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   895篇
  免费   21篇
  国内免费   5篇
  2022年   1篇
  2021年   5篇
  2020年   6篇
  2019年   5篇
  2018年   6篇
  2017年   3篇
  2016年   9篇
  2015年   12篇
  2014年   9篇
  2013年   31篇
  2012年   13篇
  2011年   14篇
  2010年   10篇
  2009年   20篇
  2008年   24篇
  2007年   23篇
  2006年   40篇
  2005年   24篇
  2004年   32篇
  2003年   28篇
  2002年   28篇
  2001年   31篇
  2000年   20篇
  1999年   23篇
  1998年   51篇
  1997年   36篇
  1996年   39篇
  1995年   21篇
  1994年   39篇
  1993年   32篇
  1992年   30篇
  1991年   39篇
  1990年   20篇
  1989年   20篇
  1988年   34篇
  1987年   22篇
  1986年   14篇
  1985年   21篇
  1984年   24篇
  1983年   7篇
  1982年   13篇
  1981年   15篇
  1980年   9篇
  1979年   5篇
  1978年   2篇
  1977年   4篇
  1972年   7篇
排序方式: 共有921条查询结果,搜索用时 15 毫秒
1.
The complete or partial loss of shattering ability occurred independently during the domestication of several crops. Therefore, the study of this trait can provide an understanding of the link between phenotypic and molecular convergent evolution. The genetic dissection of ‘pod shattering’ in Phaseolus vulgaris is achieved here using a population of introgression lines and next‐generation sequencing techniques. The ‘occurrence’ of the indehiscent phenotype (indehiscent versus dehiscent) depends on a major locus on chromosome 5. Furthermore, at least two additional genes are associated with the ‘level’ of shattering (number of shattering pods per plant: low versus high) and the ‘mode’ of shattering (non‐twisting versus twisting pods), with all of these loci contributing to the phenotype by epistatic interactions. Comparative mapping indicates that the major gene identified on common bean chromosome 5 corresponds to one of the four quantitative trait loci for pod shattering in Vigna unguiculata. None of the loci identified comprised genes that are homologs of the known shattering genes in Glycine max. Therefore, although convergent domestication can be determined by mutations at orthologous loci, this was only partially true for P. vulgaris and V. unguiculata, which are two phylogenetically closely related crop species, and this was not the case for the more distant P. vulgaris and G. max. Conversely, comparative mapping suggests that the convergent evolution of the indehiscent phenotype arose through mutations in different genes from the same underlying gene networks that are involved in secondary cell‐wall biosynthesis and lignin deposition patterning at the pod level.  相似文献   
2.
A. S?ber 《Photosynthetica》1997,34(4):599-603
A positive correlation was found between steady state values of hydraulic (L pA) and stomatal conductance (g s) of French bean leaves: both were lower in the dark than in the light and lower in water-deficient plants than in the well-watered ones. The relative rate of stomatal opening after a pressure rise in the xylem was also positively related to L pA. The L pA and g s were both related to the maximal photosynthetic rate at saturating CO2 concentrations. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   
3.
4.
以菜豆黄化幼苗作为试验材料,探讨了铅(Pb)或PEG(聚乙二醇)胁迫下交替呼吸途径在植物转绿过程中对叶绿素含量以及叶绿素荧光特性的影响,以阐明逆境胁迫下植物交替呼吸途径的生理学作用。结果显示:(1)与菜豆黄化幼苗正常转绿过程(对照)相比,Pb或PEG胁迫导致菜豆黄化幼苗的叶绿素含量积累延迟,使叶片PSⅡ潜在最大光化学量子效率(Fv/Fm)、光适应下最大光化学效率(Fv′/Fm′)、PSⅡ光适应下实际光化学效率(Y(Ⅱ))和光化学荧光猝灭系数(qP)显著下降,而非光化学猝灭系数(NPQ)则显著增加。(2)在菜豆黄化幼苗转绿过程中,Pb或PEG胁迫导致其交替呼吸途径容量较对照均显著上升。(3)Pb或PEG胁迫下,交替呼吸途径抑制剂[水杨基氧肟酸(SHAM,1 mmol/L)]使菜豆黄化幼苗转绿过程中叶绿素含量、Fv/FmFv′/Fm′、Y(Ⅱ)和qP进一步下降, NPQ却进一步增加,说明抑制交替呼吸途径会加剧Pb或PEG胁迫对PSⅡ反应中心活性的进一步抑制,使还原力积累加剧,造成热耗散进一步增加。研究表明,Pb或PEG胁迫均显著降低了菜豆黄化幼苗PSⅡ对光能的利用率,进而阻碍了菜豆黄化幼苗转绿进程;交替呼吸途径有助于在胁迫条件下缓解PSⅡ的过度还原,可能在一定程度上缓解了Pb或PEG胁迫对其转绿进程的阻碍作用。  相似文献   
5.
