全文获取类型
收费全文 | 2368篇 |
免费 | 177篇 |
专业分类
2545篇 |
出版年
2023年 | 26篇 |
2022年 | 29篇 |
2021年 | 61篇 |
2020年 | 45篇 |
2019年 | 48篇 |
2018年 | 75篇 |
2017年 | 54篇 |
2016年 | 97篇 |
2015年 | 128篇 |
2014年 | 145篇 |
2013年 | 139篇 |
2012年 | 201篇 |
2011年 | 168篇 |
2010年 | 134篇 |
2009年 | 111篇 |
2008年 | 106篇 |
2007年 | 129篇 |
2006年 | 129篇 |
2005年 | 102篇 |
2004年 | 92篇 |
2003年 | 76篇 |
2002年 | 57篇 |
2001年 | 40篇 |
2000年 | 41篇 |
1999年 | 31篇 |
1998年 | 21篇 |
1997年 | 20篇 |
1996年 | 9篇 |
1995年 | 15篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1992年 | 18篇 |
1991年 | 17篇 |
1990年 | 13篇 |
1989年 | 9篇 |
1988年 | 12篇 |
1987年 | 13篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1982年 | 7篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1972年 | 6篇 |
1970年 | 5篇 |
1967年 | 6篇 |
排序方式: 共有2545条查询结果,搜索用时 15 毫秒
101.
Eulália Silva dos Santos Pinheiro Fernanda Costa de Queirós Pedro Montoya Cleber Luz Santos Marion Alves do Nascimento Clara Hikari Ito Manuela Silva David Barros Nunes Santos Silvia Benevides José Garcia Vivas Miranda Katia Nunes Sá Abrah?o Fontes Baptista 《PloS one》2016,11(2)
The main objective of this study is to review and summarize recent findings on electroencephalographic patterns in individuals with chronic pain. We also discuss recent advances in the use of quantitative Electroencephalography (qEEG) for the assessment of pathophysiology and biopsychosocial factors involved in its maintenance over time. Data collection took place from February 2014 to July 2015 in PubMed, SciELO and PEDro databases. Data from cross-sectional studies and longitudinal studies, as well as clinical trials involving chronic pain participants were incorporated into the final analysis. Our primary findings related to chronic pain were an increase of theta and alpha EEG power at rest, and a decrease in the amplitude of evoked potentials after sensory stimulation and cognitive tasks. This review suggests that qEEG could be considered as a simple and objective tool for the study of brain mechanisms involved in chronic pain, as well as for identifying the specific characteristics of chronic pain condition. In addition, results show that qEEG probably is a relevant outcome measure for assessing changes in therapeutic studies. 相似文献
102.
Enhancement of transient gene expression by fed-batch culture of HEK 293 EBNA1 cells in suspension 总被引:1,自引:0,他引:1
Enhanced green fluorescence protein (GFP) and erythropoietin (EPO) were used as reporters to assess and improve transient
gene expression in HEK 293 EBNA1 cells. The production of EPO only lasted 3 days and reached 18.1 mg/l in suspension cultures
in 1 l batch bioreactors. However, GFP expression examined in well-plate experiments persisted for 12 days in transfected
cells but decreased rapidly within the next 15 days. These results suggest that the retaining of a plasmid in cells may not
be a limiting factor for protein expression in large-scale transient transfection. To improve cell maintenance and protein
expression, a fed-batch culture was performed using an enriched medium, a mixture of equal volumes of 293 SFM II medium and
a 5 × amino acid solution prepared based on DMEM/F12 medium formula. EPO reached 33.6 mg/l, representing 86% increase over
that of the batch culture. Moreover, the total amount of EPO produced was increased by 165% in view of the volume increase
in the fed-batch culture. The serum-free medium used in this work enables cells growing well and transfection without medium
change. Thus, the process reported here is simple and easy to scale up. 相似文献
103.
