全文获取类型
收费全文 | 4793篇 |
免费 | 282篇 |
出版年
2023年 | 52篇 |
2022年 | 62篇 |
2021年 | 151篇 |
2020年 | 107篇 |
2019年 | 146篇 |
2018年 | 178篇 |
2017年 | 135篇 |
2016年 | 187篇 |
2015年 | 299篇 |
2014年 | 298篇 |
2013年 | 363篇 |
2012年 | 389篇 |
2011年 | 371篇 |
2010年 | 210篇 |
2009年 | 209篇 |
2008年 | 238篇 |
2007年 | 227篇 |
2006年 | 235篇 |
2005年 | 167篇 |
2004年 | 139篇 |
2003年 | 136篇 |
2002年 | 114篇 |
2001年 | 89篇 |
2000年 | 85篇 |
1999年 | 60篇 |
1998年 | 40篇 |
1997年 | 24篇 |
1996年 | 21篇 |
1995年 | 19篇 |
1994年 | 17篇 |
1993年 | 13篇 |
1992年 | 27篇 |
1991年 | 24篇 |
1990年 | 15篇 |
1989年 | 22篇 |
1988年 | 12篇 |
1987年 | 15篇 |
1986年 | 20篇 |
1985年 | 15篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 14篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1976年 | 6篇 |
1975年 | 8篇 |
1974年 | 10篇 |
1973年 | 7篇 |
1968年 | 5篇 |
排序方式: 共有5075条查询结果,搜索用时 234 毫秒
941.
Duílio Mazzoni Zerbinato de Andrade Silva Cristian Araya-Jaime Masakane Yamashita Mateus Rossetto Vidal Claudio Oliveira Fbio Porto-Foresti Roberto Ferreira Artoni Fausto Foresti 《Genetics and molecular biology》2021,44(3)
B chromosomes are non-essential additional genomic elements present in several animal and plant species. In fishes, species of the genus Psalidodon (Characiformes, Characidae) harbor great karyotype diversity, and multiple populations carry different types of non-essential B chromosomes. This study analyzed how the dispensable supernumerary B chromosome of Psalidodon paranae behaves during meiosis to overcome checkpoints and express its own meiosis-specific genes. We visualized the synaptonemal complexes of P. paranae individuals with zero, one, or two B chromosomes using immunodetection with anti-medaka SYCP3 antibody and fluorescence in situ hybridization with a (CA)15 microsatellite probe. Our results showed that B chromosomes self-pair in cells containing only one B chromosome. In cells with two identical B chromosomes, these elements remain as separate synaptonemal complexes or close self-paired elements in the nucleus territory. Overall, we reveal that B chromosomes can escape meiotic silencing of unsynapsed chromatin through a self-pairing process, allowing expression of their own genes to facilitate regular meiosis resulting in fertile individuals. This behavior, also seen in other congeneric species, might be related to their maintenance throughout the evolutionary history of Psalidodon. 相似文献
942.
Schroth Götz Teixeira Wenceslau Geraldes Seixas Rosangela Ferreira da Silva Luciana Schaller Michaela Macêdo Jeferson L.V. Zech Wolfgang 《Plant and Soil》2000,221(2):143-156
The spatio-temporal patterns of soil fertility and soil solution chemistry in a multi-strata agroforestry system with perennial crops were analysed as indicators for the effects of crop species and management measures on soil conditions under permanent agriculture in central Amazonia. The study was carried out in a plantation with locally important tree crop species and a leguminous cover crop at two fertilization levels on a xanthic Ferralsol. Soil fertility to 2 m soil depth was evaluated 3.5 years after the establishment of the plantation, and soil solution chemistry at 10, 60 and 200 cm soil depth was monitored over 2 years. Several soil fertility characteristics exhibited spatial patterns within the multi-strata plots which reflected the differing properties of the plant species and their management, including the fertilizer input. Significant differences between species could be detected to 150 cm depth, and between fertilization treatments to 200 cm depth. Favourable effects on nutrient availability in the soil were found for annatto (Bixa orellana) (P, K) and cupuaçu (Theobroma grandiflorum) (Ca, Mg) in comparison with peach palm (Bactris gasipaes) and Brazil nut (Bertholletia excelsa). Nutrient concentrations of the soil solution showed pronounced fluctuations in the topsoil, corresponding to fertilizer applications. Large nutrient concentrations in the soil solution were accompanied by increased concentrations of aluminium and low pH values, caused by exchange reactions between fertilizer and sorbed acidity and reinforced by the acidifying effect of nitrification. The soil solution under the leguminous cover crop Pueraria phaseoloides had relatively large N concentrations during periods when those under the tree crops were small, and this could partly explain why no yield responses to N fertilization were observed at this site. 相似文献
943.
