全文获取类型
收费全文 | 1627篇 |
免费 | 102篇 |
出版年
2023年 | 15篇 |
2022年 | 25篇 |
2021年 | 66篇 |
2020年 | 39篇 |
2019年 | 48篇 |
2018年 | 60篇 |
2017年 | 51篇 |
2016年 | 66篇 |
2015年 | 98篇 |
2014年 | 111篇 |
2013年 | 107篇 |
2012年 | 123篇 |
2011年 | 128篇 |
2010年 | 68篇 |
2009年 | 64篇 |
2008年 | 85篇 |
2007年 | 84篇 |
2006年 | 77篇 |
2005年 | 57篇 |
2004年 | 50篇 |
2003年 | 46篇 |
2002年 | 40篇 |
2001年 | 34篇 |
2000年 | 30篇 |
1999年 | 21篇 |
1998年 | 13篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1987年 | 3篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 8篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1974年 | 6篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1971年 | 2篇 |
1968年 | 2篇 |
排序方式: 共有1729条查询结果,搜索用时 46 毫秒
971.
In order to understand the main ecological factors that influence the distribution of mountain vegetation in Azores and to
use it as a model for nature conservation, a study on Santa Bárbara Mountain on Terceira Island was performed. A multivariate
analysis was done on vegetation data and the abiotic factors governing the vegetation pattern are discussed. The major factors
contributing to the observed vegetation patterns are wind exposure, soil water saturation and historical human impacts. The
vegetation analysis showed that Azorean Mountain habitats have a high variation of vegetation structure as a result of the
habitat heterogeneity and the extreme ecological conditions. Using the co-dominant plants as indicator species, eco-zones
are distinguished, characterized by the combination of different ecological–human factors which contribute to the distribution
of specific types of natural vegetation communities. The studies of vegetation distribution give important information about
the relation between vegetation and landscape that is essential for conservation, restoration proposals and landscape planning.
Azores terrestrial Natura 2000 sites are largely dominated by mountain vegetation, therefore this work provides essential
background data for the management plans of these sites. 相似文献
972.
Igor Santos Fonte B?a Marcella Leite Porto Ana Claudia Hertel Pereira Jean Pierre Louzada Ramos Rodrigo Scherer Jairo Pinto Oliveira Breno Valentim Nogueira Silvana Santos Meyrelles Elisardo Corral Vasquez Denise Coutinho Endringer Thiago Melo Costa Pereira 《PloS one》2015,10(12)
Contrast-induced nephropathy (CIN) is an iatrogenic medical event for which there is not yet a successful therapy. Increasing evidence in rodents has suggested that this disease is associated with renal tubular and vascular injury that is triggered directly by oxidative stress. In the present study, we evaluated whether the antioxidant resin from Virola oleifera (RV) could attenuate renal damage in an experimental mouse model of CIN. Adult male Swiss mice were divided into six groups and pre-treated orally with RV (10, 100 and 300 mg/kg), N-acetylcysteine (200 mg/kg) or vehicle for 5 days before the induction of CIN and Control group. Renal function was assessed by measuring plasma creatinine and urea levels. Additionally, renal oxidative stress and apoptosis/cell viability were determined with flow cytometry. Finally, kidney tissues were sectioned for histopathological examination. In this CIN model, pre-treatment with RV improved renal function, lowered the mortality rate, and reduced oxidative stress and apoptosis in both the medulla and cortex renal cells in a dose-dependent manner. Moreover, the RV treatment had beneficial effects on kidney histopathology that were superior to the standard treatment with N-acetylcysteine. These data suggest that because of its antioxidative and antiapoptotic effects and its ability to preserve renal function, resin from Virola oleifera may have potential as a new therapeutic approach for preventing CIN. 相似文献
973.
