全文获取类型
收费全文 | 2322篇 |
免费 | 123篇 |
国内免费 | 1篇 |
出版年
2023年 | 5篇 |
2022年 | 24篇 |
2021年 | 39篇 |
2020年 | 26篇 |
2019年 | 48篇 |
2018年 | 50篇 |
2017年 | 34篇 |
2016年 | 59篇 |
2015年 | 108篇 |
2014年 | 111篇 |
2013年 | 194篇 |
2012年 | 158篇 |
2011年 | 165篇 |
2010年 | 108篇 |
2009年 | 109篇 |
2008年 | 139篇 |
2007年 | 153篇 |
2006年 | 130篇 |
2005年 | 103篇 |
2004年 | 103篇 |
2003年 | 101篇 |
2002年 | 92篇 |
2001年 | 21篇 |
2000年 | 20篇 |
1999年 | 28篇 |
1998年 | 21篇 |
1997年 | 25篇 |
1996年 | 21篇 |
1995年 | 19篇 |
1994年 | 8篇 |
1993年 | 24篇 |
1992年 | 12篇 |
1991年 | 16篇 |
1990年 | 12篇 |
1989年 | 10篇 |
1988年 | 12篇 |
1987年 | 13篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1978年 | 5篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1972年 | 4篇 |
1959年 | 3篇 |
排序方式: 共有2446条查询结果,搜索用时 15 毫秒
991.
Angelo Monguzzi Francesco Bianchi Alberto Bianchi Michele Mauri Roberto Simonutti Riccardo Ruffo Riccardo Tubino Francesco Meinardi 《Liver Transplantation》2013,3(5):680-686
Optically active materials able to up‐convert the frequency of the incident radiation can be used to enhance the performance of photovoltaic and photocatalityc cells, recovering sub‐bandgap photons not directly absorbed by the devices. Actually, sensitized up‐conversion (SUC) based on multi‐component organic systems is the most promising approach for these photon energy managing processes, being efficient also at the solar irradiance. However, applications of SUC on real devices have not been yet accomplished because its conversion yield usually drops dramatically in the solid state where the low dye mobility inhibits the diffusion controlled mechanisms ruling SUC photophysics. To overcome this limit, we prepared a single‐phase elastomer (poly‐butylacrilate) doped with proper dyes (platinum (II) octaetyl‐porphyrin and 9,10‐diphenylanthracene) to fabricate an efficient photon up‐converting material. Thanks to the residual molecular diffusion provided by the soft host, and to the quenching reduction of involved metastable electronic excited‐states in a solid environment compared to a liquid one, we obtained a record SUC yield of 17% at the solid state. SUC efficiency has been studied as function of the excitation power and sample temperature, elucidating the photophysical processes at the base of the high observed yield and assessing the guidelines for the fabrication of technologically appealing low power up‐converting materials. 相似文献
992.
Angelo Rambelli 《Plant biosystems》2013,147(3):99-107
993.
Coram Amber Abreo Neil Angelo S. Ellis Robert P. Thompson Kirsten F. 《Biodiversity and Conservation》2021,30(8-9):2341-2359
Biodiversity and Conservation - Litter in the marine environment, in particular plastic, is a significant threat to marine megafauna. Cetaceans are known to ingest or become entangled in marine... 相似文献
994.
Irradiation (254 nm) of five alkyl and benzyl ethyl sulfides causes efficient (Φr 0.27-0.90) homolytic cleavage of the C-S bond. Of the resulting fragments, thiyl radicals mainly couple, while alkyl radicals abstract hydrogen, disproportionate or couple when stabilized (benzyl). Selective trapping of either of the two types of radicals occurs in the presence of nucleophilic (methyl vinyl ether and 1-hexene) and, respectively, electrophilic (acrylonitrile) alkenes. When an easily oxidized radical is formed, e.g. cumyl, secondary electron transfer leads to the corresponding cation. 相似文献
995.
996.
