全文获取类型
收费全文 | 994篇 |
免费 | 73篇 |
专业分类
1067篇 |
出版年
2023年 | 5篇 |
2022年 | 15篇 |
2021年 | 25篇 |
2020年 | 21篇 |
2019年 | 21篇 |
2018年 | 29篇 |
2017年 | 27篇 |
2016年 | 30篇 |
2015年 | 44篇 |
2014年 | 71篇 |
2013年 | 88篇 |
2012年 | 89篇 |
2011年 | 102篇 |
2010年 | 44篇 |
2009年 | 56篇 |
2008年 | 62篇 |
2007年 | 56篇 |
2006年 | 54篇 |
2005年 | 33篇 |
2004年 | 43篇 |
2003年 | 41篇 |
2002年 | 34篇 |
2001年 | 16篇 |
2000年 | 10篇 |
1999年 | 12篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有1067条查询结果,搜索用时 12 毫秒
991.
Fabio S Raposo do Amaral Matthew J Miller Luís Fábio Silveira Eldredge Bermingham Anita Wajntal 《BMC evolutionary biology》2006,6(1):10-10
Background
The family Accipitridae (hawks, eagles and Old World vultures) represents a large radiation of predatory birds with an almost global distribution, although most species of this family occur in the Neotropics. Despite great morphological and ecological diversity, the evolutionary relationships in the family have been poorly explored at all taxonomic levels. Using sequences from four mitochondrial genes (12S, ATP8, ATP6, and ND6), we reconstructed the phylogeny of the Neotropical forest hawk genus Leucopternis and most of the allied genera of Neotropical buteonines. Our goals were to infer the evolutionary relationships among species of Leucopternis, estimate their relationships to other buteonine genera, evaluate the phylogenetic significance of the white and black plumage patterns common to most Leucopternis species, and assess general patterns of diversification of the group with respect to species' affiliations with Neotropical regions and habitats. 相似文献992.
The aim of this work was to investigate the putative modulation of glucose uptake in trophoblast cells by several dietary compounds and by drugs of abuse. For this, the acute (26 min) and chronic (48 h) effect of these substances on the apical uptake of (3)H-2-deoxy-d-glucose ((3)H-DG) by a human choriocarcinoma cell line (BeWo) was determined. (3)H-DG apical uptake by BeWo cells was time dependent, displayed saturable kinetics (V(max) = 1210 +/- 29 nmol mg protein(-1) 6 min(-1) and K(m) = 13.4 +/- 0.5 mM) and was insulin-insensitive and cytochalasin B-sensitive (by up to 60%). Acutely, acetaldehyde (30-100 mM), resveratrol, xanthohumol, epigallocatechin-3-gallate (100 muM), chrysin and quercetin (10-100 muM) decreased (3)H-DG apical uptake, whereas rutin, catechin (10-100 muM), epicatechin (100 muM) and ethanol (10 mM) increased it. Quercetin and xanthohumol seem to be non-competitive inhibitors of (3)H-DG apical uptake, whereas both epigallocatechin-3-gallate and acetaldehyde decreased both the K(m) and V(max) values. Chronically, rutin and myricetin increased the apical uptake of (3)H-DG both isolated (0.1-1 muM) and in combination (both at 1 muM), whereas theophylline (0.1-1 muM) and amphetamine, 3,4-methylenedioxymethamphetamine (0.25-1 muM) and Delta(9)-tetrahydrocannabinol (1 nM) decreased it. In conclusion, (3)H-DG apical uptake by BeWo cells is differentially modulated by different compounds present in drinks and by drugs of abuse. 相似文献
993.
Gravina L Gil SM Ruiz F Zubero J Gil J Irazusta J 《Journal of strength and conditioning research / National Strength & Conditioning Association》2008,22(4):1308-1314
The aim of this article was to identify differences in the anthropometric and physiological characteristics of first team and reserve young soccer players (10-14 years old) at both the beginning and end of the soccer season. Body composition was calculated by measuring weight, height, skinfold, limb circumference, and joint diameter. Vo2max was estimated by Astrand's test. Sprint and jump tests were also performed. In general, first team players (FTPs) were taller and leaner. However, the most relevant difference that we found at the beginning of the season was that FTPs had shorter sprint times than reserves in the 30-m test (both flat and with 10 cones). Moreover, these differences in sprint time were more marked at the end of the season. In addition, jump test performance by the reserves declined from the beginning to the end of the season. These results indicate that sprint time is an important factor associated with selection as an FTP between the ages of 10 and 14 years. The progression of the FTPs during the course of the season is better than that of the reserves and is associated with a different degree of growth and maturity. These findings should be taken into account by trainers and coaches to avoid a bias against late maturing or younger soccer players. 相似文献
994.
Vale N Matos J Gut J Nogueira F do Rosário V Rosenthal PJ Moreira R Gomes P 《Bioorganic & medicinal chemistry letters》2008,18(14):4150-4153
The synthesis of imidazolidin-4-one derivatives of primaquine containing the five-membered ring at the C-terminus of a dipeptide backbone coupled to the parent drug is described. These peptidomimetic derivatives were active against a chloroquine-resistant Plasmodium falciparum strain and inhibited the development of the sporogonic cycle of Plasmodium berghei, affecting the appearance of oocysts in the midguts of the mosquitoes. The novel imidazolidin-4-ones are extremely stable, both in human plasma and in pH 7.4 buffer, as a result of N1-acylation. Thus, ‘internal’ imidazolidin-4-ones derived from dipeptidyl 8-aminoquinolines represent a new entry in antimalarial structure–activity relationships. 相似文献
995.