Ana Luiza de Brito Portela-Castro Horácio Ferreira Júlio Júnior Patrícia Belini Nishiyama 《Genetica》2000,110(3):277-283
The Moenkhausia sanctaefilomenae specimens showed a karyotype consisting of 2n = 50 chromosomes with 12 metacentrics, 36 submetacentrics and two subtelocentrics. In addition to the basic karyotype, all
the males specimens have cells ranging from zero to two B microchromosomes in mitotic metaphases. These chromosomes were not
observed in the female specimens. C-band analysis showed a distribution pattern of characteristic heterochromatin with interstitial
and centromeric blocks. However, the B chromosomes were faintly stained with C-banding and were not fluorescent with CMA3 staining. The meiotic studies showed the formation of bivalents in metaphase I and in pachytene under an optical microscope.
Through synaptonemal complex analysis with an electron microscope, the pachytene showed 25 bivalents completely paired and
a small bivalent corresponding to the B chromosomes. In the same preparation, one of the B chromosomes was observed in a univalent
form. On the basis of pairing behavior and morphology it is assumed that B chromosomes of M. sanctaefilomenae show homology between them and their evolutionary aspects are discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
944.
Carla Oliveira-Ribeiro Maria Inês Fernandes Pimentel Liliane de Ftima Antonio Oliveira rica de Camargo Ferreira e Vasconcellos Fatima Conceio-Silva Armando de Oliveira Schubach Aline Fagundes Cintia Xavier de Mello Eliame Mouta-Confort Luciana de Freitas Campos Miranda Claudia Maria Valete-Rosalino Ana Cristina da Costa Martins Raquel de Vasconcellos Carvalhaes de Oliveira Leonardo Pereira Quintella Marcelo Rosandiski Lyra 《PLoS neglected tropical diseases》2021,15(9)
BackgroundTreatment of cutaneous leishmaniasis (CL) remains challenging since the drugs currently used are quite toxic, thus contributing to lethality unrelated to the disease itself but to adverse events (AE). The main objective was to evaluate different treatment regimens with meglumine antimoniate (MA), in a reference center in Rio de Janeiro, Brazil.MethodologyA historical cohort of 592 patients that underwent physical and laboratory examination were enrolled between 2000 and 2017. The outcome measures of effectiveness were epithelialization and complete healing of cutaneous lesions. AE were graded using a standardized scale. Three groups were evaluated: Standard regimen (SR): intramuscular (IM) MA 10–20 mg Sb5+/kg/day during 20 days (n = 46); Alternative regimen (AR): IM MA 5 mg Sb5+/kg/day during 30 days (n = 456); Intralesional route (IL): MA infiltration in the lesion(s) through subcutaneous injections (n = 90). Statistical analysis was performed through Fisher exact and Pearson Chi-square tests, Kruskal-Wallis, Kaplan-Meier and log-rank tests.ResultsSR, AR and IL showed efficacy of 95.3%, 84.3% and 75.9%, with abandonment rate of 6.5%, 2.4% and 3.4%, respectively. IL patients had more comorbidities (58.9%; p = 0.001), were mostly over 50 years of age (55.6%), and had an evolution time longer than 2 months (65.6%; p = 0.02). Time for epithelialization and complete healing were similar in IL and IM MA groups (p = 0.9 and p = 0.5; respectively). Total AE and moderate to severe AE that frequently led to treatment interruption were more common in SR group, while AR and IL showed less toxicity.Conclusions/SignificanceAR and IL showed less toxicity and may be good options especially in CL cases with comorbidities, although SR treatment was more effective. IL treatment was an effective and safe strategy, and it may be used as first therapy option as well as a rescue scheme in patients initially treated with other drugs. 相似文献
945.
Shyam Visweswaran Antonio Ferreira Guilherme A. Ribeiro Alexandre C. Oliveira Gregory F. Cooper 《PloS one》2015,10(6)
Deriving predictive models in medicine typically relies on a population approach where a single model is developed from a dataset of individuals. In this paper we describe and evaluate a personalized approach in which we construct a new type of decision tree model called decision-path model that takes advantage of the particular features of a given person of interest. We introduce three personalized methods that derive personalized decision-path models. We compared the performance of these methods to that of Classification And Regression Tree (CART) that is a population decision tree to predict seven different outcomes in five medical datasets. Two of the three personalized methods performed statistically significantly better on area under the ROC curve (AUC) and Brier skill score compared to CART. The personalized approach of learning decision path models is a new approach for predictive modeling that can perform better than a population approach. 相似文献
946.
