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541.
Studies on lysostaphin. Separation and characterization of three enzymes 总被引:11,自引:0,他引:11
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J Foss? O H Iversen P O Thune 《Virchows Archiv. B, Cell pathology including molecular pathology》1980,34(3):213-217
One-hundred-and-twenty hairless mice were irradiated with UVB (310 nm, exposure 60 mJ/cm2) on a limited area of the dorsal skin. At different time intervals after irradiation, the rate of endogenous dehydrogenase activity per mg dry epidermis was measured by the tetrazolium reduction method. The amount of formazan deposited remained normal for 18 h, and then increased, reaching a peak significantly higher than normal at 24 h, and thereafter returned to normal. At day 8 there was a new, probably significant peak. The reaction was followed for 14 days. It was concluded that UVB irradiation provokes a period of increased formazan deposition in the epidermis, similar to what has been observed after ionizing radiation and chemical carcinogens. The validity of the tetrazolium test for skin carcinogenic irritaments was thus also confirmed. 相似文献
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Hairless mice were given 2 mg Bleomycin i.p. in 1-0 ml saline on two successive days. By a stathmokinetic method, by micro-flow fluorometry and by autoradiography certain kinetic parameters were measured during 10 days after the last injection. Cell counts were made and the turnover time of the differentiating cells estimated. Protein synthesis was estimated by the uptake of radioactive histidine, and dry cell mass measured by weighing. Bleomycin affected cell proliferation in the epidermis by depressing biphasically both the number of cells in, and the passage of cells through, the cell cycle phases: S, G2 and M, most probably by directly affecting late G1 cells and cells in mitosis. The time between the two minima of depressed DNA synthesis corresponded to the mean generation time of the basal cells. Histidine uptake and dry cell mass were slightly affected, but the turnover time of the differentiating cells was prolonged. Bleomycin thus had a strong long-lasting inhibitory effect on epidermal cell proliferation and a marked inhibitory effect on epidermal cell maturation in mice. 相似文献
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S B Refsum E H?skjold R Bjerknes O H Iversen 《Virchows Archiv. B, Cell pathology including molecular pathology》1991,60(4):225-230
The rat corneal epithelium has been chosen as a model for studying growth regulation. In this epithelium a large single cohort of cells enters the S phase during a fairly short time period once a day. The factor responsible for this wave of cell proliferation is unknown, but it may be a chemical signal from the central nervous system (the suprachiasmatic nucleus or the corpus pineale). The mature cell compartment of the corneal epithelium is assumed to produce a negative feedback factor (chalone), counteracting the effect of the circadian proliferative factor on the local cell proliferation. When no circadian factor is being produced, during most of the 24 h, the chalone seems to enhance the maturation process. During diminished chalone production (e.g. after cell injury and subsequent regeneration), we will get a more or less unrestricted cell proliferation in the tissue with a delayed maturation process prolonging the chalone depletion. This interaction between the circadian proliferative factor and the negative feedback factor for regulation of proliferation with its accompanying stimulatory effect on maturation, may represent a general mechanism in the regulation of cell proliferation in any tissue. Since in at least some organs virtually all cells entering the S phase do this as a single wave once a day, this mechanism may be enough to explain the regulation of cell proliferation during both normal and regenerative conditions. 相似文献
547.
Walid M El-Sharoud Stephen O'Brien Carmen Negredo Carol Iversen Séamus Fanning Brendan Healy 《BMC microbiology》2009,9(1):24
Background
Cronobacter is a recently proposed genus consisting of six genomospecies that encompass the organisms previously identified as Enterobacter sakazakii. Cronobacter are opportunistic pathogens and are known to cause serious infections in infants, particularly neonates. High case fatality rates have been associated with infections and acute sequelae can occur in survivors with severe ramifications on neurological development. Infant formula has been identified as one route of transmission for infection in infants. However, the primary reservoirs for subsequent contamination of foods with Cronobacter remain undefined due to the ubiquitous nature of these organisms. More recently, infections in adults have been reported, especially amongst the elderly and patients who are immunocompromised. To help prevent the transmission of infection, it is important to identify the main food sources for Cronobacter. The aim of this study was to identify and characterize Cronobacter isolated from dried-milk and related products available in an Egyptian food market. 相似文献548.
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