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21.
Characterization of succinate dehydrogenase and alpha-glycerophosphate dehydrogenase in pancreatic islets 总被引:1,自引:0,他引:1
Succinate dehydrogenase activities in homogenates of rat and ob/ob mouse pancreatic islets were only 13% of the activities in homogenates of liver and were also several times lower than in homogenates of pancreatic acinar tissue. This indicates that the content of mitochondria in pancreatic islet cells is very low. The very low activity of succinate dehydrogenase is in agreement with the low mitochondrial volume in the cytoplasmic ground substance of pancreatic islet cells as observed in morphometric studies. This may represent the poor equipment of pancreatic islet cells with electron transport chains and thus provide a regulatory role for the generation of reducing equivalents and chemical energy for the regulation of insulin secretion. The activities of succinate dehydrogenase in tissue homogenates of pancreatic islets, pancreatic acinar tissue, and liver were significantly inhibited by malonate and diazoxide but not by glucose, mannoheptulose, streptozotocin, or verapamil. Tolbutamide inhibited only pancreatic islet succinate dehydrogenase significantly, providing evidence for a different behavior of pancreatic islet cell mitochondria. Therefore diazoxide and tolbutamide may affect pancreatic islet function through their effects on succinate dehydrogenase activity. The activities of alpha-glycerophosphate dehydrogenase in homogenates of pancreatic islets and liver from rats and ob/ob mice were in the same range, while activities in homogenates of pancreatic acinar tissue were lower. None of the test agents affected alpha-glycerophosphate dehydrogenase activity. Thus the results provide no support for the recent contention that alpha-glycerophosphate dehydrogenase activity may be critical for the regulation of insulin secretion. 相似文献
22.
Dr. Uwe Hiller 《Zoomorphology》1972,73(3):263-278
Zusammenfassung Kurz nach einer Hdutung wird bei Tarentola m. m. bereits die übemächste Epidermisgeneration — und somit auch die der Haftborsten —angelegt. Das geschieht vornehmlich in der Oz- (Oberhäutchenzellen-) und in der Hs-Schicht (clear layer). Zunächst entstehen die Aufspaltungen der Haftborstenenden, indem Keratinfilamentbündel nach einem bestimmten System von den Oz-Zellen aus in die Hs-Zellen einwachsen. Auf these Weise fungieren die Zellen der Hs-Schicht als Matrix der Haftborsten. Nach Abschluß dieses Prozesses werden die eigentlichen Haftborsten gebildet unter gleichzeitigem Auseinanderrücken der Hs- und Oz-Schichten. Die Hs-Schicht behdlt ihre Matrizen-Funktion bis zur anschließenden Häutung bei.
Light and electron microscope studies of developing setae of Tarentola m. mauritanica (Rept., Gekkonidae)
Summary In Tarentola m. mauritanica the next epidermis generation but one and therefore the adhesive setae of the generation after this begin to develop shortly after a skin has been shed. This development takes place principally in the horny layer (Oz) and the clear layer. First bundles of keratin filaments radiate from the horny layer into the clear layer, thus giving rise to the split distal parts of the adhesive bristles. Thus the cells in the clear layer act as a matrix for the setae. When this stage is complete the formation of the setae proper begins, while the horny layer and the clear layer become separated from each other. The clear layer retains its function as matrix for the setae until the next time a skin is shed.相似文献
23.
Uwe Sleytr 《Archives of microbiology》1970,72(3):238-251
Zusammenfassung Drei thermophile und ein mesophiler Bacillus sphaericus-Stamm wurden gefriergeätzt und ihre Feinstruktur verglichen. Mit Ausnahme eines thermophilen Stammes konnte bei allen untersuchten Organismen eine aus 13 nm großen Einheiten aufgebaute, rechtwinkelig geordnete Zellwandoberflächenstruktur nachgewiesen werden. Die Zellwand ließ sich bei sämtlichen Stämmen zweischichtig aufspalten. An ihren Querbrüchen traten 10–20 nm dicke Fibrillen auf, die als Subeinheiten der Zellwand gedeutet werden. Das Gefrierätzbild der Cytoplasmamembran läßt eine Deutung im Sinne einer teilweisen Aufspaltung längs einer zentralen Ebene zu.An aufgebrochenen Reservestoffgranula wurden hornartige Artefakte dargestellt, deren Entstehung teilweise auf eine schlagartige Expansion eines komprimierten, streng abgrenzbaren zentralen Teiles zurückgeführt wird.
Freeze etching of different strains of Bacillus sphaericus
Summary The fine structures of three thermophilic and one mesophilic strain of Bacillus sphaericus have been compared by means of freeze etching. With the exception of one thermophilic strain, all strains had a rectangular cell wall surface structure consisting of 13 nm units. With all strains it was possible to split the cell wall into two layers. On its cross fractures 10–20 nm thick fibrils could be observed, presumably subunits of the cell wall.The image yielded by the freeze etched cytoplasmic membrane can be interpreted as due to partial cleaving along a central plane. The formation of hornlike artefacts rising from cross-fractured storage granules is explained partially by a sudden expansion of a compressed central part.相似文献
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26.
