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   673篇
  免费   120篇
  国内免费   13篇
  806篇
  2024年   6篇
  2023年   45篇
  2022年   48篇
  2021年   58篇
  2020年   49篇
  2019年   55篇
  2018年   32篇
  2017年   30篇
  2016年   27篇
  2015年   31篇
  2014年   53篇
  2013年   49篇
  2012年   33篇
  2011年   43篇
  2010年   19篇
  2009年   30篇
  2008年   28篇
  2007年   26篇
  2006年   16篇
  2005年   16篇
  2004年   18篇
  2003年   12篇
  2002年   10篇
  2001年   8篇
  2000年   12篇
  1999年   1篇
  1998年   3篇
  1997年   7篇
  1996年   2篇
  1995年   2篇
  1994年   1篇
  1993年   7篇
  1992年   1篇
  1991年   2篇
  1990年   3篇
  1988年   1篇
  1987年   2篇
  1985年   3篇
  1984年   5篇
  1983年   3篇
  1982年   3篇
  1981年   2篇
  1980年   1篇
  1978年   1篇
  1977年   2篇
排序方式: 共有806条查询结果,搜索用时 15 毫秒
231.
Insomnia poses significant challenges to public health. It is a common condition associated with marked impairment in function and quality of life, psychiatric and physical morbidity, and accidents. As such, it is important that effective treatment is provided in clinical practice. To this end, this paper reviews critical aspects of the assessment of insomnia and the available treatment options. These options include both non‐medication treatments, most notably cognitive behavioral therapy for insomnia, and a variety of pharmacologic therapies such as benzodiazepines, “z‐drugs”, melatonin receptor agonists, selective histamine H1 antagonists, orexin antagonists, antidepressants, antipsychotics, anticonvulsants, and non‐selective antihistamines. A review of the available research indicates that rigorous double‐blind, randomized, controlled trials are lacking for some of the most commonly administered insomnia therapies. However, there are an array of interventions which have been demonstrated to have therapeutic effects in insomnia in trials with the above features, and whose risk/benefit profiles have been well characterized. These interventions can form the basis for systematic, evidence‐based treatment of insomnia in clinical practice. We review this evidence base and highlight areas where more studies are needed, with the aim of providing a resource for improving the clinical management of the many patients with insomnia.  相似文献   
232.
Cognitive development of children is influenced by different environmental factors like nutritional and socio‐economic status. The objectives of the present study were to determine the influence of grades of undernutrition and socio‐economic status (SES) on the cognitive development of school children of Kolkata. Five hundred sixty six (566) school children having 5–12 years of age were selected from different schools of Kolkata. The cognitive development was measured by the scores of Raven's colored progressive matrices (RCPM). The chronic and acute nutritional statuses were measured from height‐for‐age (HAZ) and weight‐for‐age (WAZ) Z scores respectively with reference to the values of WHO. SES was determined by updated Kuppuswamy scale. The prevalences of undernutrition in the observed children were 57.95% (according to HAZ) and 52.82% (according to WAZ). The age dependent growth curve of RCPM scores of the observed children remains in between the 10th and 25th centile of British children. The children belonging to superior and intellectual deficit IQ classes were 21.55 and 36.40%, respectively of the total subjects. Most of the subjects belong to lower middle (39.93%) and upper middle (36.40%) class of SES. RCPM scores of school children were gradually decreased with the grades of undernutrition and SES. RCPM scores were significantly correlated with HAZ, WAZ, SES, age, and sex (P < 0.001) and strongly associated with HAZ, SES, age, and sex (P < 0.001, P < 0.05). Present study indicates that cognitive development of school children of Kolkata is influenced by the grade of undernutrition and SES. Am J Phys Anthropol 156:274–285, 2015. © 2014 Wiley Periodicals, Inc.  相似文献   
233.
234.
Coenzyme Q (CoQ, ubiquinone) is an essential component of the respiratory chain, a cofactor of pyrimidine biosynthesis and acts as an antioxidant in extra mitochondrial membranes. More recently CoQ has been identified as a modulator of apoptosis, inflammation and gene expression. CoQ deficient Caenorhabditis elegans clk-1 mutants show several phenotypes including a delayed postembryonic growth. Using wild type and two clk-1 mutants, here we established an experimental set-up to study the consequences of endogenous CoQ deficiency or exogenous CoQ supply on gene expression and growth. We found that a deficiency of endogenous CoQ synthesis down-regulates a cluster of genes that are important for growth (i.e., RNA polymerase II, eukaryotic initiation factor) and up-regulates oxidation reactions (i.e., cytochrome P450, superoxide dismutase) and protein interactions (i.e., F-Box proteins). Exogenous CoQ supply partially restores the expression of these genes as well as the growth retardation of CoQ deficient clk-1 mutants. On the other hand exogenous CoQ supply does not alter the expression of a further sub-set of genes. These genes are involved in metabolism (i.e., succinate dehydrogenase complex), cell signalling or synthesis of lectins. Thus, our work provides a comprehensive overview of genes which can be modulated in their expression by endogenous or exogenous CoQ. As growth retardation in CoQ deficiency is linked to the gene expression profile we suggest that CoQ promotes growth via gene expression.  相似文献   
235.
This article focuses on conducting global testing for association between a binary trait and a set of rare variants (RVs), although its application can be much broader to other types of traits, common variants (CVs), and gene set or pathway analysis. We show that many of the existing tests have deteriorating performance in the presence of many nonassociated RVs: their power can dramatically drop as the proportion of nonassociated RVs in the group to be tested increases. We propose a class of so-called sum of powered score (SPU) tests, each of which is based on the score vector from a general regression model and hence can deal with different types of traits and adjust for covariates, e.g., principal components accounting for population stratification. The SPU tests generalize the sum test, a representative burden test based on pooling or collapsing genotypes of RVs, and a sum of squared score (SSU) test that is closely related to several other powerful variance component tests; a previous study (Basu and Pan 2011) has demonstrated good performance of one, but not both, of the Sum and SSU tests in many situations. The SPU tests are versatile in the sense that one of them is often powerful, although its identity varies with the unknown true association parameters. We propose an adaptive SPU (aSPU) test to approximate the most powerful SPU test for a given scenario, consequently maintaining high power and being highly adaptive across various scenarios. We conducted extensive simulations to show superior performance of the aSPU test over several state-of-the-art association tests in the presence of many nonassociated RVs. Finally we applied the SPU and aSPU tests to the GAW17 mini-exome sequence data to compare its practical performance with some existing tests, demonstrating their potential usefulness.  相似文献   
236.
The analysis of species co‐occurrence patterns continues to be a main pursuit of ecologists, primarily because the coexistence of species is fundamentally important in evaluating various theories, principles and concepts. Examples include community assembly, equilibrium versus non‐equilibrium organization of communities, resource partitioning and ecological character displacement, the local–regional species diversity relationship, and the metacommunity concept. Traditionally, co‐occurrence has been measured and tested at the level of an entire species presence–absence matrix wherein various algorithms are used to randomize matrices and produce statistical null distributions of metrics that quantify structure in the matrix. This approach implicitly recognizes a presence–absence matrix as having some real ecological identity (e.g. a set of species exhibiting nestedness among a set of islands) in addition to being a unit of statistical analysis. An emerging alternative is to test for non‐random co‐occurrence between paired species. The pairwise approach does not analyse matrix‐level structure and thus views a species pair as the fundamental unit of co‐occurrence. Inferring process from pattern is very difficult in analyses of co‐occurrence; however, the pairwise approach may make this task easier by simplifying the analysis and resulting inferences to associations between paired species.  相似文献   
237.

