全文获取类型
收费全文 | 115篇 |
免费 | 8篇 |
国内免费 | 9篇 |
专业分类
132篇 |
出版年
2022年 | 1篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2017年 | 1篇 |
2015年 | 11篇 |
2014年 | 9篇 |
2013年 | 8篇 |
2012年 | 5篇 |
2011年 | 10篇 |
2010年 | 8篇 |
2009年 | 7篇 |
2008年 | 3篇 |
2007年 | 4篇 |
2006年 | 7篇 |
2005年 | 1篇 |
2004年 | 4篇 |
2003年 | 3篇 |
2002年 | 1篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 7篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 6篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1982年 | 2篇 |
1977年 | 2篇 |
1955年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有132条查询结果,搜索用时 15 毫秒
31.
铁皮石斛的离体开花 总被引:9,自引:0,他引:9
铁皮石斛(Dendrobium candidum),为一种野生兰科植物,在栽培条件下,从种子萌发到开花通常需要3~4a.研究了多种植物激素和多胺对该种石斛组织培养中花芽形成的影响,结果表明在培养基中加入合适浓度的亚精胺(spermidine)或BA(6-苄基腺嘌呤),或同时加入NAA(萘乙酸)和BA均可诱导原球茎或由之形成的无根小苗在3~6个月开花,频率在31.6%~45.8%.当将原球茎在加有ABA(脱落酸)的培养基上预培养后再移到加有BA的培养基上,花芽形成的频率可提高到平均达82.8%(个别实验中可达100%),这种诱导提早开花的现象也与实验材料的发育阶段(原球茎、无根小苗、已生根的小苗)有关,通常发生在根的形成受到完全或部分抑制的情况中. 相似文献
32.
Tyrosine phosphorylation of Munc18‐1 inhibits synaptic transmission by preventing SNARE assembly 下载免费PDF全文
Marieke Meijer Bernhard Dörr Hanna CA Lammertse Chrysanthi Blithikioti Jan RT van Weering Ruud FG Toonen Thomas H Söllner Matthijs Verhage 《The EMBO journal》2018,37(2):300-320
Tyrosine kinases are important regulators of synaptic strength. Here, we describe a key component of the synaptic vesicle release machinery, Munc18‐1, as a phosphorylation target for neuronal Src family kinases (SFKs). Phosphomimetic Y473D mutation of a SFK phosphorylation site previously identified by brain phospho‐proteomics abolished the stimulatory effect of Munc18‐1 on SNARE complex formation (“SNARE‐templating”) and membrane fusion in vitro. Furthermore, priming but not docking of synaptic vesicles was disrupted in hippocampal munc18‐1‐null neurons expressing Munc18‐1Y473D. Synaptic transmission was temporarily restored by high‐frequency stimulation, as well as by a Munc18‐1 mutation that results in helix 12 extension, a critical conformational step in vesicle priming. On the other hand, expression of non‐phosphorylatable Munc18‐1 supported normal synaptic transmission. We propose that SFK‐dependent Munc18‐1 phosphorylation may constitute a potent, previously unknown mechanism to shut down synaptic transmission, via direct occlusion of a Synaptobrevin/VAMP2 binding groove and subsequent hindrance of conformational changes in domain 3a responsible for vesicle priming. This would strongly interfere with the essential post‐docking SNARE‐templating role of Munc18‐1, resulting in a largely abolished pool of releasable synaptic vesicles. 相似文献
33.
Efficiencies of different genes and different tree-building methods in recovering a known vertebrate phylogeny 总被引:18,自引:6,他引:18
The relative efficiencies of different protein-coding genes of the
mitochondrial genome and different tree-building methods in recovering a
known vertebrate phylogeny (two whale species, cow, rat, mouse, opossum,
chicken, frog, and three bony fish species) was evaluated. The
tree-building methods examined were the neighbor joining (NJ), minimum
evolution (ME), maximum parsimony (MP), and maximum likelihood (ML), and
both nucleotide sequences and deduced amino acid sequences were analyzed.
