods. Male S. hiemalis had highest levels of trunk muscle glycogen followed by those of S. rizilbilis and S. crospedospilus, respectively. There was no correlation between total lipid content in trunk muscle and calling rate among different species,
suggesting that other metabolic aspects may be responsible for the energetic support for vocal activity. The levels of lipids
and carbohydrates in trunk and hindlimb muscles and liver of males collected at the beginning and 4 h into the calling period
were similar across species, so the extent of energetic reserves does not appear to constrain vocal or locomotor activity.
Finally, we found exceptionally high levels of carbohydrates and lipids in the liver of S. rizibilis, a trait perhaps related to a long and demanding breeding period. 相似文献
193.
Ramos DR García MV Canle L M Santaballa JA Furtmüller PG Obinger C 《Journal of inorganic biochemistry》2008,102(5-6):1300-1311
Myeloperoxidase (MPO) is a dominating enzyme of circulating polymorphonuclear neutrophils that catalyzes the two-electron oxidation of chloride, thereby producing the strong halogenating agent hypochlorous acid (ClO−/HOCl). In absence of MPO the tripeptide Pro-Gly-Gly reacts with HOCl faster than the amino acid taurine (2-aminoethanesulfonic acid, Tau), while the MPO-mediated chlorination shows reverse order. A comparative study of the enzymatic oxidation of both substrates at pH 4.0–6.0, varying H2O2 concentration is presented. Initial and equilibrium rates studies have been carried on, reaction rates in the latter being slower due to the chemical equilibrium between MPO-I and MPO-II–HO2. A maximum of chlorination rate is observed for Pro-Gly-Gly and Tau when [H2O2] ≈ 0.3–0.7 mM and pH ≈ 4.5–5.0. Several mechanistic possibilities are considered, the proposed one implies that chlorination takes place via two pathways. One, for bulkier substrates, involves chlorination by free HOCl outside the heme cavity; ClO− is released from the active center, diffuses away the heme cavity, and undergoes protonation to HOCl. The other implies the existence of compound I–Cl− complex (MPO-I–Cl), capable of chlorinating smaller substrates in the heme pocket. Electronic structure calculations show the size of Pro-Gly-Gly comparable to the available gap in the substrate channel, this tripeptide being unable to reach the active site, and its chlorination is only possible by free HOCl outside the enzyme. 相似文献
194.
Rodolfo Martínez-Mota Carolina Valdespino Juan Arturo Rivera Rebolledo Rupert Palme 《International journal of primatology》2008,29(5):1365-1373
Measuring fecal glucocorticoid metabolites is now a common practice to assess the stress response in primates. Nevertheless,
it is important to validate the utilized immunoassay for each primate species before the technique is applied to populations
in the wild. We determined the stress response of black howlers (Alouatta pigra) via 2 different group-specific enzyme immunoassays (EIAs). 11-oxoetiocholanolone EIAs are suited to assess the stress response
of black howlers via fecal glucocorticoid metabolites. Levels of fecal glucocorticoid metabolites increased after we applied
a stressor, i.e. anesthesia, reaching peak concentrations 24–96 h poststressor. Both basal and stress-induced fecal glucocorticoid
metabolite levels showed individual variations. The increase of fecal glucocorticoid metabolites after the stressor (paralleling
increases in serum) indicates that one can effectively measure adrenocortical activity in Alouatta pigra via these 2 enzyme immunoassays. However, it is important to consider individual variations in the excretion of fecal glucocorticoid
metabolites when planning field endocrinological research on Alouatta pigra. Fecal glucocorticoid metabolite excretion takes 1–3 d poststressor depending on the individual. Further, there is an important
individual variability in the concentrations of glucocorticoid metabolites, which might reflect differences in stress reactivity
or fecal glucocorticoid metabolite metabolism and excretion. 相似文献
195.
