全文获取类型
收费全文 | 248篇 |
免费 | 15篇 |
专业分类
263篇 |
出版年
2022年 | 1篇 |
2021年 | 3篇 |
2020年 | 1篇 |
2019年 | 3篇 |
2018年 | 6篇 |
2017年 | 4篇 |
2016年 | 4篇 |
2015年 | 5篇 |
2014年 | 15篇 |
2013年 | 12篇 |
2012年 | 21篇 |
2011年 | 18篇 |
2010年 | 9篇 |
2009年 | 11篇 |
2008年 | 26篇 |
2007年 | 23篇 |
2006年 | 19篇 |
2005年 | 21篇 |
2004年 | 12篇 |
2003年 | 4篇 |
2002年 | 15篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 6篇 |
1998年 | 7篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有263条查询结果,搜索用时 15 毫秒
1.
Role of Thidiazuron (TDZ) in inducing adventitious organogenesis in Pongamia was studied. TDZ at different concentrations (0, 0.45, 2.27, 4.54, 6.71, 9.08, 11.35, 13.12 and 22.71 μM) were used for induction
of caulogenic bud formation in deembryonated cotyledon explants. Each cotyledon was cut into three segments and identified
as proximal, middle and distal. Duration of TDZ exposure, influence of the segment and orientation of the explant were studied.
TDZ at 11.35 μM concentration was optimum for the induction of shoots and rapid elongation. Shoots induced at higher concentration
elongated after several passages in growth regulator free medium, thereby extending the period of differentiation. Exposure
of the explant for 20 days yielded more number of buds than 10 days. Proximal segment of the cotyledon was more responsive.
Contact of abaxial surface in the medium was more effective and generated more buds than the adaxial side. Buds differentiated
and elongated on transfer to MS basal medium for 8–12 passages of 15 days each. Rooting and elongation of shoots was achieved
in charcoal supplemented half-strength MS medium. Rooted plantlets survived on transfer to sand soil mixture. The plants were
hardened and transferred to green house. This is the first report on in vitro regeneration of Pongamia pinnata via adventitious organogenesis using TDZ. This protocol may find application in studies in genetic transformation, isolation
of somaclonal variants and in induction of mutants. It also provides a system to study the inhibitory role of TDZ on shoot
differentiation. 相似文献
2.
John Paul Wanner Roopashree Subbaiah Yelenna Skomorovska-Prokvolit Yousef Shishani Eric Boilard Sujatha Mohan Robert Gillespie Masaru Miyagi Reuben Gobezie 《Arthritis research & therapy》2013,15(6):R180
Introduction
The development of effective treatments for osteoarthritis (OA) has been hampered by a poor understanding of OA at the cellular and molecular levels. Emerging as a disease of the ''whole joint’, the importance of the biochemical contribution of various tissues, including synovium, bone and articular cartilage, has become increasingly significant. Bathing the entire joint structure, the proteomic analysis of synovial fluid (SF) from osteoarthritic shoulders offers a valuable ''snapshot’ of the biologic environment throughout disease progression. The purpose of this study was to identify differentially expressed proteins in early and late shoulder osteoarthritic SF in comparison to healthy SF.Methods
A quantitative 18O labeling proteomic approach was employed to identify the dysregulated SF proteins in early (n = 5) and late (n = 4) OA patients compared to control individuals (n = 5). In addition, ELISA was used to quantify six pro-inflammatory and two anti-inflammatory cytokines.Results
Key results include a greater relative abundance of proteins related to the complement system and the extracellular matrix in SF from both early and late OA. Pathway analyses suggests dysregulation of the acute phase response, liver x receptor/retinoid x receptor (LXR/RXR), complement system and coagulation pathways in both early and late OA. The network related to lipid metabolism was down-regulated in both early and late OA. Inflammatory cytokines including interleukin (IL) 6, IL 8 and IL 18 were up-regulated in early and late OA.Conclusions
The results suggest a dysregulation of wound repair pathways in shoulder OA contributing to the presence of a ''chronic wound’ that progresses irreversibly from early to later stages of OA. Protease inhibitors were downregulated in late OA suggesting uncontrolled proteolytic activity occurring in late OA. These results contribute to the theory that protease inhibitors represent promising therapeutic agents which could limit proteolytic activity that ultimately leads to cartilage destruction. 相似文献3.
