全文获取类型
收费全文 | 1041篇 |
免费 | 81篇 |
专业分类
1122篇 |
出版年
2023年 | 8篇 |
2022年 | 10篇 |
2021年 | 25篇 |
2020年 | 14篇 |
2019年 | 10篇 |
2018年 | 22篇 |
2017年 | 21篇 |
2016年 | 24篇 |
2015年 | 35篇 |
2014年 | 49篇 |
2013年 | 52篇 |
2012年 | 89篇 |
2011年 | 77篇 |
2010年 | 48篇 |
2009年 | 33篇 |
2008年 | 52篇 |
2007年 | 44篇 |
2006年 | 63篇 |
2005年 | 49篇 |
2004年 | 34篇 |
2003年 | 42篇 |
2002年 | 46篇 |
2001年 | 20篇 |
2000年 | 21篇 |
1999年 | 13篇 |
1998年 | 10篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 14篇 |
1991年 | 16篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 14篇 |
1987年 | 9篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1983年 | 9篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1976年 | 7篇 |
1974年 | 7篇 |
1970年 | 5篇 |
1968年 | 4篇 |
1967年 | 8篇 |
排序方式: 共有1122条查询结果,搜索用时 15 毫秒
921.
Yokomizo AY Jorge SA Astray RM Fernandes I Ribeiro OG Horton DS Tonso A Tordo N Pereira CA 《Biotechnology journal》2007,2(1):102-109
Recombinant rabies virus glycoprotein (rRVGP) was expressed in Drosophila melanogaster Schneider 2 (S2) cells. The cDNA encoding the entire RVGP gene was cloned in an expression plasmid under the control of the constitutive actin promoter (Ac), which was co-transfected into S2 cells together with a hygromycin selection plasmid. Selected S2 cell populations (S2AcRVGP) had a decreased ability to grow and consume substrates, when compared to the non-transfected cells (S2). They were shown, by PCR, to express the RVGP gene and mRNA and, by immunoblotting, to synthesize the rRVGP in its expected molecular mass of 65 kDa. ELISA kinetic studies showed the rRVGP expression in cell lysates and supernatants attaining concentrations of 300 microg/L. By flow cytometry analysis, about 30% of the cells in the co-transfected populations were shown to express the rRVGP. Cell populations selected by limiting dilution expressed higher rRVGP yields. Mice immunized with rRVGP were shown to synthesize antibodies against rabies virus and be protected against experimental infection with rabies virus. The data presented here show that S2 cells can be suitable hosts for the rRVGP expression, allowing its synthesis in a high degree of physical and biological integrity. 相似文献
922.
Fruiting body formation of Myxococcus xanthus, like biofilm formation of many other organisms, involves the production of an extracellular matrix (ECM). While the polysaccharide component has been studied, the protein component has been largely unexplored. Proteins associated with the ECM were solubilized from purified ECM by boiling with sodium dodecyl sulfate and were identified by liquid chromatography-tandem mass spectrometry of tryptic fragments. The ECM is enriched in proteins of novel function; putative functions were assigned for only 5 of the 21 proteins. Thirteen putative ECM proteins had lipoprotein secretion signals. The genes for many ECM proteins were disrupted in the wild-type (WT), fibA, and pilA backgrounds. Disruption of the MXAN4860 gene had no effect in the WT or fibA background but in the pilA background resulted in a 24-h delay in aggregation and sporulation compared to its parent. The results of this study show that the M. xanthus ECM proteome is diverse and novel. 相似文献
923.
Microbiology - Lichens are currently interpreted as complex self-sustaining ecosystems formed by the interaction of the primary symbionts and other microorganisms. These microorganisms, which... 相似文献
924.
Ana Paula Gomes Soares Eduardo A. Guillin Leandro Luiz Borges Amanda C. T. da Silva álvaro M. R. de Almeida Pablo E. Grijalba Alexandra M. Gottlieb Burton H. Bluhm Luiz Orlando de Oliveira 《PloS one》2015,10(8)
Diseases of soybean caused by Cercospora spp. are endemic throughout the world’s soybean production regions. Species diversity in the genus Cercospora has been underestimated due to overdependence on morphological characteristics, symptoms, and host associations. Currently, only two species (Cercospora kikuchii and C. sojina) are recognized to infect soybean; C. kikuchii causes Cercospora leaf blight (CLB) and purple seed stain (PSS), whereas C. sojina causes frogeye leaf spot. To assess cryptic speciation among pathogens causing CLB and PSS, phylogenetic and phylogeographic analyses were performed with isolates from the top three soybean producing countries (USA, Brazil, and Argentina; collectively accounting for ~80% of global production). Eight nuclear genes and one mitochondrial gene were partially sequenced and analyzed. Additionally, amino acid substitutions conferring fungicide resistance were surveyed, and the production of cercosporin (a polyketide toxin produced by many Cercospora spp.) was assessed. From these analyses, the long-held assumption of C. kikuchii as the single causal agent of CLB and PSS was rejected experimentally. Four cercosporin-producing lineages were uncovered with origins (about 1 Mya) predicted to predate agriculture. Some of the Cercospora spp. newly associated with CLB and PSS appear to represent undescribed species; others were not previously reported to infect soybeans. Lineage 1, which contained the ex-type strain of C. kikuchii, was monophyletic and occurred in Argentina and Brazil. In contrast, lineages 2 and 3 were polyphyletic and contained wide-host range species complexes. Lineage 4 was monophyletic, thrived in Argentina and the USA, and included the generalist Cercospora cf. flagellaris. Interlineage recombination was detected, along with a high frequency of mutations linked to fungicide resistance in lineages 2 and 3. These findings point to cryptic Cercospora species as underappreciated global considerations for soybean production and phytosanitary vigilance, and urge a reassessment of host-specificity as a diagnostic tool for Cercospora. 相似文献
925.
