全文获取类型
收费全文 | 311篇 |
免费 | 30篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 5篇 |
2018年 | 4篇 |
2017年 | 7篇 |
2016年 | 5篇 |
2015年 | 11篇 |
2014年 | 10篇 |
2013年 | 21篇 |
2012年 | 13篇 |
2011年 | 16篇 |
2010年 | 13篇 |
2009年 | 14篇 |
2008年 | 7篇 |
2007年 | 11篇 |
2006年 | 8篇 |
2005年 | 8篇 |
2004年 | 8篇 |
2003年 | 13篇 |
2002年 | 8篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 9篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 2篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1972年 | 5篇 |
1971年 | 5篇 |
1970年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有341条查询结果,搜索用时 15 毫秒
1.
A procedure involving treatment of cells in suspension culture and soft-agar cloning was developed for measuring mutation of Chinese hamster ovary (CHO) cells to 6-thioguanine (6TG) resistance. The use of suspension cultures precluded the need for trypsinization and also permitted a 5-fold increase in cell population for compound exposure and mutant selection as compared to former monolayer techniques. Soft-agar cloning reduced the opportunity for metabolic cooperation and permitted the use of non-dialyzed fetal calf serum which resulted in spontaneous mutant frequencies of 6.6 +/- 3.2 X 10(-6) and cloning efficiencies of 91 +/- 18%. Relative total growth values were calculated based on suspension growth and cloning efficiencies such that an assessment of toxicity could be estimated from treatment through cloning. Dose-dependent mutagenic responses were observed in CHO cells following treatment with ethyl methanesulfonate, methyl methanesulfonate, 4-nitroquinoline-1-oxide, methylnitrosourea and N-methyl-N'-nitro-N-nitrosoguanidine. Clones of 6TG-resistant cells harvested from soft agar maintained 6TG resistance and methotrexate sensitivity and did not incorporate [3H]hypoxanthine into DNA. These preliminary findings indicate that the use of suspension cultures and soft-agar cloning has improved the efficiency and cost effectiveness of the CHO/HGPRT mutation assay. 相似文献
2.
DNA regions associated with the nuclear matrix of Ehrlich ascites cells expose single-stranded sites after deproteinization 总被引:2,自引:0,他引:2
Ehrlich ascites cells were pulse-labeled with [3H]thymidine and subjected to prolonged labeling with [14C]thymidine. The isolated nuclei were digested with the restriction endonuclease BspRI and then processed to yield a 'matrix fraction' and a 'non-matrix fraction'. The DNA fragments purified from these fractions and from whole digested nuclei were examined for nitrocellulose-binding sites before and after digestion with single-strand-specific (S1) nuclease. Both, pulse-labeled and long-time-labeled fragments, isolated from the matrix fraction, exhibited a significantly increased content of nitrocellulose-binding sites. The major portion of these sites were rendered non-binding by digestion with single-strand-specific nuclease and consisted most probably of structures exposing relatively small stretches of non-base-paired DNA. The nature of the minor portion of binding sites which was insensitive to single-strand-specific nuclease is not clear. Both types of binding sites are possible candidates for mediating the attachment of DNA to the nuclear matrix. 相似文献
3.
Alzheimer''s paired helical filaments share epitopes with neurofilament side arms. 总被引:15,自引:1,他引:14 下载免费PDF全文
C C Miller J P Brion R Calvert T K Chin P A Eagles M J Downes J Flament-Durand M Haugh J Kahn A Probst et al. 《The EMBO journal》1986,5(2):269-276
A panel of monoclonal antibodies to neurofilaments have been investigated with regard to the location of their respective epitopes on neurofilament polypeptides and their ability to label the neurofibrillary tangles and paired helical filaments (PHF) which are characteristic of Alzheimer's disease. All of the neurofilament monoclonal antibodies that label tangles and PHF are directed against epitopes in the side arm domains of the two larger neurofilament polypeptides, NF-H and NF-M, and do not recognise the alpha-helical rod domains of these proteins. Immuno-electron microscopy demonstrates that the neurofilament antibodies label the constituent PHF per se and do not simply stain neurofilaments that might be admixed with PHF. These neurofilament epitopes are differentially retained by PHF, following isolation. Thus, antibody labelling of PHF is not simply due to the presence of normal neurofilament polypeptides. We propose that in tangle-bearing neurons, neurofilaments are degraded by proteases and that it is fragments of the side arms which contribute to the composition of PHF. 相似文献
4.
Antagonistic regulation of the glucose/glucose 6-phosphate cycle by insulin and glucagon in cultured hepatocytes. 总被引:1,自引:0,他引:1 下载免费PDF全文
Flux through the glucose/glucose 6-phosphate cycle in cultured hepatocytes was measured with radiochemical techniques. Utilization of [2-3H]glucose was taken as a measure of glucokinase flux. Liberation of [14C]glucose from [U-14C]glycogen and from [U-14C]lactate, as well as the difference between the utilization of [2-3H]glucose and of [U-14C]glucose, were taken as measures of glucose-6-phosphatase flux. At constant 5 mM-glucose and 2 mM-lactate concentrations insulin increased glucokinase flux by 35%; it decreased glucose-6-phosphatase flux from glycogen by 50%, from lactate by 15% and reverse flux from external glucose by 65%, i.e. overall by 40%. Glucagon had essentially no effect on glucokinase flux; it enhanced glucose-6-phosphatase flux from glycogen by 700%, from lactate by 45% and reverse flux from external glucose by 20%, i.e. overall by 110%. At constant glucose concentrations cellular glucose 6-phosphate concentrations were essentially not altered by insulin, but were increased by glucagon by 230%. In conclusion, under basic conditions without added hormones the glucose/glucose 6-phosphate cycle showed only a minor net glucose uptake, of 0.03 mumol/min per g of hepatocytes; this flux was increased by insulin to a net glucose uptake of 0.21 mumol/min per g and reversed by glucagon to a net glucose release of 0.22 mumol/min per g. Since the glucose 6-phosphate concentrations after hormone treatment did not correlate with the glucose-6-phosphatase flux, it is suggested that the hormones influenced the enzyme activity directly. 相似文献
5.
