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   1997篇
  免费   187篇
  国内免费   15篇
耳鼻咽喉   14篇
儿科学   46篇
妇产科学   42篇
基础医学   322篇
口腔科学   21篇
临床医学   191篇
内科学   536篇
皮肤病学   97篇
神经病学   114篇
特种医学   53篇
外科学   391篇
综合类   8篇
一般理论   1篇
预防医学   57篇
眼科学   14篇
药学   122篇
中国医学   10篇
肿瘤学   160篇
  2023年   16篇
  2022年   103篇
  2021年   131篇
  2020年   56篇
  2019年   71篇
  2018年   93篇
  2017年   66篇
  2016年   86篇
  2015年   69篇
  2014年   104篇
  2013年   91篇
  2012年   126篇
  2011年   147篇
  2010年   77篇
  2009年   66篇
  2008年   113篇
  2007年   124篇
  2006年   112篇
  2005年   116篇
  2004年   85篇
  2003年   67篇
  2002年   60篇
  2001年   17篇
  2000年   9篇
  1999年   13篇
  1998年   12篇
  1997年   10篇
  1996年   4篇
  1995年   8篇
  1994年   3篇
  1991年   15篇
  1990年   8篇
  1989年   9篇
  1988年   4篇
  1987年   15篇
  1986年   8篇
  1985年   8篇
  1984年   8篇
  1983年   5篇
  1981年   3篇
  1977年   4篇
  1976年   3篇
  1973年   3篇
  1971年   4篇
  1970年   5篇
  1969年   4篇
  1968年   7篇
  1967年   7篇
  1934年   2篇
  1933年   2篇
排序方式: 共有2199条查询结果,搜索用时 15 毫秒
101.
The family Arecaceae includes 181 genera and 2,600 species with a high diversity in physical characteristics. Areca plants, commonly palms, which are able to grow in nearly every type of habitat, prefer tropical and subtropical climates. The most studied species Areca catechu L. contains phytochemicals as phenolics and alkaloids with biological properties. The phenolics are mainly distributed in roots followed by fresh unripe fruits, leaves, spikes, and veins, while the contents of alkaloids are in the order of roots, fresh unripe fruits, spikes, leaves, and veins. This species has been reputed to provide health effects on the cardiovascular, respiratory, nervous, metabolic, gastrointestinal, and reproductive systems. However, in many developing countries, quid from this species has been associated with side effects, which include the destruction of the teeth, impairment of oral hygiene, bronchial asthma, or oral cancer. Despite these side effects, which are also mentioned in this work, the present review collects the main results of biological properties of the phytochemicals in A. catechu. This study emphasizes the in vitro and in vivo antioxidant, antimicrobial, anticancer, and clinical effectiveness in humans. In this sense, A. catechu have demonstrated effectiveness in several reports through in vitro and in vivo experiments on disorders such as antimicrobial, antioxidant, or anticancer. Moreover, our findings demonstrate that this species presents clinical effectiveness on neurological disorders. Hence, A. catechu extracts could be used as a bioactive ingredient for functional food, nutraceuticals, or cosmeceuticals. However, further studies, especially extensive and comprehensive clinical trials, are recommended for the use of Areca in the treatment of diseases.  相似文献   
102.
Heart failure is common in adult population,accounting for substantial morbidity and mortality worldwide.The main risk factors for heart failure are coronary artery disease,hypertension,obesity,diabetes mellitus,chronic pulmonary diseases,family history of cardiovascular diseases,cardiotoxic therapy.The main factor associated with poor outcome of these patients is constant progression of heart failure.In the current review we present evidence on the role of established and candidate neurohumoral biomarkers for heart failure progression management and diagnostics.A growing number of biomarkers have been proposed as potentially useful in heart failure patients,but not one of them still resembles the characteristics of the"ideal biomarker."A single marker will hardly perform well for screening,diagnostic,prognostic,and therapeutic management purposes.Moreover,the pathophysiological and clinical significance of biomarkers may depend on the presentation,stage,and severity of the disease.The authors cover main classification of heart failure phenotypes,based on the measurement of left ventricular ejection fraction,including heart failure with preserved ejection fraction,heart failure with reduced ejection fraction,and the recently proposed category heart failure with mid-range ejection fraction.One could envisage specific sets of biomarker with different performances in heart failure progression with different left ventricular ejection fraction especially as concerns prediction of the future course of the disease and of left ventricular adverse/reverse remodeling.This article is intended to provide an overview of basic and additional mechanisms of heart failure progression will contribute to a more comprehensive knowledge of the disease pathogenesis.  相似文献   
103.
The directions of the transformation of benzene induced by low-voltage discharges at various energies of pulsed discharges were revealed. This paper shows the dependencies of the morphology and other characteristics of nanostructures obtained in the induced transformation of benzene on the energy of pulsed discharges. Nanostructures with different morphologies are formed when the energy of the low-voltage discharges changes during the induced transformation of benzene in the liquid phase. Two types of carbon nanostructures were formed in the induced destruction of benzene with a 90 μF capacitor. The first type of structure includes graphite fibers, two- and three-layer graphene sheets, as well as two- and three-layer hollow spheres and microstructures in the form of CNHs. The microstructures of the second type were onion-like spheroids. An increase in the capacitance up to 20 090 μF led to the formation of two types of nanostructures: onion-like spheroids and carbon fibers. A further increase in the capacitance to 40 090 μF caused the formation of onion-like spheroids.

