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   181篇
  免费   30篇
  国内免费   25篇
  2023年   7篇
  2022年   6篇
  2021年   9篇
  2020年   11篇
  2019年   15篇
  2018年   7篇
  2017年   7篇
  2016年   13篇
  2015年   11篇
  2014年   10篇
  2013年   12篇
  2012年   9篇
  2011年   5篇
  2010年   6篇
  2009年   9篇
  2008年   5篇
  2007年   12篇
  2006年   8篇
  2005年   5篇
  2004年   9篇
  2003年   4篇
  2002年   6篇
  2001年   3篇
  2000年   4篇
  1999年   4篇
  1997年   2篇
  1996年   5篇
  1995年   6篇
  1994年   1篇
  1993年   3篇
  1992年   2篇
  1991年   4篇
  1990年   1篇
  1989年   2篇
  1988年   1篇
  1987年   1篇
  1986年   3篇
  1983年   1篇
  1982年   1篇
  1981年   1篇
  1980年   1篇
  1979年   1篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
排序方式: 共有236条查询结果,搜索用时 29 毫秒
1.
Thermoanaerobacter brockiifermented serine to acetate and ethanol. It oxidized leucine to isovalerate, isoleucine to 2-methylbutyrate, and valine to isobutyrate only in the presence of thiosulfate, or when co-cultured withMethanobacteriumsp. This oxidative deamination was rendered thermodynamically possible by the ability ofT. brockiito reduce thiosulfate to sulfide or the transfer of reducing equivalents to the hydrogenotrophic methanogen. The results suggest thatT. brockiimay be of ecological significance in thermal environments in the turnover of amino acids, especially with thiosulfate or H2-utilizing methanogens are present.  相似文献   
2.
微生物对昆虫行为的影响研究进展   总被引:1,自引:0,他引:1  
在漫长的进化过程中,微生物与昆虫形成了多种形式的互作关系。微生物的广泛分布为与昆虫接触并影响昆虫的行为提供了背景条件。为了深入探究微生物影响昆虫行为的现象和机制,本文综述了微生物影响昆虫行为方面的研究进展。微生物通过产生可被昆虫识别的化学信号物质、参与昆虫或寄主植物信息化合物的合成等方式可影响昆虫对其寄主的定位和选择。在对昆虫种内和种间关系的研究中也发现微生物起着非常重要的作用。通过改变昆虫性信息素等方式,微生物还能影响到昆虫的繁殖行为;除此之外,微生物合成或参与合成的信息化合物还可以影响昆虫的社会性和聚集等行为。根据当前对微生物影响昆虫行为方面的研究现状,我们建议可进一步研究:(1)微生物影响昆虫行为的过程中,影响昆虫行为的信息化合物是如何产生的?(2)微生物在影响昆虫行为的过程中是否涉及更多的物种间互作?(3)对于一些在特定时期可影响昆虫行为的共生微生物来说,宿主昆虫是如何获得并维持这些微生物的?  相似文献   
3.
核桃-大豆间作系统细根分布及地下竞争   总被引:7,自引:0,他引:7  
以晋西黄土区核桃-大豆间作系统为研究对象,采用分层挖掘法对核桃-大豆间作系统细根分布特征及地下竞争状况进行研究,旨在为该地区果农间作系统的高效可持续经营提供科学依据。结果表明:核桃细根在垂直方向上主要分布在0~40cm土层内,水平方向上55.7%的细根集中分布在距树行0.5~1.5m区域中;间作物大豆的根系在垂直方向上集中分布在0~20cm土层内,水平方向上根干重随距树行距离的增加呈增加趋势;在水平方向上距树行1.0~2.5m的区域是核桃和大豆地下种间竞争主要发生区,其中以1.5~2.0m区域的竞争最为剧烈。  相似文献   
4.
