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   1701篇
  免费   129篇
  国内免费   1篇
  2023年   18篇
  2022年   8篇
  2021年   81篇
  2020年   34篇
  2019年   58篇
  2018年   47篇
  2017年   53篇
  2016年   69篇
  2015年   107篇
  2014年   106篇
  2013年   133篇
  2012年   157篇
  2011年   149篇
  2010年   94篇
  2009年   96篇
  2008年   114篇
  2007年   100篇
  2006年   84篇
  2005年   73篇
  2004年   54篇
  2003年   55篇
  2002年   39篇
  2001年   14篇
  2000年   6篇
  1999年   6篇
  1998年   2篇
  1997年   4篇
  1996年   4篇
  1995年   6篇
  1994年   4篇
  1993年   9篇
  1992年   6篇
  1991年   3篇
  1990年   4篇
  1989年   2篇
  1986年   2篇
  1985年   3篇
  1984年   2篇
  1983年   2篇
  1982年   5篇
  1981年   5篇
  1978年   1篇
  1975年   1篇
  1974年   1篇
  1970年   1篇
  1969年   2篇
  1966年   1篇
  1965年   1篇
  1964年   1篇
  1960年   1篇
排序方式: 共有1831条查询结果,搜索用时 234 毫秒
1.
ObjectivesTo identify, appraise and summarize existing knowledge and knowledge gaps in practice-relevant questions in pediatric dentistry.MethodsA systematic mapping of systematic reviews was undertaken for domains considered important in daily clinical practice. The literature search covered questions in the following domains: behavior management problems/dental anxiety; caries risk assessment and caries detection including radiographic technologies; prevention and non-operative treatment of caries in primary and young permanent teeth; operative treatment of caries in primary and young permanent teeth; prevention and treatment of periodontal disease; management of tooth developmental and mineralization disturbances; prevention and treatment of oral conditions in children with chronic diseases/developmental disturbances/obesity; diagnosis, prevention and treatment of dental erosion and tooth wear; treatment of traumatic injuries in primary and young permanent teeth and cost-effectiveness of these interventions. Abstracts and full text reviews were assessed independently by two reviewers and any differences were solved by consensus. AMSTAR was used to assess the risk of bias of each included systematic review. Reviews judged as having a low or moderate risk of bias were used to formulate existing knowledge and knowledge gaps.ResultsOut of 81 systematic reviews meeting the inclusion criteria, 38 were judged to have a low or moderate risk of bias. Half of them concerned caries prevention. The quality of evidence was high for a caries-preventive effect of daily use of fluoride toothpaste and moderate for fissure sealing with resin-based materials. For the rest the quality of evidence for the effects of interventions was low or very low.ConclusionThere is an urgent need for primary clinical research of good quality in most clinically-relevant domains in pediatric dentistry.  相似文献   
2.
Current demand for understanding the behavior of groups of related genes, combined with the greater availability of data, has led to an increased focus on statistical methods in gene set analysis. In this paper, we aim to perform a critical appraisal of the methodology based on graphical models developed in Massa et al. ( 2010 ) that uses pathway signaling networks as a starting point to develop statistically sound procedures for gene set analysis. We pay attention to the potential of the methodology with respect to the organizational aspects of dealing with such complex but highly informative starting structures, that is pathways. We focus on three themes: the translation of a biological pathway into a graph suitable for modeling, the role of shrinkage when more genes than samples are obtained, the evaluation of respondence of the statistical models to the biological expectations. To study the impact of shrinkage, two simulation studies will be run. To evaluate the biological expectation we will use data from a network with known behavior that offer the possibility of carrying out a realistic check of respondence of the model to changes in the experimental conditions.  相似文献   
3.
Low-frequency sensorineural hearing loss (LFSNHL) is an unusual type of HL in which frequencies at 2000 Hz and below are predominantly affected. Most of the families with LFSNHL carry missense mutations in WFS1 gene, coding for wolframin.  相似文献   
4.
Enhanced oxidative stress plays an important role in the progression and onset of diabetes and its complications. Strategies or efforts meant to reduce the oxidative stress are needed which may mitigate these pathogenic processes. The present study aims to investigate the in vitro ameliorative potential of nine antioxidant molecules in L6 myotubes under oxidative stress condition induced by 4-hydroxy-2-nonenal and also to comprehend the gene expression patterns of oxidative stress genes upon the supplementation of different antioxidants in induced stress condition. The study results demonstrated a marked increase in the level of malondialdehyde and protein carbonyl content with a subsequent increase in the free radicals that was reversed by the pretreatment of different dietary antioxidant. From the expression analysis of the oxidative stress genes, it is evident that the expression of these genes is modulated by the presence of antioxidants. The highest expression was found in the cells treated with Insulin in conjugation with an antioxidant. Resveratrol is the most potent modulator followed by Mangiferin, Estragole, and Capsaicin. This comparative analysis ascertains the potency of Resveratrol along with Insulin in scavenging the reactive oxygen species (ROS) generated under induced stress conditions through antioxidant defense mechanism against excessive ROS production, contributing to the prevention of oxidative damage in L6 myotubes.  相似文献   
5.

