全文获取类型
收费全文 | 460篇 |
免费 | 54篇 |
专业分类
514篇 |
出版年
2024年 | 2篇 |
2023年 | 3篇 |
2022年 | 10篇 |
2021年 | 18篇 |
2020年 | 9篇 |
2019年 | 13篇 |
2018年 | 10篇 |
2017年 | 6篇 |
2016年 | 18篇 |
2015年 | 35篇 |
2014年 | 38篇 |
2013年 | 33篇 |
2012年 | 43篇 |
2011年 | 41篇 |
2010年 | 26篇 |
2009年 | 15篇 |
2008年 | 29篇 |
2007年 | 36篇 |
2006年 | 17篇 |
2005年 | 15篇 |
2004年 | 23篇 |
2003年 | 19篇 |
2002年 | 18篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1982年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有514条查询结果,搜索用时 0 毫秒
101.
Receptor-mediated calcium entry was investigated in Fura 2 loaded FRTL-5 cells. The purinergic agonist ATP activated the release of sequestered calcium and the entry of extracellular calcium. Downregulation of protein kinase C (PKC) substantially enhanced the ATP-evoked calcium entry. Pretreatment of the cells with pertussis toxin (Ptx) decreased the ATP-evoked calcium entry by 56% and the release of sequestered calcium by 34%. In PKC-downregulated cells, the effect of Ptx treatment on the ATP-evoked increase in [Ca2+]iwas 73% and 44%, respectively. Phorbol myristic acetate (PMA) decreased the ATP-evoked calcium entry to the same extent as Ptx. In Ptx-treated cells, the ATP-evoked influx of 45Ca2+ was attenuated. Stimulation of the cells with P2p-purinergic agonist GTP evoked no entry of calcium, although GTP released the same amount of sequestered calcium as did ATP. PKC downregulation or pretreatment with Ptx had no effects on the GTP-evoked responses, whereas PMA decreased the GTP-evoked release of calcium. We conclude that the ATP-activated rapid calcium entry pathway is a second messenger-operated calcium channel. © 1995 Wiley-Liss, Inc. 相似文献
102.
Jari Kaikkonen Elina Porkkala-Sarataho Jason D. Morrow L. Jackson Roberts Kristiina Nyyssönen Riitta Salonen 《Free radical research》2013,47(6):967-978
Although the use of vitamin E supplements has been associated with a reduction in coronary events, assumed to be due to lowered lipid peroxidation, there are no previous long-term clinical trials into the effects of vitamin C or E supplementation on lipid peroxidation in vivo. Here, we have studied the long-term effects of vitamins C and E on plasma F2-isoprostanes, a widely used marker of lipid peroxidation in vivo. As a study cohort, a subset of the “Antioxidant Supplementation in Atherosclerosis Prevention” (ASAP) study was used. ASAP is a double-masked placebo-controlled randomized clinical trial to study the long-term effect of vitamin C (500 mg of slow release ascorbate daily), vitamin E (200 mg of d-α-tocopheryl acetate daily), both vitamins (CellaVie®), or placebo on lipid peroxidation, atherosclerotic progression, blood pressure and myocardial infarction (n = 520 at baseline). Lipid peroxidation measurements were carried out in 100 consecutive men at entry and repeated at 12 months. The plasma F2-isoprostane concentration was lowered by 17.3% (95% CI 3.9–30.8%) in the vitamin E group (p = 0.006 for the change, as compared with the placebo group). On the contrary, vitamin C had no significant effect on plasma F2-isoprostanes as compared with the placebo group. There was also no interaction in the effect between these vitamins. In conclusion, long-term oral supplementation of clinically healthy, but hypercholesterolemic men, who have normal vitamin C and E levels with a reasonable dose of vitamin E lowers lipid peroxidation in vivo, but a relatively high dose of vitamin C does not. This observation may provide a mechanism for the observed ability of vitamin E supplements to prevent atherosclerosis. 相似文献
103.
Genetic and environmental influences on the relationship between aggression and hyperactivity-impulsivity as rated by teachers and parents. 总被引:1,自引:0,他引:1
This study examined genetic and environmental contributions to the covariance between aggression and hyperactivity-impulsivity as rated by twins' teachers and parents. Sex-differences in these genetic and environmental contributions and rater bias/sibling interaction effects were of interest as well. Part of an ongoing nation-wide twin-family study of behavioral development and health habits, the sample consisted of 1636 Finnish twin pairs ascertained from five consecutive and complete twin birth cohorts. Data were collected at ages 11-12, using teacher and parental rating forms of the Multidimensional Peer Nomination Inventory. Bivariate analyses were performed using structural equation modeling allowing sex-limitation effects. Results show that, in addition to significant genetic and environmental influences specific to each behavior, aggression and hyperactivity-impulsivity share common genetic and environmental etiology. Results provide evidence that both genetic and environmental factors are important in creating the observed correlation between aggression and hyperactivity-impulsivity. 相似文献
104.
