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81.
The tissue of Cystoseira osmundacea (Turn.) C. Ag. (Fucales, Phaeophyta) undergoes pronounced developmental changes when in association with the fungus Haloguignardia irritans (Setchell et Estee) Cribb et Cribb (Sphaeriales, Ascomycotina). Nonmeristematic cortical cells are induced to divide and ultimately form a structure composed of tightly packed club-shaped projections. Each projection contains a single fungal ascocarp or spermogonium. A protective multilayered algal tissue surrounds the fungal reproductive structures. This association significantly alters algal morphology to the apparent protective advantage of the fungus.  相似文献   
82.
Abstract: The phorbol ester 4β-phorbol 12,13-dibutyrate increases the final extent of Ca2+-dependent glutamate release during the continuous depolarization of the synaptosomal plasma membrane. Based on this finding, we suggested that the sustained activation of protein kinase C has a positive influence on the efficiency of synaptic vesicle recycling in the presence of saturating concentrations of Ca2+. Previous work from our laboratory demonstrated that this 4β-phorbol 12,13-dibutyrate-dependent enhancement of synaptic vesicle recycling persists following the removal of 4β-phorbol 12,13-dibutyrate, requires localized Ca2+ entry through voltage-regulated channels, and is insensitive to the protein kinase inhibitor staurosporine. In the present study, we examined the possibility that the facilitation of glutamate release may be propagated through interactions between the protein kinase C- and multifunctional Ca2+/calmodulin-dependent protein kinase pathways. However, our data argue strongly against the involvement of such a mechanism in the persistent enhancement of sustained glutamate release. We observed that 4β-phorbol 12,13-dibutyrate did not increase the availability of cytosolic free calmodulin or the level of autonomous Ca2+/calmodulin-dependent protein kinase activity. In addition, we determined the effects of various serine/threonine kinase and phosphatase inhibitors on the phorbol ester-dependent enhancement of sustained glutamate release and found that protein kinase C increased the extent, but not the duration, of Ca2+-dependent glutamate release through a kinase-independent mechanism. Given our finding that the actin-depolymerizing agent cytochalasin D totally occluded the effect of 4β-phorbol 12,13-dibutyrate on release, we postulate that protein kinase C signals may be transduced through direct interactions between protein kinase C isoforms and cytoskeletal protein kinase C binding proteins.  相似文献   
83.
a cDNA library transfer system based on retroviral vectors has been developed for expression cloning in mammalian cells. The use of retroviral vectors results in stable cDNA transfer efficiencies which are at least 100-fold higher than those achieved by transfection and therefore enables the transfer and functional screening of very large libraries. In our initial application of retroviral transfer of cDNA libraries, we have selected for cDNAs which induce oncogenic transformation of NIH 3T3 fibroblasts, as measured by loss of contact inhibition of proliferation. Nineteen different transforming cDNAs were isolated from a total of 300,000 transferred cDNA clones. Three of these cDNAs were derived from known oncogenes (raf-1, lck, and ect2), while nine others were derived from genes which had been cloned previously but were not known to have the ability to transform fibroblasts (beta-catenin, thrombin receptor, phospholipase C-gamma 2 and Spi-2 protease inhibitor genes). The Spi-2 cDNA was expressed in antisense orientation and therefore is likely to act as an inhibitor of an endogenous transformation suppressor. Seven novel cDNAs with transforming activities, including those for three new members of the CDC24 family of guanine nucleotide exchange factors, were also cloned from the retroviral cDNA libraries. Retroviral transfer of libraries should be generally useful for cloning cDNAs which confer selectable phenotypes on many different types of mammalian cells.  相似文献   
84.
Molecular and Cellular Biochemistry - The testis is a complex organ in which local control is achieved by signalling between its constituent cells. Herein we describe the responses of cultured rat...  相似文献   
85.
