全文获取类型
收费全文 | 2703篇 |
免费 | 195篇 |
专业分类
2898篇 |
出版年
2024年 | 4篇 |
2023年 | 27篇 |
2022年 | 65篇 |
2021年 | 102篇 |
2020年 | 76篇 |
2019年 | 87篇 |
2018年 | 93篇 |
2017年 | 89篇 |
2016年 | 118篇 |
2015年 | 172篇 |
2014年 | 195篇 |
2013年 | 227篇 |
2012年 | 258篇 |
2011年 | 236篇 |
2010年 | 151篇 |
2009年 | 93篇 |
2008年 | 172篇 |
2007年 | 126篇 |
2006年 | 135篇 |
2005年 | 98篇 |
2004年 | 89篇 |
2003年 | 65篇 |
2002年 | 63篇 |
2001年 | 8篇 |
2000年 | 12篇 |
1999年 | 17篇 |
1998年 | 11篇 |
1997年 | 10篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1974年 | 1篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1970年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有2898条查询结果,搜索用时 15 毫秒
51.
Prat-Vericat Maria Marciszak Adrian Rufí Isaac Sorbelli Leonardo Llenas Manel Lucenti Saverio Bartolini Madurell-Malapeira Joan 《Journal of Mammalian Evolution》2022,29(3):547-569
Journal of Mammalian Evolution - Late Pleistocene cave lions are one of the most iconic species of Northern Hemisphere Quaternary taphocoenoses. Despite their often-scarce record in cave... 相似文献
52.
Robson S. Godoy Vinicius Weber Luis Esteban Krause Lanés Martin Reichard Tanise Gemelli Raquel Von Hohendorff Leonardo Maltchik 《Journal of fish biology》2021,99(4):1476-1484
Annual fish species have evolved complex adaptations to survive in temporary wetlands. The main adaptation of these fish is the ability to produce embryos that survive dry periods. Embryo development of this fish can show variation at multiple levels influenced by many environmental factors, such as photoperiod and temperature. Predator cues are another factor that can influence the embryonic stage. One way in which annual fish could adapt to predators is by using risk-spreading strategies (through bet-hedging). Nonetheless, this strategy depends on the coevolutionary history between predators and preys and on the degree of environmental unpredictability, resulting in different responses across different species. This study investigated the influence of predator cues on the embryonic development and hatching of two Austrolebias species that inhabit ponds that present differences in hydroperiod and the risk of predator presence. The results confirmed a differentiated response between the two annual fish species tested, corroborating the modulation of hatching against the risk of predation by native predatory fish. The authors further showed that development times varied between the two annual fish species, regardless of the presence of predators. They highlight that the variation in embryonic development is strongly affected by different levels of hydroperiod unpredictability faced by the two species. To unravel finer-scale local adaptations in the annual fish embryo development, future studies should focus on a region with greater spatial gradient. 相似文献
53.
54.
55.
Leonardo P. Farias Greice Krautz-Peterson Cibele A. Tararam Bogar O. Araujo-Montoya Tatiana R. Fraga Henrique K. Rofatto Floriano P. Silva-Jr Lourdes Isaac Akram A. Da'dara R. Alan Wilson Charles B. Shoemaker Luciana C. C. Leite 《PLoS neglected tropical diseases》2013,7(10)
Background
It is believed that schistosomes evade complement-mediated killing by expressing regulatory proteins on their surface. Recently, six homologues of human CD59, an important inhibitor of the complement system membrane attack complex, were identified in the schistosome genome. Therefore, it is important to investigate whether these molecules could act as CD59-like complement inhibitors in schistosomes as part of an immune evasion strategy.Methodology/Principal Findings
Herein, we describe the molecular characterization of seven putative SmCD59-like genes and attempt to address the putative biological function of two isoforms. Superimposition analysis of the 3D structure of hCD59 and schistosome sequences revealed that they contain the three-fingered protein domain (TFPD). However, the conserved amino acid residues involved in complement recognition in mammals could not be identified. Real-time RT-PCR and Western blot analysis determined that most of these genes are up-regulated in the transition from free-living cercaria to adult worm stage. Immunolocalization experiments and tegument preparations confirm that at least some of the SmCD59-like proteins are surface-localized; however, significant expression was also detected in internal tissues of adult worms. Finally, the involvement of two SmCD59 proteins in complement inhibition was evaluated by three different approaches: (i) a hemolytic assay using recombinant soluble forms expressed in Pichia pastoris and E. coli; (ii) complement-resistance of CHO cells expressing the respective membrane-anchored proteins; and (iii) the complement killing of schistosomula after gene suppression by RNAi. Our data indicated that these proteins are not involved in the regulation of complement activation.Conclusions
Our results suggest that this group of proteins belongs to the TFPD superfamily. Their expression is associated to intra-host stages, present in the tegument surface, and also in intra-parasite tissues. Three distinct approaches using SmCD59 proteins to inhibit complement strongly suggested that these proteins are not complement inhibitors and their function in schistosomes remains to be determined. 相似文献56.
