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   233篇
  免费   9篇
  国内免费   8篇
  250篇
  2022年   1篇
  2021年   1篇
  2020年   1篇
  2019年   5篇
  2018年   5篇
  2017年   8篇
  2016年   7篇
  2015年   2篇
  2014年   11篇
  2013年   11篇
  2012年   8篇
  2011年   14篇
  2010年   11篇
  2009年   5篇
  2008年   7篇
  2007年   11篇
  2006年   6篇
  2005年   6篇
  2004年   7篇
  2003年   5篇
  2002年   16篇
  2001年   2篇
  2000年   6篇
  1999年   5篇
  1998年   8篇
  1997年   7篇
  1996年   2篇
  1995年   2篇
  1994年   1篇
  1993年   1篇
  1992年   7篇
  1991年   4篇
  1990年   5篇
  1989年   6篇
  1988年   6篇
  1987年   12篇
  1986年   5篇
  1985年   7篇
  1984年   1篇
  1979年   1篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
  1973年   1篇
  1972年   2篇
  1971年   2篇
  1969年   1篇
  1968年   1篇
  1965年   2篇
排序方式: 共有250条查询结果,搜索用时 15 毫秒
21.
Zokors (Myospalacinae) is a group of rodents specialized for underground life, endemics of eastern Asia, which is taxonomically and evolutionarily poorly studied. We examined genetic diversity and phylogenetic relationships among zokors (Myospalax myospalax, Myospalax aspalax, Myospalax armandii, Myospalax psilurus, Myospalax smithii) using RAPD-PCR. The subfamily Myospalacinae was shown to be monophyletic and contain four evolutionary branches: M. myospalax, M. aspalax-M. armandii, M. smithii and M. psilurus. Genetic differences and high differentiation were found among the species and between two geographic forms of Manchurian zokor M. psilurus from the marginal parts of the range, Transbaikalia and Primorye. The psiluris phylogroup was shown to be dichotomically divided into two clades according to the geographical distribution of animals from Transbaikalia and Primorye. The genetic differentiation between the geographic forms of M. psilurus corresponded to the differentiation between morphologically similar species M. aspalax and M. armandii. M. armandii is a sister taxon with regard to M. aspalax. This new evidence on the evolutionary relationships among zokors does not contradict the traditional views inferred from morphological, karyological, and allozyme data, on apartness of M. myospalax and the character of evolution in this group. The species status of Myospalax psilurus Milne-Edwards, 1874, M. epsilanus Thomas, 1912, and M. armandii Milne-Edwards, 1867, which had been suggested earlier on the basis of biochemical and karyological data, was confirmed.  相似文献   
22.
The ultrastructure of sinus and atrioventricular nodes was studied in white rats with experimental myocardial infarction. 24 hours after the induction of the disease mitochondrial enlargement characterized by the increase in their area, decrease in the number of cristae and the decline in the rate of mitochondrial energy effectiveness was detected. Different degrees of nuclear chromatin aggregation and membrane permeability for colloidal lanthanum were observed. Characteristic types of conduction cellular lesions were revealed in experimental myocardial infarction.  相似文献   
23.
Activity of 50 dopamine and 67 non-dopamine neurons was studied during motivated behavioural actions in the cat brain black substance. 66% of former and 88% of latter neurons modified their activity before and during autoinitiated voluntary movements. The data obtained suggest that dopamine neurons are involved in organisation of movements in behavioural actions with cognitive components.  相似文献   
24.
