全文获取类型
收费全文 | 594篇 |
免费 | 37篇 |
专业分类
631篇 |
出版年
2023年 | 2篇 |
2022年 | 8篇 |
2021年 | 16篇 |
2020年 | 3篇 |
2019年 | 7篇 |
2018年 | 10篇 |
2017年 | 10篇 |
2016年 | 5篇 |
2015年 | 20篇 |
2014年 | 23篇 |
2013年 | 32篇 |
2012年 | 44篇 |
2011年 | 45篇 |
2010年 | 31篇 |
2009年 | 30篇 |
2008年 | 47篇 |
2007年 | 48篇 |
2006年 | 37篇 |
2005年 | 36篇 |
2004年 | 36篇 |
2003年 | 29篇 |
2002年 | 26篇 |
2001年 | 7篇 |
2000年 | 11篇 |
1999年 | 7篇 |
1998年 | 13篇 |
1997年 | 10篇 |
1996年 | 2篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1978年 | 2篇 |
1973年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有631条查询结果,搜索用时 0 毫秒
101.
Characterization of Ejl,the cell-wall amidase coded by the pneumococcal bacteriophage Ej-1 下载免费PDF全文
Sáiz JL López-Zumel C Monterroso B Varea J Arrondo JL Iloro I García JL Laynez J Menéndez M 《Protein science : a publication of the Protein Society》2002,11(7):1788-1799
The Ejl amidase is coded by Ej-1, a temperate phage isolated from the atypical pneumococcus strain 101/87. Like all the pneumococcal cell-wall lysins, Ejl has a bimodular organization; the catalytic region is located in the N-terminal module, and the C-terminal module attaches the enzyme to the choline residues of the pneumococcal cell wall. The structural features of the Ejl amidase, its interaction with choline, and the structural changes accompanying the ligand binding have been characterized by CD and IR spectroscopies, differential scanning calorimetry, analytical ultracentrifugation, and FPLC. According to prediction and spectroscopic (CD and IR) results, Ejl would be composed of short beta-strands (ca. 36%) connected by long loops (ca. 17%), presenting only two well-predicted alpha-helices (ca. 12%) in the catalytic module. Its polypeptide chain folds into two cooperative domains, corresponding to the N- and C-terminal modules, and exhibits a monomer <--> dimer self-association equilibrium. Choline binding induces small rearrangements in Ejl secondary structure but enhances the amidase self-association by preferential binding to Ejl dimers and tetramers. Comparison of LytA, the major pneumococcal amidase, with Ejl shows that the sequence differences (15% divergence) strongly influence the amidase stability, the organization of the catalytic module in cooperative domains, and the self-association state induced by choline. Moreover, the ligand affinity for the choline-binding locus involved in regulation of the amidase dimerization is reduced by a factor of 10 in Ejl. Present results evidence that sequence differences resulting from the natural variability found in the cell wall amidases coded by pneumococcus and its bacteriophages may significantly alter the protein structure and its attachment to the cell wall. 相似文献
102.
The occurrence of strains that are resistant to oxolinic acid, oxytetracycline, sulfamethoxazole-trimethoprim, and nitrofurantoin among heterotrophic bacteria, including human and fish pathogens, in two freshwater eel farms was investigated. High levels of individual- and multiple-drug-resistant bacteria were detected, although sampling events were not correlated with clinical outbreaks and drug therapy. 相似文献
103.
Nuclear actin in plants 总被引:2,自引:0,他引:2
104.
Yuriy A. Knirel Sof’ya N. Senchenkova Consuelo Esteve Susana Merino 《Carbohydrate research》2009,344(4):479-25643
A polysaccharide was isolated by GPC after mild acid treatment of the lipopolysaccharide of Vibrio vulnificus CECT4602 and found to contain l-Rha, d-GlcpNAc and 2-acetamido-2,3,6-trideoxy-3-(3-hydroxybutanoylamino)-l-mannose (l-RhaNAc3NHb). GLC analysis of the trifluoroacetylated (S)-2-octyl esters derived by full acid hydrolysis of the polysaccharide showed that ∼80% of the 3-hydroxybutanoic acid has the S configuration and ∼20% the R configuration. The following structure of the polysaccharide was established by 1H and 13C NMR spectroscopies, including 2D ROESY and 1H/13C HMBC experiments: 相似文献
105.
