全文获取类型
收费全文 | 5213篇 |
免费 | 295篇 |
国内免费 | 1篇 |
出版年
2023年 | 48篇 |
2022年 | 90篇 |
2021年 | 167篇 |
2020年 | 149篇 |
2019年 | 172篇 |
2018年 | 197篇 |
2017年 | 173篇 |
2016年 | 230篇 |
2015年 | 306篇 |
2014年 | 359篇 |
2013年 | 394篇 |
2012年 | 472篇 |
2011年 | 402篇 |
2010年 | 233篇 |
2009年 | 210篇 |
2008年 | 252篇 |
2007年 | 228篇 |
2006年 | 214篇 |
2005年 | 162篇 |
2004年 | 158篇 |
2003年 | 139篇 |
2002年 | 121篇 |
2001年 | 89篇 |
2000年 | 70篇 |
1999年 | 44篇 |
1998年 | 26篇 |
1997年 | 17篇 |
1996年 | 20篇 |
1995年 | 16篇 |
1994年 | 8篇 |
1993年 | 14篇 |
1992年 | 27篇 |
1991年 | 26篇 |
1990年 | 14篇 |
1989年 | 22篇 |
1988年 | 15篇 |
1987年 | 10篇 |
1986年 | 14篇 |
1985年 | 20篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 18篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1975年 | 7篇 |
1974年 | 8篇 |
1973年 | 7篇 |
排序方式: 共有5509条查询结果,搜索用时 15 毫秒
1.
Sacramento Doralice Rodrigues Coelho Rosalie Reed Rodrigues Wigg Márcia Dutra Toledo Luna Linhares Luiz Fernando de Matos dos Santos Marta Gonçalves Azevedo Soares Semêdo Luzia Teixeira de Ribeiro da Silva Antonio Jorge 《World journal of microbiology & biotechnology》2004,20(3):225-229
A promising producer of bioactive compounds isolated from a Brazilian tropical soil was tested for its range of antimicrobial
activities. Strain 606, classified as Streptomyces sp., could not be identified up to species level, suggesting a possible new taxon. The supernatant and 10 extracts and fractions,
obtained by extraction and chromatographic techniques, presented antimicrobial activity using antibiograms. The methanolic
fraction was highly active against pathogenic bacteria, phytopathogenic fungi and the human pathogenic yeast Candida albicans. It also possessed high antiviral activity inhibiting the propagation of an acyclovir-resistant herpes simplex virus type
1 strain on HEp-2 cells at non-cytotoxic concentration. The strong cytotoxic effect suggests an antitumour action.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
2.
Transthyretin (TTR) protects against A-Beta toxicity by binding the peptide thus inhibiting its aggregation. Previous work showed different TTR mutations interact differently with A-Beta, with increasing affinities correlating with decreasing amyloidogenecity of the TTR mutant; this did not impact on the levels of inhibition of A-Beta aggregation, as assessed by transmission electron microscopy. Our work aimed at probing differences in binding to A-Beta by WT, T119M and L55P TTR using quantitative assays, and at identifying factors affecting this interaction. We addressed the impact of such factors in TTR ability to degrade A-Beta. Using a dot blot approach with the anti-oligomeric antibody A11, we showed that A-Beta formed oligomers transiently, indicating aggregation and fibril formation, whereas in the presence of WT and T119M TTR the oligomers persisted longer, indicative that these variants avoided further aggregation into fibrils. In contrast, L55PTTR was not able to inhibit oligomerization or to prevent evolution to aggregates and fibrils. Furthermore, apoptosis assessment showed WT and T119M TTR were able to protect against A-Beta toxicity. Because the amyloidogenic potential of TTR is inversely correlated with its stability, the use of drugs able to stabilize TTR tetrameric fold could result in increased TTR/A-Beta binding. Here we showed that iododiflunisal, 3-dinitrophenol, resveratrol, [2-(3,5-dichlorophenyl)amino] (DCPA) and [4-(3,5-difluorophenyl)] (DFPB) were able to increase TTR binding to A-Beta; however only DCPA and DFPB improved TTR proteolytic activity. Thyroxine, a TTR ligand, did not influence TTR/A-Beta interaction and A-Beta degradation by TTR, whereas RBP, another TTR ligand, not only obstructed the interaction but also inhibited TTR proteolytic activity. Our results showed differences between WT and T119M TTR, and L55PTTR mutant regarding their interaction with A-Beta and prompt the stability of TTR as a key factor in this interaction, which may be relevant in AD pathogenesis and for the design of therapeutic TTR-based therapies. 相似文献
3.
