全文获取类型
收费全文 | 1183篇 |
免费 | 66篇 |
国内免费 | 1篇 |
专业分类
1250篇 |
出版年
2023年 | 13篇 |
2022年 | 26篇 |
2021年 | 33篇 |
2020年 | 19篇 |
2019年 | 24篇 |
2018年 | 33篇 |
2017年 | 30篇 |
2016年 | 46篇 |
2015年 | 53篇 |
2014年 | 84篇 |
2013年 | 101篇 |
2012年 | 107篇 |
2011年 | 110篇 |
2010年 | 46篇 |
2009年 | 48篇 |
2008年 | 81篇 |
2007年 | 64篇 |
2006年 | 59篇 |
2005年 | 46篇 |
2004年 | 43篇 |
2003年 | 39篇 |
2002年 | 29篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 15篇 |
1998年 | 11篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 13篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1990年 | 2篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1968年 | 3篇 |
1966年 | 1篇 |
1965年 | 2篇 |
1963年 | 1篇 |
1958年 | 1篇 |
1901年 | 1篇 |
排序方式: 共有1250条查询结果,搜索用时 15 毫秒
41.
Pehuén Pereyra Gerber Mercedes Cabrini Carolina Jancic Luciana Paoletti Claudia Banchio Catalina von Bilderling Lorena Sigaut Lía I. Pietrasanta Gabriel Duette Eric O. Freed Genevieve de Saint Basile Catarina Ferreira Moita Luis Ferreira Moita Sebastian Amigorena Philippe Benaroch Jorge Geffner Matías Ostrowski 《The Journal of cell biology》2015,209(3):435-452
During the late stages of the HIV-1 replication cycle, the viral polyprotein Pr55Gag is recruited to the plasma membrane (PM), where it binds phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) and directs HIV-1 assembly. We show that Rab27a controls the trafficking of late endosomes carrying phosphatidylinositol 4-kinase type 2 α (PI4KIIα) toward the PM of CD4+ T cells. Hence, Rab27a promotes high levels of PM phosphatidylinositol 4-phosphate and the localized production of PI(4,5)P2, therefore controlling Pr55Gag membrane association. Rab27a also controls PI(4,5)P2 levels at the virus-containing compartments of macrophages. By screening Rab27a effectors, we identified that Slp2a, Slp3, and Slac2b are required for the association of Pr55Gag with the PM and that Slp2a cooperates with Rab27a in the recruitment of PI4KIIα to the PM. We conclude that by directing the trafficking of PI4KIIα-positive endosomes toward the PM, Rab27a controls PI(4,5)P2 production and, consequently, HIV-1 replication. 相似文献
42.
Delphine Martire Sarah Garnier Sébastien Sagnol Annick Bourret Stéphane Marchal Norbert Chauvet Amandine Guérin Dominique Forgues Dominique Berrebi Christophe Chardot Marc Bellaiche John Rendu Nicolas Kalfa Sandrine Faure Pascal de Santa Barbara 《Journal of cellular and molecular medicine》2021,25(8):4028-4039
Smooth Muscle Cells (SMC) are unique amongst all muscle cells in their capacity to modulate their phenotype. Indeed, SMCs do not terminally differentiate but instead harbour a remarkable capacity to dedifferentiate, switching between a quiescent contractile state and a highly proliferative and migratory phenotype, a quality often associated to SMC dysfunction. However, phenotypic plasticity remains poorly examined in the field of gastroenterology in particular in pathologies in which gut motor activity is impaired. Here, we assessed SMC status in biopsies of infants with chronic intestinal pseudo-obstruction (CIPO) syndrome, a life-threatening intestinal motility disorder. We showed that CIPO-SMCs harbour a decreased level of contractile markers. This phenotype is accompanied by an increase in Platelet-Derived Growth Factor Receptor-alpha (PDGFRA) expression. We showed that this modulation occurs without origin-related differences in CIPO circular and longitudinal-derived SMCs. As we characterized PDGFRA as a marker of digestive mesenchymal progenitors during embryogenesis, our results suggest a phenotypic switch of the CIPO-SMC towards an undifferentiated stage. The development of CIPO-SMC culture and the characterization of SMC phenotypic switch should enable us to design therapeutic approaches to promote SMC differentiation in CIPO. 相似文献
43.
