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   98篇
  免费   2篇
  100篇
  2021年   2篇
  2017年   1篇
  2016年   2篇
  2015年   5篇
  2014年   8篇
  2013年   7篇
  2012年   2篇
  2011年   9篇
  2010年   11篇
  2009年   9篇
  2008年   9篇
  2007年   5篇
  2006年   3篇
  2005年   3篇
  2004年   4篇
  2003年   1篇
  2002年   1篇
  2001年   1篇
  2000年   4篇
  1999年   2篇
  1998年   1篇
  1997年   2篇
  1996年   1篇
  1995年   1篇
  1993年   1篇
  1991年   1篇
  1989年   1篇
  1985年   1篇
  1983年   1篇
  1978年   1篇
排序方式: 共有100条查询结果,搜索用时 15 毫秒
81.
Transposable elements of the mariner family are widespread among insects and other invertebrates, and initial analyses of their relationships indicated frequent occurrence of horizontal transfers between hosts. A specific PCR assay was used to screen for additional members of the irritans subfamily of mariners in more than 400 arthropod species. Phylogenetic analysis of cloned PCR fragments indicated that relatively recent horizontal transfers had occurred into the lineages of a fruit fly Drosophila ananassae, the horn fly Haematobia irritans, the African malaria vector mosquito Anopheles gambiae, and a green lacewing Chrysoperla plorabunda. Genomic dot-blot analysis revealed that the copy number in these species varies widely, from about 17,000 copies in the horn fly to three copies in D. ananassae. Multiple copies were sequenced from genomic clones from each of these species and four others with related elements. These sequences confirmed the PCR results, revealing extremely similar elements in each of these four species (greater than 88% DNA and 95% amino acid identity). In particular, the consensus sequence of the transposase gene of the horn fly elements differs by just two base pairs out of 1,044 from that of the lacewing elements. The mosquito lineage has diverged from the other Diptera for over 200 Myr, and the neuropteran last shared a common ancestor with them more than 265 Myr ago, so this high similarity implies that these transposons recently transferred horizontally into each lineage. Their presence in only the closest relatives in at least the lacewing lineage supports this hypothesis. Such horizontal transfers provide an explanation for the evolutionary persistence and widespread distribution of mariner transposons. We propose that the ability to transfer horizontally to new hosts before extinction by mutation in the current host constitutes the primary selective constraint maintaining the sequence conservation of mariners and perhaps other DNA-mediated elements.   相似文献   
82.

Background

An imbalance in Matrix MetalloProteases (MMPs) and Tissue Inhibitors of MMPs (TIMPs) contributes to Chronic Obstructive Pulmonary Disease (COPD) development. Longitudinal studies investigating Single Nucleotide Polymorphisms (SNPs) in MMPs and TIMPs with respect to COPD development and lung function decline in the general population are lacking.

Methods

We genotyped SNPs in MMP1 (G-1607GG), MMP2 (-1306 C/T), MMP9 (3 tagging SNPs), MMP12 (A-82G and Asn357Ser) and TIMP1 (Phe124Phe and Ile158Ile) in 1390 Caucasians with multiple FEV1 measurements from a prospective cohort study in the general population. FEV1 decline was analyzed using linear mixed effect models adjusted for confounders. Analyses of the X-chromosomal TIMP1 gene were stratified according to sex. All significant associations were repeated in an independent general population cohort (n = 1152).

Results

MMP2 -1306 TT genotype carriers had excess FEV1 decline (-4.0 ml/yr, p = 0.03) compared to wild type carriers. TIMP1 Ile158Ile predicted significant excess FEV1 decline in both males and females. TIMP1 Phe124Phe predicted significant excess FEV1 decline in males only, which was replicated (p = 0.10) in the second cohort. The MMP2 and TIMP1 Ile158Ile associations were not replicated. Although power was limited, we did not find associations with COPD development.

