全文获取类型
收费全文 | 928篇 |
免费 | 45篇 |
专业分类
973篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 15篇 |
2021年 | 31篇 |
2020年 | 12篇 |
2019年 | 19篇 |
2018年 | 28篇 |
2017年 | 17篇 |
2016年 | 55篇 |
2015年 | 57篇 |
2014年 | 59篇 |
2013年 | 78篇 |
2012年 | 96篇 |
2011年 | 84篇 |
2010年 | 47篇 |
2009年 | 39篇 |
2008年 | 61篇 |
2007年 | 55篇 |
2006年 | 56篇 |
2005年 | 36篇 |
2004年 | 31篇 |
2003年 | 16篇 |
2002年 | 27篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有973条查询结果,搜索用时 15 毫秒
941.
942.
A Miro F Ungaro F Balzano S Masi P Musto P La Manna G Uccello-Barretta F Quaglia 《Carbohydrate polymers》2012,90(3):1288-1298
The molecular foundations of the use of (2-hydroxypropyl)-β-cyclodextrin (HPβCD) as solubility promoter of triamcinolone acetonide (TrA), a corticosteroid with very low aqueous solubility, was investigated by a multidisciplinary spectroscopic and computational approach. Aqueous solutions of TrA and HPβCD were investigated by UV and NMR spectroscopies. The association constant was determined by phase solubility diagrams and by the Foster-Fyfe method whereas the nature of the drug/cyclodextrin aggregates was probed by using the NMR DOSY technique. ROE measurements in solution led to stereochemical information regarding the nature of inclusion processes. TrA/HPβCD powders were prepared and investigated by Raman spectroscopy supported by computational methods. A molecular interaction of the hydroxyacyl chain with cyclodextrin, not identified in solution, was detected. Raman imaging experiments confirmed the attainment of a molecularly homogeneous system when the TrA/HPβCD molar ratio was 1:7 whereas TrA crystallized for mixtures richer in TrA (1:3.5) forming domains with size in the range of 10-15μm. We demonstrate that the combined use of several spectroscopical techniques with specific responsivities allows a detailed depiction of drug/cyclodextrin interaction useful in the development of novel pharmaceutical formulation. 相似文献
943.
In this paper airborne pollen concentration is compared to meteorological data of Trento and S. Michele all’Adige, two sites
in the Adige Valley, in Trentino (North Italy). Pollen ofCorylus, Alnus, Betula andOstrya, four winter-spring flowering plants are considered. Pollen sampling was carried out in 1996 by volumetric Hirst-type samplers.
For all pollen types considered, maximum pollen concentration coincided in both stations and there was a good overlap of the
main pollen season length; the pollen curves of S. Michele a/A and Trento showed a highly positive correlation. The daily
airborne pollen concentrations, defined as the number of pollen grains per cubic meter of air (P/m3), were compared to daily meteorological data: minimum and maximum air temperature (°C), average relative humidity (%), precipitation
(mm), global incident radiation (cal/cm2), average wind direction (°) and wind speed (m/s). A highly positive correlation was found forCorylus and maximum temperature in both monitoring stations.Betula was positively, whereasOstrya was negatively correlated to relative humidity. With this first analytical approach sharp differences in the atmospheric
pollen presence between the stations located at Trento and S. Michele all’Adige were not found. 相似文献
944.
The patterns of synonymous codon usage in 91 Drosophila melanogaster genes
have been examined. Codon usage varies strikingly among genes. This
variation is associated with differences in G+C content at silent sites,
but (unlike the situation in mammalian genes) these differences are not
correlated with variation in intron base composition and so are not easily
explicable in terms of mutational biases. Instead, those genes with high
G+C content at silent sites, resulting from a strong "preference" for a
particular subset of the codons that are mostly C- ending, appear to be the
more highly expressed genes. This suggests that G+C content is reduced in
sequences where selective constraints are weaker, as indeed seen in a
pseudogene. These and other data discussed are consistent with the effects
of translational selection among synonymous codons, as seen in unicellular
organisms. The existence of selective constraints on silent substitutions,
which may vary in strength among genes, has implications for the use of
silent molecular clocks.
相似文献
945.
Manetti AG Zingaretti C Falugi F Capo S Bombaci M Bagnoli F Gambellini G Bensi G Mora M Edwards AM Musser JM Graviss EA Telford JL Grandi G Margarit I 《Molecular microbiology》2007,64(4):968-983
Group A Streptococcus (GAS, Streptococcus pyogenes) is a Gram-positive human pathogen responsible for several acute diseases and autoimmune sequelae that account for half a million deaths worldwide every year. GAS infections require the capacity of the pathogen to adhere to host tissues and assemble in cell aggregates. Furthermore, a role for biofilms in GAS pathogenesis has recently been proposed. Here we investigated the role of GAS pili in biofilm formation. We demonstrated that GAS pilus-negative mutants, in which the genes encoding either the pilus backbone structural protein or the sortase C1 have been deleted, showed an impaired capacity to attach to a pharyngeal cell line. The same mutants were much less efficient in forming cellular aggregates in liquid culture and microcolonies on human cells. Furthermore, mutant strains were incapable of producing the typical three-dimensional layer with bacterial microcolonies embedded in a carbohydrate polymeric matrix. Complemented mutants had an adhesion and aggregation phenotype similar to the wild-type strain. Finally, in vivo expression of pili was indirectly confirmed by demonstrating that most of the sera from human patients affected by GAS-mediated pharyngitis recognized recombinant pili proteins. These data support the role of pili in GAS adherence and colonization and suggest a general role of pili in all pathogenic streptococci. 相似文献
946.
