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   319篇
  免费   11篇
  国内免费   4篇
  334篇
  2018年   2篇
  2015年   6篇
  2014年   7篇
  2013年   13篇
  2012年   9篇
  2011年   9篇
  2010年   14篇
  2009年   17篇
  2008年   5篇
  2007年   6篇
  2006年   8篇
  2005年   2篇
  2004年   5篇
  2003年   4篇
  2000年   6篇
  1999年   4篇
  1998年   15篇
  1997年   6篇
  1996年   5篇
  1995年   3篇
  1994年   6篇
  1993年   2篇
  1992年   4篇
  1989年   2篇
  1988年   2篇
  1986年   3篇
  1985年   2篇
  1984年   2篇
  1983年   5篇
  1977年   2篇
  1974年   1篇
  1972年   6篇
  1971年   4篇
  1970年   2篇
  1968年   2篇
  1967年   2篇
  1960年   2篇
  1959年   6篇
  1958年   16篇
  1957年   14篇
  1956年   10篇
  1955年   16篇
  1954年   12篇
  1953年   8篇
  1952年   15篇
  1951年   8篇
  1950年   5篇
  1949年   6篇
  1948年   8篇
  1946年   3篇
排序方式: 共有334条查询结果,搜索用时 0 毫秒
321.
Fluorescence-labeled neuropeptide Y (NPY) has been used in flow cytometric binding assays for the determination of affinity constants of NPY Y1, Y2, and Y5 receptor ligands. Because the binding of fluorescent NPY is insufficient for competition studies at the human Y4 receptor (hY4R), we replaced Glu-4 in hPP with Lys for the derivatization with cyanine-5. Because cy5-[K4]hPP has high affinity (Kd 5.6 nM) to the hY4R, it was used as a probe in a flow cytometric binding assay. Specific binding of cy5-[K4]hPP to hY4R was visualized by confocal microscopy. The hY4R, the chimeric G protein Gqi5 and mitochondrially targeted apoaequorin were stably coexpressed in CHO cells. Aequorin luminescence was quantified in a microplate reader and by a CCD camera. By application of these methods 3-cyclohexyl-N-[(3-1H-imidazol-4-ylpropylamino)(imino)methyl]propanamide (UR-AK49) was discovered as the first nonpeptidic Y4R antagonist (pKi 4.17), a lead to be optimized in terms of potency and selectivity.  相似文献   
322.
Palaua (Malveae, Malvaceae) comprises 15 species endemic to the hyperarid coastal desert of Chile and Peru. So far, chromosome counts have been known for two diploid species (2n = 2x = 10) only. Here we report new chromosome numbers for 12 species of Palaua and four of its sister group Fuertesimalva. Karyotypes including 4',6'-diamidino-2-phenylindole dihydrochloride (DAPI)/chromomycin (CMA3) fluorescent banding are presented for selected species representative of each of the main clades of Palaua. An important finding is the discovery of polyploids in one exclusively tetraploid species (P. Trisepald) and four species with mixed diploid and tetraploid cytorypes (P. Dissecta, P. Mollendoensis, P. Moschata, and P. Tomentosa). The diploid and tetraploid karyotypes are all unimodal, symmetrical and show one or two pairs of satellite chromosomes with their associated CMA+/DAPI-band depending on the cytotype. For some of the tetraploids an autopolyploid origin is suggested.  相似文献   
323.
324.
The destruction of periodontal tissues during periodontitis is the result of the immune-inflammatory reactions to the bacteria of dental biofilm. Probiotics may reduce dysbiosis by the modification of the dental microbiome, which can influence the immune-inflammatory mechanisms. The aim of this study was to estimate the clinical and microbiological parameters, before and after 30 days of application of the dietary supplement containing Lactobacillus salivarius SGL03 or placebo. The study was conducted in 51 patients with stage I or II periodontitis during the maintenance phase of treatment. The clinical parameters and the number of colony forming units (CFU) of bacteria in supragingival plaque were assessed before and after 30 days of the oral once daily administration of the dietary supplement in the form of suspension containing L. salivarius SGL03 or placebo. There were no changes in the PI scores between and within the groups. The value of BOP decreased in both groups. In the study group the significant reduction of the mean pocket depth was revealed (from 2.5 to 2.42, p = 0,027) but without the difference between the groups. There were no significant changes in the number of bacteria within the groups. In the control, but not the study group, positive correlations were observed between the clinical parameters (variables) and the number of bacteria. The use of the dietary supplement containing L. salivarius SGL03 may reduce pocket depth despite the lack of changes in other clinical parameters and the number of bacteria in supragingival plaque.Key words: probiotics, periodontal treatment, Lactobacillus salivarius  相似文献   
325.
