全文获取类型
收费全文 | 4928篇 |
免费 | 337篇 |
国内免费 | 1篇 |
出版年
2023年 | 33篇 |
2022年 | 46篇 |
2021年 | 123篇 |
2020年 | 88篇 |
2019年 | 103篇 |
2018年 | 116篇 |
2017年 | 98篇 |
2016年 | 172篇 |
2015年 | 260篇 |
2014年 | 292篇 |
2013年 | 375篇 |
2012年 | 461篇 |
2011年 | 381篇 |
2010年 | 266篇 |
2009年 | 230篇 |
2008年 | 314篇 |
2007年 | 302篇 |
2006年 | 272篇 |
2005年 | 234篇 |
2004年 | 195篇 |
2003年 | 202篇 |
2002年 | 161篇 |
2001年 | 42篇 |
2000年 | 46篇 |
1999年 | 44篇 |
1998年 | 27篇 |
1997年 | 27篇 |
1996年 | 34篇 |
1995年 | 30篇 |
1994年 | 23篇 |
1993年 | 25篇 |
1992年 | 30篇 |
1991年 | 25篇 |
1990年 | 20篇 |
1989年 | 19篇 |
1988年 | 16篇 |
1987年 | 11篇 |
1986年 | 14篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 10篇 |
1978年 | 9篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1973年 | 8篇 |
排序方式: 共有5266条查询结果,搜索用时 15 毫秒
911.
Wu Yin Stefano Romeo Shurong Chang Nick V. Grishin Helen H. Hobbs Jonathan C. Cohen 《The Journal of biological chemistry》2009,284(19):13213-13222
Angiopoietin-like protein 4 (ANGPTL4) is a secreted protein that modulates
the disposition of circulating triglycerides (TG) by inhibiting lipoprotein
lipase (LPL). Here we examine the steps involved in the synthesis and
post-translational processing of ANGPTL4, and the effects of a naturally
occurring sequence variant (E40K) that is associated with lower plasma TG
levels in humans. Expression of the wild-type and mutant proteins in HEK-293A
cells indicated that ANGPTL4 formed dimers and tetramers in cells prior to
secretion and cleavage of the protein. After cleavage at a canonical
proprotein convertase cleavage site (161RRKR164), the
oligomeric structure of the N-terminal domain was retained whereas the
C-terminal fibrinogen-like domain dissociated into monomers. Inhibition of
cleavage did not interfere with oligomerization of ANGPTL4 or with its ability
to inhibit LPL, whereas mutations that prevented oligomerization severely
compromised the capacity of the protein to inhibit LPL. ANGPTL4 containing the
E40K substitution was synthesized and processed normally, but no monomers or
oligomers of the N-terminal fragments accumulated in the medium; medium from
these cells failed to inhibit LPL activity. Parallel experiments performed in
mice recapitulated these results. Our findings indicate that oligomerization,
but not cleavage, of ANGPTL4 is required for LPL inhibition, and that the E40K
substitution destabilizes the protein after secretion, preventing the
extracellular accumulation of oligomers and abolishing the ability of the
protein to inhibit LPL activity.Angiopoietin-like protein 4
(ANGPTL4)4 is a 50-kDa
protein that is synthesized and secreted from several metabolically active
tissues and has been implicated in the trafficking of circulating TG
(1,
2). Triglycerides, either
acquired from the diet or synthesized endogenously, circulate in blood as
constituents of chylomicrons and very low density lipoproteins (VLDL). As
these lipoproteins circulate in tissues they encounter lipoprotein lipase
(LPL) at the vascular endothelial surfaces. LPL hydrolyzes the TG, producing
free fatty acids that are taken up by the surrounding tissues. ANGPTL4
inhibits the activity of LPL, thereby limiting the uptake of TG-derived fatty
acids by the underlying cells
(3,
4). Overexpression of ANGPTL4
in mice causes severe hypertriglyceridemia, whereas mice lacking ANGPTL4 have
increased LPL activity and low plasma levels of TG
(5,
6). In mice, ANGPTL4 is
predominantly expressed in adipose tissue and is strongly induced by fasting
(2). Accordingly it has been
proposed that ANGPTL4 inhibits LPL activity in adipose tissue to reroute fatty
acids away from fat to muscle and other tissues when food intake is low
(3,
4).ANGPTL4 belongs to a family of seven structurally similar secreted proteins
(ANGPTL1-ANGPTL7) that contain a signal sequence followed by an
α-helical region predicted to form a coiled-coil, and a globular
fibrinogen-like domain at the C terminus
(1). Gel filtration studies of
recombinant ANGPTL4 indicate that the protein assembles into oligomers that
are stabilized by disulfide bonds
(7). Substitution of two highly
conserved cysteine residues at positions 76 and 80 in the α-helical
domain prevents oligomerization of ANGPTL4 and impairs the ability of the
recombinant protein to increase plasma TG levels when overexpressed in the
livers of rats (7).Upon secretion into the circulation, ANGPTL4 is cleaved into an N-terminal
domain and a C-terminal fibrinogen-like domain
(8). The N-terminal peptide
circulates as an oligomer, and the fibrinogen-like domain circulates as a
monomer (8). The N-terminal
helical region of ANGPTL4 is necessary and sufficient for inhibition of LPL
(9). A peptide corresponding to
amino acids 1-187 of the protein binds LPL with high affinity and converts the
enzyme from catalytically active dimers to inactive monomers, thereby
inhibiting LPL activity (10).