《植物生态学报》2016,40(6):604
Aims Root exudates have specialized roles in nutrient cycling and signal transduction between a root system and soil, as well as in plant responses to environmental stresses. They are the key regulators in the rhizosphere communications and can modify the biological and physical interactions between roots and soil organisms. Phytoremediation is an important measure to remove organic pollutants from contaminated soil, and root exudates are considered to be closely related to the mechanisms in the phytoremediation of soils contaminated by organic pollutants.This study was designed to determine the characteristics of root exudates in five Festuca species under the stress of benzo [α] pyrene (BaP) and to identify the effects of BaP on the organic compounds of low molecule weight in root exudates.Methods Five Festuca species, which had been tested to be tolerant to the BaP stress, were used in this study. A soil-cultivating test, with rhizobag technique, was conducted to investigate the effect of BaP concentration on the organic compounds of low molecule weight in root exudates at different growth stages (30-70 days). The BaP concentrations in the contaminated soils were set for 10.25 mg·kg-1, 20.37 mg·kg-1, 40.45 mg·kg-1, 80.24 mg·kg-1, and 161.74 mg·kg-1(denoted by T1, T2, T3, T4 and T5, respectively).Important findings The presence of vegetation enhanced the dissipation of BaP in soils. This effect was especially marked in treatment with F. arundinacea, followed sequentially by that of F. chelungkiangnica, F. rubra subsp. arctica and F. sinomutica; the dissipation of BaP in treatment with F. stapfiwas lowest during the entire experiment. The contents of soluble sugars, organic acids, and amino acids in root exudates were all increased by the BaP treatments. The contents of soluble sugars in root exudates increased notably at relatively low BaP levels (T1-T3) or in earlier stress stages (30-40 days), and declined at relatively high BaP levels (T4-T5) or in later stress stages (40-70 days), with highest values always occurring in the T3 treatments on day 50 of the experiments. In the five Festuca species, oxlic acid, acetic acid, lactic acid and malic acid are the main constituents of organic acids in root exudates, at greater than 97.34% in total in all treatments. However, there are traces of fumaric acid in the root exudates of Festuca species with stronger remediation potentials. When the contents of organic acids in root exudates reached the peak, the stronger the remediation potentials of plants were, the higher the concentrations of BaP would be to induce stress. Nineteen types of common amino acids were found in root exudates of Festuca and the proportion of total amino acids in root exudates remain stable under all the BaP stress treatments, albeit varying contents of the 19 types of amino acids under different BaP concentrations. The contents of all amino acid in root exudates increased with increasing BaP concentrations; especially, the contents of secreted threonine, serine, glycine and alanine increased significantly among the 19 types of amino acids and the differences were significant among all treatments with different BaP concentrations (p< 0.05). However, proline, hydroxyproline, and aspartic acid participated in the stress responses of plants almost in the form of additive or synergistic effects, and their contents in root exudates increased markedly with increasing BaP concentrations in soils; the differences among different treatments were significant (p< 0.05). The more constituents of amino acids there were in stress responses, the stronger the remediation potentials of plants would be. All these illustrate that the characteristics of root exudates in Festuca were closely related to their remediation potential under the BaP stress. The greater the remediation potentials were, the more organic compounds of low molecular weight there were and the more complex those compounds would be. Moreover, they also showed a stronger environment adaptability and physiological plasticity.  相似文献   
5.
A major challenge in understanding the response of populations to climate change is to separate the effects of local drivers acting independently on specific populations, from the effects of global drivers that impact multiple populations simultaneously and thereby synchronize their dynamics. We investigated the environmental drivers and the demographic mechanisms of the widespread decline in marine survival rates of Atlantic salmon (Salmo salar) over the last four decades. We developed a hierarchical Bayesian life cycle model to quantify the spatial synchrony in the marine survival of 13 large groups of populations (called stock units, SU) from two continental stock groups (CSG) in North America (NA) and Southern Europe (SE) over the period 1971–2014. We found strong coherence in the temporal variation in postsmolt marine survival among the 13 SU of NA and SE. A common North Atlantic trend explains 37% of the temporal variability of the survivals for the 13 SU and declines by a factor of 1.8 over the 1971–2014 time series. Synchrony in survival trends is stronger between SU within each CSG. The common trends at the scale of NA and SE capture 60% and 42% of the total variance of temporal variations, respectively. Temporal variations of the postsmolt survival are best explained by the temporal variations of sea surface temperature (SST, negative correlation) and net primary production indices (PP, positive correlation) encountered by salmon in common domains during their marine migration. Specifically, in the Labrador Sea/Grand Banks for populations from NA, 26% and 24% of variance is captured by SST and PP, respectively and in the Norwegian Sea for populations from SE, 21% and 12% of variance is captured by SST and PP, respectively. The findings support the hypothesis of a response of salmon populations to large climate‐induced changes in the North Atlantic simultaneously impacting populations from distant continental habitats.  相似文献   
6.
