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91.
M K Hoffmann S Koenig R S Mittler H F Oettgen P Ralph C Galanos U Hammerling 《Journal of immunology (Baltimore, Md. : 1950)》1979,122(2):497-502
Peritoneal macrophages of the mouse produce, in response to cell wall components of Gram-negative bacteria (lipopolysaccharide and lipoproteins), a factor that causes antigen-stimulated B cells of differentiate into antibody-producing cells. Unlike lipopolysaccharide, this factor is not mitogenic for B cells. Production of the macrophage factor does not depend on participation of T cells or other accessory cells since it is readily produced by several cloned macrophage cell lines as well as by peritoneal macrophages of athymic nude mice. The factor is active only in conjunction with antigen. T cells, although apparently not necessary, amplify its effect. The factor induces phenotypic differentiation of B cell precursors as selectively as thymopoietin induces differentiation of prothymocytes. 相似文献
92.
DNase Induced After Infection of KB Cells by Herpes Simplex Virus Type 1 or Type 2 II. Characterization of an Associated Endonuclease Activity 下载免费PDF全文
Purified preparations of the "exonuclease" specified by herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) possess an endonuclease activity. The exonuclease and endonuclease activities copurify and cosediment in a sucrose density gradient. Endonuclease activity is only observed in the presence of a divalent cation, and Mg(2+) or Mn(2+) is equally effective as a cofactor with an optimal concentration of 2 mM. A slight amount of endonuclease activity is observed in the presence of Ca(2+), whereas no activity occurs in the presence of Zn(2+). In the presence of Mg(2+), Ca(2+) and Zn(2+) are inhibitory. Comparison of exonuclease and endonuclease activity in the presence of various divalent cations revealed that, at concentrations of Mn(2+) greater than 1 mM, only endonuclease activity occurs whereas endonuclease and exonuclease activity occur at all concentrations of Mg(2+). The endonuclease was affected by putrescine and spermidine to the same extent as the exonuclease activity, but in marked contrast the endonuclease was inhibited by a 10-fold-lower concentration of spermine compared to the exonuclease. The activity specified by HSV-1 and HSV-2 has very similar properties. HSV-1 and HSV-2 endonuclease cleave covalently closed circular DNA to yield, firstly, nicked circles and then linear DNA which is subsequently hydrolyzed to small oligonucleotides. Cleavage does not appear to be base sequence specific. Conversion of nicked circles to linear DNA and subsequent degradation of linear DNA occurs more rapidly in the presence of Mg(2+) than Mn(2+) presumably by virtue of the presence of the exonuclease activity. Nonsuperhelical covalently closed circular duplex DNA is cleaved by the endonucleases at a rate 60 times slower than the rate observed on the supercoiled form. These data indicate that the HSV-1 and HSV-2 endonuclease preferentially recognize single-stranded DNA regions. 相似文献
93.
M K Hoffmann 《Journal of immunology (Baltimore, Md. : 1950)》1978,121(2):619-621
Serum from C3H/HeJ mice in contrast to serum from other mouse strains does not convert EA into EAC. A factor in supportive serum permits nonsupportive C3H/HeJ serum to produce a functional EAC-rosetting reagent. This factor is heat stable. Its concentration in serum parallels the sensitivity of mice to LPS. It is absent or inoperative when sensitivity is reduced on a genetic basis and increased when sensitivity is increased by treatment with BCG. 相似文献
94.
95.
