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   5076篇
  免费   408篇
  2023年   40篇
  2022年   81篇
  2021年   150篇
  2020年   109篇
  2019年   131篇
  2018年   129篇
  2017年   114篇
  2016年   183篇
  2015年   271篇
  2014年   295篇
  2013年   321篇
  2012年   337篇
  2011年   365篇
  2010年   241篇
  2009年   190篇
  2008年   255篇
  2007年   260篇
  2006年   250篇
  2005年   204篇
  2004年   215篇
  2003年   194篇
  2002年   180篇
  2001年   80篇
  2000年   66篇
  1999年   61篇
  1998年   58篇
  1997年   44篇
  1996年   49篇
  1995年   26篇
  1994年   33篇
  1993年   34篇
  1992年   47篇
  1991年   32篇
  1990年   36篇
  1989年   36篇
  1988年   28篇
  1987年   23篇
  1986年   34篇
  1985年   32篇
  1984年   26篇
  1983年   24篇
  1982年   26篇
  1981年   14篇
  1980年   8篇
  1979年   26篇
  1978年   23篇
  1977年   13篇
  1976年   12篇
  1974年   7篇
  1972年   11篇
排序方式: 共有5484条查询结果,搜索用时 125 毫秒
981.
982.

Objective

Patients with temporal lobe epilepsy (TLE) with hippocampal sclerosis (HS) have diffuse subtle gray matter (GM) atrophy detectable by MRI quantification analyses. However, it is not clear whether the etiology and seizure frequency are associated with this atrophy. We aimed to evaluate the occurrence of GM atrophy and the influence of seizure frequency in patients with TLE and either normal MRI (TLE-NL) or MRI signs of HS (TLE-HS).

Methods

We evaluated a group of 172 consecutive patients with unilateral TLE-HS or TLE-NL as defined by hippocampal volumetry and signal quantification (122 TLE-HS and 50 TLE-NL) plus a group of 82 healthy individuals. Voxel-based morphometry was performed with VBM8/SPM8 in 3T MRIs. Patients with up to three complex partial seizures and no generalized tonic-clonic seizures in the previous year were considered to have infrequent seizures. Those who did not fulfill these criteria were considered to have frequent seizures.

Results

Patients with TLE-HS had more pronounced GM atrophy, including the ipsilateral mesial temporal structures, temporal lobe, bilateral thalami and pre/post-central gyri. Patients with TLE-NL had more subtle GM atrophy, including the ipsilateral orbitofrontal cortex, bilateral thalami and pre/post-central gyri. Both TLE-HS and TLE-NL showed increased GM volume in the contralateral pons. TLE-HS patients with frequent seizures had more pronounced GM atrophy in extra-temporal regions than TLE-HS with infrequent seizures. Patients with TLE-NL and infrequent seizures had no detectable GM atrophy. In both TLE-HS and TLE-NL, the duration of epilepsy correlated with GM atrophy in extra-hippocampal regions.

Conclusion

Although a diffuse network GM atrophy occurs in both TLE-HS and TLE-NL, this is strikingly more evident in TLE-HS and in patients with frequent seizures. These findings suggest that neocortical atrophy in TLE is related to the ongoing seizures and epilepsy duration, while thalamic atrophy is more probably related to the original epileptogenic process.  相似文献   
983.

Introduction

This analysis explores the association between elements of surgical efficiency in voluntary medical male circumcision (VMMC), quality of surgical technique, and the amount of time required to conduct VMMC procedures in actual field settings. Efficiency outcomes are defined in terms of the primary provider’s time with the client (PPTC) and total elapsed operating time (TEOT).

Methods

Two serial cross-sectional surveys of VMMC sites were conducted in Kenya, Republic of South Africa, Tanzania and Zimbabwe in 2011 and 2012. Trained clinicians observed quality of surgical technique and timed 9 steps in the VMMC procedure. Four elements of efficiency (task-shifting, task-sharing [of suturing], rotation among multiple surgical beds, and use of electrocautery) and quality of surgical technique were assessed as explanatory variables. Mann Whitney and Kruskal Wallis tests were used in the bivariate analysis and linear regression models for the multivariate analyses to test the relationship between these five explanatory variables and two outcomes: PPTC and TEOT. The VMMC procedure TEOT and PPTC averaged 23–25 minutes and 6–15 minutes, respectively, across the four countries and two years. The data showed time savings from task-sharing in suturing and use of electrocautery in South Africa and Zimbabwe (where task-shifting is not authorized). After adjusting for confounders, results demonstrated that having a secondary provider complete suturing and use of electrocautery reduced PPTC. Factors related to TEOT varied by country and year, but task-sharing of suturing and/or electrocautery were significant in two countries. Quality of surgical technique was not significantly related to PPTC or TEOT, except for South Africa in 2012 where higher quality was associated with lower TEOT.

