全文获取类型
收费全文 | 517篇 |
免费 | 7篇 |
国内免费 | 15篇 |
出版年
2022年 | 5篇 |
2021年 | 8篇 |
2020年 | 11篇 |
2019年 | 10篇 |
2018年 | 12篇 |
2017年 | 5篇 |
2016年 | 7篇 |
2015年 | 13篇 |
2014年 | 30篇 |
2013年 | 24篇 |
2012年 | 16篇 |
2011年 | 28篇 |
2010年 | 19篇 |
2009年 | 28篇 |
2008年 | 30篇 |
2007年 | 30篇 |
2006年 | 23篇 |
2005年 | 26篇 |
2004年 | 32篇 |
2003年 | 18篇 |
2002年 | 17篇 |
2001年 | 9篇 |
2000年 | 11篇 |
1999年 | 11篇 |
1998年 | 10篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 8篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 6篇 |
排序方式: 共有539条查询结果,搜索用时 171 毫秒
451.
Peroxisomal enzyme activities in attached senescing leaves 总被引:4,自引:0,他引:4
Recently it has been demonstrated that detached leaves show glyoxysomal enzyme activities when incubated in darkness for several days. In this report glyoxylate-cycle enzymes have been detected in leaves of rice (Oryza sativa L.) and wheat (Triticum durum L.) from either naturally senescing or dark-treated plants. Isolated peroxisomes of rice and wheat show isocitrate lyase (EC 4.1.3.1), malate synthase (EC 4.1.3.2) and -oxidation activities. Leaf peroxisomes from dark-induced senescing leaves show glyoxylic-acid-cycle enzyme activities two to four times higher than naturally senescing leaves. The glyoxysomal activities detected in leaf peroxisomes during natural foliar senescence may represent a reverse transition of the peroxisomes into glyoxysomes.This work was supported by CNR Italy, special grant RAISA, subproject 2, paper no. 26. 相似文献
452.
The effect of pollen and senescent petals on the suppression of alfalfa (Medicago sativa L.) blossom blight (Sclerotinia sclerotiorum) by the mycoparasite Coniothyrium minitans was investigated. When incubated at 20°C for 39 h, germination of conidia of C. minitans and ascospores of S. sclerotiorum was 99.9 and 98.6%, respectively, in the presence of alfalfa pollen (9×104 pollen grains mL?1), whereas spore germination of both organisms was <0.5% in the absence of pollen (in water). In the presence of a commercial pollen product, Swiss? pollen granules (mainly bee pollen), germination was 99.6% for C. minitans and 98.3% for S. sclerotiorum when the pollen concentration was 1.0% (w/v). When the pollen concentration was reduced to 0.1% (w/v), germination was reduced to 13.0% for C. minitans and 10.8% for S. sclerotiorum. Tests on detached alfalfa florets showed that the colonization of alfalfa florets by S. sclerotiorum was significantly suppressed by C. minitans in the presence of pollen (1.0% Swiss? pollen granules), especially when C. minitans was inoculated 1-day before S. sclerotiorum. In vivo inoculation tests revealed that the efficacy of C. minitans in the protection of alfalfa pods from the infection by S. sclerotiorum was affected by the time at which C. minitans was applied. When C. minitans was applied on young blossoms of alfalfa at the anthesis stage, pod infection was 96.6% for the treatment of C. minitans+S. sclerotiorum and 99.6% for the treatment of S. sclerotiorum alone. However, when C. minitans was applied on senescent petals of alfalfa at the pod development stage, pod infection was 8.0% for the treatment of C. minitans+S. sclerotiorum compared to 90.8% for the treatment of S. sclerotiorum alone. These results suggest that timing of the application of C. minitans is critical for the mycoparasite to compete with S. sclerotiorum for the source of nutrients from pollen and senescent petals, and for its control of alfalfa blossom blight caused by S. sclerotiorum. 相似文献
453.
454.
Type C stay-green mutants are defined as being defective in the pathway of chlorophyll breakdown, which involves pheophorbide
a oxygenase (PAO), required for loss of green color. By analyzing senescence parameters, such as protein degradation, expression
of senescence-associated genes and loss of photosynthetic capacity, we demonstrate that JI2775, the green cotyledon (i) pea line used by Gregor Mendel to establish the law of genetics, is a true type C stay-green mutant. STAY-GREEN (SGR) had earlier been shown to map to the I locus. The defect in JI2775 is due to both reduced expression of SGR and loss of SGR protein function. Regulation of PAO through SGR had been proposed. By determining PAO protein abundance and
activity, we show that PAO is unaffected in JI2775. Furthermore we show that pheophorbide a accumulation in the mutant is independent of PAO. When silencing SGR expression in Arabidopsis
pao1 mutant, both pheophorbide a accumulation and cell death phenotype, typical features of pao1, are lost. These results confirm that SGR function within the chlorophyll catabolic pathway is independent and upstream of
PAO.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
455.
