全文获取类型
收费全文 | 137篇 |
免费 | 17篇 |
出版年
2021年 | 1篇 |
2019年 | 2篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2015年 | 3篇 |
2014年 | 4篇 |
2013年 | 6篇 |
2012年 | 4篇 |
2011年 | 6篇 |
2010年 | 5篇 |
2009年 | 3篇 |
2008年 | 4篇 |
2007年 | 8篇 |
2006年 | 6篇 |
2005年 | 8篇 |
2004年 | 1篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 1篇 |
2000年 | 9篇 |
1999年 | 6篇 |
1998年 | 10篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 9篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1972年 | 3篇 |
1969年 | 7篇 |
1966年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有154条查询结果,搜索用时 15 毫秒
1.
2.
The kinetics of denaturation of DNA have been studied by relaxation techniques. Examination of the terminal relaxation times for a variety of DNA's under a variety of conditions has shown that DNA denaturation is principally a hydrodynamically limited process. Measurements within the helix–coil transition have demonstrated that the experimentally measured terminal relaxation times are a function of the following: (1) position in the helix–coil transition; (2) ionic strength of the solvent; (3) solvent viscosity; (4) DNA concentration; (5) molecular weight; (6) number and position of single-strand breaks. The dependence of the terminal relaxation time on the above mentioned factors can be attributed to hydrodynamic effects. Thus a hydrodynamic model for DNA unwinding is required. The model which best fits the data involves the assumption of a rotational frictional coefficient independent of molecular weight. This assumption is suggested by the fact that the relaxation time is proportional to the first power of the molecular weight. 相似文献
3.
Data from measurements of optical density of intact tissue and of anthocyanins in extracts resolved on cellulose thin layer plates were compared with visual evaluations of color quality and intensity in poinsettia, rose, and snapdragon. Visual evaluation was in good agreement with both instrumental and chemical determinations. However, the number or kinds of anthocyanins present could not be predicted from the visual evaluation or from the spectra of the fresh tissue. Data from the resolved extracts did not provide a basis for predicting the optical-density spectrum or the color of the intact tissue. In addition to the genetic factors which have been shown to control (1) the type of anthocyanin, (2) the amount of anthocyanin, and (3) the distribution of anthocyanins within the flower, we suggest another group of genes which apparently affect color through control of structural modification of individual anthocyanins in the living cell through shift in pH, metal chelation, and/or copigmentation. Such genes are apparently responsible for the modification of red color within the Wh Wh genotype of poinsettias containing both pelargonidin and cyanidin glycosides and for a very similar pink color in a snapdragon and a rose, each containing a single anthocyanin, a pelargonidin glycoside, and a cyanidin glycoside, respectively. 相似文献
4.
It is now well documented that apoptosis represents the prevalent mode of cell death in hybridoma cultures. Apoptotic or programmed cell death occurs spontaneously in late exponential phase of batch cultures. Until lately, no specific triggering factors had been identified. Recently, we observed that glutamine, cystine or glucose deprivation induced apoptosis in both hybridoma and myeloma cell lines whereas accumulation of toxic metabolites induced necrotic cell death in these cells. Other triggering factors such as oxygen deprivation might also be responsible for induction of apoptosis. In the present study, induction of cell death by exposure to anoxia was examined in batch culture of the SP2/0-derived hybridoma D5 clone. The mode of cell death was studied by morphological examination of acridine orange-ethidium bromide stained cells in a 1.5 L bioreactor culture grown under anoxic conditions for 75 hours. Under such conditions, viable cell density levelled off rapidly and remained constant for 25 hours. After 45 hours of anoxia, cell viability had decreased to 30% and the dead cell population was found to be 90% apoptotic. In terms of cellular metabolism, anoxia resulted in an increase in the utilization rates of glucose and arginine, and in a decrease in the utilization rate of glutamine. The lactate production rate and the yield of lactate on glucose increased significantly while the MAb production rate decreased. These results demonstrate that glycolysis becomes the main source of energy under anoxic conditions.Cells incubated for 10 hours or less under anoxic conditions were able to recuperate almost immediately and displayed normal growth rates when reincubated in oxic conditions whereas cells incubated for 22 hours or more displayed reduced growth rates. Nonetheless, even after 22 h or 29 h of anoxia, cells reincubated in oxic conditions showed no further progression into apoptosis. Therefore, upon removal of the triggering signal, induction of apoptosis ceased.Abbreviations VNA
Viable non-apoptotic cells
- VA
Viable apoptotic cells
- NVNA
Nonviable non-apoptotic or necrotic cells
- NVA
Nonviable apoptotic cells
- CF
Chromatin-free cells (late nonviable apoptotic cells)
- AO
Acridine orange
- EB
Ethidium Bromide
- MAb
Monoclocnal antibody
- D.O.
