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1.
Using comparative ion-exchange chromatography on Dowex 1X4, the product of dephosphorylation of fructose 2,6-bisphosphate with purified yeast fructose-2,6-bisphosphate 6-phosphohydrolase, was shown to be identical to the furanose form of fructose 2-phosphate prepared by chemical synthesis according to Pontis and Fischer [Biochem. J. 89, 452-459 (1963)]. As expected for the furanose form of fructose 2-phosphate, the enzymatically formed product consumes 1 mol periodate/mol fructose 2-phosphate, whereas the chemically synthesized pyranose form consumes 2 mol periodate/mol. In addition, it is shown that the enzymatic product behaves identically to the furanose, not the pyranose, form of fructose 2-phosphate in hydrolysis of the ester bond at pH 4 and 37 degrees C, as described previously for the chemically synthesized compounds [Pontis and Fischer (1963) vide supra].  相似文献   
2.
Metabolic regulation of the trehalose content of vegetative yeast.   总被引:6,自引:0,他引:6  
We have investigated the mechanism by which heat shock conditions lead to a reversible accumulation of trehalose in growing yeast. When cells of S. cerevisiae M1 growing exponentially at 30 degrees C were shifted to 45 degrees C for 20 min, or to 39 degrees C for 40 min, the concentration of trehalose increased by about 25-fold; an effect reversed upon lowering the temperature to 30 degrees C. This was compared to the more than 50-fold rise in trehalose levels obtained upon transition from the exponential to the stationary growth phase. Whereas the latter was paralleled by a 12-fold increase in the activity of trehalose-6-phosphate synthase, no significant change in the activities of trehalose-synthesizing and -degrading enzymes was measured under heat shock conditions. Accordingly, cycloheximide did not prevent the heat-induced accumulation of trehalose. However, the concentrations of the substrates for trehalose-6-phosphate synthase, i.e. glucose-6-phosphate and UDP-glucose, were found to rise during heat shock by about 5-10-fold. Since the elevated levels of both sugars are still well below the Km-values determined for trehalose-6-phosphate synthase in vitro, they are likely to contribute to the increase in trehalose under heat shock conditions. A similar increase in the steady-state levels was obtained for other intermediates of the glycolytic pathway between glucose and triosephosphate, including ATP. This suggests that temperature-dependent changes in the kinetic parameters of glycolytic enzymes vary in steady-state levels of intermediates of sugar metabolism, including an increase of those that are required for trehalose synthesis. Trehalose, glucose-6-phosphate, UDP-glucose, and ATP, were all found to increase during the 40 min heat treatment at 39 degrees C. Since this also occurs in a mutant lacking the heat shock-induced protein HSP104 (delta hsp104), this protein cannot be involved in the accumulation of trehalose under these heat shock conditions. However, mutant delta hsp104, in contrast to the parental wild-type, was sensitive towards a 20 min incubation at 50 degrees C. Since this mutant also accumulated normal levels of trehalose, we conclude that HSP104 function, and not towards a 20 min incubation at 50 degrees C. Since this mutant also accumulated normal levels of trehalose, we conclude that HSP104 function, and not the accumulation of trehalose, protects S. cerevisiae from the damage caused by a 50 degrees C treatment.  相似文献   
3.
4.
Summary Numerous mitoses were noted in testicular tissue from adult men with early germ cell tumors. More than 15 Leydig cells undergoing mitosis were found in the interstitial compartment. The presence of specific crystalline intracytoplasmatic inclusions demonstrated for the first time that differentiated Leydig cells are capable of proliferation. Occasionally cells are difficult to discriminate during mitosis. To establish reference criteria, the light- and electron-microscopic features of the following mitotic cells were examined: Leydig cells, fibroblasts, perivascular cells, peritubular cells, and lymphocytes. Supplementary mitoses in germ cell tumors and in a case of Leydig cell tumor were investigated. In the literature, only single reports of mitoses in Leydig cells are available. The frequent incidence of Leydig cell mitosis in early germ cell tumors may be due to the presence of growth-promoting factors in the testicular tissue.  相似文献   
5.
The orientation of the superior articular processes with regard to the upper end-plate of the sacrum does not depend on the inclination of the sacrum. This assertion can be made by interpreting certain angles already described in literature and may be confirmed by a research following strict biomechanic principles: The orientation of the articular processes is put in relation to the direction of the forward shear brought upon by the Vth lumbar vertebra and caused by the inclination of the sacrum. This is achieved by measuring the angle between the articular facet and a plane normal to the mentioned forward shear. The result is that the size of this angle does not at all depend on the degree of the inclination of the sacrum.  相似文献   
6.
Summary Two recent articles have reported the linkage of a gene for recessive spinal muscular atrophy (SMA) on the chromosome region 5q11.2–13.3. Our data show no linkage of the dominantly inherited forms of SMA to this chromosome region.  相似文献   
7.
The protein synthesis pattern of a set of stage and tissue specific proteins has previously been described in Drosophila melanogaster. The analysis of this set of follicle cell proteins (Fc proteins) is here extended to cover several sibling species of Drosophila melanogaster, namely D. simulans, D. mauritiana, D. erecta and D. yakuba. Even though a similar set of proteins were synthesized in these species, minor differences in size of the proteins were found between the species. Some of the species exhibited variation within species.  相似文献   
8.