(A-C-B) human proinsulin, a novel insulin agonist and intermediate in the synthesis of biosynthetic human insulin. 总被引:2,自引:0,他引:2
W F Heath R M Belagaje G S Brooke R E Chance J A Hoffmann H B Long S G Reams C Roundtree W N Shaw L J Slieker 《The Journal of biological chemistry》1992,267(1):419-425
The hormone insulin is synthesized in the beta cell of the pancreas as the precursor, proinsulin, where the carboxyl terminus of the B-chain is connected to the amino terminus of the A-chain by a connecting or C-peptide. Proinsulin is a weak insulin agonist that possesses a longer in vivo half-life than does insulin. A form of proinsulin clipped at the Arg65-Gly66 bond has been shown to be more potent than the parent molecule with protracted in vivo activity, presumably as a result of freeing the amino terminal residue of the A-chain. To generate a more active proinsulin-like molecule, we have constructed an "inverted" proinsulin molecule where the carboxyl terminus of the A-chain is connected to the amino terminus of the B-chain by the C-peptide, leaving the critical Gly1 residue free. Transformation of Escherichia coli with a plasmid coding for A-C-B human proinsulin led to the stable production of the protein. By a process of cell disruption, sulfitolysis, anion-exchange chromatography, refolding, and reversed-phase high-performance liquid chromatography, two forms of the inverted proinsulin differing at their amino termini as Gly1 and Met0-Gly1 were identified and purified to homogeneity. Both proteins were shown by a number of analytical techniques to be of the inverted sequence, with insulin-like disulfide bonding. Biological analyses by in vitro techniques revealed A-C-B human proinsulin to be intermediate in potency when compared to human insulin and proinsulin. The time to maximal lowering of blood glucose in the fasted normal rat appeared comparable to that of proinsulin. Additionally, we were able to generate fully active, native insulin from A-C-B human proinsulin by proteolytic transformation. The results of this study lend themselves to the generation of novel insulin-like peptides while providing a simplified route to the biosynthetic production of insulin. 相似文献
96.
H Zorbas T Rein A Krause K Hoffmann E L Winnacker 《The Journal of biological chemistry》1992,267(12):8478-8484
Methylation interference and missing contact analyses demonstrate that nuclear factor I (NF I) recognizes an NF I-like site (5'-GGG(N)6GCCAG-3') within the alpha-globin promoter rather than the adjacent CCAAT box. Consistent with this, mutations within the CCAAT box do not alter significantly the affinity and specificity of the interaction whereas elimination of the 5'-GGG-3' half-site of the recognition sequence reduces the DNA binding strength of NF I by 2 orders of magnitude down to the range of unspecific interaction. On the other hand, the mutated alpha-globin promoter sequence that is no longer bound by NF I, although it retains an intact CCAAT box, interacts specifically with a protein component from nuclear extracts of HeLa cells. From these results we conclude that NF I is not the factor that interacts with the CCAAT box and that the second half of the canonical 5'-TGG(N)6GCCAA-3' NF I binding site cannot be regarded as identical with the CCAAT promoter element, as suggested previously. 相似文献
97.
Duk-Su Koh Peter Jonas Michael E. Bräu Werner Vogel 《The Journal of membrane biology》1992,130(2):149-162
A novel potassium-selective channel which is active at membrane potentials between -100 mV and +40 mV has been identified in peripheral myelinated axons of Xenopus laevis using the patch-clamp technique. At negative potentials with 105 mM-K on both sides of the membrane, the channel at 1 kHz resolution showed a series of brief openings and closings interrupted by longer closings, resulting in a flickery bursting activity. Measurements with resolution up to 10 kHz revealed a single-channel conductance of 49 pS with 105 mM-K and 17 pS with 2.5 mM-K on the outer side of the membrane. The channel was selective for K ions over Na ions (PNa/PK = 0.033). The probability of being within a burst in outside-out patches varied from patch to patch (> 0.2, but often > 0.9), and was independent of membrane potential. Open-time histograms were satisfactorily described with a single exponential (tau o = 0.09 msec), closed times with the sum of three exponentials (tau c = 0.13, 5.9, and 36.6 msec). Sensitivity to external tetraethylammonium was comparatively low (IC50 = 19.0 mM). External Cs ions reduced the apparent unitary conductance for inward currents at Em = -90 mV (IC50 = 1.1 mM). Ba and, more potently, Zn ions lowered not only the apparent single-channel conductance but also open probability. The local anesthetic bupivacaine with high potency reduced probability of being within a burst (IC50 = 165 nM). The flickering K channel is clearly different from the other five types of K channels identified so far in the same preparation. We suggest that this channel may form the molecular basis of the resting potential in vertebrate myelinated axons. 相似文献
98.