Introduction

Polycystic Ovary Syndrome (PCOS) is a complex endocrine disorder, of multifactorial etiology, which affects 6–10% of women of reproductive age. It is considered the leading cause of anovulatory infertility, menstrual disorders and hyperandrogenism in this population. The genetic basis of PCOS is still largely unknown despite significant family clustering; determining its mode of inheritance is particularly difficult given the heterogenic presentation of the disease.

Materials and methods

130 Brazilian women, aged 14–42 years, who met the 2003 Rotterdam criteria for PCOS diagnosis, were included, and 96 healthy women constituted the control group. Presence of hirsutism was classified using the modified Ferriman–Gallwey score (F–G score) as absent (≤ 7), mild (8–14), and severe (≥ 15). Blood levels of luteinizing hormone (LH), total testosterone (TT), dehydroepiandrosterone sulfate (DHEA-S) and androstenedione were determined. The coding region of the luteinizing hormone beta-subunit (LHB) gene was amplified and sequenced. Differences in allelic and genotypic frequency distribution of each polymorphism across controls and cases were estimated by the Mantel–Haenszel chi-square or Fisher's exact test (p < 0.05), and the probability of an association between the detection of a polymorphism and presence of a diagnosis of PCOS, by logistic regression.

Result(s)

Sequencing detected 8 polymorphisms in the LHB gene coding region. Two polymorphisms in linkage disequilibrium were significantly more prevalent in the presence of hyperandrogenemia: rs1800447/rs34349826 (Trp28Arg/Ile35Thr) (p = 0.02).

Conclusion(s)

