首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   149篇
  免费   16篇
  国内免费   1篇
  166篇
  2021年   3篇
  2018年   2篇
  2017年   5篇
  2016年   9篇
  2015年   6篇
  2014年   6篇
  2013年   6篇
  2012年   6篇
  2011年   9篇
  2010年   14篇
  2009年   9篇
  2008年   9篇
  2007年   9篇
  2006年   7篇
  2005年   2篇
  2004年   4篇
  2003年   6篇
  2002年   2篇
  2001年   6篇
  2000年   3篇
  1999年   3篇
  1998年   10篇
  1997年   6篇
  1996年   4篇
  1995年   1篇
  1994年   2篇
  1993年   6篇
  1991年   1篇
  1990年   1篇
  1987年   1篇
  1983年   1篇
  1982年   1篇
  1981年   1篇
  1979年   1篇
  1978年   1篇
  1977年   1篇
  1975年   2篇
排序方式: 共有166条查询结果,搜索用时 15 毫秒
11.
Aims of the study were to measure insulin‐like growth factor‐binding protein‐2 (IGFBP‐2) expression by abdominal subcutaneous adipocytes and to assess the relationship between IGFBP‐2 expression, circulating IGFBP‐2, obesity, and insulin sensitivity in obese children. Thirty‐eight obese children were recruited. Insulin sensitivity was assessed by intravenous glucose tolerance test and body composition by total‐body dual‐energy X‐ray absorptiometry. Serum free and total IGF‐I, IGFBP‐2, adiponectin, and leptin were measured. Relative quantification of IGFBP‐2 mRNA by subcutaneous adipose tissue biopsies was obtained using real‐time PCR. Circulating IGFBP‐2 was positively associated with insulin sensitivity, in agreement with previous studies. IGFBP‐2 expression was associated with fat mass percentage (r = 0.656; P < 0.02), insulin sensitivity (r = ?0.604; P < 0.05), free IGF‐I (r = 0.646; P < 0.05), and leptin (r = 0.603; P < 0.05), but not with circulating IGFBP‐2 (r = 0.003, P = ns). The association between IGFBP‐2 expression and adiposity (r = 0.648; P < 0.05) was independent of insulin sensitivity (covariate). In conclusion, circulating IGFBP‐2 was positively associated with insulin sensitivity. IGFBP‐2 was expressed by subcutaneous abdominal adipocytes of obese children and increased with adiposity, independently from the level of insulin sensitivity. IGFBP‐2 expression may potentially be one of the local mechanisms used by adipocytes to limit further fat gain.  相似文献   
12.

Background  

The Beijing lineage of Mycobacterium tuberculosis is causing concern due to its global distribution and its involvement in severe outbreaks. Studies focused on this lineage are mainly restricted to geographical settings where its prevalence is high, whereas those in other areas are scarce. In this study, we analyze Beijing isolates in the Mediterranean area, where this lineage is not prevalent and is mainly associated with immigrant cases.  相似文献   
13.
Beta-D-galactofuranosidase is a good chemotherapeutic target for the design of inhibitors, since beta-D-galactofuranose is a constituent of important parasite glycoconjugates but is not present in the host mammals. With this aim, we have synthesized for the first time alkyl, benzyl and aryl 1-thio-beta-D-galactofuranosides by condensation of penta-O-benzoyl-alpha,beta-D-galactofuranose with the corresponding thiols, in the presence of SnCl4as catalyst. The complete chemical and spectroscopical characterization of these compounds showed that the reaction was stereoselective. Debenzoylation with sodium methoxide afforded the beta-S-galactofuranosides in high yield. The thioglycosides were tested as inhibitors of the beta-D- galactofuranosidase of Penicillium fellutanum, using for the first time 4-nitrophenyl-beta-D-galactofuranoside as chromogenic substrate. The 4- aminophenyl-1-thio-beta-D-galactofuranoside, obtained by catalytic hydrogenation of the nitrophenyl derivative, was the best inhibitor being then an adequate ligand for the preparation of an affinity phase aimed at the isolation of beta-d-galactofuranosidases from different sources. Also the inhibitory activity of d-galactono-1, 4-lactone was shown.   相似文献   
14.
Marmosets (genus Callithrix) are a diverse group of platyrrhine primates with 13-15 purported taxa, many of them considered endangered. Morphological analyses constitute most of the basis for recognition of these forms as distinct taxa. The purpose of this study was to provide a molecular view, based on mitochondrial control region sequences, of the evolutionary history of the marmosets, concomitant with a molecular phylogenetic perspective on species diversity within the group. An additional purpose was to provide the first comparative examination of a complete New World monkey control region sequence with those of other mammals. The phylogenetic analyses provide convincing support for a split between the Atlantic forest and Amazonian marmosets, with the inclusion of the pygmy marmoset (Cebuella pygmaea) at the base of the Amazonian clade. The earliest branch of the Atlantic forest group was C. aurita. In the Amazonian group, the analyses do not support the recognition of C. humeralifer and the recently described C mauesi as distinct taxa. They do, however, support a clear distinction between C. argentata and a strongly supported mixed clade of C. humeralifer and C. mauesi. In the Atlantic forest group, the phylogenetic tree suggests mixing between C. penicillata, C. kuhli, and possibly C. jacchus. Most of the sequence features characteristic of other mammal control regions were also evident in marmosets, with the exception that conserved sequence blocks (CSBs) 2 and 3 were not clearly identifiable. Tandem repeat units often associated with heteroplasmy in a variety of other mammals were not evident in the marmoset sequences.   相似文献   
15.

