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1.
Carbon and nitrogen stable isotope analyses have improved our understanding of food webs and movement patterns of aquatic
organisms. These techniques have recently been applied to diet studies of elasmobranch fishes, but isotope turnover rates
and isotope diet–tissue discrimination are still poorly understood for this group. We performed a diet switch experiment on
captive sandbar sharks (Carcharhinus plumbeus) as a model shark species to determine tissue turnover rates for liver, whole blood, and white muscle. In a second experiment,
we subjected captive coastal skates (Leucoraja spp.) to serial salinity reductions to measure possible impacts of tissue urea content on nitrogen stable isotope values.
We extracted urea from spiny dogfish (Squalus acanthias) white muscle to test for effects on nitrogen stable isotopes. Isotope turnover was slow for shark tissues and similar to
previously published estimates for stingrays and teleost fishes with low growth rates. Muscle isotope data would likely fail
to capture seasonal migrations or diet switches in sharks, while liver and whole blood would more closely reflect shorter
term movement or shifts in diet. Nitrogen stable isotope values of skate blood and skate and dogfish white muscle were not
affected by tissue urea content, suggesting that available diet–tissue discrimination estimates for teleost fishes with similar
physiologies would provide accurate estimates for elasmobranchs. 相似文献
2.
Combining experimental evolution with whole‐genome resequencing is a promising new strategy for investigating the dynamics of evolutionary change. Published studies that have resequenced laboratory‐selected populations of sexual organisms have typically focused on populations sampled at the end of an evolution experiment. These studies have attempted to associate particular alleles with phenotypic change and attempted to distinguish between different theoretical models of adaptation. However, neither the population used to initiate the experiment nor multiple time points sampled during the evolutionary trajectory are generally available for examination. In this issue of Molecular Ecology, Orozco‐terWengel et al. (2012) take a significant step forward by estimating genome‐wide allele frequencies at the start, 15 generations into and at the end of a 37‐generation Drosophila experimental evolution study. The authors identify regions of the genome that have responded to laboratory selection and describe the temporal dynamics of allele frequency change. They identify two common trajectories for putatively adaptive alleles: alleles either gradually increase in frequency throughout the entire 37 generations or alleles plateau at a new frequency by generation 15. The identification of complex trajectories of alleles under selection contributes to a growing body of literature suggesting that simple models of adaptation, whereby beneficial alleles arise and increase in frequency unimpeded until they become fixed, may not adequately describe short‐term response to selection. 相似文献
3.
4.
Abstract In Trichodesmium contortum , nitrogenase was detected in only a limited number (about 10%) of microscopically distinguishable, consecutively arranged cells in central regions of the trichomes. Cells with nitrogenase also contained the photosystem II associated pigment phycoerythrin. These cells were not distinguishable from other cells on a structural basis, but were clearly visible at low magnification microscopy as all in the zone were more compact and shorter than those on either side. The compartmentalisation of nitrogenase into a chain of cells and in a possibly photosynthetic environment represents a previously undescribed phenomenon. The nitrogenase containing cells apparently perform the O2 protective function of heterocysts yet are different in several aspects. 相似文献
5.
Metabolic activation and toxicity of a DDT-metabolite, 3-methylsulphonyl-DDE, in the adrenal zona fasciculata in mice 总被引:4,自引:0,他引:4
Whole-body autoradiography of 14C-labelled 3-methylsulphonyl-DDE (3-MeSO2-DDE) in female C57BL mice revealed a heavy accumulation in the adrenal cortex. Fairly high radioactivity appeared in the nasal mucosa and fat, while the labelling of the liver was intermediate. The adrenal radioactivity remained largely unextracted in tissue-sections treated with organic solvents. In the liver and intestinal contents the radioactivity was partly extracted, whereas in all other tissues almost completely extracted. According to light microscopic autoradiography, the tissue-bound adrenal radioactivity was confined to the zona fasciculata, leaving the other adrenal zones devoid of bound material. Incubation of 3-MeSO2-DDE with adrenal tissue (300 X g supernatant) revealed a dose- and time-dependent covalent binding to protein and formation of water-soluble metabolites. The cytochrome P-450 inhibitors metyrapone and carbon monoxide inhibited both covalent binding and polar metabolite formation. Addition of reduced glutathione decreased binding, while polar metabolite formation was increased. Histopathological examination of adrenals from 3-MeSO2-DDE-treated mice revealed extensive vacuolation and necrosis of the zona fasciculata 1-12 days after single doses down to 25 mg/kg. Degenerative changes were observed at 12.5 mg/kg. In contrast to 3-MeSO2-DDE, 14C-labelled 3,3'-bis(methylsulphonyl)-DDE was not accumulated in the adrenal cortex. 3-MeSO2-DDE is thus a persistent environmental pollutant with a unique ability to produce acute toxicity subsequent to metabolic activation in a mammalian tissue. 相似文献
6.
