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   2025篇
  免费   142篇
  2023年   18篇
  2022年   23篇
  2021年   51篇
  2020年   46篇
  2019年   35篇
  2018年   51篇
  2017年   50篇
  2016年   74篇
  2015年   116篇
  2014年   138篇
  2013年   160篇
  2012年   175篇
  2011年   148篇
  2010年   85篇
  2009年   94篇
  2008年   124篇
  2007年   103篇
  2006年   102篇
  2005年   78篇
  2004年   78篇
  2003年   79篇
  2002年   64篇
  2001年   17篇
  2000年   13篇
  1999年   23篇
  1998年   21篇
  1997年   16篇
  1996年   21篇
  1995年   21篇
  1994年   17篇
  1993年   15篇
  1992年   13篇
  1991年   7篇
  1990年   11篇
  1989年   5篇
  1988年   6篇
  1987年   4篇
  1986年   6篇
  1985年   4篇
  1984年   9篇
  1982年   6篇
  1980年   3篇
  1979年   3篇
  1977年   3篇
  1974年   3篇
  1973年   3篇
  1972年   3篇
  1971年   3篇
  1968年   2篇
  1962年   2篇
排序方式: 共有2167条查询结果,搜索用时 921 毫秒
71.
Episiotomy is still a controversy issue among physicians, despite the enormous growth of clinical research. Therefore, the potential of numerical modeling of anatomical structures to simulate biomechanical processes was exploited to realize quantitatively the real effects of the episiotomy and its consequences on the pelvic floor muscle. As such, a numerical model was used composed of pelvic floor muscles, a surface delimiting the anterior region, and a fetus body. A normal vaginal delivery without and with different episiotomies was simulated with the fetus in vertex presentation and occipitoanterior position. According to our numerical results, a mediolateral episiotomy has a protective effect, reducing the stress on the muscles, and the force required to delivery successfully up to 52.2 %. The intervention also has benefits on muscle injury, reducing the damage to a small zone. This study demonstrates the feasibility of using a computational modeling approach to study parturition, namely the capability to isolate and evaluate the mechanical significance of a single feature. It must, however, be taken into account that the numerical model does not assess problems that may occur as blood loss, infections and others, so it is necessary to examine whether the benefits of an intervention outweigh the risks.  相似文献   
72.

Background

Cynomolgus macaques (Macaca fascicularis) represent a feasible model for research on Chagas disease since natural T. cruzi infection in these primates leads to clinical outcomes similar to those observed in humans. However, it is still unknown whether these clinical similarities are accompanied by equivalent immunological characteristics in the two species. We have performed a detailed immunophenotypic analysis of circulating leukocytes together with systems biology approaches from 15 cynomolgus macaques naturally infected with T. cruzi (CH) presenting the chronic phase of Chagas disease to identify biomarkers that might be useful for clinical investigations.

Methods and Findings

Our data established that CH displayed increased expression of CD32+ and CD56+ in monocytes and enhanced frequency of NK Granzyme A+ cells as compared to non-infected controls (NI). Moreover, higher expression of CD54 and HLA-DR by T-cells, especially within the CD8+ subset, was the hallmark of CH. A high level of expression of Granzyme A and Perforin underscored the enhanced cytotoxicity-linked pattern of CD8+ T-lymphocytes from CH. Increased frequency of B-cells with up-regulated expression of Fc-γRII was also observed in CH. Complex and imbricate biomarker networks demonstrated that CH showed a shift towards cross-talk among cells of the adaptive immune system. Systems biology analysis further established monocytes and NK-cell phenotypes and the T-cell activation status, along with the Granzyme A expression by CD8+ T-cells, as the most reliable biomarkers of potential use for clinical applications.

Conclusions

Altogether, these findings demonstrated that the similarities in phenotypic features of circulating leukocytes observed in cynomolgus macaques and humans infected with T. cruzi further supports the use of these monkeys in preclinical toxicology and pharmacology studies applied to development and testing of new drugs for Chagas disease.  相似文献   
73.
Sensory reweighting is a characteristic of postural control functioning adopted to accommodate environmental changes. The use of mono or binocular cues induces visual reduction/increment of moving room influences on postural sway, suggesting a visual reweighting due to the quality of available sensory cues. Because in our previous study visual conditions were set before each trial, participants could adjust the weight of the different sensory systems in an anticipatory manner based upon the reduction in quality of the visual information. Nevertheless, in daily situations this adjustment is a dynamical process and occurs during ongoing movement. The purpose of this study was to examine the effect of visual transitions in the coupling between visual information and body sway in two different distances from the front wall of a moving room. Eleven young adults stood upright inside of a moving room in two distances (75 and 150 cm) wearing a liquid crystal lenses goggles, which allow individual lenses transition from opaque to transparent and vice-versa. Participants stood still during five minutes for each trial and the lenses status changed every one minute (no vision to binocular vision, no vision to monocular vision, binocular vision to monocular vision, and vice-versa). Results showed that farther distance and monocular vision reduced the effect of visual manipulation on postural sway. The effect of visual transition was condition dependent, with a stronger effect when transitions involved binocular vision than monocular vision. Based upon these results, we conclude that the increased distance from the front wall of the room reduced the effect of visual manipulation on postural sway and that sensory reweighting is stimulus quality dependent, with binocular vision producing a much stronger down/up-weighting than monocular vision.  相似文献   
74.