A rapid cellular fractionation technique [the preceding paper, Shears & Kirk (1984) Biochem. J., 219, 375-382] was employed to separate a mitochondria-rich fraction from hepatocytes within seconds. Mitochondrial Ca was estimated to be no more than 41% of total cell Ca. At least half of the mitochondrial Ca was present in an energy-dependent pool; 20% of total cell Ca was accessible to EGTA within 10s. The alpha-adrenergic agonist phenylephrine stimulated glycogen phosphorylase activity by 100% within 0.5 min and induced a loss of 20% of total cell Ca after 10 min from the EGTA-inaccessible pool. However, between 0.5 and 10 min after the addition of phenylephrine to hepatocytes there was no significant change in the Ca content of the mitochondria-rich fraction. Hepatocytes that were preloaded with Ca2+ during 90 min incubation at 0-4 degrees C expelled this cation during 20 min incubation at 37 degrees C. After this time, phenylephrine failed to alter the Ca content of a mitochondria-rich fraction. It is concluded that alpha-adrenergic agonists do not mobilize Ca2+ from hepatocyte mitochondria.  相似文献   
86.
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88.
A colorimetric assay for the assessment of cytotoxicity of yeasts   总被引:2,自引:0,他引:2  
A colorimetric assay for the quantitation of microbial cytotoxicity has been developed using cells from a monocyte-like human cell line (U937), epithelial cells (Hela), and fibroblast-like cells (Vero) as targets. The fraction of surviving cells was determined by their content of the dye neutral red which is retained only by live cells and can be quantitated photometrically after controlled lysis. The neutral red retention assay was at least as sensitive as the 51Cr-release assay; it was considerably less laborious, faster, and avoided handling of radioactivity. Among the different Candida species tested, the highest cytotoxicity was associated with C. albicans and C. tropicalis; a lower degree of cytotoxicity was exhibited by C. glabrata, C. guilliermondii, C. krusei, C. parapsilosis, and C. pseudotropicalis. Among the strains of a given fungal species cytotoxicity varied by up to 40%.  相似文献   
89.
Vasopressin, angiotensin II and the catecholamines decreased ketogenesis from oleate but increased ketogenesis from butyrate in hepatocytes from fed rats. The hormones increase CO2 production from both oleate and butyrate. It is suggested that whereas the mitochondrial uptake of butyrate is linked to its rate of oxidation, that of oleate is independent of its intramitochondrial metabolism, and consequently the oxidation of oleate to CO2 occurs at the expense of ketogenesis. Effects of the hormones on ketogenesis from oleate or butyrate were not observed after pre-treatment of the hepatocytes with dibutyryl cyclic AMP for 1 hour. The insensitivity of ketogenesis to the hormones after this treatment (which mimics the effects of acute carbohydrate deprivation in vivo) questions the physiological significance of hormonal regulation of ketogenesis other than at the onset of starvation.  相似文献   
90.
Isoelectric focussing (IEF) in thin layer polyacrylamide gels pH range 4-6.5 has been used to analyse the GC phenotypes of 4233 individuals from 28 different population groups in the Asian, Pacific, and Australian area. Because this technique reveals subtypes of the common GC*1 allele, there is almost a two-fold increase in the mean heterozygosity at the GC locus using IEF compared with conventional electrophoresis. The highest frequency (above 50%) of the GC*1S allele was encountered in Indian populations, reflecting genetic affinities with Europeans. By comparison, east and south east Asians are unique offing maximum values of the GC*1F allele (50%). With the exception of a few Pacific populations which show similar frequencies to east Asians, all other groups in the Pacific area, including Australia, have values of GC*1F similar to GC*1S ranging from 27% to 40%. The GC*2 frequency in most populations varies from 20% to 30%. However, some Polynesian groups have values up to 40% and Australian Aborigines less than 10%. Among other alleles, GC*1A1 is found to be widely distributed among Australian Aborigines and Melanesians and occurs sporadically in Polynesians, Micronesians, and in the Lesser Sunda Islands. Four new alleles, GC*1C24, GC*1C35 Aborigine, GC*1A21, and GC*1A22 are described. The gene frequency data at the GC locus has been used to calculate Nei genetic distances between the populations studied.  相似文献   
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