全文获取类型
收费全文 | 267篇 |
免费 | 17篇 |
国内免费 | 1篇 |
出版年
2022年 | 5篇 |
2021年 | 5篇 |
2019年 | 2篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 2篇 |
2015年 | 9篇 |
2014年 | 7篇 |
2013年 | 10篇 |
2012年 | 14篇 |
2011年 | 14篇 |
2010年 | 11篇 |
2009年 | 12篇 |
2008年 | 11篇 |
2007年 | 6篇 |
2006年 | 10篇 |
2005年 | 9篇 |
2004年 | 10篇 |
2003年 | 7篇 |
2002年 | 4篇 |
2001年 | 9篇 |
2000年 | 2篇 |
1999年 | 10篇 |
1998年 | 8篇 |
1996年 | 5篇 |
1995年 | 11篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 6篇 |
1973年 | 1篇 |
1972年 | 3篇 |
1950年 | 1篇 |
1946年 | 1篇 |
1941年 | 1篇 |
1940年 | 1篇 |
排序方式: 共有285条查询结果,搜索用时 31 毫秒
71.
72.
Hulbert AJ 《Biological reviews of the Cambridge Philosophical Society》2000,75(4):519-631
The thyroid hormones are very hydrophobic and those that exhibit biological activity are 3',5',3,5-L-tetraiodothyronine (T4), 3',5,3-L-triiodothyronine (T3), 3',5',3-L-triiodothyronine (rT3) and 3,5',-L-diiothyronine (3,5-T2). At physiological pH, dissociation of the phenolic -OH group of these iodothyronines is an important determinant of their physical chemistry that impacts on their biological effects. When non-ionized these iodothyronines are strongly amphipathic. It is proposed that iodothyronines are normal constituents of biological membranes in vertebrates. In plasma of adult vertebrates, unbound T4 and T3 are regulated in the picomolar range whilst protein-bound T4 and T3 are maintained in the nanomolar range. The function of thyroid-hormone-binding plasma proteins is to ensure an even distrubtion throughout the body. Various iodothyronines are produced by three types of membrane-bound cellular deiodinase enzyme systems in vertebrates. The distribution of deiodinases varies between tissues and each has a distinct developmental profile. Thyroid hormones. (1) the nuclear receptor mode is especially important in the thyroid hormone axis that controls plasma and cellular levels of these hormones. (2) These hormones are strongly associated with membranes in tissues and normally rigidify these membranes. (3) They also affect the acyl composition of membrane bilayers and it is suggested that this is due to the cells responding to thyroid-hormone-induced membrane rigidificataion. Both their immediate effects on the physical state of membranes and the consequent changes in membrane composition result in several other thyroid hormone effects. Effects on metabolism may be due primarily to membrane acyl changes. There are other actions of thyroid hormones involving membrane receptors and influences on cellular interactions with the extracellulara matrix. The effects of thyroid hormones are reviewed and appear to b combinations of these various modes of action. During development, vertebrates show a surge in T4 and other thyroid hormones, as well as distinctive profiles in the appearance of the deiodinase enzymes and nuclear receptors. Evidence from the use of analogues supports multiple modes of action. Re-examination of data from th early 1960s supports a membrane action. Findings from receptor 'knockout' mice supports an important role for receptors in the development of the thyroid axis. These iodothyronines may be better thought of as 'vitamone'-like molecules than traditional hormonal messengers. 相似文献
73.
Genes at the maize Rp1 rust resistance complex often mispair in meiosis, which allows genes to recombine unequally, creating recombinant haplotypes. Four recombinant haplotypes were identified from progeny of an Rp1-D/Rp1-I heterozygote that conferred a nonparental resistance specificity designated Rp1-I*. Sequence comparisons of paralogs in the recombinant and parental haplotypes demonstrated that all four recombinants were derived from intergenic (between gene) recombination events. The sequence of paralogs in the HRp1-I parental haplotype indicated this haplotype includes 41 or more rp1 genes, at least 31 of which are transcribed. The results indicate that most of the novel resistance specificities that have arisen spontaneously at Rp1 are the result of reassort ment of existing Rp1 genes. 相似文献
74.
The concept of basal metabolic rate (BMR) was developed to compare the metabolic rate of animals and initially was important in a clinical context as a means of determining thyroid status of humans. It was also important in defining the allometric relationship between body mass and metabolic rate of mammals. The BMR of mammals varies with body mass, with the same allometric exponent as field metabolic rate and with many physiological and biochemical rates. The membrane pacemaker theory proposes that the fatty acid composition of membrane bilayers is an important determinant of a species BMR. In both mammals and birds, membrane polyunsaturation decreases and monounsaturation increases with increasing body mass and a decrease in mass-specific BMR. The secretion and production of thyroid hormones in mammals are related to body mass, with the allometric exponent similar to BMR; yet there is no body size-related variation in either total or free concentrations of thyroid hormones in plasma of mammals. It is suggested that in different-sized mammals, the secretion/production of thyroid hormones is a result of BMR differences rather than their cause. BMR is a useful concept in some situations but not in others. 相似文献
75.
