全文获取类型
收费全文 | 702篇 |
免费 | 41篇 |
专业分类
743篇 |
出版年
2023年 | 5篇 |
2022年 | 11篇 |
2021年 | 22篇 |
2020年 | 20篇 |
2019年 | 20篇 |
2018年 | 18篇 |
2017年 | 20篇 |
2016年 | 30篇 |
2015年 | 37篇 |
2014年 | 47篇 |
2013年 | 53篇 |
2012年 | 70篇 |
2011年 | 61篇 |
2010年 | 37篇 |
2009年 | 40篇 |
2008年 | 36篇 |
2007年 | 42篇 |
2006年 | 25篇 |
2005年 | 19篇 |
2004年 | 28篇 |
2003年 | 19篇 |
2002年 | 20篇 |
2001年 | 2篇 |
2000年 | 5篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1975年 | 4篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1961年 | 1篇 |
1954年 | 1篇 |
1942年 | 1篇 |
1940年 | 2篇 |
1938年 | 1篇 |
1933年 | 1篇 |
排序方式: 共有743条查询结果,搜索用时 15 毫秒
91.
Inter‐ and intraspecific variability in physiological traits and post‐anoxia recovery of photosynthetic efficiency in grasses under oxygen deprivation 下载免费PDF全文
Antonio Pompeiano Thais Huarancca Reyes Tommaso M. Moles Marco Villani Marco Volterrani Lorenzo Guglielminetti Andrea Scartazza 《Physiologia plantarum》2017,161(3):385-399
Low oxygen conditions occur in grass sites due to high and frequent precipitation, poor soil quality, and over‐irrigation followed by slow drainage. Three warm‐season and one cool‐season grass were analyzed at metabolic level during a time‐course experiment performed in a controlled anoxic environment. Prolonged oxygen depletion proved detrimental by leading to premature death to all the species, with the exception of seashore paspalum. Moreover, the anoxia tolerance observed in these grasses has been associated with slow use of carbohydrates, rather than with their relative abundance, which was more important than their antioxidant capacity. Further physiological characterization of eight seashore paspalum genotypes to anoxia was also performed, by examining the variation in photosystem II (PSII) efficiency and gas exchange during post‐anoxia recovery. Multivariate analysis highlighted the presence of three main clusters of seashore paspalum genotypes, characterized by different ability to restore the PSII photochemistry during recovery after one day of anoxia. Taken together, our data demonstrate that the analysis of post‐anoxia recovery of fluorescence and gas exchange parameters can represent a fast and reliable indicator for selecting species and cultivars more able to acclimate their photosynthetic apparatus. 相似文献
92.
Neuronal synchrony mediated by astrocytic glutamate through activation of extrasynaptic NMDA receptors 总被引:31,自引:0,他引:31
Fast excitatory neurotransmission is mediated by activation of synaptic ionotropic glutamate receptors. In hippocampal slices, we report that stimulation of Schaffer collaterals evokes in CA1 neurons delayed inward currents with slow kinetics, in addition to fast excitatory postsynaptic currents. Similar slow events also occur spontaneously, can still be observed when neuronal activity and synaptic glutamate release are blocked, and are found to be mediated by glutamate released from astrocytes acting preferentially on extrasynaptic NMDA receptors. The slow currents can be triggered by stimuli that evoke Ca2+ oscillations in astrocytes, including photolysis of caged Ca2+ in single astrocytes. As revealed by paired recording and Ca2+ imaging, a striking feature of this NMDA receptor response is that it occurs synchronously in multiple CA1 neurons. Our results reveal a distinct mechanism for neuronal excitation and synchrony and highlight a functional link between astrocytic glutamate and extrasynaptic NMDA receptors. 相似文献
93.
Francesca Chiarini Francesca Paganelli Tommaso Balestra Cristina Capanni Antonietta Fazio Maria Cristina Manara Lorena Landuzzi Stefania Petrini Camilla Evangelisti Pier-Luigi Lollini Alberto M. Martelli Giovanna Lattanzi Katia Scotlandi 《Cell death & disease》2022,13(4)
Lamin A, a main constituent of the nuclear lamina, is involved in mechanosignaling and cell migration through dynamic interactions with the LINC complex, formed by the nuclear envelope proteins SUN1, SUN2 and the nesprins. Here, we investigated lamin A role in Ewing Sarcoma (EWS), an aggressive bone tumor affecting children and young adults. In patients affected by EWS, we found a significant inverse correlation between LMNA gene expression and tumor aggressiveness. Accordingly, in experimental in vitro models, low lamin A expression correlated with enhanced cell migration and invasiveness and, in vivo, with an increased metastatic load. At the molecular level, this condition was linked to altered expression and anchorage of nuclear envelope proteins and increased nuclear retention of YAP/TAZ, a mechanosignaling effector. Conversely, overexpression of lamin A rescued LINC complex organization, thus reducing YAP/TAZ nuclear recruitment and preventing cell invasiveness. These effects were also obtained through modulation of lamin A maturation by a statin-based pharmacological treatment that further elicited a more differentiated phenotype in EWS cells. These results demonstrate that drugs inducing nuclear envelope remodeling could be exploited to improve therapeutic strategies for EWS.Subject terms: Nuclear organization, Cancer 相似文献
94.
