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111.
Wim E. J. M. Ghijsen Elly Besselsen Vincent Geukers Willem Kamphuis Fernando H. Lopes da Silva 《Journal of neurochemistry》1992,59(2):482-486
The effect of long-term potentiation (LTP) on endogenous amino acid release from rat hippocampus slices was studied. LTP was induced in vivo by application of a tetanus (200 Hz, 200 ms) to the Schaffer collateral fibers in unanesthetized rats. Endogenous release of glutamate and gamma-aminobutyric acid (GABA) was investigated 60 min after tetanization in CA1 subslices of potentiated and control rats. No significant effects of LTP were observed in basal and K(+)-induced Ca(2+)-independent release components of these amino acids. In contrast, K(+)-induced Ca(2+)-dependent release of both glutamate and GABA increased approximately 100% in slices from potentiated rats. No differences were observed in total content of glutamate and GABA between the subslices from control and LTP animals. These results suggest a persistent increase in the recruitment of the presynaptic vesicular pool of glutamate and GABA during LTP. 相似文献
112.
J Fuentes Mota J Fernández-Bola?os Guzmán J M García Fernández W Moreda C Ortiz M A Pradera I Robina C Welsh 《Carbohydrate research》1992,232(1):47-57
The preparation of 2,3,4-tri-O-benzyl- (3), 2,3,4-tri-O-acetyl- (4), and 2,3,4-tri-O-benzoyl-N-(2,2-diethoxycarbonylvinyl)-6-O-trityl-beta- D-glucopyranosylamine (5) is described. The reaction of 3-5 with 2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyl bromide yields 2,3,4-tri-O-benzyl- (9), 2,3,4-tri-O-acetyl- (10), and 2,3,4-tri-O-benzoyl-N-(2,2-diethoxycarbonylvinyl)-6-O-(2,3,4,6-tet ra-O- acetyl-beta-D-glucopyranosyl)-beta-D-glucopyranosylamine (11), respectively. 2,3,4-Tri-O-benzyl- (6), 2,3,4-tri-O-acetyl- (7), and 2,3,4-tri-O- benzoyl-N-(2,2-diethoxycarbonylvinyl)-beta-D-glucopyranosylamine (8) are also described. 相似文献
113.
V P Miller G D DePillis J C Ferrer A G Mauk P R Ortiz de Montellano 《The Journal of biological chemistry》1992,267(13):8936-8942
Recombinant cytochrome c peroxidase (CcP) and a W51A mutant of CcP, in contrast to other classical peroxidases, react with phenylhydrazine to give sigma-bonded phenyl-iron complexes. The conclusion that the heme iron is accessible to substrates is supported by the observation that CcP and W51A CcP oxidize thioanisole to the racemic sulfoxide with quantitative incorporation of oxygen from H2O2. Definitive evidence for an open active site is provided by stereoselective epoxidation by both enzymes of styrene, cis-beta-methylstyrene, and trans-beta-methylstyrene. trans-beta-methylstyrene yields exclusively the trans-epoxide, but styrene yields the epoxide and phenylacetaldehyde, and cis-beta-methylstyrene yields both the cis- and trans-epoxides and 1-phenyl-2-propanone. The sulfoxide, stereoretentive epoxides, and 1-phenyl-2-propanone are formed by ferryl oxygen transfer mechanisms because their oxygen atom derives from H2O2. In contrast, the oxygen in the trans-epoxide from the cis-olefin derives primarily from molecular oxygen and is probably introduced by a protein cooxidation mechanism. cis-[1,2-2H]-1-Phenyl-1-propene is oxidized to [1,1-2H]-1-phenyl-2-propanone without a detectable isotope effect on the epoxide:ketone product ratio. The phenyl-iron complex is not formed and substrate oxidation is not observed when the prosthetic group is replaced by delta-meso-ethylheme. CcP thus has a sufficiently open active site to form a phenyl-iron complex, to oxidize thioanisole to the sulfoxide, and to epoxidize styrene and beta-methylstyrene. The results indicate that a ferryl (Fe(IV) = O)/protein radical pair can be coupled to achieve two-electron oxidations. The unique ability of CcP to catalyze monooxygenation reactions does not conflict with its peroxidase function because cytochrome c is oxidized at a distinct surface site (DePillis, G. D., Sishta, B. P., Mauk, A. G., and Ortiz de Montellano, P. R. (1991) J. Biol. Chem. 266, 19334-19341). 相似文献
114.
