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   1174篇
  免费   84篇
  2023年   5篇
  2022年   20篇
  2021年   32篇
  2020年   14篇
  2019年   21篇
  2018年   34篇
  2017年   19篇
  2016年   25篇
  2015年   65篇
  2014年   64篇
  2013年   84篇
  2012年   93篇
  2011年   118篇
  2010年   55篇
  2009年   44篇
  2008年   63篇
  2007年   78篇
  2006年   76篇
  2005年   83篇
  2004年   60篇
  2003年   61篇
  2002年   34篇
  2001年   10篇
  2000年   3篇
  1999年   9篇
  1998年   5篇
  1997年   11篇
  1996年   8篇
  1995年   7篇
  1994年   8篇
  1993年   7篇
  1992年   8篇
  1991年   5篇
  1990年   2篇
  1988年   2篇
  1987年   1篇
  1986年   2篇
  1985年   2篇
  1983年   4篇
  1982年   3篇
  1981年   1篇
  1980年   1篇
  1979年   2篇
  1978年   2篇
  1973年   1篇
  1965年   1篇
  1964年   1篇
  1954年   1篇
  1946年   1篇
  1925年   1篇
排序方式: 共有1258条查询结果,搜索用时 31 毫秒
981.
A review of species in the genus Praon Haliday, 1833 is presented. Twenty described species are keyed and illustrated with scanning electron micrographs and line drawings. The Praon species presented in this work have been identified from 67 aphid taxa occurring on 120 plant taxa. Furthermore, 87 original parasitoid–aphid–plant associations of the species mentioned in the key are presented. Phylogenetic relationships among Praon species are reconstructed using parsimony and cladistic distance methods. Praon abjectum is the sister taxon to the remaining Praon species. We recognized three species group: “Parapraon”, “dorsale-yomenae” and “rosaecola”. Monophyly is suggested for “Parapraon” species group and paraphyly for “dorsale-yomenae” group. Finally, by phylogenetic reconstruction, a close phylogenetic relationship between “Parapraon” and “dorsale-yomenae” species group was found.  相似文献   
982.
983.
Gilles de la Tourette syndrome is a neuropsychiatric disorder characterized by motor and phonic tics that can be considered motor responses to preceding inner urges. It has been shown that Tourette patients have inferior performance in some motor learning tasks and reduced synaptic plasticity induced by transcranial magnetic stimulation. However, it has not been investigated whether altered synaptic plasticity is directly linked to impaired motor skill acquisition in Tourette patients. In this study, cortical plasticity was assessed by measuring motor-evoked potentials before and after paired associative stimulation in 14 Tourette patients (13 male; age 18–39) and 15 healthy controls (12 male; age 18–33). Tic and urge severity were assessed using the Yale Global Tic Severity Scale and the Premonitory Urges for Tics Scale. Motor learning was assessed 45 minutes after inducing synaptic plasticity and 9 months later, using the rotary pursuit task. On average, long-term potentiation-like effects in response to the paired associative stimulation were present in healthy controls but not in patients. In Tourette patients, long-term potentiation-like effects were associated with more and long-term depression-like effects with less severe urges and tics. While motor learning did not differ between patients and healthy controls 45 minutes after inducing synaptic plasticity, the learning curve of the healthy controls started at a significantly higher level than the Tourette patients'' 9 months later. Induced synaptic plasticity correlated positively with motor skills in healthy controls 9 months later. The present study confirms previously found long-term improvement in motor performance after paired associative stimulation in healthy controls but not in Tourette patients. Tourette patients did not show long-term potentiation in response to PAS and also showed reduced levels of motor skill consolidation after 9 months compared to healthy controls. Moreover, synaptic plasticity appears to be related to symptom severity.  相似文献   
984.

Background  

Climatic or meteorological condition changes have been implicated in the pathogenesis of Bell's palsy (BP). We evaluate the influence of meteorological parameters, such as temperature, humidity, and atmospheric pressure, and their variation and covariation on the incidence of BP and present a review of the literature on the effect of meteorological conditions on facial nerve function.  相似文献   
985.
