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   102篇
  免费   9篇
  2021年   1篇
  2019年   2篇
  2018年   2篇
  2017年   3篇
  2015年   1篇
  2014年   6篇
  2013年   4篇
  2012年   6篇
  2011年   7篇
  2010年   3篇
  2009年   5篇
  2008年   5篇
  2007年   5篇
  2006年   5篇
  2005年   4篇
  2004年   10篇
  2003年   12篇
  2002年   6篇
  2001年   5篇
  2000年   1篇
  1999年   1篇
  1997年   3篇
  1996年   3篇
  1995年   1篇
  1992年   2篇
  1991年   1篇
  1986年   1篇
  1984年   1篇
  1982年   2篇
  1968年   1篇
  1964年   1篇
  1960年   1篇
排序方式: 共有111条查询结果,搜索用时 131 毫秒
1.
Based on a sample of 237 live births recorded over a period of 30 years, a tendency for longer interbirth intervals following the birth of daughters than sons was recognized, in the provisioned Arashiyama troop of Japanese macaques. This may indicate that female infants were more costly to produce than male infants. This tendency seemed to be independent of a mother’s rank.  相似文献   
2.
Over a 30-year period from 1954 to 1983, 975 live births were recorded for Japanese macaque females at the Iwatayama Monkey Park, Arashiyama, Japan. Excluding unknown birth dates, primiparous mothers gave birth to 185 infants (182 cases with age of mother known) and multiparous mothers gave birth to 723 infants (603 cases with age of mother known). The peak month of birth was May with 52.3% of the total births occurring during the period. Multiparous females who had not given birth the previous year did so earlier than multiparous females who had given birth the previous year and also earlier than primiparous females. Among the females who had given birth the previous year, females whose infant had died gave birth earlier than females who had reared an infant the previous year. The offspring sex ratio (1:0.97) was not significantly different from 1:1, and revealed no consistent association with mother's age. Age-fecundity exhibited a humped curve. The annual birth rate was low at the age of 4 years but increased thereafter, ranging between 46.7% and 69.0%, at between 5 and 19 years of age, but again decreased for females between 20 and 25 years of age. Some old females displayed clear reproductive senescence. The infant mortality within the first year of age was quite low (10.3%) and the neonatal (less than 1 month old) mortality rate accounted for 49.0% of all infant deaths. There was no significant difference between the mortality rates of male and female infants. A female's rank-class had no apparent effect on the annual birth rate, infant mortality, and offspring sex ratio. These long-term data are compared with those from other primate populations.  相似文献   
3.
It has been known in amphibians and starfishes that a cytoplasmic factor called maturation-promoting factor (MPF), produced in maturing oocytes under the influence of the maturation-inducing hormones, can induce germinal vesicle breakdown (GVBD) and the subsequent process of meiotic maturation. The present study revealed that injection of cytoplasm of maturing starfish oocytes (starfish MPF) into immature sea cucumber oocytes brought about maturation of the recipients. Amphibian MPF obtained from mature oocytes of Xenopus laevis or Bufo bufo was found to induce maturation of starfish oocytes following injection. Cytoplasm taken from cleaving starfish blastomeres induced maturation when injected into immature starfish oocytes. The maturation-inducing activity of cytoplasm of starfish blastomeres changed along with the mitotic cell cycle during 1- to 4-cell stages so far tested and reached a peak just before cleaving. Furthermore, an extract of mammalian cultured cells, CHO or V-79, synchronized in M phase, induced GVBD in starfish oocytes following injection, whereas S phase extract had little activity. These facts suggest that MPF generally brings about nuclear membrane breakdown in both meiosis and mitosis, and that the nature of MPF is very similar among vertebrates and invertebrates.  相似文献   
4.
5.
6.
Two sublines of the benzpyrene-induced mouse hepatoma cell line, G-1 and G-5, showed low and high metastatic ability, respectively, to the lung. We produced a polyclonal antibody (pAb) against RAE-1alpha. Five isoforms of RAE-1 have been identified to date, and this pAb recognized all isoforms and was named anti-"pan" RAE-1 pAb. The level of RAE-1 was approximately 5-fold higher in G-5 than in G-1, which was almost RAE-1-negative, as determined using anti-pan RAE-1 pAb. Expression levels of other markers including MHC class I (MHC-I) and Qa-1b were very low and indistinguishable in these sublines. NK-mediated cytotoxicity was determined with these sublines; G-5 was highly susceptible to NK-mediated cytolysis, while G-1 was relatively resistant. The NK-mediated G-5 > G-1 killing profile was diminished if the G-5 cells were pretreated with F(ab)(2)(') of anti-pan RAE-1 pAb. G-1, when transfected with Rae-1alpha cDNA, acquired NK-responsiveness similar to that of G-5. These and additional data using mouse cell lines with low MHC-I levels and various RAE-1 levels also demonstrated that RAE-1 level is critically associated with NK-susceptibility in tumor cells.  相似文献   
7.