Reductions in reproductive performance with age have been predicted to result from a general deterioration of performance,
i.e. senescence. Variation among species in the onset and rate of this deterioration depends on the age-independent extrinsic
mortality rate. If few individuals reach a specific age, the strength of selection for mechanisms that retard senescence will
be reduced. The aim of this study was to investigate the age-dependent variation in two reproductive traits in a species,
the Treecreeper (Certhia familiaris), with a low between-year survival rate. Clutch size did not vary with age, but egg size decreased from the first to the
second breeding season. Compared with published age-dependent reductions in egg size, Treecreepers demonstrate the earliest
onset of senescence, but they also have the highest total mortality rate, corroborating the predictions from the evolutionary
theory of senescence. Production of eggs seems to be demanding for female Treecreepers, as egg size is also positively dependent
on ambient temperature, further stressing the vulnerability of this trait for small reductions in female performance. 相似文献
456.
457.
458.
Oxygen free radicals have a major impact on senescence of primary human cells. In replicative senescence, which is induced by uncapping of telomeres, the rate of telomere shortening is largely determined by telomere-specific accumulation of DNA damage induced by reactive oxygen species (ROS). More intense ROS-generating stressors can induce premature senescence via generation of telomere-independent DNA damage. Interestingly, ROS levels were also elevated when premature senescence was triggered by pathways downstream or independent of DNA damage. This has led to the suggestion that ROS generation could be a specific component of the signalling pathways inducing senescence. However, the available data are compatible with the concept that senescence is triggered as a DNA damage response. ROS appear to be involved as inducers of DNA damage rather than as specific signalling molecules. The upregulation of ROS production often seen in premature senescence might be related to retrograde response initiated by mitochondria. 相似文献
459.
Yi-Hsin Hsu Li-Jen Liao Chuan-Hang Yu Chun-Pin Chiang Jing-Ru Jhan Lien-Cheng Chang Yann-Jang Chen Pei-Jen Lou Jing-Jer Lin 《The Journal of biological chemistry》2010,285(29):22630-22638
Pituitary tumor transforming gene (PTTG1, securin) is involved in cell-cycle control through inhibition of sister-chromatid separation. Elevated levels of PTTG1 were found to be associated with many different tumor types that might be involved in late stage tumor progression. However, the role of PTTG1 in early stage of tumorigenesis is unclear. Here we utilized the adenovirus expression system to deliver PTTG1 into normal human fibroblasts to evaluate the role of PTTG1 in tumorigenesis. Expressing PTTG1 in normal human fibroblasts inhibited cell proliferation. Several senescence-associated (SA) phenotypes including increased SA-β-galactosidase activities, decreased bromodeoxyuridine incorporation, and increased SA-heterochromatin foci formation were also observed in PTTG1-expressing cells, indicating that PTTG1 overexpression induced a senescent phenotype in normal cells. Significantly, the PTTG1-induced senescence is p53-dependent and telomerase-independent, which is distinctively different from that of replicative senescence. The mechanism of PTTG1-induced senescence was also analyzed. Consistent with its role in regulating sister-chromatid separation, overexpression of PTTG1 inhibited the activation of separase. Consequently, the numbers of cells with abnormal nuclei morphologies and chromosome separations were increased, which resulted in activation of the DNA damage response. Thus, we concluded that PTTG1 overexpression in normal human fibroblasts caused chromosome instability, which subsequently induced p53-dependent senescence through activation of DNA-damage response pathway. 相似文献
460.
Many physiological and biochemical plant processes affected by salt stress trigger premature nodule senescence and decrease
their ability to fix nitrogen. The objective of this study was to evaluate the role of arbuscular mycorrhiza (AM) in moderating
salt-induced premature nodule senescence in Cajanus cajan (L.) Millsp. Greenhouse experiments were conducted in which the plants were exposed to salinity stress of 4, 6, and 8 dSm−1. Various parameters linked to nodule senescence were assessed at 80 days after sowing. Nodulation, leghemoglobin content,
and nitrogenase enzyme activity measured as acetylene-reducing activity (ARA) were evaluated. Two groups of antioxidant enzymes
were studied: (1) enzymes involved in the detoxification of O2− radicals and H2O2, namely, superoxide dismutase (SOD), catalase (CAT) and peroxidase (POX), and (2) enzymes that are important components of
the ascorbate glutathione pathway responsible for the removal of H2O2, namely, glutathione reductase (GR) and ascorbate peroxidase (APOX). Exposure of plants to salinity stress enhanced nodule
formation; however, nodule growth suffered remarkably and a marked decline in nodule biomass, relative permeability, and lipid
peroxidation was observed. Leghemoglobin content and ARA were reduced under saline conditions. AM significantly improved nodulation,
leghemoglobin content, and nitrogenase activity under salt stress. Activities of SOD, CAT, APOX, POX, and GR increased markedly
in mycorrhizal-stressed plants. A synthesis of the evidence obtained in this study suggests a correlation between enhanced
levels of antioxidant enzyme activities, reduced membrane permeability, reduced lipid peroxidation, and improved nitrogen-fixing
efficiency of AM plants under stressed and unstressed conditions. These factors could be responsible for the protective effects
of mycorrhiza against stress-induced premature nodule senescence. 相似文献