Mette Ilander Anna Kreutzman Peter Rohon Teresa Melo Edgar Faber Kimmo Porkka Jukka Vakkila Satu Mustjoki 《PloS one》2014,9(1)
A small proportion of chronic myeloid leukemia patients treated with interferon-α (IFN-α) monotherapy are able to discontinue the treatment without disease relapse although residual leukemia cells are present. Recently, we showed that these patients have increased amount of NK-cells and a distinct blood cytokine profile. We now aimed to study the function of NK- and T-cells in order to understand the role of the immune system in maintaining the treatment response after IFN-α discontinuation. The study included 13 patients: 5 patients were still treated with IFN-α monotherapy (IFN-ON, median treatment time 163 months) and 8 had stopped the treatment successfully (IFN-OFF, median time without therapy 42 months). Detailed immunophenotype and cytokine production of NK- and T-cells was analyzed with flow cytometry. In addition, the cytotoxicity of NK-cells was studied using K562 as target cells and both the degranulation and direct killing was measured. Compared to healthy controls, IFN-OFF patients had increased proportion of CD4+ effector memory (CCR7−CD45RA−; median 23% vs. healthy 16%, p = 0.009) and CD8+ central memory T-cells (CCR7+CD45RA−; median 26% vs. healthy 14%, p = 0.004). Further, upon stimulation the IFN-γ/TNF-α cytokine secretion by CD4+ T-cells was significantly enhanced in IFN-OFF patients (median 13.7% vs. healthy 7.8%, p = 0.01), and CD4+ effector and central memory cells were the main cytokine producers. No similar increase was observed in IFN-ON group (6.5%). In addition, the proportion of NK-cells was significantly increased in IFN-OFF patients (median IFN-OFF 24%, healthy 13%, p = 0.04), but their direct killing of K562 cells was impaired. The cytotoxicity of NK-cells was also diminished in IFN-ON patients. To conclude, in addition to elevated NK-cell count, IFN-OFF patients have increased amount of memory T-cells, which are able to induce strong cytokine response upon stimulation. This activity may contribute to the maintenance of prolonged remission after successful IFN-α discontinuation. 相似文献
974.
Jean Carlos Rodrigues Silva Luis Henrique Souza Guimarães José Carlos Santos Salgado Rosa Prazeres Melo Furriel Maria Lourdes T. M. Polizeli José César Rosa João Atilio Jorge 《Folia microbiologica》2013,58(6):561-568
Two cellulases from Scytalidium thermophilum were purified and characterized, exhibiting tolerance to glucose and cellobiose. Characterization of purified cellulases I and II by mass spectrometry revealed primary structure similarities with an exoglucanase and an endoglucanase, respectively. Molecular masses were 51.2 and 45.6 kDa for cellulases I and II, respectively, as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Cellulases I and II exhibited isoelectric points of 6.2 and 6.9 and saccharide contents of 11 and 93 %, respectively. Optima of temperature and pH were 60–65 °C and 4.0 for purified cellulase I and 65 °C and 6.5 for purified cellulase II. Both cellulases maintained total CMCase activity after 60 min at 60 °C. Cysteine, Mn2+, dithiotreitol and ß-mercaptoethanol-stimulated cellulases I and II. The tolerance to cellulose hydrolysis products and the high thermal stabilities of Scytalidium cellulases suggest good potential for industrial applications. 相似文献
975.
C. J. H. Souza A. S. McNeilly M. V. Benavides E. O. Melo J. C. F. Moraes 《Animal genetics》2014,45(5):732-739
Litter size (LS) in sheep is determined mainly by ovulation rate (OR). Several polymorphisms have been identified in the growth differentiation factor 9 (GDF9) gene that result in an increase in OR and prolificacy of sheep. Screening the databank of the Brazilian Sheep Breeders Association for triplet delivery, we identified flocks of prolific Ile de France ewes. After resequencing of GDF9, a point mutation (c.943C>T) was identified, resulting in a non‐conservative amino acid change (p.Arg315Cys) in the cleavage site of the propeptide. This new allele was called Vacaria (FecGv). A flock of half‐sib ewes was evaluated for OR in the first three breeding seasons, and Vacaria heterozygotes had higher OR (P < 0.001), averaging 2.1 ± 0.1 when compared to 1.2 ± 0.1 in wild‐type ewes. The OR was also influenced by age, increasing in the second and third breeding seasons (P < 0.001). In flocks segregating this allele, the LS was higher in mutant sheep (P < 0.001), averaging 1.61 ± 0.07 in heterozygotes and 1.29 ± 0.03 in wild‐type ewes. Analysis of homozygote reproductive tract morphology revealed uterine and ovarian hypoplasia. Ovarian follicles continue to develop up to small antral stages, although with abnormal oocyte morphology and altered arrangement of granulosa cells. After the collapse of the oocyte in most follicles, the remaining cells formed clusters that persisted in the ovary. This SNP is useful to improve selection for dam prolificacy and also as a model to investigate GDF9 post‐translation processing and the fate of the follicular cells that remain after the oocyte demise. 相似文献
976.
