全文获取类型
收费全文 | 5528篇 |
免费 | 411篇 |
国内免费 | 3篇 |
出版年
2022年 | 45篇 |
2021年 | 79篇 |
2020年 | 37篇 |
2019年 | 59篇 |
2018年 | 119篇 |
2017年 | 85篇 |
2016年 | 140篇 |
2015年 | 190篇 |
2014年 | 211篇 |
2013年 | 319篇 |
2012年 | 393篇 |
2011年 | 381篇 |
2010年 | 255篇 |
2009年 | 223篇 |
2008年 | 281篇 |
2007年 | 265篇 |
2006年 | 250篇 |
2005年 | 264篇 |
2004年 | 264篇 |
2003年 | 209篇 |
2002年 | 197篇 |
2001年 | 144篇 |
2000年 | 91篇 |
1999年 | 116篇 |
1998年 | 59篇 |
1997年 | 65篇 |
1996年 | 46篇 |
1995年 | 63篇 |
1994年 | 54篇 |
1993年 | 49篇 |
1992年 | 70篇 |
1991年 | 84篇 |
1990年 | 72篇 |
1989年 | 59篇 |
1988年 | 43篇 |
1987年 | 49篇 |
1986年 | 48篇 |
1985年 | 37篇 |
1984年 | 44篇 |
1983年 | 45篇 |
1982年 | 33篇 |
1981年 | 34篇 |
1980年 | 20篇 |
1979年 | 32篇 |
1978年 | 25篇 |
1977年 | 29篇 |
1976年 | 29篇 |
1975年 | 29篇 |
1973年 | 24篇 |
1967年 | 20篇 |
排序方式: 共有5942条查询结果,搜索用时 15 毫秒
11.
12.
The recovery of Lactobacillus bulgaricus was studied in correlation to the kinetics of cell drying. When bacteria were dehydrated at 30 °C, either in the presence
or the absence of sucrose, the drying kinetics corresponds to a Fickean diffusion in correspondence with a short lag time.
In contrast, when the bacteria were dehydrated at 70 °C in the absence of sugar, the kinetics corresponds to an anomalous
diffusion, and the lag time is four to five times higher than that at 30 °C. However, when drying at 70 °C was carried out
in the presence of sucrose, drying kinetics turned into a Fickean process parallel to a substantial decrease in the lag time.
The pattern of water desorption was correlated with the critical water activity. When the drying kinetics corresponds to a
Fickean diffusion, the lag time started to increase at 0.7 water activity, but when the cells were dried at 70 °C, the damage
started at 0.5 water activity. This observation indicates that the drying rate affects the pattern of water desorption, and
it can change the value of critical water activity. These results put into relevance that the cell recovery is due to the
drying history and that the recovery increase produced by sucrose can be related to the maintenance of kinetic barriers for
water desorption. 相似文献
13.
L Morbiato F Tombola S Campello G Del Giudice R Rappuoli M Zoratti E Papini 《FEBS letters》2001,508(3):479-483
The protein vacuolating toxin A (VacA) of Helicobacter pylori converts late endosomes into large vacuoles in the presence of permeant bases. Here it is shown that this phenomenon corresponds to an accumulation of permeant bases and Cl(-) in HeLa cells and requires the presence of extracellular Cl(-). The net influx of Cl(-) is due to electroneutral, Na(+), K(+), 2Cl(-) cotransporter-mediated transport. Cell vacuolation leads to cell volume increase, consistent with water flux into the cell, while hyper-osmotic media decreased vacuole formation. These data represent the first evidence that VacA-treated cells undergo an osmotic unbalance, reinforcing the hypothesis that the VacA chloride channel is responsible for cell vacuolation. 相似文献
14.