John C. Zwonitzer David M. Bubeck Dinakar Bhattramakki Major M. Goodman Consuelo Arellano Peter J. Balint-Kurti 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2009,118(5):911-925
B73 is a historically important maize line with excellent yield potential but high susceptibility to the foliar disease southern
leaf blight (SLB). NC292 and NC330 are B73 near-isogenic lines (NILs) that are highly resistant to SLB. They were derived
by repeated backcrossing of an elite source of SLB resistance (NC250P) to B73, with selection for SLB resistance among and
within backcross families. The goal of this paper was to characterize the loci responsible for the increased SLB resistance
of NC292 and NC330 and to determine how many of the SLB disease resistance quantitative trait loci (dQTL) were selected for
in the development of NC292 and NC330. Genomic regions that differentiated NC292 and NC330 from B73 and which may contribute
to NC292 and NC330s enhanced SLB resistance were identified. Ten NC250P-derived introgressions were identified in both the
NC292 and NC330 genomes of which eight were shared between genomes. dQTL were mapped in two F2:3 populations derived from lines very closely related to the original parents of NC292 and NC330—(B73rhm1 × NC250A and NC250A × B73). Nine SLB dQTL were mapped in the combined populations using combined SLB disease data over all
locations (SLB AllLocs). Of these, four dQTL precisely colocalized with NC250P introgressions in bins 2.05–2.06, 3.03, 6.01,
and 9.02 and three were identified near NC250P introgressions in bins 1.09, 5.05–5.06, and 10.03. Therefore the breeding program
used to develop NC292 and NC330 was highly effective in selecting for multiple SLB resistance alleles.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
106.
Consuelo Borrás Sergey Stvolinsky Tatiana Fedorova Alexander Boldyrev 《FEBS letters》2009,583(13):2287-2293
The validity of the free radical theory of aging has been recently questioned. Our aim was to test whether there is oxidative stress in tissues critically involved in accelerated aging (senescence-accelerated mice, SAM) and whether this correlates with lower glucose consumption in vivo and behavioural tests. Positron emission tomography shows that brains of old SAM-prone animals consume less glucose than young ones. Behavioural characteristics, mitochondrial peroxide production, and damage in both the central nervous system and bone marrow stem cells also indicate that SAM-prone animals age faster than SAM-resistant ones. Our results support the role of the free radical theory of aging in critical tissues involved in aging and that this correlates with glucose consumption. 相似文献
107.
Blizzard TA Gude C Morgan JD Chan W Birzin ET Mojena M Tudela C Chen F Knecht K Su Q Kraker B Mosley RT Holmes MA Sharma N Fitzgerald PM Rohrer SP Hammond ML 《Bioorganic & medicinal chemistry letters》2006,16(4):834-838
A series of 19-substituted androstenediol derivatives was prepared. Some of the novel analogs were surprisingly potent and selective ligands for ER-beta. 相似文献
108.
van Bockel DJ Price DA Munier ML Venturi V Asher TE Ladell K Greenaway HY Zaunders J Douek DC Cooper DA Davenport MP Kelleher AD 《Journal of immunology (Baltimore, Md. : 1950)》2011,186(1):359-371
CD8(+) T cells play a significant role in the control of HIV replication, yet the associated qualitative and quantitative factors that determine the outcome of infection remain obscure. In this study, we examined Ag-specific CD8(+) TCR repertoires longitudinally in a cohort of HLA-B*2705(+) long-term nonprogressors with chronic HIV-1 infection using a combination of molecular clonotype analysis and polychromatic flow cytometry. In each case, CD8(+) T cell populations specific for the immunodominant p24 Gag epitope KRWIILGLNK (KK10; residues 263-272) and naturally occurring variants thereof, restricted by HLA-B*2705, were studied at multiple time points; in addition, comparative data were collected for CD8(+) T cell populations specific for the CMV pp65 epitope NLVPMVATV (NV9; residues 495-503), restricted by HLA-A*0201. Dominant KK10-specific clonotypes persisted for several years and exhibited greater stability than their contemporaneous NV9-specific counterparts. Furthermore, these dominant KK10-specific clonotypes exhibited cross-reactivity with antigenic variants and expressed significantly higher levels of CD127 (IL-7Rα) and Bcl-2. Of note, we also found evidence that promiscuous TCR α-chain pairing associated with alterations in fine specificity for KK10 variants could contribute to TCR β-chain prevalence. Taken together, these data suggest that an antiapoptotic phenotype and the ability to cross-recognize variant epitopes contribute to clonotype longevity and selection within the peripheral memory T cell pool in the presence of persistent infection with a genetically unstable virus. 相似文献
109.
Gall-inducing insects exert a unique level of control over the physiology of their host plants. This control can extend to
host–plant defenses so that some, if not most, gall-inducing species appear to avoid or modify host plant defenses to effect
production of their gall. Included among gall insects is Hessian fly (Mayetiola destructor [Say], Diptera: Cecidomyiidae), a damaging pest of wheat (Triticum aestivum L.) and an emerging model system for studying plant–insect interactions. We studied the dynamics of some defense-related
phytohormones and associated fatty acids during feeding of first instar Hessian fly larvae on a susceptible variety of wheat.
We found that Hessian fly larvae significantly elevated in their host plants’ levels of linolenic and linoleic acids, fatty
acids that may be nutritionally beneficial. Hessian fly larvae also elevated levels of indole-3-acetic acid (IAA), a phytohormone
hypothesized to be involved in gall formation, but not the defense-related hormones jasmonic (JA) and salicylic acids. Moreover,
we detected in Hessian fly-infested plants a significant negative relationship between IAA and JA that was not present in
control plants. Our results suggest that Hessian fly larvae may induce nutritionally beneficial changes while concomitantly
altering phytohormone levels, possibly to facilitate plant-defense avoidance. 相似文献