Dissolved oxygen
- qMAb
Specific MAb production rate (mg. (109 cells)–1.day–1)
-
Specific growth rate (h–1)
- Xv
Viable cell number (105 cells.mL–1)
- Xt
Total cell number (105 cells.mL–1)
- Ylac/glc
Yield coefficient of lactate on glucose (mM lactate produced/mM glucose consumed) 相似文献
5.
Suspension cultures of Sf-9 cells at different stages of growth were infected with a recombinant baculovirus expressing -galactosidase, using a range of multiplicities of infection (MOI) of 0.05 to 50. Following infection, the cells were resuspended either in the medium in which they had been grown or in fresh medium. Specific -galactosidase yields were not markedly affected by either MOI or medium change in cultures infected in early exponential phase (3×106 cells mL–1). In cultures infected at later growth stages, -galactosidase yields could only be maintained by medium replacement. The possibility that this requirement for medium replacement is due either to the accumulation of an inhibitory byproduct or nutrient limitation was examined. Alanine, a major byproduct of cultured insect cell metabolism, did not significantly reduce recombinant protein yield when added to infected cultures in concentrations of up to 40 mM. Following a factorial design, various nutrient concentrates were added alone or in combination to cultures infected in late exponential phase. Additions that included both yeastolate ultrafiltrate and an amino acid mixture restored specific -galactosidase yields to levels observed at earlier growth stages or in late stages with medium replacement; the addition of these concentrates, by permitting production at higher cell density, led to increases in the volumetric yield of recombinant protein. Together or separately, the concentrates when added to uninfected late exponential phase cultures, lead to a doubling of the maximum total cell protein level normally supported by unamended medium. 相似文献
6.
Scale-up of the adenovirus expression system for the production of recombinant protein in human 293S cells 总被引:6,自引:0,他引:6
Alain Garnier Johanne Côté Isabelle Nadeau Amine Kamen Bernard Massie 《Cytotechnology》1994,15(1-3):145-155
Human 293S cells, a cell line adapted to suspension culture, were grown to 5×106 cells/mL in batch with calcium-free DMEM. These cells, infected with new constructions of adenovirus vectors, yielded as much as 10 to 20% recombinant protein with respect to the total cellular protein content. Until recently, high specific productivity of recombinant protein was limited to low cell density infected cultures of no more than 5×105 cells/mL. In this paper, we show with a model protein, Protein Tyrosine Phosphatase 1C how high product yield can be maintained at high cell densities of 2×106 cells/mL by a medium replacement strategy. This allows the production of as much as 90 mg/L of active recombinant protein per culture volume. Analysis of key limiting/inhibiting medium components showed that glucose addition along with pH control can yield the same productivity as a medium replacement strategy at high cell density in calcium-free DMEM. Finally, the above results were reproduced in 3L bioreactor suspension culture thereby establishing the scalability of this expression system. The process we developed is used routinely with the same success for the production of various recombinant proteins and viruses.Abbreviations CFDMEM
calcium-free DMEM
- CS
bovine calf serum
- hpi
hours post-infection
- J+
enriched Joklik medium
- MLP
major late promoter
- MOI
multiplicity of infection (# of infectious viral particle/cell)
- q
specific consumption rate (mole/cell.h)
- pfu
plaque forming unit (# of infectious viral particle)
- Y
yield (g/E6 cells or mole/cell) 相似文献
7.
