全文获取类型
收费全文 | 3761篇 |
免费 | 408篇 |
出版年
2023年 | 25篇 |
2022年 | 54篇 |
2021年 | 77篇 |
2020年 | 57篇 |
2019年 | 92篇 |
2018年 | 122篇 |
2017年 | 95篇 |
2016年 | 143篇 |
2015年 | 190篇 |
2014年 | 204篇 |
2013年 | 228篇 |
2012年 | 302篇 |
2011年 | 270篇 |
2010年 | 211篇 |
2009年 | 155篇 |
2008年 | 195篇 |
2007年 | 186篇 |
2006年 | 177篇 |
2005年 | 138篇 |
2004年 | 149篇 |
2003年 | 131篇 |
2002年 | 130篇 |
2001年 | 60篇 |
2000年 | 77篇 |
1999年 | 54篇 |
1998年 | 34篇 |
1997年 | 25篇 |
1996年 | 34篇 |
1995年 | 24篇 |
1994年 | 30篇 |
1993年 | 27篇 |
1992年 | 32篇 |
1991年 | 37篇 |
1990年 | 34篇 |
1989年 | 35篇 |
1988年 | 31篇 |
1987年 | 21篇 |
1986年 | 23篇 |
1985年 | 20篇 |
1984年 | 19篇 |
1983年 | 13篇 |
1982年 | 12篇 |
1981年 | 14篇 |
1980年 | 15篇 |
1979年 | 13篇 |
1977年 | 21篇 |
1975年 | 13篇 |
1974年 | 15篇 |
1973年 | 16篇 |
1972年 | 14篇 |
排序方式: 共有4169条查询结果,搜索用时 35 毫秒
81.
The induction of granulocyte and macrophage colony formation by the granulocyte-macrophage colony stimulating factor (GM-CSF) on bone marrow cells (BMC) was evaluated as a function of time in agar cultures. We found that while macrophage cell clusters were very abundant on the first two days of culture, granulocytic cell clusters did not appear until the third day. We also found that macrophage colonies were present from the fourth day of culture, while granulocyte colonies did not appear until the fifth day. When two day cell clusters were transferred to cultures with GM-CSF we observed that only macrophage-colonies developed. On the other hand, when four day clusters were transferred, both granulocyte and macrophage colony formation was obtained in a similar way as the one obtained when using GM-CSF with fresh BMC. Two day clusters did not respond to granulocyte colony stimulating factor (G-CSF) while fourth day clusters generated granulocytic colonies in a similar way as when G-CSF was used with fresh BMC. In order to test the hypothesis that granulocyte colony formation in these assays could be a result of the secretion of G-CSF by the macrophages previously induced by GM-CSF, lysates from macrophage colonies were used to induce colony formation on BMC. We observed that colonies, mainly granulocytic, were induced in a similar way as when G-CSF was used. Finally, the possibility that GM-CSF is just a macrophage inducer with the property to produce cells that secrete G-CSF is discussed. 相似文献
82.
83.
Neuro-2a cells incubated for 1 hour with 0.1 mM vanadate showed an increase in cell membrane permeability. This effect is dose dependent, e.g. with 0.01 mM, 0.1 mM and 1 mM vanadate, there was {20, 30 and 40% increase. In contrast, no alteration in permeability was observed in HEp-2 cells under the same conditions.Ethanol (3%, 1 h incubation) also enhanced membrane permeability. The increase was also greater with Neuro-2a cells ({80%) than with HEp-2 cells (~30%). When the cells were incubated with ethanol plus vanadate (0.1 mM), there was a marked potentiation ({200%) in cell membrane permeability in Neuro-2a cells, and again a lesser increase in permeability ({50%) with HEp-2 cells.These results seem to be due to a preferential effect of vanadate on passive permeability of Neuro-2a cells because parallel measurements demonstrate equal inhibition of (Na+K) ATPase with both Neuro-2a and HEp-2 cells. 相似文献
84.
E Santiago N López-Moratalla M J López-Zabalza A J Iriarte 《Revista Espanola de Fisiología》1981,37(3):263-268
The hydrolytic activity of F1-ATPase isolated from rat liver was enhanced in the presence of NADH, FADH2, QH2 or reduced cyt c. The extent of this activation depended largely on substrate concentration. F1-ATPase sensitivity to bicarbonate or dinitrophenol activators decreased in the presence of any of those electron donors, which originated as well a slight sensitivity to oligomycin and a sensitivity increase to the inhibitory anion OCN-. In the presence of oxidized carriers the sensitivity to bicarbonate, dinitrophenol, or OCN- was not modified, and the enzyme remained oligomycin insensitive. 相似文献
85.