The qualitative distribution and quantitative estimates of nitrogenase (EC 1.7.99.2), glutamine synthetase (EC 6.3.1.2), phycoerythrin and ribulose 1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) were studied in the cyanobacterium Nostoc residing in internal cephalodia of the tripartite lichen Nephroma arcticum L. Polyclonal antisera, raised in rabbit against the proteins, and goat anti-rabbit IgG conjugated to 10 nm gold were used as probes to detect the antigens by transmission electron microscopy. Western blot analyses demonstrated the monospecificity of the antisera. Nitrogenase was localized in heterocysts, with vegetative cells showing a label intensity comparable to the background. Distribution of the antigen within the heterocysts was uniform. Glutamine synthetase labelling was very low, but appeared to be distributed in both cell types. An intense phycoerythrin labelling was associated with the thylakoid region of the vegetative cells, whereas a much lower labelling was observed in the heterocyst. No significant differences were found between cyanobionts in younger and older cephalodia except for the nitrogenase labelling, which was higher in heterocysts of the cyanobiont in younger cephalodia. Most of the ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) label was present in vegetative cells. The Rubisco label was pronounced in the carboxysomes, whereas the label in the cytoplasm, on a unit area basis, was much lower. Heterocysts showed a label intensity similar to that of the vegetative cell cytoplasm. In Nostoc of the bipartite lichen Peltigera canina L., the Rubisco protein showed a comparable distribution pattern, but the average number of carboxysomes per vegetative cell was about 4 times higher. 相似文献
7.
Ellen B. Braun-Howland Peter Lindblad Sandra A. Nierzwicki-Bauer Birgitta Bergman 《Planta》1988,176(3):319-322
Transmission electron microscopy and immunocytological labeling were used to study the distribution and ontological occurrence of dinitrogenase reductase (Fe-protein) of nitrogenase in cyanobacterial symbionts within young leaves of the water-ferns Azolla filiculoides Lamarck, A. caroliniana Willdenow, and A. pinnata R. Brown. Rabbit anti-dinitrogenase reductase antisera and goat anti-rabbit-immunoglobulin G antibody conjugated to colloidal gold were used as probes. Western blot analyses showed that a polypeptide of approx. 36 kDa (kdalton) was recognized in the symbionts of all three Azolla species and that the polyclonal sera used were monospecific. In all symbionts, nitrogenase was immunologically recognizable within heterocysts. It was absent from vegetative cells, and also from the akinetes of the A. caroliniana and A. pinnata symbionts. The differentiation of vegetative cells into heterocysts in all three symbionts was initiated by formation of additional external cell-wall layers and narrowing of the neck followed by loss of glycogen, mild vesiculation of thylakoid membranes, and the appearance of polar nodules. No nitrogenase was detected at these early stages, but it appeared in the intermediate proheterocyst stage concomitantly with the formation of contorted membranes, and reached the strongest labeling in mature heterocysts, containing extensive tightly packed membranes. Nitrogenase was evenly distributed throughout heterocysts except at the polar regions, which contained honey-comb configurations and large polar nodules. With increased age of the A. caroliniana and A. pinnata symbionts, heterocysts became highly vesiculated, with a concomitant decrease in the amount of nitrogenase detected.Abbreviations IgG
Immunoglobulin G
- PAGE
polyacrylamide gel electrophoresis
- SDS
sodium dodecyl sulfate
- TEM
transmission electron micrograph 相似文献
8.
9.
Antinociception of imipramine (I) and its effect in combination with fentanyl (F) was evaluated in rabbits using electrically-induced lick chew responses via tooth pulp stimulation as the model of nociception. Acute i.v. injections of I elicited a graded dose response comparable to i.v. morphine (M) with I ED 50 = 4.35 mg/kg (2.31-8.14, 95% CL) and M ED 50 = 1.81 mg/kg (1.11-3.90), with no differences in the slopes between the two curves. The lethal dose of I was 10 mg/kg. An i.v. dose of I twice the ED 50 elicited an antinociceptive effect of more than 50% maximum possible effect (MPE) for 90 minutes with peak effect of 82% MPE occurring at 15 minutes. These effects of I were not reversed by a morphine-reversal dose of naloxone (0.1 mg/kg i.v.) but were reversed with a ten fold dose of naloxone. F ED 50 values (mcg/kg) were lowered from 11.35 to 2.70, 0.74 and 0.33 with increasing pretreatment doses of I (1.0, 2.1 and 3.2 mg/kg). These magnitudes of potency increases of F were 4.2, 15.3 and 34.4 fold respectively. A single i.v. ED 50 dose of I extended the time to 50% MPE of an ED 90 dose of F from 26 minutes to 77 minutes; of a 2 X ED 50 dose of F from 17 minutes to 28 minutes. Data points for three different combinations of I and F fell significantly within the synergistic field of an ED 50 isobologram and a polynomial equation described the curve best fitting the data points. F alone (i.v. ED 50 dose) increased the PaCO2 values to 74% above controls and three different combinations with I showed no increases in PaCO2 values above controls. I alone did not significantly cause any change in PaCO2 values from controls. 相似文献
10.
The release of endogenous acetylcholine and dopamine and the appearance of their metabolites, choline and dihydroxyphenylacetic acid (DOPAC), from neostriatal slices prepared from Fischer 344 rats was examined under various experimental conditions. There was a dose-dependent increase in the amount of neurotransmitter or metabolite as the medium potassium concentration was increased from 5 to 50 mM. Over an eight minute period in Krebs Ringer bicarbonate buffer containing 25 mM potassium, the rate of release of acetylcholine was 6 to 13 times greater than that of dopamine. The dopamine endogenous to the slice preparation appeared to have little effect on the release of endogenous acetylcholine since manipulations that significantly altered dopamine release (depletion with 6-hydroxydopamine or uptake inhibition with nomifensine) had minimal effects on the cholinergic neurons. In contrast, increasing the endogenous acetylcholine in the preparation by inhibiting acetylcholinesterase resulted in a 1.2 to 12 fold increase in dopamine release depending upon the incubation time and the potassium concentration. These studies indicate that within the neostriatal slices there is minimal influence of the endogenous dopamine on the cholinergic neurons, whereas the extracellular acetylcholine can influence dopamine release when its concentration is increased by inhibition of acetylcholinesterase. 相似文献