Conclusions

SYMMACS data confirm the efficiency benefits of task-sharing of suturing and use of electrocautery for decreasing TEOT. Reduced TEOT and PPTC in high volume setting did not result in decreased quality of surgical care.  相似文献   
984.

Purpose

To evaluate whether optic disc hemorrhages are associated with faster rates of estimated retinal ganglion cell (RGC) loss in glaucoma.

Methods

A longitudinal observational cohort study of 222 eyes of 122 patients with glaucoma recruited from the Diagnostic Innovations Glaucoma Study (DIGS) followed for an average of 3.74±0.85 years. All subjects had optical coherence tomography and standard automated perimetry during follow up. Optic disc hemorrhages were detected by masked evaluation of stereophotographs. Rates of change in estimated numbers of RGCs were determined using a previously described method. A random coefficients model was used to investigate the relationship between disc hemorrhages and rates of change in estimated RGC counts over time.

Results

19 eyes of 18 subjects had at least one disc hemorrhage during follow up. At baseline, average estimated RGC counts in eyes with and without disc hemorrhages were 677,994 cells and 682,021 cells, respectively (P = 0.929). Eyes with optic disc hemorrhages during follow-up had significantly faster rates of estimated RGC loss than eyes without disc hemorrhages (22,233 cells/year versus 10,704 cells/year, P = 0.020). The effect of disc hemorrhages on the rates of estimated RGC loss remained significant after adjusting for confounding variables.

Conclusion

Eyes with disc hemorrhages showed faster rates of RGC loss compared to eyes without disc hemorrhages. These results provide further evidence that disc hemorrhages should be considered as an indicator of increased risk for faster neural loss in glaucoma.  相似文献   
985.

Background

Recently, the World Health Organisation and the International Union Against Tuberculosis and Lung Disease published a Collaborative Framework for the Care and Control of Tuberculosis (TB) and Diabetes (DM) (CFTB/DM) proposing bidirectional screening and joint management.

Objective

To evaluate the feasibility and effectiveness of the CFTB/DM in Mexico. Design. Prospective observational cohort. Setting. 15 primary care units in 5 states in Mexico. Participants: Patients aged ≥20 years diagnosed with DM or pulmonary TB who sought care at participating clinics. Intervention: The WHO/Union CFTB/DM was adapted and implemented according to official Mexican guidelines. We recruited participants from July 2012 to April 2013 and followed up until March 2014. Bidirectional screening was performed. Patients diagnosed with TB and DM were invited to receive TB treatment under joint management. Main outcome measures. Diagnoses of TB among DM, of DM among TB, and treatment outcomes among patients with DM and TB.

Results

Of 783 DM patients, 11 (1.4%) were unaware of their TB. Of 361 TB patients, 16 (4.4%) were unaware of their DM. 95 TB/DM patients accepted to be treated under joint management, of whom 85 (89.5%) successfully completed treatment. Multiple linear regression analysis with change in HbA1c and random capillary glucose as dependent variables revealed significant decrease with time (regression coefficients (β)  = −0.660, (95% confidence interval (CI), −0.96 to −0.35); and β = −1.889 (95% CI, −2.77 to −1.01, respectively)) adjusting by sex, age and having been treated for a previous TB episode. Patients treated under joint management were more likely to experience treatment success than patients treated under routine DM and TB programs as compared to historical (adjusted OR (aOR), 2.8, 95%CI 1.28–6.13) and same period (aOR 2.37, 95% CI 1.13–4.96) comparison groups.

Conclusions

Joint management of TB and DM is feasible and appears to improve clinical outcomes.  相似文献   
986.
987.

Background

The vast majority of the population around the world has always used medicinal plants as first source of health care to fight infectious and non infectious diseases. Most of these medicinal plants may have scientific evidence to be considered in general practice.

Objective

The aim of this work was to investigate the antioxidant capacities and anti-inflammatory activities of ethanol extracts of leaves of Cassia alata, Eleusine indica, Carica papaya, Eremomastax speciosa and the stem bark of Polyscias fulva, collected in Cameroon.

Methods

Chemiluminescence was used to analyze the antioxidant activities of plant extracts against hydrogen peroxide or superoxide anion. Comet assays were used to analyze the protection against antioxidant-induced DNA damage induced in white blood cells after treating with hydrogen peroxide. Flow cytometry was used to measure γδ T cells proliferation and anti-inflammatory activity of γδ T cells and of immature dendritic cells (imDC) in the presence of different concentrations of plant extracts.

Results

Ethanol extracts showed strong antioxidant properties against both hydrogen peroxide and superoxide anion. Cassia alata showed the highest antioxidant activity. The effect of plant extracts on γδ T cells and imDC was evidenced by the dose dependent reduction in TNF-α production in the presence of Cassia alata, Carica papaya, Eremomastax speciosa Eleusine indica, and Polyscias fulva. γδ T cells proliferation was affected to the greatest extent by Polyscias fulva.