Mattia Criscuoli Cristina Ulivieri Irene Filippi Sara Monaci Giuditta Guerrini Bianca Crifò Domiziana De Tommaso Giuliana Pelicci Cosima T. Baldari Cormac T. Taylor Fabio Carraro Antonella Naldini 《Journal of cellular physiology》2020,235(11):8058-8070
Hypoxia occurs in physiological and pathological conditions. T cells experience hypoxia in pathological and physiological conditions as well as in lymphoid organs. Indeed, hypoxia-inducible factor 1α (HIF-1α) affects T cell survival and functions. Rai, an Shc family protein member, exerts pro-survival effects in hypoxic neuroblastoma cells. Since Rai is also expressed in T cells, we here investigated its role in hypoxic T cells. In this work, hypoxia differently affected cell survival, proapoptotic, and metabolic programs in T cells, depending upon Rai expression. By using Jurkat cells stably expressing Rai and splenocytes from Rai−/−mice, we demonstrated that Rai promotes T cell survival and affects cell metabolism under hypoxia. Upon exposure to hypoxia, Jurkat T cells expressing Rai show (a) higher HIF-1α protein levels; (b) a decreased cell death and increased Akt/extracellular-signal-regulated kinase phosphorylation; (c) a decreased expression of proapoptotic markers, including caspase activities and poly(ADP-ribose) polymerase cleavage; (d) an increased glucose and lactate metabolism; (e) an increased activation of nuclear factor-kB pathway. The opposite effects were observed in hypoxic splenocytes from Rai−/−mice. Thus, Rai plays an important role in hypoxic signaling and may be relevant in the protection of T cells against hypoxia. 相似文献
95.
Cathepsin B in osteoblasts 总被引:2,自引:0,他引:2
Active cathepsin B has been found in cell extract and medium of human osteoblast-like cells and MG-63 cells. The released form is stable at neutral and alkaline pH and, in both cell types, intracellular and extracellular cathepsin B activities are increased by interleukin-1 beta (IL-1beta) and parathyroid hormone (PTH). To evaluate the physiological role of cathepsin B in osteoblasts, we investigated the production and secretion of this enzyme in normal human synovial fibroblasts and modulation by IL-1beta and PTH. Lactate secretion concurrent with release of cathepsin B and comparable responses in osteoblasts were also examined. Our data show that synovial fibroblasts respond differently to treatment with the two agents, suggesting a cell-specific regulation of cathepsin B and possible involvement in osteoblast physiology. Cathepsin B involvement was then evaluated in the activation of plasminogen activator (PA) in MG-63 cells using two specific inhibitors of cathepsin B, CA074 and CA074-Me, in constitutive conditions and after treatment with IL-1beta. As results of PA activity obtained in the presence of IL-beta were in contrast with previous reports, we examined the activities of PA, pro-PA activated with trypsin, and plasmin in cell extract and media of MG-63 cells after 24-h treatment with IL-1beta. Results show that in normal conditions and in the presence of IL-1beta, cathepsin B is involved in the activation of PA. Moreover, IL-1beta stimulates PA, pro-PA activated by trypsin, and plasmin activity in medium, whereas in cell extract it stimulates pro-PA activated by trypsin and plasmin activity. IL-1beta has no effect on cell extract-associated PA. 相似文献
96.
97.
