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排序方式: 共有103条查询结果,搜索用时 15 毫秒
31.
Rosemary J Redfield Wendy A Findlay Janine Bossé J Simon Kroll Andrew DS Cameron John HE Nash 《BMC evolutionary biology》2006,6(1):82-15
Background
Many bacteria can take up DNA, but the evolutionary history and function of natural competence and transformation remain obscure. The sporadic distribution of competence suggests it is frequently lost and/or gained, but this has not been examined in an explicitly phylogenetic context. Additional insight may come from the sequence specificity of uptake by species such as Haemophilus influenzae, where a 9 bp uptake signal sequence (USS) repeat is both highly overrepresented in the genome and needed for efficient DNA uptake. We used the distribution of competence genes and DNA uptake specificity in H. influenzae 's family, the Pasteurellaceae, to examine the ancestry of competence. 相似文献32.
Rasmussen SA Lammer EJ Shaw GM Finnell RH McGehee RE Gallagher M Romitti PA Murray JC;National Birth Defects Prevention Study 《Teratology》2002,66(4):177-184
BACKGROUND: Advances in quantitative analysis and molecular genotyping have provided unprecedented opportunities to add biological sampling and genetic information to epidemiologic studies. The purpose of this article is to describe the incorporation of DNA sample collection into the National Birth Defects Prevention Study (NBDPS), an ongoing case-control study in an eight-state consortium with a primary goal to identify risk factors for birth defects. METHODS: Babies with birth defects are identified through birth defects surveillance systems in the eight participating centers. Cases are infants with one or more of over 30 major birth defects. Controls are infants without defects from the same geographic area. Epidemiologic information is collected through an hour-long interview with mothers of both cases and controls. We added the collection of buccal cytobrush DNA samples for case-infants, control-infants, and their parents to this study. RESULTS: We describe here the methods by which the samples have been collected and processed, establishment of a centralized resource for DNA banking, and quality control, database management, access, informed consent, and confidentiality issues. CONCLUSIONS: Biological sampling and genetic analyses are important components to epidemiologic studies of birth defects aimed at identifying risk factors. The DNA specimens collected in this study can be used for detection of mutations, study of polymorphic variants that confer differential susceptibility to teratogens, and examination of interactions among genetic risk factors. Information on the methods used and issues faced by the NBDPS may be of value to others considering the addition of DNA sampling to epidemiologic studies. 相似文献
33.
Repeated evolution of an acetate-crossfeeding polymorphism in long-term populations of Escherichia coli 总被引:1,自引:0,他引:1
Six out of 12 independent replicate populations of Escherichia coli
maintained in long-term glucose-limited continuous culture for up to
approximately 1,750 generations evolve polymorphisms maintained by acetate
crossfeeding. In all cases, the acetate-crossfeeding phenotype is
associated with semiconstitutive overexpression of acetyl CoA synthetase,
which allows for the enhanced uptake of low levels of exogenous acetate.
Mutations in the 5' regulatory region of the acetyl CoA synthetase locus
are responsible for all the acetate crossfeeding phenotypes found. These
changes were either transposable-element insertions or a single T-->A
nucleotide substitution at position -93 relative to the acs gene
translation start site.
相似文献
34.
Gabriel R. McAndrews Andrew L. Yeang Yuchun Cai Christopher J. Barile Michael D. McGehee 《Liver Transplantation》2023,13(1):2202843
Dynamic windows based on reversible metal electrodeposition (RME) can electronically adjust light transmission from ≈70% to <0.1% to improve building aesthetics and energy efficiency by controlling light and heat flow. For RME devices using Cu and Bi, the windows reach “privacy state” (<0.1% transmission) when ≈180 nm of metal is electrodeposited on the transparent conducting electrode. When films with a plated atomic Cu–Bi ratio of ≈2:1 rest in the privacy state, sinusoidal cracks form across the entire film, and the metal delaminates in <1 day. This mechanical failure renders the window unusable as specks of metal are visually unattractive and reduce the dynamic range of the window. The Cu–Bi film is stress free upon deposition, but after 4 h of resting, 38 MPa of tensile stress develops. The tension in Cu–Bi and Cu films combined with the Cu(ClO4)2 in the electrolyte results in severe, widespread fractures and delamination due to stress corrosion cracking. In contrast, electrodeposited Bi films have compressive stress, likely due to high self-diffusion and insertion of atoms into grain boundaries while plating, which results in a Bi-based dynamic window with crack-free resting stability that exceeds 9 weeks. 相似文献
35.
In this paper we develop a mathematical model in which any number of competing species can coexist on four resources which regenerate according to an algebraic relationship. We show that previous attempts to prove that n species cannot coexist on fewer that n resources (the “competitive exclusion principle”) all make use of the very restrictive assumption that the specific growth rates of all competing species are linear functions of resource densities. When this restriction is relaxed, it becomes possible to find situations in which n species can coexist on fewer than n resources. On the basis of this and other observations we conclude that the competitive exclusion principle should be considered to apply only to coexistence at fixed densities. 相似文献
36.
37.
The molecular mechanisms that regulate cellular differentiation during development and throughout life are complex. It is now recognized that precise patterns of differentially expressed genes ultimately direct a particular cell toward a given lineage and many of these are regulated during the earliest stages of differentiation. Using a microarray-based expression analysis, we have examined gene expression profiles during the first 24 h of 3T3-L1 adipocyte differentiation. RNA was isolated at times 0, 2, 8, 16, and 24 h following stimulation of differentiation and hybridized in duplicate to high density Affymetrix microarray gene chips containing a series of 13,179 cDNA/expressed sequence tag (EST) probe sets. Two hundred and eighty-five cDNA/ESTs were shown to have at least a fivefold change in expression levels during this time course and both hierarchical and self-organizing map clustering analysis was performed to categorize them by expression profiles. Several genes known to be regulated during this time period were confirmed and Western blot analysis of the proteins encoded by some of the identified genes revealed expression profiles similar to their mRNA counterparts. As expected, many of the genes identified have not been examined in such a critical time period during adipogenesis and may well represent novel adipogenic mediators. 相似文献
38.
39.
George Y. Margulis Brian E. Hardin I‐Kang Ding Eric T. Hoke Michael D. McGehee 《Liver Transplantation》2013,3(7):959-966
The internal quantum efficiency (IQE) of solid‐state dye sensitized solar cells (ssDSCs) is measured using a hybrid optical modeling plus absorptance measurement approach which takes into account the parasitic absorption of the hole transport material (HTM). Across device thicknesses of 1 to 4 microns, ssDSCs sensitized with Z907 and TT1 dyes display relatively constant IQEs of approximately 88% and 36%, respectively, suggesting excellent charge collection efficiencies for both dyes but poor carrier injection for TT1 devices. The addition of more coadsorbent is shown to increase the IQE of TT1 up to approximately 58%, but significantly lowers dye loading. Finally, optical losses due to absorption by the HTM are quantified and found to be a significant contribution to photocurrent losses for ssDSCs sensitized with poor absorbers such as Z907, as the weak absorption of the dye gives the HTM opportunity for significant parasitic absorption within the active layer. 相似文献
40.