C-reactive protein (CRP) is a serum protein that shows rapid increases of as much as 1000-fold in concentration in response to infection, traumatic injury, or inflammation. CRP reacts with the phosphocholine moiety of pneumococcal cell wall C-polysaccharide, and this reaction can lead to complement activation in vitro and protection against pneumococcal infection in vivo. We have previously studied the chemiluminescence response of human neutrophils to Streptococcus pneumoniae as a measure of in vitro opsonophagocytosis by CRP and complement. CRP in the presence of complement was an effective opsonin for S. pneumoniae serotype 27 (Pn27), but not for serotypes 3 or 6. Because Pn27 differs from most serotypes of S. pneumoniae in containing phosphocholine in its capsular polysaccharide, we have determined the sites of CRP and C3 fixation to Pn27 and S. pneumoniae serotype 4 (Pn4), and related these to the ability of CRP and complement to opsonize these serotypes in vitro. By using a chemiluminescence (CL) assay to measure opsonophagocytosis, CRP was shown to enhance the response of human neutrophils and monocytes to Pn27 in the presence of normal human serum. The CL response of neutrophils and monocytes to Pn4 was not affected by the addition of CRP to serum. The addition of anti-capsular antibody to Pn4 and Pn27 enhanced the CL responses of both neutrophils and monocytes to both bacteria. The localization of bound CRP and C3 on Pn4 and Pn27 was determined by immunoelectron microscopy. CRP bound to Pn4 only in the cell wall region and C3 was located in this area whether or not CRP was present. Anti-capsular antibody deposited C3 in the capsule of Pn4. In contrast, Pn27 bound CRP throughout the capsule and cell wall areas. C3 was deposited in the cell wall region of Pn27 by serum alone and in the cell wall region and capsule when CRP or anti-capsular antibody was present. Because C3 fixation to the capsule was consistently associated with enhanced responses by phagocytic cells, it appears that the site of CRP binding and subsequent complement activation may be critical in the opsonophagocytosis of S. pneumoniae. These findings extend the correlation between capsular C3 and opsonization to a nonimmune system. By using CRP and different pneumococcal serotypes we have shown that the same molecules that are effective in the stimulation of phagocytic cells when bound to the capsule are not effective when bound to the cell wall.  相似文献   
9.
After addition of 5 mM sulfite or nitrite to glucose-metabolizing cells of Saccharomyces cerevisiae a rapid decrease of the ATP content and an inversely proportional increase in the level of inorganic phosphate was observed. The concentration of ADP shows only small and transient changes. Cells of the yeast mutant pet 936, lacking mitochondrial F1ATPase, after addition of 5 mM sulfite or nitrite exhibit changes in ATP, ADP and inorganic phosphate very similar to those observed in wild type cells. They key enzyme of glucose degradation, glyceraldehyde-3-phosphate dehydrogenase was previously shown to be the most sulfiteor nitrite-sensitive enzyme of the glycolytic pathway. This enzyme shows the same sensitivity to sulfite or nitrite in cells of the mutant pet 936 as in wild type cells. It is concluded that the effects of sulfite or nitrite on ATP, ADP and inorganic phosphate are the result of inhibition of glyceraldehyde-3-phosphate dehydrogenase and not of inhibition of phosphorylation processes in the mitochondria. Levels of GTP, UTP and CTP show parallel changes to ATP. This is explained by the presence of very active nucleoside monophosphate kinases which cause a rapid exchange between the nucleoside phosphates. The effects of the sudden inhibition of glucose degradation by sulfite or nitrite on levels of ATP, ADP and inorganic phosphate are discussed in terms of the theory of Lynen (1942) on compensating phosphorylation and dephosphorylation in steady state glucose metabolizing yeast.Abbreviations ATP adenosine triphosphate - ADP adenosine diphosphate - AMP adenosine monophosphate - Pi inorganic orthophosphate Dedicated to Prof. Dr. Hans Grisebach on the occasion of his sixtieth birthday  相似文献   
10.
Vertical stratification is a key feature of tropical forests and structures plant–frugivore interactions. However, it is unclear whether vertical differences in plant-frugivore interactions are due to differences among strata in plant community composition or inherent preferences of frugivores for specific strata. To test this, we observed fruit removal of a diverse frugivore community on the liana Marcgravia longifolia in a Peruvian rain forest. Unlike most other plants, Marcgravia longifolia produces fruits across forest strata. This enabled us to study effects of vertical stratification on fruit removal without confounding effects of plant species and stratum. We found a high number of visits of a few frugivore species in the understorey and a low number of visits of many different frugivores in the canopy and midstorey. Whereas partial and opportunistic frugivores foraged across strata with differing frequencies, obligate frugivores were only found eating fruits in the higher strata. Avian frugivores foraging in the canopy were mainly large species with pointed wings, whereas under- and midstorey avian foragers were smaller with rounded wings. Our findings suggest a continuous shift in the frugivore community composition along the vertical gradient, from a few generalized frugivores in the understorey to a diverse set of specialized frugivores in the canopy. This shift in the frugivore community leads to correlated, reciprocal changes from specialized to generalized plant-frugivore interactions. Thus, we conclude that vertical niche differentiation between species in tropical forests persists even when food resources are available across strata. This highlights its role for promoting biodiversity and ecosystem functioning.  相似文献   
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