Comparing the Device Physics and Morphology of Polymer Solar Cells Employing Fullerenes and Non‐Fullerene Acceptors 下载免费PDF全文
Jason T. Bloking Tommaso Giovenzana Andrew T. Higgs Andrew J. Ponec Eric T. Hoke Koen Vandewal Sangwon Ko Zhenan Bao Alan Sellinger Michael D. McGehee 《Liver Transplantation》2014,4(12)
There is a need to find electron acceptors for organic photovoltaics that are not based on fullerene derivatives since fullerenes have a small band gap that limits the open‐circuit voltage (VOC), do not absorb strongly and are expensive. Here, a phenylimide‐based acceptor molecule, 4,7‐bis(4‐(N‐hexyl‐phthalimide)vinyl)benzo[c]1,2,5‐thiadiazole (HPI‐BT), that can be used to make solar cells with VOC values up to 1.11 V and power conversion efficiencies up to 3.7% with two thiophene polymers is demonstrated. An internal quantum efficiency of 56%, compared to 75–90% for polymer‐fullerene devices, results from less efficient separation of geminate charge pairs. While favorable energetic offsets in the polymer‐fullerene devices due to the formation of a disordered mixed phase are thought to improve charge separation, the low miscibility (<5 wt%) of HPI‐BT in polymers is hypothesized to prevent the mixed phase and energetic offsets from forming, thus reducing the driving force for charges to separate into the pure donor and acceptor phases where they can be collected. 相似文献
98.
Tommaso Campedelli Guglielmo Londi Giuditta Miniati Simonetta Cutini Guido Tellini Florenzano 《Biodiversity and Conservation》2016,25(9):1695-1710
The Mediterranean basin is considered one of the most important biodiversity hotspots. This extraordinary richness originates mainly from thousands of years of human activities that deeply modified the landscape. Safeguarding the so-called cultural landscapes plays a key role in biodiversity conservation. In this paper we present the results of our monitoring of the effects of the life project “Preservation of mountain grasslands of the Tuscan Apennines”, mainly characterized by shrub-cutting actions, on bird populations in the Pratomagno pasture, one of the two areas where the project was implemented, a SPA in eastern Tuscany. The monitoring plan covers a period of 5 years. We tested the effects of shrub clearing on a series of bird community parameters, such as abundance and richness of common species and of some ecological guilds. We also tested the timing of the response to the interventions (immediate or drawn out over time). Our results show a dramatic decrease of birds associated with shrubland, while there were no important increases in grassland species, with the sole exception of Woodlark. Regardless of their positive or negative effects, our results show different response times for individual species or groups of species. Moreover, species with a bad regional conservation status increased less than those with a good one. Broadly speaking, these results suggest that the efficacy of such projects depends on a careful preliminary assessment of a number of aspects, encompassing the nature of the interventions themselves and the characteristics of the target sites, but also the type of response of target species and the conservation status of target populations. 相似文献
99.
Milena Nasi Sara De Biasi Elena Bianchini Lara Gibellini Marcello Pinti Tiziana Scacchetti Tommaso Trenti Vanni Borghi Cristina Mussini Andrea Cossarizza 《PloS one》2015,10(1)
Background
An accurate and affordable CD4+ T cells count is an essential tool in the fight against HIV/AIDS. Flow cytometry (FCM) is the “gold standard” for counting such cells, but this technique is expensive and requires sophisticated equipment, temperature-sensitive monoclonal antibodies (mAbs) and trained personnel. The lack of access to technical support and quality assurance programs thus limits the use of FCM in resource-constrained countries. We have tested the accuracy, the precision and the carry-over contamination of Partec CyFlow MiniPOC, a portable and economically affordable flow cytometer designed for CD4+ count and percentage, used along with the “CD4% Count Kit-Dry”.Materials and Methods
Venous blood from 59 adult HIV+ patients (age: 25–58 years; 43 males and 16 females) was collected and stained with the “MiniPOC CD4% Count Kit-Dry”. CD4+ count and percentage were then determined in triplicate by the CyFlow MiniPOC. In parallel, CD4 count was performed using mAbs and a CyFlow Counter, or by a dual platform system (from Beckman Coulter) based upon Cytomic FC500 (“Cytostat tetrachrome kit” for mAbs) and Coulter HmX Hematology Analyzer (for absolute cell count).Results
The accuracy of CyFlow MiniPOC against Cytomic FC500 showed a correlation coefficient (CC) of 0.98 and 0.97 for CD4+ count and percentage, respectively. The accuracy of CyFlow MiniPOC against CyFlow Counter showed a CC of 0.99 and 0.99 for CD4 T cell count and percentage, respectively. CyFlow MiniPOC showed an excellent repeatability: CD4+ cell count and percentage were analyzed on two instruments, with an intra-assay precision below ±5% deviation. Finally, there was no carry-over contamination for samples at all CD4 values, regardless of their position in the sequence of analysis.Conclusion
The cost-effective CyFlow MiniPOC produces rapid, reliable and accurate results that are fully comparable with those from highly expensive dual platform systems. 相似文献100.
Elizabeth?J?Rahn Tommaso?Iannitti Renee?R?Donahue Bradley?K?TaylorEmail author 《Biology of sex differences》2014,5(1):4