Emmanuelle Fontoura José Darival Ferreira Jamile Bubadué Ana Maria Ribeiro Leonardo Kerber 《Journal of morphology》2020,281(10):1223-1240
A diverse fossil record of Cervidae (Mammalia) has been documented in the South American Pleistocene, when these animals arrived during the Great American Biotic Interchange. Using computed tomography-scanning techniques, it is possible to access the endocranial morphology of extinct species. Here, we studied the brain endocast of the extinct late Pleistocene cervid Antifer ensenadensis from southern Brazil, one of the largest forms that lived on this continent, using comparative morphology, geometric morphometrics, and encephalization quotients. The analyzed endocasts demonstrate that A. ensenadensis had a gyrencephalic brain, showing a prominent longitudinal sinus (=sagittal superior sinus), which is also observed in the large South American cervid Blastocerus dichotomus. The encephalization quotient is within the variation of extant cervids, suggesting maintenance of the pattern of encephalization from at least the late Pleistocene. Geometric morphometric analysis suggested a clear and linear allometric trend between brain endocast size and shape, and highlights A. ensenadensis as an extreme form within the analyzed cervids regarding brain morphology. 相似文献
4.
5.
Felipe Silva de Andrade Thiago Ribeiro de Carvalho Lucas Borges Martins Ariovaldo Antonio Giaretta 《Studies on Neotropical Fauna and Environment》2017,52(2):157-167
In this study, we re-describe the advertisement and territorial calls of Boana pardalis, carry out an acoustic comparison between the studied species and the other congeners of the B. faber group, and report for the first time the tympanic amplexus for the studied species. The advertisement call of B. pardalis can be used to supplement its diagnosis in the B. faber group based on temporal call traits, e.g. emission rate and emission pattern, as well as the call envelope. 相似文献
6.
Morphological and histological study of castration-induced degeneration and androgen-induced regeneration in the mouse prostate 总被引:3,自引:0,他引:3
Degenerative and regenerative changes in the ductal architecture of the ventral and dorsolateral prostates (VP and DLP) of the adult mouse were investigated in microdissected specimens over a time-course of 14 days following castration and subsequently during 14 days of administration of testosterone propionate. After castration, about 35% of the ductal tips and branch-points were lost in distal regions (usually near the capsule) in both prostatic lobes. By contrast, in more proximal regions of the prostate (closer to the urethra), the ducts survived in an atrophic condition. The ductal morphology that had been lost in the distal regions completely regenerated after testosterone propionate was administered to the castrated males. In the VP, androgen replacement simply returned the gland to its former size with moderate ductal distension; in the DLP, excessive epithelial infoldings and ductal distension were elicited in the distal regions of the ducts after 14 days of treatment with testosterone propionate. These results suggest that androgenic responsiveness and dependency are different in distal versus proximal ducts. Distal ducts are exquisitely androgen-dependent and androgen-sensitive; in proximal regions, androgen-dependency is not as strict. 相似文献
7.