Sylvia Toet Johannes H. C. Cornelissen Rien Aerts Richard S. P. van Logtestijn Miranda de Beus Rob Stoevelaar 《Plant Ecology》2006,182(1-2):27-40
We studied the effects of elevated CO2 (180–200 ppmv above ambient) on growth and chemistry of three moss species (Sphagnum palustre, S. recurvum and Polytrichum commune) in a lowland peatland in the Netherlands. Thereto, we conducted both a greenhouse experiment with both Sphagnum species and a field experiment with all three species using MiniFACE (Free Air CO2 Enrichment) technology during 3 years. The greenhouse experiment showed that Sphagnum growth was stimulated by elevated CO2 in the short term, but that in the longer term (≥1 year) growth was probably inhibited by low water tables and/or down-regulation
of photosynthesis. In the field experiment, we did not find significant changes in moss abundance in response to elevated
CO2, although CO2 enrichment appeared to reduce S. recurvum abundance. Both Sphagnum species showed stronger responses to spatial variation in hydrology than to increased atmospheric CO2 concentrations. Polytrichum was insensitive to changes in hydrology. Apart from the confounding effects of hydrology, the relative lack of growth response
of the moss species may also have been due to the relatively small increase in assimilated CO2 as achieved by the experimentally added CO2. We calculated that the added CO2 contributed at most 32% to the carbon assimilation of the mosses, while our estimates based on stable C isotope data even
suggest lower contributions for Sphagnum (24–27%). Chemical analyses of the mosses showed only small elevated CO2 effects on living tissue N concentration and C/N ratio of the mosses, but the C/N ratio of Polytrichum was substantially lower than those of the Sphagnum species. Continuing expansion of Polytrichum at the expense of Sphagnum could reduce the C sink function of this lowland Sphagnum peatland, and similar ones elsewhere, as litter decomposition rates would probably be enhanced. Such a reduction in sink
function would be driven mostly by increased atmospheric N deposition, water table regulation for agricultural purposes and
land management to preserve the early successional stage (mowing, tree and shrub removal), since these anthropogenic factors
will probably exert a greater control on competition between Polytrichum and Sphagnum than increased atmospheric CO2 concentrations. 相似文献
104.
Sérgio Oyama Jr. M. Terêsa M. Miranda Sumika Kiyota Angelo G. Gambarini 《Journal of molecular modeling》1999,5(4):90-96
Molecular modeling has allowed us to propose that one main contact surface of the Fibroblast Growth Factor Receptor -1 (FGFR-1) to the ligand FGF-1 is formed by a 16 amino acid sequence comprised by the C-terminal region of the domain II (DII) plus the hinge linking DII and DIII domains and the N-terminal region of domain III (DIII). Therefore, this sequence was used to design the following three peptides: Ac-YQLDVVERS-NH2 (R1); Ac-YQLDVVERSPHRPILQ-NH2 (R2) and Ac-RSPHRPILQ-NH2 (R3). The synthetic peptides were tested in their ability to inhibit the mitogenic activity of FGF-1 and FGF-2 in cultured Balb/c 3T3 fibroblasts. The results showed that R1 and R2 inhibited the activity of FGF-1 (ID50 = 40 -50 7M) but not that of FGF-2. Molecular modeling studies of R1 and its docking to FGF-1 suggested that this peptide could assume a conformation very similar to that found in the corresponding segment of FGFR-1. All these results support our hypothesis that the C-terminal residues of the DII domain, represented by peptide R1, are part of a surface responsible for the binding of FGF-1 to FGFR-1 but not of FGF-2. Also, they indicate that peptide R1 may be useful for the development of small selective peptide inhibitors of the FGF-1 biological activities. 相似文献
105.
Influence of supplemental ultraviolet-B on indoleacetic acid and calmodulin in the leaves of rice (Oryza sativa L.) 总被引:9,自引:0,他引:9
Shaobai Huang Qiujie Dai Shaobing Peng Arlene Q. Chavez Ma. Lourdes L. Miranda Romeo M. Visperas Benito S. Vergara 《Plant Growth Regulation》1997,21(1):59-64
IR68 and Dular rice cultivars were grown under ambient, 13.0 (simulating 20% ozone depletion) and 19.1 (simulating 40% ozone depletion) kJ m-2 day-1 of biologically effective ultraviolet-B (UV-BBE) for 4 weeks. Plant height and leaf area were significantly reduced by supplemental UV-BBE radiation. Greater reduction in leaf area than of plant height was observed. A decrease in indole-3-acetic acid (IAA) content and increase in peroxidase and IAA oxidase activities of UV-B treated plants in both cultivars were observed compared with ambient control. Calmodulin content also decreased after plants were treated with high supplemental UV-B for two weeks and medium UV-B treatment for four weeks. The results indicated that peroxidase and IAA oxidase activities in rice leaves were stimulated by supplemental UV-B, resulting in the destruction of IAA which in turn may cause inhibition of rice leaf growth. Although the mechanism is unclear, calmodulin is most likely involved in leaf growth. 相似文献
106.
107.
