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771.
Glyoxylate transamination in intact leaf peroxisomes   总被引:2,自引:0,他引:2       下载免费PDF全文
Intact spinach (Spinacia oleracea L.) leaf peroxisomes were supplied with glycolate and one to three of the amino acids serine, glutamate, and alanine, and the amount of the respective α-keto acids formed in glyoxylate transamination was assayed. At 1 millimolar glycolate and 1 millimolar each of the three amino acids in combination, the transamination reaction reached saturation; reduction of either glycolate or amino acid concentration decreased the activity. The relative serine, glutamate, and alanine transamination at equal amino acid concentrations was roughly 40, 30, and 30%, respectively. The three amino acids exhibited mutual inhibition to one another in transamination due to the competition for the supply of glyoxylate. In addition to this competition for glyoxylate, competitive inhibition at the active site of enzymes occurred between glutamate and alanine, but not between serine and glutamate or alanine. Alteration of the relative concentrations of the three amino acids changed their relative transamination. Similar work was performed with intact oat (Avena sativa L.) leaf peroxisomes. At 1 millimolar of each of the three amino acids in combination, the relative serine, glutamate, and alanine transamination was roughly 60, 23, and 17%, respectively. Similarly, alteration of the relative concentration of the three amino acids changed their relative transamination. The contents of the three amino acids in leaf extracts were analyzed, and the relative contribution of the three amino acids in glycine production in photorespiration was assessed and discussed.  相似文献   
772.
An initiation study of mineral oil-induced plasmacytoma (MOPC) 315 heavy chain immunoglobulin (H315) in vitro has been conducted using formyl-[35S]methionyl-tRNAfMet and a highly purified 18 S message from MOPC 315 solid tumor in a crude rabbit reticulocyte lysate system. The product was specifically precipitated by antibodies directed against MOPC 315 immunoglobulin and H315. The in vitro H315 products terminally labeled with formyl-[35S]methionine or internally labeled with [3H]leucine were electrophoretically identical with in vivo H315 on sodium dodecyl sulfate-polyacrylamide gels. All of the [35S]-methionine was incorporated at the NH2 terminus, not internally, since there is a near complete recovery of [35S]methionine following one cycle of Edman degradation. The NH2-terminal cyanogen bromide peptide, CN2, of in vivo and in vitro H315 co-migrated exactly on gel electrophoresis under conditions which completely resolved two proteins differing in size by only 14 amino acids. These data strongly suggest that there is no NH2-terminal precursor of H315 in this system. Cyanogen bromide peptide profiles of in vivo and in vitro H315 were chromatographically indistinguishable. Three peptides, CN1, CN2, and CN4, which represent approximately 85% of the total amino acids of H315 were isolated and further characterized by electrophoresis and paper chromatography. All were very similar to the corresponding peptides of authentic H315. We conclude that the fidelity of H315 translation is preserved in vitro.  相似文献   
773.
The mechanism of enhancement of Ca2+ uptake by the T cell mitogen concanavalin A (Con A) was studied in murine thymocytes. Native Con A enhanced the rate of Ca2+ uptake as much as 9-fold, an increase being observed within five minutes after Con A addition. The effect of Con A was reversed completely by alpha-methyl mannopyranoside (alpha-MM). Increased Ca2+ uptake was observed with increasing concentrations of Con A, between 2 and 400 microgram/ml, indicating that the stimulation of Ca2+ uptake is not restricted to mitogenic lectin concentrations (0.5-2 microgram/ml). Succinyl Con A exhibits only a slight effect in the same concentration ranges as native Con A. Ca2+ uptake, both in the absence and presence of Con A, is strongly dependent on energy metabolism and is carrier mediated. The augmentation of Ca2+ uptake by native Con A is due to an enhanced Vmax. Uptake of the anion, CrO42-, by thymocytes, found to be a non-saturable process, was also enhanced by Con A. The effect of Con A on CrO42- permeability appears to be independent of its effect on Ca2+ uptake.  相似文献   
774.