为了探讨UV-B辐射引起的Rubisco含量降低的可能机制,研究了两个绿豆品种(秦豆-20和中绿-1)幼苗在UV-B辐射下叶片Rubisco含量、蛋白水解酶活性和H2O2含量的变化.结果表明:UV-B辐射显著加速了两个绿豆品种幼苗叶片H2O2含量和蛋白水解酶活性上升,使Rubiscco含量下降.秦豆-20品种在UV-B辐射下H2O2含量和蛋白水解酶活性的上升程度明显大于中绿-1,相应其Rubisco含量的下降程度也大于中绿-1.抗坏血酸处理能明显降低UV-B辐射下两品种幼苗叶片H2O2含量,同时明显抑制蛋白水解酶活性的上升及Rubisco含量的下降.结果说明UV-B辐射诱导Rubisco含量的降低可能通过提高H2O2水平从而加强蛋白水解酶系统的活化而加速了Rubisco的降解.  相似文献   
6.
Efforts to develop molecular tools for genetic analysis and breeding of common bean in the tropics are still limited. The number of microsatellite markers available for the crop is small compared to other crops of similar social and economic importance. As part of a project to broaden the use of molecular tools in bean breeding, a genomic library enriched for AG/TC repeat sequences was constructed for Phaseolus vulgaris. Twenty microsatellite markers were initially developed and 10 were characterized using a panel of 85 representative accessions of the bean gene bank. The number of alleles per marker ranged from three to 10. The polymorphism information content (PIC) varied from 0.23 to 0.80. The results indicate that the new markers can be readily used in genetically analysis of common bean.  相似文献   
7.
Adventitious rooting contributes to efficient phosphorus acquisition by enhancing topsoil foraging. However, metabolic investment in adventitious roots may retard the development of other root classes such as basal roots, which are also important for phosphorus acquisition. In this study we quantitatively assessed the potential effects of adventitious rooting on basal root growth and whole plant phosphorus acquisition in young bean plants. The geometric simulation model SimRoot was used to dynamically model root systems with varying architecture and C availability growing for 21 days at 3 planting depths in 3 soil types with contrasting nutrient mobility. Simulated root architectures, tradeoffs between adventitious and basal root growth, and phosphorus acquisition were validated with empirical measurements. Phosphorus acquisition and phosphorus acquisition efficiency (defined as mol phosphorus acquired per mol C allocated to roots) were estimated for plants growing in soil in which phosphorus availability was uniform with depth or was greatest in the topsoil, as occurs in most natural soils. Phosphorus acquisition and acquisition efficiency increased with increasing allocation to adventitious roots in stratified soil, due to increased phosphorus depletion of surface soil. In uniform soil, increased adventitious rooting decreased phosphorus acquisition by reducing the growth of lateral roots arising from the tap root and basal roots. The benefit of adventitious roots for phosphorus acquisition was dependent on the specific respiration rate of adventitious roots as well as on whether overall C allocation to root growth was increased, as occurs in plants under phosphorus stress, or was lower, as observed in unstressed plants. In stratified soil, adventitious rooting reduced the growth of tap and basal lateral roots, yet phosphorus acquisition increased by up to 10% when total C allocation to roots was high and adventitious root respiration was similar to that in basal roots. With C allocation to roots decreased by 38%, adventitious roots still increased phosphorus acquisition by 5%. Allocation to adventitious roots enhanced phosphorus acquisition and efficiency as long as the specific respiration of adventitious roots was similar to that of basal roots and less than twice that of tap roots. When adventitious roots were assigned greater specific respiration rates, increased adventitious rooting reduced phosphorus acquisition and efficiency by diverting carbohydrate from other root types. Varying the phosphorus diffusion coefficient to reflect varying mobilities in different soil types had little effect on the value of adventitious rooting for phosphorus acquisition. Adventitious roots benefited plants regardless of basal root growth angle. Seed planting depth only affected phosphorus uptake and efficiency when seed was planted below the high phosphorus surface stratum. Our results confirm the importance of root respiration in nutrient foraging strategies, and demonstrate functional tradeoffs among distinct components of the root system. These results will be useful in developing ideotypes for more nutrient efficient crops.  相似文献   
8.
