全文获取类型
收费全文 | 1082篇 |
免费 | 82篇 |
国内免费 | 1篇 |
出版年
2023年 | 9篇 |
2022年 | 12篇 |
2021年 | 28篇 |
2020年 | 11篇 |
2019年 | 16篇 |
2018年 | 29篇 |
2017年 | 32篇 |
2016年 | 44篇 |
2015年 | 55篇 |
2014年 | 48篇 |
2013年 | 66篇 |
2012年 | 81篇 |
2011年 | 85篇 |
2010年 | 43篇 |
2009年 | 39篇 |
2008年 | 59篇 |
2007年 | 68篇 |
2006年 | 53篇 |
2005年 | 72篇 |
2004年 | 44篇 |
2003年 | 48篇 |
2002年 | 46篇 |
2001年 | 11篇 |
2000年 | 6篇 |
1999年 | 15篇 |
1998年 | 7篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 11篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 9篇 |
1978年 | 3篇 |
1977年 | 7篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1971年 | 3篇 |
1969年 | 2篇 |
排序方式: 共有1165条查询结果,搜索用时 26 毫秒
31.
Silvio Schueler Stefan Kapeller Heino Konrad Thomas Geburek Michael Mengl Michele Bozzano Jarkko Koskela François Lefèvre Jason Hubert Hojka Kraigher Roman Longauer Ditte C. Olrik 《Biodiversity and Conservation》2013,22(5):1151-1166
Genetic resources of forest trees are considered as a key factor for the persistence of forest ecosystems because the ability of tree species to survive under changing climate depends strongly on their intraspecific variation in climate response. Therefore, utilizing available genetic variation in climate response and planting alternative provenances suitable for future climatic conditions is considered as an important adaptation measure for forestry. On the other hand, the distribution of adaptive genetic diversity of many tree species is still unknown and the predicted shift of ecological zones and species’ distribution may threaten forest genetic resources that are important for adaptation. Here, we use Norway spruce in Austria as a case study to demonstrate the genetic variation in climate response and to analyse the existing network of genetic conservation units for its effectiveness to safeguard the hotspots of adaptive and neutral genetic diversity of this species. An analysis of the climate response of 480 provenances, clustered into 9 groups of climatically similar provenances, revealed high variation among provenance groups. The most productive and promising provenance clusters for future climates originate from three regions that today depict the warmest and driest areas of the natural spruce distribution in Austria. Gap analysis of the Austrian genetic conservation units in the EUFGIS Portal suggests adequate coverage of the genetic hotspots in southern parts of Austria, but not in eastern and northern Austria. Therefore conservation measures and sustainable utilization of the valuable genetic resources in these regions need to be expanded to cover their high adaptive genetic variation and local adaptation to a warmer climate. The study shows that current conservation efforts need to be evaluated for their effectiveness to protect genetic resources that are important for the survival of trees in a future climate. 相似文献
32.
Maria A. De Marco Stefano Porru Paolo Cordioli Bruno M. Cesana Ana Moreno Laura Calzoletti Lebana Bonfanti Arianna Boni Antonio Scotto Di Carlo Cecilia Arici Angela Carta Maria R. Castrucci Isabella Donatelli Paola Tomao Vittoria M. Peri Livia Di Trani Nicoletta Vonesch 《PloS one》2013,8(2)
Background
Pigs play a key epidemiologic role in the ecology of influenza A viruses (IAVs) emerging from animal hosts and transmitted to humans. Between 2008 and 2010, we investigated the health risk of occupational exposure to swine influenza viruses (SIVs) in Italy, during the emergence and spread of the 2009 H1N1 pandemic (H1N1pdm) virus.Methodology/Principal Findings
Serum samples from 123 swine workers (SWs) and 379 control subjects (Cs), not exposed to pig herds, were tested by haemagglutination inhibition (HI) assay against selected SIVs belonging to H1N1 (swH1N1), H1N2 (swH1N2) and H3N2 (swH3N2) subtypes circulating in the study area. Potential cross-reactivity between swine and human IAVs was evaluated by testing sera against recent, pandemic and seasonal, human influenza viruses (H1N1 and H3N2 antigenic subtypes). Samples tested against swH1N1 and H1N1pdm viruses were categorized into sera collected before (n. 84 SWs; n. 234 Cs) and after (n. 39 SWs; n. 145 Cs) the pandemic peak. HI-antibody titers ≥10 were considered positive. In both pre-pandemic and post-pandemic peak subperiods, SWs showed significantly higher swH1N1 seroprevalences when compared with Cs (52.4% vs. 4.7% and 59% vs. 9.7%, respectively). Comparable HI results were obtained against H1N1pdm antigen (58.3% vs. 7.7% and 59% vs. 31.7%, respectively). No differences were found between HI seroreactivity detected in SWs and Cs against swH1N2 (33.3% vs. 40.4%) and swH3N2 (51.2 vs. 55.4%) viruses. These findings indicate the occurrence of swH1N1 transmission from pigs to Italian SWs.Conclusion/Significance
A significant increase of H1N1pdm seroprevalences occurred in the post-pandemic peak subperiod in the Cs (p<0.001) whereas SWs showed no differences between the two subperiods, suggesting a possible occurrence of cross-protective immunity related to previous swH1N1 infections. These data underline the importance of risk assessment and occupational health surveillance activities aimed at early detection and control of SIVs with pandemic potential in humans. 相似文献33.