Davide Cavazzini Francesca Meschi Romina Corsini Angelo Bolchi Gian Luigi Rossi Oliver Einsle Simone Ottonello 《The Journal of biological chemistry》2013,288(3):1533-1547
Fungal phospholipases are members of the fungal/bacterial group XIV secreted phospholipases A2 (sPLA2s). TbSP1, the sPLA2 primarily addressed in this study, is up-regulated by nutrient deprivation and is preferentially expressed in the symbiotic stage of the ectomycorrhizal fungus Tuber borchii. A peculiar feature of this phospholipase and of its ortholog from the black truffle Tuber melanosporum is the presence of a 54-amino acid sequence of unknown functional significance, interposed between the signal peptide and the start of the conserved catalytic core of the enzyme. X-ray diffraction analysis of a recombinant TbSP1 form corresponding to the secreted protein previously identified in T. borchii mycelia revealed a structure comprising the five α-helices that form the phospholipase catalytic module but lacking the N-terminal 54 amino acids. This finding led to a series of functional studies that showed that TbSP1, as well as its T. melanosporum ortholog, is a self-processing pro-phospholipase A2, whose phospholipase activity increases up to 80-fold following autoproteolytic removal of the N-terminal peptide. Proteolytic cleavage occurs within a serine-rich, intrinsically flexible region of TbSP1, does not involve the phospholipase active site, and proceeds via an intermolecular mechanism. Autoproteolytic activation, which also takes place at the surface of nutrient-starved, sPLA2 overexpressing hyphae, may strengthen and further control the effects of phospholipase up-regulation in response to nutrient deprivation, also in the context of symbiosis establishment and mycorrhiza formation. 相似文献
997.
998.
Murilo Sander de Abreu Gessi Koakoski Daiane Ferreira Thiago Acosta Oliveira Jo?o Gabriel Santos da Rosa Darlan Gusso Ana Cristina Varrone Giacomini Angelo Luis Piato Leonardo José Gil Barcellos 《PloS one》2014,9(7)
The presence of pharmaceutical products in the aquatic environment has been reported in several studies. However, the impact of these drugs on living organisms is still uncharacterized. Here, we investigated the effects of acute exposure to either diazepam or fluoxetine on the stress response in Danio rerio. We showed that diazepam and fluoxetine inhibited the stress axis in zebrafish. Intermediate concentrations of diazepam suppressed the stress response as measured by cortisol levels, whereas fluoxetine inhibited cortisol increase at concentrations similar to those found in the environment. These data suggest that the presence of psychoactive drugs in aquatic ecosystems could cause neuroendocrine dysfunction in fish. 相似文献
999.
Salvatore Sotgia Elisabetta Pisanu Gianfranco Pintus Gian Luca Erre Gerard Aime Pinna Luca Deiana Ciriaco Carru Angelo Zinellu 《PloS one》2013,8(7)
Two sensitive and reproducible capillary electrophoresis and high-performance liquid chromatography-fluorescence procedures were established for quantitative determination of L-egothioneine in plasma. After derivatization of L-ergothioneine with 5-iodoacetamidofluorescein, the separation was carried out by HPLC on an ODS-2 C-18 sperisorb column by using a linear gradient elution and by HPCE on an uncoated fused silica capillary, 50 µm id, and 60 cm length. The methods were validated and found to be linear in the range of 0.3 to 10 µmol/l. The limit of quantification was 0.27 µmol/l for HPCE and 0.15 µmol/l for HPLC. The variations for intra- and inter-assay precision were around 6 RSD%, and the mean recovery accuracy close to 100% (96.11%). 相似文献
1000.
Thymic microenvironments are essential for the proper development and selection of T cells critical for a functional and self-tolerant adaptive immune response. While significant turnover occurs, it is unclear whether populations of adult stem cells contribute to the maintenance of postnatal thymic epithelial microenvironments. Here, the slow cycling characteristic of stem cells and their property of label-retention were used to identify a K5-expressing thymic stromal cell population capable of generating clonal cell lines that retain the capacity to differentiate into a number of mesenchymal lineages including adipocytes, chondrocytes and osteoblasts suggesting a mesenchymal stem cell-like phenotype. Using cell surface analysis both culture expanded LRCs and clonal thymic mesenchymal cell lines were found to express Sca1, PDGFRα, PDGFRβ,CD29, CD44, CD49F, and CD90 similar to MSCs. Sorted GFP-expressing stroma, that give rise to TMSC lines, contribute to thymic architecture when reaggregated with fetal stroma and transplanted under the kidney capsule of nude mice. Together these results show that the postnatal thymus contains a population of mesenchymal stem cells that can be maintained in culture and suggests they may contribute to the maintenance of functional thymic microenvironments. 相似文献