全文获取类型
收费全文 | 5764篇 |
免费 | 465篇 |
专业分类
6229篇 |
出版年
2023年 | 20篇 |
2022年 | 48篇 |
2021年 | 102篇 |
2020年 | 59篇 |
2019年 | 86篇 |
2018年 | 93篇 |
2017年 | 103篇 |
2016年 | 125篇 |
2015年 | 244篇 |
2014年 | 269篇 |
2013年 | 396篇 |
2012年 | 463篇 |
2011年 | 455篇 |
2010年 | 324篇 |
2009年 | 272篇 |
2008年 | 388篇 |
2007年 | 397篇 |
2006年 | 371篇 |
2005年 | 326篇 |
2004年 | 319篇 |
2003年 | 279篇 |
2002年 | 279篇 |
2001年 | 68篇 |
2000年 | 61篇 |
1999年 | 62篇 |
1998年 | 68篇 |
1997年 | 48篇 |
1996年 | 37篇 |
1995年 | 34篇 |
1994年 | 26篇 |
1993年 | 22篇 |
1992年 | 37篇 |
1991年 | 22篇 |
1990年 | 29篇 |
1989年 | 22篇 |
1988年 | 30篇 |
1987年 | 18篇 |
1986年 | 15篇 |
1985年 | 18篇 |
1984年 | 16篇 |
1983年 | 12篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1979年 | 10篇 |
1978年 | 13篇 |
1977年 | 11篇 |
1975年 | 10篇 |
1974年 | 10篇 |
1973年 | 12篇 |
1966年 | 8篇 |
排序方式: 共有6229条查询结果,搜索用时 15 毫秒
131.
Gauthier Dobigny Caroline Tatard Philippe Gauthier Khalilou Ba Jean-Marc Duplantier Laurent Granjon Gael J. Kergoat 《PloS one》2013,8(11)
A phylogeographic study was conducted on the Nile grass rat, Arvicanthis niloticus, a rodent species that is tightly associated with open grasslands from the Sudano-Sahelian regions. Using one mitochondrial (cytochrome b) and one nuclear (intron 7 of Beta Fibrinogen) gene, robust patterns were retrieved that clearly show that (i) the species originated in East Africa concomitantly with expanding grasslands some 2 Ma, and (ii) four parapatric and genetically well-defined lineages differentiated essentially from East to West following Pleistocene bioclimatic cycles. This strongly points towards allopatric genetic divergence within savannah refuges during humid episodes, then dispersal during arid ones; secondary contact zones would have then stabilized around geographic barriers, namely, Niger River and Lake Chad basins. Our results pertinently add to those obtained for several other African rodent as well as non-rodent species that inhabit forests, humid zones, savannahs and deserts, all studies that now allow one to depict a more comprehensive picture of the Pleistocene history of the continent south of the Sahara. In particular, although their precise location remains to be determined, at least three Pleistocene refuges are identified within the West and Central African savannah biome. 相似文献
132.
Benjamin G. Jacob Robert J. Novak Laurent D. Toe Moussa Sanfo Daniel A. Griffith Thomson L. Lakwo Peace Habomugisha Moses N. Katabarwa Thomas R. Unnasch 《PLoS neglected tropical diseases》2013,7(7)
Background
Recently, most onchocerciasis control programs have begun to focus on elimination. Developing an effective elimination strategy relies upon accurately mapping the extent of endemic foci. In areas of Africa that suffer from a lack of infrastructure and/or political instability, developing such accurate maps has been difficult. Onchocerciasis foci are localized near breeding sites for the black fly vectors of the infection. The goal of this study was to conduct ground validation studies to evaluate the sensitivity and specificity of a remote sensing model developed to predict S. damnosum s.l. breeding sites.Methodology/Principal Findings
Remote sensing images from Togo were analyzed to identify areas containing signature characteristics of S. damnosum s.l. breeding habitat. All 30 sites with the spectral signature were found to contain S. damnosum larvae, while 0/52 other sites judged as likely to contain larvae were found to contain larvae. The model was then used to predict breeding sites in Northern Uganda. This area is hyper-endemic for onchocerciasis, but political instability had precluded mass distribution of ivermectin until 2009. Ground validation revealed that 23/25 sites with the signature contained S. damnosum larvae, while 8/10 sites examined lacking the signature were larvae free. Sites predicted to have larvae contained significantly more larvae than those that lacked the signature.Conclusions/Significance
This study suggests that a signature extracted from remote sensing images may be used to predict the location of S. damnosum s.l. breeding sites with a high degree of accuracy. This method should be of assistance in predicting communities at risk for onchocerciasis in areas of Africa where ground-based epidemiological surveys are difficult to implement. 相似文献133.
134.
135.