8.
We expressed the Arabidopsis thaliana gene for phytochelatin synthase (PCS(At)) in Mesorhizobium huakuii subsp. rengei B3, a microsymbiont of Astragalus sinicus, a legume used as manure. The PCS(At) gene was expressed under the control of the nifH promoter, which regulates the nodule-specific expression of the nifH gene. The expression of the PCS(At) gene was demonstrated in free-living cells under low-oxygen conditions. Phytochelatin synthase (PCS) was expressed and catalyzed the synthesis of phytochelatins [(gamma-Glu-Cys)(n)-Gly; PCs] in strain B3. A range of PCs, with values of n from 2 to 7, was synthesized by cells that expressed the PCS(At) gene, whereas no PCs were found in control cells that harbored the empty plasmid. The presence of CdCl(2) activated PCS and induced the synthesis of substantial amounts of PCs. Cells that contained PCs accumulated 36 nmol of Cd(2+)/mg (dry weight) of cells. The expression of the PCS(At) gene in M. huakuii subsp. rengei B3 increased the ability of cells to bind Cd(2+) approximately 9- to 19-fold. The PCS protein was detected by immunostaining bacteroids of mature nodules of A. sinicus containing the PCS(At) gene. When recombinant M. huakuii subsp. rengei B3 established the symbiotic relationship with A. sinicus, the symbionts increased Cd(2+) accumulation in nodules 1.5-fold.  相似文献   
9.
We assessed vaccine effectiveness (VE) against medically attended, laboratory-confirmed influenza in children 6 months to 15 years of age in 22 hospitals in Japan during the 2013–14 season. Our study was conducted according to a test-negative case-control design based on influenza rapid diagnostic test (IRDT) results. Outpatients who came to our clinics with a fever of 38°C or over and had undergone an IRDT were enrolled in this study. Patients with positive IRDT results were recorded as cases, and patients with negative results were recorded as controls. Between November 2013 and March 2014, a total of 4727 pediatric patients (6 months to 15 years of age) were enrolled: 876 were positive for influenza A, 66 for A(H1N1)pdm09 and in the other 810 the subtype was unknown; 1405 were positive for influenza B; and 2445 were negative for influenza. Overall VE was 46% (95% confidence interval [CI], 39–52). Adjusted VE against influenza A, influenza A(H1N1)pdm09, and influenza B was 63% (95% CI, 56–69), 77% (95% CI, 59–87), and 26% (95% CI, 14–36), respectively. Influenza vaccine was not effective against either influenza A or influenza B in infants 6 to 11 months of age. Two doses of influenza vaccine provided better protection against influenza A infection than a single dose did. VE against hospitalization influenza A infection was 76%. Influenza vaccine was effective against influenza A, especially against influenza A(H1N1)pdm09, but was much less effective against influenza B.  相似文献   
10.
The human ATP‐binding cassette (ABC) transporter superfamily consists of 48 integral membrane proteins that couple the action of ATP binding and hydrolysis to the transport of diverse substrates across cellular membranes. Defects in 18 transporters have been implicated in human disease. In hundreds of cases, disease phenotypes and defects in function can be traced to nonsynonymous single nucleotide polymorphisms (nsSNPs). The functional impact of the majority of ABC transporter nsSNPs has yet to be experimentally characterized. Here, we combine experimental mutational studies with sequence and structural analysis to describe the impact of nsSNPs in human ABC transporters. First, the disease associations of 39 nsSNPs in 10 transporters were rationalized by identifying two conserved loops and a small α‐helical region that may be involved in interdomain communication necessary for transport of substrates. Second, an approach to discriminate between disease‐associated and neutral nsSNPs was developed and tailored to this superfamily. Finally, the functional impact of 40 unannotated nsSNPs in seven ABC transporters identified in 247 ethnically diverse individuals studied by the Pharmacogenetics of Membrane Transporters consortium was predicted. Three predictions were experimentally tested using human embryonic kidney epithelial (HEK) 293 cells stably transfected with the reference multidrug resistance transporter 4 and its variants to examine functional differences in transport of the antiviral drug, tenofovir. The experimental results confirmed two predictions. Our analysis provides a structural and evolutionary framework for rationalizing and predicting the functional effects of nsSNPs in this clinically important membrane transporter superfamily.  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