基于戴云山固定样地黄山松群落物种组成与结构研究   总被引:1,自引:0,他引:1  
黄山松是亚热带中部山区主要建群种,研究其物种组成及群落结构对探讨中亚热带植被演替规律具有重要意义。戴云山自然保护区分布有大面积黄山松群落,该研究采用网格布点法,建立86块(25.82 m×25.82 m)共5.7 hm~2固定样地,对样地内黄山松群落的物种组成特征、分布区类型、胸径和树高结构、空间分布格局4个方面特征进行了探讨。结果表明:(1)样地内共出现木本植物32 603株219种,隶属于59科108属。乔灌木优势种有黄山松、马尾松、木荷、肿节少穗竹、岩柃、窄基红褐柃等,其中稀有种和偶见种分别占总物种数的33.79%、25.75%和45.21%、24.66%。(2)在区系分布类型上,热带分布类型的科属多于温带分布类型的科属,热带分布类型中又以泛热带分布类型,温带分布类型以北温带占据最大比例。(3)样地内优势种的胸径分布呈倒"J"型,表明更新状态良好。垂直结构上,各优势种树高为倒"J"型或近似倒"J"型。黄山松和其他优势乔木大部分树高为4~10 m,灌木除短尾越桔0~1 m个体数最多外,其他优势灌木1~2 m个体数最多。(4)经计算,样地内乔灌木各优势种均呈聚集分布,聚集程度有所差异,乔木层黄山松最低,灌木层短尾越桔最低。该研究结果表明戴云山保护区黄山松群落物种组成丰富、更新良好,反映了亚热带高山针叶林的典型特征,其空间分布格局可能与取样方式等因素有关。  相似文献   
25.
We studied the frequency and amplitude properties of the EEG μ rhythm in children (n = 38) aged 4–14 years under the condition of visual fixation (VF) on a video image of a computer mouse, as well as the parameters of its desynchronization during the tasks involving self-controlled performance, observation, imitation, and auditory recognition of the hand circular movements (SPM, OM, IM, and ARM, respectively) with a computer mouse. We observed age-related increment in the modal frequency of μ rhythm in loci C 3 and C z. During the SPM process, a significant decrease in the amplitude of μ rhythm was found in loci C 3 (26.7%) and C z (10.3%); during the OM, in locus C z only (9.9%). The effects of the μ rhythm desynchronization during both self-paced and observed movements might be an evidence of well-developed neural matching mechanisms that provide the processes of performing and observing similar actions in children aged 4 to 14 years. During the IM, the desynchronization of μ rhythm was significant in loci C 3 (27.4%) and C z (15.3%). We hypothesize that the statistically significant increase (from SPM to IM) in the depression of μ rhythm in locus C z is likely to be an effect of a social gaming context common for the situations when children imitate the movements of adults. The index of desynchronization of μ rhythm under the studied conditions did not depend on the age of children. Possible relations of identified modulations of the μ rhythm to the activity of the mirror neuron system were also discussed.  相似文献   
26.
We estimated the efficacy of using the technique of feedback (FB) by EEG characteristics (EEG-FB, neurotherapy) with the aim of reducing increased anxiety levels in healthy 10- to 14-year-old children. The anxiety level was estimated using the Prikhojan anxiety test, the Spielberger–Khanin questionnaire, and the House–Tree–Person projective drawing technique. Positive effects of series of neurotherapy sessions were obvious. After training was completed, we observed significant increases in the ratios of the amplitudes of alpha and theta rhythms, semsorimotor and theta rhythms, as well as of the modal frequency of the EEG alpha rhythm in tested persons of the experimental group (n = 7). In the control group (n = 10), changes in these values did not reach the significance level. In the experimental group of tested persons subjected to EEG-FB sessions, the anxiety level decreased appreciably; in addition, the indices “feeling of inferiority” and “frustration” decreased significantly. In the control group, alterations of these psychological indices were not unidirectional. Therefore, modifications of the EEG pattern, which occurred in the course of training and were accompanied by a decrease in the anxiety level in the experimental group, can be indicative of the expediency of EEG-FB for the reduction of high anxiety levels in children and teenagers.  相似文献   
27.
