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   3303篇
  免费   162篇
  国内免费   9篇
耳鼻咽喉   58篇
儿科学   281篇
妇产科学   53篇
基础医学   306篇
口腔科学   129篇
临床医学   279篇
内科学   675篇
皮肤病学   69篇
神经病学   138篇
特种医学   88篇
外科学   437篇
综合类   123篇
预防医学   161篇
眼科学   97篇
药学   347篇
中国医学   29篇
肿瘤学   204篇
  2023年   44篇
  2022年   118篇
  2021年   156篇
  2020年   85篇
  2019年   91篇
  2018年   160篇
  2017年   107篇
  2016年   133篇
  2015年   129篇
  2014年   174篇
  2013年   203篇
  2012年   253篇
  2011年   277篇
  2010年   153篇
  2009年   112篇
  2008年   132篇
  2007年   133篇
  2006年   125篇
  2005年   101篇
  2004年   79篇
  2003年   86篇
  2002年   57篇
  2001年   55篇
  2000年   46篇
  1999年   31篇
  1998年   26篇
  1997年   21篇
  1996年   10篇
  1995年   14篇
  1994年   8篇
  1993年   11篇
  1992年   21篇
  1991年   31篇
  1990年   28篇
  1989年   29篇
  1988年   36篇
  1987年   23篇
  1986年   23篇
  1985年   26篇
  1984年   9篇
  1983年   10篇
  1979年   21篇
  1978年   22篇
  1977年   7篇
  1976年   7篇
  1973年   5篇
  1972年   4篇
  1970年   4篇
  1969年   10篇
  1968年   5篇
排序方式: 共有3474条查询结果,搜索用时 15 毫秒
41.
Treatment guidelines in many countries for Helicobacter pylori (H. pylori) may differ. Owing to the various characteristics of bacteria, clinical manifestations, resistance to antibiotics and recurrence rate, treatment regimens may change. In this letter, we would like to give an Indian perspective on H. pylori treatment guidelines.  相似文献   
42.
43.

Primary objective

The purpose of this study was to develop an objective way to assess human visual attention using the alpha-band component of the visual-evoked potential (VEP).

Design and methods

Six different attentional conditions were tested: eyes-open, eyes-closed, eyes-closed with backwards number counting, and three rapid-serial visual presentation (RSVP) tasks. Eighteen visually normal, young-adult subjects (ages 21–28 years) were tested binocularly at 1 m for each condition on two separate days. The Diopsys? NOVA-TR system was used to obtain the visual-evoked potential (VEP) and extracted alpha wave and its related power spectrum. Additionally, the Visual Search and Attention Test (VSAT) was administered as a subjective measure of visual attention.

Results

Subjects exhibited significant decreases in power in the alpha band when comparing the eyes-closed with the eyes-open conditions, with power in the eyes-closed condition being, on average, twice as large. The response from the other four conditions did not reflect the differential attentional demands. The ratio of the power in the eyes-closed condition to the eyes-open condition in the lower-alpha frequencies (8–10 Hz) was found to be significantly correlated with the group’s performance on the VSAT, especially the 10-Hz component.

Conclusions

An individual’s ability to attenuate their alpha component during visual processing may be a predictor of their visual attentional state. These findings solidify the role of the VEP alpha subcomponent as an objective electrophysiological correlate of visual attention, which may be useful in the diagnosis and treatment of human visual attention disorders in the future.  相似文献   
44.
The Ho3+-doped YVO4 phosphors were successfully prepared via a sol–gel process in which citric acid was used as a chelating agent. X-ray diffraction (XRD) confirmed the effective inclusion of Ho3+ ions into the host matrix with the formation of single phase YVO4. The surface morphology was observed using SEM, the results of which showed a grain growth propensity and the agglomeration of prepared phosphors. The V–O (VO43−) vibration mode was analyzed through Fourier transform infrared (FTIR) spectra. The spectroscopic properties were reported through UV-vis-NIR diffuse reflectance and photoluminescence (PL) spectra. The Judd–Ofelt (J–O) intensity parameters Ω2 = 0.03 × 10−20 cm2, Ω4 = 0.22 × 10−20 cm2, and Ω6 = 0.23 × 10−20 cm2 obtained for the Y0.97VO4:0.03Ho3+ phosphors were used to obtain the total transition probabilities (AT), radiative lifetimes (τrad) and branching ratios (β) for the certain transitions of Ho3+ ions. Under 310 nm UV excitation, the visible emission spectra were measured, and an intense emission was observed around 541 nm (green region) for all the samples. The emission cross-section σP(λ) was 3.22 × 10−21 cm2 and the branching ratio (β) was 0.816; these were investigated to capture the optimal concentration of the Y0.97VO4:0.03Ho3+ phosphor. The estimated color coordinates were observed in the green region of CIE diagram. Ultimately, the superior properties (σP(λ), β, and color purity) of Y0.97VO4:0.03Ho3+ phosphor may make it suitable for green emitting devices.