326.
327.
328.
The mealybug tribe Xenococcini (Hemiptera: Pseudococcidae) comprises three genera, Eumyrmococcus Silvestri, Neochavesia Williams & Granara de Willink and Xenococcus Silvestri, trophobiotically associated with ants of the genus Acropyga Roger (Hymenoptera: Formicidae). Alate Acropyga queens vertically transmit trophobionts by carrying them along on the nuptial flight, a unique behaviour termed trophophoresy. Xenococcine mealybugs have never been collected without ant associates, and putatively only associate with Acropyga. Xenococcine mealybugs are characterized by the absence of dorsal ostioles, presence of distally cup‐shaped circuli and a female pupal instar rather than a third feeding instar. The phylogeny of this tribe is derived for the first time using morphological data from adult females (53 characters) through Bayesian inference and maximum parsimony methods. Monophyly of the clade is strongly supported and a discussion of their taxonomy is included. The Neotropical genus Neochavesia was recovered as monophyletic. Eumyrmococcus, as previously defined, was recovered as paraphyletic, and thus two species are transferred to Xenococcus: Xenococcus kinomurai (Williams & Terayama) comb.n. and Xenococcus neoguineensis (Williams) comb.n . Two species groups are recognized within Eumyrmococcus: the Eumyrmococcus scorpioides species group, restricted to the eastern Mediterranean and Afrotropics, and the Eumyrmococcus smithii species group, restricted to the Orient and Indo‐Australasia. Six new species are described: Eumyrmococcus adornocapillus sp.n. from Australia; Eumyrmococcus sarnati sp.n. from Fiji; Eumyrmococcus ordinotersus sp.n. and Xenococcus baryglobosus sp.n. from the Solomon Islands; Neochavesia cephalonodus sp.n. from French Guiana; and Neochavesia linealuma sp.n. from Guyana. The systematics and biology of the xenococcine mealybugs is discussed in the context of obligate ant symbiosis.  相似文献   
329.
Metaxylem tracheary elements of roots have differentiation between end walls and lateral walls in both Euryale and Victoria End walls have narrower, more closely spaced bars and scalariform plates. primary walls of end walls (and, to a lesser extent, lateral walls) have striations that are thickened primary wall portions orientated in an axial direction. These striations are less common in Victoria than in Euryale. Although secondary wall strands between perforations occur in some dicotyledons, the report of primary wall striations is new; these can be seen with scanning electron microscopy (SEM) but not with light microscopy. Perforations occur irregularly and sometimes sparsely on end walls of tracheary elements of Victoria , but perforations were not observed in Euryale. Thus, Euryale satisfies one criterion for the presence of vessel (end wall different from lateral wall), whereas Barclaya satisfies another (perforations in end walls) and Victoria satisfies both. Vessel origins in Nymphaeaceae are important in illustrating that there may be multiple vessel origins in dicotyledons.  相似文献   
330.
We have studied the accumulation of water, dry matter (DM) andglucose and fructose (G + F) in selected grape berries cv. Dolcettoof varying initial size growing on leafed and defoliated vines.The first measurements at 2 d after veraison were obtained non-destructivelyfrom correlations with linear dimensions and deformability;the final measurements were made when the berries were harvested13 d later. The increments in DM and G + F per pericarp increased with initialberry size thus discounting an hypothesis of an equal amountof solutes supplied to all berries. The increments in weightof DM and G + F per increment of pericarp volume were constantin berries of different size, supporting an hypothesis of acontrol determined by concentration in the solution availablefor accumulation in all berries. Defoliation reduced the incrementsper pericarp and per g fr. wt. by about the same proportionand its effects were consistent with the above interpretations. Key words: Grape pericarp, sugar accumulation, phloem unloading, Vitis vinifera.  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