After disrupting the LPL dimer, ANGPTL4 is released. The LPL monomers remain
folded and stable but fail to re-form active dimers. These data suggest that
the N-terminal domain of ANGPTL4 interacts directly but transiently with LPL,
triggering a stable conformational switch in LPL that irreversibly inactivates
the enzyme.Recently, we used a population-based resequencing strategy to examine the
metabolic role of ANGPTL4 in humans
(11). Resequencing the coding
region of ANGPTL4 in a large (n = 3,501), multiethnic sample
revealed multiple rare sequence variations that alter an amino acid in the
protein and are associated with low plasma TG levels. In addition, we
identified a more common variant (E40K), that was present in ∼3% of
European-Americans and was associated with significantly lower plasma levels
of TG and low density lipoprotein-cholesterol (LDL-C), and higher levels of
high density lipoprotein (HDL)-C in two large epidemiological studies
(11). These association
studies confirmed that ANGPTL4 is involved in TG metabolism in humans, and
also revealed additional roles in humans in the metabolism of HDL and LDL,
which were not apparent from studies in genetically modified mice.Here we examined the synthesis, secretion, and processing of ANGPTL4 and
determine the mechanism by which substitution of a basic (lysine) for an
acidic (glutamate) residue at residue 40 affects the function of the
protein. 相似文献
912.
Maria Filippa Addis Alessandro Tanca Daniela Pagnozzi Stefano Rocca Sergio Uzzau 《Proteomics》2009,9(18):4329-4339
In the past decade, encouraging results have been obtained in extraction and analysis of proteins from formalin‐fixed, paraffin‐embedded (FFPE) tissues. However, 2‐D PAGE protein maps with satisfactory proteomic information and comparability to fresh tissues have never been described to date. In the present study, we report 2‐D PAGE separation and MS identification of full‐length proteins extracted from FFPE skeletal muscle tissue. The 2‐D protein profiles obtained from FFPE tissues could be matched to those achieved from frozen tissues replicates. Up to 250 spots were clearly detected in 2‐D maps of proteins from FFPE tissue following standard mass‐compatible silver staining. Protein spots from both FFPE and frozen tissue 2‐D gels were excised, subjected to in situ hydrolysis, and identified by MS analysis. Matched spots produced matched protein identifications. Moreover, 2‐D protein maps from FFPE tissues were successfully subjected to Western immunoblotting, producing comparable results to fresh‐frozen tissues. In conclusion, this study provides evidence that, when adequately extracted, full‐length proteins from FFPE tissues might be suitable to 2‐D PAGE‐MS analysis, allowing differential proteomic studies on the vast existing archives of healthy and pathological‐fixed tissues. 相似文献
913.
Jon Bielby Stefano Bovero Giuseppe Sotgiu Giulia Tessa Marco Favelli Claudio Angelini Stefano Doglio Frances C. Clare Enrico Gazzaniga Federica Lapietra Trenton W. J. Garner 《EcoHealth》2009,6(1):27-32
Batrachochytrium dendrobatidis (Bd), the causative agent of the amphibian disease chytridiomycosis, is an important factor in the global decline of amphibians. Within Europe, animals that exhibit clinical signs of the disease have only been reported in Spain despite the pathogen’s wide, but patchy, distribution on the continent. Recently, another occurrence of chytridiomycosis was reported in Euproctus platycephalus, the Sardinian brook newt, on the Mediterranean island of Sardinia, but without any evidence of fatal disease. We report further evidence of the emergence of Bd on Sardinia and the first evidence of lethal chytridiomycosis outside of Spain. Unusual mortalities of the Tyrrhenian painted frog (Discoglossus sardus) were found at three sites in the Limbara mountains of northern Sardinia. Molecular and histological screens of corpses, frogs, and tadpoles from these sites revealed infection with Bd. Infection and mortality occurred at locations that are unusual in terms of the published habitat requirements of the pathogen. Given the endemicity, the IUCN Red List status of the amphibian species on Sardinia, and the occurrence of infection and mortality caused by chytridiomycosis, there is serious reason for concern for the impact that disease emergence may have on the conservation of the amphibians of the island. 相似文献
914.
Maurizio Cutolo Stefano Soldano Paola Montagna Alberto Sulli Bruno Seriolo Barbara Villaggio Pierfranco Triolo Paolo Clerico Lamberto Felli Renata Brizzolara 《Arthritis research & therapy》2009,11(6):R176-10
Introduction
Co-stimulatory signal B7(CD80/CD86):CD28 is needed in order to activate T cells in immune response. Cytotoxic T lymphocyte-associated antigen-4-immunoglobulin (CTLA4-Ig) binding to the B7 molecules on antigen-presenting cells downregulates this activation and represents a recent biological treatment in rheumatoid arthritis (RA). Objectives of the study were to investigate the presence of the B7.2 (CD86) molecule and its masking by CTLA4-Ig on cultures of both RA synovial macrophages (RA SM), and of macrophages differentiated from THP-1 cells (M). In addition, the anti-inflammatory effects of CTLA4-Ig on co-cultures of RA SM and M with activated T cells were tested. 相似文献915.
