全文获取类型
收费全文 | 5900篇 |
免费 | 414篇 |
国内免费 | 201篇 |
专业分类
6515篇 |
出版年
2024年 | 10篇 |
2023年 | 59篇 |
2022年 | 144篇 |
2021年 | 210篇 |
2020年 | 122篇 |
2019年 | 174篇 |
2018年 | 192篇 |
2017年 | 146篇 |
2016年 | 240篇 |
2015年 | 376篇 |
2014年 | 380篇 |
2013年 | 455篇 |
2012年 | 570篇 |
2011年 | 486篇 |
2010年 | 310篇 |
2009年 | 276篇 |
2008年 | 348篇 |
2007年 | 339篇 |
2006年 | 287篇 |
2005年 | 250篇 |
2004年 | 206篇 |
2003年 | 194篇 |
2002年 | 196篇 |
2001年 | 62篇 |
2000年 | 42篇 |
1999年 | 51篇 |
1998年 | 32篇 |
1997年 | 21篇 |
1996年 | 20篇 |
1995年 | 23篇 |
1994年 | 11篇 |
1993年 | 17篇 |
1992年 | 30篇 |
1991年 | 19篇 |
1990年 | 17篇 |
1989年 | 20篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1986年 | 16篇 |
1985年 | 15篇 |
1984年 | 9篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 11篇 |
1979年 | 11篇 |
1977年 | 10篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1974年 | 7篇 |
1973年 | 6篇 |
排序方式: 共有6515条查询结果,搜索用时 0 毫秒
31.
G. Menestrina C. Pederzolli M. Dalla Serra M. Bregante F. Gambale 《The Journal of membrane biology》1996,149(2):113-121
Escherichia coli hemolysin is known to cause hemolysis of red blood cells by forming hydrophilic pores in their cell membrane. Hemolysin-induced
pores have been directly visualized in model systems such as planar lipid membranes and unilamellar vesicles. However this
hemolysin, like all the members of a related family of toxins called Repeat Toxins, is a potent leukotoxin. To investigate
whether the formation of channels is involved also in its leukotoxic activity, we used patch-clamped human macrophages as
targets. Indeed, when exposed to the hemolysin, these cells developed additional pores into their membrane. Such exogenous
pores had properties very different from the endogenous channels already present in the cell membrane (primarily K+ channels), but very similar to the pores formed by the toxin in purely lipidic model membranes. Observed properties were:
large single channel conductance, cation over anion selectivity but weak discrimination among different cations, quasilinear
current-voltage characteristic and the existence of a flickering pre-open state of small conductance. The selectivity properties
of the toxin channels appearing in phospholipid vesicles were also investigated, using a specially adapted polarization/depolarization
assay, and were found to be completely consistent with that of the current fluctuations observed in excised macrophage patches.
Received: 14 August 1995/Revised: 2 October 1995 相似文献
32.
We present a list of Italian freshwater and marine Oligochaeta in the families Lumbriculidae, Haplotaxidae, Tubificidae, Naididae, Propappidae, Criodrilidae, and Lumbricidae, representing 57 genera and 130 species. Published data reflect the incomplete knowledge of the Italian oligochaete fauna, restricted to certain geographical areas. Subterranean aquatic and marine fauna are of particular interest as these have been studied the least. We provide a comprehensive review of the Naididae including, for the first time, southern Italy and the islands of Sicily and Sardinia. The distribution of species is discussed and taxonomic problems arising from the morphological variability of Italian material are examined. 相似文献
33.
34.
Halide permeation through three types of epithelial anion channels after reconstitution into giant liposomes 总被引:1,自引:0,他引:1
Anion-selective channels from apical membranes of cultured CFPAC-1 cells were isolated and incorporated into giant liposomes for patch clamp recording. Liposomes were formed from L--lecithin by a dehydration-hydration method. Ion channels were characterized using the excised inside-out patch clamp configuration. The most commonly observed anion channels were similar to those observed in native epithelial tissues. The linear 20 pS Cl channel had the halide permeability sequence Cl– > I– Br– > F–, and showed anomalous mole-fraction behavior in solutions containing different proportions of Cl– and F–, ions. The autwardly rectifying Cl– channel had the halide permeability sequence I– > Br– > Cl– > F–, and also showed anomalous molefraction behavior, indicating that both these channels probably contain multi-ion pores. The third, voltage-dependent anion channel showed at least five different substrates, had a conductance of 390 pS in the main state, and showed two types of kinetics, fast (openings and closings < 1 ms), and slow (openings and closings > 1 s). The channel was seen more frequently after reconstitution into giant liposomes than in intact cells. It was not selective amongst the halides, and there was no deviation from a linear dependence of relative current on molar fractions, indicating relatively simple permeation through the pore. Differences in halide permeabilities suggest that different anion channels may be related to different membrane proteins. Comparison with the chloride channel proteins isolated biochemically from epithelial cell membranes is discussed.
