全文获取类型
收费全文 | 14233篇 |
免费 | 1403篇 |
国内免费 | 10篇 |
专业分类
15646篇 |
出版年
2024年 | 16篇 |
2023年 | 110篇 |
2022年 | 266篇 |
2021年 | 591篇 |
2020年 | 269篇 |
2019年 | 335篇 |
2018年 | 393篇 |
2017年 | 333篇 |
2016年 | 594篇 |
2015年 | 937篇 |
2014年 | 934篇 |
2013年 | 1065篇 |
2012年 | 1375篇 |
2011年 | 1318篇 |
2010年 | 781篇 |
2009年 | 627篇 |
2008年 | 844篇 |
2007年 | 814篇 |
2006年 | 792篇 |
2005年 | 636篇 |
2004年 | 569篇 |
2003年 | 512篇 |
2002年 | 468篇 |
2001年 | 98篇 |
2000年 | 68篇 |
1999年 | 93篇 |
1998年 | 94篇 |
1997年 | 49篇 |
1996年 | 62篇 |
1995年 | 34篇 |
1994年 | 46篇 |
1993年 | 45篇 |
1992年 | 53篇 |
1991年 | 35篇 |
1990年 | 38篇 |
1989年 | 29篇 |
1988年 | 13篇 |
1987年 | 20篇 |
1986年 | 17篇 |
1985年 | 23篇 |
1984年 | 25篇 |
1983年 | 16篇 |
1982年 | 18篇 |
1981年 | 23篇 |
1980年 | 15篇 |
1979年 | 14篇 |
1978年 | 15篇 |
1977年 | 15篇 |
1975年 | 12篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Ezdihar A. Hassoun Jacquelyn Cearfoss Brian Musser Sarah Krispinsky Noor Al‐Hassan Ming‐Cheh Liu 《Journal of biochemical and molecular toxicology》2013,27(4):237-242
In this study, groups of B6C3F1 male mice were treated with dichloroacetate (DCA), trichloroacetate (TCA), and mixtures of the compounds (Mix I, II, and III) daily by gavage, for 13 weeks. The tested doses were 7.5, 15, and 30 mg DCA/kg/day and 12.5, 25, and 50 mg TCA/kg/day. The DCA: TCA ratios in Mix I, II, and III were 7.5:12.5, 15:25, and 30:50 mg/kg/day, respectively. Peritoneal lavage cells were collected at the end of the treatment period and assayed for the biomarkers of phagocytic activation, including superoxide anion and tumor necrosis factor‐alpha production, and myeloperoxidase activity. The mixtures produced nonlinear effects on the biomarkers of phagocytic activation, with Mix I and II effects were found to be additive, but Mix III effects were found to be less than additive. © 2013 Wiley Periodicals, Inc. J BiochemMol Toxicol 27:237‐242, 2013; View this article online at wileyonlinelibrary.com . DOI 10.1002/jbt.21476 相似文献
992.
Ajay Narendra Sarah Gourmaud Jochen Zeil 《Proceedings. Biological sciences / The Royal Society》2013,280(1765)
Ants are efficient navigators, guided by path integration and visual landmarks. Path integration is the primary strategy in landmark-poor habitats, but landmarks are readily used when available. The landmark panorama provides reliable information about heading direction, routes and specific location. Visual memories for guidance are often acquired along routes or near to significant places. Over what area can such locally acquired memories provide information for reaching a place? This question is unusually approachable in the solitary foraging Australian jack jumper ant, since individual foragers typically travel to one or two nest-specific foraging trees. We find that within 10 m from the nest, ants both with and without home vector information available from path integration return directly to the nest from all compass directions, after briefly scanning the panorama. By reconstructing panoramic views within the successful homing range, we show that in the open woodland habitat of these ants, snapshot memories acquired close to the nest provide sufficient navigational information to determine nest-directed heading direction over a surprisingly large area, including areas that animals may have not visited previously. 相似文献
993.