Generally speaking, amino acid sequences were better than nucleotide
sequences in obtaining the true tree (topology) or trees close to the true
tree. However, when only first and second codon positions data were used,
nucleotide sequences produced reasonably good trees. Among the 13 genes
examined, Nd5 produced the true tree in all tree-building methods or
algorithms for both amino acid and nucleotide sequence data. Genes Cytb and
Nd4 also produced the correct tree in most tree-building algorithms when
amino acid sequence data were used. By contrast, Co2, Nd1, and Nd41 showed
a poor performance. In general, large genes produced better results, and
when the entire set of genes was used, all tree-building methods generated
the true tree. In each tree-building method, several distance measures or
algorithms were used, but all these distance measures or algorithms
produced essentially the same results. The ME method, in which many
different topologies are examined, was no better than the NJ method, which
generates a single final tree. Similarly, an ML method, in which many
topologies are examined, was no better than the ML star decomposition
algorithm that generates a single final tree. In ML the best substitution
model chosen by using the Akaike information criterion produced no better
results than simpler substitution models. These results question the
utility of the currently used optimization principles in phylogenetic
construction. Relatively simple methods such as the NJ and ML star
decomposition algorithms seem to produce as good results as those obtained
by more sophisticated methods. The efficiencies of the NJ, ME, MP, and ML
methods in obtaining the correct tree were nearly the same when amino acid
sequence data were used. The most important factor in constructing reliable
phylogenetic trees seems to be the number of amino acids or nucleotides
used.
相似文献
34.
目的:探讨胸内正压对正常人左室射血及充盈的影响及其力学原理。方法:超声心动图观测30例正常人初始时与标准乏氏动作张力期10s时左室舒张末容积(LVEDV)、左室收缩末容积(LVESV)、每搏量(SV)、射血分值(EF)、流入道血流速度(E峰、A峰)、E/A值、二尖瓣环舒张早期运动速度(e)及舒张早期充盈压(E/e)的变化。结果:与初始时比较,标准乏氏动作张力期LVEDV、LVESV及SV减低而心率(陬)增快(P均〈0.001),EF值增加,但无统计学意义(P〉0.05);E峰与E/A值减低(P均〈O.05);e没有变化(P〉0.05).E/e值减低(P〈O.05)。结论:胸内正压对左室游离壁的力学作用促进了左室收缩运动而阻碍了左室舒张运动,会引起EF值增加,E峰及E/A值减低;2,胸内正压降低了肺静脉系统与心脏的跨壁压力,增加了血流阻力也是导致肺静脉系统与左室血液回流减少.E峰减低.E/e值减低的一个原因。 相似文献
35.
Steens SC Bosma GP Steup-Beekman GM le Cessie S Huizinga TW van Buchem MA 《Arthritis research & therapy》2006,8(2):R38-7
The pathogenetic role of anticardiolipin antibodies (aCLs) in patients with neuropsychiatric systemic lupus erythematosus
(NPSLE) without cerebral infarcts remains elusive. Magnetization transfer imaging (MTI) has proved to be a sensitive tool
for detecting diffuse microscopic brain damage in NPSLE patients. In this study we examined the correlation between grey and
white matter magnetization transfer ratio (MTR) parameters and the presence of IgM and IgG aCLs and lupus anticoagulant in
18 patients with systemic lupus erythematosus and a history of NPSLE but without cerebral infarcts on conventional magnetic
resonance imaging. Lower grey matter mean MTR (P < 0.05), white matter mean MTR (P < 0.05), white matter peak location (P < 0.05) and grey matter peak location (trend toward statistical significance) were observed in IgM aCL-positive patients
than in IgM aCL-negative patients. No significant differences were found in MTR histogram parameters with respect to IgG aCL
and lupus anticoagulant status, nor with respect to anti-dsDNA or anti-ENA (extractable nuclear antigen) status. This is the
first report of an association between the presence of aCLs and cerebral damage in grey and white matter in NPSLE. Our findings
suggest that aCLs are associated with diffuse brain involvement in NPSLE patients. 相似文献
36.
Fucose is a major constituent of the protein- and lipid-linked glycans of
the various life-cycle stages of schistosomes. These fucosylated glycans
are highly antigenic and seem to play a role in the pathology of
schistosomiasis. In this article we describe the identification and
characterization of two fucosyltransferases (FucTs) in cercariae of the
avian schistosome Trichobilharzia ocellata, a GDP-Fuc:[Galbeta1--
>4]GlcNAcbeta-R alpha1-->3-FucT and a novel GDP-Fuc:Fucalpha-R
alpha1-- >2-FucT. Triton X-100 extracts of cercariae were assayed for
FucT activity using a variety of acceptor substrates. Type 1 chain
(Galbeta1- ->3GlcNAc) based compounds were poor acceptors, whereas those
based on a type 2 chain (Galbeta1-->4GlcNAc), whether
alpha2'-fucosylated, alpha3'-sialylated, or unsubstituted, and whether
present as oligosaccharide or contained in a glycopeptide or glycoprotein,
all served as acceptor substrates. In this respect the schistosomal alpha3-
FucT resembles human FucT V and VI rather than other known FucTs. N-
ethylmaleimide, an inhibitor of several human FucTs, had no effect on the
activity of the schistosomal alpha3-FucT, whereas GDP-beta-S was strongly
inhibitory. Large scale incubations were carried out with
Galbeta1-->4GlcNAc, GalNAcbeta1-->4GlcNAcbeta-O -(CH2)8COOCH3 and
Fucalpha1-->3GlcNAcbeta1-->2Man as acceptor substrates and the
products of the incubations were isolated using a sequence of
chromatographic techniques. By methylation analysis and 2D-TOCSY and
ROESY1H-NMR spectroscopy the products formed were shown to be Galbeta1--
>4[Fucalpha1-->2Fucalpha1-->3]GlcNAc,
GalNAcbeta1-->4[Fucalpha1-- >2Fucalpha1-->3]GlcNAcbe
ta-O-(CH2)8COOCH3, and Fucalpha1-->2Fucalpha1--
>3GlcNAcbeta1-->2Man, respectively. It is concluded that the alpha2-
FucT and alpha3-FucT are involved in the biosynthesis of the (oligomeric)
Lewisx sequences and the Fucalpha1-->2Fucalpha1-->3GlcNAc structural
element that have been described on schistosomal glycoconjugates.