Mohamed El Yaagoubi Hicham Mechqoq Sergio Ortiz Carlos Cavaleiro Marylin Lecsö-Bornet Catarina Guerreiro Pereira Maria João Rodrigues Luísa Custódio Abdelhamid El Mousadik Laurent Picot Marina Kritsanida Fouad Msanda Noureddine El Aouad Raphaël Grougnet 《化学与生物多样性》2021,18(12):e2100653
The chemical composition and in vitro biological activities of the essential oil (EO) of Micromeria macrosiphon Coss. and M. arganietorum (J. Emb.) R. Morales, two Lamiaceae endemic to south Morocco, were investigated. GC/MS analysis resulted in the identification of 36 metabolites from the EO of M. macrosiphon, 45 from M. arganietorum. Borneol was the major metabolite in both oils and together with related derivatives such as camphor, accounted for 2/3 of the EO of M. macrosiphon, 1/3 of those of M. arganietorum. Pinene and terpinene derivatives were also present in high proportions. From a chemotaxonomic point of view, the composition of the examined samples may be related to those of other species endemic to Macaronesia. Both EOs showed significant toxicity towards liver HepG2 and melanoma B16 4A5 tumor cell lines at 100 μg/mL; however, they were also cytotoxic towards S17 normal cell lines, with a selectivity index <1. No antibacterial activity was noticed against 52 strains at 100 μg/mL. 相似文献
44.
45.
A secretory form of human α3-fucosyltransferase IX (sFUT9) was overexpressed in Spodoptera frugiperda (Sf9) insect cells using the stable expression vector pIB/V5-His-TOPO and the signal sequence of human interleukin 2 for
efficient secretion. sFUT9 was active and its three potential N-glycosylation sites were occupied. sFUT9 efficiently fucosylated the type II acceptors Galbeta4GlcNAC-R and Fucalpha2Galbeta4GlcNAc-R
(R = (CH2)3NHCO(CH2)5–NH-biotin) but not the corresponding sialylated acceptor, and only very poorly the type I (Galbeta3GlcNAc-R)
related acceptors. sFUT9 showed a clear preference for glycoproteins containing type II acceptors, with values of 121, 113
and 110 microU/million cell for asialofetuin, erythropoietin and asialoerythropoietin, respectively, values approximately
11-fold higher than those obtained for the small acceptors. 相似文献
46.
Lopes AC Rodrigues JF Clementino MB Miranda CA Nascimento AP de Morais Júnior MA 《Memórias do Instituto Oswaldo Cruz》2007,102(7):827-832
PCR analysis of 16S-23S internal transcribed spacer (PCR ribotyping) and tRNA intergenic spacer (tDNA-PCR) were evaluated for their effectiveness in identification of clinical strains of Klebsiella pneumoniae and differentiation with related species. For this purpose both methods were applied to forty-three clinical isolates biochemically identified as K. pneumoniae subsp. pneumoniae isolated from patients clinical specimens attended at five hospitals in three Brazilian cities. References strains of K. pneumoniae subsp. pneumoniae, K. pneumoniae subsp. ozaenae, K. oxytoca, K. planticola and Enterobacter aerogenes were also analyzed. Both PCR methods showed specific patterns for each species. A conserved PCR ribotype pattern was observed for all clinical K. pneumoniae isolates, while differing from other related analyzed species. tDNA-PCR revealed five distinct patterns among the K. pneumoniae clinical isolates studied, demonstrating a predominant group with 90.6% of isolates presenting the same pattern of K. pneumoniae type strain. Both PCR-based methods were not able to differentiate K. pneumoniae subspecies. On the basis of the results obtained, both methods were efficient to differentiate the Klebsiella species analyzed, as well as E. aerogenes. Meanwhile tDNA-PCR revealed different tRNA arrangements in K. pneumoniae, suggesting intra-species heterogeneity of their genome organization, the polymorphism of the intergenic spacers between 16S and 23S rRNA genes appears to be highly conserved whithin K. pneumoniae clinical isolates, showing that PCR ribotyping can be an useful tool for identification of K. pneumoniae isolates. 相似文献
47.