H Probst K Hamprecht V Gekeler 《Biochemical and biophysical research communications》1983,110(2):688-693
When Ehrlich ascites cells were cultured for 2 h under oxygen-free atmosphere, a shut-down of initiation of new replication units was observed by chain length analysis of the nascent daughter strands and by DNA fibre autoradiography. The intracellular level of ATP, ADP and AMP remained virtually normal in the anaerobized cells, while that of diadenosine 5',5'-P1,P4-tetraphosphate was found reduced by about two orders of magnitude. It is proposed that the ceasing of DNA synthesis after O2 removal is at actively controlled regulatory response of the cells in which diadenosine 5',5"'-P1,P4-tetraphosphate is probably involved. 相似文献
6.
Metabolism and non-random occurrence of nonnascent short chains in the DNA of Ehrlich ascites cells 总被引:3,自引:0,他引:3
H Probst T Hofstaetter H S Jenke P R Gentner D Müller-Scholz 《Biochimica et biophysica acta》1983,740(2):200-211
The DNA of Ehrlich ascites cells was labeled with radioactive thymidine using different labeling schedules: Incubation periods between 15 s and 4 h; pulse/pulse-chase experiments with pulses in the range of a few minutes; longtime incubation followed by a longtime chase (both in the range of 1 cell generation). From the purified DNA of the labeled cells a fraction (0.3-0.4%) of short chains was separated and partially fractionated by means of a hydroxyapatite thermochromatography procedure. The evaluation of the labelling patterns of the short chains indicated that less than 5% of them can be regarded as replication intermediates ('Okazaki pieces'). The rest, termed nonnascent pieces, exhibited a slow turnover. The life span of the nonnascent pieces was estimated to be about 1 cell generation. On helical DNA, nonnascent pieces were distributed in a non-random manner. Their preferential localisation was nearby sites which caused binding of the DNA, after purification, to nitrocellulose and which occurred about every 60-80 microns on the nuclear DNA of the cells. 相似文献
7.
Selective and synchronous activation of early-S-phase replicons of Ehrlich ascites cells. 总被引:3,自引:3,他引:0 下载免费PDF全文
Twelve-hour exposure of G1 Ehrlich ascites cells to controlled hypoxia (200 ppm of O2 at 1 bar) suppressed replicon initiation. Synchronous cycling, beginning with a normal S phase, was released by reoxygenation immediately. The addition of cycloheximide at reoxygenation largely resuppressed, after a short initial burst, succeeding replicon initiations. Alkaline sedimentation analysis of growing daughter strand DNA, DNA fiber autoradiography, and analysis of the newly formed DNA demonstrated that normal chain growth and DNA maturation (replicon termination) in the initially activated replicons continued in the presence of cycloheximide. After 2 to 3 h, a low level of cycloheximide-insensitive background replication emerged out of the then-ebbing single surge of activity of the initially released replicons. 相似文献
8.
Inhibition of Bordetella pertussis filamentous hemagglutinin-mediated cell adherence with monoclonal antibodies 总被引:6,自引:0,他引:6
Elizabeth Leininger Peter G. Probst Michael J. Brennan James G. Kenimer 《FEMS microbiology letters》1993,106(1):31-38
Abstract Filamentous hemagglutinin (FHA), a 220-kDa protein located on the surface of Bordetella pertussis , is one of the major cell adhesins of this bacterium. We have produced three hybridoma cell lines that express monoclonal antibodies (mAbs) against FHA: X3C, X3E and X4B. The anti-FHA mAbs X3C and X3E reacted with 220-kDa FHA protein bands on Western blots. The mAb X4B, which reacted with FHA in ELISA, did not bind to FHA in a Western blot assay. All three mAbs seemed to be directed to the same epitope or to epitopes in close proximity as suggested by competition ELISAs. All three mAbs were able to inhibit the adherence of Chinese hamster ovary cells to purified FHA, and they could also inhibit the FHA-mediated agglutination of goose red blood cells. The attachment of B. pertussis to epithelial cell monolayers was inhibited by the mAb X3C. These antibodies are very useful probes to identify the presence of FHA in bordetellae species and in clinical reagents such as pertussis vaccines, and to characterize the functional domains of this important bacterial adhesin. 相似文献
9.
Cytochrome c-551.5 of the anaerobic sulfur-reducing bacterium Desulfuromonas acetoxidans has been purified to homogeneity and characterized. It elicits absorption bands at 551.5, 522.5 and 418 nm in the reduced form; the absorptivity ratio Aalpha(red)/A280nm(ox) equals 3.8 for the pure preparation. The molecular weight was estimated to be 9800 by gel filtration. Determination of the amion acid composition and analysis of the N-terminal amino acid sequence showed the cytochrome to be identical with the threehaem cytochrome c-551.5 (c7) isolated from the syntrophic mixed culture Chloropseudomonas ethylica strain 2K. The occurrence of multihaem cytochromes c in bacteria is discussed. 相似文献
10.