全文获取类型
收费全文 | 4903篇 |
免费 | 389篇 |
国内免费 | 1篇 |
出版年
2024年 | 5篇 |
2023年 | 34篇 |
2022年 | 76篇 |
2021年 | 176篇 |
2020年 | 108篇 |
2019年 | 145篇 |
2018年 | 147篇 |
2017年 | 143篇 |
2016年 | 209篇 |
2015年 | 319篇 |
2014年 | 309篇 |
2013年 | 366篇 |
2012年 | 431篇 |
2011年 | 432篇 |
2010年 | 244篇 |
2009年 | 229篇 |
2008年 | 276篇 |
2007年 | 289篇 |
2006年 | 266篇 |
2005年 | 231篇 |
2004年 | 187篇 |
2003年 | 166篇 |
2002年 | 154篇 |
2001年 | 39篇 |
2000年 | 26篇 |
1999年 | 37篇 |
1998年 | 36篇 |
1997年 | 7篇 |
1996年 | 12篇 |
1995年 | 8篇 |
1994年 | 17篇 |
1993年 | 6篇 |
1992年 | 13篇 |
1991年 | 19篇 |
1990年 | 9篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 9篇 |
1986年 | 13篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1982年 | 10篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1977年 | 3篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1971年 | 6篇 |
1970年 | 3篇 |
排序方式: 共有5293条查询结果,搜索用时 15 毫秒
31.
Abstract: We studied the action of H2 O2 on the exocytosis of glutamate by cerebrocortical synaptosomes. The treatment of synaptosomes with H2 O2 (50–150 µ M ) for a few minutes results in a long-lasting depression of the Ca2+ -dependent exocytosis of glutamate, induced by KCl or by the K+ -channel inhibitor 4-aminopyridine. The energy state of synaptosomes, as judged by the level of phosphocreatine and the ATP/ADP ratio, was not affected by H2 O2 , although a transient decrease was observed after the treatment. H2 O2 did not promote peroxidation, as judged by the formation of malondialdehyde. In indo-1-loaded synaptosomes, the treatment with H2 O2 did not modify significantly the KCl-induced increase of [Ca2+ ]i . H2 O2 inhibited exocytosis also when the latter was induced by increasing [Ca2+ ]i with the Ca2+ ionophore ionomycin. The effects of H2 O2 were unchanged in the presence of superoxide dismutase and the presence of the Fe3+ chelator deferoxamine. These results appear to indicate that H2 O2 , apparently without damaging the synaptosomes, induces a long-lasting inhibition of the exocytosis of glutamate by acting directly on the exocytotic process. 相似文献
32.
Keith Ashman Tony Houthaeve Jonathan Clayton Matthias Wilm Alexandre Podtelejnikov Ole N. Jensen Matthias Mann 《Letters in Peptide Science》1997,4(2):57-65
The rapid accumulation of sequence data generated by the various genome sequencingprojects and the generation of expressed sequence tag databases has resulted in the need forthe development of fast and sensitive methods for the identification and characterisation oflarge numbers of gel electrophoretically separated proteins to translate the sequence data intobiological function. To achieve this goal it has been necessary to devise new approaches toprotein analysis: matrix-assisted laser desorption and electrospray mass spectrometry havebecome important protein analytical tools which are both fast and sensitive. When combinedwith a robotic system for the in-gel digestion of electrophoretically separated proteins, itbecomes possible to rapidly identify many proteins by searching databases with MS data. Thepower of this combination of techniques is demonstrated by an analysis of the proteins presentin the myofibrillar lattice of the indirect flight muscle of Drosophila melanogaster. Theproteins were separated by SDS-PAGE and in-gel proteolysis was performed bothautomatically and manually. All 16 major proteins could quickly be identified by massspectrometry. Although most of the protein components were known to be present in theflight muscle, two new components were also identified. The combination of methodsdescribed offers a means for the rapid identification of large numbers of gel separatedproteins. 相似文献
33.
Experiments were performed to elucidate the role of cyclic guanosine monophosphate (cGMP) on platelet activation induced by protein kinase C (PKC) activators and calcium ionophore. Human platelets were pretreated with acetylsalicylic acid and with hirudin and apyrase. Aggregation and ATP secretion in response to the PKC activators 4 beta-phorbol 12-myristate 13-acetate (PMA) and 1-oleoyl 2-acetylglycerol (OAG) were inhibited by the nitrovasodilator sodium nitroprusside (SNP), an activator of guanylate cyclase, and by 8-bromo-cyclic GMP (8-Br-cGMP). The experiments were performed in the presence of M&B 22948, an inhibitor of cGMP phosphodiesterase. SNP and 8-Br-cGMP also inhibited platelet aggregation and secretion evoked by the ionophore ionomycin. In fura-2 loaded platelets SNP did not affect basal cytosolic Ca2+ level nor the rise induced by low concentrations of ionomycin, both in the presence and absence of extracellular Ca2+. The phosphorylation of the 47 and 20 kDa protein induced by ionomycin or PMA were not significantly decreased by SNP or 8-Br-cGMP. The present results suggest that cGMP is able to inhibit both the PKC and the Ca(2+)-dependent pathways leading to platelet activation by interfering, similarly to cAMP, with processes following protein phosphorylation, close to the effector systems. 相似文献
34.