Membrane fusion activity of the influenza virus hemagglutinin: interaction of HA2 N-terminal peptides with phospholipid vesicles 总被引:7,自引:0,他引:7
M Rafalski A Ortiz A Rockwell L C van Ginkel J D Lear W F DeGrado J Wilschut 《Biochemistry》1991,30(42):10211-10220
We have investigated the interaction of a number of synthetic 20-residue peptides, corresponding to the HA2 N-terminus of the influenza virus hemagglutinin (X31 strain), with phospholipid vesicles and monolayers. Besides the wild-type sequence, two peptides were studied with mutations corresponding to those previously studied in entire HA's expressed in transfected cells [Gething et al., (1986) J. Cell. Biol. 102, 11-23]. These mutations comprised a single Glu replacement for Gly at the N-terminus ("El" mutant) or at position 4 ("E4") of the HA2 subunit and were shown to produce striking alterations in virus-induced hemolysis and syncytia formation, especially for E1. The X31 "wild-type" (wt) peptide and its E4 variant are shown here to have the capacity to insert into phosphatidylcholine (POPC) large unilamellar vesicle (LUV) membranes in a strictly pH-dependent manner, penetration being marginal at pH 7.4 and significant at pH 5.0. Bilayer insertion was evident from a shift in the intrinsic Trp fluorescence of the wt and E4 peptides and from the induction of calcein leakage from POPC LUV and correlated well with the peptides' ability at pH 5.0 to penetrate into POPC monolayers at initial surface pressures higher than 30 mN/m. By contrast, the E1 peptide was found, at pH 5.0, to bind less tightly to vesicles (assessed by a physical separation method) and to cause much less leakage of POPC LUV than the wt, even under conditions where the peptides were bound to approximately the same extent. Consistent with the correlation between leakage and penetration observed for the wt peptide at pH 5 versus 7, the E1 peptide, even at low pH, showed much less lipid-vesicle-induced shift of its Trp fluorescence than wt, caused a much slower rate of leakage of vesicle contents, and did not insert into POPC monolayers at surface pressures beyond 28.5 mN/m. Circular dichroism spectroscopy measurements of peptides in POPC SUV showed that the conformations of all three peptides are sensitive to pH, but only the wt and E4 peptides became predominantly alpha-helical at acid pH. 相似文献
115.
H C Haspel D C Mynarcik P A Ortiz R A Honkanen M G Rosenfeld 《Molecular endocrinology (Baltimore, Md.)》1991,5(1):61-72
Antibody to the carboxyl-terminal of hexose transporter protein GLUT-1 was used to localize this carrier in normal rat kidney (NRK) cells during D-glucose (Glc) deprivation. Glc-deprivation of NRK cells induces increased hexose transport, inhibits the glycosylation of GLUT-1, and increases the content of both native, 55,000 apparent mol wt (Mr) and aglyco, 38,000 Mr GLUT-1 polypeptides. The distribution of GLUT-1 protein in subcellular fractions isolated from Glc-fed NRK cells shows that the 55,000 Mr polypeptide is most abundant in intracellular membrane fractions. Glc-fed cells that have been tunicamycin treated contain principally the 38,000 Mr GLUT-1 polypeptide, which is found predominantly in intracellular membrane fractions. In Glc-deprived cells the 55,000 Mr GLUT-1 polypeptide localizes predominantly in the Golgi and plasma membrane fractions, whereas the more abundant 38,000 Mr GLUT-1 polypeptide is distributed throughout all membrane fractions. In Glc-deprived but fructose-fed cells only the 55,000 Mr GLUT-1 polypeptide is detected, and it is found predominantly in the plasma membrane and Golgi fractions. The localization of GLUT-1 protein was directly and specifically visualized in NRK cells by immunofluorescence microscopy. Glc-fed cells show little labeling of cell borders and a small punctate juxtanuclear pattern suggestive of localization to the Golgi and, perhaps, endoplasmic reticulum. Glc-fed cells that have been tunicamycin treated show large punctate intracellular accumulations suggestive of localization to distended Golgi and perhaps endoplasmic reticulum. Glc-deprived cells exhibited intense labeling of cell borders as well as intracellular accumulations. Glc-deprived but fructose-fed cells show fewer intracellular accumulations, and the labeling is, in general, limited to the cell borders. Our results suggest that Glc deprivation induces the selective accumulation of GLUT-1 in the plasma membrane of NRK cells. 相似文献
116.