In the present investigation, intracellular sodium ([Na+]i) levels were determined in GH4C1 cells using the fluorescent probe SBFI. Fluorescence was determined by excitation at 340 nm and 385 nm, and emission was measured at 500 nm. Intracellular free sodium ([Na+]i) was determined by comparing the ratio 340/385 to a calibration curve. The ratio was linear between 10 and 60 mM Na+. Resting [Na+]i in GH4C1 cells was 26 ± 6.2 mM (mean ± SD). In cells incubated in Na+-buffer [Na+]i decreased to 3 ± 3.6 mM. If Na+/K+ ATPase was inhibited by incubating the cells with 1 mM ouabain, [Na+]i increased to 47 ± 12.8 mM in 15 min. Stimulating the cells with TRH, phorbol myristyl acetete, or thapsigargin had no effect on [Na+]i. Incubating the cells in Ca2+-buffer rapidly increased [Na+]i. The increase was not inhibited by tetrodotoxin. Addition of extracellular Ca2+, nimodipine, or Ni2+ to these cells immediately decreased [Na+]i, whereas Bay K 8644 enhanced the influx of Na+. In cells where [Na+]i was increased the TRH-induced increase in intracellular free calcium ([Ca2+]i) was decreased compared with control cells. Our results suggest that Na+ enters the cells via Ca2+ channels, and [Na+]i may attenuate TRH-induced changes in [Ca2+]i in GH4C1 cells. © 1993 Wiley-Liss, Inc. 相似文献
105.
Anne-Mari Luhtanen Eeva Eronen-Rasimus Hermanni Kaartokallio Janne-Markus Rintala Riitta Autio Elina Roine 《Extremophiles : life under extreme conditions》2014,18(1):121-130
In search for sea ice bacteria and their phages from the Baltic Sea ice, two ice samples were collected from land-fast ice in a south-west Finland coastal site in February and March 2011. Bacteria were isolated from the melted sea ice samples and phages were screened from the same samples for 43 purified isolates. Plaque-producing phages were found for 15 bacterial isolates at 3 °C. Ten phage isolates were successfully plaque purified and eight of them were chosen for particle purification to analyze their morphology and structural proteins. Phage 1/32 infecting an isolate affiliated to phylum Bacteroidetes (Flavobacterium sp.) is a siphovirus and six phages infecting isolates affiliated to γ-Proteobacteria (Shewanella sp.) hosts were myoviruses. Cross titrations between the hosts showed that all studied phages are host specific. Phage solutions, host growth and phage infection were tested in different temperatures revealing phage temperature tolerance up to 45 °C, whereas phage infection was in most of the cases retarded above 15 °C. This study is the first to report isolation and cultivation of ice bacteria and cold-active phages from the Baltic Sea ice. 相似文献
106.
Saila Vepsäläinen Henna Koivisto Elina Pekkarinen Petra Mäkinen Gary Dobson Gordon J. McDougall Derek Stewart Annakaisa Haapasalo Reijo O. Karjalainen Heikki Tanila Mikko Hiltunen 《The Journal of nutritional biochemistry》2013,24(1):360-370
A growing body of epidemiological evidence suggests that fruit and vegetable juices containing various phenolic compounds can reduce the risk of Alzheimer's disease (AD). As the altered amyloid precursor protein (APP) processing leading to increased β-amyloid (Aβ) production is a key pathogenic feature of AD, we elucidated the effects of different polyphenols on neuroprotection and APP processing under different in vitro stress conditions. The effects of these compounds were also investigated in transgenic AD mice (APdE9). Free radical toxicity and apoptosis were induced in human SH-SY5Y neuroblastoma cells overexpressing APP751. Menadione-induced production of reactive oxygen species was significantly decreased upon treatment with myricetin, quercetin or anthocyanin-rich extracts in a dose-dependent manner. However, these extracts did not affect caspase-3 activation, APP processing or Aβ levels upon staurosporine-induced apoptosis. APdE9 mice fed with anthocyanin-rich bilberry or blackcurrant extracts showed decreased APP C-terminal fragment levels in the cerebral cortex as compared to APdE9 mice on the control diet. Soluble Aβ40 and Aβ42 levels were significantly decreased in bilberry-fed mice as compared to blackcurrant-fed mice. Conversely, the ratio of insoluble Aβ42/40 was significantly decreased in blackcurrant-fed mice relative to bilberry-fed mice. Both berry diets alleviated the spatial working memory deficit of aged APdE9 mice as compared to mice on the control diet. There were no changes in the expression or phosphorylation status of tau in APdE9 mice with respect to diet. These data suggest that anthocyanin-rich bilberry and blackcurrant diets favorably modulate APP processing and alleviate behavioral abnormalities in a mouse model of AD. 相似文献
107.