Geferson Fischer Fabricio R. Conceição Fábio P. L. Leite Carina M. Moraes Lílian N. Ferreira Camila O. Vilela Clarissa F. Caetano Gilberto D. Vargas Sílvia O. Hübner Telmo Vidor Paulo M. Roehe 《World journal of microbiology & biotechnology》2010,26(3):489-495
Information on the use of Escherichia coli heat-labile enterotoxin B subunit (LTB) as a parenteral adjuvant is scarce. We evaluate the adjuvant effect of different concentrations of recombinant LTB (rLTB), as well as the influence of administration route (intramuscular and subcutaneous) on mice immune response. The use of 10 μg/dose of rLTB as adjuvant of an inactivated vaccine composed by Suid herpesvirus type 1 (SuHV-1), used to immunize mice intramuscularly, induced the highest average titers of anti-SuHV-1 antibodies (P < 0.05). The same vaccines used subcutaneously induced lower titers of antibodies. The lower the anti-rLTB humoral response determined by ELISA, the higher was its adjuvant activity. In the challenge experiment with SuHV-1, 56% (14/25) (P < 0.05) of the animals inoculated intramuscularly and 32% (8/25) inoculated subcutaneously survived, highlighting the influence of the concentration and the route of administration of rLTB on its performance as an adjuvant. Therefore, rLTB can significantly help in the induction of immunity against SuHV-1 in mice, especially if used intramuscularly in the concentration of 10 μg/dose, representing the best cost-benefit ratio. 相似文献
947.
Valeria Silva-álvarez Gisela R. Franchini Jorge L. Pórfido Malcolm W. Kennedy Ana M. Ferreira Betina Córsico 《PLoS neglected tropical diseases》2015,9(3)
BackgroundThe hydatid disease parasite Echinococcus granulosus has a restricted lipid metabolism, and needs to harvest essential lipids from the host. Antigen B (EgAgB), an abundant lipoprotein of the larval stage (hydatid cyst), is thought to be important in lipid storage and transport. It contains a wide variety of lipid classes, from highly hydrophobic compounds to phospholipids. Its protein component belongs to the cestode-specific Hydrophobic Ligand Binding Protein family, which includes five 8-kDa isoforms encoded by a multigene family (EgAgB1-EgAgB5). How lipid and protein components are assembled into EgAgB particles remains unknown. EgAgB apolipoproteins self-associate into large oligomers, but the functional contribution of lipids to oligomerization is uncertain. Furthermore, binding of fatty acids to some EgAgB subunits has been reported, but their ability to bind other lipids and transfer them to acceptor membranes has not been studied.Conclusions/SignificanceWe show that EgAgB apolipoproteins can oligomerize in the absence of lipids, and can bind and transfer fatty acids to phospholipid membranes. Since imported fatty acids are essential for Echinococcus granulosus, these findings provide a mechanism whereby EgAgB could engage in lipid acquisition and/or transport between parasite tissues. These results may therefore indicate vulnerabilities open to targeting by new types of drugs for hydatidosis therapy. 相似文献
948.
949.
The identification of macrophyte reference communities represents a significant challenge in Mediterranean zones, where few aquatic taxa exist compared to other regions of the world. In the highly seasonal rivers of Portugal, we explored the contribution of bryophytes to enhance the compositional and ecological characterization of reference conditions. We performed partitioning, classification, and ordination analyses and obtained eight groups of bryophytic assemblages explained by water availability and quality. Groups A, B, and H assemblages are type-specific of the inland areas of the northern eco-region, reflecting the neutral minerotrophic currents with summer low currents. Groups C and D are type-specific of acidic oligotrophic shifting currents dependent of precipitation events in the mountainous streams of the North Atlantic eco-region. Groups E, F, and G are widespread in continental northern, central, and southern zones in neutral and highly mineralized watercourses with seasonal dryness. We propose bryophytes as a tool in the characterization of the reference conditions for two main reasons: (i) many of the recorded taxa are capable of withstanding the natural seasonal desiccation, and (ii) the type-specific bryophytes have perennial life-strategies and can be assessed at any time of year as a support for other type-specific macrophytes in compositional assessments of reference conditions. 相似文献
950.