Bakker BM Overkamp KM van Maris AJ Kötter P Luttik MA van Dijken JP Pronk JT 《FEMS microbiology reviews》2001,25(1):15-37
In Saccharomyces cerevisiae, reduction of NAD(+) to NADH occurs in dissimilatory as well as in assimilatory reactions. This review discusses mechanisms for reoxidation of NADH in this yeast, with special emphasis on the metabolic compartmentation that occurs as a consequence of the impermeability of the mitochondrial inner membrane for NADH and NAD(+). At least five mechanisms of NADH reoxidation exist in S. cerevisiae. These are: (1) alcoholic fermentation; (2) glycerol production; (3) respiration of cytosolic NADH via external mitochondrial NADH dehydrogenases; (4) respiration of cytosolic NADH via the glycerol-3-phosphate shuttle; and (5) oxidation of intramitochondrial NADH via a mitochondrial 'internal' NADH dehydrogenase. Furthermore, in vivo evidence indicates that NADH redox equivalents can be shuttled across the mitochondrial inner membrane by an ethanol-acetaldehyde shuttle. Several other redox-shuttle mechanisms might occur in S. cerevisiae, including a malate-oxaloacetate shuttle, a malate-aspartate shuttle and a malate-pyruvate shuttle. Although key enzymes and transporters for these shuttles are present, there is as yet no consistent evidence for their in vivo activity. Activity of several other shuttles, including the malate-citrate and fatty acid shuttles, can be ruled out based on the absence of key enzymes or transporters. Quantitative physiological analysis of defined mutants has been important in identifying several parallel pathways for reoxidation of cytosolic and intramitochondrial NADH. The major challenge that lies ahead is to elucidate the physiological function of parallel pathways for NADH oxidation in wild-type cells, both under steady-state and transient-state conditions. This requires the development of techniques for accurate measurement of intracellular metabolite concentrations in separate metabolic compartments. 相似文献
76.
A re-assessment of the tricellular region of epithelial cell tight junctions in trachea of guinea pig 总被引:3,自引:0,他引:3
The tricellular region of epithelial tight junctions was previously dismissed as a possible avenue of permeability. One reason was that the two parallel vertical fibers, which penetrate the depth of the tight junction, were apparently cross-linked. Another reason was that the tricellular region of the tight junction is deeper than the adjacent bicellular regions. In the course of several freeze-fracture studies of epithelial tight junctions we have made observations which led us to re-assess the tricellular region as an avenue of permeability. We believe that information from ectoplasmic fracture faces is less subject to artifacts and, in ectoplasmic fracture faces of tricellular regions, cross-linking of the vertical furrows has not been observed. In guinea pig tracheal epithelium the tricellular junction is only about 1 micron deep. Following exposure to cigarette smoke, lanthanum ion staining has been observed in some tricellular junctions. It seems that earlier reasons for dismissing tricellular regions of the tight junction as permeability sites may be insufficient and that there is some evidence to support a role in permeability. 相似文献
77.
78.
Louis Grandjean Tomotada Iwamoto Anna Lithgow Robert H Gilman Kentaro Arikawa Noriko Nakanishi Laura Martin Edith Castillo Valentina Alarcon Jorge Coronel Walter Solano Minoo Aminian Claudia Guezala Nalin Rastogi David Couvin Patricia Sheen Mirko Zimic David AJ Moore 《PloS one》2015,10(5)
BackgroundThe comparison of Mycobacterium tuberculosis bacterial genotypes with phenotypic, demographic, geospatial and clinical data improves our understanding of how strain lineage influences the development of drug-resistance and the spread of tuberculosis.MethodsTo investigate the association of Mycobacterium tuberculosis bacterial genotype with drug-resistance. Drug susceptibility testing together with genotyping using both 15-loci MIRU-typing and spoligotyping, was performed on 2,139 culture positive isolates, each from a different patient in Lima, Peru. Demographic, geospatial and socio-economic data were collected using questionnaires, global positioning equipment and the latest national census.ResultsThe Latin American Mediterranean (LAM) clade (OR 2.4, p<0.001) was significantly associated with drug-resistance and alone accounted for more than half of all drug resistance in the region. Previously treated patients, prisoners and genetically clustered cases were also significantly associated with drug-resistance (OR''s 2.5, 2.4 and 1.8, p<0.001, p<0.05, p<0.001 respectively).ConclusionsTuberculosis disease caused by the LAM clade was more likely to be drug resistant independent of important clinical, genetic and socio-economic confounding factors. Explanations for this include; the preferential co-evolution of LAM strains in a Latin American population, a LAM strain bacterial genetic background that favors drug-resistance or the "founder effect" from pre-existing LAM strains disproportionately exposed to drugs. 相似文献
79.
ZhiXin Zhu AJ Harris Mir Muhammad Nizamani Andrew H. Thornhill Rosa A. Scherson HuaFeng Wang 《Ecology and evolution》2021,11(5):2100
To better identify biodiversity hotspots for conservation on Hainan Island, a tropical island in southern China, we assessed spatial variation in phylogenetic diversity and species richness using 18,976 georeferenced specimen records and a newly reconstructed molecular phylogeny of 957 native woody plants. Within this framework, we delineated bioregions based on vegetation composition and mapped areas of neoendemism and paleoendemism to identify areas of priority for conservation. Our results reveal that the southwest of Hainan is the most important hot spot for endemism and plant diversity followed by the southeast area. The distribution of endemic species showed a scattered, rather than clustered, pattern on the island. Based on phylogenetic range‐weighted turnover metrics, we delineated three major vegetational zones in Hainan. These largely correspond to natural secondary growth and managed forests (e.g., rubber and timber forests) in central Hainan, old‐growth forests and natural secondary growth forest at the margins of Hainan, and nature reserves on the island (e.g., Jianfeng and Diaoluo National Nature Reserves). Our study helps to elucidate potential botanical conservation priorities for Hainan within an evolutionary, phylogenetic framework. 相似文献
80.
Laurin AJ Mueller Karl G Kugler Michael Netzer Armin Graber Matthias Dehmer 《Biology direct》2011,6(1):1-15