Summary Cell-attached patch-clamp recordings from Ehrlich ascites tumor cells reveal nonselective cation channels which are activated by mechanical deformation of the membrane. These channels are seen when suction is applied to the patch pipette or after osmotic cell swelling. The channel activation does not occur instantaneously but within a time delay of 1/2 to 1 min. The channel is permeable to Ba2+ and hence presumably to Ca2+. It seems likely that the function of the nonselective, stretch-activated channels is correlated with their inferred Ca2+ permeability, as part of the volume-activated signal system. In isolated insideout patches a Ca2+-dependent, inwardly rectifying K+ channel is demonstrated. The single-channel conductance recorded with symmetrical 150 mm K+ solutions is for inward current estimated at 40 pS and for outward current at 15 pS. Activation of the K+ channel takes place after an increase in Ca2+ from 10–7 to 10–6
m which is in the physiological range. Patch-clamp studies in cellattached mode show K+ channels with spontaneous activity and with characteristics similar to those of the K+ channel seen in excised patches. The single-channel conductance for outward current at 5 mm external K+ is estimated at about 7 pS. A K+ channel with similar properties can be activated in the cellattached mode by addition of Ca2+ plus ionophore A23187. The channel is also activated by cell swelling, within 1 min following hypotonic exposure. No evidence was found of channel activation by membrane stretch (suction). The time-averaged number of open K+ channels during regulatory volume decrease (RVD) can be estimated at 40 per cell. The number of open K+ channels following addition of Ca2+ plus ionophore A23187 was estimated at 250 per cell. Concurrent activation in cell-attached patches of stretch-activated, nonselective cation channels and K+ channels in the presence of 3 mm Ca2+ in the pipette suggests a close spatial relationship between the two channels. In excised inside-out patches (with NMDG chloride on both sides) a small 5-pS chloride channel with low spontaneous activity is observed. The channel activity was not dependent on Ca2+ and could not be activated by membrane stretch (suction). In cell-attached mode singlechannel currents with characteristics similar to the channels seen in isolated patches are seen. In contrast to the channels seen in isolated patches, the channels in the cell-attached mode could be activated by addition of Ca2+ plus ionophore A23187. The channel is also activated by hypotonic exposure with a single-channel conductance at 7 pS (or less) and with a time delay at about 1 min. The number of open channels during RVD is estimated at 80 per cell. Two other types of Cl– channels were regularly recorded in excised inside-out patches: a voltage-activated 400-pS channel and a 34-pS Cl– channel which show properties similar to the Cl– channel in the apical membrane in human airway epithelial cells. There is no evidence for a role in RVD for either of these two channels. 相似文献
99.
A new simplified procedure for determination of nitric oxide (NO) in biological solutions is described utilizing a new reducing system of nitric oxide prior to chemiluminescence. Advantages of the new method makes heating of the reducing solution unnecessary and avoids cooling and condensation of generated vapors. Only traces of acid with a high boiling point are used. The method permits analysis of small sample volumes (200 microL). The basal production of nitric oxide by freshly harvested endothelial cells ranged from 100 to 880 picomoles. 相似文献
100.
A method was elaborated by which the pH in leaf apoplast can be measured. The technique is based on the pH dependent fluorescence of 5-carboxyfluorescein (5-CF) or fluorescein isothiocyanate (FITC). The fluorescein isothiocyanate is coupled with a macromolecular dextran molecule (FITC-dextran). For eliminating the effect of the absolute dye concentration the dual excitation technique was applied. It was shown that the ratio of fluorescence excited by light of 491 nm and 463 nm was virtually independent of the concentration of 5-CF and that this fluorescence ratio was related to the pH. The plasmalemma is practically impermeable to FITC-dextran and in the test we carried out over a period of 6 h not the slightest indication was found that it may penetrate the plasma membrane. For 5-CF this cannot be ruled out completely. It is possible that at pH values below 4.5 it may penetrate biological membranes at low rates.
Experiments with leaves of sunflower ( Helianthus animus cv. Erika) perfused with 5-carboxyfluorescein and supplied with different nitrogen forms showed that NH+ 4 application resulted in a decrease and NO+ 3 application in an increase of the leaf apoplast pH. Leaf spraying with fasicoccin was followed by a pH decrease, while leaf spraying with the protonophores p -trifluoromethoxy carbonytcyanide phenylhydra-zon (FCCP) or nigericin resulted in neutral apoplastic pH. These results provide evidence that the method is well suited for measuring the response of the leaf apoplast pH to changing physiological conditions. 相似文献
Experiments with leaves of sunflower ( Helianthus animus cv. Erika) perfused with 5-carboxyfluorescein and supplied with different nitrogen forms showed that NH