Conclusions

We for the first time show that TIMP1 Phe124Phe contributes to excess FEV1 decline in two independent prospective cohorts, albeit not quite reaching conventional statistical significance in the replication cohort. SNPs in MMPs evidently do not contribute to FEV1 decline in the general population.  相似文献   
83.
Emtricitabine (FTC) and tenofovir (TFV) are widely used antiviral agents that require intracellular phosphorylation to become active. This article describes the development and validation of an assay for the simultaneous quantification of FTC mono-, di- and triphosphate (FTC-MP, -DP and -TP), TFV and TFV mono- and diphosphate (TFV-MP and -DP) in peripheral blood mononuclear cells. Reference compounds and internal standards were obtained by thermal degradation of FTC-TP, TFV-DP, stable isotope-labeled TFV-DP and stable isotope-labeled cytosine triphosphate. Cells were lysed in methanol:water (70:30, v/v) and the extracted nucleotides were analyzed using weak anion-exchange chromatography coupled with tandem mass spectrometry. Calibration ranges in PBMC lysate from 0.727 to 36.4, 1.33 to 66.4 and 1.29 to 64.6 nM for FTC-MP, FTC-DP and FTC-TP and from 1.51 to 75.6, 1.54 to 77.2 and 2.54 to 127 nM for TFV, TFV-MP and TFV-DP, respectively, were validated. Accuracies were within ?10.3 and 16.7% deviation at the lower limit of quantification at which the coefficients of variation were less than 18.2%. At the other tested levels accuracies were within ?14.3 and 9.81% deviation and the coefficients of variation lower than 14.7%. The stability of the compounds was assessed under various analytically relevant conditions. The method was successfully applied to clinical samples.  相似文献   
84.
In this paper, we reported the butterflies and moths that are consumed in Mexico. We identified 67 species of Lepidoptera that are eaten principally in their larval stage in 17 states of Mexico. These species belong to 16 families: Arctiidae, Bombycidae, Castniidae, Cossidae, Geometridae, Hepialidae, Hesperiidae, Lasiocampidae, Noctuidae, Nymphalidae, Papilionidae, Pieridae, Pyralidae, Saturniidae, Sesiidae, and Sphingidae. Saturniidae, Pieridae, Noctuidae and Nymphalidae were the more species consumed with 16, 11, 9, and 8 species, respectively. The genera with the largest numbers of species were: Phassus, Phoebis, Hylesia and Spodoptera, with three species. Their local distribution, corresponding to each state of Mexico, is also presented.  相似文献   
85.

Introduction  

Undifferentiated arthritis (UA) has a variable disease course; 40 to 50% of UA patients remit spontaneously, while 30% develop rheumatoid arthritis (RA). Identifying the UA patients who will develop RA is essential to initiate early disease-modifying anti-rheumatic drug (DMARD) therapy. Although the presence of bone erosions at baseline is predictive for a severe destructive disease course in RA, the prognostic importance of erosive joints for disease outcome in UA is unknown. This study evaluates the predictive value of erosive joints for the disease outcome in UA as measured by RA development and disease persistency.  相似文献   
86.
87.

Introduction

This study aimed to investigate rheumatoid factor (RF) and anti-citrullinated protein antibody (ACPA) status and levels as predictors of mortality in two large cohorts of patients with early inflammatory arthritis (EIA).

Methods

Data from the Norfolk Arthritis Register (NOAR) and Leiden Early Arthritis Clinic (EAC) cohorts were used. At baseline, patients had demographic data and smoking status recorded; RF, ACPA and inflammatory markers were measured in the local laboratories. Patients were flagged with national death registers until death or censor date. Antibody status was stratified as negative, low or high positive by RF and ACPA levels individually. In addition, patients were grouped as seronegative, RF positive, ACPA positive or double antibody (RF and ACPA) positive. Cox regression models explored associations between antibody status and mortality adjusting for age, sex, smoking status, inflammatory markers and year of enrolment.

Results

A total of 4962 patients were included, 64% were female. Median age at onset was 56 (NOAR) and 54 (EAC) years. In NOAR and EAC respectively, 35% and 42% of patients were ACPA/RF positive. When antibody status was stratified as negative, low or high positive, there were no consistent findings between the two cohorts. Double antibody positivity was associated with excess mortality in both cohorts compared to seronegative patients: NOAR and EAC respective adjusted HR (95% confidence interval) 1.35 (1.09 to 1.68) and 1.58 (1.16 to 2.15).

Conclusions

Patients with EIA who are seropositive for both RF and ACPA have increased mortality compared to those who are single positive or seronegative. Antibody level in seropositive patients was not consistently associated with excess mortality.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-014-0483-3) contains supplementary material, which is available to authorized users.  相似文献   
88.

Background

Familial adenomatous polyposis (FAP) is a disease characterized by the development of hundreds to thousands of adenomatous polyps in the colorectum early in life. Virtually all patients with FAP will develop colorectal cancer before the age of 40 to 50 years, unless prophylactic colectomy is performed, which significantly improves their prognosis. The mortality pattern has changed and duodenal cancer now is one of the main cancer-related causes of death in these patients. Practically all patients with FAP develop premalignant duodenal adenomas, which may develop to duodenal cancer in approximately 3-7% of patients. Duodenal cancer in patients with FAP has a poor prognosis. The clinical challenge is to identify patients at high-risk for duodenal carcinoma. Chemoprevention would be desirable to avoid duodenectomy. The main goal of this study is to identify risk markers in normal duodenal mucosa of patients with FAP, that could help identify patients at increased risk for malignant transformation.