Sujatha Srinivasan Martin T. Morgan Congzhou Liu Frederick A. Matsen Noah G. Hoffman Tina L. Fiedler Kathy J. Agnew Jeanne M. Marrazzo David N. Fredricks 《PloS one》2013,8(10)
Bacterial vaginosis (BV) is a highly prevalent condition associated with adverse health outcomes. Gram stain analysis of vaginal fluid is the standard for confirming the diagnosis of BV, wherein abundances of key bacterial morphotypes are assessed. These Lactobacillus, Gardnerella, Bacteroides, and Mobiluncus morphotypes were originally linked to particular bacterial species through cultivation studies, but no studies have systematically investigated associations between uncultivated bacteria detected by molecular methods and Gram stain findings. In this study, 16S-rRNA PCR/pyrosequencing was used to examine associations between vaginal bacteria and bacterial morphotypes in 220 women with and without BV. Species-specific quantitative PCR (qPCR) and fluorescence in Situ hybridization (FISH) methods were used to document concentrations of two bacteria with curved rod morphologies: Mobiluncus and the fastidious BV-associated bacterium-1 (BVAB1). Rank abundance of vaginal bacteria in samples with evidence of curved gram-negative rods showed that BVAB1 was dominant (26.1%), while Mobiluncus was rare (0.2% of sequence reads). BVAB1 sequence reads were associated with Mobiluncus morphotypes (p<0.001). Among women with curved rods, mean concentration of BVAB1 DNA was 2 log units greater than Mobiluncus (p<0.001) using species-specific quantitative PCR. FISH analyses revealed that mean number of BVAB1 cells was 2 log units greater than Mobiluncus cells in women with highest Nugent score (p<0.001). Prevotella and Porphyromonas spp. were significantly associated with the “Bacteroides morphotype,” whereas Bacteroides species were rare. Gram-negative rods designated Mobiluncus morphotypes on Gram stain are more likely BVAB1. These findings provide a clearer picture of the bacteria associated with morphotypes on vaginal Gram stain. 相似文献
4.
To elucidate how human DNA polymerase β (pol β) discriminates dATP from dCTP when processing 8-oxoguanine (8-oxoG), we analyze a series of dynamics simulations before and after the chemical step with dATP and dCTP opposite an 8-oxoG template started from partially open complexes of pol β. Analyses reveal that the thumb closing of pol β before chemistry is hampered when the incorrect nucleotide dATP is bound opposite 8-oxoG; the unfavorable interaction between active-site residue Tyr271 and dATP that causes an anti to syn change in the 8-oxoG (syn):dATP complex explains this slow motion, in contrast to the 8-oxoG (anti):dCTP system. Such differences in conformational pathways before chemistry for mismatched versus matched complexes help explain the preference for correct insertion across 8-oxoG by pol β. Together with reference studies with a nonlesioned G template, we propose that 8-oxoG leads to lower efficiency in pol β's incorporation of dCTP compared with G by affecting the requisite active-site geometry for the chemical reaction before chemistry. Furthermore, because the active site is far from ready for the chemical reaction after partial closing or even full thumb closing, we suggest that pol β is tightly controlled not only by the chemical step but also by a closely related requirement for subtle active-site rearrangements after thumb movement but before chemistry. 相似文献
5.
An in vitro propagation system for Artemisia vulgaris L., a traditional medicinal plant, has been developed. The best organogenic response, including adventitious shoot number
and elongation, was obtained when hypocotyl segments were cultured onto MS medium supplemented with 4.54 μM TDZ (N-phenyl-N′-(1,2,3-thidiazol-yl) urea). Up to 28 shoots formed per explant for an optimal duration of exposure of 48 days. Regenerated
shoots formed roots when subcultured onto a medium containing 8.56 μM IAA (indole-3-acetic acid). Healthy plantlets were transferred
to a garden soil:farmyard soil:sand (2:1:1) mixture for acclimatization, which was successful, and subsequent maturity was
achieved under greenhouse conditions over a six-month period. The survival rate of the plantlets varied under acclimatization.
The regeneration protocol developed in this study provides a basis for germplasm conservation and for further investigation
of medicinally active constituents of A. vulgaris. This optimized protocol has been successfully employed for genetic transformation studies in A. vulgaris, which are currently underway in our laboratory. 相似文献
6.
Jayaraman Sujatha; Teitler Leah; Skalski Bohdan; Verkman A. S. 《American journal of physiology. Cell physiology》1999,277(5):C1008
Limitations of available indicators [such as6-methoxy-N-(3-sulfopropyl)quinolinium(SPQ)] for measurement of intracellular Cl are their relatively dimfluorescence and need for ultraviolet excitation. A series oflong-wavelength polar fluorophores was screened to identify compoundswith Cl and/orI sensitivity, brightfluorescence, low toxicity, uniform loading of cytoplasm with minimalleakage, and chemical stability in cells. The best compound found was7-(-D-ribofuranosylamino)-pyrido[2,1-h]-pteridin-11-ium-5-olate (LZQ). LZQ is brightly fluorescent with excitation andemission maxima at 400-470 and 490-560 nm, molar extinction11,100 M1 · cm1(424 nm), and quantum yield 0.53. LZQ fluorescence is quenched byI by a collisionalmechanism (Stern-Volmer constant 60 M1) and is not affectedby other halides, nitrate, cations, or pH changes (pH 5-8). AfterLZQ loading into cytoplasm by hypotonic shock or overnight incubation,LZQ remained trapped in cells (leakage <3%/h). LZQ stained cytoplasmuniformly, remained chemically inert, did not bind to cytoplasmiccomponents, and was photobleached by <1% during 1 h of continuousillumination. Cytoplasmic LZQ fluorescence was quenched selectively byI (50% quenching at 38 mMI). LZQ was used tomeasure forskolin-stimulatedI/ClandI/NO3exchange in cystic fibrosis transmembrane conductance regulator(CFTR)-expressing cell lines by fluorescence microscopy and microplatereader instrumentation using 96-well plates. The substantially improvedoptical and cellular properties of LZQ over existing indicators shouldpermit the quantitative analysis of CFTR function in gene deliverytrials and high-throughput screening of compounds for correction of thecystic fibrosis phenotype. 相似文献
7.