相似文献
37.
38.
Neuza M Alcantara-Neves Samuel J Badaró Mariese CA dos Santos Lain Pontes-de-Carvalho Maurício L Barreto 《Respiratory research》2010,11(1):114
Background
The elucidation of factors that trigger the development of transient wheezing in early childhood may be an important step toward understanding the pathogenesis of asthma and other allergic diseases later in life. Transient wheezing has been mainly attributed to viral infections, although sensitisation to aeroallergens and food allergens may occur at an early age. In developing countries, intestinal helminthic infections have also been associated with allergy or atopy-related disorders.Objective
The aim of this study was to explore the association of Trichuris trichiura and Ascaris lumbricoides infections with wheezing and atopy in early childhood.Study design
A cross-sectional study using a Portuguese-language ISAAC phase I questionnaire, adapted for preschool-aged children, nested in a cohort study of childhood diarrhoea, was conducted on 682 children. Two faecal samples per child were examined for the presence of intestinal helminthic infection. IgE antibodies against three allergenic preparations (Dermatophagoides pteronyssinus, Blomia tropicalis and common child food), as well as against A. lumbricoides antigens, were measured in a sub-sample of these children, whose parents allowed the procedure. Atopy was defined by the presence of levels of serum IgE antibodies ≥0.35 kU/L against at least one of the three tested allergenic preparations.Results
Active T. trichiura infection but not A. lumbricoides infection was positively associated with wheezing in the total studied children population [adjusted OR = 2.60; CI = 1.54;4.38] and in the atopic children sub-population [adjusted OR = 3.07; CI = 1.00;9.43]. The association with atopy was also positive and statistically significant only in the brute analysis [OR = 2.13; CI = 1.03;4.40]. Anti-A. lumbricoides IgE antibodies, but not current A. lumbricoides infection, were positively associated with wheezing in atopic children [adjusted OR = 2.01; CI = 1.00;4.50] and in non-atopic children [adjusted OR = 3.07; CI = 1.13;8.35] and it was also associated with atopy [adjusted OR = 7.29; CI = 3.90; 13.4]. On the other hands, reports of wheezing were not significantly associated with atopy.Conclusions
These data corroborate previous studies showing that wheezing is predominantly associated with infection in early childhood and shows that anti-A. lumbricoides IgE antibodies, but not active Ascaris infections, are associated with wheezing and atopy. Additionally, the data demonstrate that T. trichiura infection may play a role in the pathogenesis of atopic wheezing in early childhood. 相似文献39.
40.
目的:探究尿毒症皮肤瘙瘁患者采取腹膜透析与血液透析治疗的临床效果,并为该病的临床治疗提供经验积累。方法:选取我院肾内科于2005年1月-2012年12月收治的52例尿毒症皮肤瘙痒患者,利用随机数字表法进行分组,分别设为研究组和对照组。其中对照组实施血液透析治疗,而研究组开展腹膜透析治疗。记录两组在治疗前和治疗后第8周末血生化客观指标及皮肤瘙痒程度,并做好对比。结果:两组在治疗前的皮肤瘙痒评分、β2-MG、PTH、p3,BUN、SCr值差异无统计学意义(P〉0.05);治疗后,研究组皮肤瘙瘁评分为(3.4±0.8)分,对照组为(5.8±0.9)分,差异有统计学意义(P〈0.05)。治疗后,研究组β2-MG、PTH及Ps.均低于对照组,差异有统计学意义(P〈0.05)。结论:尿毒症皮肤瘙痒患者的主要致敏因子为大中分子,采取腹膜透析能够有效清除大分子物质,进而达到瘙痒程度的有效改善。 相似文献