Population changes and shifts in geographic range boundaries induced by climate change have been documented for many insect species. On the basis of such studies, ecological forecasting models predict that, in the absence of dispersal and resource barriers, many species will exhibit large shifts in abundance and geographic range in response to warming. However, species are composed of individual populations, which may be subject to different selection pressures and therefore may be differentially responsive to environmental change. Asystematic responses across populations and species to warming will alter ecological communities differently across space. Common garden experiments can provide a more mechanistic understanding of the causes of compositional and spatial variation in responses to warming. Such experiments are useful for determining if geographically separated populations and co‐occurring species respond differently to warming, and they provide the opportunity to compare effects of warming on fitness (survivorship and reproduction). We exposed colonies of two common ant species in the eastern United States, Aphaenogaster rudis and Temnothorax curvispinosus, collected along a latitudinal gradient from Massachusetts to North Carolina, to growth chamber treatments that simulated current and projected temperatures in central Massachusetts and central North Carolina within the next century. Regardless of source location, colonies of A. rudis, a keystone seed disperser, experienced high mortality and low brood production in the warmest temperature treatment. Colonies of T. curvispinosus from cooler locations experienced increased mortality in the warmest rearing temperatures, but colonies from the warmest locales did not. Our results suggest that populations of some common species may exhibit uniform declines in response to warming across their geographic ranges, whereas other species will respond differently to warming in different parts of their geographic ranges. Our results suggest that differential responses of populations and species must be incorporated into projections of range shifts in a changing climate.  相似文献   
7.
环境微生物群落结构与功能多样性研究方法   总被引:6,自引:0,他引:6  
微生物群落的结构及群落内种间相互作用是影响其生态功能的决定性因素。尽管微生物群落是地球生物化学循环的主要驱动者,但是由于传统的微生物培养方法只能分离约1%10%的环境微生物,对复杂的环境微生物群落结构和功能多样性了解甚少。元基因组学、单细胞分析和群落遗传学等方法的出现,及其与微生物学的交叉融合,使得人们能够从微生物群落组成、物种功能、种间相互作用和预测模型等方面分析微生物群落。重点综述了元基因组学、单细胞分析和群落遗传学等方法及其在环境微生物群落结构和功能多样性中的应用进展。  相似文献   
8.
《Anthrozo?s》2013,26(2):150-165
Abstract

This paper describes a field study on the effects of attachment styles on the subjective well-being of institutionalized older persons after participating in a pet visitation program. We compared how attachment style (i.e., secure, anxious ambivalent, dismissive avoidant, and fearful avoidant) moderated the impact of a dog visitation program in 52 elderly residents of an assisted-living facility. Controlling for pre-visitation mood, the results revealed that the secure style related to increases in positive mood after interacting with the dogs. The anxious ambivalent style related to increases in positive mood and decreases in ratings of depression. Most importantly, the fearful avoidant style related to increases in depression after interacting with the dogs. The results highlight the notion that not all participants benefit from taking part in pet visitation programs. Theoretically, this study presents preliminary evidence for the relevance of attachment styles in understanding human–pet interactions.  相似文献   
9.
10.
Protein aggregation is a widespread phenomenon with important implications in many scientific areas. Although amyloid formation is typically considered as detrimental, functional amyloids that perform physiological roles have been identified in all kingdoms of life. Despite their functional and pathological relevance, the structural details of the majority of molecular species involved in the amyloidogenic process remains elusive. Here, we explore the application of AlphaFold, a highly accurate protein structure predictor, in the field of protein aggregation. While we envision a straightforward application of AlphaFold in assisting the design of globular proteins with improved solubility for biomedical and industrial purposes, the use of this algorithm for predicting the structure of aggregated species seems far from trivial. First, in amyloid diseases, the presence of multiple amyloid polymorphs and the heterogeneity of aggregation intermediates challenges the “one sequence, one structure” paradigm, inherent to sequence-based predictions. Second, aberrant aggregation is not the subject of positive selective pressure, precluding the use of evolutionary-based approaches, which are the core of the AlphaFold pipeline. Instead, amyloid polymorphism seems to be constrained by the need for a defined structure-activity relationship in functional amyloids. They may thus provide a starting point for the application of AlphaFold in the amyloid landscape.  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