Ho3+-doped YVO4 phosphors were successfully prepared via a sol–gel process in which citric acid was used as a chelating agent.  相似文献   
45.
IntroductionSince the start of the COVID-19 pandemic 2019, quite a few patients became critical and needed ICU admission with ventilator assistance. Tracheostomy, which was initially performed late during the course of patient on ventilator, has now been considered a procedure that can be performed relatively early as this leads to early weaning of patients and overcomes the shortage of critical beds.ObjectiveThis study aims to focus on the outcomes of tracheotomised COVID-19 patients in terms of survival and any tracheostomy related morbidity.MethodsA prospective study was performed on COVID-19 patients undergoing tracheostomy at this tertiary care teaching hospital, which also was a dedicated centre for treating COVID-19 patients. The duration of this study was from April 2020 to September 2021. Following tracheostomy, all patients were followed up regularly and clinical changes were recorded. Points that were specifically noted were timing of the tracheostomy, change in ventilator settings, tracheostomy related complications, requirement of oxygen, days needed to wean the patient, decanulation, and, if death, the cause of death.ResultsA total of 136 surgical open tracheostomies were performed on COVID-19 patients over the study period. The mean duration of intubation (timing of tracheostomy) was 12 days. A total of 73 out of 136 (53.6%) patients survived. 51 patients (37.5%) got decannulated during the course of the hospital stay. 9 patients were decanulated during the follow up visits and 13 patients were lost to follow up. 63 out of 136 (46.3%) patients died due to COVID pneumonia. Most of the patients who died had gone into multi-organ failure. Air leak syndromes (pneumothorax and pneumomediastinum) were common findings. 10 patients already had surgical emphysema before taking up for tracheostomy and 6 developed 2–3 days after tracheostomy. The most common complication was bleeding, which was seen in 28 out of 136 patients. The Median weaning of period of patients who survived was 5 days.ConclusionPerforming tracheostomy early in COVID-19 patients helps in early weaning of the patient from the ventilator and makes nursing care easier and increases the availability of ICU beds. The mortality rate was 46% amongst the 136 tracheostomies done in COVID-19 patients. Local site bleeding was the most common complication and surgical emphysema was also seen more than routine tracheostomies.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12070-022-03248-1.  相似文献   
46.
Biliverdin IX-alpha (BV), a tetrapyrrole, is found ubiquitously in most living organisms. It functions as a metabolite, pigment, and signaling compound. While BV is known to bind to diverse protein families such as heme-metabolizing enzymes and phytochromes, not many BV-bound lipocalins (ubiquitous, small lipid-binding proteins) have been studied. The molecular basis of binding and conformational selectivity of BV in lipocalins remains unexplained. Sandercyanin (SFP)–BV complex is a blue lipocalin protein present in the mucus of the Canadian walleye (Stizostedion vitreum). In this study, we present the structures and binding modes of BV to SFP. Using a combination of designed site-directed mutations, X-ray crystallography, UV/VIS, and resonance Raman spectroscopy, we have identified multiple conformations of BV that are stabilized in the binding pocket of SFP. In complex with the protein, these conformers generate varied spectroscopic signatures both in their absorption and fluorescence spectra. We show that despite no covalent anchor, structural heterogeneity of the chromophore is primarily driven by the D-ring pyrrole of BV. Our work shows how conformational promiscuity of BV is correlated to the rearrangement of amino acids in the protein matrix leading to modulation of spectral properties.