Daniel Maximo Correa Alcantara Camila Silveira Souza Gustavo Graciolli Silvio Shigueo Nihei 《Studies on Neotropical Fauna and Environment》2016,51(3):235-238
The selection of roosts is considered a critical factor to the survival of Noctilio albiventris. Thus, we located and identified N. albiventris day roosts in the Pantanal, near the Miranda River. We identified four species of tree: Banara arguta, Inga vera, Ocotea diospyrifolia and Vitex cymosa. Additional studies are important to understand the impact of specific requirements in the selection of roosts for Noctilio albiventris and to compare the observed patterns in different environments. 相似文献
34.
Annalisa?Barera Silvio?Buscemi Roberto?Monastero Calogero?Caruso Rosalia?Caldarella Marcello?CiaccioEmail author 《Immunity & ageing : I & A》2016,13(1):14
Background
It is well known that Mediterranean Diet can positively influence the health of each individual, in particular it is know that fibers have an important role. However, in Mediterranean cities most people do not have a close adherence to Mediterranean diet. Thus, in our study, we considered fibers like β-glucans that have been added to pasta with a percentage of 6 %. Our study aimed to evaluate the capacity of β-glucans intake on oxidative stress and inflammation in a cohort of middle aged slightly overweight subjects.Methods
We used a longitudinal study design. The study lasted 30 days during which time, each participant acted with no food restriction. Participants underwent morning fasting blood venous sample for blood chemistry and other biological parameters at the beginning of the study and after 30 days of pasta supplemented with 6 % of β-glucan intake 4 times a week. We performed anthropometric, biochemical, oxidative stress and cytokine analysis at the beginning and the end of study.Results
After the 30 days of pasta intake we obtained a significant decrease of LDL-cholesterol, IL-6 and AGEs levels.Conclusion
The results confirmed a capacity of β-glucans intake to lower oxidative stress. Additional longitudinal observation on community-based cohorts are needed to confirm these data and investigate the biological mechanisms through which effects are induced, and to fully explore the therapeutic potential of β-glucans.35.
Sasa Savic Silvio Keckes Zivomir Petronijevic 《Biocatalysis and Biotransformation》2016,34(5):226-235
Horseradish peroxidase is a well-known member of the peroxidase family that catalyzes oxidation of flavonoids and phenolic substrates to free phenoxyl or semiquinone radicals. Aim of this study was to investigate in vitro oxidation of quercetin by horseradish peroxidase in the presence of l-cysteine as nucleophilic agent, and its influence on previously formed semiquinone- and quinone-type metabolites. The obtained results showed that in the reaction without l-cysteine several products were present, such as quercetin quinone methide, phloroglucinol carboxylic acid, protocatechuic acid, as well as quercetin heterodimer and derivates of quercetin heterodimer. On the other hand, in the presence of l-cysteine only three products were obtained, quercetin quinone methide and two new isomeric mono-cysteine derivatives of quercetin with mass exp. m/z 420.04?±?0.1 [quercetin?+?cysteine–H]– (theor. m/z 420.0389 [quercetin?+?cysteine–H]–). 相似文献
36.
37.