Albuquerque AS Cortesão CS Foxall RB Soares RS Victorino RM Sousa AE 《Journal of immunology (Baltimore, Md. : 1950)》2007,178(5):3252-3259
IL-7 is a nonredundant cytokine for T cell homeostasis. Circulating IL-7 levels increase in lymphopenic clinical settings, including HIV-1 infection. HIV-2 infection is considered a "natural" model of attenuated HIV disease given its much slower rate of CD4 decline than HIV-1 and limited impact on the survival of the majority of infected adults. We compared untreated HIV-1- and HIV-2-infected patients and found that the HIV-2 cohort demonstrated a delayed increase in IL-7 levels during the progressive depletion of circulating CD4 T cells as well as a dissociation between the acquisition of markers of T cell effector differentiation and the loss of IL-7Ralpha expression. This comparison of two persistent infections associated with progressive CD4 depletion and immune activation demonstrates that a better prognosis is not necessarily associated with higher levels of IL-7. Moreover, the delayed increase in IL-7 coupled with sustained expression of IL-7Ralpha suggests a maximization of available resources in HIV-2. The observation that increased IL-7 levels early in HIV-1 infection were unable to reduce the rate of CD4 loss and the impaired expression of the IL-7Ralpha irrespective of the state of cell differentiation raises concerns regarding the use of IL-7 therapy in HIV-1 infection. 相似文献
48.
Cunha-Oliveira T Rego AC Garrido J Borges F Macedo T Oliveira CR 《Journal of neurochemistry》2007,101(2):543-554
Cortical function has been suggested to be highly compromised by repeated heroin self-administration. We have previously shown that street heroin induces apoptosis in neuronal-like PC12 cells. Thus, we analysed the apoptotic pathways involved in street heroin neurotoxicity using primary cultures of rat cortical neurons. Our street heroin sample was shown to be mainly composed by heroin, 6-monoacetylmorphine and morphine. Exposure of cortical neurons to street heroin induced a slight decrease in metabolic viability, without loss of neuronal integrity. Early activation of caspases involved in the mitochondrial apoptotic pathway was observed, culminating in caspase 3 activation, Poly-ADP Ribose Polymerase (PARP) cleavage and DNA fragmentation. Apoptotic morphology was completely prevented by the non-selective caspase inhibitor z-VAD-fmk, indicating an important role for caspases in neurodegeneration induced by street heroin. Ionotropic glutamate receptors, opioid receptors and oxidative stress were not involved in caspase 3 activation. Interestingly, street heroin cytotoxicity was shown to be independent of a functional mitochondrial respiratory chain, as determined using NT-2 rho(0) cells. Nonetheless, in street heroin-treated cortical neurons, cytochrome c was released, accompanied by a decrease in mitochondrial potential and Bcl-2/Bax. Pure heroin hydrochloride similarly decreased metabolic viability but only slightly activated caspase 3. Altogether, our data suggest an important role for mitochondria in mediating street heroin neurotoxic effects. 相似文献
49.