Dilution of a stationary phase culture of Scarlet Rose results in an increased rate of protein synthesis. This study compares the time course of this increase with the changes in polyribosome content and the levels of adenine and guanine nucleotides. During the first two hours after dilution, protein synthesis increases 2- to 3-fold; much of the large monoribosome pool that characterizes the stationary state disappears and a steady state situation is reached in which 70% of the ribosomes are in polyribosomes. Between two and eight hours, there is no further change in polyribosome content although the rate of protein synthesis increases an additional 2- to 3-fold. During this initial 8-hour period there is little change in the levels of ATP and GTP. An explanation consistent with these observations is that the initial activation (within the first 2 hours), characterized by the monoribosome to polysome transition, is at the level of a component(s) of the initiation system, and that between two and eight hours, since neither mRNA availability nor energy level are primary determinants, protein synthesis is augmented by the activation of a translational component, perhaps an elongation factor. After 24 hours, there is a proliferative phase characterized by the onset of ribosome accumulation. By day 5, maximum ribosome levels, 5-fold that of 24-hour cells, are reached, but the rate of protein synthesis increases only 2.5-fold during this period. The lack of quantitative coincidence between the changes in polyribosome content and the rates of protein synthesis again suggests that factors other than mRNA availability are involved in determining the overall rate of protein synthesis. Finally at days 6–8, while the growth of the culture is still in the exponential phase, the rate of protein synthesis per unit fresh weight drops markedly concomitant with a decline in ribosome content. At days 11–12, the monoribosome to polysome ratio begins to change with the monoribosome pool increasing. Presence of either actinomycin D or cordycepin inhibits increased protein synthesis in direct relation to the ability of these compounds to inhibit RNA synthesis. This suggests that the protein synthetic processes occurring after dilution require either the synthesis of the mRNA that is being translated or of an RNA functioning in a closely linked reaction.  相似文献   
775.
776.
Contour-length measurements of both nondenatured and partially denatured DNA from purified extracellular human cytomegalovirus indicate that more than one size class of viral DNA is encapsidated. In addition to a size class averaging about 100 x 10(6) daltons, a much less abundant class of larger viral DNA molecules, 150 x 10(6) to 155 x 10(6) daltons, was extracted from purified extracellular virus. As predicted by melting-curve analysis, partial denaturation of human cytomegalovirus DNA generates denaturation maps showing distinctive adenine plus thymidine (A+T)-rich and guanine plus cytosine (G+C)-rich localizations. Alignment of partial denaturation maps of both 100 x 10(6)- and 150 x 10(6)- to 155 x 10(6)-dalton molecules from maximum overlap of common A+T- and G+C-rich zones clearly shows six unique zones contained in a length equal to the longest class, 150 x 10(6) to 155 x 10(6) daltons. However, various alignments of the smaller class of the molecules within the confines of the approximately 100 x 10(6)-dalton-length equivalent are nondistinctive. Of the six unique A+T- and G+C-rich zones, five are linked in a specific sequence and maintain the same relative orientation; these features indicate the absence of major inversions within these zones. The sixth unique zone may occur at either end of this five-zone series, but it was never found at both ends of the same molecule. Additionally, this terminal zone appears to undergo complete inversions at least at one end of the alignment, and perhaps at both. These data indicate that 150 x 10(6)- to 155 x 10(6)-dalton molecules comprise human cytomegalovirus-specific genetic information.  相似文献   
777.