Snap bean fields in 12 of the 25 governorates of Egypt were surveyed to determine the distribution and taxonomy of snap bean-nodulating rhizobia. Nodulation rates in the field were very low, indicating that Egyptian soils do not have sufficient numbers of snap bean-compatible Rhizobium spp. A total of 87 rhizobial isolates were assayed on the most commonly grown cultivars in order to identify the most effective strains. The five most effective isolates (R11, R13, R28, R49 and R52) were fast-growing and utilized a wide range of carbon and nitrogen sources. A phylogenetic assignment of these strains by analysis of the 16S ribosomal RNA gene suggested that all fell within the Rhizobium etliRhizobium leguminosarum group. Strains R11, R49 and R52 all clustered with other identified R. etli strains, while strains R13 and R28 were more distinct. The distinctness of R13 and R28 was supported by physiological characteristics, such as their ability to utilize citrate, erythritol, dulcitol and lactate. Strains R13 and R28 also yielded the highest plant nitrogen content of all isolates.The highly effective strains isolated in this study, in particular strains R13 and R28, are promising candidates for improving crop yields. The data also suggested that these two strains represented a novel sub-group within the R. etli–R. leguminosarum group. As snap bean is a crop of great economic value to Egypt, the identification of highly effective rhizobial strains adapted to Egyptian soils, such as strains R13 and R28, is of great interest.  相似文献   
9.
Summary Yield stability of determinate and indeterminate dry bean (Phaseolus vulgaris L.) cultivars was compared using regression of genotypic performance on environmental means. Yields of 28 dry bean cultivars differing in plant growth habit and commercial class designation were obtained from 42 Michigan performance nurseries over the 6 year period 1980 to 1985. The determinate type I large-seeded kidney and cranberry bean cultivars had below-average seed yield and large mean square deviations from regression. Lower yielding determinate small-seeded navy cultivars had low deviation mean square values, while higher yielding determinate navy cultivars had correspondingly higher mean square deviations from regression. Although seed yield of cultivars with an indeterminate growth habit was greater than determinate cultivars, prostrate type III indeterminate cultivars had deviation mean square values equivalent to those of large-seeded determinate cultivars. The erect, short vine type II indeterminate cultivars (architypes) had greater than average seed yields and minimum deviations from regression. Compared with other plant types, the architype group showed a greater yield response to more productive environments, with regression coefficient values significantly greater than unity. These results indicate that the type II growth habit offers the breeder the best opportunity of obtaining greater seed yield without incurring loss of yield stability as occurs with the type I and type III growth habits. Since the dry bean cultivars utilized in this study represent two distinct centers of domestication, the regression analysis suggests that cultivars from the predominant genetic center demonstrate more yield stability. A non-significant rank correlation coefficient between the combined and separate analyses for deviation mean square values of large-seeded cultivars implies that commercial dry bean classes should be compared separately based on center of domestication.Contributions from Michigan Bean Commission, Michigan Bean Shippers Assoc. and Michigan Agric. Exp. Sta., Michigan Agric. Exp. Sta. Journal Article No. 11986  相似文献   
10.
Measurements related to gas exchange and chlorophyll fluorescence emission were taken from healthy and diseased bean leaves with rust, angular leaf spot, and anthracnose during lesion development for each disease. The experiments were performed at different temperatures of plant incubation, and using two bean cultivars. The main effect of temperature of plant incubation was in disease development. There was no significant difference between cultivars in relation to disease development and in magnitude of physiological alterations when disease severity was the same for each cultivar. These diseases reduced the net photosynthetic rate and increased the dark respiration of infected leaves after the appearance of visible symptoms and the differences between healthy and diseased leaves increased with disease development. The transpiration rate and stomatal conductance were stable during the monocycle of rust, however, these two variables decreased in leaves with angular leaf spot and anthracnose beginning with symptom appearance and continuing until lesion development was complete. Carboxylation resistance was probably the main factor related to reduction of photosynthetic rate of the apparently healthy area of leaves with rust and angular leaf spot. Reduction of the intercellular concentration of CO2, due to higher stomatal resistance, was probably the main factor for leaves with anthracnose. Chlorophyll fluorescence assessments suggested that there was no change in electron transport capacity and generation of ATP and NADPH in apparently healthy areas of diseased leaves, but decreases in chlorophyll fluorescence emission occurred on visibly lesioned areas for all diseases. Minimal fluorescence was remarkably reduced in leaves with angular leaf spot. Maximal fluorescence and optimal quantum yield of photosystem II of leaves were reduced for all three diseases. Bean rust, caused by a biotrophic pathogen, induced less damage to the regulation mechanisms of the physiological processes of the remaining green area of diseased leaves than did bean angular leaf spot or anthracnose, caused by hemibiotrophic pathogens. The magnitude of photosynthesis reduction can be related to the host–pathogen trophic relationships.  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