Viani FC Cazares Viani PR Gutierrez Rivera IN Gonçalves da Silva E Rodrigues Paula C Gambale W 《Revista iberoamericana de micología》2007,24(1):19-23
Microsporum canis is the main zoophylic dermatophyte in dogs and cats, and it is also an important zoonotic agent. The literature showed that cats are asymptomatic carriers of M. canis. This is apparently due to host resistance and/or the presence of strains with lower virulence. This study was aimed to evaluate the keratinolytic, elastinolytic and collagenolytic activities of M. canis strains and their relationship with symptomatic and asymptomatic cats. In addition, these strains were analysed by RFLP. The strains isolated from cats with clinical dermatophytosis had higher keratinase and elastase activity than those isolated from asymptomatic animals (p minus than 0.05). There were not differences in RFLP patterns based on Hind III digestion. 相似文献
50.
Life cycle assessment of a multi-material car component 总被引:1,自引:1,他引:0
Catarina Ribeiro José V. Ferreira Paulo Partidário 《The International Journal of Life Cycle Assessment》2007,12(5):336-345
Background, Aims and Scope In recent years, the automotive industry has been experiencing an increasing concern with environmental requirements. A particular
focus is being given to light-weighting of cars, to reducing fuel consumption and to the use of different recycling materials.
Consequently, decisions on product design and development must involve economic and technological as well as environmental
considerations. In adequate conditions, the LCA methodology enables one to assist an effective integration of the environmental
considerations in the decision-making process [1]. In this paper, a multi-material car component which is part of the current
automotive brake system, has been modified by its original manufacturer. Such a modification included the use of a new multi-material
injection moulding process and the consumption of recyclable materials. The new and the current component were comparatively
assessed throughout their life cycles in order to evaluate their respective environmental impacts and, thus, to verify if
the new component offers a lower environmental load. The results described in this paper are part of the outcome of a broader
research project involving industrial companies, university, technological centres and research institutes based in Portugal,
Spain and Germany.
Main Features The car component under focus has four subcomponents whose base materials consist of steel and plastic. The LCA methodology
is used to evaluate two scenarios describing the new car component, on the one hand, and the reference scenario, which consists
of the existing car component, on the other. The former results from the selection of new subcomponents materials, aiming
to use a new production process together with a recycling strategy.
Results and Discussion The inventory analysis shows a lower energy consumption in the alternative scenario (4.2 MJ) compared to the reference scenario
(6.1 MJ). Most of that energy is still non-renewable, relating in particular to crude consumption in the car use phase and
in the production phase (transports and plastics production). The life cycle inventory analysis indicates also that the alternative
scenario has lower air emissions of CO2, CO, NOx, SOx, NM VOC and PM10, as well as lower solid wastes and water emissions of oils and BOD5. Otherwise, the water emissions of undissolved
substances and COD are higher for the alternative scenario. Most of the energy consumed and the air pollutants inventoried
occur as a consequence of the use phase. Otherwise, for most of the life cycle water emissions inventoried and solid wastes,
the production phase is the major contributor. The impact assessment, performed with the CML method, allows one to conclude
that the alternative scenario exhibits lower results in all the impact categories. Both scenarios have similar environmental
profiles, being: (i) the use phase, the major contributor for the abiotic depletion, global warming, photochemical oxidation,
acidification and eutrophication; and (ii) the production phase, the main contributor for ozone depletion, human toxicity,
fresh water aquatic ecotoxicity, marine aquatic ecotoxicity and terrestrial ecotoxicity. The sensitivity analysis, with respect
to the fuel consumption reduction value, the impact assessment method and the final disposal scenario, performed in this study
allows one to confirm, as a main conclusion, that the alternative scenario is environmentally preferable to the reference
scenario.
Conclusion The results obtained through the application of the LCA methodology enable one to conclude that the alternative component
has a lower environmental load than the reference component.
Recommendations and Perspectives Considering that the time required for the inventory data collection is a critical issue in LCA practise, the insights provided
by this particular case study are likely to be useful to product developers in the car component manufacturing industry, particularly
to brake system manufacturers supporting the environmental design within the sector. 相似文献