Fabiana Antognoni Silvia Fornalè Claudia Grimmer Ewald Komor Nello Bagni 《Planta》1998,204(4):520-527
Polyamine content and enzyme activities in the biosynthetic and degradative pathways of polyamine metabolism were investigated
in sieve-tube sap, xylem sap and tissues of seedlings and adult plants of Ricinus communis L. Polyamines were present in tissues and translocation fluids of both seedlings and adult plants in relatively high amounts.
Only free polyamines were translocated through the plant, as indicated by the finding that only the free form was detected
in the phloem and the xylem sap. Removal of the endosperm increased the polyamine content in the sieve-tube exudate of seedlings.
The level and pattern of polyamines in tissue of adult leaves changed during leaf age, but not, however, in the sieve-tube
sap. Xylem sap was relatively poor in polyamines. Polyamine loading in the phloem was demonstrated by incubating cotyledons
with [14O]putrescine and several unlabelled polyamines. Feeding cotyledons with cadaverine and spermidine led to a decrease in the
level of putrescine in sieve-tube sap, indicating a competitive effect. Comparison of polyamine content in the tissue and
export rate showed that the export would deplete the leaves of polyamines within 1–3 d, if they were not replenished by biosynthesis.
Polyamine biosynthesis in Ricinus proceeds mostly via arginine decarboxylase, which in vitro is 100-fold more active than ornithine decarboxylase. The highest
arginine decarboxylase, ornithine decarboxylase and diamine oxidase activities were detected in cotyledons, while in sieve-tube
sap only a slight arginine decarboxylase activity was found.
Received: 18 March 1997 / Accepted: 20 August 1997 相似文献
947.
Sarah A. C. Falc?o Tiffany Weinkopff Benjamin P. Hurrell Fabiana S. Celes Rebecca P. Curvelo Deboraci B. Prates Aldina Barral Valeria M. Borges Fabienne Tacchini-Cottier Camila I. de Oliveira 《PLoS neglected tropical diseases》2015,9(3)
BackgroundNeutrophils are the first line of defense against invading pathogens and are rapidly recruited to the sites of Leishmania inoculation. During Leishmania braziliensis infection, depletion of inflammatory cells significantly increases the parasite load whereas co-inoculation of neutrophils plus L. braziliensis had an opposite effect. Moreover, the co-culture of infected macrophages and neutrophils also induced parasite killing leading us to ask how neutrophils alone respond to an L. braziliensis exposure. Herein we focused on understanding the interaction between neutrophils and L. braziliensis, exploring cell activation and apoptotic fate.ConclusionsWe show that L. braziliensis induces neutrophil recruitment in vivo and that neutrophils exposed to the parasite in vitro respond through activation and release of inflammatory mediators. This outcome may impact on parasite elimination, particularly at the early stages of infection. 相似文献
948.
949.
Madsen O; Deen PM; Pesole G; Saccone C; de Jong WW 《Molecular biology and evolution》1997,14(4):363-371
A 328-bp sequence from exon 1 of the gene for aquaporin-2 (AQP2) was
compared in 12 mammalian species, representing as many eutherian orders.
This sequence encodes the N-terminal half of this kidney- specific water
channel protein. Most amino acid replacements, as well as an insertion,
have occurred in extracellular loops connecting the transmembrane helices,
in agreement with a lower functional importance of these loops.
Phylogenetic analyses were performed with parsimony, distance, and
maximum-likelihood methods. The AQP2 data set, alone as well as in
combination with previously published alpha A-crystallin protein sequences,
strongly supports a clade consisting of elephant, hyrax, aardvark, and
elephant shrew, reaching bootstrap values of 99%. This finding fully agrees
with the only other presently available sequence data sets that include
these taxa, those of von Willebrand factor and interphotoreceptor
retinoid-binding protein, and suggests that this extended paenungulate
clade is one of the most conspicuous superordinal groupings in eutherian
phylogeny. Some support was obtained for an artiodactyl/perissodactyl
clade, while the grouping of pholidotes with edentates was contradicted.
相似文献
950.
La s Vicari de Figueiredo Pess a Fabiana Fernandes Bressan Kristine Karla Freude 《World journal of stem cells》2019,11(8):491-505
Up until the mid 2000s, the capacity to generate every cell of an organism was exclusive to embryonic stem cells. In 2006, researchers Takahashi and Yamanaka developed an alternative method of generating embryonic-like stem cells from adult cells, which they coined induced pluripotent stem cells (iPSCs). Such iPSCs possess most of the advantages of embryonic stem cells without the ethical stigma associated with derivation of the latter. The possibility of generating “custom-made” pluripotent cells, ideal for patient-specific disease models, alongside their possible applications in regenerative medicine and reproduction, has drawn a lot of attention to the field with numbers of iPSC studies published growing exponentially. IPSCs have now been generated for a wide variety of species, including but not limited to, mouse, human, primate, wild felines, bovines, equines, birds and rodents, some of which still lack well-established embryonic stem cell lines. The paucity of robust characterization of some of these iPSC lines as well as the residual expression of transgenes involved in the reprogramming process still hampers the use of such cells in species preservation or medical research, underscoring the requirement for further investigations. Here, we provide an extensive overview of iPSC generated from a broad range of animal species including their potential applications and limitations. 相似文献