Sampathkumar P Mak MW Fischer-Witholt SJ Guigard E Kay CM Lemieux MJ 《Biochimica et biophysica acta》2012,1818(12):3090-3097
Rhomboid peptidases (proteases) play key roles in signaling events at the membrane bilayer. Understanding the regulation of rhomboid function is crucial for insight into its mechanism of action. Here we examine the oligomeric state of three different rhomboid proteases. We subjected Haemophilus influenzae, (hiGlpG), Escherichia coli GlpG (ecGlpG) and Bacillus subtilis (YqgP) to sedimentation equilibrium analysis in detergent-solubilized dodecylmaltoside (DDM) solution. For hiGlpG and ecGlpG, rhomboids consisting of the core 6 transmembrane domains without and with soluble domains respectively, and YqgP, predicted to have 7 transmembrane domains with larger soluble domains at the termini, the predominant species was dimeric with low amounts of monomer and tetramers observed. To examine the effect of the membrane domain alone on oligomeric state of rhomboid, hiGlpG, the simplest form from the rhomboid class of intramembrane proteases representing the canonical rhomboid core of six transmembrane domains, was studied further. Using gel filtration and crosslinking we demonstrate that hiGlpG is dimeric and functional in DDM detergent solution. More importantly co-immunoprecipitation studies demonstrate that the dimer is present in the lipid bilayer suggesting a physiological dimer. Overall these results indicate that rhomboids form oligomers which are facilitated by the membrane domain. For hiGlpG we have shown that these oligomers exist in the lipid bilayer. This is the first detailed oligomeric state characterization of the rhomboid family of peptidases. 相似文献
994.
Highly Infectious CJD Particles Lack Prion Protein but Contain Many Viral‐Linked Peptides by LC‐MS/MS
下载免费PDF全文
![点击此处可从《Journal of cellular biochemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Terry Kipkorir Sarah Tittman Sotirios Botsios Laura Manuelidis 《Journal of cellular biochemistry》2014,115(11):2012-2021
995.
Disentangling species and functional group richness effects on soil N cycling in a grassland ecosystem
下载免费PDF全文
![点击此处可从《Global Change Biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Xiaorong Wei Peter B. Reich Sarah E. Hobbie Clare E. Kazanski 《Global Change Biology》2017,23(11):4717-4727
Species richness (SR) and functional group richness (FGR) are often confounded in both observational and experimental field studies of biodiversity and ecosystem function. This precludes discernment of their separate influences on ecosystem processes, including nitrogen (N) cycling, and how those influences might be moderated by global change factors. In a 17‐year field study of grassland species, we used two full factorial experiments to independently vary SR (one or four species, with FGR = 1) and FGR (1–4 groups, with SR = 4) to assess SR and FGR effects on ecosystem N cycling and its response to elevated carbon dioxide (CO2) and N addition. We hypothesized that increased plant diversity (either SR or FGR) and elevated CO2 would enhance plant N pools because of greater plant N uptake, but decrease soil N cycling rates because of greater soil carbon inputs and microbial N immobilization. In partial support of these hypotheses, increasing SR or FGR (holding the other constant) enhanced total plant N pools and decreased soil nitrate pools, largely through higher root biomass, and increasing FGR strongly reduced mineralization rates, because of lower root N concentrations. In contrast, increasing SR (holding FGR constant and despite increasing total plant C and N pools) did not alter root N concentrations or net N mineralization rates. Elevated CO2 had minimal effects on plant and soil N metrics and their responses to plant diversity, whereas enriched N increased plant and soil N pools, but not soil N fluxes. These results show that functional diversity had additional effects on both plant N pools and rates of soil N cycling that were independent of those of species richness. 相似文献
996.
Consumer-resource dynamics of hosts with their pathogens are modulated by complex interactions between various branches of hosts’ immune systems and the imperfectly perceived pathogen. Multistrain SIR models tend to sweep competitive interaction terms between different pathogen strains into a single parameter representing cross-immunity. After reviewing several hypotheses about the generation of immune responses, we look into the consequences of assuming that hosts with identical immune repertoires respond to new pathogens identically. In particular, we vary the breadth of the typical immune response, or the average number of pathogen epitopes a host perceives, and the probability of perceiving a particular epitope. The latter quantity in our model is equivalent both to the degree of diversity in host responses at the population level and the relative immunodominance of different epitopes. We find that a sharp transition to strain coexistence occurs as host responses become narrow or skewed toward one epitope. Increasing the breadth of the immune response and the immunogenicity of different epitopes typically increases the range of cross-immunity values in which chaotic strain dynamics and competitive exclusion occur. Models attempting to predict the outcomes of strain competition should thus consider the potential diversity and specificity of hosts’ responses to infection. 相似文献
997.
Cell cycle checkpoints are essential for maintaining genomic integrity. Human topoisomerase II binding protein 1 (TopBP1) shares sequence similarity with budding yeast Dpb11, fission yeast Rad4/Cut5, and Xenopus Cut5, all of which are required for DNA replication and cell cycle checkpoints. Indeed, we have shown that human TopBP1 participates in the activation of replication checkpoint and DNA damage checkpoints, following hydroxyurea treatment and ionizing radiation. In this study, we address the physiological function of TopBP1 in S phase by using small interfering RNA. In the absence of exogenous DNA damage, TopBP1 is recruited to replicating chromatin. However, TopBP1 does not appear to be essential for DNA replication. TopBP1-deficient cells have increased H2AX phosphorylation and ATM-Chk 2 activation, suggesting the accumulation of DNA double-strand breaks in the absence of TopBP1. This leads to formation of gaps and breaks at fragile sites, 4N accumulation, and aberrant cell division. We propose that the cellular function of TopBP1 is to monitor ongoing DNA replication. By ensuring proper DNA replication, TopBP1 plays a critical role in the maintenance of genomic stability during normal S phase as well as following genotoxic stress. 相似文献
998.