Phospholipid turnover during phagocytosis in human polymorphonuclear leucocytes 总被引:1,自引:0,他引:1
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Merche García Gil Fernando Alonso Vicente Alvarez Chiva Mariano Sánchez Crespo José M. Mato 《The Biochemical journal》1982,206(1):67-72
We have previously observed that the phagocytosis of zymosan particles coated with complement by human polymorphonuclear leucocytes is accompanied by a time- and dose-dependent inhibition of phosphatidylcholine synthesis by transmethylation [García Gil, Alonso, Sánchez Crespo & Mato (1981) Biochem. Biophys. Res. Commun. 101, 740–748]. The present studies show that phosphatidylcholine synthesis by a cholinephosphotransferase reaction is enhanced, up to 3-fold, during phagocytosis by polymorphonuclear cells. This effect was tested by both measuring the incorporation of radioactivity into phosphatidylcholine in cells labelled with [Me-14C]choline, and by assaying the activity of CDP-choline:diacylglycerol cholinephosphotransferase. The time course of CDP-choline:diacylglycerol cholinephosphotransferase activation by zymosan mirrors the inhibition of phospholipid methyltransferase activity previously reported. The extent of incorporation of radioactivity into phosphatidylcholine induced by various doses of zymosan correlates with the physiological response of the cells to this stimulus. This effect was specific for phosphatidylcholine, and phosphatidyl-ethanolamine turnover was not affected by zymosan. The purpose of this enhanced phosphatidylcholine synthesis is not to provide phospholipid molecules rich in arachidonic acid. The present studies show that about 80% of the arachidonic acid generated in response to zymosan derives from phosphatidylinositol. A transient accumulation of arachidonoyldiacylglycerol has also been observed, which indicates that a phospholipase C is responsible, at least in part, for the generation of arachidonic acid. Finally, isobutylmethylxanthine and quinacrine, inhibitors of phosphatidylinositol turnover, inhibit both arachidonic acid generation and phagocytosis, indicating a function for this pathway during this process. 相似文献
117.
Following i.c.v. (intracerebral ventricular) injections ofd,l-[3H]pipecolic acid (PA), it is reabsorbed from the ventricles and redistributed to various brain regions. The highest accumulation is found in three brain regions ipsilateral to the injection site, hippocampus, neocortex, striatum, and in the diencephalon. Following preloading in vivo, the radioactivity is released from hippocampus slices in the perfusion medium after depolarization induced by high K+. During perfusion with a Ca++ free medium containing EGTA, a significant reduction of release is observed.The radioactivity ofd,l-[3H]PA in the brain shows a more rapid phase of decrease from 0 to 2 hours and a slower phase from 2 to 5 hours. At 5 hours, only 28% radioactivity, represented mainly by PA, is left in the brain. Kidney secretion represents the major route of elimination of the injected PA. The presence of -aminoadipic acid both in brain and urine was observed. Probenecid (200 mg/kg) significantly increases the accumulation of i.c.v. injectedd,l-[3H]PA in brain and kidney. The presence of a regional accumulation of PA in certain brain regions, its metabolism in brain, its enhanced retention following probenecid administration and its Ca++ dependent release following high K+ stimulation, all constitute indirect evidence for a neuronal localization of this brain endogenous iminoacid. 相似文献
118.