Background  

CTCF (CCCTC-binding factor) is an evolutionarily conserved zinc finger protein involved in diverse functions ranging from negative regulation of MYC, to chromatin insulation of the beta-globin gene cluster, to imprinting of the Igf2 locus. The 11 zinc fingers of CTCF are known to differentially contribute to the CTCF-DNA interaction at different binding sites. It is possible that the differences in CTCF-DNA conformation at different binding sites underlie CTCF's functional diversity. If so, the CTCF binding sites may belong to distinct classes, each compatible with a specific functional role.  相似文献   
6.
In extant primates, the posterior parietal cortex is involved in visuospatial integration, attention, and eye‐hand coordination, which are crucial functions for foraging and feeding behaviors. Paleoneurology studies brain evolution through the analysis of endocasts, that is molds of the inner surface of the braincase. These may preserve imprints of cortical structures, such as sulci, which might be of interest for locating the boundaries of major cortical regions. Old World monkeys (Cercopithecidae) represent an interesting zoological group for evolutionary studies, because of their diverse ecologies and locomotor behaviors. In this study, we quantify parietal lobe variation within the cercopithecid family, in a sample of 30 endocasts including 11 genera and 17 species, by combining landmark‐based and landmark‐free geometric morphometric analyses. More specifically, we quantitatively assess variation of the parietal proportions based on landmarks placed on reliable anatomical references and of parietal lobe surface morphology through deformation‐based methods. The main feature associated with the cercopithecid endocranial variation regards the inverse proportions of parietal and occipital lobes, with colobines, Theropithecus, and Papio displaying relatively larger parietal lobes and smaller occipital lobes compared with cercopithecins. The parietal surface is anteroposteriorly longer and mediolaterally flatter in colobines, while longitudinally shorter but laterally bulging in baboons. Large parietal lobes in colobines and baboons are likely to be independent evolutionary traits, and not necessarily associated with analogous functions or morphogenetic mechanisms.  相似文献   
7.
8.
Steroid metabolites in urine from neonates with 21-hydroxylase deficiency are predominantly polyhydroxylated 17-hydroxyprogesterone and androgen metabolites, and most have incompletely defined structure. This study forms part of a comprehensive project to characterize and identify these in order to enhance diagnosis and to further elucidate neonatal types of steroid metabolism.Steroids were analyzed, after extraction and enzymatic conjugate hydrolysis, as methyloxime-trimethylsilyl ether derivatives on gas-chromatographs coupled to quadrupole and ion-trap mass-spectrometers. GC-MS and GC-MS/MS spectra, obtained with constant excitation conditions, were used together to determine the structure of the D-ring and the side chain of 20-oxo and 20-hydroxy pregnane(ene)s without oxo groups on the A-, B-, and C-ring.All possible combinations of D-ring and side chain configuration were considered. Most fragmentations could be interpreted as partial or complete D-ring cleavages with loss of the side chain, aided by comparison with spectra of deuterated derivatives and of borohydride reduced metabolites. Possible rearrangement ions are also discussed. More than 140 endogenous metabolites were characterized.GC-MS/MS was especially beneficial for characterization of compounds with 16,17-dihydroxy-20-oxo structure, interpreted as markers of intra-uterine enzyme induction. It also assisted the differentiation of 16-hydroxy-20-oxo metabolites, present in urine of non-affected neonates, from the diagnostic 17-hydroxy-20-oxosteroids and enabled the detection of 15,17-dihydroxy-20-oxo compounds in low concentrations. The presence of 17,21-dihydroxylated pregnane(ene)s despite the deficit in CYP21A2 is discussed.We conclude that GC-MS combined with GC-MS/MS allows reliable identification of the structure of the D-ring and side chain of pregnane(ene)s without prior isolation, even when in low concentrations in urine.  相似文献   
9.
Decreasing dietary sodium intake, which can be achieved by reducing salt content in food, is recommended. Salt contributes to the taste of foods and makes them more enjoyable. Whether a food is liked or disliked is an important determinant of food intake, especially among children. However, the role of salt in children''s food acceptance has received little attention. The impact of salt content on children''s hedonic rating and intake of two foods was investigated in children. Using a within-subject crossover design, we recruited 75 children (8–11 years) to participate in five lunches in their school cafeteria. The target foods were green beans and pasta. The added salt content was 0, 0.6 or 1.2 g/100 g. The children''s intake (g) of all lunch items was measured. The children provided their hedonic rating of the food, a preference ranking and a saltiness ranking in the laboratory. Children could rank the foods according to salt content, and they preferred the two saltier options. A food-specific effect of salt content on intake was observed. Compared to the intermediate level (0.6 g salt/100 g), not adding salt decreased green bean intake (−21%; p = 0.002), and increasing the salt content increased pasta intake (+24%; p<0.0001). Structural Equation Modeling was used to model the relative weights of the determinants of intake. It showed that the primary driver of food intake was the child''s hunger; the second most important factor was the child''s hedonic rating of the food, regardless of its salt content, and the last factor was the child''s preference for the particular salt content of the food. In conclusion, salt content has a positive and food-specific effect on intake; it impacted food preferences and intake differently in children. Taking into account children''s preferences for salt instead of their intake may lead to excessive added salt.  相似文献   
10.
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