Correspondence to: M. Duszyk 相似文献
35.
The expression of smooth muscle myosin light chain kinase (MLCK) was investigated during chicken gizzard development. The molecular weight and the antigenic properties of MLCK did not change during development. The use of anion exchange high performance liquid chromatography (HPLC) enabled us to distinguish between MLCKs from post-hatched and adult chickens. A partial amino acid sequence determination of 4-day-old gizzard MLCK failed to disclose differences in the primary sequences of the two proteins. The results suggest that MLCK has the same primary sequence in all sequences of the two proteins. The results suggest that MLCK has the same primary sequence in all stages of gizzard development, although charge variants due to post-translational modifications may exist. 相似文献
36.
Serafina Perrone Chiara Lembo Maurizio Giordano Chiara Petrolini Laura Cannavò Eloisa Gitto 《Journal of biochemical and molecular toxicology》2023,37(6):e23349
Oxidative stress is a pathological condition characterized by an overload of oxidant products, named free radicals, which are not well counteracted by antioxidant systems. Free radicals induce oxidative damage to many body organs and systems. In neonatal red blood cells, free-radical mediated-oxidative stress leads to eryptosis, a suicidal death process of erythrocytes consequent to alteration of cell integrity. Neonatal red blood cells are targets and at the same time generators of free radicals through the Fenton and Haber-Weiss reactions. Enhanced eryptosis in case of oxidative stress damage may cause anemia if the increased loss of erythrocytes is not enough compensated by enhanced new erythrocytes synthesis. The oxidative disruption of the red cells may cause unconjugated idiopathic hyperbilirubinemia in neonates. High levels of bilirubin are recognized to be dangerous for the central nervous system in newborns, however, many studies have highlighted the antioxidant function of bilirubin. Recently, it has been suggested that physiologic concentration of bilirubin correlates with higher antioxidant status while high pathological bilirubin levels are associated with pro-oxidants effects. The aim of this educational review is to provide an updated understanding of the molecular mechanisms underlying erythrocyte oxidant injury and its reversal in neonatal idiopathic hyperbilirubinemia. 相似文献
37.
Elisabetta Zennaro Ilaria Ciabatti Francesca Cutruzzola Rosanna D'Alessandro Maria Chiara Silvestrini 《FEMS microbiology letters》1993,109(2-3):243-250
Abstract The expression of nitrite reductase has been tested in a wild-type strain of Pseudomonas aeruginosa (Pao1) as a function of nitrate concentration under anaerobic and aerobic conditions. Very low levels of basal expression are shown under non-denitrifying conditions (i.e. absence of nitrate, in both aerobic and anaerobic conditions); anaerobiosis is not required for high levels of enzyme production in the presence of nitrate. A Pseudomonas aeruginosa strain, mutated in the nitrite reductase gene, has been obtained by gene replacement. This mutant, the first of this species described up to now, is unable to grow under anaerobic conditions in the presence of nitrate. The anaerobic growth can be restored by complementation with the wild-type gene. 相似文献
38.
39.
Fiorito Serena Collevecchio Chiara Epifano Francesco Genovese Salvatore Palumbo Lucia 《Phytochemistry Reviews》2023,22(1):73-84
Phytochemistry Reviews - Oxyprenylated secondary metabolites of plant, fungal, and microbial origin have emerged as biologically active natural compounds with a great potential for the next future.... 相似文献
40.
C. Olivari Maria Chiara Pugliarello Franca Rasi-Caldogno Maria Ida De Michelis 《Plant biology (Stuttgart, Germany)》1993,106(1):13-19
The aqueous two-phase partitioning technique was utilized to isolate a plasma membrane (PM) fraction from etiolated seedlings of Arabidopsis thaliana. The purification procedure adopted yielded a fraction highly enriched in PM as compared to inner membranes, with a recovery of about 30%, as judged from the activities of PM markers such as vanadate-sensitive ATPase, FC binding and UDP-glucose sterol glucosyltransferase. The purified PM fraction displayed vanadate-sensitive H+ pumping activity. Its purity was confirmed by the biochemical characteristics of its ATPase activity assayed in the absence of Ca2+: sensitivity to vanadate (IC50 ca. 1 μM), Mg2+-dependence, insensitivity to molybdate, oligomycin and nitrate, pH optimum at 6.6. The PM H+-ATPase activity was stimulated by fusicoccin and by a controlled treatment of the PM with trypsin. In both cases stimulation was much stronger on the activity assayed at pH 7.5 than on the activity at pH 6.6. Moreover, neither fusicoccin nor the treatment with trypsin stimulated the portion of activity (30 to 40% at pH 7.5) which decayed upon preincubation of the PM in assay medium without ATP. 相似文献