全文获取类型
收费全文 | 39010篇 |
免费 | 2490篇 |
国内免费 | 15篇 |
专业分类
41515篇 |
出版年
2023年 | 225篇 |
2022年 | 524篇 |
2021年 | 912篇 |
2020年 | 523篇 |
2019年 | 676篇 |
2018年 | 949篇 |
2017年 | 788篇 |
2016年 | 1335篇 |
2015年 | 2008篇 |
2014年 | 2165篇 |
2013年 | 2969篇 |
2012年 | 3387篇 |
2011年 | 3246篇 |
2010年 | 1986篇 |
2009年 | 1701篇 |
2008年 | 2410篇 |
2007年 | 2365篇 |
2006年 | 2093篇 |
2005年 | 1885篇 |
2004年 | 1770篇 |
2003年 | 1703篇 |
2002年 | 1545篇 |
2001年 | 311篇 |
2000年 | 211篇 |
1999年 | 299篇 |
1998年 | 390篇 |
1997年 | 262篇 |
1996年 | 253篇 |
1995年 | 236篇 |
1994年 | 229篇 |
1993年 | 220篇 |
1992年 | 136篇 |
1991年 | 150篇 |
1990年 | 148篇 |
1989年 | 117篇 |
1988年 | 102篇 |
1987年 | 91篇 |
1986年 | 71篇 |
1985年 | 96篇 |
1984年 | 98篇 |
1983年 | 73篇 |
1982年 | 86篇 |
1981年 | 84篇 |
1980年 | 83篇 |
1979年 | 75篇 |
1978年 | 41篇 |
1977年 | 53篇 |
1976年 | 39篇 |
1975年 | 40篇 |
1973年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Thomas C. Darton Claire Jones Christoph J. Blohmke Claire S. Waddington Liqing Zhou Anna Peters Kathryn Haworth Rebecca Sie Christopher A. Green Catherine A. Jeppesen Maria Moore Ben A. V. Thompson Tessa John Robert A. Kingsley Ly-Mee Yu Merryn Voysey Zoe Hindle Stephen Lockhart Marcelo B. Sztein Gordon Dougan Brian Angus Myron M. Levine Andrew J. Pollard 《PLoS neglected tropical diseases》2016,10(8)
BackgroundTyphoid persists as a major cause of global morbidity. While several licensed vaccines to prevent typhoid are available, they are of only moderate efficacy and unsuitable for use in children less than two years of age. Development of new efficacious vaccines is complicated by the human host-restriction of Salmonella enterica serovar Typhi (S. Typhi) and lack of clear correlates of protection. In this study, we aimed to evaluate the protective efficacy of a single dose of the oral vaccine candidate, M01ZH09, in susceptible volunteers by direct typhoid challenge.ConclusionsDespite successfully demonstrating the use of a human challenge study to directly evaluate vaccine efficacy, a single-dose M01ZH09 failed to demonstrate significant protection after challenge with virulent Salmonella Typhi in this model. Anti-Vi antibody detected prior to vaccination played a major role in outcome after challenge.
Trial registration
ClinicalTrials.gov () and EudraCT (number 2011-000381-35). NCT01405521相似文献962.
Ricardo Andrade Zampieri Maria Fernanda Laranjeira-Silva Sandra Marcia Muxel Ana Carolina Stocco de Lima Jeffrey Jon Shaw Lucile Maria Floeter-Winter 《PLoS neglected tropical diseases》2016,10(2)
Background
Protozoan parasites of the genus Leishmania cause a large spectrum of clinical manifestations known as Leishmaniases. These diseases are increasingly important public health problems in many countries both within and outside endemic regions. Thus, an accurate differential diagnosis is extremely relevant for understanding epidemiological profiles and for the administration of the best therapeutic protocol.Methods/Principal Findings
Exploring the High Resolution Melting (HRM) dissociation profiles of two amplicons using real time polymerase chain reaction (real-time PCR) targeting heat-shock protein 70 coding gene (hsp70) revealed differences that allowed the discrimination of genomic DNA samples of eight Leishmania species found in the Americas, including Leishmania (Leishmania) infantum chagasi, L. (L.) amazonensis, L. (L.) mexicana, L. (Viannia) lainsoni, L. (V.) braziliensis, L. (V.) guyanensis, L. (V.) naiffi and L. (V.) shawi, and three species found in Eurasia and Africa, including L. (L.) tropica, L. (L.) donovani and L. (L.) major. In addition, we tested DNA samples obtained from standard promastigote culture, naturally infected phlebotomines, experimentally infected mice and clinical human samples to validate the proposed protocol.Conclusions/Significance
HRM analysis of hsp70 amplicons is a fast and robust strategy that allowed for the detection and discrimination of all Leishmania species responsible for the Leishmaniases in Brazil and Eurasia/Africa with high sensitivity and accuracy. This method could detect less than one parasite per reaction, even in the presence of host DNA. 相似文献963.
