全文获取类型
收费全文 | 515篇 |
免费 | 55篇 |
国内免费 | 1篇 |
专业分类
571篇 |
出版年
2022年 | 7篇 |
2021年 | 5篇 |
2020年 | 6篇 |
2019年 | 4篇 |
2018年 | 6篇 |
2017年 | 8篇 |
2016年 | 16篇 |
2015年 | 11篇 |
2014年 | 18篇 |
2013年 | 12篇 |
2012年 | 16篇 |
2011年 | 31篇 |
2010年 | 14篇 |
2009年 | 19篇 |
2008年 | 25篇 |
2007年 | 27篇 |
2006年 | 17篇 |
2005年 | 26篇 |
2004年 | 18篇 |
2003年 | 8篇 |
2002年 | 19篇 |
2001年 | 14篇 |
2000年 | 19篇 |
1999年 | 11篇 |
1998年 | 10篇 |
1997年 | 4篇 |
1996年 | 13篇 |
1995年 | 7篇 |
1994年 | 3篇 |
1993年 | 7篇 |
1992年 | 16篇 |
1991年 | 14篇 |
1990年 | 12篇 |
1989年 | 12篇 |
1988年 | 17篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 13篇 |
1984年 | 13篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1969年 | 3篇 |
1967年 | 3篇 |
排序方式: 共有571条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
Extensive evidence indicate that platelet-derived growth factor (PDGF) and epidermal growth factor (EGF) play a key role in the stimulation of the 3T3 fibroblast replication: in this connection, PDGF and EGF act as a competence and a progression factor, respectively. We have previously demonstrated that EGF alone leads density-arrested EL2 rat fibroblasts to synthesize DNA and proliferate in serum-free cultures. Here, we have analyzed the role of EGF in the control of EL2 cell proliferation. Our data show a dose-related effect of EGF on DNA synthesis and cell growth, with maximal stimulation for both parameters at 20 ng/ml. On the other hand, autocrine production of PDGF or PDGF-like substances by EL2 cells is seemingly excluded by experiments with anti-PDGF serum or medium conditioned by EL2 fibroblasts. EGF binding studies show that EL2 cells possess high affinity EGF receptors, at a density level 3 to 4-fold higher than other fibroblastic lines. In addition, EL2 cells show a normal down-regulation of EGF receptors, following exposure to EGF, but PDGF, fibroblast growth factor (FGF), transforming growth factor beta (TGF beta) and bombesin have not decreased the affinity of EGF receptor for its ligand. Moreover, in EL2 cells, the EGF is able to induce the synthesis of putative intracellular regulatory proteins that govern the PDGF-induced competence in 3T3 cells. Our data indicate that EGF in EL2 cells may act as both a competence and a progression factor, via induction of the mechanisms, regulated in other cell lines by cooperation between different growth factors.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
5.
Isolation of highly multidrug-resistant P388 cells from drug-sensitive P388/S cells by flow cytometric cell sorting 总被引:1,自引:0,他引:1
To investigate the spontaneous frequency of occurrence of stable multidrug-resistant cells in a population of drug-sensitive cells, we exposed drug sensitive P388/S cells to daunorubicin (dnr) for 1 h, then used fluorescence-activated cell sorting based on intracellular dnr fluorescence to isolate cells within P388/S having different intracellular content of drug. One of the sort windows chosen (low dnr content sort window) isolated only P388/S cells with intracellular drug content equal to or less than that of the known multidrug-resistant subline P388/adr. This sort window constituted approximately 3% of P388/S cells with lowest dnr content. By such a procedure we were able, on one of seven attempts, to isolate and cultivate stable, highly multidrug-resistant cells (comparable to that of P388/adr) from the P388/S cells obtained from the low dnr-content sort window. Net growth of cells in culture was observed 15-20 days after sorting, indicating that of the P388/S cells collected from the low dnr-content sort window, very few were actually highly drug-resistant. On no occasion could resistant cells be cultivated from cells sorted from P388/S with higher dnr content, as would be expected if mutation to a multidrug-resistant phenotype had occurred as a result of exposure to drug. The resistant cells isolated from P388/S by sorting (called P388/LoSort) displayed low intracellular accumulation of dnr that was enhanced by verapamil, were cross-resistant to vincristine and actinomycin-D, and distinct from P388/S, possessed a 150- to 160-kD membrane species identified by Vinca alkaloid photoaffinity labeling.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
6.
The application of 31P nuclear magnetic resonance spectroscopy to the study of metabolism in roots of intact corn seedlings is described. 31P-NMR spectra of developmentally distinct parts of primary roots of whole seedlings are presented. The spectra are of quality comparable to those of excised pieces of plant tissue. 相似文献
7.
Ethidium bromide was added to cultured human leukemic bone marrow and solid tumor cells to evaluate its inhibitory effect on mitotic chromosome condensation and its possible application to high-resolution banding analysis. In most experiments ethidium bromide treatment resulted in a high proportion of mitotic cells having elongated chromosomes, without remarkable reduction in either the mitotic index or quality of metaphase chromosomes. Optimal effect on chromosome length was obtained by adding 10 micrograms/ml of ethidium bromide during the final 2 hr of culture. Because of the simplicity and reproducibility of the technique involved, ethidium bromide can be used routinely to extend the length of chromosomes for fine-banding analysis of malignant cells. 相似文献
8.
9.
M. Rouis P. Thomopoulos F. Louache U. Testa C. Hervy M. Titeux 《Experimental cell research》1985,157(2):539-543
The monocyte-like human cell line U-937 has been differentiated in vitro by incubation with either 1 alpha,25-dihydroxyvitamin D3 or retinoic acid (RA) plus dibutyryl cyclic AMP (db-cAMP). Both methods were effective in inducing the appearance of maturation markers. Their actions on insulin receptors were the opposite, however; 1 alpha,25-dihydroxyvitamin D3 increased the binding of the hormone, while RA plus db-cAMP decreased the binding. These effects were specific for insulin, since the transferrin receptors were reduced by both methods of differentiation. Thus, the changes in insulin receptors during maturation in vitro depend on the inducing agent and are not causally related to the differentiation process. 相似文献
10.
R Antonicelli G Coppa M Piani I Testa P Russo 《Bollettino della Società italiana di biologia sperimentale》1985,61(1):151-158
The measurements of intracellular "Na+ activity" was performed in 10 ml of heparinized venous blood. First the blood was three times washed in isotonic magnesium chloride solution (114 mmol/l). Thereby the buffy coat was removed. Then the microhematrocrit was taken for packet cell volume determination. After the erythrocytes were lysed by ultrasound. Sodium "Na+ Activity" is measured in the hemolysate by Ion-Selective electrode. With this method all "pipetting" operations are eliminated and for the "Na+ activity" determination was used ion-selective electrode with an indirect measurements, which is less influenced by the matrix. Reference intervals determined for a healthy population were 7.3 +/- 0.6 mmol/l. 相似文献