The objective of this research was to study the effect of the chelated form of the iron salt of ethylenediamine di-o-hydroxyphenylacetic acid (Fe-EDDHA) (6% Fe) on in vitro rooting of the rootstock GF-677. The iron salt of ethylenediamine tetraacetic acid (Fe-EDTA) (12% Fe) of the MS basic medium was replaced by Fe-EDDHA, which was applied in three concentrations: 93.5, 187.0 and 280 mg l−1 (5.6, 11.2 and 16.8 mg l−1 Fe, respectively). For each treatment of Fe-EDDHA, the effect of ascorbic acid added in four concentrations (0, 0.1, 1.0 and 10 mg l−1) was studied. After 4 weeks of culture, the explants growing on the medium with 280 mg l−1 Fe-EDDHA gave the best rooting results. Regarding ascorbic acid, no clear stimulating effect on rooting was found.  相似文献   
986.
The tendency of predators to preferentially attack phenotypically odd prey in groups (the oddity effect) is a clear example of how predator cognition can impact behaviour and morphology in prey. Through targeting phenotypically odd prey, predators are thought to avoid the cognitive constraints that delay and limit the success of attacks on homogenous prey groups (the confusion effect). In addition to influencing which prey a predator will attack, the confusion and oddity effects would also predict that attacks on odd prey can occur more rapidly than attacking the majority prey type, as odd prey are more easily targeted, but this prediction has yet to be tested. Here, we used kerri tetra fish, Inpaichthys kerri, presented with mixed phenotypic groups of Daphnia dyed red or black to investigate whether odd prey in groups are preferentially attacked and whether these attacks were faster than those on the majority prey type. In agreement with previous work, odd prey were targeted and attacked more often than expected from their frequency in the prey groups, regardless of whether the odd prey was red in a group of black prey or vice versa. However, no difference was found in the time taken to attack odd vs. majority prey items, contrary to our predictions. Our results suggest that the time taken to make an attack is determined by a wider range of factors or is subject to greater variance than the choice of which prey is selectively targeted in a group.  相似文献   
987.
Pentameric ligand-gated ion channels (pLGICs) of the Cys loop family are transmembrane glycoproteins implicated in a variety of biological functions. Here, we present a solution NMR study of the extracellular domain of a prokaryotic pLGIC homologue from the bacterium Gloeobacter violaceus that is found to be a monomer in solution.  相似文献   
988.
989.
Adult emergence of univoltine temperate insect species and its synchronization with specific host phenological stages is mainly regulated by obligatory pupal diapause. Although a few studies have investigated the factors affecting diapause intensity, little attention has been paid to the physiological alterations and metabolic regulation that take place during diapause. Here, we describe differences in diapause between a highland and a coastal Greek population of the European cherry fruit fly Rhagoletis cerasi, a major pest of sweet and sour cherries in many European countries. Pupae of both populations were exposed to the environmental conditions prevailing in the two areas and diapause termination was observed under laboratory conditions. The regulation of energetic metabolites during the long pupae stage was examined under both field and laboratory conditions. Differences in diapause intensity revealed that the two populations have adapted to the local geographical and climatic conditions and have different requirements for low temperatures to terminate diapause. The coastal population undergoes a shorter diapause and adults emerge more rapidly, especially in the highland area. The highland population failed to terminate diapause (<40% adult emergence) in the coastal area. Both populations draw on their major energetic reserves (lipids and protein) similarly during diapause. Nevertheless, regulation of carbohydrate and glycogen reserves seems to vary between the populations: major peaks of these stored nutrients occur on different dates in the two populations, suggesting a differential regulation. Differences in diapause intensity imply a genetic differentiation between the two populations. The importance of our findings in understanding the physiological patterns during obligatory diapause of a univoltine insect species, as well as the practical implications for the development of specific phenological models for the European cherry fruit fly are discussed.  相似文献   
990.
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