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   257篇
  免费   11篇
  国内免费   9篇
  277篇
  2023年   2篇
  2021年   4篇
  2020年   2篇
  2017年   3篇
  2015年   2篇
  2014年   10篇
  2013年   12篇
  2012年   9篇
  2011年   21篇
  2010年   7篇
  2009年   7篇
  2008年   6篇
  2007年   13篇
  2006年   8篇
  2005年   7篇
  2004年   11篇
  2003年   10篇
  2002年   8篇
  2001年   5篇
  2000年   15篇
  1999年   4篇
  1998年   3篇
  1997年   2篇
  1995年   2篇
  1992年   4篇
  1991年   8篇
  1990年   3篇
  1989年   6篇
  1988年   6篇
  1987年   6篇
  1985年   4篇
  1984年   3篇
  1983年   2篇
  1982年   2篇
  1981年   3篇
  1980年   3篇
  1979年   2篇
  1978年   3篇
  1977年   3篇
  1976年   5篇
  1975年   2篇
  1974年   2篇
  1973年   4篇
  1971年   2篇
  1970年   8篇
  1969年   5篇
  1967年   2篇
  1957年   3篇
  1953年   1篇
  1935年   1篇
排序方式: 共有277条查询结果,搜索用时 9 毫秒
11.
Removal of the micronuclei of Paramecium tetraurelia and Paramecium jenningsi by micropipetting generates amicronucleate cell lines. These cell lines go through a period of growth depression for several dozen fissions, but they gradually recover. Amicronucleate cells in the depression period characteristically exhibit abnormal oral development, particularly reduction in the length of the buccal cavity and an abnormal pattern of the oral membranelles. To test the notion that the macronucleus is involved in the recovery of amicronucleate cell lines, DNA demethylation drugs were administered to amicronucleates in the depression period. After at least 4 fissions, the treated amicronucleates were assessed for their progress in recovery by scoring the proportion of cells with normal oral membranelles. Cvtidine analogues which demethylate cytosine specifically at the 5 position, namely 5-azacytidine, 5-aza-2'- deoxycytidine and 5-fluoro-2'-deoxycytidine. promoted recovery of the amicronucleates. Cytidine, 6-azacytidine, 2'-fluoro-2'-deoxy-cytidine and cytosine-β-D-arabinofuranoside did not. These results suggest that (i) 5-methylcytosine is present in the macronucleus of these Paramecium species, probably in small amounts and (ii) recovery of amicronucleates involves demethylation of macronuclear DNA. This implies that in normal cells the micronuclei are involved in maintaining the macronuclear DNA in a methylated state and hence the inactivation of the macronuclear sequences that are to be employed for stomatogenic recovery. A general mechanism for the control of gene expression may therefore be employed for the regulation of specific sequences.  相似文献   
12.
13.
14.
15.
This paper reports the isolation and characterization of 24 polymorphic microsatellite markers in an important tropical timber species, Koompassia malaccensis (Leguminosae). The primers were designed from a genomic library enriched for dinucleotide (CT) repeats and screened on 24 samples from a natural population. The number of alleles detected per locus ranged from two to 13 while the observed heterozygosity ranged from 0.042 to 1.000. Significant departure from Hardy–Weinberg equilibrium (P < 0.05) was detected in two loci. These microsatellite markers were tested across 13 timber species of the same family. The amplification success appeared to be associated with taxonomy classification at the genus but not subfamily levels.  相似文献   
16.
Individual cells are basic units of life. Despite extensive efforts to characterize the cellular heterogeneity of different organisms, cross-species comparisons of landscape dynamics have not been achieved. Here, we applied single-cell RNA sequencing (scRNA-seq) to map organism-level cell landscapes at multiple life stages for mice, zebrafish and Drosophila. By integrating the comprehensive dataset of > 2.6 million single cells, we constructed a cross-species cell landscape and identified signatures and common pathways that changed throughout the life span. We identified structural inflammation and mitochondrial dysfunction as the most common hallmarks of organism aging, and found that pharmacological activation of mitochondrial metabolism alleviated aging phenotypes in mice. The cross-species cell landscape with other published datasets were stored in an integrated online portal—Cell Landscape. Our work provides a valuable resource for studying lineage development, maturation and aging.  相似文献   
17.
Indirect enzyme immunoassay based on immobilized conjugate of aflatoxin B1 carboxymethyloxime with bovine serum albumin and polyclonal rabbit antibodies allows determining aflatoxin B1 with a low relative cross-reactivity against aflatoxin B2, G1, G2, M1, B2a and G2a and sterigmatocystin (15.5, 15.5, 1.7, 1.0, 0.03, 0.03 and 0.01%, respectively) with a sensitivity of 0.04 ng per well or 4.0 ng per ml organic solvent.  相似文献   
18.
Ochratoxin A was quantitatively monitored in grain extracts by indirect solid-phase enzyme immunoassay with the use of an immobilized conjugate of the toxin with gelatin and polyclonal rabbit antibodies raised against the ochratoxin A-BSA conjugate. This monitoring found that 1.7 to 18.5% of the samples were contaminated with the toxin at a concentration of 25.9-291.7 micrograms/kg. An analysis of forage grain found ochratoxin A at concentrations of 440-3250 micrograms/kg.  相似文献   
19.
The tissue inhibitor of metalloproteinases-3 (TIMP3) is a multifunctional protein tightly associated with the extracellular matrix (ECM). A specific type of mutation in TIMP3 which results in potentially unpaired cysteine residues at the C-terminus of the protein has been shown to cause Sorsby fundus dystrophy (SFD), an autosomal dominant retinopathy of late onset. An early finding in SFD is a striking accumulation of protein and lipid material in Bruch's membrane, a multilayered ECM structure located between the choroid and the RPE. To study the molecular mechanisms underlying SFD pathology, we recently generated two mouse lines, one deficient in Timp3 (Timp3(-/-)) and one carrying an SFD-related mutation in the orthologous murine Timp3 gene (Timp3(S156C/S156C)). We now established immortalized fibroblast cells from the mutant mouse strains and provide evidence that the various cell lines display distinct morphological and physiological features that are dependent on the mutational status of the Timp3 protein in the secreted ECM. We show that matrix metalloproteinase (MMP) activity and inhibitory properties of Timp3 are not affected by the SFD-associated mutation. We further demonstrate that Timp3(S156C) protein accumulates in the ECM of the mutant fibroblast cells and that this accumulation is not due to a prolonged turnover rate of mutant vs. normal Timp3. We also show that the relative abundance of mutant and normal Timp3 in the ECM has no measurable effects on cellular phenotypes. Together, these findings suggest (i) a functional role of normal Timp3 in pathways determining cellular morphology and (ii) a loss of this particular function as a consequence of the Ser156Cys mutation. We therefore hypothesize that SFD pathogenesis is due to a loss-of-function mutation in TIMP3.  相似文献   
20.
SYNOPSIS. An ultrastructural investigation has been carried out on 180°-rotated ciliary meridians (inverted meridians) in Tetrahymena pyriformis temperature-sensitive mutant (molb/molb), syngen 1, strain B. The longitudinal, transverse and postciliary microtubular bands, the kinetodesmal fiber, and the parasomal sac, are shown to be disposed at a 180° angle to their normal positions or orientations. Other abnormalities are as folows: the first 2 basal bodies of the inverted meridian fail to organize into “couplets” and the inverted meridian intrudes into the anterior pole region; an extra longitudinal microtubular band is found in one of the cell lines.  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