The catalytic mechanism of cytochrome P-450. Spin-trapping evidence for one-electron substrate oxidation 总被引:3,自引:0,他引:3
O Augusto H S Beilan P R Ortiz de Montellano 《The Journal of biological chemistry》1982,257(19):11288-11295
Cytochrome P-450 is destroyed during catalytic oxidation of several 4-substituted 3,5-bis(ethoxycarbonyl)-2,6-dimethyl-1,4-dihydropyridine substrates. A qualitative correlation has been found between the ability to destroy cytochrome P-450 and the stability of the 4-substituent as a radical. Destruction of the enzyme by the 4-ethyl (DDEP), 4-propyl, and 4-isobutyl analogues is due to transfer of the 4-alkyl group from the substrate to a nitrogen of the prosthetic heme, a process which gives rise to isolable N-alkylprotoporphyrin IX derivatives. Little enzyme destruction is observed when the 4-alkyl group is of low radical stability (methyl, phenyl) and good destruction, but no isolable heme adducts when the 4-substituent is of very high radical stability (isopropyl, benzyl). Spin-trapping studies have established that the 4-ethyl group in DDEP is lost as a radical as a result of oxidation by cytochrome P-450. Of three commonly used spin traps, only alpha-(4-pyridyl-1-oxide) N-tert-butylnitrone was found suitable for such studies. The other spin traps, 5,5-dimethyl-1-pyrroline-N-oxide and alpha-phenyl N-tert-butylnitrone, were found to be ineffective, the latter because it strongly inhibits cytochrome P-450. Hydrogen peroxide formed in situ can support a part of the cytochrome P-450-catalyzed ethyl radical formation and DDEP-dependent self-inactivation. The results provide persuasive evidence that oxidation of the nitrogen in DDEP by cytochrome P-450 proceeds in one-electron steps. Cytochrome P-450 may thus function, at least with certain substrates, as a one-electron oxidant. 相似文献
119.
H-2 loss variant sublines of a sarcoma (M-AS), induced by methylcholanthrene in an (A × A.SW)F1 mouse, were used to study the role of the MHC products in the recognition of MC-TSTA. The two reciprocal variant sublines (M-A and M-S) were found to express the TSTA of the original tumor as shown by cross-reactions in graft rejection experiments performed in (A × A.SW)F1 mice. In the A/Sn and A.SW mice the presence of the reciprocal parental H-2 antigens on the immunizing cells decreased the response against the tumor antigens. An admixture of lymphocytes derived from hyperimmune mice inhibited the outgrowth of the tumor cells. The growth inhibition was mediated by T cells and was H-2 restricted. Cells derived from hyperimmune syngeneic mice inhibited the outgrowth of the variant subline used for immunization but had no effect on the reciprocal variant subline. 相似文献
120.
M.Carmen Aragón Cecilio Giménez Federico Mayor Juan G. Marvizón Fernando Valdivieso 《生物化学与生物物理学报:生物膜》1981,646(3):465-470
Tyrosine uptake by membrane vesicles derived from rat brain has been investigated. The uptake is dependent on an Na+ gradient ([). The uptake is transport into an osmotically active space and not a binding artifact as indicated by the effect of increasing the medium osmolarity. The process is stimulated by a membrane potential (negative inside) as demonstrated by the effect of the ionophores valinomycin and carbonyl cyanide and anions with different permeabilities. Kinetic data show that tyrosine is accumulated by two systems with different affinities. Tyrosine uptake is inhibited by the presence of phenylalanine and tryptophan. 相似文献