After reviewing the use of non-human primates of the Old and New Worlds for human malaria research, we concluded that another experimental animal which is easily available to use and possible to rear indoors is needed. Thus, we studied the susceptibility of the marmoset Callithrix penicillata to Plasmodium falciparum erythrocytic infections. The marmosets received various P. falciparum human isolates, directly from a patient and from continuous cultures. The Palo Alto strain, which has been adapted to the night monkey Aotus trivirgatus and further maintained in the squirrel monkey Saimiri sciureus was also used. In a total of 20 marmosets we performed 31 inoculations, with 10(5) to 10(9) parasites, intraperitoneally, intracardiacly or intravenously. Blood samples from each animal were examined daily up to day 90 post-inoculation. None of the intact marmosets developed patent infections. Four out of 19 C. penicillata, previously splenectomized, showed circulating parasites for up to five days after intravenous inoculation with the Palo Alto strain, becoming negative thereafter. Neither the addition to the simian diet of p-aminobenzoic acid, essential for the parasite metabolism, nor drug-immunosuppression, improved the marmoset susceptibility to P. falciparum. 相似文献
15.
16.
G Del Boccio C Di Ilio E Casalone A Pennelli A Aceto P Sacchetta G Federici 《The Italian journal of biochemistry》1987,36(1):8-17
An anionic (pI 4.6) isoenzyme of glutathione transferase was purified to homogeneity from human thyroid by affinity chromatography followed by isoelectric focusing. The content of enzyme was calculated to constitute about 0.2% of soluble proteins. The enzyme is formed by two identical subunits of 23,000 daltons approximately. The thyroid transferase did not catalyze the reduction of peroxides. Physical, catalytic and immunological analyses demonstrated extensive similarities between the thyroid transferase and the transferase from placenta, erythrocytes and breast. On the other hand, the thyroid transferase appears catalytically different from transferase 7-7, even if both cross-react with the antibodies raised against human placenta transferase. 相似文献
17.
G Del Bino R Silvestrini A Costa G Mazzini P Giordano 《Basic and applied histochemistry》1987,31(2):183-190
A flow cytometric study of DNA and protein contents was performed on cell suspensions obtained from 73 adult patients with non-Hodgkin lymphoma. Bivariate analysis identified a second subpopulation, not revealed by DNA determination, in 25% of the tumors. Protein heterogeneity was more frequently observed in diffuse than in nodular histology according the Rappaport classification and in high-grade than in low-grade malignancy tumors by the Kiel classification and the Working Formulation, but it was not related to ploidy or cell proliferative rate. The presence of an additional subpopulation, detected by protein analysis, defined as monoclonal by DNA analysis, could adversely affect clinical outcome in terms of response to treatment and overall survival. 相似文献
18.
Abstract. This study was designed to define some biological aspects of cell suspensions, obtained by mechanical or enzymatic disaggregations, and to verify whether single cell suspensions are representative of original solid tumours. The study was performed on a series of 25 human solid tumours including breast carcinoma, ovarian carcinoma and malignant melanoma. A higher cell viability and a loss of aneuploid subpopulations, or a lower fraction of aneuploid cells, were observed in enzymatically-released samples than in samples obtained by the mechanical procedure. Moreover, the proliferative activity, which was generally similar for the cell suspensions obtained by the two disaggregation procedures, was always markedly lower in the cell suspensions than in solid samples from the same tumour. In conclusion, the results from this study indicate that many changes, such as selective release of cell populations from the tumour matrix, damage and destruction of aneuploid and proliferating cells can be induced to various extents by different disaggregation procedures. 相似文献
19.
20.
M Fidanza M Dentini V Crescenzi P Del Vecchio 《International journal of biological macromolecules》1989,11(6):372-376
Viscosity, optical activity, and differential scanning calorimetry data clearly point out that partial and/or total removal of charged substituent groups, i.e. succinate and pyruvyl residues, from succinoglycan lead to water soluble derivatives exhibiting a higher stability order → disorder conformational changes with respect to the native polysaccharide. The new succinoglycan derivatives also exhibit very little, if any, hysteresis upon ‘renaturation’ (cooling) as opposed to the case of the parent polymer. The absence of ionized groups is thus beneficial, thermodynamically and kinetically, to the attainment in dilute aqueous solution of an ordered conformation by the uncharged succinoglycan backbone, as allowed by the regular enchainment of its constituent sugar residues. 相似文献