8.
The efficiency of lgM production by hybridoma cells (1) cultured in suspension; (2) entrapped in alginate beads; or (3) packed in hollowfiber cartridge bioreactors, were compared in long-term perfusion cultures. The results showed that steady-state cell concentration and antibody production, per liter of perfused medium per day, were similar when cells were either entrapped in alginate beads of maintained in suspension. These values were also similar whether cells were maintained at high density in a hollowfiber cartridge bioreactro, or at low density in suspension. This work points out that cell behavior and antibody yield are comparable overall in the various perfusion systems currently used. However, a significant reduction of antibody production appeared whenever a part of the viable cells was lost in the filtrate. The reduction was due both to a decrease of viable cell yield and a decline of lgM productivity on a percell basis. This result is well in agreement with the previously presented model of "grow or die" cell cycle system of hybridoma, which proposes that the ratio of arrested to proliferating cells in perfusion cultures, should be increased in proportion to cell retention in the bioreactor, with a concomitant increase of lgM productivity. 相似文献
9.
Danilo ML Prado Fabiana B Benatti Ana L de Sá-Pinto Ana P Hayashi Bruno Gualano Rosa MR Pereira Adriana ME Sallum Eloisa Bonfá Clovis A Silva Hamilton Roschel 《Arthritis research & therapy》2013,15(2):R46
Introduction
Exercise training has emerged as a promising therapeutic strategy to counteract physical dysfunction in adult systemic lupus erythematosus. However, no longitudinal studies have evaluated the effects of an exercise training program in childhood-onset systemic lupus erythematosus (C-SLE) patients. The objective was to evaluate the safety and the efficacy of a supervised aerobic training program in improving the cardiorespiratory capacity in C-SLE patients.Methods
Nineteen physically inactive C-SLE patients were randomly assigned into two groups: trained (TR, n = 10, supervised moderate-intensity aerobic exercise program) and non-trained (NT, n = 9). Gender-, body mass index (BMI)- and age-matched healthy children were recruited as controls (C, n = 10) for baseline (PRE) measurements only. C-SLE patients were assessed at PRE and after 12 weeks of training (POST). Main measurements included exercise tolerance and cardiorespiratory measurements in response to a maximal exercise (that is, peak VO2, chronotropic reserve (CR), and the heart rate recovery (ΔHRR) (that is, the difference between HR at peak exercise and at both the first (ΔHRR1) and second (ΔHRR2) minutes of recovery after exercise).Results
The C-SLE NT patients did not present changes in any of the cardiorespiratory parameters at POST (P > 0.05). In contrast, the exercise training program was effective in promoting significant increases in time-to-exhaustion (P = 0.01; ES = 1.07), peak speed (P = 0.01; ES = 1.08), peak VO2 (P = 0.04; ES = 0.86), CR (P = 0.06; ES = 0.83), and in ΔHRR1 and ΔHRR2 (P = 0.003; ES = 1.29 and P = 0.0008; ES = 1.36, respectively) in the C-SLE TR when compared with the NT group. Moreover, cardiorespiratory parameters were comparable between C-SLE TR patients and C subjects after the exercise training intervention, as evidenced by the ANOVA analysis (P > 0.05, TR vs. C). SLEDAI-2K scores remained stable throughout the study.Conclusion
A 3-month aerobic exercise training was safe and capable of ameliorating the cardiorespiratory capacity and the autonomic function in C-SLE patients.Trial registration
NCT01515163. 相似文献10.
Emilie M. M. Santos Wiro J. Niessen Albert J. Yoo Olvert A. Berkhemer Ludo F. Beenen Charles B. Majoie Henk. A. Marquering MR CLEAN investigators 《PloS one》2016,11(1)