964.
Payam Vahmani William J. Meadus Maria L.P. da Silva Alec D. Mitchell Cletos Mapiye Pascale Duff David C. Rolland Michael E.R. Dugan 《Biochemistry and Biophysics Reports》2016
Beef fat is a natural source of trans (t) fatty acids, and is typically enriched with either t10-18:1 or t11-18:1. Little is known about the bioactivity of individual t-18:1 isomers, and the present study compared the effects of t9-18:1, cis (c)9-18:1 and trans (t)-18:1 fractions isolated from beef fat enriched with either t10-18:1 (HT10) or t11-18:1 (HT11). All 18:1 isomers resulted in reduced human liver (HepG2) cell viability relative to control. Both c9-18:1 and HT11were the least toxic, t9-18:1had dose response increased toxicity, and HT10 had the greatest toxicity (P<0.05). Incorporation of t18:1 isomers was 1.8–2.5 fold greater in triacylglycerol (TG) than phospholipids (PL), whereas Δ9 desaturation products were selectively incorporated into PL. Culturing HepG2 cells with t9-18:1 and HT10 increased (P<0.05) the Δ9 desaturation index (c9–16:1/16:0) compared to other fatty acid treatments. HT10 and t9-18:1 also increased expression of lipogenic genes (FAS, SCD1, HMGCR and SREBP2) compared to control (P<0.05), whereas c9-18:1 and HT11 did not affect the expression of these genes. Our results suggest effects of HT11 and c9-18:1 were similar to BSA control, whereas HT10 and t-9 18:1 (i.e. the predominant trans fatty acid isomer found in partially hydrogenated vegetable oils) were more cytotoxic and led to greater expression of lipogenic genes. 相似文献
965.
966.
Description of a new epibiotic relationship (Suctorian–Copepoda) in NE Atlantic waters: from morphological to phylogenetic analyses 下载免费PDF全文
Maria Gregori Gregorio Fernández‐Leborans Álvaro Roura Ángel F. González Santiago Pascual 《Acta zoologica》2016,97(2):165-176
Paraeuchaeta hebes is one of the most important carnivorous copepods in the coastal upwelling system off Galician waters (Ría de Vigo, NE Atlantic). A suctorian epibiont of the genus Pelagacineta was found attached to the surface of these copepods. The abundance and distribution on the copepod surface were analysed, taking into account the sex of the crustacean, revealing some preference for females and also a different attachment point in both sexes. The morphological study allowed us to identify a new species of this Suctoria epibiont as Pelagacineta hebensis. Moreover, the 18S rRNA gene was partially sequenced to inspect the phylogenetic position of Pelagacineta hebensis within the subclass Phyllopharyngea. The maximum‐likelihood (ML) tree obtained was consistent with the morphological and with previous molecular studies and showed that P. hebensis belongs to the order Endogenina, as a sister clade of the few taxa sequenced within this order. Including new genetic data to the Endogenina will allow building new hypothesis about the evolution of the most derived clade of suctorians. 相似文献
967.
Contemporary patterns of genetic diversity of cedrela fissilis offer insight into the shaping of seasonal forests in eastern South America 下载免费PDF全文
968.
969.
Lívia Tavares Colombo Marcelo Nagem Valério de Oliveira Deisy Guimarães Carneiro Robson Assis de Souza Mariana Caroline Tocantins Alvim Josenilda Carlos dos Santos Cynthia Canêdo da Silva Pedro Marcus Pereira Vidigal Wendel Batista da Silveira Flávia Maria Lopes Passos 《Antonie van Leeuwenhoek》2016,109(9):1217-1233
970.
Functional connectivity and genetic diversity of Eulaema atleticana (Apidae,Euglossina) in the Brazilian Atlantic Forest Corridor: assessment of gene flow 下载免费PDF全文
The mobility and dispersal of organisms affect population genetics and dynamics, and consequently affect persistence and the risk of extinction. Thus, it is important to understand how organisms move in the fragmented landscapes in order to manage populations and predict the effects of habitat changes on species persistence. This study evaluated the functional connectivity of an orchid bee (Eulaema atleticana Nemésio, 2009) with a high fidelity to forest habitats in the Brazilian Atlantic Forest Corridor by analyzing genetic diversity, spatial genetic structure, and gene flow estimated from microsatellite and mitochondrial markers. Genetic diversity was not correlated with area of the forest fragments, or with forest isolation. At the mosaic scale, Eulaema atleticana showed no significant or low genetic differentiation, indicating genetic homogeneity among forest fragments. A previous field study indicated that Eulaema atleticana was one of the most sensitive Euglossina bees to forest fragmentation but the present molecular analyses demonstrates that current gene flow is sufficient to maintain genetic variability at the mosaic scale. 相似文献