Are the information processing steps that support short-term sensory memory common to all the senses? Systematic, psychophysical comparison requires identical experimental paradigms and comparable stimuli, which can be challenging to obtain across modalities. Participants performed a recognition memory task with auditory and visual stimuli that were comparable in complexity and in their neural representations at early stages of cortical processing. The visual stimuli were static and moving Gaussian-windowed, oriented, sinusoidal gratings (Gabor patches); the auditory stimuli were broadband sounds whose frequency content varied sinusoidally over time (moving ripples). Parallel effects on recognition memory were seen for number of items to be remembered, retention interval, and serial position. Further, regardless of modality, predicting an item's recognizability requires taking account of (1) the probe's similarity to the remembered list items (summed similarity), and (2) the similarity between the items in memory (inter-item homogeneity). A model incorporating both these factors gives a good fit to recognition memory data for auditory as well as visual stimuli. In addition, we present the first demonstration of the orthogonality of summed similarity and inter-item homogeneity effects. These data imply that auditory and visual representations undergo very similar transformations while they are encoded and retrieved from memory. 相似文献
108.
Comparison of design strategies for a three‐arm clinical trial with time‐to‐event endpoint: Power,time‐to‐analysis,and operational aspects 下载免费PDF全文
Elina Asikanius Kaspar Rufibach Jasmin Bahlo Gabriele Bieska Hans Ulrich Burger 《Biometrical journal. Biometrische Zeitschrift》2016,58(6):1295-1310
To optimize resources, randomized clinical trials with multiple arms can be an attractive option to simultaneously test various treatment regimens in pharmaceutical drug development. The motivation for this work was the successful conduct and positive final outcome of a three‐arm randomized clinical trial primarily assessing whether obinutuzumab plus chlorambucil in patients with chronic lympocytic lymphoma and coexisting conditions is superior to chlorambucil alone based on a time‐to‐event endpoint. The inference strategy of this trial was based on a closed testing procedure. We compare this strategy to three potential alternatives to run a three‐arm clinical trial with a time‐to‐event endpoint. The primary goal is to quantify the differences between these strategies in terms of the time it takes until the first analysis and thus potential approval of a new drug, number of required events, and power. Operational aspects of implementing the various strategies are discussed. In conclusion, using a closed testing procedure results in the shortest time to the first analysis with a minimal loss in power. Therefore, closed testing procedures should be part of the statistician's standard clinical trials toolbox when planning multiarm clinical trials. 相似文献
109.
Ivanklin Soares Campos‐Filho Paula Beatriz Araujo Maria Elina Bichuette Eleonora Trajano Stefano Taiti 《Zoological Journal of the Linnean Society》2014,172(2):360-425
To date, six species of terrestrial isopods were known from Brazilian caves, but only four could be classified as troglobites. This article deals with material of Oniscidea collected in many Brazilian karst caves in the states of Pará, Bahia, Minas Gerais, Mato Grosso do Sul, and São Paulo, and deposited in the collections of the Museu de Zoologia, Universidade de São Paulo, the Coleção de Carcinologia do Departamento de Zoologia, Universidade Federal do Rio Grande do Sul, and the collection of the Natural History Museum, Section of Zoology ‘La Specola’, Florence. Three new genera have been recognized: Spelunconiscus gen. nov. and Xangoniscus gen. nov. (Styloniscidae), and Leonardoscia gen. nov. (Philosciidae). Twenty‐two species have been identified, 11 of which in the families Styloniscidae, Philosciidae, Scleropactidae, Plathyartridae, Dubioniscidae, and Armadillidae are new to science: Leonardoscia hassalli sp. nov., Metaprosekia quadriocellata sp. nov. , Metaprosekia caupe sp. nov. , Amazoniscus leistikowi sp. nov. , Novamundoniscus altamiraensis sp. nov. , Trichorhina yiara sp. nov. , Trichorhina curupira sp. nov. , and Ctenorillo ferrarai sp. nov. from Pará; Xangoniscus aganju sp. nov. from Bahia; and Spelunconiscus castroi sp. nov. and Trichorhina anhanguera sp. nov. from Minas Gerais. Four new species in the families Styloniscidae ( Spelunconiscus castroi sp. nov. and Xangoniscus aganju sp. nov. ), Philosciidae ( Leonardoscia hassalli sp. nov. ), and Scleropactidae ( Amazoniscus leistikowi sp. nov. ) with highly troglomorphic traits can be considered as troglobitic, whereas all the remaining species are either troglophilic or accidentals. Brazilian caves are now under potential threat because of recent legislation, and the knowledge of the subterranean biodiversity of the country is thus of primary importance. © 2014 The Linnean Society of London 相似文献
110.
Gavin M. Lewis Monica Macal Charles R. Hesser Elina I. Zu?iga 《Journal of virology》2015,89(6):3343-3355