Gallo MB Marques AS Vieira PC da Silva MF Fernandes JB Silva M Guido RV Oliva G Thiemann OH Albuquerque S Fairlamb AH 《Zeitschrift für Naturforschung. C, Journal of biosciences》2008,63(5-6):371-382
Hexanic, methanolic, and hydroalcoholic extracts, and 34 isolated compounds from Vitex polygama Cham. (Lamiaceae, formely Verbenaceae) and Siphoneugena densiflora O. Berg (Myrtaceae) were screened for their trypanocidal effects on bloodstream forms of Trypanosoma cruzi and T brucei, as well as for their enzymatic inhibitory activities on glycosomal glyceraldehyde-3-phosphate dehydrogenase (gGAPDH) and trypanothione reductase (TR) enzymes from T cruzi and adeninephosphoribosyl transferase (APRT) enzyme from Leishmania tarentolae. In general, polar extracts displayed strong effects and some of the tested compounds have shown good results in comparison to positive controls of the bioassays. 相似文献
996.
997.
Alais S Simoes S Baas D Lehmann S Raposo G Darlix JL Leblanc P 《Biology of the cell / under the auspices of the European Cell Biology Organization》2008,100(10):603-615
Background information. TSEs (transmissible spongiform encephalopathies) are neurodegenerative disorders affecting humans and animals. PrPSc, a conformationally altered isoform of the normal prion protein (PrPC), is thought to be the pathogenic agent. However, the biochemical composition of the prion agent is still matter of debate. The potential transmission risk of the prion agent through biological fluids has been shown, but the development of competitive diagnostic tests and treatment for TSEs requires a more comprehensive knowledge of the agent and the cellular mechanisms by which it is disseminated. With this aim, we initiated characterization of the prion agent and the pathways by which it can be propagated using the cellular model system neuroblastoma (N2a). Results. The present study shows that N2a cells infected with scrapie release the prion agent into the cell culture medium in association with exosome‐like structures and viral particles of endogenous origin. We found that both prion proteins and scrapie infectivity are mainly associated with exosome‐like structures that contain viral envelope glycoprotein and nucleic acids, such as RNAs. Conclusions. The dissemination of prions in N2a cell culture is mediated through the exosomal pathway. 相似文献
998.
Regulation of retromer recruitment to endosomes by sequential action of Rab5 and Rab7 总被引:2,自引:0,他引:2
Rojas R van Vlijmen T Mardones GA Prabhu Y Rojas AL Mohammed S Heck AJ Raposo G van der Sluijs P Bonifacino JS 《The Journal of cell biology》2008,183(3):513-526
The retromer complex mediates retrograde transport of transmembrane cargo from endosomes to the trans-Golgi network (TGN). Mammalian retromer is composed of a sorting nexin (SNX) dimer that binds to phosphatidylinositol 3-phosphate–enriched endosomal membranes and a vacuolar protein sorting (Vps) 26/29/35 trimer that participates in cargo recognition. The mammalian SNX dimer is necessary but not sufficient for recruitment of the Vps26/29/35 trimer to membranes. In this study, we demonstrate that the guanosine triphosphatase Rab7 contributes to this recruitment. The Vps26/29/35 trimer specifically binds to Rab7–guanosine triphosphate (GTP) and localizes to Rab7-containing endosomal domains. Interference with Rab7 function causes dissociation of the Vps26/29/35 trimer but not the SNX dimer from membranes. This blocks retrieval of mannose 6-phosphate receptors to the TGN and impairs cathepsin D sorting. Rab5-GTP does not bind to the Vps26/29/35 trimer, but perturbation of Rab5 function causes dissociation of both the SNX and Vps26/29/35 components from membranes through inhibition of a pathway involving phosphatidylinositol 3-kinase. These findings demonstrate that Rab5 and Rab7 act in concert to regulate retromer recruitment to endosomes. 相似文献
999.
Dinora Lopes Kanchana Rungsihirunrat Fátima Nogueira Aree Seugorn José Pedro Gil Virgilio E do Rosário Pedro Cravo 《Malaria journal》2002,1(1):12-11
Background
The increasing levels of Plasmodium falciparum resistance to chloroquine (CQ) in Thailand have led to the use of alternative antimalarials, which are at present also becoming ineffective. In this context, any strategies that help improve the surveillance of drug resistance, become crucial in overcoming the problem. 相似文献1000.
Phytochemical analysis and analgesic properties of Curcuma zedoaria grown in Brazil. 总被引:7,自引:0,他引:7
D de Fátima Navarro M M de Souza R A Neto V Golin R Niero R A Yunes F Delle Monache V Cechinel Filho 《Phytomedicine》2002,9(5):427-432
The present study describes the phytochemical analysis and analgesic activity of Curcuma zedoaria rhizomes grown in Brazil. The results showed that the hydroalcoholic extract, fractions, specially dichloromethane, and a pure compound, denoted as curcumenol (1), exhibited potent and dose-related analgesic activity when evaluated in several models of pain in mice, including writhing, formalin and capsaicin. Compound (1), which seems to be the main active principle from this plant, presented promising analgesic effects, being several times more potent than different reference drugs evaluated in the same experimental models. The calculated ID50 values (micromol/kg, i.p) were 22 and 12 when evaluated in writhing and capsaicin tests, respectively, and 29 micromol/kg in relation to the second phase of the formalin model. The lack of effect in the hot plate test suggests that (1) act by a mechanism which do not involves the participation of the opioid system. The phytochemical analysis indicated that the chemical composition of the plant grown in Brazil is similar to that grown in other countries. The results confirm and justify the popular use of this plant for the treatment of dolorous processes. 相似文献