Methods

Messenger RNA (mRNA) levels of glutathione S-transferase A1 (GSTA1), glutathione S-transferase P1 (GSTP1), KIAA1199, E-cadherin, peroxisome proliferative activated receptor δ (PPARδ), caspase-3, cyclin D1, β-catenin, and cyclooxygenase-2 (COX-2) were measured in duodenal mucosa, using the QuantiGene 2.0 Plex assay. Levels in normal appearing mucosa of patients with FAP (n?=?37) were compared with levels in non-FAP patient controls (n?=?16). In addition, levels before and after treatment with either celecoxib & ursodeoxycholic acid (UDCA, n?=?14) or celecoxib & placebo (n?=?13) were evaluated in patients with FAP.

Results

mRNA levels of glutathione S-transferase A1 (28.16% vs. 38.24%, p?=?0.008) and caspase-3 (3.30% vs. 5.31%, p?=?0.001) were significantly lower in patients with FAP vs. non-FAP patient controls, respectively. COX-2 mRNA levels in normal duodenal mucosa of patients with FAP were found to be unexpectedly low. None of the potential risk markers was influenced by celecoxib or celecoxib & UDCA.

Conclusions

Protection against toxins and carcinogens (GSTA1) and apoptosis (caspase-3) is low in patients with FAP, which could contribute to increased susceptibility for malignant transformation of duodenal mucosa.

Trial registration

http://ClinicalTrials.gov number NCT00808743
  相似文献   
89.
IntroductionMorning stiffness is assessed daily in the diagnostic process of arthralgia and arthritis, but large-scale studies on the discriminative ability are absent. This study explored the diagnostic value of morning stiffness in 5,202 arthralgia and arthritis patients and the prognostic value in early rheumatoid arthritis (RA).MethodsIn arthralgia patients referred to the Early Arthritis Recognition Clinics (EARC) of Leiden (n = 807) and Groningen (n = 481) or included in the Rotterdam Early Arthritis Cohort (REACH) study (n = 353), the associations (cross-sectional analyses) between morning stiffness and presence of arthritis at physical examination were studied. In early arthritis patients, included in the Leiden Early Arthritis Clinic (EAC) (n = 2,748) and Evaluation et Suivi de POlyarthrites Indifférenciées Récentes (ESPOIR) (n = 813), associations with fulfilling the 2010-RA criteria after one year were assessed. In 2010-RA patients included in the EAC (n = 1,140) and ESPOIR (n = 677), association with the long-term outcomes of disease-modifying antirheumatic drug (DMARD)-free sustained remission and radiological progression were determined. Morning stiffness was defined as a duration ≥60 minutes; sensitivity analyses were performed for other definitions.ResultsIn arthralgia, morning stiffness (≥60 minutes) associated with the presence of arthritis; Leiden EARC odds ratio (OR) 1.49 (95% CI 1.001 to 2.20), Groningen EARC OR 2.21 (1.33 to 3.69) and REACH OR 1.55 (0.97 to 2.47) but the areas under the receiver operating characteristic curve (AUCs) were low (0.52, 0.57, 0.54). In early arthritis, morning stiffness was associated with 2010-RA independent of other predictors (Leiden EAC OR 1.72 (95% CI 1.31 to 2.25, AUC 0.68), ESPOIR OR 1.68 (1.03 to 2.74, AUC 0.64)). Duration of ≥30 minutes provided optimal discrimination for RA in early arthritis. Morning stiffness was not associated with radiological progression or DMARD-free sustained remission.ConclusionsMorning stiffness in arthralgia and early arthritis is associated with arthritis and RA respectively. This supports the incorporation of morning stiffness in the diagnostic process.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0616-3) contains supplementary material, which is available to authorized users.  相似文献   
90.
Primate population assessments provide the basis for comparative studies and are necessary prerequisites in determining conservation status. The most widely used assessment method is line transect sampling, which generates systematic data quickly and comparatively inexpensively. In contrast, the presumably most reliable method is long-term monitoring of known groups, which is both slow and costly. To assess the reliability of various analytical methods, we compared group and population densities for white-handed gibbons (Hylobates lar carpenteri) and Phayre’s leaf monkeys (Trachypithecus phayrei crepusculus) derived from transect walks with those from long-term group follows at Phu Khieo Wildlife Sanctuary, Thailand. Our assistants and we regularly walked a 4-km transect over 30 mo (480 km total), resulting in 155 gibbon sightings and 125 leaf monkey sightings. We then estimated densities via 1) DISTANCE and 2) the Kelker method based on perpendicular distances (PD) or animal-to-observer distances (AOD). We compared the 3 estimates to values based on known home ranges (95% kernels), accounting for home range overlap, combined with group size data. Analyses of line transect data consistently overestimated group densities for both species, while underestimating group size for leaf monkeys. Quality of results varied according to the group size and spread of each species. However, we found, in accordance with previous studies, that values derived via AOD (or its derivations) matched most closely with population estimates based on home range data.  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