Introduction  

The aim of this study was to investigate whether serum biomarker levels of C2C, C1,2C, CS846, and CPII can predict the long-term course of disease activity and radiographic progression early in the disease course of rheumatoid arthritis (RA).  相似文献   
16.
17.
Molecular evolution of the period gene in Drosophila athabasca   总被引:1,自引:0,他引:1  
We measured nucleotide variability within and between the three semispeciesof the Drosophila athabasca complex, at the period (per) gene by using apolymerase chain reaction-based four-cutter restriction- enzyme analysis.The levels of polymorphism varied considerably between the threesemispecies. Our results for per, combined with previous data for X-linkedallozymes, suggest that the X chromosome in the western- northernsemispecies is less variable than expected under an equilibrium-neutralmodel. Both the pattern of divergence between the semispecies and acladistic clustering of per haplotypes support the previously hypothesizedgrouping of eastern A and eastern B as the two most recently divergedsemispecies. A 21-bp in-frame segment in the region of per which sharessequence similarity with the neuronal development gene single minded isdeleted in all eastern A and eastern B flies examined but is present in allof the western-northern flies and all other published per sequences.Despite these hints that there may be significant differences at the pergene between the semispecies, especially the western-northern group versusthe two eastern groups, there is no compelling evidence that per isinvolved in the mating song differences between the semispecies.  相似文献   
18.
Reduced farrowing rates due to late pregnancy loss (LPL) is a manifestation of seasonal infertility in pigs. This study was undertaken to determine sow- and gilt-specific risk factors leading to LPL during the seasonal infertility period (January to April) in Australia. Age at first service was considered to be a major gilt-specific risk factor, whereas sow-specific factors considered included parity, prior wean-to-service interval, prior lactation length, and number of piglets weaned in the lactation period immediately preceding the mating/pregnancy event under scrutiny. Logistic regression analysis of these factors was undertaken on 13,213 animals from three farms (Farms A, B, and C). Age at first service for gilts had an effect on LPL (P < 0.05) on Farm C when compared with that for Farms A and B, with those mated at approximately 220 d having the lowest rate of LPL. For older sows, parity was a factor on Farms A and C (P < 0.001), with the proportion of sows with LPL increasing with increasing parity. When the data from each farm were combined and analyzed, there was a significant farm by WSI interaction, with animals from Farm C being most at-risk for LPL. Sows with shorter lactation periods (P < 0.05) and smaller litters (P < 0.05) at the previous lactation had a greater chance of LPL on all farms. Under the conditions of this study, we were able to identify risk factors for LPL that producers can manipulate during the seasonal infertility period to improve breeding herd productivity.  相似文献   
19.
20.
    
Temperature is one of the main factors that determine sexual reproduction in terrestrial and emergent aquatic plant species. The effect of temperature on sexual reproduction and seed production of Glyceria maxima (Hartm.) Holmb. in the southern hemisphere is unknown. Glyceria maxima collections in February 2010 at three isolated infestations in KwaZulu-Natal failed to yield a single seed, only empty panicles. Laboratory experiments showed that vernalisation had no consistent effect on seed production. Field- and laboratory-grown plants produced seeds in the 2010/2011 season, because of having sufficient time at optimum temperatures required for seed production (1 491 and 1 585 hours, respectively), compared to a shorter period (1 352 hours) of suitable temperatures during the 2009/2010 growing season. An inadequate period of optimum temperatures (15–25°C) during seed production resulted in the lack of seeds in the field in the 2009/2010 growing season. This study showed that temperature and duration of exposure thereto during the seed-production period play vital roles in G. maxima sexual reproduction.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号