全文获取类型
收费全文 | 4546篇 |
免费 | 325篇 |
国内免费 | 1篇 |
出版年
2024年 | 3篇 |
2023年 | 33篇 |
2022年 | 77篇 |
2021年 | 127篇 |
2020年 | 52篇 |
2019年 | 83篇 |
2018年 | 114篇 |
2017年 | 133篇 |
2016年 | 173篇 |
2015年 | 232篇 |
2014年 | 276篇 |
2013年 | 334篇 |
2012年 | 420篇 |
2011年 | 427篇 |
2010年 | 231篇 |
2009年 | 170篇 |
2008年 | 250篇 |
2007年 | 274篇 |
2006年 | 255篇 |
2005年 | 268篇 |
2004年 | 226篇 |
2003年 | 192篇 |
2002年 | 174篇 |
2001年 | 53篇 |
2000年 | 19篇 |
1999年 | 28篇 |
1998年 | 45篇 |
1997年 | 19篇 |
1996年 | 17篇 |
1995年 | 21篇 |
1994年 | 10篇 |
1993年 | 15篇 |
1992年 | 9篇 |
1991年 | 8篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 10篇 |
1987年 | 14篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1968年 | 2篇 |
1967年 | 2篇 |
排序方式: 共有4872条查询结果,搜索用时 15 毫秒
191.
Adding distracters to a display impairs performance on visual tasks (i.e. the set-size effect). While keeping the display characteristics constant, we investigated this effect in three tasks: 2 target identification, yes-no detection with 2 targets, and 8-alternative localization. A Signal Detection Theory (SDT) model, tailored for each task, accounts for the set-size effects observed in identification and localization tasks, and slightly under-predicts the set-size effect in a detection task. Given that sensitivity varies as a function of spatial frequency (SF), we measured performance in each of these three tasks in neutral and peripheral precue conditions for each of six spatial frequencies (0.5-12 cpd). For all spatial frequencies tested, performance on the three tasks decreased as set size increased in the neutral precue condition, and the peripheral precue reduced the effect. Larger set-size effects were observed at low SFs in the identification and localization tasks. This effect can be described using the SDT model, but was not predicted by it. For each of these tasks we also established the extent to which covert attention modulates performance across a range of set sizes. A peripheral precue substantially diminished the set-size effect and improved performance, even at set size 1. These results provide support for distracter exclusion, and suggest that signal enhancement may also be a mechanism by which covert attention can impose its effect. 相似文献
192.
Sola M Bavro VN Timmins J Franz T Ricard-Blum S Schoehn G Ruigrok RW Paarmann I Saiyed T O'Sullivan GA Schmitt B Betz H Weissenhorn W 《The EMBO journal》2004,23(13):2510-2519
Gephyrin is a bi-functional modular protein involved in molybdenum cofactor biosynthesis and in postsynaptic clustering of inhibitory glycine receptors (GlyRs). Here, we show that full-length gephyrin is a trimer and that its proteolysis in vitro causes the spontaneous dimerization of its C-terminal region (gephyrin-E), which binds a GlyR beta-subunit-derived peptide with high and low affinity. The crystal structure of the tetra-domain gephyrin-E in complex with the beta-peptide bound to domain IV indicates how membrane-embedded GlyRs may interact with subsynaptic gephyrin. In vitro, trimeric full-length gephyrin forms a network upon lowering the pH, and this process can be reversed to produce stable full-length dimeric gephyrin. Our data suggest a mechanism by which induced conformational transitions of trimeric gephyrin may generate a reversible postsynaptic scaffold for GlyR recruitment, which allows for dynamic receptor movement in and out of postsynaptic GlyR clusters, and thus for synaptic plasticity. 相似文献
193.
194.
195.
196.
Spontaneous autoimmunity in 129 and C57BL/6 mice-implications for autoimmunity described in gene-targeted mice 总被引:1,自引:1,他引:0
Bygrave AE Rose KL Cortes-Hernandez J Warren J Rigby RJ Cook HT Walport MJ Vyse TJ Botto M 《PLoS biology》2004,2(8):e243
Systemic lupus erythematosus (SLE) is a multisystem autoimmune disorder in which complex genetic factors play an important role. Several strains of gene-targeted mice have been reported to develop SLE, implicating the null genes in the causation of disease. However, hybrid strains between 129 and C57BL/6 mice, widely used in the generation of gene-targeted mice, develop spontaneous autoimmunity. Furthermore, the genetic background markedly influences the autoimmune phenotype of SLE in gene-targeted mice. This suggests an important role in the expression of autoimmunity of as-yet-uncharacterised background genes originating from these parental mouse strains. Using genome-wide linkage analysis, we identified several susceptibility loci, derived from 129 and C57BL/6 mice, mapped in the lupus-prone hybrid (129 × C57BL/6) model. By creating a C57BL/6 congenic strain carrying a 129-derived Chromosome 1 segment, we found that this 129 interval was sufficient to mediate the loss of tolerance to nuclear antigens, which had previously been attributed to a disrupted gene. These results demonstrate important epistatic modifiers of autoimmunity in 129 and C57BL/6 mouse strains, widely used in gene targeting. These background gene influences may account for some, or even all, of the autoimmune traits described in some gene-targeted models of SLE. 相似文献
197.