The first type microstructure in the sample 90 μF: (a) BF TEM image of the graphene layers with hollow spheres (arrowed) and the area with graphite (marked by G).  相似文献   
104.
105.
AIDS and Behavior - Little is known about the intersection of HIV stigma and substance use stigma. Using data from 188 HIV-positive people who inject drugs (PWID) in Russia, we examined the...  相似文献   
106.
N‐(2‐methylpropyl)‐N‐(1‐diethylphosphono‐2,2‐dimethylpropyl)‐O‐(2‐carboxyprop‐2‐yl) hydroxylamine (BlocBuilder MA) is, among the commercially available alkoxyamines, one of the most efficient for nitroxide‐mediated polymerization (NMP). However, recent results have shown that it does not perform well for the NMP of isoprene. The occurrence of intramolecular hydrogen bonding (IHB) between the carboxylic function and the diethoxyphosphoryl group has been proposed as the reason for its low efficiency. In this article, the presence of this IHB is confirmed using IR, 31P NMR, 31P‐1H HOESY, and DFT calculation results. The solvent effect on this IHB and consequently on kd values is also investigated. However, combining kinetic analysis and rate measurements in various solvents, the influence of this IHB on the C? ON bond homolysis and reformation in alkoxyamine is shown to be very weak.

  相似文献   

107.
Alterations in regional subcortical brain volumes have been investigated as part of the efforts of an international consortium, ENIGMA, to identify reliable neural correlates of major depressive disorder (MDD). Given that subcortical structures are comprised of distinct subfields, we sought to build significantly from prior work by precisely mapping localized MDD-related differences in subcortical regions using shape analysis. In this meta-analysis of subcortical shape from the ENIGMA-MDD working group, we compared 1,781 patients with MDD and 2,953 healthy controls (CTL) on individual measures of shape metrics (thickness and surface area) on the surface of seven bilateral subcortical structures: nucleus accumbens, amygdala, caudate, hippocampus, pallidum, putamen, and thalamus. Harmonized data processing and statistical analyses were conducted locally at each site, and findings were aggregated by meta-analysis. Relative to CTL, patients with adolescent-onset MDD (≤ 21 years) had lower thickness and surface area of the subiculum, cornu ammonis (CA) 1 of the hippocampus and basolateral amygdala (Cohen's d = ?0.164 to ?0.180). Relative to first-episode MDD, recurrent MDD patients had lower thickness and surface area in the CA1 of the hippocampus and the basolateral amygdala (Cohen's d = ?0.173 to ?0.184). Our results suggest that previously reported MDD-associated volumetric differences may be localized to specific subfields of these structures that have been shown to be sensitive to the effects of stress, with important implications for mapping treatments to patients based on specific neural targets and key clinical features.  相似文献   
108.
109.

Objectives

One of the most reliable methods for diagnosing bladder cancer is cystoscopy. Depending on the findings, this may be followed by a referral to a more experienced urologist or a biopsy and histological analysis of suspicious lesion. In this work, we explore whether computer-assisted triage of cystoscopy findings can identify low-risk lesions and reduce the number of referrals or biopsies, associated complications, and costs, although reducing subjectivity of the procedure and indicating when the risk of a lesion being malignant is minimal.

Materials and methods

Cystoscopy images taken during routine clinical patient evaluation and supported by biopsy were interpreted by an expert clinician. They were further subjected to an automated image analysis developed to best capture cancer characteristics. The images were transformed and divided into segments, using a specialised color segmentation system. After the selection of a set of highly informative features, the segments were separated into 4 classes: healthy, veins, inflammation, and cancerous. The images were then classified as healthy and diseased, using a linear discriminant, the naïve Bayes, and the quadratic linear classifiers. Performance of the classifiers was measured by using receiver operation characteristic curves.

Results

The classification system developed here, with the quadratic classifier, yielded 50% false-positive rate and zero false-negative rate, which means, that no malignant lesions would be missed by this classifier.

Conclusions

Based on criteria used for assessment of cystoscopy images by medical specialists and features that human visual system is less sensitive to, we developed a computer program that carries out automated analysis of cystoscopy images. Our program could be used as a triage to identify patients who do not require referral or further testing.  相似文献   
110.
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