Alfonso Baldi Raffaele Murace Emanuele Dragonetti Mario Manganaro Oscar Guerra Stefano Bizzi Luca Galli 《Biomedical engineering online》2009,8(1):18-10
Background
New generations of image-based diagnostic machines are based on digital technologies for data acquisition; consequently, the diffusion of digital archiving systems for diagnostic exams preservation and cataloguing is rapidly increasing. To overcome the limits of current state of art text-based access methods, we have developed a novel content-based search engine for dermoscopic images to support clinical decision making. 相似文献916.
As a result of the global decline of fish stocks, an increasing number of fish species are becoming targets of heavy exploitation, often concomitantly with a lack of biological knowledge on their structure and demographics. Here we present 11 new polymorphic microsatellite loci, isolated from the slinger sea bream (Chrysoblephus puniceus, Sparidae), a relatively recent target of coastal fisheries in eastern South Africa. Levels of genetic diversity were assessed in 39 individuals collected from the KwaZulu-Natal coast (Park Rynie, South Africa). Observed and expected heterozygosities varied between 0.39 and 0.97 and between 0.53 and 0.96, respectively. One locus (SL35) showed significant heterozygote deficiency and linkage disequilibrium was detected between SL35 and SL1. Importantly, five of these microsatellites cross-amplify in Cheimerius nufar, a sympatric species also subjected to exploitation. 相似文献
917.
Tomasz Kotwicki Stefano Negrini Theodoros B Grivas Manuel Rigo Toru Maruyama Jacek Durmala Fabio Zaina 《Scoliosis》2009,4(1):1-16
Background
Comprehensive evaluation of the morphology of the spine and of the whole body is essential in order to correctly manage patients suffering from progressive idiopathic scoliosis. Although methodology of clinical and radiological examination is well described in manuals of orthopaedics, there is deficit of data which clinical and radiological parameters are considered in everyday practise. Recently, an increasing tendency to extend scoliosis examination beyond the measure of the Cobb angle can be observed, reflecting a more patient-oriented approach. Such evaluation often involves surface parameters, aesthetics, function and quality of life.Aim of the study
To investigate current recommendations of experts on methodology of evaluation of the patient with spinal deformity, essentially idiopathic scoliosis.Methods
Structured Delphi procedure for collecting and processing knowledge from a group of experts with a series of questionnaires and controlled opinion feedback was performed. Experience and opinions of the professionals - physicians and physiotherapists managing scoliosis patients - were studied. According to Delphi method a Meeting Questionnaire (MQ) has been developed, resulting from a preliminary Pre-Meeting Questionnaire (PMQ) which had been previously discussed and approved on line. The MQ was circulated among the SOSORT experts during Consensus Session on "Measurements" which took place at the Annual Meeting of the Society, totally 23 panellists being engaged. Clinical, radiological and surface topography parameters were checked for agreement.Results
90% agreement or more was reached in 35 items and superior than 75% agreement was reached in further 25 items. An evaluation form was proposed to be used by clinicians and researchers.Conclusion
The consensus was reached on evaluation of the morphology of the patient with idiopathic scoliosis, comprising clinical, radiological and, to less extend, surface topography assessment. Considering the variety of parameters indicated by the panellists, the Cobb angle, yet the gold standard, can be seen neither as the unique nor the only decisive parameter in the management of patients with idiopathic scoliosis. 相似文献918.
919.
920.
Antonio Di Stefano Eleonora D'Aurizio Oriana Trubiani Rossella Grande Emanuela Di Campli Mara Di Giulio Soraya Di Bartolomeo Piera Sozio Antonio Iannitelli Antonia Nostro Luigina Cellini 《Microbial biotechnology》2009,2(6):634-641
The viscoelastic properties of mono‐microbial biofilms produced by ocular and reference staphylococcal strains were investigated. The microorganisms were characterized for their haemolytic activity and agr typing and the biofilms, grown on stainless steel surface under static conditions, were analysed by Confocal Laser Scanning Microscopy. Static and dynamic rheometric tests were carried out to determine the steady‐flow viscosity and the elastic and viscous moduli. The analysed biofilms showed the typical time‐dependent behaviour of viscoelastic materials with considerable elasticity and mechanical stability except for Staphylococcus aureus ATCC 29213 biofilm which showed a very fragile structure. In particular, S. aureus 6ME biofilm was more compact than other staphylococcal biofilms studied with a yield stress ranging between 2 and 3 Pa. The data obtained in this work could represent a starting point for developing new therapeutic strategies against biofilm‐associated infections, such as improving the drug effect by associating an antimicrobial agent with a biofilm viscoelasticity modifier. 相似文献