Determination of new derivatives of genistein in culture media by liquid chromatography 总被引:1,自引:0,他引:1
Ksycińska H Sobik B Popiołkiewicz J Polkowski K Krzeczyński P Ramza J Pucko W Grynkiewicz G 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2004,799(2):217-231
Methods for determination of genistein and its four new analogues in culture media have been developed to support studies on their potential anticancer activities. The investigated compounds were extracted from the media using liquid-liquid extraction with appropriate solvent. After evaporation of organic solvents each of the dry extracts was reconstituted in appropriate mobile phase. Reversed-phase HPLC was applied to quantitative determining of tested compounds. The methods are specific, sensitive and technically simple. They were used to evaluate concentration level of investigated compounds in experiments with human promyelocytic leukemia cells (HL-60 cell line). 相似文献
198.
Davezac N Tondelier D Lipecka J Fanen P Demaugre F Debski J Dadlez M Schrattenholz A Cahill MA Edelman A 《Proteomics》2004,4(12):3833-3844
Cystic fibrosis (CF) is a genetic disease caused by mutations in the CF gene (cftr). Physiologically, CF is characterized by an abnormal chloride secretion in epithelia due to a dysfunction of a mutated cystic fibrosis transmembrane conductance regulator (CFTR). CFTR is a cAMP-dependent chloride channel whose most frequent mutation, deltaF508, leads to an aberrantly folded protein which causes a dysfunction of the channel. However, a growing number of reports suggest that modifier genes and environmental factors are involved in the physiology of CF. To identify proteins whose expression depends on wild-type WT-CFTR or deltaF508-CFTR, we chose a global proteomic approach based on the use of two-dimensional gel electrophoresis (2-DE) and mass spectrometry. The experiments were carried out with HeLa cells stably transfected with WT-CFTR (pTCFWT) or deltaF508-CFTR (pTCFdeltaF508). These experiments unmasked keratin 8 (K8) and 18 (K18) which were differentially expressed in pTCFWT vs. pTCFdeltaF508. An immunoblot of K18 confirmed the 2-DE results. Intracellular localization experiments of WT-CFTR, deltaF508-CFTR, K8, and K18 suggest that the expression of these proteins are linked, and that the concentrations of K8 and K18 and/or their distribution may be involved in the traffic of WT-CFTR/deltaF508-CFTR. A functional assay for CFTR revealed that specifically lowering K18 expression or changing its distribution leads to the delivery of functional deltaF508-CFTR to the plasma membrane. This work suggests a novel function of K18 in CF. 相似文献
199.
Golankiewicz B Januszczyk P Zeidler J Popenda M 《Nucleosides, nucleotides & nucleic acids》2004,23(1-2):127-136
Two new types of imidazole derivatives: N-(2-R1-5-R2-1H-imidazol-4-yl) thioureas 7a-g and N-(2-R1-5-R2-1H-imidazol-4-yl) formamides 8b,c,g were obtained in high yields by the hydrolytic degradation of 6-R1-8-R2-2-thioxo-2,3-dihydroimidazo[1,5-a]-1,3,5-triazin-4(1H)-ones 5a-g and 6-R1-8-R2-imidazo[1,5-a]-1,3,5-triazin-4(3H)-ones 6b,c,d, respectively. The tautomeric preferences of the new imidazoles were determined. 相似文献
200.
Qualitative and quantitative composition of pigments in Phaeodactylum tricornutum (Bacillariophyceae) stressed by iron 总被引:1,自引:0,他引:1
The effect of Fe(III) deficiency on qualitative and quantitative changes in pigment composition in Phaeodactylum tricornutum Bohlin was demonstrated by HPLC and AAS. Maximum content of pigments showed the diatom cells incubated at the optimum iron concentration, i.e., 10 M. The contents of chlorophyll a, chlorophyll c
1+c
2, fucoxanthin, diadinoxanthin and ,-carotene were 109.99, 20.16, 40.39, 1.29 and 1.48 fg per cell, respectively. The results obtained showed that Fe(III) affected qualitative and quantitative pigment composition in P. tricornutum. The content of individual pigments, proportions between accompanying pigments and their ratios to chlorophyll a were important indicators of phytoplankton response to iron stress. The strong reduction in ,-carotene content, several times (2–5) increase in diadinoxanthin level as compared to ,-carotene, and high amount of diadinoxanthin in relation to chlorophyll a were observed in algae growing at very low Fe(III) concentrations, 0.001 and 0.01 M. The data suggested that phytoplankton pigments could be a potential physiological marker. 相似文献