Li J Dokka S Wang L Shi X Castranova V Yan Y Costa M Huang C 《Molecular and cellular biochemistry》2004,255(1-2):217-225
Vanadium is a metal widely distributed in the environment. Although vanadate-containing compounds exert potent toxic effects on a wide variety of biological systems, the mechanisms by which vanadate mediates adverse effects are not well understood. The present study investigated the vanadate-induced phosphorylation of Akt and p70S6K, two kinases known to be vital for cell survival, growth, transformation, and transition of the cell cycle in mammals. Exposure of mouse epidermal JB6 cells to vanadium led to phosphorylation of Akt and p70S6K in a time- and dose-dependent manner. Vanadium exposure also caused translocation of atypical isoforms of PKC (lambda, zeta) from the cytosol to the membrane, but had no effect on PKCalpha translocation, suggesting that the atypical PKCs (aPKC) were specifically involved in vanadium-induced cellular response. Importantly, overexpression of a dominant negative mutant PKClambda blocked Akt phosphorylation at Ser473 and Thr308, whereas it did not inhibit p70S6k phosphorylation at Thr389 and Thr421/Ser424, suggesting that aPKC activation is specifically involved in vanadium-induced activation of Akt, but not in activation of p70S6k. Furthermore, vanadium-induced p70S6k phosphorylation at Thr389 and Thr421/Ser424 and Akt phosphorylation at Thr308 occurred through a PI-3K-dependent pathway because a PI-3K dominant negative mutant inhibited induction as compared with vector control cells. These results indicate that there was a differential role of aPKC in vanadate-induced phosphorylation of Akt and p70S6k, suggesting that signal transduction pathways leading to the activation of Akt and p70S6k were different. 相似文献
8.
Galactose-binding proteins characterize an important subgroup of sugar-binding proteins that are involved in a variety of biological processes. Structural studies have shown that the Gal-specific proteins encompass a diverse range of primary and tertiary structures. The binding sites for galactose also seem to vary in different protein-galactose complexes. No common binding site features that are shared by the Gal-specific proteins to achieve ligand specificity are so far known. With the assumption that common recognition principles will exist for common substrate recognition, the present study was undertaken to identify and characterize any unique galactose-binding site signature by analyzing the three-dimensional (3D) structures of 18 protein-galactose complexes. These proteins belong to 7 nonhomologous families; thus, there is no sequence or structural similarity across the families. Within each family, the binding site residues and their relative distances were well conserved, but there were no similarities across families. A novel, yet simple, approach was adopted to characterize the binding site residues by representing their relative spatial dispositions in polar coordinates. A combination of the deduced geometrical features with the structural characteristics, such as solvent accessibility and secondary structure type, furnished a potential galactose-binding site signature. The signature was evaluated by incorporation into the program COTRAN to search for potential galactose-binding sites in proteins that share the same fold as the known galactose-binding proteins. COTRAN is able to detect galactose-binding sites with a very high specificity and sensitivity. The deduced galactose-binding site signature is strongly validated and can be used to search for galactose-binding sites in proteins. PROSITE-type signature sequences have also been inferred for galectin and C-type animal lectin-like fold families of Gal-binding proteins. 相似文献
9.
10.
Cloning, overexpression, and characterization of a serine/threonine protein kinase pknI from Mycobacterium tuberculosis H37Rv 总被引:1,自引:0,他引:1
Protein phosphorylation-dephosphorylation is the principal mechanism for translation of external signals into cellular responses. Eukaryotic-like serine/threonine kinases have been reported to play important roles in bacterial development and/or virulence. The PknI protein is one of the 11 eukaryotic-like serine/threonine kinases in Mycobacterium tuberculosis H37Rv. From the bioinformatic studies, PknI protein has been shown to have an N-terminal cytoplasmic domain followed by a transmembrane region and an extracellular C-terminus suggestive of a sensor molecule. In this study, we have cloned, overexpressed, and characterized the entire coding region and the cytoplasmic domain of PknI as a fusion protein with an N-terminal histidine tag, and used immobilized metal affinity chromatography for purification of recombinant proteins. The purified recombinant proteins were found to be functionally active through in vitro phosphorylation assay and phosphoamino acid analysis. In vitro kinase assay of both proteins revealed that PknI is capable of autophosphorylation and showed manganese-dependent activity. Phosphoamino acid analysis indicated phosphorylation at serine and threonine residues. Southern blot analysis with genomic DNA highlighted the conserved nature of pknI among the various mycobacterial species. In silico analysis revealed a close homology of PknI to Stk1 from Streptococcus agalactiae, shown to have a role in virulence and cell segregation of the organism. 相似文献