In the short day plant Chenopodium rubrum and the long day plant Nicotiana tabacum cv. Havana 425, adenylate kinase (EC 2.7.4.3) occurs as a family of isoforms, with at least two members localized in the chloroplast representing the main isoforms. In this work, isoforms were separated by anion exchange chromatography and relative isoform activities were compared between vegetative plants and plants induced to flowering. In both species examined, a light regime leading to floral induction resulted in a significant decrease in the activity of one chloroplast isoform. This decrease modified considerably the relative distribution of isoform activities, especially that between the two chloroplast activities. 相似文献
27.
28.
Uwe Scherf Brigitte Söhling Gerhard Gottschalk Dietmar Linder Wolfgang Buckel 《Archives of microbiology》1994,161(3):239-245
Anaerobically prepared cell extracts of Clostridium kluyveri grown on succinate plus ethanol contained high amounts of 4-hydroxybutyryl-CoA dehydratase, which catalyzes the reversible dehydration of 4-hydroxybutyryl-CoA to crotonyl-CoA. The enzyme was purified 12-fold under strictly anaerobic conditions to over 95% homogeneity and had a specific activity of 123 nkat mg-1. The finding of this dehydratase means that all of the enzymes necessary for fermentation of succinate plus ethanol by C. kluyveri have now been demonstrated to exist in this organism and confirms the proposed pathway involving a reduction of succinate via 4-hydroxybutyrate to butyrate. Interestingly, the enzyme is almost identical to the previously isolated 4-hydroxybutyryl-CoA dehydratase from Clostridium aminobutyricum. The dehydratase was revealed as being a homotetramer (m=59 kDa/subunit), containing 2±0.2 mol FAD, 13.6±0.8 mol Fe and 10.8±1.2 mol inorganic sulfur. The enzyme was irreversibly inactivated after exposure to air. Reduction by sodium dithionite also yielded an inactive enzyme which could be reactivated, however, up to 84% by oxidation with potassium hexacyanoferrate(III). The enzyme possesses an intrinsic vinylacetyl-CoA isomerase activity which was also found in 4-hydroxybutyryl-CoA dehydratase from C. aminobutyricum. Moreover, the N-terminal sequences of the dehydratases from both organisms were found to be 63% identical. 相似文献
29.
Dieter Heineke Kathrin Wildenberger Uwe Sonnewald Lothar Willmitzer Hans W. Heldt 《Planta》1994,194(1):29-33
The subcellular distribution of hexoses, sucrose and amino acids among the stromal, cytosolic and vacuolar compartments was analysed by a nonaqueous fractionation technique in leaves of tobacco (Nicotiana tabaccum L.) wild-type and transgenic plants expressing a yeast-derived invertase in the cytosolic, vacuolar or apoplasmic compartment. In the wild-type plants the amino acids were found to be located in the stroma and in the cytosol, sucrose mainly in the cytosol and up to 98% of the hexoses in the vacuole. In the leaves of the various transformants, where the contents of hexoses were greater than in wild-type plants, again 97–98% of these hexoses were found in the vacuoles. It is concluded that leaf vacuoles contain transporters for the active uptake of glucose and fructose against a high concentration gradient. A comparison of estimated metabolite concentrations in the subcellular compartments of wild-type and transformant plants indicated that the decreased photosynthetic capacity of the transformants is not due to an osmotic effect on photosynthesis, as was shown earlier to be the case in transformed potato leaves, but is the result of a long-term dedifferentiation of tobacco leaf cells to heterotrophic cells.Abbreviations apo-inv
tobacco plant with yeast invertase in the apoplasm
- Chl
chlorophyll
- cy-inv
tobacco plant with yeast invertase in the cytosol
- vac-inv
tobacco plant with yeast invertase in the vacuole
- WT
wild-type tobacco plant
The authors thank A. Großpietsch for her able technical assistance. This work has been supported by the Bundesminister für Forschung und Technologie. 相似文献
30.
Photosynthetic characteristics of transgenic tobacco (Nicotiana tabacum L.) plants with a soluble pyrophosphatase in the cytosol of their leaf cells were compared to those of wild-type plants. Although the development of the transgenic plants was somewhat retarded compared to the wild type, as shown by stunted growth and delayed flowering, photosynthetic responses were comparable in transgenic and wild-type leaves of similar physiological age. In particular, light-dependent proton transport into the vacuoles of leaf mesophyll cells was not decreased in leaves of the transgenic plants, which did not contain pyrophosphate in the cytosol owing to the presence of a soluble pyrophosphase. This shows that light-stimulated proton pumping did not require the pumping activity of the tonoplast pyrophosphatase. Apparently, light-stimulated proton pumping can be based solely on the activity of the tonoplast ATPase.Abbreviation CDCF
5-(and 6-)arboxy-2,7-dichlorofluorescein
This work was supported within the Sonderforschungsbereiche 176 and 251 of the University of Würzburg. 相似文献