Samy Omri Francine Behar-Cohen Pierre-Rapha?l Rothschild Emmanuelle Gélizé Laurent Jonet Jean Claude Jeanny Boubaker Omri Patricia Crisanti 《PloS one》2013,8(11)
Aims/hypothesis
Diabetic macular edema represents the main cause of visual loss in diabetic retinopathy. Besides inner blood retinal barrier breakdown, the role of the outer blood retinal barrier breakdown has been poorly analyzed. We characterized the structural and molecular alterations of the outer blood retinal barrier during the time course of diabetes, focusing on PKCζ, a critical protein for tight junction assembly, known to be overactivated by hyperglycemia.Methods
Studies were conducted on a type2 diabetes Goto-Kakizaki rat model. PKCζ level and subcellular localization were assessed by immunoblotting and immunohistochemistry. Cell death was detected by TUNEL assays. PKCζ level on specific layers was assessed by laser microdissection followed by Western blotting. The functional role of PKCζ was then evaluated in vivo, using intraocular administration of its specific inhibitor.Results
PKCζ was localized in tight junction protein complexes of the retinal pigment epithelium and in photoreceptors inner segments. Strikingly, in outer segment PKCζ staining was restricted to cone photoreceptors. Short-term hyperglycemia induced activation and delocalization of PKCζ from both retinal pigment epithelium junctions and cone outer segment. Outer blood retinal barrier disruption and photoreceptor cone degeneration characterized long-term hyperglycemia. In vivo, reduction of PKCζ overactivation using a specific inhibitor, restored its tight-junction localization and not only improved the outer blood retinal barrier, but also reduced photoreceptor cell-death.Conclusions
In the retina, hyperglycemia induced overactivation of PKCζ is associated with outer blood retinal barrier breakdown and photoreceptor degeneration. In vivo, short-term inhibition of PKCζ restores the outer barrier structure and reduces photoreceptor cell death, identifying PKCζ as a potential target for early and underestimated diabetes-induced retinal pathology. 相似文献136.
137.
Jerome Hottin Edy Wijaya Laurent Hay Sophie Maricot Mohamed Bouazaoui Jean-Pierre Vilcot 《Plasmonics (Norwell, Mass.)》2013,8(2):619-624
A large majority of surface plasmon resonance (SPR) sensors reported in the literature are designed to operate in the visible electromagnetic spectrum. However, the near-infrared, particularly at the telecommunications wavelength of 1550 nm, is also especially attractive for SPR sensing applications. In fact, SPR sensors operating in this region benefit from narrower resonance and deeper field penetration. In this paper, we report a theoretical and experimental study of an SPR sensor operating at a fixed wavelength of 1550 nm. The influence of the choice of metals and the interrogation methods on the sensitivity of the resulting SPR sensor is investigated. Two types of sensor chips (simple gold (Au) and bimetallic silver/Au structure) and three interrogation methods (monitoring of the position of the reflectivity minimum, the position of the centroid, and the intensity evolution of the reflectivity) are examined. We show that a refractive index resolution of 2.7?×?10?6 refractive index unit can be easily obtained, and with further optimization of the measurement system, the ultimate limit of detection is expected to be even lowered. Therefore, the approach discussed here already shows a promising potential for highly sensitive SPR sensors. 相似文献
138.
Paul J. Norman Jill A. Hollenbach Neda Nemat-Gorgani Lisbeth A. Guethlein Hugo G. Hilton Marcelo J. Pando Kwadwo A. Koram Eleanor M. Riley Laurent Abi-Rached Peter Parham 《PLoS genetics》2013,9(10)
Interactions between HLA class I molecules and killer-cell immunoglobulin-like receptors (KIR) control natural killer cell (NK) functions in immunity and reproduction. Encoded by genes on different chromosomes, these polymorphic ligands and receptors correlate highly with disease resistance and susceptibility. Although studied at low-resolution in many populations, high-resolution analysis of combinatorial diversity of HLA class I and KIR is limited to Asian and Amerindian populations with low genetic diversity. At the other end of the spectrum is the West African population investigated here: we studied 235 individuals, including 104 mother-child pairs, from the Ga-Adangbe of Ghana. This population has a rich diversity of 175 KIR variants forming 208 KIR haplotypes, and 81 HLA-A, -B and -C variants forming 190 HLA class I haplotypes. Each individual we studied has a unique compound genotype of HLA class I and KIR, forming 1–14 functional ligand-receptor interactions. Maintaining this exceptionally high polymorphism is balancing selection. The centromeric region of the KIR locus, encoding HLA-C receptors, is highly diverse whereas the telomeric region encoding Bw4-specific KIR3DL1, lacks diversity in Africans. Present in the Ga-Adangbe are high frequencies of Bw4-bearing HLA-B*53:01 and Bw4-lacking HLA-B*35:01, which otherwise are identical. Balancing selection at key residues maintains numerous HLA-B allotypes having and lacking Bw4, and also those of stronger and weaker interaction with LILRB1, a KIR-related receptor. Correspondingly, there is a balance at key residues of KIR3DL1 that modulate its level of cell-surface expression. Thus, capacity to interact with NK cells synergizes with peptide binding diversity to drive HLA-B allele frequency distribution. These features of KIR and HLA are consistent with ongoing co-evolution and selection imposed by a pathogen endemic to West Africa. Because of the prevalence of malaria in the Ga-Adangbe and previous associations of cerebral malaria with HLA-B*53:01 and KIR, Plasmodium falciparum is a candidate pathogen. 相似文献
139.
140.
Laurent Dujeancourt Ricarda Richter Zofia M. Chrzanowska-Lightowlers Nathalie Bonnefoy Christopher J. Herbert 《Mitochondrion》2013,13(6):871-880
Mitochondrial translation synthesizes key subunits of the respiratory complexes. In Schizosaccharomyces pombe, strains lacking Mrf1, the mitochondrial stop codon recognition factor, are viable, suggesting that other factors can play a role in translation termination. S. pombe contains four predicted peptidyl tRNA hydrolases, two of which (Pth3 and Pth4), have a GGQ motif that is conserved in class I release factors. We show that high dosage of Pth4 can compensate for the absence of Mrf1 and loss of Pth4 exacerbates the lack of Mrf1. Also Pth4 is a component of the mitochondrial ribosome, suggesting that it could help recycling stalled ribosomes. 相似文献