Cynthia?A. Stanich Aurelia?R. Honerkamp-Smith Gregory?Garbès Putzel Christopher?S. Warth Andrea?K. Lamprecht Pritam Mandal Elizabeth Mann Thien-An?D. Hua Sarah?L. Keller 《Biophysical journal》2013,105(2):444-454
We investigate isothermal diffusion and growth of micron-scale liquid domains within membranes of free-floating giant unilamellar vesicles with diameters between 80 and 250 μm. Domains appear after a rapid temperature quench, when the membrane is cooled through a miscibility phase transition such that coexisting liquid phases form. In membranes quenched far from a miscibility critical point, circular domains nucleate and then progress within seconds to late stage coarsening in which domains grow via two mechanisms 1), collision and coalescence of liquid domains, and 2), Ostwald ripening. Both mechanisms are expected to yield the same growth exponent, α = 1/3, where domain radius grows as timeα. We measure α = 0.28 ± 0.05, in excellent agreement. In membranes close to a miscibility critical point, the two liquid phases in the membrane are bicontinuous. A quench near the critical composition results in rapid changes in morphology of elongated domains. In this case, we measure α = 0.50 ± 0.16, consistent with theory and simulation. 相似文献
999.
Differential Transmission of the Genospecies of Borrelia burgdorferi Sensu Lato by Game Birds and Small Rodents in England 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Klaus Kurtenbach Mick Peacey Sjoerd G. T. Rijpkema Andrew N. Hoodless Patricia A. Nuttall Sarah E. Randolph 《Applied microbiology》1998,64(4):1169-1174
The genetic diversity of Borrelia burgdorferi sensu lato was assessed in a focus of Lyme borreliosis in southern Britain dominated by game birds. Ticks, rodents, and pheasants were analyzed for spirochete infections by PCR targeting the 23S-5S rRNA genes, followed by genotyping by the reverse line blot method. In questing Ixodes ricinus ticks, three genospecies of B. burgdorferi sensu lato were detected, with the highest prevalences found for Borrelia garinii and Borrelia valaisiana. B. burgdorferi sensu stricto was rare (<1%) in all tick stages. Borrelia afzelii was not detected in any of the samples. More than 50% of engorged nymphs collected from pheasants were infected with borreliae, mainly B. garinii and/or B. valaisiana. Although 19% of the rodents harbored B. burgdorferi sensu stricto and/or B. garinii in internal organs, only B. burgdorferi sensu stricto was transmitted to xenodiagnostic tick larvae (it was transmitted to 1% of the larvae). The data indicate that different genospecies of B. burgdorferi sensu lato can be maintained in nature by distinct transmission cycles involving the same vector tick species but different vertebrate host species. Wildlife management may have an influence on the relative risk of different clinical forms of Lyme borreliosis. 相似文献
1000.
Competing for blood: the ecology of parasite resource competition in human malaria–helminth co‐infections
下载免费PDF全文
![点击此处可从《Ecology letters》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Sarah A. Budischak Aprilianto E. Wiria Firdaus Hamid Linda J. Wammes Maria M. M. Kaisar Lisette van Lieshout Erliyani Sartono Taniawati Supali Maria Yazdanbakhsh Andrea L. Graham 《Ecology letters》2018,21(4):536-545
Ecological theory suggests that co‐infecting parasite species can interact within hosts directly, via host immunity and/or via resource competition. In mice, competition for red blood cells (RBCs) between malaria and bloodsucking helminths can regulate malaria population dynamics, but the importance of RBC competition in human hosts was unknown. We analysed infection density (i.e. the concentration of parasites in infected hosts), from a 2‐year deworming study of over 4000 human subjects. After accounting for resource‐use differences among parasites, we find evidence of resource competition, priority effects and a competitive hierarchy within co‐infected individuals. For example reducing competition via deworming increased Plasmodium vivax densities 2.8‐fold, and this effect is limited to bloodsucking hookworms. Our ecological, resource‐based perspective sheds new light into decades of conflicting outcomes of malaria–helminth co‐infection studies with significant health and transmission consequences. Beyond blood, investigating within‐human resource competition may bring new insights for improving human health. 相似文献