Hernández-Negrete I Carretero-Ortega J Rosenfeldt H Hernández-García R Calderón-Salinas JV Reyes-Cruz G Gutkind JS Vázquez-Prado J 《The Journal of biological chemistry》2007,282(32):23708-23715
Polarized cell migration results from the transduction of extra-cellular cues promoting the activation of Rho GTPases with the intervention of multidomain proteins, including guanine exchange factors. P-Rex1 and P-Rex2 are Rac GEFs connecting Gbetagamma and phosphatidylinositol 3-kinase signaling to Rac activation. Their complex architecture suggests their regulation by protein-protein interactions. Novel mechanisms of activation of Rho GTPases are associated with mammalian target of rapamycin (mTOR), a serine/threonine kinase known as a central regulator of cell growth and proliferation. Recently, two independent multiprotein complexes containing mTOR have been described. mTORC1 links to the classical rapamycin-sensitive pathways relevant for protein synthesis; mTORC2 links to the activation of Rho GTPases and cytoskeletal events via undefined mechanisms. Here we demonstrate that P-Rex1 and P-Rex2 establish, through their tandem DEP domains, interactions with mTOR, suggesting their potential as effectors in the signaling of mTOR to Rac activation and cell migration. This possibility was consistent with the effect of dominant-negative constructs and short hairpin RNA-mediated knockdown of P-Rex1, which decreased mTOR-dependent leucine-induced activation of Rac and cell migration. Rapamycin, a widely used inhibitor of mTOR signaling, did not inhibit Rac activity and cell migration induced by leucine, indicating that P-Rex1, which we found associated to both mTOR complexes, is only active when in the mTORC2 complex. mTORC2 has been described as the catalytic complex that phosphorylates AKT/PKB at Ser-473 and elicits activation of Rho GTPases and cytoskeletal reorganization. Thus, P-Rex1 links mTOR signaling to Rac activation and cell migration. 相似文献
38.
Cutrona G Boffa LC Mariani MR Matis S Damonte G Millo E Roncella S Ferrarini M 《Oligonucleotides》2007,17(1):146-150
The present study aims to evaluate the antigenicity of a PNA complementary to the Emu sequence (PNAEmu) with cancer therapeutic potential properties in Burkitt's lymphoma (BL). In BL cells, the c-myc oncogene is repositioned next to the Emu enhancer of the immunoglobulin (Ig) locus, due to chromosomal translocation, and up-regulated. PNAEmu linked to a nuclear localization signal peptide was shown specifically to block c-myc hyperexpression by inhibiting cell growth in vitro and in vivo. Recently, we reported that the administration of PNAEmu to mice, following inoculation with BL cells, hinders tumor growth without toxic effects. To investigate the potential use of PNAEmu in clinical applications further, we tested its antigenicity. Mice were inoculated with an emulsion of free PNA or PNA crosslinked to the immunogenic carrier keyhole limpet hemocyanin (KLH) with Freund's adjuvant. Antibodies to free PNA were undetected, whereas both IgG and IgM antibodies to PNA-KLH were detected in mouse serum 28 and 38 days after inoculation. 相似文献
39.
Heemskerk FM Zorad S Xu N Gutkind SJ Saavedra JM 《Cellular and molecular neurobiology》1999,19(2):277-288
1. A high expression of angiotensin II receptors and of angiotensin-converting enzyme (ACE) activity was detected in confluent NIH 3T3 fibroblasts.2. Characterization with selective ligands, dithiothreitol, and GTPS, indicated that only the AT2 subtype was expressed.3. AT2 receptors and ACE expression were strictly dependent on the cell density and growth phase of the cells, with AT2 receptors being expressed earlier than ACE. In contrast, high expression of AT2 receptors irrespective of their growth state was observed in NIH 3T3 cells lacking contact inhibition upon neoplastic transformation with ras.4. Our results imply a possible relation of AT2 receptors to cell growth and cell–cell contact. 相似文献
40.
Interactions of protein kinase CK2 subunits 总被引:3,自引:0,他引:3
Korn I Gutkind S Srinivasan N Blundell TL Allende CC Allende JE 《Molecular and cellular biochemistry》1999,191(1-2):75-83
Several approaches have been used to study the interactions of the subunits of protein kinase CK2. The inactive mutant of CK2 that has Asp 156 mutated to Ala (CK2A156) is able to bind the CK2 subunit and to compete effectively in this binding with wild-type subunits and . The interaction between CK2A156 and CK2 was also demonstrated by transfection of epitope-tagged cDNA constructs into COS-7 cells. Immunoprecipitation of epitope-tagged CK2A156 coprecipitated the subunit and vice-versa. The assay of the CK2 activity of the extracts obtained from cells transiently transfected with these different subunits yielded some surprising results: The CK2 specific phosphorylating activity of these cells transfected with the inactive CK2A156 was considerably higher than the control cells transfected with vectors alone. Assays of the immunoprecipitated CK2A156 expressed in these cells, however, demonstrated that the mutant was indeed inactive. It can be concluded that transfection of the inactive CK2A156 affects the endogenous activity of CK2. Transfection experiments with CK2 and subunits and CK2A156 were also used to confirm the interaction of CK2 with the general CDK inhibitor p21WAF1/CIP1 co-transfected into these cells. Finally a search in the SwissProt databank for proteins with properties similar to those derived from the amino acid composition of CK2 indicated that CK2 is related to protein phosphatase 2A and to other phosphatases as well as to a subunit of some ion-transport ATPases. 相似文献