José P. Vaqué Nerea Martínez Ignacio Varela Fidel Fernández Marta Mayorga Sophia Derdak Sergi Beltrán Thaidy Moreno Carmen Almaraz Gonzalo De las Heras Mónica Bayés Ivo Gut Javier Crespo Miguel A. Piris 《PloS one》2015,10(3)
We have performed a comparative ultrasequencing study of multiple colorectal lesions obtained simultaneously from four patients. Our data show that benign lesions (adenomatous or hyperplastic polyps) contain a high mutational load. Additionally multiple synchronous colorectal lesions show non overlapping mutational signatures highlighting the degree of heterogeneity between multiple specimens in the same patient. Observations in these cases imply that considering not only the number of mutations but an effective oncogenic combination of mutations can determine the malignant progression of colorectal lesions. 相似文献
926.
927.
928.
Udo A. Ernst Xiao Chen Lisa Bohnenkamp Fingal Orlando Galashan Detlef Wegener 《PLoS computational biology》2021,17(11)
Sudden changes in visual scenes often indicate important events for behavior. For their quick and reliable detection, the brain must be capable to process these changes as independently as possible from its current activation state. In motion-selective area MT, neurons respond to instantaneous speed changes with pronounced transients, often far exceeding the expected response as derived from their speed tuning profile. We here show that this complex, non-linear behavior emerges from the combined temporal dynamics of excitation and divisive inhibition, and provide a comprehensive mathematical analysis. A central prediction derived from this investigation is that attention increases the steepness of the transient response irrespective of the activation state prior to a stimulus change, and irrespective of the sign of the change (i.e. irrespective of whether the stimulus is accelerating or decelerating). Extracellular recordings of attention-dependent representation of both speed increments and decrements confirmed this prediction and suggest that improved change detection derives from basic computations in a canonical cortical circuitry. 相似文献
929.
Roberta Spadaccini Orlando Crescenzi Delia Picone Teodorico Tancredi Piero Andrea Temussi 《Journal of peptide science》1999,5(7):306-312
Dynorphin A, the endogenous agonist for the κ opioid receptor, has been studied by NMR spectroscopy in methanol, acetonitrile, DMSO and in mixtures of hexafluoroacetone/water and DMSO/water. NMR data in the DMSO/water cryomixture at 278 K are consistent with a conformer in which the N‐terminal part, like the corresponding message domain of enkephalins, is poorly ordered, whereas the C‐terminal part is folded in a loop centred around Pro10. The folded structure of the C‐terminal part (address moiety) may shed light on the role of the essential residues Arg7, Lys11 and Lys13. Copyright © 1999 European Peptide Society and John Wiley & Sons, Ltd. 相似文献
930.
Benedetta Maria Bonora Maria Teresa Palano Gianluca Testa Gian Paolo Fadini Elena Sangalli Fabiana Madotto Giuseppe Persico Francesca Casciaro Rosa Vono Ornella Colpani Francesco Scavello Roberta Cappellari Pasquale Abete Patrizia Orlando Franco Carnelli Andrea Giovanni Berardi Stefano De Servi Angela Raucci Marco Giorgio Paolo Madeddu Gaia Spinetti 《Aging cell》2022,21(3)
Frailty affects the physical, cognitive, and social domains exposing older adults to an increased risk of cardiovascular disease and death. The mechanisms linking frailty and cardiovascular outcomes are mostly unknown. Here, we studied the association of abundance (flow cytometry) and gene expression profile (RNAseq) of stem/progenitor cells (HSPCs) and molecular markers of inflammaging (ELISA) with the cardiorespiratory phenotype and prospective adverse events of individuals classified according to levels of frailty. Two cohorts of older adults were enrolled in the study. In a cohort of pre‐frail 35 individuals (average age: 75 years), a physical frailty score above the median identified subjects with initial alterations in cardiorespiratory function. RNA sequencing revealed S100A8/A9 upregulation in HSPCs from the bone marrow (>10‐fold) and peripheral blood (>200‐fold) of individuals with greater physical frailty. Moreover higher frailty was associated with increased alarmins S100A8/A9 and inflammatory cytokines in peripheral blood. We then studied a cohort of 104 more frail individuals (average age: 81 years) with multidomain health deficits. Reduced levels of circulating HSPCs and increased S100A8/A9 concentrations were independently associated with the frailty index. Remarkably, low HSPCs and high S100A8/A9 simultaneously predicted major adverse cardiovascular events at 1‐year follow‐up after adjustment for age and frailty index. In conclusion, inflammaging characterized by alarmin and pro‐inflammatory cytokines in pre‐frail individuals is mirrored by the pauperization of HSPCs in frail older people with comorbidities. S100A8/A9 is upregulated within HSPCs, identifying a phenotype that associates with poor cardiovascular outcomes. 相似文献