Summary Mouse morulae are known to undergo cavitation as soon as some external cells have entered the sixth cell cycle (Garbutt et al. 1987). Since the early cytological features of cavitation are still unclear, we undertook a careful ultrastructural analysis of late morulae-nascent blastocysts. In addition, since maturation of lysosomes might be involved in the first step of cavity formation, we focused our attention on these organelles by means of the cytochemical localization of trimetaphosphatase activity and by the study of the effects of chloroquine on precavitation embryos. Our results suggest that cavitation starts in a few external cells (presumably competent cells entering the sixth cell cycle), by the chloroquine-sensitive formation of degradative autophagic vacuoles engulfing lipid droplets and vacuoles containing osmiophilic material. These complex structures enlarge (as a result of lipid metabolism?) and so transform into intrablastomeric cavities which, by means of a membrane fusion process, very rapidly become extracellular cavities that coalesce. The abembryonic pole of the blastocyst is determined in this way. Moreover, we suggest that the juxtacoelic cytoplasmic processes covering the inner cell mass (ICM) cells, which are known to restrict the expression of their totipotency during early cavitation (Fleming et al. 1984), are the latest remnants of the walls of the growing intrablastomeric cavities. 相似文献
35.
Michael R. Boarder Alexandre J. Lockfeld Jack D. Barchas 《Journal of neurochemistry》1982,38(2):299-304
Abstract: A specific and sensitive radioimmunoassay procedure for Metenkephalin[Arg6 ,Phe7 ] which allows its measurement in regions of the rat brain is described. The antiserum was raised against the methionine sulphoxide derivative of the peptide, and all samples and standards were oxidized with hydrogen peroxide prior to use in the assay with chloramine T-oxidized 125 I-labelled Met(O)-enkephalin[Arg6 ,Phe7 ]. The only significant cross-reactivity was 30% with the reduced heptapeptide Met-enkephalin[Arg6 ,Phe7 ]. The assay showed less than 0.15% cross-reactivity with fragments of the heptapeptide and with leucine-enkephalin-containing peptides. Acid acetone extraction of rat striatum followed by Sephadex G-50 chromatography and reverse-phase high pressure liquid chromatography showed that essentially all immunoreactivity co-chromatographed with Met-enkephalin[Arg6 ,Phe7 ]. This confirmed the specificity of the assay and showed that the striatum does not contain a high concentration of larger molecular weight forms with the heptapeptide at the COOH terminus. Distribution of the heptapeptide followed that of methionine enkephalin, with highest concentrations in the globus pallidus, intermediate levels in caudate-putamen and hypothalamus, and low levels in cortex and cerebellum. 相似文献
36.
37.
38.
Alexandre Rich 《Biochimie》1975,56(11-12)
The three-dimensional structure of yeast phenylalanine transfert RNA has been determined in orthorhombic crystals. The current status of this work is reviewed together with the relationship of the transfer RNA structure in the crystal to its biologically active form. In addition some speculations are put forward regarding the mode of interaction of tRNA molecules in the ribosome and the manner in which tRNA interacts with aminoacyl synthetase. 相似文献
39.
40.
Catarina Macedo-Silva Vera Miranda-Gonalves Ana Lameirinhas Joana Lencart Alexandre Pereira Joo Lobo Rita Guimares Ana Teresa Martins Rui Henrique Isabel Bravo Carmen Jernimo 《Cell death & disease》2020,11(12)
Esophageal squamous cell carcinoma (ESCC), the most frequent esophageal cancer (EC) subtype, entails dismal prognosis. Hypoxia, a common feature of advanced ESCC, is involved in resistance to radiotherapy (RT). RT response in hypoxia might be modulated through epigenetic mechanisms, constituting novel targets to improve patient outcome. Post-translational methylation in histone can be partially modulated by histone lysine demethylases (KDMs), which specifically removes methyl groups in certain lysine residues. KDMs deregulation was associated with tumor aggressiveness and therapy failure. Thus, we sought to unveil the role of Jumonji C domain histone lysine demethylases (JmjC-KDMs) in ESCC radioresistance acquisition. The effectiveness of RT upon ESCC cells under hypoxic conditions was assessed by colony formation assay. KDM3A/KDM6B expression, and respective H3K9me2 and H3K27me3 target marks, were evaluated by RT-qPCR, Western blot, and immunofluorescence. Effect of JmjC-KDM inhibitor IOX1, as well as KDM3A knockdown, in in vitro functional cell behavior and RT response was assessed in ESCC under hypoxic conditions. In vivo effect of combined IOX1 and ionizing radiation treatment was evaluated in ESCC cells using CAM assay. KDM3A, KDM6B, HIF-1α, and CAIX immunoexpression was assessed in primary ESCC and normal esophagus. Herein, we found that hypoxia promoted ESCC radioresistance through increased KDM3A/KDM6B expression, enhancing cell survival and migration and decreasing DNA damage and apoptosis, in vitro. Exposure to IOX1 reverted these features, increasing ESCC radiosensitivity and decreasing ESCC microtumors size, in vivo. KDM3A was upregulated in ESCC tissues compared to the normal esophagus, associating and colocalizing with hypoxic markers (HIF-1α and CAIX). Therefore, KDM3A upregulation in ESCC cell lines and primary tumors associated with hypoxia, playing a critical role in EC aggressiveness and radioresistance. KDM3A targeting, concomitant with conventional RT, constitutes a promising strategy to improve ESCC patients’ survival.Subject terms: Predictive markers, Cancer 相似文献