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   302篇
  免费   28篇
  国内免费   5篇
  2023年   4篇
  2022年   4篇
  2021年   5篇
  2020年   3篇
  2019年   7篇
  2018年   9篇
  2017年   8篇
  2016年   5篇
  2014年   16篇
  2013年   25篇
  2012年   9篇
  2011年   22篇
  2010年   10篇
  2009年   22篇
  2008年   20篇
  2007年   13篇
  2006年   12篇
  2005年   16篇
  2004年   14篇
  2003年   9篇
  2002年   8篇
  2001年   7篇
  2000年   4篇
  1999年   13篇
  1998年   5篇
  1997年   6篇
  1996年   3篇
  1995年   4篇
  1994年   4篇
  1993年   5篇
  1992年   2篇
  1989年   6篇
  1987年   2篇
  1986年   2篇
  1983年   3篇
  1982年   1篇
  1981年   1篇
  1980年   1篇
  1978年   1篇
  1977年   1篇
  1976年   3篇
  1975年   1篇
  1973年   2篇
  1970年   1篇
  1967年   2篇
  1965年   1篇
  1964年   1篇
  1963年   4篇
  1953年   3篇
  1952年   1篇
排序方式: 共有335条查询结果,搜索用时 15 毫秒
1.
Moment-based criteria for determining bioequivalence   总被引:1,自引:0,他引:1  
  相似文献   
2.
DNA分子标记在动物个体识别与亲权鉴定方面的应用   总被引:9,自引:0,他引:9  
自从DNA分子标记技术建立以来,各种DNA分子标记相继被广泛地应用于遗传图谱的构建,评估遗传多样性以及个体识别,亲权鉴定等方面,综述了利用DNA分子标记技术,进行动物个体识别与亲权鉴定的原理,研究进展,现状及其应用前景与存在的问题。  相似文献   
3.
Because of their mediating role in the stress response and potential effects on fitness, glucocorticoid (GC) hormones are increasingly used to assess the physiological costs of environmental and behavioral variation among wild vertebrates. Identifying the proximate causes of GC variation, however, is complicated by simultaneous exposure to multiple potentially stressful stimuli. Here, we use data from a partially provisioned social group of Sykes' monkeys to evaluate the effects of potential psychological and metabolic stressors on temporal and individual variation in fecal GC (fGC) excretion among 11 adult females. Despite high rates of agonism over provisioned foods fGCs declined during periods of high provisioning frequency when fruit availability was dominated by neem (Azadirachta indica), an item requiring great feeding effort. Provisioned foods did not prevent fGC increases when availability of the most preferred main fruit item, tamarind (Tamarindus indica), declined drastically. Although rank-related differences in access to provisioned foods and rates of agonism did not lead to an overall effect of rank on fGCs, low-ranking females excreted more fGCs than high-ranking females during a period of high provisioning intensity and low fruit availability. The emergence of this rank effect was associated with elevated feeding effort in all females, a greater access to provisioned items by high-ranking females, and a higher proportion of time spent moving in low-ranking females. Our findings suggest that metabolic stressors were the primary determinants of both temporal and individual variation in fGCs, indicating potential fitness benefits for high-ranking females when food availability is limited.  相似文献   
4.
5.
Summary Responses to single trait selection on individual phenotype and sire-family mean phenotype for survivor's egg weight and rate of lay were measured for a single generation in 13 replicates. Each replicate-selection criterion-trait subclass consisted of eight sire families or 72 females measured and was reproduced from the best 25% of the families or individuals. The realized heritability of egg weight was 0.39 and that of rate of lay was 0.31, both of which were significantly greater than zero but not significantly different from the predicted values based on halfsib correlations in the base population.The standardized response to sire-family selection was less than the response to individual selection for both traits and the difference was significant for rate of lay (0.10; 0.31) but not for egg weight (0.22; 0.39). The predicted responses to sire-family selection were less than those for individual selection for both traits, and the observed responses to sire-family selection were not significantly different from the predicted values for either trait.These experimental results do not disagree with the theoretical expectations of the relative efficiencies of individual and sire-family selection.Journal paper no. 7479, Purdue University, Agricultural Experiment Station. This investigation was conducted as a part of the cooperative research of the NC-89 Regional Poultry Breeding Project entitled Nature and Utilization of Genetic Variation in Poultry Improvement  相似文献   
6.
