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31.
1.  Up to 9 kHz, the tympanal membrane of the grasshopper Chorthippus biguttulus responds with equal sensitivity at the attachment sites of the low and the high-frequency receptors; at the latter site it is also particularly sensitive between 10 and 20 kHz.
2.  The frequency spectra of the songs of both sexes exhibit maxima at 7–8 kHz, to which the membrane is well matched. In the high-frequency region, where the male songs have a peak at 30 kHz, there is no corresponding maximum in the membrane oscillation.
3.  Because the tympanal membrane is immediately adjacent to air sacs in the tracheal system, it is deflected inward and outward by as much as 80 m during the respiratory cycle.
4.  Measurements by laser vibrometry show that acoustically induced membrane oscillations are attenuated severely due to the respiratory displacement of the membrane for frequencies up to 10–12 kHz. By contrast, at higher frequencies the membrane sensitivity is doubled or tripled.
5.  As a result of these membrane effects, the discharge in the tympanal nerve was profoundly reduced in the low-frequency range, whereas above 11 kHz there was a marked increase. This modulation of auditory sensitivity affects the animals' ability to detect conspecific songs.
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32.
The 13C resonances of Nα,N-[13C]dimethylserine of partially 13C reductively methylated glycophorin AM were monitored as a function of pH at 45°C. For comparison, limited data are also presented for the pH dependence of the 13C resonances of Nα,N- [13C]dimethylserine of fully 13C reductively methylated deglycosylated glycophorin AM. The ‘major’ component of Nα,N- [13C]dimethylserine of glycophorin AM did not titrate, whereas the ‘minor’ component titrated with a pKa of 7.80 (Hill coefficient of 0.95). Similar results are also indicated for the Nα,N- [13C]dimethylserine resonances of 13C reductively methylated deglycosylated glycophorin AM.  相似文献   
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Limited chymotryptic cleavage of soluble chicken gizzard desmin protofilaments allows the characterization of three structurally distinct domains. A surface-exposed very basic amino-terminal region (the headpiece) with an amino acid sequence excluding a-helical organization (7.5 kd) is separated from the perhaps globular carboxy-terminal 48 residues (the tailpiece) by a distinctly different middle domain of approximately 330 residues. This 38 kd domain is very rich in α-helix (at least 83%), and electron microscopy reveals a thin rod with a length of 500 ± 50 Å. Amino acid sequence data also show that the rod domain is interrupted by a nonhelical portion. An a-helical array is able to form a coiled-coil spanning the carboxy-terminal half of the 38 kd domain. The a-type diffraction pattern of 10 nm filaments arises from a coiled-coil conformation displayed through most but not all of the middle domain of the protofilaments.  相似文献   
35.
Three strains (2ac9, 3ac10 and 4ac11) of oval to rodshaped, Gram negative, nonsporing sulfate-reducing bacteria were isolated from brackish water and marine mud samples with acetate as sole electron donor. All three strains grew in simple defined media supplemented with biotin and 4-aminobenzoic acid as growth factors. Acetate was the only electron donor utilized by strain 2ac9, while the other two strains used in addition ethanol and/or lactate. Sulfate served as electron acceptor and was reduced to H2S. Complete oxidation of acetate to CO2 was shown by stoichiometric measurements with strain 2ac9 in batch cultures using sulfate, sulfite or thiosulfate as electron acceptors. With sulfate an average growth yield of 4.8 g cell dry weight was obtained per mol of acetate oxidized; with sulfite or thiosulfate the growth yield on acetate was about twice as high. None of the strains contained desulfoviridin. In strain 2ac9 cytochromes of the b- and c-type were detected. Strain 2ac9 is described as type strain of the new species and genus, Desulfobacter postgatei.  相似文献   
36.
Archives of Microbiology - A new strictly anaerobic, polarly flagellated, sporing, acetate-oxidizing, sulfate-reducing bacterium was isolated from anaerobic fresh or sea water mud samples. The...  相似文献   
37.
A procedure is described which inserts asymmetrically cerebroside sulfate (‘sulfatide’) into the outer leaflet of bilayered phospholipid vesicles. Cerebroside sulfate is adsorbed onto a cellulose, filter-paper support and, when incubated with phosphatidylcholine vesicles is transferred to and inserted into the outer leaflet of these vesicles. This transfer occurs at, or above the transition temperature of the phospholipid and follows a similar pattern with small or larger (‘fused’) unilamellar vesicles. The transfer is linear with time for 1–2 h and is maximal after about 6 h, when the sulfatide content reaches about 6 mol% of the total quantity of phospholipid, corresponding to about 10 mol% of the phospholipids present in the outer layer. Initial rates of sulfatide transfer were somewhat increased when the vesicles contained a positively charged lipid (e.g. stearylamine) and decreased when this lipid was negatively charged (e.g. dicetyl phosphate) or hydrophobic (e.g. cholesterol). Divalent ions markedly inhibited sulfatide transfer and monovalent ions did so to a lesser degree. Once incorporated into the outer leaflet of the vesicle, the sulfatide could not be removed by washing with buffer, 1 M NaCl or 1 M urea.  相似文献   
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In order to titrate and understand the role of arginyl residues of D-β-hydroxybutyrate dehydrogenase, arginyl specific reagents: butanedione, 1,2-cyclohexanedione and phenylglyoxal were incubated with three different forms of the enzyme; native enzyme (inner mitochondrial membrane bound), purified apoenzyme (phospholipid -free) and phospholipid-enzyme complex (reconstituted active form).After complete inactivation of the enzyme by [14C]-phenylglyoxal, the number of modified arginyl residues was different: one with the lipid-free apoenzyme and three with the phospholipid-enzyme complex, suggesting a conformational change of the enzyme triggered by the presence of phospholipids.After exhaustive chemical modification either of the apoenzyme or of the phospholipid-enzyme complex with [14C]-phenylglyoxal, four arginyl residues were titrated indicating that these residues are located in the hydrophilic part of the enzyme, not interacting with phospholipids.Reconstituted enzyme inactivated by butanedione could no longer bind a pseudosubstrate (succinate) which indicates that an arginyl residue is involved in the enzyme-substrate complex formation.The values of second order rate constants of D-β-hydroxybutyrate dehydrogenase inactivation by butanedione and 1,2-cyclohexanedione were unchanged with the three enzyme forms, suggesting that phospholipids are not involved in the substrate binding mechanism.  相似文献   
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