Biliverdin IX-alpha undergoes rotation around the D-ring pyrrole and displays a broad far-red absorbance on binding to monomeric Sandercyanin variant (orange) compared to the wild-type tetrameric protein (cyan).  相似文献   
47.
Purpose:An unprecedented surge has been noted in rhino-orbital-Cerebral mucormycosis (ROCM) in times of current COVID-19 pandemic. The present prospective study aims to evaluate clinico-epidemiological profile, risk factors, management, and outcome of the cases of ROCM that presented to our tertiary care center during the study period from April to June 2021.Methods:All patients were subjected to complete history taking, ophthalmological examination, and imaging studies. The patients were staged and were treated with intravenous liposomal amphotericin B (AMB) and sino-nasal debridement of local necrotic tissue. Transcutaneous retrobulbar AMB (TRAMB), orbital decompression, and exenteration were instituted as indicated. All patients were followed up for a minimum of 6 months before arriving at the final outcome. Statistical analysis was performed.Results:A total of 49 patients presented during the study period, with a mean age of 42.2 years. The major risk factors included uncontrolled diabetes (89.8%), COVID-19 positivity (51.02%), and concurrent steroid use (38.77%). The most common presenting symptom was facial pain/swelling (43.65%), while the most common presenting sign was deterioration in vision (75.51%). Intravenous liposomal AMB was given to all patients along with sino-nasal debridement (85.71%), TRAMB (57.14%), orbital decompression (14.28%), and exenteration (12.24%). Overall, mortality at 6 months was 22.45% (11 patients). Age more than 60 years, intracranial extension, and HbA1c of more than 8.0% were observed to be statistically significant indicators of mortality.Conclusion:Early suspicion and timely diagnosis of mucormycosis at rhino-orbital stage is warranted in order to salvage life as well as visual function. TRAMB may prove as potentially favorable treatment modality in cases with limited orbital involvement.  相似文献   
48.
Background: Studies of thunderstorm asthma to understand risk factors using high-resolution climate data and asthma outcomes on a large scale are scarce. Moreover, thunderstorm asthma is not well studied in the United States.Objectives: We examined whether climate parameters involved in thunderstorms are associated with emergency department (ED) visits for acute asthma attacks in the United States.Methods: We analyzed 63,789 asthma-related, daily ED visits for all age groups, and thunderstorm-associated climate data in Louisiana during 2010 through 2012. We performed time-series analyses using quasi-Poisson regression models with natural cubic splines of date, parish, holiday, day of week, season, daily maximum concentrations of ozone (O3) and fine particulate matter [PM 2.5μm in aerodynamic diameter (PM2.5)], and daily mean pressure, precipitation, and temperature. Because of a significant interaction effect between temperature and lightning days on asthma-related visits, we performed stratified analyses by days with/without lightning or thunderstorm (defined by any lightning and precipitation).Results: On thunderstorm days, higher asthma-related ED visits were associated with higher daily mean precipitation [relative risk (RR)=1.145 per 1g/m2/s (95% CI: 1.009, 1.300)] and lower daily mean temperature [RR=1.011 per 1°C change (1.000–1.021)] without carry-over effect to the next non-thunderstorm day. These higher risks were found mainly among children and adults <65 years of age. We observed similar results on lightning days. However, we did not find similar associations for non-thunderstorm or non-lightning days. Daily maximum O3 and PM2.5 levels were not significantly associated with asthma ED visits on thunderstorm days.Discussion: Higher precipitation and lower temperature on thunderstorm days appear to contribute to asthma attacks among people with asthma, suggesting they should consider taking precautions during thunderstorms. EDs should consider preparing for a potential increase of asthma-related visits and ensuring sufficient stock of emergency medication and supplies for forecasted severe thunderstorm days. https://doi.org/10.1289/EHP10440  相似文献   
49.
Subcondylar fracture of the mandible accounts for 25–35% of all mandibular fractures. In the past, most subcondylar fractures were managed non-surgically. The traditional method of fixation for subcondylar fractures uses two miniplates; however some bench studies have reported that trapezoidal plates are superior. The aim of this study was to compare the outcomes of subcondylar fractures fixed either with two non-parallel straight miniplates or with one trapezoidal plate. A randomized clinical trial was designed and implemented. Fifty-two consecutive patients with subcondylar fractures were recruited. All patients underwent surgery via a retromandibular approach. The time taken for fixation of the plate after fracture reduction and postoperative outcomes and complications were compared between the groups. The trapezoidal plates were superior in terms of ease of adaptation and time taken for fixation (P =  0.0001). Plate fracture was observed only in the two miniplates group, in four (16%) patients. Outcomes were similar in the two groups in terms of occlusion, mouth opening, protrusion, and lateral excursion. In conclusion, both systems – two miniplates and the trapezoidal plate – provide functionally stable fixation. The outcome was significantly better for the trapezoidal plate than for two miniplates regarding the time taken for insertion and ease of adaptation, but not for other parameters.  相似文献   
50.
The cyclical pattern of violence in the lives of homeless female ex-offenders may precipitate ongoing substance use and recidivism; all of which have shown to be mounting public health issues affecting successful reentry. This paper, which analyzed baseline data from a longitudinal study of 126 female ex-offenders in Los Angeles and Pomona, California, highlighted the factors found to be associated with violent crime among homeless female ex-offenders. A multiple logistic regression model for whether or not the last conviction was for a violent offense indicated that poor housing (p = .011) and self-reported anger or hostility (p < .001) were significant correlates. An ordinal regression model for the number of violent offenses also indicated that affectionate support was associated with committing fewer number of violent crimes (p = .001), while positive social interactions (p = .007), and anger/hostility (p = .015) were associated with greater number of violent crimes. Implications for developing a comprehensive array of strategies that can mitigate the pattern of violence often seen in the lives of homeless female who have recently exited jails and prisons is discussed.  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