Gabriele?MatteucciEmail author Paolo?Rossini Stefano?Guerzoni Alessandro?Arcangeli Paolo?Fonti Leonardo?Langone Stefano?Miserocchi 《Hydrobiologia》2005,550(1):167-173
From 2000 to 2002, sediment contamination by Cd, Cu, Hg, Pb and Zn was analysed in the Pialassa Baiona salt marsh, which receives petrochemical wastewaters from the industrial district of Ravenna (Italy). The recent contamination levels were compared with data of previous studies carried out in 1982, in order to assess whether environmental policies and remedial measures reduced sediment pollution. Sedimentary profiles of Cu and Pb were homogeneous along the uppermost 0–10 cm horizon, which corresponded to the sedimentation in the last 30 years. Concentrations of Zn attained a peak (up to 800 mg kg−1 dry weight) in the 0–4 cm sediment horizon, which was assumed to correspond to the last 10–15 years. A wide-spread contamination by Hg was detected in the salt marsh as well as in the main channel with peaks up to 20–40 mg kg−1 dry weight. Nonetheless, recent sediments resulted less contaminated, since Hg discharge from industrial plants ceased about 20 years ago. Contamination levels by Hg values were two orders of magnitude higher than the international sediment quality standards. Cadmium, which was analysed for the first time in 2000–2002, attained a peak in the surface layers (1–2.5 mg kg−1 d.w.), with a progressive decline along the sediment column. Through comparison with pre-industrial values detected in the deeper sediment horizons (before 1920), Hg showed the highest enrichment factor, up to 300 times. Cd and Zn concentrations in recent sediments were from 2 to 10 times higher than background values. In terms of possible adverse effects, Hg posed the highest risk, and Cd and Zn were frequently above the recommended thresholds. 相似文献
57.
Serini S Donato V Piccioni E Trombino S Monego G Toesca A Innocenti I Missori M De Spirito M Celleno L Fasano E Ranelletti FO Calviello G 《The Journal of nutritional biochemistry》2011,22(9):874-885
The dramatic increase in the incidence of nonmelanoma skin cancer over the last decades has been related to the augmented exposure to ultraviolet (UV) radiation (UVR). It is known that apoptosis is induced as a protective mechanism after the acute irradiation of keratinocytes, whereas apoptotic resistance and carcinogenesis may follow the chronic exposure to UVR. We found that not all the human keratinocytes lines studied underwent apoptosis following acute exposure to UVR (10-60 mJ/cm2). Whereas UVR induced apoptosis in the HaCaT cells, NCTC 2544 and nr-HaCaT cells showed apoptosis resistance. The cytokeratin pattern of the apoptosis-resistant cells indicated that they possessed a degree of differentiation lower than that of HaCaT cells. They also showed an enhanced expression of cyclooxygenase-2 (COX-2), an early marker of carcinogenesis in various tissues, including skin. n-3 polyunsaturated fatty acids have drawn increasing interest as nutritional factors with the potential to reduce UVR carcinogenesis, and since they are apoptosis inducers and COX-2 inhibitors in cancer cells, we investigated the ability of n-3 polyunsaturated fatty acids to influence the resistance to UVR-induced apoptosis in keratinocytes. We observed that docosahexaenoic acid (DHA) reverted the resistance of nr-HaCaT cells to UVR-induced apoptosis, increasing the Bax/Bcl-2 ratio and caspase-3 activity, and reduced COX-2 levels by inhibiting the expression of the human antigen R (HuR), a known COX-2 mRNA stabilizer in keratinocytes. The transfection of nr-HaCaT cells with HuR siRNA mimicked the proapoptotic effect of DHA. Overall, our findings further support the role of DHA as a suitable anticarcinogenic factor against nonmelanoma skin cancers. 相似文献
58.
Hydroxyl Radicals and a Thylakoid-Bound Endopeptidase are Involved in Light- and Oxygen-Induced Proteolysis in Oat Chloroplasts 总被引:4,自引:0,他引:4
Casano Leonardo M.; Lascano H. Ramiro; Trippi Victorio S. 《Plant & cell physiology》1994,35(2):145-152
The hypothesis that light- and oxygen-induced proteolysis inchloroplasts is mediated by active oxygen species was examined.In order to determine whether or not H2O2 and/or {dot}OH radicalsare involved in these degradative processes we compared thedegradation of proteins in isolated oat chloroplasts exposedto white light at 80 W m-2 with that in chloroplasts incubatedin darkness in the absence or presence of H2O2 or a {dot}OH-generatingsystem composed by ascorbic acid, FeCl3 and H2O2 (Asc-Fe-H2O2).Light enhanced the rate of degradation of at least 18 polypeptides,while proteolysis was almost negligible in darkness in the abscenceof additives. H2O2 had a very small effect. However, Asc-Fe-H2O2-treatedchloroplasts in darkness showed a pattern of protein degradationalmost identical to that observed in the light. A thylakoid-boundendopeptidase (EP), the activity of which increased under photooxidativeenvironmental conditions and treatment with an {dot}OH-generatingsystem, was partially purified and characterized as a serinetypeprotease. Treatments with inhibitors of serine-type proteaseprevented both light- and Asc- Fe-H2O2-induced proteolysis.EP was more active against both soluble and membranous proteinsthat had been pretreated with Asc-Fe-H2O2 than against untreatedproteins. It is proposed that a high dose of light irradiationpromotes proteolysis by increasing the formation of {dot}OH,which may modify proteins such that they become more susceptibleto EP-catalyzed hydrolysis.
1Fisiología Vegetal, Dept. de Biología Vegetal,Universidad de Alcalá de Henares, Present address: 28871Alcalá de Henares (Madrid), España. 相似文献
59.
Sato Nana Yuzawa Mao Aminul Md Islam Tomokiyo Mikado Albarracin Leonardo Garcia-Castillo Valeria Ideka-Ohtsubo Wakako Iwabuchi Noriyuki Xiao Jin-zhong Garcia-Cancino Apolinaria Villena Julio Kitazawa Haruki 《Probiotics and antimicrobial proteins》2021,13(3):824-836
Probiotics and Antimicrobial Proteins - The use of in vitro systems that allow efficient selection of probiotic candidates with immunomodulatory properties could significantly minimize the use of... 相似文献
60.