Abstract. A spatially explicit model was developed to study the relationships between the dynamics and spatial structure of forest stands. The objective was to test whether tree spatial structure can be used as an indicator of stand dynamics. The model simulates the growth, mortality and recruitment of trees in a multi‐specific and uneven‐aged stand. It includes deterministic and stochastic processes so that repeated simulations do not lead to the same stand but provide several possible results for a given dynamic (defined by a set of parameters). Second‐order neighbourhood analyses were used to characterize the resulting spatial structures. They showed a high variability for a given set of parameters. Only the main trends in the spatial structure can be interpreted. Sensitivity analyses, concerning the influence of competition on spatial structure, showed that in heterogeneous stands confounding effects can hinder the interpretation of the spatial structure if all the trees are considered. The spatial structure of the canopy trees alone proved easier to interpret as it is directly linked to post recruitment competition. Inference on the dominant modality of competition (one‐sided or two‐sided) based on the spatial structure proved difficult.  相似文献   
7.
表观遗传学(epigenetics)是指不涉及DNA序列改变、可以通过有丝分裂和减数分裂进行遗传的基因表达变化的遗传学分支领域。目前研究主要集中在DNA甲基化、组蛋白密码、染色质重塑和非编码RNA调控等方面。早期负性经历是指个体出生早年所经历的不良生活事件,还包括个体出生前所经历的负性生活事件。大量研究表明早期负性经历对个体成年后的行为会造成明显影响。本文将综述早期负性经历中表观遗传的各种机制。  相似文献   
8.
IntroductionWe investigated the extent to which the corticospinal inputs delivered to Ia inhibitory interneurons influence the strength of disynaptic reciprocal Ia inhibition.MethodsSeventeen healthy subjects participated in this study. The degree of reciprocal Ia inhibition was determined via short-latency (condition-test interval: 1–3 ms) suppression of Sol H-reflex by conditioning stimulation of common peroneal nerve. The effect of corticospinal descending inputs on Ia inhibitory interneurons was assessed by evaluating the conditioning effect of transcranial magnetic stimulation (TMS) on the Sol H-reflex. Then, we determined the relationship between the degree of reciprocal Ia inhibition and the conditioning effect of TMS on the Sol H-reflex.ResultWe found that the degree of reciprocal Ia inhibition and the extent of change in the amplitude of the TMS-conditioned H-reflex, which was measured from short latency facilitation to inhibition, displayed a strong correlation (r = 0.76, p < 0.01) in the resting conditions.ConclusionThe extent of reciprocal Ia inhibition is affected by the corticospinal descending inputs delivered to Ia inhibitory interneurons, which might explain the inter-individual variations in reciprocal Ia inhibition.  相似文献   
9.
This ERP study used electrophysiological technique to examine how individual differences in the speed of working memory updating influence the use of syntactic and semantic information during on-line sentence argument interpretation, and the time course of that working memory updating effect. The basic structure of the experimental sentences was “Noun + Verb + adverb + ‘le’ + a two-character word”, with the Noun being the sentence initial argument. This initial argument is animate or inanimate and the following verb disambiguates it as an agent or patient. The results at the initial argument revealed that, the quick-updating group elicited a larger positivity over the frontal cortex (within 500–800 ms post-noun onset) as compared with the slow-updating group. At the following disambiguating verb, the slow-updating group only showed a word order effect, indicating that the patient-first condition elicited a larger P600 (within 500–1,000 ms post-verb onset) than the agent-first one; for the quick-updating group, at the early stage of processing, the patient-first sentences elicited a larger N400 (within 300–500 ms post-verb onset) than the agent-first ones only when the initial argument was inanimate; however, at the late stage, the patient-first sentences elicited an enhanced P600 (within 800–1,000 ms post-verb onset) only when the initial argument was animate. These results suggested that the speed of working memory updating not only influences the maintenance of sentence argument when the contents of working memory change but also influences the efficiency of integrating that argument with the verb at a late time point. When integrating the argument with the disambiguating verb, individuals with quick-updating ability can combine multiple sources of information (both noun animacy and word order), and conduct rapid and fine-grained two-stage processing; individuals with slow-updating ability, however, only rely on one dominant source of information types (word order), and conducted slow and course-grained processing.  相似文献   
10.
由于标记缺失、生产记录不详、亲权关系不明及部分个体来源不清等历史问题,中国小熊猫圈养种群存在谱系错漏、近亲繁殖等风险。近年来,随着小熊猫种群规模不断扩大,管理者们对谱系的准确性提出了更高的需求,亲子鉴定工作也成为了研究的重点。本文采用26个微卫星标记,对国内3个小熊猫圈养种群进行了亲缘关系运算,完成了相关谱系的查错与整理。26个位点多态性与稳定性良好,联合非亲排除概率达到0.9999以上,可解决国内小熊猫圈养种群的各类亲子鉴定需求。在单亲未知或双亲未知的情况下,8或11个位点组合可实现亲子鉴定。5个位点组合可进行个体识别。在小熊猫圈养管理过程中,应用一套亲子鉴定体系对小熊猫圈养的谱系进行查漏补缺,有利于制定科学的配对计划、避免近亲繁殖,对小熊猫种群保护有着重要意义。  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