S Ribeiro C S Alviano F C Silva-Filho E F da Silva J Angluster W de Souza 《Microbios》1989,57(231):121-129
The surface anionic groups of Entamoeba invadens were analysed by cell electrophoresis, by ultrastructural cytochemistry, and by identification of sialic acids using paper and gas-liquid chromatography. Binding of colloidal iron hydroxide (CIH) and of cationized ferritin (CF) particles at pH 1.8 and 7.2, respectively, was observed on the cell surface. E. invadens has a highly negative surface charge (-0.96 microns s-1 V-1 cm). Treatment of the cells with trypsin and neuraminidase significantly reduced the electrophoretic mobility by 24% and 40%, respectively. Treatment of the amoebae with neuraminidase also markedly decreased the binding of CIH to the cell surface. This finding suggests that sialic acid residues are the major anionogenic groups exposed on the surface of E. invadens. Paper and gas-liquid chromatography showed that N-acetylneuraminic acid was the only derivative characterized in E. invadens. 相似文献
8.
E Mansini E G Oestreicher L P Ribeiro 《Archives internationales de physiologie et de biochimie》1989,97(6):447-453
Purified mitochondrial malate dehydrogenase isoenzyme (m-MDH) of Toxocara canis muscle presented maximum activity at 48 degrees C. A clear change in slope of the Arrhenius plot was observed. The energy of activation calculated for the catalytic process showed values of 3.2 kcal/mol and 10.5 kcal/mol. Thermal inactivation of m-MDH showed that it is more thermolabile than the s-isoenzyme. The inactivation of the enzyme by heat could be reduced at least in part by the addition of 0.1 mM NADH. The heat denaturation showed to be a first-order process. The rate constant (k) was calculated as being of the order of 5.28 X 10(-4) s-1 at 40 degrees C. The activation energy for the heat inactivation process was 16.45 kcal/mol between 30 degrees C and 40 degrees C and 13.79 kcal/mol between 40 degrees C and 48 degrees C. 相似文献
9.
Observations were made on the evolutive cycle of Triatoma vitticeps, held under laboratory conditions and fed weekly in mice. Of the 435 eggs obtained, from 4 virgin couples, 149 were purposed for the biological cycle study and 286 to evaluate their resistance to starvation, which shall be a second part of this work. Only 50 specimens reached the adult stage in a period of means (S) = 270 +/- 45 days. At the incubation time, the first and second instars were of less than a month for each, while the third, fourth and fifth instars requires approximately one, two and three months, respectively. The search for the first meal occurred clearly on the 3rd, 6th and 10th day. During all the stages, more than 50% of the specimens had only one blood-meal, except the fifth one, when two blood-meals were required. In relation to the time-lapse between the presenting of the blood-meal and the beginning of feeding, as well as the length of the blood-meal, it was observed that these increased gradually according to the stage. From the 423 blood-meals performed, 390 were not followed by defecation in the settled period of 10 min. Under this point of view, T. vitticeps seems to be a poor transmissor of T. cruzi. The experiment was carried out for 13 months and by this time the averages of minimum and maximum temperatures and the humidity were 25 +/- 2 degrees C - 28 +/- 2 degrees C and 80 +/- 2%, respectively. The material belongs to the triatomine colony held at the Oswaldo Cruz Institute, Department of Entomology. 相似文献
10.
R C de Oliveira D T Ribeiro R G Nigro P Di Mascio C F Menck 《Nucleic acids research》1992,20(16):4319-4323
In order to characterize the molecular nature of singlet oxygen (1O2) induced mutations in mammalian cells, a SV40-based shuttle vector (pi SVPC13) was treated with singlet oxygen arising from the thermal decomposition of the water-soluble endoperoxide of 3,3'-(1,4-naphthylidene) dipropionate (NDPO2). After the passage of damaged plasmid through monkey COS7 cells, the vector was shuffled into E. coli cells, allowing the screening of supF mutants. The mutation spectrum analysis shows that single and multiple base substitutions arose in 82.5% of the mutants, the others being rearrangements. The distribution of mutations within the supF gene is not random and some hotspots are evident. Most of the point mutations (98.4%) involve G:C base pairs and G:C to T:A transversion was the most frequent mutation (50.8%), followed by G:C to C:G transversion (32.8%). These results indicate that mutagenesis in mammalian cells, mediated by 1O2-induced DNA damage, is targeted selectively at guanine residues. 相似文献