In this series, a modulatory effect of LHB polymorphisms on hyperandrogenemia phenotype of PCOS was observed; however, this finding needs to be replicated in other populations.  相似文献   
238.
The hepatitis C virus (HCV), the main cause of morbidity and mortality, is endemic worldwide. HCV causes cirrhosis and other complications that often lead to death. HCV is most common in underdeveloped nations, with the highest prevalence rates in Egypt. Tumor suppressor gene (P53) induces the expression of apoptotic antigen-1 gene (APO-1) by binding to its promoter for mediating apoptosis; an important mechanism for limiting viral replication. This study aims at investigating the impact of P53 72 Arg/Pro and APO-1 − 670 A/G polymorphisms on HCV genotype 4a susceptibility. Two hundred and forty volunteers were enrolled in this study and divided into two major groups; 160 HCV infected patient group and 80 healthy control group. HCV patients were classified according to Metavir scoring system into two subgroups; 72 patients in F0/1-HCV subgroup (patients with no or mild fibrotic stages) and 38 patients in F3/4-HCV subgroup (patients with advanced fibrotic stages). Quantification of HCV-RNA by qRT-PCR and fibrotic scores as well as genotyping of HCV-RNA, P53 at 72 Arg/Pro, and APO-1 at − 670 A/G were performed for all subjects. It was resulted that F0/1-HCV patients have significant differences of P53 at 72 (Pro/Pro and Arg/Arg) genotypes and dominant/recessive genetic models as well as APO-1 − 670 A/A genotype and dominant genetic model as compared to F3/4-HCV patients. Moreover, HCV patients have significant differences of P53 at 72 (Pro/Pro) genotype and recessive genetic model as well as APO-1 − 670 A/A genotype and dominant genetic model as compared to those of healthy individuals. Finally, it was concluded that P53 rs 1042522 (Pro/Pro and Arg/Arg) genotypes and APO-1 rs 1800682 A/A genotype may be potentially used as sensitive genetic markers for HCV genotype 4a susceptibility.  相似文献   
239.

Background

Left ventricular dysfunction (LVD) is a complex, multifactorial condition, caused by mechanical, neurohormonal, and genetic factors. We have previously observed association of renin–angiotensin–aldosterone system (RAAS), matrix metalloproteinases (MMPs) and inflammatory pathway genes with LVD. Therefore the present study was undertaken to identify the combination of genetic variants and their possible interactions contributing towards genetic susceptibility to LVD in the background of coronary artery disease (CAD).

Methods and results

The study included 230 healthy controls and 510 consecutive patients with angiographically confirmed CAD. Among them, 162 with reduced left ventricle ejection fraction (LVEF ≤ 45%) were categorized as having LVD. We analyzed 11 polymorphisms of RAAS, MMPs and inflammatory pathways. Single locus analysis showed that AT1 A1166C (p value < 0.001; OR = 3.67), MMP9 R668Q (p value = 0.007; OR = 3.48) and NFKB1-94 ATTG ins/del (p value = 0.013; OR = 2.01) polymorphisms were independently associated with LVD when compared with both non-LVD patients and healthy controls. High-order gene–gene interaction analysis, using classification and regression tree (CART) and multifactor dimensionality reduction (MDR) revealed that AT1 A1166C and NFKB1-94 ATTG ins/del polymorphisms jointly increased the risk of LVD to great extent (p-value = 0.001; OR = 8.55) and best four-factor interaction model consisted of AT1 A1166C, MMP7 A-181G, MMP9 R668Q and NFKB1-94 ATTG ins/del polymorphisms with testing accuracy of 0.566 and cross validation consistency (CVC) = 9/10 (permutation p < 0.001) showed increased risk for LVD respectively.

Conclusion

AT1 A1166C independently and in combination with MMP9 R668Q and NFKB1-94 ATTG ins/del polymorphisms plays important role in conferring genetic susceptibility to LVD in CAD patients.  相似文献   
240.
Calpastatin has been introduced as a potential candidate gene for growth and meat quality traits. In this study, genetic variability was investigated in the exon 6 and its intron boundaries of ovine CAST gene by PCR-SSCP analysis and DNA sequencing. Also a protein sequence and structural analysis were performed to predict the possible impact of amino acid substitutions on physicochemical properties and structure of the CAST protein. A total of 487 animals belonging to four ancient Iranian sheep breeds with different fat metabolisms, Lori-Bakhtiari and Chall (fat-tailed), Zel-Atabay cross-bred (medium fat-tailed) and Zel (thin-tailed), were analyzed. Eight unique SSCP patterns, representing eight different sequences or haplotypes, CAST-1, CAST-2 and CAST-6 to CAST-11, were identified. Haplotypes CAST-1 and CAST-2 were most common with frequency of 0.365 and 0.295. The novel haplotype CAST-8 had considerable frequency in Iranian sheep breeds (0.129). All the consensus sequences showed 98–99%, 94–98%, 92–93% and 82–83% similarity to the published ovine, caprine, bovine and porcine CAST locus sequences, respectively. Sequence analysis revealed four SNPs in intron 5 (C24T, G62A, G65T and T69-) and three SNPs in exon 6 (c.197A > T, c.282G > T and c.296C > G). All three SNPs in exon 6 were missense mutations which would result in p.Gln 66 Leu, p.Glu 94 Asp and p.Pro 99 Arg substitutions, respectively, in CAST protein. All three amino acid substitutions affected the physicochemical properties of ovine CAST protein including hydrophobicity, amphiphilicity and net charge and subsequently might influence its structure and effect on the activity of Ca2 + channels; hence, they might regulate calpain activity and afterwards meat tenderness and growth rate. The Lori-Bakhtiari population showed the highest heterozygosity in the ovine CAST locus (0.802). Frequency difference of haplotypes CAST-10 and CAST-8 between Lori-Bakhtiari (fat-tailed) and Zel (thin-tailed) breeds was highly significant (P < 0.001), indicating that these two haplotypes might be breed-specific haplotypes that distinguish between fat-tailed and thin-tailed sheep breeds.  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