Stimulation of Cellular Thymidine Kinases by Human Cytomegalovirus   总被引:29,自引:6,他引:23       下载免费PDF全文
Thymidine kinase (TK) activity in WI-38 and MRC-5 human fibroblasts was analyzed by discontinuous polyacrylamide gel electrophoresis (disc-PAGE) and discontinuous glycerol gradient electrophoresis (disc-GEP) after subculture or human cytomegalovirus (HCMV) infection. Two peaks of TK activity with different relative fraction-of-migration (R(f)) values were resolved by disc-PAGE or disc-GEP in extracts from log-phase and infected cells. Growing WI-38 cells expressed a slowly migrating (R(f) = 0.14 PAGE, R(f) = 0.4 GEP) peak of TK activity, which was partially inhibited by 1.0 mM dCTP, but which retained little activity at pH 4.5. Growing MRC cells also displayed a slowly migrating peak (R(f) = 0.10 PAGE) with similar properties. Both cell types expressed a faster-migrating TK activity (R(f) = 0.45 PAGE, R(f) = 0.7 GEP) in the growing and resting state that was strongly inhibited by 1 mM dCTP but retained 50% activity at pH 4.5. When either cell type was infected with HCMV, there was a rapid and high-level stimulation of the slowly migrating form of TK and a slight stimulation of the faster-migrating form. Two strains of HCMV (AD169 and Town) failed to produce an electrophoretically distinct virus TK in either cell type after infection. TK enzymes were partially purified by disc-GEP from extracts of log-phase WI-38 or AD169-infected WI-38 cells. Characterization of these enzymes with respect to phosphate donor specificity, pH optima, thermostability, and salt inhibition showed the HCMV-stimulated TKs to be of cellular origin.  相似文献   
778.
Bilateral lesions of the nucleus locus coeruleus in 7 female stumptail monkeys were followed by long lasting hyperphagia and hyperdipsia. The percentage increase in weight at five weeks after lesioning correlated highly with 3-methoxy-4-hydroxy-phenethylene glycol (MHPG) concentration in the cerebral cortex. This relationship suggests that the effects are due to the locus coeruleus system and are not the result of variable destruction of the ventral noradrenergic or adjacent non-noradrenergic pathways.  相似文献   
779.
The DNA of the nonoccluded baculovirus (Hz-1V) obtained from the IMC-Hz-1 cell line was characterized by physicochemical and restriction endonuclease techniques. Hz-1V DNA isolated from purified virus had buoyant densities of 1.58 and 1.54 g/ml in CsCl-ethidium bromide density gradients, which corresponded to supercoiled and to relaxed circular and linear DNA, respectively. Neutral CsCl equilibrium centrifugation indicated that the Hz-1V DNA had a buoyant density of 1.7024 g/ml, which corresponded to a guanine-plus-cytosine (G+C) content of 43%. Thermal denaturation indicated a high G+C domain(s) in the Hz-1V genomic DNA. The domain(s), which included about 11% of the total genomic DNA, exhibited a T(m) of 97 degrees C. The remaining portion (89%) of the DNA had a T(m) of 86.5 degrees C. The T(m)s corresponded to G+C contents of 42 and 67%, respectively. The mean genetic complexity of Hz-1V DNA determined by DNA reassociation kinetic analysis was found to be 152 x 10(6). A possible rapidly reassociating component comprising approximately 13% of the genome was observed. The mean molecular weights from restriction endonuclease digests were 159 x 10(6) for both HindIII and EcoRI. Genomic heterogeneity was found in both the wild-type Hz-1V stock and in two plaque isolates. Of 12 single-plaque isolates, 3 basic restriction endonuclease DNA fragment patterns were observed. The molecular size estimates from electron microscopic contour lengths of uncloned viral DNA ranged from 70 to 158 megadaltons, and the mode was the 130- to 140-megadalton class.  相似文献   
780.
A new lignan, (+)-aretigenin has been isolated from the roots of Wikstroemia indica (Nan-Ling-Jao-Hua) and identified as 8(R) 8′(S)-4′-hydroxy-3, 4,3′-trimethoxylignan-olid (9, 9′) on the basis of spectral evidence as well as a direct comparison with its enantiomer, (?)-arctigenin.  相似文献   
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