Phylogeography and diversification of an Amazonian understorey hummingbird: paraphyly and evidence for widespread cryptic speciation in the Plio‐Pleistocene 下载免费PDF全文
Lucas E. Araújo‐Silva Leonardo S. Miranda Lincoln Carneiro Alexandre Aleixo 《Ibis》2017,159(4):778-791
Straight‐billed Hermit Phaethornis bourcieri inhabits the understorey of upland terra firme forest throughout most of the Amazon basin. Currently, two allopatric taxa regarded as subspecies are recognized: P. b. bourcieri and P. b. major. However, the validity, interspecific limits and evolutionary history of these taxa are not yet fully elucidated. We use molecular characters to propose a phylogenetic hypothesis for populations and taxa grouped under Phaethornis bourcieri. Our results showed that P. bourcieri is part of the ‘Ametrornis’ clade, along with Phaethornis philippii and Phaethornis koepckeae, and that the subspecies major is more closely related to the latter two species than to populations grouped under nominate bourcieri. Our phylogenetic hypotheses recovered three main reciprocally monophyletic clades under nominate bourcieri separated by the lower Negro River and the Branco River or the Branco–Negro interfluve (clades B and C) and the upper Amazon (Solimões) or lower Marañon/Ucayali Rivers (clades C and D). Based on multi‐locus phylogeographic and population genetics approaches, we show that P. b. major is best treated as a separate species, and that P. b. bourcieri probably includes more than one evolutionary species, whose limits remain uncertain. The diversification of the ‘Ametrornis’ clade (P. bourcieri, P. philippii and P. koepckeae) is centred in the Amazon and appears to be closely linked to the formation of the modern Amazon drainage during the Plio‐Pleistocene. 相似文献
108.
109.
Ectopic expression of an amino acid transporter (VfAAP1) in seeds of Vicia narbonensis and pea increases storage proteins 下载免费PDF全文
Rolletschek H Hosein F Miranda M Heim U Götz KP Schlereth A Borisjuk L Saalbach I Wobus U Weber H 《Plant physiology》2005,137(4):1236-1249
Storage protein synthesis is dependent on available nitrogen in the seed, which may be controlled by amino acid import via specific transporters. To analyze their rate-limiting role for seed protein synthesis, a Vicia faba amino acid permease, VfAAP1, has been ectopically expressed in pea (Pisum sativum) and Vicia narbonensis seeds under the control of the legumin B4 promoter. In mature seeds, starch is unchanged but total nitrogen is 10% to 25% higher, which affects mainly globulin, vicilin, and legumin, rather than albumin synthesis. Transgenic seeds in vitro take up more [14C]-glutamine, indicating increased sink strength for amino acids. In addition, more [14C] is partitioned into proteins. Levels of total free amino acids in growing seeds are unchanged but with a shift toward higher relative abundance of asparagine, aspartate, glutamine, and glutamate. Hexoses are decreased, whereas metabolites of glycolysis and the tricarboxylic acid cycle are unchanged or slightly lower. Phosphoenolpyruvate carboxylase activity and the phosphoenolpyruvate carboxylase-to-pyruvate kinase ratios are higher in seeds of one and three lines, indicating increased anaplerotic fluxes. Increases of individual seed size by 20% to 30% and of vegetative biomass indicate growth responses probably due to improved nitrogen status. However, seed yield per plant was not altered. Root application of [15N] ammonia results in significantly higher label in transgenic seeds, as well as in stems and pods, and indicates stimulation of nitrogen root uptake. In summary, VfAAP1 expression increases seed sink strength for nitrogen, improves plant nitrogen status, and leads to higher seed protein. We conclude that seed protein synthesis is nitrogen limited and that seed uptake activity for nitrogen is rate limiting for storage protein synthesis. 相似文献
110.
Postma B Kleibeuker W Poppelier MJ Boonstra M Van Kessel KP Van Strijp JA de Haas CJ 《The Journal of biological chemistry》2005,280(3):2020-2027
Chemotaxis inhibitory protein of Staphylococcus aureus (CHIPS) is excreted by the majority of S. aureus strains and is a potent inhibitor of C5a- and formylated peptide-mediated chemotaxis of neutrophils and monocytes. Recently, we reported that CHIPS binds to the C5a receptor (C5aR) and the formylated peptide receptor, thereby blocking activation by C5a and formylated peptides, respectively. The anaphylatoxin C5a plays an important role in host immunity and pathological inflammatory processes. For C5a a two-site binding model is proposed in which C5a initially binds the C5aR N terminus, followed by interaction of the C5a C-terminal tail with an effector domain on the receptor. We have shown here that CHIPS does not affect activation of the C5aR by a peptide mimic of the C5a C terminus. Moreover, CHIPS was found to bind human embryonic kidney 293 cells expressing only the C5aR N terminus. Deletion and mutation experiments within this C5aR N-terminal expression system revealed that the binding site of CHIPS is contained in a short stretch of 9 amino acids (amino acids 10-18), of which the aspartic acid residues at positions 10, 15, and 18 plus the glycine at position 12 are crucial. Binding studies with C5aR/C3aR and C5aR/IL8RA chimeras confirmed that CHIPS binds only to the C5aR N terminus without involvement of its extracellular loops. CHIPS may provide new strategies to block the C5aR, which may lead to the development of new C5aR antagonists. 相似文献