977.
Nadia Melo Matthew Capek Oscar M. Arenas Ali Afify Ayse Yilmaz Christopher J. Potter Peter J. Laminette Alessia Para Marco Gallio Marcus C. Stensmyr 《Current biology : CB》2021,31(9):1988-1994.e5
- Download : Download high-res image (157KB)
- Download : Download full-size image
978.
Carla S. Alves Manuel N. Melo Henri G. Franquelim Rafael Ferre Marta Planas Lidia Feliu Eduard Bardají Wioleta Kowalczyk David Andreu Nuno C. Santos Miguel X. Fernandes Miguel A. R. B. Castanho 《The Journal of biological chemistry》2010,285(36):27536-27544
The potential of antimicrobial peptides (AMPs) as an alternative to conventional therapies is well recognized. Insights into the biological and biophysical properties of AMPs are thus key to understanding their mode of action. In this study, the mechanisms adopted by two AMPs in disrupting the Gram-negative Escherichia coli bacterial envelope were explored. BP100 is a short cecropin A-melittin hybrid peptide known to inhibit the growth of phytopathogenic Gram-negative bacteria. pepR, on the other hand, is a novel AMP derived from the dengue virus capsid protein. Both BP100 and pepR were found to inhibit the growth of E. coli at micromolar concentrations. Zeta potential measurements of E. coli incubated with increasing peptide concentrations allowed for the establishment of a correlation between the minimal inhibitory concentration (MIC) of each AMP and membrane surface charge neutralization. While a neutralization-mediated killing mechanism adopted by either AMP is not necessarily implied, the hypothesis that surface neutralization occurs close to MIC values was confirmed. Atomic force microscopy (AFM) was then employed to visualize the structural effect of the interaction of each AMP with the E. coli cell envelope. At their MICs, BP100 and pepR progressively destroyed the bacterial envelope, with extensive damage already occurring 2 h after peptide addition to the bacteria. A similar effect was observed for each AMP in the concentration-dependent studies. At peptide concentrations below MIC values, only minor disruptions of the bacterial surface occurred. 相似文献
979.
980.
Cleiton A. Domingos José W. Da S. Melo Manoel G. C. GondimJr. Gilberto J. De Moraes Rachid Hanna Late M. Lawson-Balagbo Peter Schausberger 《Experimental & applied acarology》2010,50(3):201-215
Neoseiulus baraki Athias-Henriot (Acari: Phytoseiidae) has been reported from the Americas, Africa and Asia, often in association with Aceria guerreronis Keifer (Acari: Eriophyidae), one of the most important pests of coconut (Cocos nucifera L.) in different parts of the world. That phytoseiid has been considered one of the most common predators associated with
A. guerreronis in Brazil. The objective of this study was to evaluate the feeding preference and the effect of food items commonly present
on coconut fruits and several temperature regimes on the life history of a Brazilian population of N. baraki. Completion of immature development was possible when N. baraki was fed A. guerreronis, Steneotarsonemus concavuscutum Lofego and Gondim Jr., and Tyrophagus putrescentiae (Schrank). Fecundity was highest on T. putrescentiae (39.4 eggs), followed by A. guerreronis (24.8 eggs). In choice tests, irrespective of the food on which N. baraki was reared, a larger number of adults of this predator chose leaf discs containing A. guerreronis than discs containing other food items, demonstrating a preference of the former for the latter as food. Egg to adult thermal
developmental time was calculated as 84.2 degree-days, above a threshold of 15.8°C. This lower developmental threshold is
higher than previously published for phytoseiid species from higher latitudes. Neoseiulus
baraki was shown to have higher biotic potential at 30°C (r
m 0.29). The results suggest N. baraki to be a promising biological control agent of A. guerreronis, well adapted to survive and develop in areas with relatively high temperatures, where that pest prevails. 相似文献