Joaquin Timoneda Ruth Wallace Santiago Grisolía 《Biochemical and biophysical research communications》1981,101(2):555-562
Rat liver glutamate dehydrogenase (L-glutamate: NAD(P) oxidoreductase, deaminating) E.C. 1.4.1.3.) is inactivated by the mitochondrial matrix in combination with lysosomal preparations. Neither lysosomal or mitochondrial matrix extracts per se inactivate the enzyme appreciably under the conditions used. Fractionation of the matrix indicates that a low molecular weight factor is responsible for the potentiation of inactivation of glutamate dehydrogenase by lysosomes. Its absorption spectrum and chromatographic behaviour suggest that this factor is NADP. 相似文献
86.
A A Reyes 《Canadian journal of microbiology》1979,25(2):227-229
Populations of Fusarium oxysporum f. sp. spinaciae in root tissues and rhizosphere soil of diseased spinach plants were higher than in the root tissues and rhizosphere soil of healthy plants. Populations in soil rhizosphere were higher than in nonrhizosphere soil. The fungus populations were very low in the root tissues of the nonsusceptible strawberry, broccoli, chinese cabbage, and mustard grown in the infested field. The populations were low at the beginning of the season, increased, and remained high during the summer, then dropped in the fall. The fungus populations ranged from 1600 to 2600 propagules/g in the top 10 cm of soil, declined sharply between 11 and 20 cm, and were nondetectable between 41 and 60 cm. 相似文献
87.
Polyamines have been shown to bind to doubled stranded regions of rRNA [3]. Therefore, ribosomal proteins that can be cross linked to these molecules in the ribosomes structure must be bound to or located in the vicinity of the RNA. This technique is the first to yield results on the proteins associated with the rRNA in the eukaryotic ribosome where the lack of purified ribosomal proteins does not allow the use of direct binding studies as in bacterial systems. Proteins S7, S10, S13, S21, S22 and S27 in the small subunit and L2/3, L5, L10/12, L19/20, L22, L23, L36/37, L42 and L43' in the large subunit are labelled when cross linked to [14C]spermidine using 1,5-difluoro 2,4-dinitrobenzene and are good candidates to be RNA-binding proteins in ribosomes from Saccharomyces cerevisiae. 相似文献
88.
Rat liver ribosome treatment with ethanol and 1 M NH4Cl releases some 31–33 ribosomal proteins. This split protein fraction binds Phe-tRNA, Ac-Phe-tRNA, Met-tRNAM and f-Met-tRNAF in the absence of K+ and Mg++ ions. When the split protein fraction is passed through Sephadex G-100 only six proteins are retained in the column: S10, S14, S15, S19, L35, and L36. The aminoacyl-tRNA binding activity of this protein fraction retained in the Sephadex G-100 column is similar to that of the total split protein fraction, suggesting that the above six proteins, or only some of them, are involved in the binding reaction. 相似文献
89.
Lytic enzymes in the autolysis of filamentous fungi 总被引:4,自引:0,他引:4
The degrees of autolysis attained by five different genera of filamentous fungi during an incubation period of 60 days, under the same culture conditions were: 87.3% for Penicillium oxalicum; 65.9% for Neurospora crassa; 62.7% for Polystictus versicolor; 51.7% for Aspergillus niger and 23.5% for Nectria galligena. N. crassa, A. niger and P. versicolor reached the end of the autolysis during this incubation period (60 days), whereas P. oxalicum and N. galligena did not.The excretion of the lytic enzymes -N-acetyl-glucosaminidase, -1–3 glucanase, chitinase, invertase and acid phosphatase into the culture medium during growth and autolysis was investigated. The excretion of these enzymes was consistent with the degree of autolysis reached, the maximum excretion belonging to P. oxalicum and the minimum to N. galligena. The N. crassa invertase was excreted into the culture liquid at levels very much higher than the other enzymes studied, and at levels very much higher than the invertases excreted by the other fungi. 相似文献
90.