Conclusion

These results clearly show the antioxidant capacity and anti-inflammatory activities of plant extracts collected in Cameroon. These properties of leaves and stem bark extracts may contribute to the value for these plants in traditional medicine and in general medical practice.  相似文献   
988.

Purpose

In addition to excess adiposity, low cardiorespiratory fitness (CRF) and low musculoskeletal fitness (MSF) are important independent risk factors for future cardio-metabolic disease in adolescents, yet global fitness surveillance in adolescents is poor. The objective of this study was to describe and investigate geographical variation in levels of health-related physical fitness, including CRF, MSF, body mass index (BMI), and waist circumference (WC) in Chilean 8th graders.

Methods

This cross-sectional study was based on a population-based, representative sample of 19,929 8th graders (median age = 14 years) in the 2011 National Physical Education Survey from Chile. CRF was assessed with the 20-meter shuttle run test, MSF with standing broad jump, and body composition with BMI and WC. Data were classified according to health-related standards. Prevalence of levels of health-related physical fitness was mapped for each of the four variables, and geographical variation was explored at the country level by region and in the Santiago Metropolitan Area by municipality.

Results

Girls had significantly higher prevalence of unhealthy CRF, MSF, and BMI than boys (p<0.05). Overall, 26% of boys and 55% of girls had unhealthy CRF, 29% of boys and 35% of girls had unhealthy MSF, 29% of boys and 44% of girls had unhealthy BMI, and 31% of adolescents had unhealthy WC. High prevalence of unhealthy fitness levels concentrates in the northern and middle regions of the country and in the North and Southwest sectors for the Santiago Metropolitan Area.

Conclusion

Prevalence of unhealthy CRF, MSF, and BMI is relatively high among Chilean 8th graders, especially in girls, when compared with global estimates. Identification of geographical regions and municipalities with high prevalence of unhealthy physical fitness presents opportunity for targeted intervention.  相似文献   
989.
Next-generation sequencing technology has increased the capacity to generate molecular data for plant biological research, including phylogenetics, and can potentially contribute to resolving complex phylogenetic problems. The evolutionary history of Medicago L. (Leguminosae: Trifoliae) remains unresolved due to incongruence between published phylogenies. Identification of the processes causing this genealogical incongruence is essential for the inference of a correct species phylogeny of the genus and requires that more molecular data, preferably from low-copy nuclear genes, are obtained across different species. Here we report the development of 50 novel LCN markers in Medicago and assess the phylogenetic properties of each marker. We used the genomic resources available for Medicago truncatula Gaertn., hybridisation-based gene enrichment (sequence capture) techniques and Next-Generation Sequencing to generate sequences. This alternative proves to be a cost-effective approach to amplicon sequencing in phylogenetic studies at the genus or tribe level and allows for an increase in number and size of targeted loci. Substitution rate estimates for each of the 50 loci are provided, and an overview of the variation in substitution rates among a large number of low-copy nuclear genes in plants is presented for the first time. Aligned sequences of major species lineages of Medicago and its sister genus are made available and can be used in further probe development for sequence-capture of the same markers.  相似文献   
990.
Lipoteichoic acids (LTA) are amphiphilic polymers that are important constituents of the cell wall of many Gram-positive bacteria. The chemical structures of LTA vary among organisms, albeit in the majority of Gram-positive bacteria the LTAs feature a common poly-1,3-(glycerolphosphate) backbone. Previously, the specificity of opsonic antibodies for this backbone present in some Gram-positive bacteria has been demonstrated, suggesting that this minimal structure may be sufficient for vaccine development. In the present work, we studied a well-defined synthetic LTA-fragment, which is able to inhibit opsonic killing of polyclonal rabbit sera raised against native LTA from Enterococcus faecalis 12030. This promising compound was conjugated with BSA and used to raise rabbit polyclonal antibodies. Subsequently, the opsonic activity of this serum was tested in an opsonophagocytic assay and specificity was confirmed by an opsonophagocytic inhibition assay. The conjugated LTA-fragment was able to induce specific opsonic antibodies that mediate killing of the clinical strains E. faecalis 12030, Enterococcus faecium E1162, and community-acquired Staphylococcus aureus strain MW2 (USA400). Prophylactic immunization with the teichoic acid conjugate and with the rabbit serum raised against this compound was evaluated in active and passive immunization studies in mice, and in an enterococcal endocarditis rat model. In all animal models, a statistically significant reduction of colony counts was observed indicating that the novel synthetic LTA-fragment conjugate is a promising vaccine candidate for active or passive immunotherapy against E. faecalis and other Gram-positive bacteria.  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