战凯  姚涓  肖云鹏  于宣  洪梅 《生物磁学》2014,(2):386-388,400
放化疗综合应用是癌症治疗中的常用方法。研究表明,放化疗综合应用可以有效地控制杀伤肿瘤,但过程中对正常细胞的毒副作用严重制约着放化疗的剂量和疗效。如何在有效杀伤肿瘤细胞的同时减轻放化疗综合应用中对正常细胞的毒副作用已经成为探索更好的治疗策略的关键。随着研究的不断深入,各种相关的新药和新治疗思路层出不穷,比如针对肿瘤发生及代谢过程的靶向类新药、用于辐射增敏的新的基因靶点等都已进入研究者的视线。另外,近年来关于肿瘤细胞中药物转运蛋白的研究也为综合治疗靶点寻找提供了一定依据。本文根据当前研究现状,着重总结近年来放化疗综合治疗靶向研究在上述几方面的一些新进展。  相似文献   
28.
草地贪夜蛾是新入侵我国的重大危险性害虫,了解野外条件下天敌的发生情况对于挖掘和利用本地天敌资源开展生物防治有重要意义。2019年4月至7月,定期在广州及香港地区的玉米田中开展草地贪夜蛾发生情况调查时,发现野外两种卵寄生蜂寄生草地贪夜蛾。通过分子生物学方法鉴定为夜蛾黑卵蜂和螟黄赤眼蜂,并分别建立实验种群,为人工扩繁及田间应用打下基础,为利用本地天敌开展草地贪夜蛾生物防治提供重要参考。  相似文献   
29.
目的:比较异丙酚和氯胺酮对大鼠离体缺血再灌注损伤心肌脂质过氧化的影响。方法:成年Wistar大鼠18只,雌雄不拘。体重240-300g,随机分为3组(T1=6):心肌缺血再灌注损伤组(I/R组),异丙酚组(P组),氯胺酮组(K组)。采用Langendorff灌装置建立离体心脏缺血再灌注模型,将心脏连接至Langendorff逆灌装置,3组均以K-H液平衡灌注10min后,再分别以K.H液、含30μmol/L。异丙酚的K-H液、含10μmol-L-1氯胺酮的K-H液灌注10min,然后全心停灌25min,再分别以停灌前相同的灌注液恢复灌注30min。留取冠脉流出液测定总LDH活性;灌注末取左室心肌组织置于2.5%的戊二醛固定,观察心肌的超微结构;心尖部心肌组织留待检测8-异前列腺素和SOD活性。结果:与I/R组比较,P组8-异前列腺素含量降低,SOD活性升高,LDH活性降低(P〈0.05);K组8-异前列腺素含量,SOD及LDH活性均无统计学意义(P〉0.05);与P组比较,K组8-异前列腺素含量升高,SOD及LDH活性降低(P〈0.05);P组心肌超微结构损伤较m组和K组也明显改善。结论:异丙酚可显著减轻心肌缺血再灌注损伤大鼠的脂质过氧化和心肌缺血再灌注损伤,而氯胺酮没有抗心肌缺血再灌注损伤心肌脂质过氧化的作用。  相似文献   
30.
Polar auxin transport plays a divergent role in plant growth and developmental processes including root and embryo development, vascular pattern formation and cell elongation. Recently isolated Arabidopsis pin gene family was believed to encode a component of auxin efflux carrier (G(?)lweiler et al, 1998). Based on the Arabidopsis pin1 sequence we have isolated a Brassica juncea cDNA (designated Bjpin1), which encoded a 70-kDa putative auxin efflux carrier. Deduced BjPIN1 shared 65% identities at protein level with AtPINl and was highly homologous to other putative PIN proteins of Arabidopsis (with highest homology to AtPIN3). Hydrophobic analysis showed similar structures between BjPINl and AtPIN proteins. Presence of 6 exons (varying in size between 65 bp and 1229 bp) and 5 introns (sizes between 89 bp and 463 bp) in the genomic fragment was revealed by comparing the genomic and cDNA sequences. Northern blot analysis indicated that Bjpin1 was expressed in most of the tissues tested, with a relatively h  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