Cell pattern generation has a fundamental role in both artificial and natural development. This paper presents results from a model in which a genetic algorithm (GA) was used to evolve an artificial regulatory network (ARN) to produce predefined 2D cell patterns through the selective activation and inhibition of genes. The ARN used in this work is an extension of a model previously used to create simple geometrical patterns. The GA worked by evolving the gene regulatory network that was used to control cell reproduction, which took place in a testbed based on cellular automata (CA). After the final chromosomes were produced, a single cell in the middle of the CA lattice was allowed to replicate controlled by the ARN found by the GA, until the desired cell pattern was formed. The model was applied to the problem of generating a French flag pattern. 相似文献
196.
197.
We initiated a study of the effects of mycorrhizal fungal community composition on the restoration of tropical dry seasonal forest trees. Tree seedlings were planted in a severely burned experimental site (1995 fire) during the growing season of 1998 at the El Edén Ecological Reserve, in north Quintana Roo, Mexico. Seedlings of Leucaena leucocephala, Guazuma ulmifolia, Caesalpinia violacea, Piscidia piscipula, Gliricidia sepium, and Cochlospermum vitifolium were germinated in steam‐sterilized soil and either remained uninoculated (nonmycorrhizal at transplanting) or were inoculated with mycorrhizal fungi in soils from early‐seral (recently burned) or late‐seral (mature forest) inoculum. Inoculum from the early‐seral soil was largely Glomus spp., whereas a diverse community of arbuscular mycorrhizal fungi were reintroduced from the mature forest including species of Scutellospora, Gigaspora, Glomus, Sclerocystis, and Acaulospora. Plants grew better when associated with the mature forest inoculum, unlike a previous experiment in which plants grew taller with the early‐seral inoculum. Reasons for the different responses include a less‐intense burn resulting in more residual organic matter. In addition to mycorrhizal responses, plants were severely affected by deer browsing. One tree species, C. vitifolium found in the region but not in the reserve, was eliminated by a resident fungal facultative pathogen. Several practical conclusions for restoration can be made. The common nursery practice of soil sterilization may be detrimental because it eliminates beneficial mycorrhizal fungi; species not native to the site may not survive because they may not be adapted to the local pathogens; and herbivory can be severe depending on the landscape context of the restoration. 相似文献
198.
Tuya Fernando Boyra Arturo Sanchez-Jerez Pablo Barbera Carmen Haroun Ricardo 《Hydrobiologia》2004,519(1-3):211-214
We sampled 36 coastal rocky reefs throughout the overall Canarian Archipelago and consider (1) the daily macroalgal consumption of the long-spined sea urchin Diadema antillarum and (2) the daily net production of macroalgae along temperate rocky-substrates, to provide evidence that Diadema antillarum plays an important role in the structure of the shallow benthic environment of the eastern Atlantic. D. antillarum was found to be the main key-herbivore species, as it controls by its own the algal assemblages, with negligible contribution of other grazing species. 相似文献
199.
The Ku autoantigen is a heterodimeric protein of 70- and 83-kDa subunits, endowed with duplex DNA end-binding capacity and DNA helicase activity (Human DNA Helicase II, HDH II). HDH II/Ku is well established as the DNA binding component, the regulatory subunit as well as a substrate for the DNA-dependent protein kinase DNA-PK, a complex involved in the repair of DNA double-strand breaks and in V(D)J recombination in eukaryotes. The effects of phosphorylation by this kinase on the helicase activity of Escherichia coli-produced HDH II/Ku were studied. The rate of DNA unwinding by recombinant HDH II/Ku heterodimer is stimulated at least fivefold upon phosphorylation by DNA-PKcs. This stimulation is due to the effective transfer of phosphate residues to the helicase rather than the mere presence of the complex. In vitro dephosphorylation of HeLa cellular HDH II/Ku caused a significant decrease in the DNA helicase activity of this enzyme. 相似文献
200.
Chiliotrichiopsis peruviana Nesom, H. Rob. & Granda, a new species from Dept. Ayacucho in southwestern Peru, is described and illustrated. It is the
only rayless species of the genus, now expanded to four species, and the only one that occurs outside of Argentina.Chiliotrichiopsis is one of six shrubby South American genera of Astereae (subtribe Hinterhuberinae) with paleate receptacles. Observations
on morphology and a key to these genera provide perspective for the generic placement of the new species. 相似文献