Background

About 15 million children are born under 37 weeks of gestation worldwide. Prematurity is the leading cause of neonatal deaths and short/long term morbidities, entailing consequences not only for the individual, but also their family, health agencies, facilities and all community. The provider-initiated preterm birth is currently one of the most important obstetric conditions related to preterm births, particularly in middle and high income countries, thus decreasing the need for therapeutic preterm birth is essential to reduce global prematurity. Therefore detailed knowledge on the factors associated with provider-initiated preterm birth is essential for the efforts to reduce preterm birth rates and its consequences. In this current analysis we aimed to assess the proportion of provider-initiated (pi-PTB) among preterm births in Brazil and identify associated factors.

Methods and Findings

This is an analysis of a multicenter cross-sectional study with a nested case-control component called Brazilian Multicenter Study on Preterm Birth (EMIP). EMIP was conducted in 20 referral obstetric hospitals located in the three most populated of the five Brazilian regions. We analysed data of women with pi-PTB, defined as childbirth occurring at less than 37 weeks, medically indicated for maternal/fetal compromise or both; and women with term birth, childbirth at or after 37 weeks. Maternal, sociodemographic, obstetric, prenatal care, delivery, and postnatal characteristics were assessed as possible factors associated with pi-PTB, compared to term births. The overall prevalence of preterm births was 12.3%. Of these, approximately one-third of cases were initiated by the provider. Hypertensive disorders, placental abruption, and diabetes were the main maternal conditions leading to pi-PTB. Caesarean section was the most common mode of delivery. Chronic hypertension (OR 7.47; 95%CI 4.02–13.88), preeclampsia/eclampsia/HELLP syndrome (OR 15.35; 6.57–35.88), multiple pregnancy (OR 12.49; 4.86–32.05), and chronic diabetes (OR 5.24; 2.68–10.25) were the most significant factors independently associated with pi-PTB.

Conclusions

pi-PTB is responsible for about one-third of all preterm births, requiring special attention. The decision-making process relative to the choice of provider-initiated birth is complex, and many factors should be elucidated to improve strategies for its prevention, including evidence-based guidelines on proper management of the corresponding clinical conditions.  相似文献   
75.
New proposals for models and applications of prediction processes with data on molecular markers may help reduce the financial costs of and identify superior genotypes in maize breeding programs. Studies evaluating Genomic Best Linear Unbiased Prediction (GBLUP) models including dominance effects have not been performed in the univariate and multivariate context in the data analysis of this crop. A single cross hybrid construction procedure was performed in this study using phenotypic data and actual molecular markers of 4,091 maize lines from the public database Panzea. A total of 400 simple hybrids resulting from this process were analyzed using the univariate and multivariate GBLUP model considering only additive effects additive plus dominance effects. Historic heritability scenarios of five traits and other genetic architecture settings were used to compare models, evaluating the predictive ability and estimation of variance components. Marginal differences were detected between the multivariate and univariate models. The main explanation for the small discrepancy between models is the low- to moderate-magnitude correlations between the traits studied and moderate heritabilities. These conditions do not favor the advantages of multivariate analysis. The inclusion of dominance effects in the models was an efficient strategy to improve the predictive ability and estimation quality of variance components.  相似文献   
76.
The effects of Alfalfa mosaic virus (AMV) infection on essential oil (EO) content and composition of a Sweet Basil cv. Gigante di Napoli were evaluated. A 10‐fold lower extraction yield from infected plants was observed, suggesting that morphological alterations induced by the disease may affect abundance and efficacy of secretive tissues. Organoleptic properties and thus quality of EO were severely affected and EO composition resulted severely altered, with a great increase in sesquiterpenes (from 72.8 to 19.8%) and a decrease in both monoterpenes (from 35 to 11%) and phenylpropanoids (from 44.5 to 15.8%, despite a slight increase in eugenol). Such report is indicative of possible direct or indirect metabolic consequences of AMV in a commercially important species like Ocimum basilicum is. The possible consequences of linalool and transβ‐farnesene content changes on the dispersion of viruliferous aphids are also examined and discussed.  相似文献   
77.
78.
79.
Cattle tick control remains a serious problem in cattle farms worldwide, due to the limited success achieved with chemicals. Although the use of vaccines for tick control may open possibilities for an integrated approach, the search for other protective antigens is still necessary to improve control. Boophilus microplus is a rich source of BmTIs, serine proteinase inhibitors that are present throughout the tick's lifecycle. The present paper reports a pen trial conducted to evaluate the performance of a synthetic BmTI N-terminal fragment as antigen against the tick in bovines. The trial was conducted with two groups of eight crossbred cattle under controlled infestation: one group was vaccinated with BmTI peptide using saponin as adjuvant and the other was kept as control. Challenge was performed with 15,000 larvae. The specific IgG response was measured by ELISA, with successful outcomes for vaccinated animals. Vaccination resulted in an 18.4% level of efficacy when compared with the control group.  相似文献   
80.
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